Abstract
The potential of cotton gin waste, a considerable challenge to the gin owners, has not been fully investigated as a renewable energy source via anaerobic digestion. The weathered cotton gin trash and inoculum for triplicate biomethane potential assays were obtained from a local cotton gin mill and a municipal wastewater treatment plant, respectively. The moisture, total solids, volatile solids, and C, H, N, S, hemicellulose + cellulose, and lignin contents of gin waste were determined in triplicates. The biomethane potential of untreated and pretreated (hot water and 6% NaOH (wet CGT weight basis) gin waste was determined at different inoculum to substrate ratios. The highest cumulative biomethane yield of 111.8 mL gvs-1 was observed in inoculum to substrate ratio of 2.3, and it was statistically similar to the values; 101.8, 104.7, 100.5, and 108.9 gvs-1, observed in 0.8, 1.2, 1.5, and 1.9, respectively. The biomethane yield at the inoculum to substrate ratio of 0.4 was significantly lower than all higher ratios. The T80-90 for biomethane production was 26-30 for the ISRs of 1.2, 1.5, and 2.3. The T80-90 for inoculum to substrate ratios of 0.4, 0.8, and 1.9 were 26-31, 27-32, and 27-31 d, respectively. The modified Gompertz equation fitted very well (R2 = 0.98-0.99) to the anaerobic digestion at all inoculum to substrate ratios and pretreatments as the observed and predicted biomethane values were similar. The model predicted a lag phase of 8-10 days for control and treatments compared to the observed of 10-15 days. The highest biodegradability of 24.8±2.6% was observed at inoculum to substrate ratio of 2.3, which was statistically similar to the values observed in ratios of 0.8, 1.2, 1.5, and 1.9, respectively. Among pretreatments, the highest biodegradability of 33.0±2.4 was observed in 6% NaOH pretreatment, and it was statistically similar to hot water treatment and non-pretreated or control. These research findings advance the knowledge in the anaerobic degradation of cotton gin trash, thus helping to maximize biomethane recovery from this agro-industrial waste.
Highlights
Cotton is one of the world's most important cultivated crops owing to its high-quality natural fiber
Once picked from the farm, cotton is further processed in gins to separate fiber, leaving behind cotton gin trash (CGT) as agro-industrial waste
The biomethane potential assays were conducted at different inoculum to substrate ratios utilizing untreated and pretreated cotton gin trash as feedstock
Summary
Cotton is one of the world's most important cultivated crops owing to its high-quality natural fiber. Cheng and Zhong (2014) investigated the effects of the F/I, pretreatment, and co-digestion (with swine manure) on the BMP of cotton stalks. Isci and Demirer (2007) reported that the addition of basal media yields higher biomethane during the anaerobic digestion of cotton oil cake, seed hull, and stalks. Two of these methods are hot water and alkaline treatments, which remove soluble and whole lignin and hemicellulose fractions, respectively (Hassan et al, 2018) The effect of these pretreatments on BMP of CGT still has not been investigated. The biomethane potential assays were conducted at different inoculum to substrate ratios utilizing untreated and pretreated (hot water and alkali) cotton gin trash as feedstock. The digester performance at each treatment was evaluated by simulating the process with mainstream mathematical models and comparing them with theoretical values
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