Assessing filter media for purification of biogas from Anaerobic Digester
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Date
2003-11-25
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Abstract
Ashanti Goldfields Company, Obuasi [A.G.C] having changed most of its septic tanks (which demanded frequent desludging) to anaerobic digesters, is now facing the problem of appropriate biogas utilization. The offensive and pungent nature of H2S and NH3 in the raw biogas is a nuisance, a threat to public health and human habitation. When released to the atmosphere could enhance the global greenhouse effect due to the presence of CO2. The corrosive nature of H2S and NH3 in the biogas, wear down the piping material and therefore renders the biogas unattractive as a source of energy.
The problem was analysed from the fundamental prospective. The 1fluent and effluent characteristics of the anaerobic digester were examined for these 15 parameters: temperature, pH, DO, BOD, COD, TDS, EC, Salinity, TS, SS, P, K, TKN, Nitrate and FC. The digester performed a remarkably well showcasing removal efficiency (%) of the following: SS (78.8%), BOD (98.3%), COD (99.8%), N03N (98.7%) and FC (99.9%). The effluent mean TKN value was twice its influent value, (100%) increase.
Interestingly, the biogas samples from the two biogas tanks vary in components and compositions. The first biogas tank had low CH4 concentration and no concentration for NH3, H2S and H2 whereas the second tank recorded high concentration of CH4 and low concentrations of NH3, H2S, H2. This variation was due to the transition process, from aerobic state of the influent material to anaerobic condition of the digester.
Five locally available materials (Charcoal, Sawdust, Laterite, Coconut fibre, Oil palm fibre) were analysed and assessed for their respective affinity to NH3 and H2S. The absorption capacities (mg/g) were as follows. Semi-burnt oil palm fibre:
NH3 (0.015 mg/g), H2S (0.0506 mg/g); Wet oil palm fibre: NH3 (0.0138 mg/g), H2S (0.0505 mg/g); Coconut: NH3 (0.0126 mg/g), H2S (0.0503 mg/g); Sawdust (0.0149 mg/g), H2S (0.0504 mg/g); Charcoal: NH3 (0.0139 mg/g), H2S (0.0508 mg/g) and laterite: NH3 (0.0148 mg/g), H2S (0.0506 mg/g). lnfact, all the five have the capacity to absorb both NH3 and H2S, semi-burnt-oil palm fibre is the best.
Description
A thesis submitted to the Board of Postgraduate Studies,
Kwame Nkrumah University of Science and Technology in partial
fulfilment of the requirements for the award of Master of Science, 2003