Strategies for enhancement of anaerobic digestion of Nile perch fish solid residues

To enhance AD of Nile Perch Fish Solid Residues three different strategies namely: biological pre-treatment in combination with thermo pre-treatment; co-digestion of biologically pre-treated fish solid residues with potato waste (PW) and cabbage waste (CW) individually at 1:1 and mixed at the ratio of 10:45:45 (biologically pre-treated fish solid waste: PW:CW); and the use of fish scales as biofilm carriers in packed bed bioreactor at different organic loading rates (OLRs) were investigated. Thermo pre-treatment alone at 130oC and 70oC for 90 seconds and 60 minutes gave the highest methane yields of 311 and 384 mL CH4/gVSadded, respectively, which were two fold higher compared to the control. A combination of thermo pre-treatment at 70oC for 60 minutes and 130oC for 90 seconds with biological pre-treatment prior to AD enhanced methane yield four times more compared to the control. Anaerobic co-digestion of biologically pre-treated NPFSW with vegetable wastes further increased methane yields to 800 and 887 mL CH4/gVSadded when CW and PW were used individually. Furthermore, co-digestion of NPFSW with the mixture of vegetable market waste fractions gave 1300 mL CH4/gVSadded, which was 135% higher compared to the control. Nile perch fish scales, pumice stones and sisal fibers were evaluated for their ability as methanogenic biofilm carriers. The best results were obtained from the bioreactor packed with Nile perch fish scales with the lowest total volatile fat acids (TVFA) accumulated at OLR in the range of 1-12g volatile solids (VS)/L/d. Moreover, it was observed that the pH increased with an increase in OLRs, with highest pH range of 8.3- 8.7 recorded at 9-12 gVS/L/d OLRs. However, the bioreactor packed with fish scales had better ability to withstand the increase in OLRs. In conclusion, this study has established the potential of novel combined thermo-microbial pre-treatment and co-digestion with vegetable market waste fractions to enhance biogas production from NPFSW. Essential baseline data for use in future research at pilot scale on anaerobic conversion of NPFSW to biogas has been obtained. Nile perch fish scales have potential as novel biofilm carrier that would work well in packed bed bioreactors (PBB) treating fish solid waste.