Acti-zyme (bio-catalyst) as a solution for enhanced municipal sewage and sewage sludge treatment: effect of mesophillic and thermophillic digestion

Abstract

The purposes of this paper is to compare the effect of mesophillic and thermophilic digestion of municipal sewage sludge utilizing Acti-zyme as the bio-catalyst as a value addition strategy to sewage sludge management. The municipal sewage sludge was digested to biogas and bio-solids (digestate). Experimental Design/Methodology/Approach: Raw sewage physicochemical properties were first characterized. Biogas and bio-solids was produced for anaerobic mesophillic conditions (37 o C) and thermophilic conditions (55 o C) for a retention period of 40 days in the bio-digester, Acti-zyme loadings of 0-70 g/m 3 and sewage sludge loadings of 5-10 g/L.day. Biogas composition was determined by a GC 5400 gas chromatography analysis whilst the The cumulative bio-solids (digestate) generated per day were recorded for possible use as biofertilisers. The nitrogen, phosphorous, and trace elements content was determined using Labtronics double beam ultra violet visible spectrophotometer (uv-vis). The potassium content was determined using a Thermo Fisher flame atomization absorption spectrophotometer. The effect of the digestion conditions were statistically quantified using a t-test. Findings: The biogas had a bio-methane (CH 4) composition of 72-78%, carbon dioxide (CO 2) composition of 16-20% and trace gases composition of 8-12%, whereas the bio-solids had a nitrogen, phosphorous and potassium composition of 8.17%, 5.84% and 1.32%. In overall biogas yield was more than 45% for all the sewage sludge loadings and Acti-zyme loadings digested at mesophillic conditions as compared to digestion at thermophilic conditions. This indicated that thermophilic catalyzed of municipal sewage sludge with Acti-zyme is not feasible as this result in less activity of the Acti-zyme hence less digestion occurs. In addition, the amount of bio-solids is about 40% higher in thermophilic digestion which can also result in landfilling problem. Research Practical implications and value: Mesophillic digestion of municipal sludge catalyst by Acti-zyme can be utilized for sewage sludge management as a value addition strategy. This can be applied for minimizing landfill problems resulting from sewage sludge from sewage treatment.