Abstract

In East Africa, Nile perch processing into fish fillets for export generates large proportions of both solid and liquid fish wastes. These wastes are improperly utilized and/or disposed off untreated leading to environmental pollution problems. On the other hand, Nile perch fish processing wastewater (FPW) contains high concentrations of lipids and proteins, which have high methane yield potential. However, anaerobic digestion (AD) of FPW for methane production is limited due to process inhibition by lipids and ammonia intoxication. To overcome these limitations, the effects of co-digestion, physical and biological pretreatments on extent of methane yield were investigated. At a loading ratio of 1:1 (inoculum to substrate) with raw FPW, a methane yield of 0.56 m³/kgVS was obtained. Co-digestion of the residue with 10% gVS of brewery wastewater enhanced methane yield to a highest increment of 66%. Long chain fatty acids (LCFA) removal prior AD enhanced methane yield to an increment of 52% at LCFA removal of 8%. Pretreatment of FPW with aerobic microbial cultures isolated from a fish waste stabilization pond enhanced methane yield to an increment of 60% after 18 h, 68% after 15 h and 76.0% after 12 h of incubation, respectively, for strains CBR 11, BR 10 and a mixture of the two (CBR 11 + BR 10). The present study reports for the first time improvement of AD of Nile perch FPW by co-digestion, physical and biological pre-treatment methods and could be used as a basis for designing a pilot scale process.

Key words: Anaerobic digestion, co-digestion, LCFA removal, biological pre-treatment, Nile perch processing wastewater.