Author: Opurum Christian Chibuzor
Department: Applied Microbiology
Affiliation: Nnamdi Azikiwe University Awka
This study evaluated the impact of alkaline pretreatment of corn stover (corn cob and corn sheath) and nitrogen sources on biogas production and methane yield. Three NaOH doses: 2%, 4% and 6% were used to treat the substrates for 48hrs and the performance investigated. Laboratory scale 3L and scale-up 10L capacity bioreactors were used for batch system anaerobic digestion of the different substrates for a hydraulic retention time of 31days under ambient temperature conditions of 25- 35Oc.The result showed there were 36.40% (1.64dm3) and 19.84%(1.21dm3) increase in biogas production in 2% NaOH pretreated corn sheath (CS) and corn cob (CC). Remarkable inhibitory effects were recorded in 4% and 6 % pretreatments. Pretreatment with NaOH alone is not an efficient approach for enhanced anaerobic biogas production from corn stover. The cumulative biogas yields from untreated corn cob and corn sheath (control) were 1.02dm3 and 1.20dm3, and gas analysis showed the methane content was 61.80% and 59.01% respectively. The result of the proximate analysis of the substrates showed that the C: N ratios of corn cob, poultry dropping, soy bean cake and fish meal (81:1, 14:1, 9:1 and 4:1, respectively) was not ideal for optimized biogas production and therefore required pretreatment. The effect of organic and inorganic nitrogen sources (urea, soy bean cake, fish meal and NPK fertilizer) on biogas production and methane yield was studied. Different dose ratios, 1:1, 2:1 and 3:1 were used for soy bean cake (SB) and fish meal (FM) while 65g/3g, 65g/6g and 65/9g substrate/nitrogen source were used for urea and NPK. Statistical analysis(T test) of the results showed a significant difference (p ≤5) in biogas production in the following tested parameters: CC/SB 1:1, CC/FM 1:1, CC/NPK(65g/9g), CS/SB 3:1, CS/FM 1:1, CS/Urea(65g/3g), CS/Urea(65g/6g) and CS/NPK(65g/6g) CS/Urea(65g/6g) and CS/NPK(65g/6g).The cumulative biogas yield and percentage methane content were 2.29dm3(62.77%), 2.07dm3(69%), 2.17dm3(73.10%), 2.86dm3(69.44%), 2.56dm3(72.08%), 3.29dm3(72.60%), 2.71dm3(70.00%) and 5.51dm3(73.46%), respectively. Studies on the effect of particle size of the substrate on biogas production revealed only 27.12% (1.29dm3) increase in biogas from corn cob of 2mm particle size. Co-digestion of the substrates with cow dung and poultry dropping at different dose ratios (1:1, 2:1 and 3:1) was investigated. Statistical study of the results showed significant different in biogas yield from the parameters: CC/CD 2:1, CS/CD 1:1 and CS/PD 1:1. The cumulative biogas yield and percentage methane content was 2.03dm3 (71%), 3.50dm3(65.50%) and 2.67dm3(74.08%), respectively. Computer aided regression analysis (SPSS) indicated that biogas production from corn stover can be predicted based on hydraulic retention time. The highest volume of biogas, 5.51 dm3 was observed in CS/NPK (65g/6g) with 359.84% increase in biogas yield and 73.46% methane content. However, in terms of sustainable biogas production, the test parameters, 3g/65g Urea to corn cob, CS/CD 1:1, CS/PD 1:1, CS/FM 2:1, 6g/ 65g Urea to corn sheath and 9g/65g Urea to corn sheath showed outstanding results and can be adopted for domestic biogas production. This research identified a number of pretreatment measures that can be adopted to optimize biogas production and methane yield from corn stover and generation of sludge which can be used in soil amendment for plant growth.
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