Effects of ultrafiltration membrane concentration and drying temperature on nutritional value of biosolids from a milk processing plant

Biosolids (sludge) from food processing plants traditionally are put into landfills or applied to land. They could be reused as animal food but have to be dewatered. Conventional dewatering methods are expensive and inefficient. Recent advancements in membrane technology could make ultrafiltration membranes a practical biosolids dewatering method used prior to conventional drying. Ultrafiltration could alter the nutritional profile of biosolids, and the temperature at which biosolids are dried can affect nutritional quality. The objective was to determine the nutritional quality of membrane concentrated biosolids dried at increasing temperatures. Biosolids samples were obtained from a milk processing plant. Part of each sample was concentrated using an ultrafiltration membrane separation system, and the remainder was unconcentrated (used as is); both samples were dried at increasing temperatures. Effects of concentration and temperature on total N, soluble N, insoluble N, organic matter, ash and available N were determined. Concentrated biosolids had higher total N (protein) and organic matter (energy) than unconcentrated. Increasing the temperature at which biosolids (both concentrated and unconcentrated) were dried increased the soluble N (protein) and available N fractions. UF membrane concentration of BS followed by conventional drying at 150–200°C resulted in BS with the highest nutritional value (highest total N, soluble N, available N and organic matter). UF membrane concentration increased the nutritional value of BS and eliminated the need for chemical coagulants and flocculents.