Recovery of dairy industry wastewaters by reverse osmosis. Production of boiler water

•Low-pollutant flash cooler condensates were processed by reverse osmosis.•High-quality boiler water requirements were sought at pilot plant scale.•Discontinuous and continuous tests were conducted to study the membrane behaviour.•An activated carbon column was used to reduce the final organic matter content.•The scale-up of the application was estimated based on the trials accomplished.

Low-pollutant dairy condensates from flash coolers of a direct UHT plant were processed through a RO spiral-wound membrane (8.4-m2 surface area) in a pilot plant in order to obtain high-quality boiler water. Conductivity, chemical oxygen demand and pH were used as the main parameters to evaluate the permeate quality. Firstly, discontinuous tests were performed with the objective of checking the membrane behaviour under different process conditions. Then, the information obtained was used to perform long-term continuous trials. Conductivity and chemical oxygen demand reductions up to 98.2% and 97.8%, respectively were achieved. To improve the organic matter removal, an activated carbon column at the outlet of the permeate line was used. A post-treatment would be necessary to adjust the permeate to the final pH. Te return of investment of an installation to treat 20 m3/h condensates was estimated as being within 2.2 years.