Alkaline and bacterial pretreatment of rice straw and water hyacinth for biogas production in a batch bioreactor
Date
2021-06
Authors
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Publisher
Federal University of Technology, Owerri
Abstract
The Presence of lignin in lignocellulosic substrates greatly limits anaerobic digestion for production of biogas. The need for initial pretreatment to sufficiently remove it became inevitable. Alkaline and bacterial pretreatment methods were used to pretreat rice straw and water hyacinth samples for
application in biogas production in a batch bioreactor. Optimum concentration of NaOH (%), mass of substrate (g) and duration (h) of the pretreatment were studied using Response surface methodology(Box Behnken design) Bacterial spp isolated from termite gut were identified by 16S rRNA gene sequencing and were used for biological pretreatment of the substrate. Each pretreated sample was co- digested with 1:1, 2:1 and 3:1 ratios of cow dung, pig waste and poultry droppings respectively, as amendments. Optimization studies on the biogas production process from the amendment that gave the highest yield in biogas was carried out. Proximate composition ,lignin, cellulose and hemicellulose content of the feedstock was determined by standard methods as well as microbial succession studies .Results obtained showed that 0.5M concentration of NaOH, 14g of sample and 39.5h exposure time were optimum of NaOH pretreatment of the samples which reduced lignin concentrationfrom17.4% to 8.3% and 17.4 % to 7.3% in bacteria pretreated samples while cellulose, reducing sugar and total sugar contents increased from 10.31% to 38.86%, 6.4%to 6.9% and 156.08%to 167.14%respectively, after chemical pretreatment of water hyacinth samples. Lignin and hemicellulose concentrations reduced from 18.01 % to 7.821 % and 11.01 % to 8.21%, while cellulose concentration increased from 10.31 % to 14.40 % after 30 days of bacterial pretreatment of water hyacinth sample. The 16S RNA gene analysis of bacterial consortium from termite gut indicated the presence of Escherichia coli and Morgenela morganii strain S4L2C (MH745964), with 100%and 98.6%similarity, respectively. There was a significant difference (P ≤ 0.05) in biogas yield in all the Alkaline pretreated rice straw (APRS) and Bacteria pretreated rice straw (BPRS) amended with animal manure compared to APRS, BPRS and URS alone. For NaOH pretreated rice straw, best ratio of rice straw to cow dung was 2:1, which yielded 22.51dm3 of biogas. For bacterial pretreated rice straw, 1:1 ratioof
rice straw to cow dung was the best combination, which yielded 27.05dm3 of biogas. For bacterial pretreated water hyacinth co-digested with cow dung, highest yield of biogas was recorded in 1:1ratio, with an average of 12.03dm3. Comparative analysis of biogas yield of APRS with BPRS with amendment at varying ratios gave 30.90% increase in biogas yield for APRS and BPRS with cow dung 2:1,45.45% for BPRS and APRS with cow dung 2:1 and 20.30% for APRS and BPRS with cow dung 3:1APRS/BPRS amended with poultry dropping at1:1,2:1and 3:1 recorded 25.01%,42.01%and19.41% respectively while APRS/BPRS amended with pig waste at 1:1,2:1 and 3:1 recorded1.43%, 3.05% and 16.37%.Result indicated that substrate concentration of 520g, Hydraulic Retention Time 22.57 days and cow dung content of 520 g were the optimum conditions with predicted biogas yield of 1.960 x104 ml for bacterial pretreated rice straw. For NaOH pretreated rice straw, 216.7go substrate at HRT of 15.5 days and 520 g of cow dung as amendment were the optimum conditions, with predicted biogas yield of 1.517 x10 4 ml. Concentrations of components gases in biogas produced by rice straw/ cow dung 2:1 which produced highest volume of biogas in this study, were CO1.149%, CO2 13.556% and CH4 64.960% .proximate characteristics of digestate, such as nitrogen, phosphorus and potassium increased, while others including carbon, total solids and total volatile solid content decreased after anaerobic digestion. Finally, microbial load of slurry during digestion decreased during an aerobic digestion from 0, 14 and 28 days. These prove that rice straw and water hyacinth can be used for large-scale biogas production using Response surface methodology (BBD) from the use of
bacterial isolate from termite gut which is significantly more effective in pretreatment than 6% NaOH.
Description
A Doctoral thesis on "water hyacinth for biogas production". It contains tables, graphs and pictures
Keywords
Lignocellulosic wastes, animal manure, pretreatments, anaerobic digestion, optimization and biogas production, Department of Microbiology, Response Surface Model
Citation
Hans-Anukam, U. S. (2021). Alkaline and bacterial pretreatment of rice straw and water hyacinth for biogas production in a batch bioreactor. (Unpublished Doctoral Thesis ). Federal University of Technology, Owerri.