1How Nature Deals with Waste1.1. Introduction1.1.1. The wastewater problemEach day, approximately 1 × 106m3 of domestic and 7 × 106m3 of industrialwastewater is produced in the UK. This, along with surface runoﬀ frompaved areas and roads, and inﬁltration water, produces over 20 × 106 m3of wastewater requiring treatment each day. To cope with this immensevolume of wastewater there were, in 1999, some 9260 sewage treatmentworks serving about 95% of the population (Water UK 2001). The sizeof these plants varies from those serving small communities of < 100, toplants like the Crossness Sewage Treatment Works operated by ThamesWater which treats the wastewater from over 1.7 million people living in a240 km2 area of London. In terms of volume or weight, the quantity of wastewater treated annu-ally in the UK far exceeds any other product (Table 1.1) including milk,steel or even beer (Wheatley 1985), with vast quantities of wastewater gen-erated in the manufacture of most industrial products (Fig. 1.1). The costof wastewater treatment and pollution control is high, and rising annually,not only due to inﬂation but to the continuous increase in environmentalquality that is expected. During the period 1994–1999, the ten main watercompanies in England and Wales invested £16.55bn into its services. Overhalf of this was on wastewater provision. In the year 1998/1999, £1.9bnwas spent on new wastewater treatment plants alone as compliance withthe European Union Urban Wastewater Treatment Directive continues. Theindustry is extremely large, with the income for these water companies for 1
2 How Nature Deals with Waste Table 1.1. The quantity of sewage treated in the UK far exceeds the quantity of other industrial products processed. Comparative values are based on 1984 sterling values (Wheatley 1985). Product Tonnes/annum (×106 ) Price (£/tonne) Water as sewage 6500 0.10 Milk 16 25 Steel 12 300 Beer 6.6 280 Inorganic fertilizer 3.3 200 Sugar 1.0 350 Cheese 0.2 1300 Baker’s yeast 0.1 460 Citric acid 0.015 700 Penicillin 0.003 45000Fig. 1.1. Tonnes of water required in the manufacture of some products that produceorganic eﬄuents.1998/1999 in excess of £6,000m with operating costs approaching £4,000m(Water UK 2001). There are two fundamental reasons for treating wastewater: to preventpollution, thereby protecting the environment; and, perhaps more impor-tantly, protecting public health by safeguarding water supplies and prevent-ing the spread of water-borne diseases (Sec. 2.1). The safe disposal of human excreta is a pre-requisite for the supply ofsafe drinking water, as water supplies can only become contaminated wheredisposal is inadequate. There are many infectious diseases transmitted in
Introduction 3excreta, the most important being the diarrhoeal diseases cholera, typhoid,and schistosomiasis. The faeces are the major source of such diseases withfew infections, apart from schistsosomiasis, associated with urine. Amongthe most common infectious water-borne diseases are bacterial infectionssuch as typhoid, cholera, bacillary dysentery, and gastro-enteritis; viral in-fections such as infectious hepatitis, poliomyelitis, and various diarrhoealinfections; the protozoal infections cryptosporidiosis, giardiasis, and amoe-bic dysentery, and the various helminth infections such as ascariasis, hook-worm, and schistosomiasis (bilharzia). Although the provision of clean wa-ter supplies will reduce the levels of infection in the short term, in thelong term it is vital that the environment is protected from faecal pollution(Feachem and Cairncross 1993; Mara 1996). Adequate wastewater treat-ment and the disinfection of water supplies has eﬀectively eliminated thesewater-borne diseases from developed countries, but they remain endemic inmany parts of the world, especially those regions where sanitation is poor ornon-existent (Chap. 9). In developed countries where there are high popula-tion densities, such as the major European cities, vast quantities of treatedwater are required for a wide variety of purposes. All the water suppliedneeds to be of the highest quality possible, although only a small propor-tion is actually consumed. To meet this demand, it has become necessary toutilise lowland rivers and groundwaters to supplement the more traditionalsources of potable water such as upland reservoirs (Gray 1997). Where thewater is reused on numerous occasions, as is the case in the River Severnand the River Thames Sec. 10.2.2, adequate wastewater treatment is vitalto ensure that the outbreaks of waterborne diseases that were so prevalentin the eighteenth and nineteenth centuries do not reoccur (Chap. 9). In terms of environmental protection, rivers are receiving large quan-tities of treated eﬄuent while estuaries and coastal waters have vastquantities of partially or completely untreated eﬄuents discharged intothem. Although in Europe, the Urban Wastewater Treatment Directivehas caused the discharge of untreated wastewater to estuarine and coastalwaters to be largely phased out. Apart from organic enrichment endan-gering the ﬂora and fauna due to deoxygenation, treated eﬄuents rich inoxidised nitrogen and phosphorus can result in eutrophication problems.Where this is a particular problem, advanced or tertiary wastewater treat-ment is required to remove these inorganic nutrients to protect rivers andlakes (Sec. 2.4). Environmental protection of surface waters is therefore amajor function of wastewater treatment. In 1998, 30% of all rivers surveyedin England and Wales (12,241 km) were classiﬁed as having doubtful, orworse, quality (i.e. class D, E and F using the Environment Agency General
4 How Nature Deals with Waste Table 1.2. The river quality in England and Wales based on the Environment Agency GQA systems. River length (%) in each quality grade A B C D E F Total km Chemical GQA 1988–1990 17.7 30.1 22.8 14.4 12.7 2.3 34161 1993–1995 26.8 32.7 21.3 10.2 8.1 0.9 40227 1994–1996 27.1 31.5 21.2 10.4 8.8 1.0 40804 Biological GQA 1990 24.0 31.6 21.6 9.8 7.3 5.7 30001 1995 34.6 31.6 18.4 8.1 5.4 1.9 37555 Nutrient GQA 1990 8.0 17.7 10.2 13.1 28.0 22.9 23003 1993–1995 14.7 22.6 11.0 13.1 27.3 11.0 34864Quality Assessment (GQA) chemical classiﬁcation system) (EnvironmentAgency 1998; Gray 1999; Water UK 2001) (Table 1.2). As in Ireland, thereis an increasing trend in eutrophication of surface waters (EPA 2000). Thecost of rehabilitating rivers, as was seen with the River Thames in the pe-riod 1960–1980, is immense. The River Mersey for example, now Britain’smost polluted river, will cost an estimated £3,700m over the next quarterof a century to raise to a standard suitable for recreation (Department ofthe Environment 1984).1.1.2. LegislationEnvironmental legislation relating to wastewater treatment and receiv-ing water quality is based largely on quality standards that are relatedto suitability of water for a speciﬁc use, the protection of receivingwaters, or emission limits on discharges. Standards are usually manda-tory with maximum permissible concentrations based on health criteriaor environmental quality standards. Table 1.3 lists the key Directivesconcerning the aquatic environment that govern legislation in countries(Member States) comprising the European Union. The principal Direc-tives are those dealing with Surface Water (75/440/EEC), Bathing Waters(76/160/EEC), Dangerous Substances (76/464/EEC; 86/280/EEC), Fresh-water Fish (78/659/EEC), Ground Water (80/68/EEC), Drinking Water
Introduction 5 Table 1.3. EU Directives concerning inland waters by year of introduction.1973Council Directive on the approximation of the laws of the Member States relating todetergents (73/404/EEC)Council Directive on the control of biodegradability of anionic surfactants (73/405/EEC)1975Council Directive concerning the quality required of surface water intended for the ab-straction of drinking water in the Member States (75/440/EEC)1976Council Directive concerning the quality of bathing waters (76/160/EEC)Concil Directive on pollution caused by certain dangerous substances discharged intothe aquatic environment (76/464/EEC)1977Council decision establishing a common procedure for the exchange of information onthe quality of surface in the Community (77/795/EEC)1978Council Directive on titanium oxide waste (78/178/EEC)Council Directive on quality of fresh waters needing protecting or improvement in orderto support ﬁsh life (78/659/EEC)1979Council Directive concerning the methods of measurement and frequencies of samplingand analysis of surface water intended for the abstraction of drinking water in the Mem-ber States (79/869/EEC)Council Directive in the quality required for shellﬁsh wates (79/923/EEC)1980Council Directive on the protection of ground water against pollution caused by certaindangerous substances (80/68/EEC)Council Directive on the approximation of the laws of the Member States relating to theexploitation and marketing of natural mineral waters (80/777/EEC)Council Directive relating to the quality of water intended for human consumption(80/778/EEC)1982Council Directive on limit values and quality objectives for mercury discharges by thechlor-alkali electrolysis industry (82/176/EEC)Council Directive on the testing of the biodegradability of non-ionic surfactants(82/883/EEC)Council Directive on the monitoring of waste from the titanium oxide industry(82/883/EEC)1983Council Directive on limit values and quality objectives for cadmium discharges(83/513/EEC)1984Council Directive on limit values and quality objectives for discharges by sectors otherthan the chlor-alkali electrolysis industry (84/156/EEC)Council Directive on limit values and quality objectives for discharges of hexachlorocy-clohexane (84/491/EEC)1985Council Directive on the assessment of the eﬀects of certain public and private projectson the environment (85/337/EEC)
6 How Nature Deals with Waste Table 1.3. (Continued )1986Council Directive on the limit values and quality objectives for discharge of cer-tain dangerous substances included in List I of the Annex to Directive 76/464/EEC(86/280/EEC)1987Council Directive on the preventation and reduction of environmental pollution by as-bestos (87/217/EEC)1988Council Directive amending Annex II to the Directive 86/280/EEC on limit values andquality objectives for discharges of certain dangerous substances included in List I of theAnnex to Directive 76/464/EEC (88/347/EEC)1990Council Directive amending Annex II to the Directive 86/280/EEC on limit values andquality objectives for discharges of certain dangerous substances included in List I of theAnnex to Directive 76/464/EEC (90/415/EEC)1991Council Directive concerning urban waste water treatment (91/271/EEC)Council Directive concerning the protection of waters against pollution caused by nitratesfrom agricultural sources (91/676/EEC)1992Council Dirrective on pollution by waste from the titanium oxide industry (92/112/EEC)1996Council Directive on integrated pollution prevention control (96/61/EEC)1998Council Directive on the quality of water intended for human consumption (98/83/EEC)2000Council Directive establishing a framework for community action in the ﬁeld of waterpolicy (00/60/EC)(80/778/EEC), Urban Waste Water Treatment (91/271/EEC), Nitrates(91/676/EEC), Integrated Pollution Prevention Control (96/61/EEC), andWater Framework (00/60/EEC). The Directive controlling sewage sludgedisposal to agricultural land (86/278/EEC) is discussed in Chap. 8. In mostDirectives both guide (G) and imperative, or mandatory, (I) values aregiven. The G values are those which Member States should be working to-wards in the long term. In most cases, nationally adopted limit values arethe I values although occasionally more stringent values are set. The Dangerous Substances Directive (76/464/EEC) requires licensing,monitoring and control of a wide range of listed substances dischargedto the aquatic environment. List I (Black List) substances have been se-lected mainly on the basis of their toxicity, persistence and potential forbioaccumulation. Those that are rapidly converted into substances that arebiologically harmless are excluded. List II (Grey List) substances are consid-ered to be less toxic, or the eﬀects of which are conﬁned to a limited area
Introduction 7Table 1.4. List I and List II substances deﬁned by the EU Dangerous Substances Di-rective (76/464/EEC).List no. 1 (‘black list’)Organohalogen compounds and substances which may form such compounds in theaquatic environmentOrganophosphorus compoundsOrganotin compoundsSubstances, the carcinogenic activity of which is exhibited in or by the equatic environ-ment (substances in List 2 which are carcinogenic are included here)Mercury and its compoundsCadmium and its compoundsPersistent mineral oils and hydrocarbons of petroleumPersistent synthetic substancesList no. 2 (‘grey list’)The following metalloids/metals and their compounds:Zinc, copper, nickel, chromium, lead, selenium, arsenic, antimony, molybdenum, tita-nium, tin, barium, beryllium, boron, uranium, vanadium, cobalt, thalium, tellurium,silverBiocides and their derivatives not appearing in List 1Substances which have a deleterious eﬀect on the taste and/or smell of products forhuman consumption derived from the aquatic environment and compounds liable togive rise to such substances in waterToxic or persistent organic compounds of silicon and substances which may give rise tosuch compounds in water, excluding those which are biologically harmless or are rapidlyconverted in water to harmless substancesInorganic compounds of phosphorus and elemental phosphorusNon-persistent mineral oils and hydrocarbons of petroleum originCyanides, ﬂuoridesCertain substances which may have an adverse eﬀect on the oxygen balance, particularlyammonia and nitriteswhich is dependent on the characteristics and location of the water intowhich they are discharged (Table 1.4). Member States are in the process ofestablishing environmental quality standards (EQS) for surface and groundwaters. These will be used as maximum permissible concentrations in wa-ters receiving discharges containing such compounds (Table 1.5). Water policy in the EU has recently been rationalized into three keyDirectives: Drinking Water (80/778/EEC), Urban Waste Water Treatment(91/271/EEC), and the Water Framework Directive (2000/60/EEC). The Water Framework Directive (2000/60/EEC) brings together the ex-isting Directives on water quality of surface fresh water, estuaries, coastalwaters and ground water. It covers all aspects of aquatic ecology and wa-ter quality, including the protection of unique and valuable habitats, theprotection of drinking water resources and the protection of bathing wa-ters. It achieves this by managing all water resources within River Basin
8 How Nature Deals with WasteTable 1.5. Environmental quality standards for List I and List II substances in Englandand Wales (Environment Agency 1998).List I substances Statutory EQSa (μg/l) Number of dischargesMercury and compounds 1 752Cadmium and compounds 5 2196Hexachlorocyclohexane (all isomers) 0.1 123DDT (all isomers) 0.025 15DDT (pp isomers) 0.01 1Pentachlorophenol 2 88Carbon tetrachloride 12 51Aldrin 0.01 35Dieldrin 0.01 58Endrin 0.005 37Isodrin 0.005 7Hexachlorobenzene 0.03 20Hexachlorobutadience 0.1 14Chloroform 12 73Trichloroethylene 10 48Tetrachloroethylene 10 51Trichlorobenzene 0.4 311,2-dichloroethane 10 87a Standards are all annual mean concentrationsList II substances Operational EQSa (μg/l) Measured asLead 10 ADChromium 20 ADZinc 75 ATCopper 10 ADNickel 150 ADArsenicb 50 ADBoron 2000 ATIron 1000 ADpH 6.0–9.0 PVanadium 20 ATTributyltinb 0.02 MTTriphenyltinb 0.02 MTPCSD 0.05 PTCyﬂuthrin 0.001 PT
Introduction 9 Table 1.5. (Continued )List II substances Operational EQSa (μg/l) Measured asSulcofuron 25 PTFlucofuron 1 PTPermethrin 0.01 PTAtrazine and simazineb 2 AAzinphos-methylb 0.01 ADichlorvosb 0.001 AEndosulphanb 0.003 AFenitrothionb 0.01 AMalathionb 0.01 ATriﬂuralinb 0.1 ADiazinon 0.01 APropetamphos 0.01 ACypermethrin 0.0001 AIsoproturon 2.0 AA = annual average, P = 95% of samples, D = dissolved, T = total, M = maximum.a Standards quoted for metals are for the protection of sensitive aquatic life at hardness100–150 mg/l CaCO3 , alternative standards may be found in DoE circular 7/89.b Standards for these substances are from the Surface Waters (Dangerous Substances)(Classiﬁcation) Regulations 1997, Sl 2560 in which case these are now statutory.Districts for which management plans will be drawn up using environmentalquality standards (EQSs) (Table 1.5). The Directive sets clear monitoringprocedures and lists speciﬁc biological, hydromorphological and physico-chemical parameters to be used for rivers, lakes, estuaries and coastal wa-ters. For each of these resource groups, deﬁnitions of high, good and fairecological quality are given for each speciﬁed parameter. The Urban Waste Water Treatment Directive (91/271/EEC) makes sec-ondary treatment mandatory for sewered domestic waste waters and alsoall biodegradable industrial (e.g. food processing) waste waters. Minimumeﬄuent standards have been set at BOD 25 mg l−1 , COD 125 mg l−1 andsuspended solids 35 mg l−1 . Those receiving waters that are consideredto be at risk from eutrophication are classiﬁed as sensitive so that dis-charges require more stringent treatment to bring nutrient concentrationsof ﬁnal eﬄuents down to a maximum total phosphorus concentration of2 mg l−1 for P and a total nitrogen concentration of 10–15 mg l−1 for N(Table 1.6). Due to the cost of nutrient removal, the designation of receiv-ing waters as sensitive has signiﬁcant cost implications for Member States.
10 How Nature Deals with Waste Table 1.6. The Urban Wastewater Treatment Directive (91/271/EEC) sets dis- charge limits for wastewater treatment plants. Values for total phosphorus and nitrogen only apply to discharges > 10, 000 population equivalents (PE) discharg- ing to surface waters classed as sensitive (e.g. those subject to eutrophication). Parameter Minimum concentration Minimum percentage reduction BOD5 25 mg O2 l−1 70–90 COD 125 mg O2 l−1 75 Suspended solids 35 mg l−1 90 Total phosphorus 1 mg P l−1a 80 2 mg P l−1b 80 Total nitrogen 10 mg N l−1a 70–80 15 mg N l−1b 70–80 a 10000–100000 PE. b >100000 PE.Strict completion dates have been set by the Commission for the provisionof minimum treatment for waste waters entering freshwater, estuaries andcoastal waters. For example, full secondary treatment (Sec. 2.1) includingnutrient removal for all discharges to sensitive waters with a populationequivalent (PE) >10,000 must be completed by the end of 1998. By 31December 2005 all waste waters from population centres <2,000 PE dis-charged to freshwaters, and <10,000 PE to coastal waters must have suf-ﬁcient treatment to allow receiving waters to meet environmental qualitystandards, while populations centres larger than these require secondarytreatment (Fig. 1.2). The Directive also requires signiﬁcant changes in thedisposal of sewage sludge including: (i) That sludge arising from waste water treatment shall be reused when- ever possible and that disposal routes shall minimise adverse eﬀects on the environment (ii) Competent authorities shall ensure that before 31 December 1998, the disposal of sludge from waste water treatment plants is subject to general rules (i.e. Codes of Practice) or legislation(iii) The disposal of sludge to surface waters by dumping from ships or discharge from pipelines or other means shall be phased out by 31 December 1998(iv) That the total amount of toxic, persistent or bioaccumable material in sewage sludge is progressively reduced This wide scoping legislation is considered in more detail in Chap. 8.The disposal options for sewage sludge are further limited if it contains
Introduction 11Fig. 1.2. The implementation of the EU Urban Wastewater Directive, with dates forcompliance by Member States.metals or listed substances which may categorise it as a hazardous wasteunder the EU Directive on Hazardous Waste (91/689/EEC). Industrial eﬄuents have in the past been a major cause of pollution.The discharge of industrial eﬄuents is generally governed by two objec-tives: (1) the protection of environmental water quality, and (2) the needto protect sewers and wastewater treatment plants (Table 1.7). To meetthese objectives, discharge standards are required that are a compromisebetween what is needed to protect and improve the environment and thedemands of industrial development. Most industrialists accept that the ap-plication of the best practical technology (i.e. eﬄuent treatment using thebest of current technology to meet local environmental requirements atthe lowest ﬁnancial cost) is a reasonable way to comply with the eﬄuentdischarge standards set. However, where discharges contain dangerous ortoxic pollutants which need to be minimised, then the application of thebest available technology is required (i.e. eﬄuent treatment using the bestof current technology to minimise local environmental change, especiallythe accumulation of toxic materials, where ﬁnancial implications are sec-ondary considerations). Where eﬄuent standards are necessary that areeven unobtainable using the best available technology, then of course in-dustries can no longer continue at that location.
12 How Nature Deals with Waste Table 1.7. Typical eﬄuent standards for discharges to sewers (Gledhill 1986). Parameter Standard ReasonspH 6 to 10 Protection of sewer and sewage works fabric from corrosion.Suspended solids 200–400 mg l−1 Protection from sewer blockages and extra load on sludge disposal system.BOD5 No general limit Local authorities would be concerned with large loads on small sewage works and bal- ancing of ﬂows may be required in order not to overload treatment units.Oils/fats/grease 100 mg l−1 Prevention of fouling of working equipment and safety of men. Soluble fats, etc. can be allowed at ambient temperature.Inﬂammables, hy- Prohibited Prevention of hazards from vapours in sewers. drocarbons, etc.Temperature 43◦ C Various reasons — promotes corrosion, in- creases solubility of other pollutants, etc.Toxic metals 10 mg l−1 Prevention of treatment inhibition. The solu- ble metal is more toxic and diﬀerent met- als can be troublesome. Total loads with a limit on soluble metals more realistic.Sulphate 500–1000 mg l−1 Protection of sewer from sulphate corrosion.Cyanides 0–1 mg l−1 Prevention of treatment inhibition. Much higher levels can also cause hazardous working conditions due to HCN gas accu- mulation in sewer. The integrated pollution prevention and control (IPPC) Directive(96/61/EEC) was adopted in September 1996. Integrated pollutionprevention and control is a major advance in pollution control in that alldischarges and environmental eﬀects to water, air and land are considered,together with the Best Practicable Environmental Option (BPEO) selectedfor disposal. In this way, pollution problems are solved rather than trans-ferred from one part of the environment to another. In the past, licensingof one environmental media (i.e. air, water or land) created an incentive torelease emissions to another. Integrated pollution prevention and controlalso minimises the risk of emissions crossing over into other environmentalmedia after discharge (e.g. acid rain, landﬁll leachate). There is only one li-cence issued under IPPC covering all aspects of gaseous, liquid, solid wasteand noise emissions, so that the operator only has to make one applicationas well as ensuring consistency between conditions attached to the licence inrelation to the diﬀerent environmental media. In Europe, IPPC applies tothe most complex and polluting industries and substances (e.g. large chem-ical works, power stations, etc.). In England and Wales, the Environment
Introduction 13Agency issues guidance for such processes to ensure that the BPEO is car-ried out. The aim of IPPC is to minimise the release of listed substancesand to render substances that are released harmless using Best AvailableTechniques Not Entailing Excessive Cost (BATNEEC). The objective of theguidance notes is to identify the types of techniques that will be used bythe Agency to deﬁne BATNEEC for a particular process. The BATNEECidentiﬁed is then used as a base for setting emission limit values (ELVs).Unlike previous practice in the identiﬁcation of BATNEEC, emphasis isplaced on pollution prevention techniques such as cleaner technologies andwaste minimisation rather than end-of-pipe treatment. Other factors forimproving emission quality include in-plant changes, raw material substi-tution, process recycling, improved material handling and storage practices.Apart from the installation of equipment and new operational proceduresto reduce emissions, BATNEEC also necessitates the adoption of an on-going programme of environmental management and control which shouldfocus on continuing improvements aimed at prevention, elimination andprogressive reduction of emissions. The selection of BATNEEC for a particular process takes into account(i) the current state of technical knowledge, (ii) the requirements of environ-mental protection, and (iii) the application of measures for these purposeswhich do not entail excessive costs, having regard to the risk of signiﬁcantenvironmental pollution. For existing facilities, the Agency considers (i) thenature, extent and eﬀect of the emissions concerned, (ii) the nature and ageof the existing facilities connected with the activity and the period duringwhich the facilities are likely to be used or to continue in operation, and(iii) the costs, which would be incurred in improving or replacing these ex-isting facilities in relation to the economic situation of the industrial sectorof the process considered. Thus, while BATNEEC guidelines are the ba-sis for setting licence emission standards, other factors such as site-speciﬁcenvironmental and technical data as well as plant ﬁnancial data are alsotaken into account. In Ireland, similar IPPC licensing procedures are op-erated by the Environmental Protection Agency (EPA 1994), and like theEnvironment Agency in England and Wales, public registers of all licencesare maintained. The introduction of the polluter which pays charging system through-out Europe and the USA is an attempt to achieve such environmentalobjectives, at least in terms of the cost to the community, by reinforcingthe philosophy that the polluter is responsible for all aspects of pollutioncontrol in relation to its own eﬄuent (Deering and Gray 1987). Two distincttypes of charges exist: eﬄuent charges are levied by local authorities for
14 How Nature Deals with Wastedischarges directly to surface waters, whereas user charges are levied for theuse of the authority’s collective treatment system (Table 1.16). By charg-ing industry for treating their eﬄuents in terms of strength and volume, itencourages them to optimise production eﬃciency by reducing the volumeand strength of their eﬄuent. Most important of all, such charging systemsensure that eﬄuent disposal and treatment costs are taken into account bymanufacturers in the overall production costs, so that the cost of the ﬁnalproduct reﬂects the true cost of production (Deering and Gray 1986). Wastewater treatment is not solely a physical phenomena controlled byengineers, it also involves a complex series of biochemical reactions involv-ing a wide range of micro-organisms. The same micro-organisms that occurnaturally in rivers and streams are utilised, under controlled conditions, torapidly oxidise the organic matter in wastewater to innocuous end productsthat can be safely discharged to surface waters. Compared with other indus-tries which also use micro-organisms, such as brewing or baking, wastewa-ter treatment is by far the largest industrial use of micro-organisms usingspecially constructed reactors. As treatment plants that were constructedduring the early expansion of wastewater treatment in the late nineteenthand early twentieth centuries now near the end of their useful lives, it isclear that the opportunities for the biotechnologists to apply new technolo-gies, such as genetic manipulation combined with new reactor designs, topollution control are enormous (Chap. 10). In the future, cheaper, more ef-ﬁcient, and more compact processes will be developed, with the traditionalaims of removing organic matter and pathogens to prevent water pollu-tion and protect public health replaced with a philosophy of environmentalprotection linked with conservation of resources and by-product recovery(Chap. 11). Natural scientists, whether they are trained as microbiologists, bio-chemists, biologists, biotechnologists, environmental scientists or any otherallied discipline, have an important role in all aspects of public health en-gineering. They already have a signiﬁcant function in the operation andmonitoring of treatment plants, but their expertise is also needed in theoptimisation of existing plants and in the design of the next generation ofwastewater treatment systems.1.2. Nature of WastewaterAlthough there has been a steady increase in the discharge of toxic in-organic and organic materials, it is still the biodegradable organic wastes
Nature of Wastewater 15that are the major cause of pollution of receiving waters in Britain andIreland (Gray and Hunter 1985; DETR 1998; Environment Agency 1998,1999; EPA 2000). Organic waste originates from domestic and commercialpremises as sewage, from urban runoﬀ, various industrial processes and agri-cultural wastes. Not all industrial wastes have a high organic content thatis amenable to biological treatment, and those with a low organic content,insuﬃcient nutrients, and which contain toxic compounds, require speciﬁcchemical treatment, such as neutralisation, chemical precipitation, chemi-cal coagulation, reverse osmosis, ion-exchange, or adsorption onto activatedcarbon (Table 1.8) (Casey 1997). This book concentrates on non-toxic wastewaters. It is these that areof particular interest to the biologist and biotechnologist in terms ofreuse, conversion, and recovery of useful constituent materials. Primar-ily sewage containing pathogenic micro-organisms is considered, althoughother wastewaters, such as agricultural wastes from intensive animal rearingand silage production, food processing wastes, and dairy industry wastesare also brieﬂy reviewed.1.2.1. Sources and variation in sewage ﬂowThe absolute minimum quantity of wastewater produced per person (percapita), without any excess water, is 4 litres per day. At this concentration,the wastewater has a dry solids content in excess of 10%. However, in mostcommunities that have an adequate water supply this minimum quantity isgreatly increased. In those countries where technology and an almost un-limited water supply has led to the widescale adoption of water-consumingdevices — many of which are now considered to be standard, if not basic,human requirements — the volume of wastewater produced has increasedby a factor of 100 or more. Flush toilets, baths, showers, automatic washingmachines, dishwashers and waste disposal units all produce vast quantitiesof diluted dirty (grey) water with a very low solids content and all requiringtreatment before being discharged to surface waters. For example, a ﬂushtoilet dilutes small volumes of waste matter (< 1 litre) to between 10 or30 litres each time it is used. Domestic sewage is diluted so much that it isessentially 99.9% water with a dry solids content of less than 0.1%. Con-ventional sewage treatment aims to convert the solids into a manageablesludge (2% dry solids) while leaving only a small proportion in the ﬁnaleﬄuent (0.003% dry solids). The total volume of wastewater produced per capita depends on thewater usage, the type of sewerage system used and the level of inﬁltration.
16 How Nature Deals with WasteTable 1.8. Main chemical and biological unit processes employed in wastewatertreatment. Process DescriptionChemical unit processesNeutralisation Non-neutral waste waters are mixed either with an alkali (e.g. NaOH) or an acid (e.g. H2 SO4 ) to bring the pH as close to neu- tral as possible to protect treatment processes. Widely used in chemical, pharmaceutical and tanning industriesPrecipitation Dissolved inorganic components can be removed by adding an acid or alkali, or by changing the temperature, by precipitation as a solid. The precipitate can be removed by sedimentation, ﬂotation or any other solids removal processIon-exchange Removal of dissolved inorganic ions by exchange with another ion attached to a resin column. For example Ca and Mg ions can replace Na ions in a resin, thereby reducing the hardness of the waterOxidation reduction Inorganic and organic materials in industrial process waters can be made less toxic or less volatile by subtracting or adding electrons between reactant (e.g. aromatic hydrocarbons, cyanides, etc.)Biological unit processesActivated sludge Liquid waste water is aerated to allow micro-organisms to utilise organic polluting matter (95% reduction). The microbial biomass and treated eﬄuent are separated by sedimentation with a portion of the biomass (sludge) returned to the aeration tank to seed the incoming waste waterBiological ﬁltration Waste water is distributed over a bed of inert medium on which micro-organisms develop and utilise the organic matter present. Aeration occurs through natural ventilation and the solids are not returned to the ﬁlterStabilisation ponds Large lagoons where waste water is stored for long periods to al- low a wide range of micro-organisms to break down organic mat- ter. Many diﬀerent types and designs of ponds including aerated, non-aerated and anaerobic ponds. Some designs rely on algae to provide oxygen for bacterial breakdown of organic matter. Sludge is not returnedAnaerobic digestion Used for high strength organic eﬄuents (e.g. pharmaceutical, food and drink industries). Waste water is stored in a sealed tank which excludes oxygen. Anaerobic bacteria breakdown organic matter into methane, carbon dioxide and organic acids. Final eﬄuent still requires further treatment as has a high BOD. Also used for the stabilisation of sewage sludge at a concentration of 2–7% solidsThe volume of wastewater varies from country to country depending onits standard of living and the availability of water supplies (Table 1.9).Generally, the volume and strength of the sewage discharged in a particularcountry can be predicted fairly accurately. For example, the mean dailyvolume of wastewater, excluding industrial waste but including inﬁltration,
Nature of Wastewater 17 Table 1.9. Speciﬁc water consumption in Europe (IWSA 1995). Household and Industry small businesses and others Total 1980 1993 1980 1993 1980 1993 Austria 155 170 100 92 255 262 Belgium 104 120 59 37 163 157 Denmark 165 155 96 74 261 229 France 109 157 58 58 167 215 Germany1 137 136 74 41 211 177 Hungary 110 121 107 63 217 184 Italy 211 251 69 78 280 329 Luxembourg 183 178 76 83 259 261 Netherlands 142 171 37 32 179 203 Norway 154 180 247 340 401 520 Spain 157 210 58 90 215 300 Sweden 195 203 120 73 315 276 Switzerland 229 242 163 120 392 362 United Kingdom 154 —2 100 —2 254 331 1 Includes former GDR. 2 UK values not available in this format.produced per capita in England is 180 l d−1 , compared 230 l d−1 in Irelandand 250 l d−1 in Scotland. The equivalent volume of sewage produced inthe USA is on average 300 l per capita per day (100 US gallons d−1 ).The amount of wastewater produced per capita can be estimated quiteaccurately from the speciﬁc water consumption. The variation in volume depends on a number of variables includingthe amount of inﬁltration water entering the sewer. The higher volume ofwastewater produced in Scotland is primarily due to the widescale use ofa larger ﬂushing cistern, 13.6 l compared with 9.0 l in England and Wales,although other factors also contribute to this variation. Guidelines fromthe Department of the Environment in England and Wales stipulate thatall new cisterns manufactured after 1993 should have a maximum ﬂushingvolume of 7.5 l. However, the reliance of water closets which function on asiphon rather than a valve to release water restricts the minimum opera-tional volume to between 4–5 l (Pearse 1987). The Building Research Es-tablishment (1987) highlights the potential water saving from the adoptionof new cistern designs and suggests the need for new British Standards.
18 How Nature Deals with WasteComparative studies were carried out using a ‘standard turd’, which is a43 mm diameter ball of non-absorbent material with a relative density of1.08, and with a cohesive shear strength, coeﬃcient of friction, and adhesiveproperties very close to the real thing. In rural areas, where water is drawn from boreholes or from small com-munity water schemes, water may be at a premium, so the necessary con-servation of supplies results in reduced volumes of stronger sewage. Occa-sionally, the water pressure from such rural supplies is too low to operateautomatic washing machines or dishwashers and results in an overall reduc-tion in water usage and subsequent wastewater discharge. In the home, wastewater comes from three main sources. Approximatelya third of the volume comes from the toilet, a third from personal washingvia the wash basin, bath, and shower, and a third from other sources suchas washing up, laundry, food and drink preparation (Tables 1.10 and 1.11).Outside the home, the strength and volume of wastewater produced percapita per day will ﬂuctuate according to source, and this variation mustbe taken into account when designing a new treatment plant. For example,the ﬂow per capita can vary from 50 l d−1 at a camping site to 300 ld−1 at a luxury hotel (Table 1.11). More detailed tables of the volume ofwastewater produced from non-industrial sources, including the strengthof such wastewater, are given by Hammer (1999) and also by Metcalf andEddy (1991). The diluted nature of wastewater has led to the development of thepresent system of treatment found in nearly all the technically-developedcountries, which is based on treating large volumes of weak wastewater.In less developed communities, the high solids concentration of the waste Table 1.10. Comparison of the percentage consumption of water for various pur- poses in a home with an oﬃce; indicating the source and make-up of wastewater from these types of premises (Mann 1979). Total water Total water Home (sources) consumed (%) Oﬃce (sources) consumed (%) WC ﬂushing 35 WC ﬂushing 43 63 Washing/bathing 25 Urinal ﬂushing 20 Food preparation/drinking 15 Washing 27 Canteen use 9 Laundry 10 Cleaning 1 Car washing/garden use 5a a May not be disposed to sewer.
Nature of Wastewater 19 Table 1.11. Daily volume of wastewater produced per capita from various non-industrial sources (Mann 1979). Volume of sewage Source category (litres/person/day) Small domestic housing 120 Luxury domestic housing 200 Hotels with private baths 150 Restaurants (toilet and kitchen wastes per customer) 30–40 Camping site with limited sanitary facilities 80–120 Day schools with meals service 50–60 Boarding schools: term time 150–200 Oﬃces: day work 40–50 Factories: per 8 hour shift 40–80Table 1.12. Comparison of the concentration of various compounds reported in urbanrunoﬀ with precipitation, strictly surface runoﬀ from roads and with combined seweroverﬂow (Pope 1980). All units are in mg l−1 unless speciﬁed. Those marked with † arein mg kg−1 and ‡ in kg curb km−1 . Reported concentration range (mg l−1 )Parameter Precipitation Road/street Urban Combined runoﬀ runoﬀ sewer overﬂowCOD 2.5–322 300 5–3100 93–2636BOD 1.1 25–165 1–700 15–685Total solids 18–24 474–1070 400–15322 150–2300Volatile total solids — 37–86 12–1600 —Suspended solids 2–13 11–5500 2–11300 20–1700Volatile suspended solids 6–16 100–1500 12–1268 113Settleable solids — — 0.5–5400 —Total dissolved solids — 66–33050 9–574 —Volatile dissolved solids — 1630 160 —Conductance (μmho cm−1 ) 8–395 10000 5.5–20000 —Turbidity (JTU) 4–7 — 3–70 —Colour (Pt-Co units) 5–10 — 5–160 —Total organic carbon 1–18 5.3–49 14–120 —Total inorganic carbon 0–2.8 — 1.17 —Oils/hydrocarbons — 28–400 0–110 —Phenols — — 0–10 —
Nature of Wastewater 21makes it diﬃcult to move to central collection and treatment sites, while themore diluted wastewater ﬂows easily through pipes, and can be transportedeasily and eﬃciently via a network of sewers to a central treatment works.In isolated areas or underdeveloped countries, human waste is normallytreated on-site, due to its smaller volume and less ﬂuid properties (Feachemand Cairncross 1993; Mara 1996). The collection and transport of sewage to the treatment plant is via anetwork of sewers. Two main types of sewerage systems are used, combinedand separate. Combined sewerage systems are common in most towns inBritain. Surface drainage from roads, paved areas, and roofs are collectedin the same sewer as the foul wastewater and piped to the treatment works.This leads to ﬂuctuations in both the volume and the strength of sewagedue to rainfall, and although the treatment works is designed to treat up tothree times the dry weather ﬂow of wastewater (DWF), problems arise if therainfall is either heavy or continuous. During such periods, the wastewaterbecomes relatively diluted and the volume too great to be dealt with bythe treatment works. Excess ﬂow is, therefore, either directly discharged toa watercourse as storm water or stored at the treatment works in stormwater tanks. The stored wastewater can be circulated back to the start ofthe treatment works once capacity is available. However, once the tanksbecome full, and then the settled wastewater passes into the river withoutfurther treatment where the watercourse, already swollen with rainwater,can easily assimilate the diluted wastewater because of the extra dilutionnow available. A separate sewerage system overcomes the problem of ﬂuctuations insewage strength and volume due to rain, by collecting and transportingonly the foul wastewater to the treatment works, and surface drainage isdischarged to the nearest water course. Such systems are common in newtowns in Britain and are mandatory in Canada and the USA. This typeof sewerage system allows more eﬃcient and economic treatment works tobe designed as the variation in the volume and strength of the wastewateris much smaller and can be more accurately predicted. A major drawbackwith separate systems is that the surface drainage water often becomespolluted. All stormwater is contaminated to some degree because of contactduring the drainage cycle: it passes over paved areas along roadside gulliesto enter the sewer via a drain with a gully pot, which catches and removessolids that might otherwise cause a blockage in the sewer pipe (Bartlett1981). The quality of urban runoﬀ is extremely variable and biochemicaloxygen demand (BOD) values have been recorded in excess of 7,500 mgl−1 (Mason 1991; Lee and Bang 2000). It is the ﬁrst ﬂush of storm water
22 How Nature Deals with Wastethat is particularly polluting as it displaces the anaerobic wastewater, richin bacteria, that has been standing in the gully pots of the roadside drainssince the last storm (Butler and Memon 1999). The runoﬀ from roads isrich in grit, suspended solids, hydrocarbons including polycyclic aromatichydrocarbons (Krein and Schorer 2000), heavy metals, pesticides such asthe herbicide atrazine (Appel and Hudak 2001), and, during the winter,chloride from road-salting operations. Surprisingly, it also contains organicmatter, not only in the form of plant debris such as leaves and twigs, butalso dog faeces (Table 1.12). It has been estimated that up to 17 g m−2y−1 of dog faeces are deposited onto urban paved areas and that the dog Table 1.13. Chemical characteristics of treated eﬄuents from three UK sewage treatment plants. Source Constituenta Stevenage Letchworth Redbridge Total solids 728 640 931 Suspended solids 15 51 Permanganate value 13 8.6 16 BOD 9 2 21 COD 63 31 78 Organic carbon 20 13 Surface-active matter Anionic (as Manoxol OT) 2.5 0.75 1.4 Non-ionic (as Lissapol NX) 0.4 Ammonia (as N) 4.1 1.9 7.1 Nitrate (as N) 38 21 26 Nitrite (as N) 1.8 0.2 0.4 Chloride 69 69 98 Sulphate 85 61 212 Total phosphate (as P) 9.6 6.2 8.2 Sodium 144 124 Potassium 26 21 Total hardness 249 295 468 pH value 7.6 7.2 7.4 Turbidity (ATU)b 66 Colour (Hazen units) 50 43 36 Coliform bacteria (no./ml) 1300 3500 a Results are given in mg l−1 , unless otherwise indicated. b Absorptiometric turbidy units
Nature of Wastewater 23population of a city the size of Manchester will produce an organic loadequivalent to the human population of a small town of 25–30,000 people. InNew York, the dog population deposits over 68,000 kg of faeces and 405,000 lof urine onto the streets each day, much of which is washed by storm waterinto local streams and rivers (Feldman 1974). The degree of contaminationof urban runoﬀ during a speciﬁc storm depends on: (i) the intensity andduration of the rainfall; (ii) the length of the preceding dry period, whichcontrols the build up of pollutants on roads and in the quality of waterstored in gully pots and gutters; (iii) seasonal variations that occur in therainfall pattern and temperature which aﬀects the degradation of organicmatter; including leaf fall and the use of grit and salt during the winter, and(iv) the eﬀectiveness of local authorities to clean roadside gullies and gullypots (Helliwell 1979). Unlike drainage from land, runoﬀ from roads andpaved areas is very rapid due to the short length of surface water sewers. Thecontaminated wastewater, therefore, reaches the receiving watercourse veryquickly and before the dry weather ﬂow has increased, so that any pollutantsentering will receive minimum dilution. Where there is an accidental ordeliberate spillage of chemicals or noxious wastes on roads, or in privateyards, serious pollution of receiving waters is bound to occur. However, withcombined sewerage systems such spillages can be conﬁned at the treatmentworks and recovered or treated before reaching the watercourse (Sec. 2.1.1).During storm events, it is possible for combined sewers in particular tobecome overloaded, leading to the operation of sewer overﬂow systems.Combined sewer overﬂows (CSOs) discharge a mixture of wastewater andsurface runoﬀ that causes severe pollution in receiving waters (Balmforth1990; Field et al. 1994). Extensive work has been undertaken to reduce thenumber of storm water overﬂows within sewer networks and to reduce theamount of storm water entering the sewer by using interception systemssuch as swales, percolation areas, porous roads and wetlands (Field et al.1994; Debo and Reese 1995; Shutes et al. 1997; Sieker 1998; Adams andPapa 2000). It is common, in both separate and combined sewers, for water notdischarged as wastewater to enter the sewer via joints and cracks in thepipework. Inﬁltration water is normally from ground water sources and canbe especially high during periods of rainfall. Few estimates of the extent ofthe problem are available, although some studies have found inﬁltration tobe as high as 80% of the total volume in badly deteriorated sewers. In theUSA, it is estimated that a mean value is 70 m3 d−1 per km of sewer (30,000US gallons per day per mile of sewer) (Clarke et al. 1971), although Grace(1979) recorded mean values some 50% less. As groundwater is generally
24 How Nature Deals with Wastevery clean, inﬁltration has the eﬀect of diluting the strength of wastewaterand at the same time increasing the volume requiring treatment. The ﬂow rate of wastewater to treatment works is extremely variable,and although such ﬂows follow a basic diurnal pattern, each treatmentworks tends to have a characteristic ﬂow pattern. This pattern is controlledby such factors as: the time taken for sewage to travel from householdsto the treatment works, which is itself a function of sewer length; the de-gree of inﬁltration; the presence of stormwater and the variability in thewater consumption practices of communities (Gower 1980). Industrial in-puts obviously have a profound eﬀect on ﬂow rates, and industrial practicessuch as discharging wastes after 8-hour shifts can completely alter the ex-pected normal ﬂow pattern to a treatment plant. The basic ﬂow patternfor a domestic wastewater treatment plant is shown in Fig. 1.3 with theminimum ﬂow normally occurring in the early hours of the morning whenwater consumption is lowest and the ﬂow consists largely of inﬁltrationwater. Flow rate rapidly increases during the morning when peak morn-ing water consumption reaches the plant, followed by a second peak in the Fig. 1.3. Example of the hourly variation in ﬂow to a sewage treatment plant.
Nature of Wastewater 25early evening. When inﬁltration, storm water, and the water used for non-sewered purposes such as garden use, are removed from a basic model ofconsumption and discharge, then the water supplied is essentially equiv-alent to the wastewater discharged to the sewer (Lenz 1983a). Thus, thewastewater discharge curve, as measured at the sewage treatment works,will closely parallel the water supply curve, as measured at the waterworks,with a lag of several hours. Inﬁltration and storm water tend to distort the basic shape of the hydro-graph of diurnal ﬂow. Inﬁltration, while increasing the total daily volume,does not alter its characteristic shape. Storm water, however, can alter theshape of the hydrograph by hiding peaks and troughs or adding new peaksas the rainfall causes rapid increases in the ﬂow. Hourly ﬂuctuations are lessclear in large catchments due to the diversity of activities taking place dur-ing the 24-hour period and the presence of industry. The variable distanceof households from the treatment works normally results in the hydrographof the diurnal pattern becoming ﬂattened and extended so that only onetrough and one peak is seen daily (Clark et al. 1977; Escritt and Haworth1984). Many problems at small to moderate sized treatment works are as-sociated with the diurnal variation in ﬂow, which is especially serious atthe smallest works where often there is no ﬂow at all during the night.Smaller variations of the average daily ﬂow rate are recorded at treatmentworks serving large catchments (50–200%) compared with smaller commu-nities (20–300%) (Painter 1958; Water Pollution Control Federation 1961).Many works overcome the problem of ﬂow variation by using ﬂow balanc-ing, where the wastewater is stored at times of high ﬂow and allowed toenter the works at a constant rate, or by recirculating treated ﬁnal eﬄuentduring periods of low ﬂow. Variation between weekday ﬂows is negligible, except in those areaswhere the household laundry is done on speciﬁc days. However, with theadvent of automatic washing machines this practice has become largely ex-tinct. With changing work patterns, many homes are now only occupiedat night and on the weekends, leading to changes in diurnal and daily ﬂowcharacteristics. Also, automatic washing of household laundry and dishesis increasingly done at night to take advantage of cheaper oﬀ-peak elec-tricity tariﬀs. Although summer discharges normally exceed winter ﬂowsby 10–20%, up to 20–30% in the USA, seasonal variations in ﬂow are duemainly to variation in population, as is the case at holiday resorts, schools,universities, and military camps. Other seasonal variations in ﬂow are dueto inﬁltration, which is linked to rainfall pattern and groundwater levels,and seasonal industrial activities such as food processing.
26 How Nature Deals with Waste1.2.2. Composition of sewageWastewater is deﬁned as domestic (sanitary) or industrial (trade). Domes-tic wastewater comes exclusively from residences, commercial buildings,and institutions such as schools and hospitals, while industrial wastewatercomes from manufacturing plants. Inevitably, large towns and cities havea mixture of domestic and industrial wastewaters which is commonly re-ferred to as municipal wastewater, and normally includes eﬄuents from theservice industries such as dairies, laundries, and bakeries, as well as a vari-ety of small factories. It is unusual for modern municipal treatment plantsto accept wastewater from major industrial complexes, such as chemicalmanufacturing, brewing, meat processing, metal processing, or paper mills,unless the treatment plant is speciﬁcally designed to do so. The practice inall European countries is now for water authorities to charge industry forthe treatment and disposal of their wastewater. Thus, the current trend isfor industry to treat its own waste in speciﬁcally designed treatment plants.In many cases, it is not cost-eﬀective for an industry to provide and oper-ate its own treatment plant, although most industries partially treat theirwaste to reduce the pollution load before discharge to the public sewer, inorder to reduce excessive treatment charges. It is of prime importance for the designer and operator of a treatmentplant to have as much knowledge of the composition of the wastewater to betreated as possible. This is particularly important when new or additionalwastes are discharged to existing plants. A full analysis of the wastewaterwill, for example: (i) determine whether pretreatment is required; (ii) determine whether an industrial waste should be treated alone or with sewage and, if so, in what proportions; (iii) determine whether an industrial waste would attack the sewer; (iv) permit a better selection of the most appropriate treatment process; (v) allow an assessment of the toxicity or disease hazards; (vi) provide indication of the resultant degree of eutrophication or organic enrichment in the form of sewage fungus in the receiving water (i.e. impact assessment); and(vii) an assessment of the recoverable or reusable fractions of the wastewater. Although there is considerable similarity in the basic content of sewage,the precise volume and characteristics will vary not only from country tocountry because of climatic conditions and social customs, but also within
Nature of Wastewater 27 Table 1.14. Volume and composition of human faeces and urine (Gloyna 1971). Faeces Urine Moist weight per capita per day 135–270 g 1.0–1.3 kg Dry weight per capital per day 35–70 g 50–70 g Moisture content 66–80% 93–96% Organic matter content (dry basis) 88–97% 65–85% Nitrogen (dry basis) 5.0–7.0% 15–19% Phosphorus (as P2 O5 ) (dry basis) 3.0–5.4% 2.5–5.0% Potassium (as K2 O) (dry basis) 1.0–2.5% 3.0–4.5% Carbon (as dry basis) 40–55% 11–17% Calcium (CaO) (dry basis) 4–5% 4.5–6.0%individual countries due to supply water characteristics, water availability,population size, and the presence of industrial wastes. Data on wastewatersis normally limited to BOD5 (the ﬁve day biochemical oxygen demand test),COD (chemical oxygen demand), suspended solids, and ammonia, while afuller characterisation of the wastewater being treated is rare (Tables 1.13and 3.11). Analysis of wastewater composition can be done directly by lab-oratory examination of the sewage itself or indirectly by predicting thecomposition by examination of the gross components. Details of the com-position of human faeces and urine are available (Table 1.14) althoughdetails of other household wastes which are more variable are less well-known, therefore, more direct methods of wastewater characterisation arepreferred. Surprisingly, little is known of the composition of sewage andfew speciﬁc studies have been carried out. Casanova et al. (2001) carriedout a detailed study of the chemical and microbial characteristics of thewastewater generated by a single family home comprising two adults inArizona in the USA. The wastewater is signiﬁcantly weaker in terms ofBOD and suspended solids compared with domestic wastewater treated ata central works. The wastewater contained high densities of total coliforms8.03 × 107 CPU 100 ml−1 , faecal coliforms 5.63 × 105 CPU 100 ml−1 , fae-cal streptococci 2.38 × 102 CPU 100 ml−1 , and Pseudomonas aeruginosa1.99 × 104 CPU 100 ml−1 . Legislation is setting even tighter controls oneﬄuent quality, especially in terms of nutrients and listed substances (Ta-ble 1.4). More attention is now being paid to eliminating these at sourcerather than providing expensive and often energy intensive end of pipe so-lutions (Chap. 11). Some individual components of sewage which causes
28 How Nature Deals with Wastespeciﬁc problems have been studied. For example, total phosphorus andnitrogen in eutrophication studies, detergents causing foaming, and indolein the control of odours. Sewage is a complex mixture of natural inorganic and organic materi-als with a small proportion of man-made substances. The main source ofpollution in sewage is human excreta with smaller contributions from foodpreparation, personal washing, laundry, and surface drainage. The chemi-cal and physical nature of wastewaters can be further complicated by theinclusion of industrial wastes which are composed of strong spent liquorsfrom main industrial processes and comparatively weak wastewaters fromrinsing, washing and condensing. The reason why sewage composition is normally measured in termsof BOD5 , COD, suspended solids, and ammonia content is because it isfrom these basic determinants that its polluting strength is assessed. Mostcharging systems are based on the Mogden formula, which uses these basicdeterminants. Other variables occasionally measured under speciﬁc circum-stances, such as total phosphorus if the ﬁnal eﬄuent is discharged to inlandlakes, or heavy metals if the sludge is to be subsequently used for agricul-ture. Charges are calculated from separate costs for reception, conveyancetreatment and disposal actually given to the trade eﬄuent. The basic for-mula is: C = R + V + (Ot/Os)B + (St/Ss)Swhere C is the total charge in pence (sterling) per 1000 litres of tradeeﬄuent, R is the reception and conveyance cost per 1000 litres, V the vol-umetric and primary treatment costs per 1000 litres, Ot the COD of tradeeﬄuent after one hour quiescent settlement (mg l−1 ), Os the COD of aver-age strength settled sewage (mg l−1 ), B the cost of biological oxidation ofsettled sewage, St the total suspended solids of the trade eﬄuent (mg l−1 ),Ss the total suspended solids of average strength settled sewage (mg l−1 ),and S the treatment and disposal cost of primary sludge per 1000 litres ofsewage. Some companies have modiﬁed the basic Mogden formula to incorporateadditional factors. These are Bv or V b, which is the additional volumecharge if there is biological treatment (p m−3 ), M is cost for treatment anddisposal where the eﬄuent goes to a sea outfall (p m−3 ), and M d or V ma supplement to M where the eﬄuent goes to a designated long sea outfall(p m−3 ). This gives a modiﬁed Mogden formula: C = R + V ([V + Bv] or V m or M ) + (Ot/Os)B + (St/Ss)S
Nature of Wastewater 29Table 1.15. Trade charging formula employed in the UK during 1999/2000. Details ofabbreviations are given in the text except: V b = V + Bv; V m = M ; M o = monitoringcosts; and P = the cost per m3 of the preliminary treatment required for foul sewage.Water service company ChargingAnglian C = R + (V or V b or V m or M ) + (Ot/Os)B + (St/Ss)SDwr Cymru C = R + V or V b + (Ot/Os)B + (St/Ss)SNorthumbrian C = R + V + (Ot/Os)B + (St/Ss)SNorth West C = R + V + M + B1 + (Ot/Os)B2 + (St/Ss)SSevern Trent C = R + V + (Ot/Os)B + (St/Ss)SSouthern C = R + (V or V b or V m) + (Ot/Os)B + (St/Ss)S + MSouth West C = R + V (or V m) +(Ot/Os)B + (St/Ss)SThames C = R + V + (Ot/Os)B + (St/Ss)SWessex C = R + V + (Ot/Os)B + (St/Ss)SYorkshire C = R + P (Ot/Os)B + (St/Ss)SNorth of Scotland C = R + V + (Ot/Os)B + (St/Ss)SEast of Scotland C = R + V + (Ot/Os)B + (St/Ss)S + M oWest of Scotland C = R + V + (Ot/Os)B + (St/Ss)SNorthern Ireland C = R + V + (Ot/Os)B + (St/Ss)SSpeciﬁc company trade eﬄuent charging formulae are given in Table 1.15,and charges in Table 1.16. Other variables are occasionally measured underspeciﬁc circumstances, such as total phosphorus if the ﬁnal eﬄuent is dis-posed of to inland lakes or heavy metals if the sludge is to be subsequentlyused for agriculture. The strength of sewage varies widely and depends on such factors asper capita water usage, inﬁltration, surface and storm water, and localhabits. The water usage in the USA is at least three times greater thanin Britain, which is why American sewage is usually weaker. Although theper capita production of organic matter is essentially the same in the USAand Britain, the diﬀerence in water consumption results in a raw sewageBOD5 of between 100–700 mg l−1 (with a mean BOD5 of 320 mg l−1 )in Britain (Painter 1971). The use of garbage grinders or disposal units,so that household kitchen waste is disposed to the sewer rather than therefuse bin, results in a 30% increase in wastewater BOD5 and 60% increasein the suspended solids. The concentration of nitrogen in domestic wastew-ater is directly related to the BOD5 , with about 40% of the total nitrogenin solution as ammonia. Proteins and urea undergo deamination releasingammonia as the wastewater ﬂows to the treatment plant. The longer the
30 Table 1.16. British trade eﬄuent tariﬀs 2000–2001. Regional Minimum strengthsWater & sewerage companies charge £ R p/m3 V p/m3 Bv p/m3 M p/m3 B p/kg S p/kg Os mg/l Ss mg/lAnglian — Green 167.00 13.49 21.12 4.08 11.31 44.05 30.99 419 402 — Orange 167.00 12.58 19.69 3.80 10.55 41.08 28.92 419 402 — Blue 167.00 12.35 19.32 3.75 10.35 40.34 28.35 419 402 — Industrial 167.00 9.53 14.93 2.89 8.01 31.16 21.92 419 402Dwr Cymru1 ˆ 112.50 17.29 19.68 8.18 11.77 25.55 26.41 500 350North West 120.00 11.20 9.00 1.30 8.60 25.50 29.20 247 232Northumbrian 230.00 18.66 9.15 — — 33.20 37.72 386 187Severn Trent2 86.60 12.53 11.81 — — 20.11 15.35 351 343South West 149.00 35.80 32.99 — 6.01 78.09 70.96 744 489Southern 180.00 24.26 17.70 2.87 15.37 51.70 31.25 452 512Thames3 71.00 6.71 8.25 — — 24.95 35.87 445 336Wessex 170.00 22.65 14.65 — 7.57 29.77 37.29 802 313Yorkshire4 202.00 20.48 20.22 — 12.13 21.94 36.00 905 314 How Nature Deals with WasteNotes: ˆ1 Dwr Cymru has a reduced charge R of 11.24p/m3 , where the volume discharged is > 100, 000m3 per annum. A ﬁxed charge of £6,050also applies to discharges > 100, 000m3 .2 Severn Trent Water has a banded charge, R ≤ 49, 999m3 charged at the standard rate of 12.53p/m3 , then ≥ 50, 000m3 to < 250, 000m3is charged at 11.49p/m3 and ≥ 250, 000m3 at 9.23p/m3 .3 Thames Water has a large user trade eﬄuent tariﬀ for customers with an annual bill > £58,000. This includes a ﬁxed charge based onmeter size, an annual charge of £10,000 and reception and treatment charges of R = 5.34p/m3 , V = 6.56p/m3 , B = 19.86p/m3 and S= 28.55p/m3 .4 Yorkshire Water has a banded charge, R ≤ 50, 000m3 charged at the standard rate of 20.48p/m3 , then > 50, 000m3 to ≤ 250, 000m3 ischarged at 11.32p/m3 and > 250, 000m3 at 7.72p/m3 . The M charge is calculated as 60% of the V charge.
Nature of Wastewater 31 Table 1.17. Comparison of typical chemical composition of raw wastewaters from the USA and UK. Parameter USA (mg l−1 ) UK (mg l−1 ) pH 7.0 7.2 BOD 250 326 COD 500 650 TOC 250 173 Total solids 700 — Suspended solids 220 127 Total nitrogen 40 66 Organic nitrogen 25 19 Ammonia nitrogen 25 47 Nitrite 0 0 Total phosphorus 12 15 Oraganic phosphorus 2 3 Inorganic phosphorus 10 12sewage is held in the sewer, the greater will be the release of ammonia. Theper capita nitrogen production in the United Kingdom is 5.9 g N per day(Painter 1958) which is essentially the same as the American ﬁgure (Bab-bitt 1947). The per capita production of phosphorus is about a third ofthe weight of nitrogen produced, about 1.4 kg per capita per year. Of this,up to 70% comes from polyphosphate builders used in synthetic detergents(Table 1.17). Detergent polyphosphate builders are slowly being replacedby alternative phosphorus free builders such as zeolites. The amount of organic matter produced per capita each day expressedin terms of BOD5 is also known as the population or person equivalent.Population equivalent (PE), expressed in kg BOD5 per capita per day, isdetermined as: mean ﬂow (l) × mean BOD5 (mg l−1 ) PE = 106Population equivalent is often used in the design of treatment plants, andthe volume and strength of industrial wastewaters are normally expressedin terms of equivalent population. In the UK, the PE of domestic sewage isequivalent to 0.055 kg BOD5 per capita d−1 . This ranges from 0.045 kg foran entirely residential area to 0.077 kg for a large industrial city. Americanﬁgures are similar for domestic sewage, being 0.052 kg for separate sewersand 0.063 kg for combined sewers. However, the recognised design ﬁgures
32 How Nature Deals with Wastein the USA and Canada are 0.077 kg BOD5 and 0.10 kg suspended solids.Apart from BOD5 and suspended solids, it is also common to quote totalnitrogen or total phosphorus in terms of PE. The PE of an industrial wastewater in Britain is calculated using therelationship: mean ﬂow (m3 d−1 ) × mean BOD5 (mg l−1 ) PE = 0.055 × 103Similar to ﬂow, the strength and composition of sewage changes on anhourly, daily, and seasonal basis. However, it is the diurnal variation that isusually the greatest. A similar diurnal pattern of sewage strength is formed,in terms of BOD5 and suspended solids, as occurs with ﬂow (Fig. 1.3). Thepeak in BOD occurs in the mid morning but, as with the ﬂow, the actualtime depends on the length of the sewers and the nature of the area served.The strength of sewage in large cities, with very long and complex sewer-age systems, does not ﬂuctuate as widely as it does in smaller catchmentswith maximum values occurring between 10 p.m. and 6 a.m. (Painter 1971).There is a wide diurnal variation in BOD5 strength. This variation is alsoreﬂected by similar ﬂuctuations in the concentrations of the various car-bohydrates and fatty acids that largely make up the biodegradable carbonfraction (Painter 1958). Peaks also occur in the concentrations of ammoniaand urea, occurring in the morning and late at night, reﬂecting the habitsof the local population served. However, only the morning peak is generallydiscernible. Strength varies from day to day due to the dilution eﬀect of surfaceand storm water. The daily ﬂuctuation in ﬂow and strength is much less attreatment plants fed by a separate sewerage system. Wastewater volumesare greater on Mondays than any other day in the USA (Heukelekian andBalmat 1959), while the concentration of detergents in the UK has beenreported as being higher on Mondays than the rest of the week (Eden andTruesdale 1961). However, this data was collected when automatic washingmachines were not widely available and the household laundry for the weekwas done by necessity on a speciﬁc day, usually Monday, so it is unlikelythat this trend is still discernible today. Seasonally, sewage strength doesnot vary signiﬁcantly, although periods of drought and excessive rainfallcan aﬀect the dilution ratio in combined sewerage systems due to reducedinﬁltration and storm water. In the summer, bacterial concentrations in thewastewater reach a maximum, as do virus concentrations (Painter 1971). Wastewater can only be treated biologically if suﬃcient nitrogen andphosphorus are present. Normally, there is a surplus of these nutrients in
Nature of Wastewater 33sewage for biological needs but it is necessary to assess the treatabilityof wastewaters by checking the ratio of carbon to nitrogen and phospho-rus (C:N:P). The optimum C:N:P weight ratio for biological treatment is100:5:1 (100 mg l−1 BOD5 , 5 mg l−1 N, 1 mg l−1 P). The C:N:P ratio forraw sewage is approximately 100:17:5 and 100:19:6 for settled sewage, bothcontaining abundant nutrients for microbial growth. The nitrogen require-ment of the micro-organisms in the biological unit of a treatment plant issatisﬁed if the ratio of carbon, measured as BOD5 , to nitrogen equals oris less than 18:1. Even at C:N ratios > 22:1 removal still occurs, but muchless eﬃciently. Micro-organisms require much lower levels of phosphorus compared withnitrogen so the phosphorus requirement will be met if the C:P ratio is lessthan 90–150:1. Above 150:1, there is an increasing loss of eﬃciency (Porges1960, Hattingh 1963, Komolrit, et al. 1967). The exact C:N:P ratio for op-timum biological growth depends on the biological process and the formin which the nutrients are available in the wastewater. Where wastes failto meet the C:N:P criteria, it becomes necessary to add nutrients in or-der to ensure that biological oxidation occurs. This is often carried outby mixing nutrient deﬁcient wastes with sewage in the correct proportions(Sec. 3.3.2). Wastewaters from the brewing and canning industries are par-ticularly deﬁcient in nitrogen and phosphorus, therefore nutrient additionis required if optimum carbonaceous oxidation is to be achieved. An exam-ple of nutrient deﬁcient wastewater is cited by Jackson and Lives (1972)who found that the BOD removal during the treatment of a cider eﬄuentusing low-rate percolating ﬁltration was increased from 92 to 99% whenthe nitrogen and phosphorus balance was corrected by the addition of aninorganic supplement.Physical propertiesThose who have not actually come into contact with raw sewage oftenharbour rather strange ideas as to what it looks and smells like. By the timeit reaches the sewage treatment plant the vast majority of the large solids,such as faeces and paper, have broken up into very small particles. Thus,apart from a small quantity of ﬂoatable material, raw sewage is a ratherturbid liquid with visible particles of organic material that readily settleout of suspension. The colour is normally grey to yellow-brown, accordingto the time of day. However, if all the oxygen has been used up duringtransit in the sewer then the wastewater becomes anaerobic or septic andtakes on a much darker colour, and in extreme cases turns black. Municipal
34 How Nature Deals with Wastewastewaters receiving industrial wastes containing dyes will take on thecolour of the dye present, and at treatment plants receiving eﬄuents fromthe textile industry in particular, the raw wastewater undergoes spectacularand frequent colour changes. Under ultraviolet light, domestic sewage hasa characteristic coloured ﬂuorescence which is due to a variety of minorconstituents present in household detergents. Generally, domestic wastewater has a musty or earthy smell which is notat all oﬀensive, although pungent odours can be produced if the wastewa-ter becomes anaerobic. Certain industrial wastes and contaminants in sur-face runoﬀ do have distinctive odours. Like a wine connoisseur, the abilityof the operator to develop a discerning nose can be extremely helpful inidentifying potential problems within the treatment plant and to identifychanges in the composition of the sewage entering the plant. The odoursproduced are usually caused by gases produced by the decomposition ofvarious fractions of the organic matter present in the wastewater. The com-monest odour encountered is the smell of rotten eggs caused by hydrogensulphide, which is produced by anaerobic bacteria reducing sulphate tosulphide. Table 1.18 lists the major categories of odours encountered atsewage treatment plants, although the quantiﬁcation of such odours foruse as a control variable has proved extremely diﬃcult (American PublicTable 1.18. Some characteristic odours produced by compounds present in wastewaters.These degradation products can be categorised into two main groups, either degradationproducts of nitrogenous or sulphurous compounds. There are other odourous compoundssuch as those associated with chlorine and phenolic wastes. Compounds General formulae Odour producedNitrogenousAmines CH3 NH2 , (CH3 )3 N FishyAmmonia NH3 Ammoniacal, pungentDiamines NH2 (CH2 )4 NH2 , NH2 (CH2 )5 NH2 Rotten ﬂeshSkatole C8 H5 NHCH3 Faecal, repulsiveSulphurousHydrogen sulphide H2 S Rotten eggsMercaptans CH3 SH, CH3 (CH2 )3 SH Strong decayed cabbageOrganic sulphides (CH3 )2 S, CH3 SSCH3 Rotten cabbageSulphur dioxide SO2 Pungent, acidicOtherChlorine Cl2 ChlorineChlorophenol Cl.C6 H4 OH Medicinal, phenolic
Nature of Wastewater 35Health Association et al. 1983; Metcalf and Eddy Inc. 1991). Some foodprocessing wastewaters produce extremely strong odours, especially dur-ing treatment and storage (Gerick 1984; Gray 1988). For example, sugarbeet wastewater undergoes partial anaerobic breakdown within the processand subsequently on storage in lagoons, with the production of a variety ofodours. The major odours come from the volatile fatty acids that comprisemost of the organic fraction of the eﬄuent. The odour threshold concen-trations for the volatile acids produced during treatment of sugar beet are24.3 ppm for acetic acid, 20.0 ppm propionic acid, 0.05 ppm iso-butyricacid, 0.24 ppm butyric acid, 0.7 ppm iso-valeric acid, and 3.0 ppm forvaleric acid. Therefore, by measuring the volatile acid concentration anddividing it by the appropriate odour threshold concentration, a measure ofthe odour production or concentration known as the odour number can becalculated (Gray 1988). Other odours associated with sugar beet process-ing include trimethylamine which has a ﬁshy odour and organic sulphideswhich produce a strong odour of rotting cabbage, as do the thiol com-pounds methyl mercaptan (CH3 SH) and ethyl mercaptan (C2 H5 SH), bothof which have very low odour thresholds of 0.0011 ppm and 0.00019 ppmrespectively (Shore et al. 1979). A detailed list of odour threshold valueshas been compiled by Fazzalari (1978). The temperature of sewage is normally several degrees warmer than theair temperature, except during the warmest months, due to the speciﬁcheat of water being much greater than that of air. Sewage temperaturesare normally several degrees warmer than the water supply and becauseof its high conductivity rarely freezes in temperate climates. In the UK,the temperature of raw sewage ranges from 8–12◦C in winter to 17–20◦Cin the summer (Painter 1971). Comparative studies have shown that thevariability in the temperature of settled sewage, as it enters the percolatingﬁltration stage at a treatment works in South Yorkshire, is 30–50% less thanthat recorded for the air temperature, a total range of 11.5◦C and 30.4◦ Crespectively. Both the sewage and air temperatures followed similar seasonalpatterns, reaching maximum and minimum temperatures during the sameperiods. However, while the mean daily air temperature varied annually,the mean daily temperature of the sewage remained constant at 12.4◦ C(Gray 1980). In hotter climates domestic sewage can be much warmer, andin India sewage temperatures of 28–30◦C are not unusual (Kothandaramanet al. 1963). The pH of sewage is usually above 7 with the actual value dependinglargely on the hardness of the supply water. Although extreme values areoccasionally encountered, soft water catchments generally have a pH range
36 How Nature Deals with Wasteof 6.7–7.5 (modal pH = 7.2) and hard water catchments a range of 7.6–8.2(modal pH = 7.8) (Painter 1971). Total solids (i.e. the weight of matter remaining after a known volume ofwastewater has been evaporated at 105◦ C) is a commonly used wastewatervariable in the USA. It provides a simple characterisation of the wastewa-ter with which the theoretical performance of unit treatment processes canbe predicted. Total solids can be classiﬁed as either suspended or ﬁlterabledepending on whether solids will pass through a standard ﬁlter (Depart-ment of the Environment 1972). The standard ﬁlter used in Britain is a Whatman GF/C ﬁlter paper, theGF referring to its glass ﬁbre structure, which has a pore size of 1.0 μm.Therefore, all the ﬁlterable solids have a particle size of < 1.0 μm. Thesuspended solids fraction ranges from colloidal particles < 1.0 μm up torecognisable gross matter. A portion of the suspended solids fraction issettleable, which is measured by measuring the volume of solids that set-tle out of suspension over a 60 minute period under quiescent conditions.An Imhoﬀ cone, which is an inverted 1 litre conical ﬂask, is used for thispurpose and provides a useful estimate of the solids removal and sludgeproduction during primary sedimentation. The ﬁlterable fraction containscolloidal and dissolved material. The colloidal solids are particulate rang-ing from 1 nm–1 μm in size, which are too small to be removed by gravitysettlement. An assessment of colloidal solids can be made by measuring thelight-transmitting properties of the wastewater, the turbidity, as colloidalmatter scatters and absorbs light. The dissolved fraction is made up of bothorganic and inorganic molecules that are in solution. Each of these major categories of solids is comprised of both organicand inorganic material, and the ratio of each can be measured by burningoﬀ the organic fraction in a muﬄe furnace at 600◦ C (Allen 1974). Certainsalts are also destroyed by heating, although only magnesium carbonateis decomposed at this temperature being transformed to magnesium oxideand carbon dioxide at 350◦ C. The major inorganic salt in domestic sewageis calcium carbonate, but this remains stable up to 825◦C. The percentageof each solids fraction in a wastewater depends on the chemical compositionof the sewage. However, Painter (1971) separated the particulate solids indomestic sewage as approximately 50% settleable (> 100 μm diameter),30–70% supra-colloidal (1–100 μm) and the remaining 17–20% as colloidal(1 nm–1 μm). However, a more detailed breakdown of the proportion ofparticular solids fractions in domestic wastewater and the organic strengthof each fraction is shown in Table 1.19.