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Matching Livestock Systems with Available Resources |
MEKARN Regional Conference 2007 |
Four biodigesters using tubular polyethylene film of 64 cm diameter were constructed in each of three locations (NLU, LRC and CelAgrid) to study effect of recycling effluent on gas production. A change-over design was used with 2 treatments in a 2*2 factorial experiment. The first factor was “Mixed effluent or non mixed effluent”; with 0, 0.25, 0.5 and 0.75% DM of effluent concentrations mixed with 4, 3.75, 3.5 and 3.25% on DM of pig manure for biodigesters. The biodigesters were charged with pig manure at a loading rate of 4 kg total solids per m³ of liquid volume per day. The second factor was retention times of 10 and 20 days. Gas production was measured daily by water displacement in inverted lightweight containers (tubular polyethylene supported by bamboo strips) suspended in 200 litre drums filled with water. Gas production was measured daily but only the data for the last 10 days of each period were used in the statistical analysis. Influent and effluent were analyzed at weekly intervals for DM, OM, pH, and total nitrogen and ammonia-nitrogen.
Gas production was increased by increasing retention times (P<0.001); 0.93 and 1.01 volumes biogas/unit liquid volume of biodigester for 10 and 20 days retention. Efficiency was better for 20 days retention (357 litres biogas/kg OM) than for 10 days retention (330 litres biogas/kg OM). With a mixed effluent input of fresh pig manure for the biodigesters, neither the rate of gas production (0.99, 1.05, 0.96 and 0.86 volumes biogas/unit liquid volume of biodigester) nor the efficiency (350, 372, 343 and 309 litres biogas/kg OM added to the biodigester), were influenced by effluent concentrations (0, 0.25, 0.5 and 0.75% DM, respectively). The proportion of ammonia-N in total-N increased from a range 0.021 to 0.026 in the fresh manure to a range of 0.38 to 0.55 in the effluent and did not appear to be affected by retention time or loading rate.
Key words: Biodigester, polyethylene, pig manure, mixing effluent, retention time, gas production, ammonia-nitrogen.