Electrocoagulation-treated poultry wastewater sludge as a sustainable feed resource for black soldier fly larvae

Black soldier fly larvae (BSFL) are an excellent protein source that can serve as a sustainable and nutritious diet to support the growth of aquaculture species. They could be an affordable and eco-friendly alternative to traditional fishmeal. BSFL can be cultivated using wastewater sludge derived from various domestic and industrial wastewater sources. This study focused on using egg-washing and poultry-slaughtering wastewater sludges to grow BSFL. The solid portion of the BSFL diet consisted of the Gainesville Diet, in which moisture was supplied from various wastewater treatment sludge and tap water sources. Electrocoagulation and flocculation methods were employed to treat wastewater from egg washing and poultry slaughter. Aluminum (Al) and iron (Fe) electrodes were used in electrocoagulation, and the pH, electric current, and treatment time for the wastewater samples were optimized. Electrocoagulation of egg-washing wastewater showed high treatment performance, with Al electrodes removing up to 81% COD, 62% ammonia, and 91% phosphate, while Fe electrodes removed 84.4% COD and 92% ammonia. In duck-slaughtering wastewater, Al electrodes provided up to 98.21% COD removal, and both Al and Fe electrodes achieved > 99% phosphate removal under optimized conditions. Ammonia removal reached ~ 99% using Al electrodes at pH 9 and 26.04 mA cm⁻². Given the remaining organic load and future perspectives, integrating electrocoagulation with anaerobic digestion could further reduce COD while enabling biogas recovery. The highest average total solids (32.00 mg/L) and inorganic solids (22.43 mg/L) were found in duck-slaughtering wastewater sludge treated with Fe electrodes. Flocculation resulted in an average of 16 mg/L of volatile solids. Larvae fed on sludge from both treatment methods showed an average weight gain equivalent to 5-8-fold increase in body weight, with the highest weight gain (corresponding to a 7.7-fold increase) achieved from duck-slaughtering sludge treated using the electrocoagulation method. The proportion of larvae reaching the pupation stage was examined during the 15-day observation period. Diet treatment based on duck slaughtering wastewater sludge using Al electrode showed the lowest proportion of individuals reaching the maturation stage.