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07/05/2016
1
Anaerobic Processes 101
Chicago is a beautiful city on Lake Michigan…..
07/05/2016
2
Chicago's Stickney WWTP is one of the crappiest places on Earth
(2.38 million-people’s worth of crap!!!)
….. ...
07/05/2016
3
….. and by the largest (32 million m3) stormwater
holding tank
SUSTAINABLE SEWERAGE
• need to consider WWT sy...
07/05/2016
4
SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY
• in OECD Countries, nutrients in WW correspond to 8% of applied min...
07/05/2016
5
SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY
• P is most commonly removed by chemical precipitation using Fe- or ...
07/05/2016
6
SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY
• while N is abundant in nature (78% of the atmosphere consists on N...
07/05/2016
7
Current available technologies for P recovery
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
07/05/2016
8
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION (INDUSTRIAL)
• Industrial water consumption can be reduced main...
07/05/2016
9
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION (INDUSTRIAL)
• reuse of Process water can be a substantial wate...
07/05/2016
10
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION (CIVIL)
• urban water consumption reduction strategies can be ...
07/05/2016
11
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION (CIVIL)
GREYWATER MANAGEMENT
with heat recovery system
for irr...
07/05/2016
12
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
REINVENTING SANITARY WATER USE
• vacuum and gravity operated t...
07/05/2016
13
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
• vacuum sewer systems transport sewage using differential pre...
07/05/2016
14
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
• a vacuum sewer system guarantees a very high level of comfor...
07/05/2016
15
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
SEWER MINING
Sewer mining has been described as the process
of...
07/05/2016
16
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
SEWER MINING
Typical reuse water applications include the foll...
07/05/2016
17
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
SEWER MINING
Residential use (including flushing of toilets an...
07/05/2016
18
SUSTAINABLE SEWERAGE
REDUCE WATER CONSUMPTION
SEWER MINING
Sewer mining drivers - Advantages (2)
• Operation...
07/05/2016
19
SUSTAINABLE WATER MANAGEMENT
TOILET TO TAP (T2T)
NOT EXACTLY….
Thursday, 22 Oct 2015 | 2:25 PM ET
LA conside...
07/05/2016
20
SINGAPORE’S NEWATER
Singapore introduced
the NEWater program
in order to reduce its
dependence for water
sup...
07/05/2016
21
SUSTAINABLE SEWERAGE
MINIMIZE ENERGY NEEDS
• WWTPs are energy-intensive facilities. Reducing their carbon fo...
07/05/2016
22
SUSTAINABLE SEWERAGE
MINIMIZE ENERGY NEEDS
There are several “general” measures that can be applied to impro...
07/05/2016
23
SUSTAINABLE SEWERAGE
MINIMIZE ENERGY NEEDS
• System controls that use SCADA feedback can be used to optimize...
07/05/2016
24
SUSTAINABLE SEWERAGE
MINIMIZE ENERGY NEEDS
• Old devices replacement.
• Variable Frequency Drives improve fa...
07/05/2016
25
SUSTAINABLE SEWERAGE
HEAT RECOVERY FROM WW
In-house and in-sewer systems
Theoretical recovery:
7 kWh/m3 per ...
07/05/2016
26
SUSTAINABLE SEWERAGE
HEAT RECOVERY FROM WW
A CONTROVERSIAL ISSUE (2)
• Analysis of an industrial WWWP in Den...
07/05/2016
27
SUSTAINABLE SEWERAGE
HEAT RECOVERY FROM WW
A CONTROVERSIAL ISSUE (4)
• From the analysis, the facility in it...
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Lectures Capodaglio - Session 2

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Sustainable Water - Energy - Centric Communities school
May 9 - 13, 2016 – Lake Como School of Advanced Studies

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Lectures Capodaglio - Session 2

  1. 1. 07/05/2016 1 Anaerobic Processes 101 Chicago is a beautiful city on Lake Michigan…..
  2. 2. 07/05/2016 2 Chicago's Stickney WWTP is one of the crappiest places on Earth (2.38 million-people’s worth of crap!!!) ….. served by the largest sewer on Earth, 115 m below ground,
  3. 3. 07/05/2016 3 ….. and by the largest (32 million m3) stormwater holding tank SUSTAINABLE SEWERAGE • need to consider WWT systems under a holistic approach, i.e. primary and secondary environmental effects and costs that a system causes (pollution at power plant to generate electricity, energy costs of producing chemicals, etc.). • to evolve towards a sustainable society we need to recycle nutrients, reduce water consumption, and minimize energy needed to operate waste treatment.
  4. 4. 07/05/2016 4 SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY • in OECD Countries, nutrients in WW correspond to 8% of applied mineral fertilizers, those in household and yard waste to another 7%. If all N & P in WW in the world were reclaimed and recycled into agriculture, application of mineral fertilizer could be reduced more than 40%. • at the same time, more than 7% of the world’s natural gas production is useda to fix atmospheric N through the Haber-Bosch Process to satisfy fertilizers demand. Somewhat less for P production. From an environmental perspective fossil fuel consumption could be significantly reduced through direct use of WW N & P as fertilizers instead of manufacturing them. (Energy is spent to rid WW of fertilizing elements, then more energy is spent again to produce them!) a 1990 figures SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY • blackwater (toilet WW) contains 90% N, 74% P, 79% K, and 30–75 % organic matter from household discharges. • the most common method of N removal in conventional treatment plants today is biological processes. A nitrogen removal step with pre- or post-denitrification more than doubles the energy consumption of a treatment plant, compared to N chemical precipitation. With biological processes, most of the removed N is discharged into the atmosphere. • chemical pre-precipitation with small amounts of MgCl2 can be used as an efficient alternative for removal of COD and nutrients. High COD precipitation could result in more biogas production from AD of primary sludge, lower oxygen consumption in the biological stage, and facilitated nitrification. Nutrients can be recycled/recovered from the effluent of the digester. Higher content of N & P will ensure a richer quality of sludge, more suitable for agriculture. • stripping from sludge dewatering streams is a cost-efficient ammonia removal and recycle technology. Sludge is conditioned with lime to increase pH, resulting in free ammonia, absorbed with nitric acid in adsorption towers. The result is a solution of ammonium nitrate (~55%), used for fertilizer production.
  5. 5. 07/05/2016 5 SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY • P is most commonly removed by chemical precipitation using Fe- or Al-salts as precipitating agents. Ferric chloride is the most commonly used, but forms strong complexes with pyrophosphates which need to be later separated, increasing costs. Aluminum salts are cheaper, produce sludge with excellent dewatering properties, and produce lower sludge volumes. With aluminum salts, P is not released during storage or digestion. Plant availability of phosphorus precipitated as Fe- or Al-phosphates can be very limited due to very low solubility under normal soil conditions. Lime-precipitated phosphates are more easily dissolved and available to the plants. • Bio-P removal is carried out by PAO bacteria (phosphate accumulating organisms) that concentrate phosphate in Poly-P granules when they are cycled between aerobic and anaerobic conditions in a WWTP. The simplest process (Phoredox) has two reactors in an anaerobic-aerobic sequence. The anaerobic zone is placed first to take advantage of electrons available in raw WW. Phosphate is released, and its concentration increases. In the aerobic zone, released phosphate is assimilated in cells and stored as PHAs (poly-β-hydroxyalkanoates) and PHBs (polyhydroxy-butyrate). SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY • cost and energy consumption of chemical precipitation processes is low compared to bio-P removal methods, since adding and mixing chemicals to WW is far more energy efficient than aeration needed for biological treatment. In Norway energy consumption for chemical precipitation is 0,23 kWh/m3 t.w. (mostly for heating and ventilation of the buildings). For bio-P (with 30% removal) is in the order of 0,37 kWh/m3 • Chemical precipitation also removes other wastewater constituents than phosphorus (COD, N, TSS) that make up a richer primary sludge for digestion. • agricultural recycling of N & P is difficult unless they are precipitated as struvite, a phosphate mineral with formula NH4MgPO4·6H2O (same as kidney stones). Originally, struvite precipitation was intended as a means of N recovery, however, its importance as a means of P recovery is even greater • magnesium removes 90% of the nutrients due its high flocculation properties. The chemical used to produce struvite (magnesium oxide) is expensive. As an alternative, magnesium contained in sea water (bittern - a reject by-product from evaporation ponds in the sea salt industry) can be used as coagulant to remove WW nutrients as is cheaper, and with a higher rate of precipitation.
  6. 6. 07/05/2016 6 SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY • while N is abundant in nature (78% of the atmosphere consists on N2) P is a finite (limited) resource, relatively scarce, and not evenly distributed across the Earth. The predominant source of P is phosphate rock (in the past, guano). According to some researchers, Earth's P reserves are expected to be completely depleted in 50–100 years and peak phosphorus (a concept to describe the time at which maximum global P production rate occurs) to be reached in approximately 2030. • rock phosphate shortages (or just significant price increases) would have a big impact on the world's food security. Many agricultural systems depend on supplies of inorganic fertilizer. Unless systems change, shortages of rock phosphate could lead to shortages of fertilizer, which could affect crop growth and cause mass starvation. • up to 97% P recovery as struvite from WW have been reported. Struvite has commercial value as P source (about £ 200/ton in 2002, with prices increasing due to projected P scarcity). Revenue from the sale of produced struvite could be significant for a WWTP. SUSTAINABLE SEWERAGE – NUTRIENT RECOVERY • urine is an excellent fertilizer and needs only 6 months storage to obtain hygienic safety for agricultural use. While the actual content will vary slightly depending on your diet, urine is generally a well balanced N rich fertilizer straight out of the body. The average person produces enough urine per year to cover 300-400 m2 of land to a level of 50-100kg N/ha, 7-15 kg P/ha and 15-30 kg K/ha. • a family of four can produce the equivalent of a 50 kg bag of NPK fertilizer from urine every year, with higher nitrogen content than most mineral fertilizers. A positive effect of using urine is that the phosphorous is in a plant-usable form, requiring no additional processing before it can be absorbed.
  7. 7. 07/05/2016 7 Current available technologies for P recovery SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION
  8. 8. 07/05/2016 8 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION (INDUSTRIAL) • Industrial water consumption can be reduced mainly by process optimization and technological process innovations. Cooling water represents a large part of water consumption for some industries . • Significant process water reductions can be obtained with optimization and internal water reuse. SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION (INDUSTRIAL) • optimisation of process water use can lower water withdrawals from local water sources, increasing water availability, increasing productivity per water input, lowering wastewater discharges and pollutant load, reducing thermal energy consumption and perhaps costs. • industry affects water resources more by WW discharges and their pollution load than by the quantity used in production. Pollutants are by-products of producing activities, the major pollutants being nutrients, pathogens, heavy metals, organic and inorganic chemicals, oil sediments and heat. Temperature changes of just one degree can trigger subtle changes in biology of aquatic organisms, causing them to change their metabolism or plant growth. • optimization and reuse programs may result in higher pollutant concentrations in industrial WW, due to lower dilution.
  9. 9. 07/05/2016 9 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION (INDUSTRIAL) • reuse of Process water can be a substantial water saving factor in industry • instead of assuming that all processes require drinking quality water, match actual water quality needed for internal processes to available waste streams, possibly with minimal treatment. For example, if a polishing machine requires water with a given particulate level, by installing a settling tank and greywater treatment the water could technically be reused over and over. • possible treatment options for water reuse include all available treatment technologies, at the simplest possible level for that application SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION (CIVIL) water use (total) population
  10. 10. 07/05/2016 10 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION (CIVIL) • urban water consumption reduction strategies can be manifold. Practically, 20- 40% of water consumption in (traditionally) sewered cities is used to flush toilets. • greywater collection and treatment could be an important part of a complete sustainable sanitation system. In Beijing, municipal regulations mandate greywater treatment with local reuse (e.g. toilet flushing) for all new residential and business developments. These measures are often disattended due to the lower cost of water from the public system. SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION (CIVIL) GREYWATER MANAGEMENT With treatment A greywater filter can be made of sand or high-tech materials
  11. 11. 07/05/2016 11 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION (CIVIL) GREYWATER MANAGEMENT with heat recovery system for irrigation/infiltration (GW recharge) 1. rooftop rainwater collection system for greywater use in toilets and landscape irigation 2. over 30% of windowsare operableto providenatural ventilation in most interiorspaces and crossventilation in some areas 3. natural daylight use is maximised through solatubes which collect and direct sunlightfrom multiple angles via mirrored inner surfaces 4. geothermalwells providehigh-efficiency winter heating and summer cooling SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION GREYWATER MANAGEMENT Researchers from UC Berkeley have proposed water-recycle system for tall buildings coupling solar disinfection of grey water with thermal storage for energy management and light transmission control. The breakthrough is the plan for a system of micro- optic lenses on exterior walls that links the grey w water disinfection process to radiant floor heating via a lightweight membrane. The solar lenses have absorption of up to about 150 degrees, and are contained inside a thin film applied to the walls.
  12. 12. 07/05/2016 12 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION REINVENTING SANITARY WATER USE • vacuum and gravity operated toilets using 0,5-1,5 liter per flush are commercially available. Experience shows that 5-7 liters of blackwater is produced per person and day with these, while using conventional flush toilets the daily procapita production would be 6–15 times higher. Low-flush toilets work with a very small amount of water, the exact amount of water varying between < 1L (for urine) 6-8 L. They toilets can operate by gravity or vacuum. Gravity toilets have specific requirements regarding the slope of the pipe. If the gradient to the sewer system is sufficient, low-flush toilets can be retrofitted into existing buildings. Vacuum toilets use much less water (0.5-1.5L for transport of faeces and urine) due to air sucked into the toilet when flushing. The system is completely closed: if there is a leak, negative pressure in the pipes reduces the risk of raw sewage spills. SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION REINVENTING SANITARY WATER USE • Experience shows that 5-7 liters of blackwater is produced per person and day with low flush or vacuum toilets, while using conventional flush toilets the daily procapita production would be 6–15 times higher. • there are two different designs for a vacuum toilet system: constant vacuum system (CVS) and vacuum on demand (VOD) system. CVS - permanent vacuum generated by VOD – vacuum is generated only when toilet is vacuum pump, to which many “fitted” flushed discharge points can be attached
  13. 13. 07/05/2016 13 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION • vacuum sewer systems transport sewage using differential pressure between atmospheric pressure and a partial vacuum maintained in the piping network. investment costs can be reduced up to 50% due to simpler trenching at shallow depths, lack of manholes, pumps, savings of material costs for small diameter pipes (PVC, MDPE, HDPE or ABS), lower cost to maintain in the long term, due to shallow trenching, easy identification of problems, no sedimentation due to self- cleansing high velocities. • there are many examples of vacuum sewer systems reliably operating for many years worldwide. Still limited diffusion is more a matter of “professional habit” than “technology maturity” SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION • The geometry of a vacuum sewer system is similar to that of a traditional system (tree pattern). Pipes are laid in a saw-tooth profile at depths ranging from 0.9-1.5 m (depending on frost conditions). The radius of action of a vacuum station is about 3 km on flat terrain, if terrain elevation differences are exploited, useful radius can increase up to 5 km. In-pipe transport velocities ranges from 3-5 m/s. • Maximum number of users (at peak flow of 2 L/min per user) on a given line depends on pipe diameter, varying from 80 users for 10 cm pipes to 750 users for 25 cm pipes. • Compared with equivalent conventional systems, capital costs are lower. Lower piping costs (dimensions are smaller), no manholes needed (only pressure-testing points), installation costs are independent from topography (low excavation required). A vacuum system requires a vacuum/gravity interface valve at each entry point, to seal the lines and maintain vacuum within. A vacuum collection vessel is installed at a central vacuum station, where pumps create the required negative pressure (~-0.6 bar). Transfer pumps convey the wastewater from the vessel to another intermediate vessel, an existing sewer, or a wastewater treatment plant.
  14. 14. 07/05/2016 14 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION • a vacuum sewer system guarantees a very high level of comfort and hygiene. There is a very low risk of contamination due to leakage, and there is practically no contact between WW and operators. • energy requirement for vacuum generation influence operating costs, but need to be compared to the positive pumping costs in traditional systems. Systems need trained workers for O&M. Risk of clogging is low, is almost no cleaning/emptying work required. • in combination to vacuum/low flush toilets, they create concentrated waste streams, allowing the use of smaller, more energetically efficient treatment processes like anaerobic ones Additional applicability criteria - Areas short of water supply that cannot afford amounts of water necessary for operation of gravity systems or attainment of flushing velocities in pipes - Areas that are ecologically sensitive - Areas where flooding can occur - Areas with obstacles to a gravity sewer route or with geology (rock layers, running sand, high groundwater table) that make deep excavation difficult - Concurrent installation of new fresh water/underground service networks, allowing pipe installation in the same (shallow) trench However, they NEED EXPERT DESIGN. SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SOURCE SEPARATION • Source separation by urine segregation, composting, or extremely water-saving toilets, can help both reduce reducing water use and facilitate collection and recycling of nutrients. • A urine-diversion toilet bowl has two sections so that urine can be separated from feces without water (a small amount of water is used to rinse the urine-collection bowl when the toilet is flushed). Urine flows into a storage tank for further use/processing, while feces are flushed with water. Advantages Reuse of urine as fertilizer Requires less water than traditional toilets No problems with odors if used correctly Disadvantages Limited commercial availability High capital and low to moderate operating costs Labour-intensive maintenance Requires training and acceptance for correct use Prone to clogging and misuse Men usually require a separate urinal for optimum collection of urine
  15. 15. 07/05/2016 15 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING Sewer mining has been described as the process of tapping into a sewer (either before or after the sewage treatment plant) and extracting sewage which is then treated as recycled water. (Sydney Water) SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING The extent of the treatment process is determined by the requirements of the water quality of the end-use. It is important to select the treatment level appropriate to provide the quality required for the purpose. Reuse of the resource requires removal of sediments and solids, bio- solids, trace metals and trace organics, nutrients, parasites as well as living organisms and pathogens including viruses and bacteria. Most of these contaminants are able to be successfully removed using various technologies and pose no ongoing risks when using the recycled product but risk elements are high for the pathogens, heavy metals and pharmacological. Appropriate legislation has been so far enacted only in Australia.
  16. 16. 07/05/2016 16 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING Typical reuse water applications include the following: •Amenity areas - parks, gardens, ovals, golf courses; •Commercial agriculture - viticulture, floriculture, turf grass, pastures, hay cropping and vegetable production; •Forestry - plantation forestry; •Industrial applications; and •Residential use as part of third pipe developments SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING Issues to be considered: • availability of resource, • appropriate technology identification and selection, • location including land use alternatives, • costs including capital and operational costs, • regulatory and legal constraints, • demand for both quantity and quality • acceptance. Despite these issues in Australia there are many examples of sewer mining plants in existence (example: irrigation of golf courses and residential dual reticulation).
  17. 17. 07/05/2016 17 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING Residential use (including flushing of toilets and gardening) requires tertiary level treatment with pathogen reduction while public places and groundwater recharge often only require secondary treatment. For ground water recharge there are site specific requirement where nutrient reduction is to be carried out. As a rule the minimum level of treatment required is secondary with limited application such as irrigation for fodder food and fibre crops. Use in irrigation may lead to health issues for nearby residence and park users thus the importance of gaining and maintaining appropriate levels of water quality are paramount precluding the transmission of pathogens. (Guidelines for wastewater reuse, World Health Organization, 1989). SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING Sewer mining drivers - Advantages • reduced demand for water and water infrastructure in an increasingly urbanized environment; • increased system resiliency (catastrophic breakdown of local wastewater treatment plant would not cause the whole system to shut down); • sewage treated to a standard fit for purpose. (treatment tailored to specific user requirements, no longer need for “one size fits all”) • minimal WTP impact on environment due to small size, self containment and lack of odours. • more flexibility in response to technological change due to small size. • WTP adaptable to a wide range of community and industrial wastewater applications ranging from residential development projects to sports facilities and parks for a range of volumes.
  18. 18. 07/05/2016 18 SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING Sewer mining drivers - Advantages (2) • Operation is relatively inexpensive, cost of sewer mining plants vary with conditions and capacity but bare minimum costs range from Eur 0.70-1.80/m3 for 100-1000 m3 plants with a capital expenditure of around Eur 700000.00 (Mallapa 2006). • Load at the end of the line treatment plant is reduced, as is the cost of transporting recycled water from the central treatment plant to the reuse site; • Reduction of discharges in open waters; • In urban setting, sewer mining turns a liability into an asset (Gagliardo , 2007). SUSTAINABLE SEWERAGE REDUCE WATER CONSUMPTION SEWER MINING Sewer mining barriers • Public perceptions and concerns, • Inadequate regulatory framework • Lack of robust financial evaluations. These have the characteristics of a “wicked problem.” In a wicked problem, there are high dynamic and behavioural complexities, key decision makers hold different assumptions, values and beliefs and component problems cannot be solved in isolation from one another (Lane and Woodman 2008). Wicked problems are not solved in a linear fashion like their “tame” problem counterparts. Critical elements in solving wicked problems relate to social processes and developing processes that look for opportunities for breakthroughs, synergies, connections and allies (Conklin and Weil, 2008).
  19. 19. 07/05/2016 19 SUSTAINABLE WATER MANAGEMENT TOILET TO TAP (T2T) NOT EXACTLY…. Thursday, 22 Oct 2015 | 2:25 PM ET LA considers $1 billion 'toilet to tap' water program OCT 30, 2015 07:00 AM ET 'Toilet to Tap' Gains Appeal in Bone-Dry West 6 January 2016 WHY WE AL NEED TO START DRINKING TOILET WATER BUT NOT SOO FAR EITHER….
  20. 20. 07/05/2016 20 SINGAPORE’S NEWATER Singapore introduced the NEWater program in order to reduce its dependence for water supply from Malaysia. NEWater now meets 30% of Singapore's total water demand. SINGAPORE’S NEWATER (2) NEWater is produced by a multiple barrier water reclamation process: The first barrier is conventional wastewater treatment in the Water Reclamation Plants. The second barrier, and first stage of the NEWater production process, uses micro- filtration/ultrafiltration to remove suspended solids, colloidal particles, disease-causing bacteria, some viruses and protozoan cysts. The filtered water after passing through the membrane contains only dissolved salts and organic molecules. The third barrier, and second stage of the NEWater production process, uses reverse osmosis (RO). A semi-permeable membrane filters out contaminants such as bacteria, viruses, heavy metals, nitrates, chlorides, sulfates, disinfection by-products, aromatic hydrocarbons, and pesticides. NEWater is thus free from viruses and bacteria and contains very low levels of salts and organic matter. At this stage, the water is of potable quality. The fourth barrier, and third stage of the NEWater production process, is a safety precaution. UV disinfection is used to ensure that all organisms are inactivated and the purity of the water can be guaranteed. After adding some alkaline chemicals to restore the pH balance, NEWater is ready for use.
  21. 21. 07/05/2016 21 SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS • WWTPs are energy-intensive facilities. Reducing their carbon footprint is particularly important not just as an environmental issue, but also for its important economic repercussions. In the last ten years in the EU, electrical energy costs have increased about 175%, from an average of 0.0756€/kWh in 2005, to 0.208 €/kWh in 2014 In sanitation systems, up to 80% of energy is used for pumping water, within WWTPs, most of the energy is used for pumping air. SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS • Assessing the real operating energy efficiency of WWTPs is the starting point for any energy-saving initiative. It is verified that energy efficiencies of WWTPs are generally quite low, with only 10% of them being “efficient”. • Plant size, quantity of organic matter removed, and type of bioreactor aeration are significant variables in explaining energy efficiency differences. In contrast, age of the plant was not a determining factor in energy consumption. • Energy is an important cost factor in WWT, generally second only to personnel costs • A global efficiency index (known as the Russell measure) can be calculated by processing outputs (pollutants removed from wastewater) and inputs (energy, staff, reagents, maintenance, waste management, and other). • As an alternatives, LCA-based analyses can be used. • By analyzing energy efficiency of WWTPs, measures having the highest potential of reducing energy consumption (and consequently GHG emissions), as well as improving (making them more competitive) can be identified. SOURCE: Hernández-Sancho, Molinos-Senante, Sala-Garrido (2011) Energy efficiency in Spanish wastewater treatment plants: A non-radial DEA approach. Science of the Total Environment, Vol. 409
  22. 22. 07/05/2016 22 SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS There are several “general” measures that can be applied to improve energy balance in a WWTP, such as: • Aeration system optimisation. The main energy consumer in a WWTP may be controlled by oxygen (or ammonia) concentration in activated sludge basins. Reducing oxygen concentration below 1.5–2.0 mg/L clearly reduces energy demand significantly, with no adverse impacts on the effluent quality. • Old devices replacement. Devices characterised by high energy demand can be substituted by new ones equipped with energy saving regulators (frequency changers) enabling more effective operation. • Sludge thickening optimisation. Low sludge concentrations dosed into digesters could be increased up to an acceptable value of 5–6%, which significantly – reduces the volume of processed sludge, – increases retention time in digesters, – increases specific biogas production from sludge, – enables one to use biodegradable waste. • Sludge heating. Reduce heat needed for sludge heating by recovery of heat from effluent digested sludge. This measure could reasonably reduce the energy demand of digester operation. SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS • Aeration system optimisation. The main energy consumer in a WWTP may be controlled by oxygen (or ammonia) concentration in activated sludge basins. Reducing oxygen concentration below 1.5–2.0 mg/L clearly reduces energy demand significantly, with no adverse impacts on the effluent quality. • Implement a Most Open Valve (MOV) strategy in which the aeration distribution zone with the highest oxygen demand is opened fully to reduce pressure at the blowers. DO levels in remaining aeration zones are controlled by valves that maintain the proper DO set point. • Upgrade from coarse to fine bubble diffusion to increase the efficiency of oxygen transfer and reduce blower load. • Position DO sensors indifferent zones of the aeration basin to provide accurate assessment of DO levels. • Adjust control systems to optimize mechanical mixing and bubble diffusion. Use mechanical mixers controls that cycle on and off in response to process control parameters. • Automated DO controls reduce aeration energy by up to 40 percent compared to control systems that use manual sampling. A DO sensor with integrated aeration control allows levels to be maintained within a narrower band, thereby reducing blower load. • Retrofit mechanical mixers with variable frequency drives, VFDs, which adjust the speed of the mixer motors to match the process needs in real-time. Typical simple payback of 2-7 years.
  23. 23. 07/05/2016 23 SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS • System controls that use SCADA feedback can be used to optimize effluent quality and energy consumption in real time. This balancing act is a continuous process. Achieving an optimal balance between quality and energy is the ultimate goal. • Intermittent (predictive) aeration controlled by on-line measurement of effluent ammonia. Air supply needs to be governed by nitrification performance while heterotrophic growth should be predominantly based on nitrate reduction. Intermittent aeration is operated between two set-points of the on-line ammonia control strategy leading to extended aeration intervals. • Maximize transfer of organics to digesters. A biological 2-stage approach supports high-rate entrapment of organics without excessive aerobic stabilization. Within an aerobic HRT of 0.5 hours, organic compounds are removed mainly by adsorption and can be rapidly introduced to thickening and digestion. Aeration energy demand depends on the F/M ratio, which can be regulated by modifying excess sludge flux to the digesters. SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS REAL TIME CONTROL OF WWT AERATION & OPERATIONS ECU
  24. 24. 07/05/2016 24 SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS • Old devices replacement. • Variable Frequency Drives improve fan efficiency by reducing speed to the minimum rpm required to satisfy flow requirements. Fan affinity laws show that flow produced by a fan is directly proportional to speed, while the power required is proportional to fan speed cubed. When less pump flow or pressure is required, pump speed and accompanying energy use will be reduced. For example, at 80 percent of full-load flow, a fan operates at 80 percent of full-load rpm, but uses only 51 percent of full-load power, yielding a steady- state energy cost reduction of 49 percent. At 50 percent of full-load flow, the fan operates at 50 percent of full-load rpm, but uses only 13 percent of full-load power, yielding energy cost savings of 87 percent. • Determine pump efficiency over the range of pumping requirements. Adjust basin fluid levels to decrease pump head and reduce load. Wet-well levels can be raised in pumping stations to reduce pump head. • Replace inefficient pumps with pumps using less energy and operating with less maintenance and downtime. Oversized pumps operating at constant flow are good candidates for impeller trims. Trimming the impeller is frequently a lower-cost alternative to making larger capital investments in pumps, motors or control technology. Install different sized pumps: as seasonal flows change, different combinations match flow needs. • Improve piping and valves to decrease friction losses. Adjust poorly calibrated valves that decrease pump efficiency. SUSTAINABLE SEWERAGE MINIMIZE ENERGY NEEDS • Sludge thickening optimisation. Low sludge concentrations dosed into digesters could be increased up to an acceptable value of 5–6%, which significantly – reduces the volume of processed sludge, – increases retention time in digesters, – increases specific biogas production from sludge, – enables one to use biodegradable waste. • Maximize transfer of organics to digesters. Favoring adsorption and entrapment of organics onto the biomass without excessive aerobic stabilization, organic compounds can be rapidly introduced to thickening and digestion, reducing aeration energy demand and increasing biogas production. • Sludge heating. Reduce heat needed for sludge heating by recovery of heat from effluent digested sludge. This measure could reasonably reduce the energy demand of digester operation. • Improve thermal insulation of digesters.
  25. 25. 07/05/2016 25 SUSTAINABLE SEWERAGE HEAT RECOVERY FROM WW In-house and in-sewer systems Theoretical recovery: 7 kWh/m3 per 6oC water temperature drop by heat extraction SUSTAINABLE SEWERAGE HEAT RECOVERY FROM WW A CONTROVERSIAL ISSUE • Reducing water temperature can have a negative effect on treatment processes (biological reaction rates depend on water temperature according to Arrhenius’ Law) and especially on nitrification, since this process depends on T more strongly than others . • Analysis of temperature regime in the Zurich WWTP (Switzerland) revealed that in the cold season, the effluent temperature is about 0.7oC higher than the influent temperature and that nitrification is not affected by a decrease of the influent wastewater temperature lasting for a couple of hours only, but it is significantly affected by longer lasting temperature decreases. • Heat recovery can however have beneficial effects if the discharged stream heat content endangeres the receiving stream habitat integrity SOURCE: Wanner O., et al., (2005) Effect of heat recovery from raw wastewater on nitrification and nitrogen removal in activated sludge plants. Water Research 39
  26. 26. 07/05/2016 26 SUSTAINABLE SEWERAGE HEAT RECOVERY FROM WW A CONTROVERSIAL ISSUE (2) • Analysis of an industrial WWWP in Denmark serving an agrofood industrial district, treating an average flow of around 10000 m3/d, with high loads both of COD (average =2400 mg/L) and nutrients (TN ~ 160 mg/L, TP ~ 50 mg/L), with average inflow temperatures ranging from above 20oC in the winter to summer peaks up to 30oC. • Violation of the local T value for discharge into the receiving waters (Tmax = 25oC), with possible negative effects on biota • Blatant situation of energy wastage, by unnecessarily discharging into the environment a potentially recoverable resource. • Heat recovery prior to WW treatment would lower process operating temperatures, modifying their efficiency (which may be result in emission standards violations), even though it would enhance oxygen solubility in the liquor and decrease overall oxygen supply requirements. SOURCE: Callegari & Capodaglio (2015) Integrated Approach to WWTP Upgrade for Energetic and Efficiency Sustainability. Recent Advances in Environment, Ecosystems and Development. WSEAS SUSTAINABLE SEWERAGE HEAT RECOVERY FROM WW A CONTROVERSIAL ISSUE (3) • Verification of denitrification efficiency: sludge age values (dots) determined in correspondence to the observed nitrogen discharge violation events in comparison with the theoretical values defined by dimensioning equations, the minimum sludge age, representing small nitrification capacity with nitrified ammonium is close to 0, and design sludge age (twice the theoretical one) under various operating conditions
  27. 27. 07/05/2016 27 SUSTAINABLE SEWERAGE HEAT RECOVERY FROM WW A CONTROVERSIAL ISSUE (4) • From the analysis, the facility in its present layout appears to be mildly under-designed as far as reactor volume is concerned. This condition becomes however evident only occasionally, under critical organic and ammonia loads, and high influent temperatures during summer months. • energy recovery prior to biological process would exacerbate the effects of the underdesign under marginal conditions, increasing the chances of effluent violations due to lower process rates. • A solution could consist of additional volume added to the nitrification/ denitrification section. Theoretical verification of post-intervention proves that this would ensure good performance even under critical (low DO = 0.5 mg/L) conditions. • After treatment, a recoverable ΔT between 9 and 15oC (depending on season) can be obtained, corresponding to roughly 17500 to 21900 Mwh/yr. or…. . “The primary problem we face is not the availability of technology for resource recovery, but the lack of a sociotechnological planning and design methodology to identify and deploy the most sustainable solution in a given geographic and cultural context. The most sustainable solution may not result in maximum, or any, recovery of resources from wastewater. Instead a sustainable water and wastewater decision-making process considers environmental, economic, and social ramifications of decisions across spatial and temporal scales to achieve the best balance identified by the project stakeholders….” SOURCES: MONTY PYTHON (1960’s) and Guest et al (2009) A New Planning and Design Paradigm to Achieve SustainableResource Recovery from Wastewater. Environ. Sci. Technol., 43,

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