Large amounts of wastewater, composed of diluted milk (lipid, protein and lactose) and cleaning chemicals (acids, alkalis and detergents), is generated in dairy processing plants and represents a waste of water and nutrients as well as pollution. Among available membrane technologies for wastewater treatment, nanofiltration (NF) and reverse osmosis (RO), has been often considered as a promising method. However, during a NF/RO concentration process, a large flux decline occurred with the increase of organic solutes and inorganic salts in retentate. Another problem for NF/RO treatment of dairy wastewater is the difficulty of nutrients recovery.

Dr. LUO jianquan, supervised by Prof. WAN Yinhua of National Key Laboratory of Biochemical Engineering at Institute of Process Engineering, developed a viable and promising two-step ultrafiltration and nanofiltration process for recycling dairy wastewater. In the first stage, protein and lipid were concentrated by UF membrane and could be used for algae cultivation to produce biodiesel and biofuel, and in the second stage, the obtained UF permeate was concentrated by NF membrane to obtain reusable water in permeate and high-concentration lactose in retentate. The latter could be used for anaerobic digestion to produce biogas.

They showed that proteins and lipids in wastewater could be efficiently concentrated by the Ultracel PLGC membrane in the first stage and the membrane exhibited an excellent antifouling performance and high transmission of lactose and inorganic salt. The UF permeate could be treated by the NF270 membrane in the second stage to obtain lactose in retentate and reusable water in permeate and high permeability, and high lactose retention as well as the low retention of salts were obtained with this NF membrane.

The research results were published recently in Bioresouce Technology (2011, 102: 7437-7442). Corresponding author: WAN Yinhua, E-mail: yhwan@home.ipe.cn.

Full-text paper can be accessed at http://www.sciencedirect.com/science/article/pii/S0960852411006511.