Anaerobic Co-Digestion of Faecal Sludge with paper or Fruit Waste for Biogas a case in Kumasi, Ghana

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Increasing attention is being given to biogas generation through anaerobic digestion (AD) all over the world due to concerns over global warming, security of energy and the need for sustainable waste management. Very few areas in Ghana are sewered, the situation is no different in Kumasi where most of the people rely on onsite sanitation systems. Faecal sludge removed periodically from these sanitation systems is further treated in waste stabilization ponds at the Oti treatment facility. However, increasing population and thus increasing volume of sludge being brought to the facility has led to operational difficulties of the facility. This study therefore sought to assess the feasibility of using anaerobic co digestion (AcoD) as an alternative means of treating the faecal sludge brought to the treatment facility before discharging into the environment. By analysing the pH, TS, VS, COD, TP, TKN and helminth eggs according to standard protocols, the physicochemical and microbiological properties of the sludge were investigated. COD: TKN ratios were calculated to assess the suitability of the sludge for anaerobic digestion. Laboratory scale batch AD tests were performed both at mesophilic (35oC) and ambient conditions (24-32oC) to assess the biogas production, the impact of the two temperatures on the treatment, and the effect of sludge retention times on biogas production and sludge stabilization. The efficiencies of the treatment processes were then assessed by computing the percentage removal of TKN and COD from the sludge. Anaerobic co digestion with paper and fruit waste enhanced the faecal sludge characteristics and improved effluent characteristics. The faecal sludge brought to the treatment facility during the period of this study had the following characteristics: pH of 7.02 ±0.2, VS of 65.75 ± 10.98 as %TS, COD of 23050 ± 681.50 mg/L, MC of 98.57 ± 0.84%, TKN of 2842 ± 1094.53 mg/L, and COD: TKN of 8.11. Statistical analysis suggested difference (p-value of 0.003) in the biogas yields under the two temperature regimes however further analysis indicated that the difference was only in the first week. The digesters were filled with faecal sludge and paper or fruit waste in the ratio 1: 0.13. The results obtained in this study showed a total biogas production and weekly methane yield as percentage by volume for Inoculum (I) only, faecal sludge and inoculum (FI), faecal sludge plus inoculum and paper (FIP) and faecal sludge plus inoculum and fruit waste (FIFW) to be 635 (10 – 16.5%), 830 (18.9 – 23.7%), 1355 (16.5 – 47.05%) and 1760 (26.1 – 39.75%) ml respectively under mesophilic temperature and 1085 (0 – 15.5%), 1110 (3.8 – 17.7%), 1515 (14.3 – 41.1%) and 1875 (19.5 – 45.7%) ml respectively under ambient temperature. Effluent characteristics were better in the 4th week for all the digesters indicating that longer sludge retention times has a positive impact on anaerobic digestion.
A thesis submitted to the Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfillment of the requirements for the award degree of Master of Science in Water Supply and Environmental Sanitation.
Anaerobic Co-Digestion, Faecal Sludge, Paper or Fruit Waste, Biogas, Kumasi, Ghana