Characterisation of Wastewater and Treatment Efficiency of Biogas Plants: Effluent Discharge Quality

Aims: To characterise wastewater, assess effluent quality and treatment efficiency of 3 existing biogas plants in 3 distinct institutions in Ghana and to provide relevant data necessary to policy makers to inform decision and influence policy.

Study Design: Laboratory analyses were conducted on wastewater samples from the University of Cape Coast (UCC), Mfantsipim Senior High School (Mfantsipim) and Ankaful Maximum Security Prisons (Ankaful), between January and April 2018.

Methodology: In all, 192 wastewater samples were collected from UCC, Mfantsipim and Ankaful for analyses. Physical, chemical and biological parameters were analysed on raw wastewater and on the effluent. Quality parameters were determined using the protocol outlined in the Standard Methods.

Results: The results showed significant differences between effluent quality from UCC, Mfantsipim and Ankaful with most of the quality parameters falling within the Ghana Environmental Protection Agency (EPA) guidelines. However, electrical conductivity (EC), total suspended solids (TSS), total dissolved solids (TDS), dissolved oxygen (DO), biological oxygen demand (BOD5), chemical oxygen demand (COD), ammonia-nitrogen (NH3-N), total coliforms (T. coli), Escherichia coli (E. coli) and Salmonella spp. (salmonella) exceeded the guideline values. The ratio between BOD5/COD was 0.5 and 0.3 for UCC and Ankaful respectively, indicating high biodegradability while Mfantsipim recorded 0.06, indicating low biodegradability. The parameters which had high treatment efficiency for the biogas plants was UCC (TSS 72.22%, total volatile solids (TVS) 78.41%, BOD5 64.22%, COD 63.56%, PO4 61.29%, T. coli 1.9 log reduction, E. coli less than 1 log reduction, salmonella 1.5 log reduction and vibrio cholerae (V. cholerae) 1 log reduction) followed by Mfantsipim (BOD5 70.45%, COD 83.84%, NO3 79.17%, T. coli 1.6 log reduction, E. coli 5 log reduction, salmonella 1.8 log reduction and V. cholerae complete removal), while Ankaful was (TDS 57.7%, TSS 68.17%, TVS 56.33%, BOD5 82.4%, COD 81.13%, T. coli less than 1 log reduction, E. coli less than 1 log reduction, salmonella less than 1 log reduction and V. cholerae 0.96 log reduction). The rest of the parameters exhibited negative and/or low values. The performance analysis of the three biogas plants showed that UCC performs a little better than Ankaful and far better than Mfantsipim in term of treatment efficiency.

Conclusion: The performance analysis indicated that the biogas plants were under-performing which could be attributed to poor maintenance, design deficiencies, poor environmental conditions and voluminous in-put loads. These factors impact the treatment efficiency resulting in relatively poor effluent quality which could put the health of the public at great risk.

It is therefore recommended that authorities and policy makers formulate appropriate regulations aimed at addressing the potential impact of poor effluent quality discharged into the environment.