Nanofiltration Membrane Technology for Dairy Wastewater Treatment and Resource Recovery

The dairy industry is characterized by high water consumption and high wastewater output. Wastewater is mainly produced from raw milk cleaning, equipment CIP cleaning, production line flushing and defective product discharge. The wastewater mixture contains residual milk protein, lactose, milk fat, organic acids and mineral salts. The high COD value of dairy wastewater brings great pressure to environmental treatment. Traditional disposal methods including sedimentation, air flotation and biochemical degradation focus only on reaching discharge standards, while discarding recoverable lactose and protein, resulting in resource waste. In addition, biochemical processes occupy large land area, have long treatment cycles and are easily affected by water quality fluctuation, making stable operation difficult for many medium and small dairy manufacturers.

Nanofiltration, as a pressure-driven membrane technology between ultrafiltration and reverse osmosis, possesses unique selective separation performance. It can effectively retain macromolecular organics such as protein and lactose, and selectively intercept multivalent ions like calcium and magnesium, while allowing partial monovalent salts and small molecule water to permeate. Different from ultrafiltration which mainly removes suspended solids and macromolecules, nanofiltration further realizes desalination and concentration of the organic permeate from the pre-treatment unit. This feature makes it highly suitable for resource recovery from dairy wastewater rather than simple pollutant removal.

A complete nanofiltration treatment system for dairy wastewater usually adopts a multi-stage combination process. The wastewater first goes through pre-treatment including screening, air flotation and ultrafiltration to remove grease, suspended solids and large protein particles, preventing rapid fouling of the nanofiltration membrane elements. The pre-treated clear liquid is then sent to the nanofiltration skid for circulating concentration and desalination. The concentrated fraction rich in lactose and protein can be further processed and reused in food or feed production; the permeate with low organic content can be recycled for workshop cleaning, equipment rinsing or other non-drinking production water, greatly cutting the factory’s fresh water demand.

The whole nanofiltration process runs at ambient or low temperature without heating or adding a large quantity of flocculants and coagulants, avoiding secondary pollution. The system adopts cross-flow circulation mode, where the fluid continuously scours the membrane surface to reduce the deposition of organic pollutants and slow down membrane fouling. Equipped with automatic pressure and flow control as well as regular CIP cleaning procedures, the system can maintain stable flux for long-term continuous operation, adapting to the fluctuating water volume and water quality of dairy production.

From economic and environmental perspectives, nanofiltration-based wastewater recycling brings remarkable benefits. It lowers the cost of biochemical operation and sludge disposal. The recovered lactose and protein can create additional economic benefits for enterprises. The recycling of permeate water reduces water intake and sewage discharge, helping dairy factories meet increasingly strict environmental assessment requirements. Modular skid-mounted nanofiltration equipment is flexible for both new wastewater stations and reconstruction of old treatment facilities, convenient for integration into existing dairy production lines.

With the global emphasis on circular economy and cleaner production, more and more dairy enterprises are shifting from simple end-of-pipe treatment to resource recycling. Nanofiltration membrane technology provides an efficient and reliable way to turn dairy wastewater into recyclable resources. It balances environmental compliance and economic returns, and will become a mainstream technical choice for sustainable development of the dairy processing industry.