Greywater Treatment with Membrane Coupled Biological Processes

Greywater reuse will play an important role in the sustainable water management approach. Depending on its intended use different treatment technologies are needed. This paper focuses on the membrane coupled biological processes like membrane bioreactor (MBR) or submerged membrane sequencing batch reactor (SM-SBR) processes. First analyses with a 30L SM-SBR treating synthetic greywater show a good performance under different boundary conditions, e.g. varying cycle times as well as the volumetric exchange ratio (VER). Introduction Wastewater generated by bathtubs, showers, bathroom sinks, and washing machines are consistently defined as sources of greywater in the literature. Wastewater from kitchen sinks and dish washing machines might be sometimes included, called “dark grey water”, but with a high potential to introduce microbial contaminants and/or oils and greases that would negatively impact the receiving treatment system. Greywater treatment with membrane coupled systems can be either of physical or biological nature. Purely physical separation simply holds back the hazardous substances of greywater due to the membrane discharging a clean effluent. The polluted concentrate is collected and treated in a further step sometimes together with a different wastewater (blackwater). The biological treatment reduces degradable organic matter measured as the chemical oxygen demand (COD) and the amount of nutrients. Within the last 20 years, biological treatment of wastewater coupled with a membrane separation unit (Figure 1) has come out of research into full scale application plants. It is an accepted and more and more used treatment technique for decentralised solutions ranging from small domestic implementations (family houses) up to wastewater treatment plants in municipalities with 80,000 inhabitants, equal to an amount of 48,000 m3/d (WWTP Nordkanal, Germany), as well as specialised industrial use [9]. In contrast to its big advantages of a small footprint and very good effluent quality stands its disadvantages of short membrane life time (up to 8 years [3]) and high membrane costs. A recent study shows that at a wastewater flow greater than 5,000 m3 MBRs needs lower investment capital as well as lower operation and maintenance costs compared to the conventional activated sludge treatment [3]. Within the Zer0-M project greywater treatment with a membrane coupled biological treatment is going to be investigated and monitored for its applicability in our Mediterranean partner countries. Although membrane bioreactors (MBR) are a high-tech application, they are anywhere suitable where space is of big concern, e.g. in hotels in tourism centres. The reuse of treated greywater plays a significant role in the sustainable water management approach, as the low polluted greywater (COD ~ 200 mg/L) represents 70% of the domestic water flow rate. Especially in regions where water restrictions are a severe problem, and water supplies are rapidly declining the utilisation of drinking water for toilet flushing seems to be inappropriate. Society has to become aware of efficient and appropriate water (re)use. Examples of such ‘demand side management’ improvements include the use of water saving Preprint of an article published in: Sustainable Water Management 1 (2005) 23-25.