Recovering water and minerals from dairy waste: Reverse osmosis of whey nanofiltration permeate

Abstract

Dairy processing generates large volumes of nanofiltration (NF) permeate, often treated as a waste stream despite its potential as a source of recoverable water. Proper handling of this by-product could contribute to more sustainable industrial operations and improved water use efficiency. This study aimed to assess the potential of reverse osmosis (RO) for water recovery from dairy NF permeate and to evaluate the reuse potential of the resulting retentate stream. NF permeate was collected from an industrial filtration plant equipped with either New or Aged membrane elements. Permeate compositions were analysed to assess the effect of membrane aging. NF permeates obtained from New membranes were mineral-dominant, whereas lactose became the main component in those from Aged membranes. Despite membrane aging, calcium and magnesium retention by NF remained consistently high. RO trials demonstrated stable permeate flux; no critical flux was detected under the tested conditions. The resulting RO permeates had less than 0.02 g 100 g–1 total solids and conductivity below 250 µS cm–1. Although the results indicated that while RO permeate shows potential for reuse in food processing, its microbiological safety and storage stability emerge as critical factors that must be carefully managed in industrial applications. Mineral-rich RO retentates had K:Na mass ratios up to 2.5. A model ayran – a widely consumed milk-based salty beverage – was formulated to evaluate the potential of RO retentate for partial NaCl substitution. As a result, Na content was reduced in the product without compromising sensory quality, and the drink maintained high overall appeal.