Effect of feeding rate and composition for bioconversion of wastewater treatment plant sludge from the milk and creamer processing industries using black soldier fly larvae

Wastewater treatment plant (WWTP) produces sludge deposits needing further treatment and handling to prevent pollution. Food and beverage industry sludge, rich in organic matter and nutrients, serves as a biomass source. Black Soldier Fly Larvae (BSFL) have degraded various organic materials, transforming nutritious organic waste into high-quality protein biomass. BSFL potentially converts sludge when mixed with other nutrient sources like food waste. This study analyzes the effect of feeding rate and composition on BSFL bioconversion of milk and creamer industrial sludge. The sludge was collected from the creamer processing industry after screw and filter pressing, and the milk processing industry after belt pressing. The substrates contained sludge, mixed fruit-vegetable wastes, and protein wastes (i.e., shrimps and fish wastes), with various ratio of 60:20:20, 60:10:30, 40:30:30, 40:20:40, 40:10:50, 50:25:25, 50:20:30, 50:10:40, and 70:15:15 (in dry weight percentage). Moisture content was kept at 65-85% and pH at 6.5-7. Feeding rates of 10, 20, and 30 mg dry matter/larva/day were assessed. Creamer processing industrial sludge, particularly from filter press is preferable for larval growth than the milk industry. The highest larva weight was obtained from substrates containing mixed fruit-vegetable wastes:fish wastes ratio of 1:1, with the addition of creamer and milk sludge of 50%, i.e., 0.250 gram WM/larva after 17 days of growth. In addition, with the recommended feeding rate is 10-20 mg dry matter/larva/day, the sludges can be bio-converted using BSFL by combining it with food wastes at around 40-60%. This offers alternatives for the treatment and handling of industrial waste sludges.