MBR AND RO TREATMENT OF DAIRY WASTEWATER: INDUSTRIAL WATER RECYCLING OPPORTUNITIES 1

2

2

3

3

B. Chapman , N. Goodman , T.H. Muster , S. Toze , L. Hodges , J. Sellahewa 1. ADI Systems Asia Pacific, Dunedin, New Zealand 2. CSIRO Land & Water Flagship, Clayton, VIC, Australia 3. CSIRO Land & Water Flagship, Dutton Park, QLD, Australia

ABSTRACT Water is a valuable resource, and commitment to environmental sustainability calls for innovative water recycling opportunities. Anaerobic treatment of food and beverage production wastewater results in the production of biogas, a renewable source of energy. However additional steps are required to enable water recycling. A membrane bioreactor (MBR) and reverse osmosis (RO) pilot trial, coupled with ultraviolet (UV) and chlorine disinfection, delivered a high quality potable water from anaerobic effluent. The MBR achieved 97% COD and 95% nitrogen removal, producing permeate suitable for direct treatment in the RO. The RO with UV and chlorine disinfection achieved potable water criteria. INTRODUCTION Food production is the largest manufacturing sector in Australia, and consumes large amounts of fresh water. Even factories with a commitment to environmentally sustainable practices through implementing water, energy and waste assessment programs and resource efficiency processes produce wastewater as a by-product. In a dairy factory, these water sources include condensate from the evaporation of skim milk and other products, and membrane filtration permeates amongst other streams. The wastewater contains not only organic pollutants (measured as COD), but also nutrients such as nitrogen and phosphorus. Various treatment options are available, However the used of anaerobic technology results in the production of biogas, a renewable source of energy (Gant et al., 2002). It is important that the correct type of anaerobic reactor is selected to match the wastewater parameters, and in this case a full-scale ® low rate ADI-BVF reactor was installed and has successfully treated the dairy effluent for many years. The biogas generated is captured, and used to operate a hot water boiler. While the anaerobic reactor successfully reduces the organic pollutants, the levels of nutrients such as nitrogen and phosphorus do not change significantly. Therefore while further treatment steps offer the ability to generate a reusable water

2

stream, they also offer a reduced cost of discharge to sewer with a reduction in flow as well as nitrogen and phosphorus load. Biological nitrogen removal can be achieved in aerobic treatment systems through the use of alternating anoxic (low oxygen) and aerobic sections. In the aerobic section the bacteria use the available oxygen to convert ammonia (NH3) to nitrate (NO3), which is known as nitrification. In the anoxic stages a different group of bacteria convert nitrate to nitrogen gas (N2), which is released into the atmosphere, in a process called denitrification. A readily available carbon source is required for denitrification to occur. Phosphorus can be removed biologically in aerobic systems, through modifying the process to enable bacteria to store phosphorus. Alternatively there are various chemical precipitation methods which can be employed, either within other treatment processes or as a standalone step. A membrane bioreactor (MBR) system is an aerobic process, using modified activated sludge technology to treat wastewater. A physical membrane barrier is used to retain the aerobic biomass within the treatment plant, rather than gravity settling or other liquid/solids separation techniques. The membrane effectively filters the treated water, which results in a very high quality final effluent with low suspended solids (often below detection levels) and low organic content (