Degremont Water Treatment Handbook Factsheets n°1 - Ultragreen
Degrémont has a tradition of sharing its Degrémont Water Treatment employees’ passion for water treatment with Handbook Factsheets the public. To supplement the Water Treatment Handbooks, Degrémont has issued the «Handbook Factsheets» to promote a better understanding of the different techniques available and discovery of the new products and major technological changes. Urban WasteWater UltragreenTM Biological process Clarification Membrane filtrationMEMBRANE CLARIFICATION OF URBAN treated water is not dependent on changes in hydraulic heads.WASTEWATER Flux During membrane clarification, at constant concentration and pressure, a ReSimilar to water treatment procedures to produce drinking water, ve r sib flux reduction can occur over time, which l ethe membrane separation technique used in urban wastewater flo w can lead to the complete blocking of the lostreatment is a real physical barrier to impurities and pathogenic sgerms. membrane: a phenomenon known asTo achieve the same water quality objective, membranes can be clogging. Backwashused to replace several stages of conventional treatment. The Timecompactness of membrane processes allows the construction Clogging is due to the formation of a colloid deposit on theof small-sized plants and modular processes can be installed in membrane surface, the adsorption of varied solutes in the pores,a wide range of plant sizes. but also the formation of precipitates on the membrane (ferric sulphate, for example). The former is essentially reversible by means of backwashing (operation that entails reversing theÎÎ Ultrafiltration membranes pressures to send the produced water through the membrane and loosen the deposit) or by a surface sweep («relaxation»)Any material that has a thin film shape (0.05 mm to 2 mm) and of the membrane without filtration. However, backwashingthe property of providing selective resistance to the transfer of or increased sweep speed has often no effect on adsorptiondifferent constituents of a liquid or gaseous fluid is a membrane or the formation of precipitates; only an appropriate chemicalthat can be used to separate elements (particles, solutes, or treatment will then «clean» the membrane.solvents) present in a fluid.Ultrafiltration membranes, with pore sizes between 1 and100 nm, allow mineral salts and organic molecules of small ÎÎ Membrane structuremolecular weight to pass; they stop only the largest solutes(macromolecules) and specific elements such as viruses, In ultrafiltration membrane separation, the separation units,bacteria, and colloids. They ensure the total elimination of called «modules», that are used in membranes are designed tosuspended solids (SS) that cause turbidity without modifying the attain two essential goals:salt composition of the water. - roup the membranes together into compact modules, that g is, to provide a maximum exchange surface per unit volume; - nsure sufficient circulation of the liquid to be treated to the e membrane in order to limit particle deposits. In the case of wastewater clarification, there are two main types of modules: Air Permeate • Hollow fibre membrane modules inlet oulet Hollow fibres, with a diameter of 0.6 to 2 mm, are produced by extrusion ofThis process leads to high rejection rates that meet the strictest membrane material through annular dies.regulatory requirements, particularly for «bathing water» Their structure allows them to stand up to(European directive) and allows anticipation of future the internal or external pressures requiredchanges. for their use. These fibres are then groupedThe physical barrier created by membranes makes it possible into modules that are easy to backwash.to control filtration and the quality of rejected suspended solids, During wastewater treatment, the fluid tocontrary to dynamic separation in a clarification tank where there be treated circulates outside of the fibresis always the possibility of a «leak» from suspended solids, and and the permeate is collected at one or Vertical fibretherefore the risk of denitrification. In addition, the quality of the both ends of the fibres. The modules are Air outlet bundle
directly immersed in the water to be treated, and the filtratesucked through the fibre by being placed under a partial vacuum Classical activated sludge line(0.2 to 0.6 bar, or 20,000 to 60,000 Pa). Raw water Pretreatment Activated sludge Clarifier Sand filter Disinfection• Flatsheet membrane modulesIn this case, the membrane Membrane Membrane Bio Reactor (MBR) support platepresses down on the two Treated water Membranes (to suction intake) Permeatsides of a planar structure Drainer Rawserving as the central plate water «process» «membrane» Excess sludge Pretreatmentsupport. The fluid to be Felt air airtreated circulates through the Permeat outlet Membranemembranes of two adjacent UltragreenTM PLATEplates. The liquid layerbetween the plates is about MODULE7 mm thick. The permeate iscollected under a vacuum in the grooves of the plates. The platesprovide mechanical support to the membranes and drainageof the permeate. The plates supporting the membranes arealso assembled in compact modules. The arrangement of themodules allows parallel circulation. Accordingly, groups of unitsof up to 140 m2 surface area can be formed.ÎÎ pplication of Membrane BioReactors (MBR) AUltrafiltration membranes can replace suspended or attached ÎÎ Presentation of the processgrowth, aerobic or anaerobic clarifiers to separate flocs and non-flocculated bacteria from treated water. Ultragreen™ is a Degrémont wastewater treatment processThe application of Membrane Bioreactors allows the that combines pollution degradation with biological activitycombination of pollution degradation through biological and clarification by ultrafiltration flatsheet membranes.activity and thorough filtration in the compact units. In additionto its exceptional rejection quality, the highly compact size of After straining through a fine mesh, the water to be purifiedMBR units is a decisive advantage for this technology, especially is sent to a reaction tank where it enters into contact with ain situations of overwhelming location and civil engineering purifying bacterial mass. The membranes are immersed into theproblems. biological liquor in a separate tank. The biological liquor is filtered by suction through the ultrafiltration membranes with the use of a pump or simply through the hydraulic head on the membrane.MBR clarification has the following advantages: The membranes thus replace traditional clarification• he certainty of obtaining perfect clarification regardless t and any tertiary filtration. The biological liquor is circulated of the state of the sludge and its sludge index since the between the two tanks. membranes can retain even non-flocculated bacteria and produce an effluent with no suspended material (turbidity Ultragreen™ works by cycles of filtration/relaxation. 1 NTU);• he disinfection of the effluent (absence of pathogens such as t helminthes eggs, bacteria, or certain viruses;• he possibility of increasing the concentration of purifier t biomass between 6 and 12 g.L-1 (since the clarifier is no longer needed). This therefore causes, at equivalent mass load, the possibility of reducing the aerator by a factor of 2 to 4 with respect to a traditional aerator in activated sludge;• he absence of a clarifier and a small-sized aerator means t lower civil engineering cost and much smaller footprint;• he membrane blocks the passage of certain macromolecular t The Ultragreen™ membranes have metabolites which leads to their gradual degradation, resulting a cutoff threshold of 0.08 µm, which in a significantly lower final COD (chemical oxygen demand) makes them a powerful physical than that which is obtained by traditional activated sludges. barrier for eliminating bacteria, helminthes eggs and for reducing fecal coliform. The quality of the treated water is excellent in terms of suspended solids and turbidity.
Degrémont Water Treatment Handbook Factsheets The membranes They are assembled Ultragreen™ up during clarification. Compared to the traditional activated used in this in modules. The functions by sludge, the required reactor volume is reduced by 50% at least, process are assembly can be suction on the because of the high sludge concentration; mechanically horizontal and/or principle of Out/ • he high concentration of suspended solids has an unfavourable t reinforced vertical. The vertical In filtration, that is, influence on oxygen transfer. This leads to a specific electrical flatsheet two-module assembly via filtration from consumption, expressed in kWh.kg-1 BOD, obviously higher membranes leads to optimum the outside of the than conventional activated sludge; manufactured by unclogging aeration. plate towards the • ltration within the tank containing the modules causes an fi TORAY. inside of the plate. overconcentration of the mixed liquor. The latter should be controlled by continuous recirculation from the tank where the modules are immersed in the aerobic and/or anoxic tank. The recirculation rate is normally set between 200 and 500% of feed flow. ÎÎ Performance The sizing calculated to ensure thorough nitrification also leads to very low concentrations of COD, BOD, and N-NH4.Filtration is done by suction, by action of a transmembrane The table below is a summary of the expected values with thispressure of less than 0.2 bars. Continuous aeration («membrane type of urban wastewater facility.air» function) creates a flux of ascending air along the plates, andgenerates a mixed solution current in the area. Parameter ConcentrationAs a curative measure, the membranes are regenerated one to Suspended Solids (mg·L–1) 2three times a year by a regeneration washing.This involves injecting a chemical solution into the membrane Turbidity (NTU) 1pocket; leaving the solution to act for 2 to 4 hours, then rinsing COD (mg.L ) –1 50*the membrane by filtration. BOD (mg.L ) –1 8ÎÎ Implementation N-NH4 (mg.L–1) 1 NT (mg.L ) –1 10Ultragreen™, like most membrane bioreactors is characterized Escherichia Coli (number per 100 mL) 100essentially by:• highly concentrated mixed liquor of 8 to 10 g.L-1, which a * depends on the hard COD of raw water allows a significant gain in reactor volume;• he presence of membranes immersed in the mixed liquor. t Ultragreen™ is appropriate for treating urban and industrial waste water and helps to obtain an effluent that can meetThese specific features require certain precautions and/or the most stringent waste standards in sensitive or veryconstraints on the design and sizing of this type of facility. sensitive environments. Generally Ultragreen™ guarantees the bathing water quality (European directive). The effluents can• Pretreatment be recycled for reuse.This is a fundamental stage for the proper functioning of the In addition, because of the small size of the basic elementfiltration unit. comprising the membrane system, its flexibility, and modularity,Straining is required to supplement careful degreasing and Ultragreen™ is ideal for small plots of land and can also bedesanding. The minimum required is filtration through a grid with easily integrated into an existing plant.a hydraulic diameter of 2 mm.• Biological reactorThe configuration of the reactors remains, with few exceptions,similar to the traditional treatment by activated sludge.The activated sludge tank generates an effluent favourable formembrane filtration.The higher concentration of sludge and the use of membraneshowever, introduce significant differences into the sizing.• n order to obtain interstitial water with good filterability, i the size of the reactor must ensure total elimination of interstitial COD under the most restrictive conditions of load and temperature. In contrast, barring mandatory standards in total nitrogen, denitrification is optional, because unlike the conventional process, there is no risk of sludge backing
Degrémont Water Treatment Handbook FactsheetsA few Degrémont references• Siepam, Val d’Arly (France) = 29 000 EH• Saint-Barthélemy (France) = 3 500 EH• Focus on the Cogolin (France) wastewater treatment plant 45,000 PE scheduled for commissioning by mid-2011 Water line Raw water Discharge Fine screening (6 mm) Parameter Guarantees Desanding / Degreasing (Daily average) SS (mg.L-1) 5 Distribution COD (mg.L ) -1 50 Straining (200 µm) BOD (mg.L-1) 10 NGL (mg.L-1) 10 Biological basins(Anaerobic, Anoxic, Aerated) Ptot (mg.L ) -1 1 Ultragreen™ membrane bioreactor = Toray flatsheet membranes Vtot = 3,000 m3, Smembrane, tot = 11,200 m2 Treated WaterThe solution chosen by the Syndicat Intercommunal d’Assainissement de Gassin will allow the town to discharge quality effluents intothe Giscle sensitive area and to reuse 40% of the treated water for watering parks and gardens.The possibility of superimposing Toray flatsheet membranes has enhanced the highly compact size of the facility and allowed the townto design a low-profile plant that blends into the environment. Degrémont Handbook Factsheets No. 1 - April 2011 – Photo credits: Degrémont Contact Ultragreen™: firstname.lastname@example.org DEGRÉMONT S.A. WWW.DEGREMONT.COM