Abstract

Wastewaters from fish processing cause a high organic load for municipal wastewater treatment and can interfere with treatment operations due to their high oil and grease content. In the present study, a modular dissolved air flotation (DAF) unit was used to remove oil, grease and other suspended solids from fish processing plant wastewater. After DAF treatment, the residual particles and nutrients were adsorbed onto a mixture of hemp and spruce biochar in a pilot-scale column filtration system. The proposed integrated treatment process aims to improve the quality of the fish processing wastewater, facilitate water reuse, and recover the dissolved nutrients in a reusable form. The DAF treatment removed nearly all the oil and grease from the wastewater. Also, chemical oxygen demand, turbidity and phosphorus concentration clearly decreased during the DAF process. The biochar filtration further clarified the DAF-treated wastewater and partly adsorbed the residual nutrients. Furthermore, in the spent biochar mixture, the nitrogen and phosphorus content increased significantly (N to 9.1–10.5 mg/g, P to 0.32–1.38 mg/g), which indicates the improved properties of the biochar as a possible soil conditioner.