Optimization of Biogas Production from Co-digestion of Palm Oil Mill Residues with Zeolite Immobilization Using Response Surface Methodology

Biogas, a renewable energy, is produced by the anaerobic digestion of organic materials into methane-rich combustible gas. In this context, this study evaluated biogas production from cafeteria food waste (CFW) and cow dung (CD) via co-digestion under mesophilic conditions using a batch digester. To assess the effectiveness of the process, key physicochemical parameters, including total solids, volatile solids, moisture content, carbon-to-nitrogen ratio, and pH, were determined before and after digestion. Furthermore, optimization of biogas production was performed using the response surface methodology with a three-factor, three-level Box–Behnken design to analyze the effects of CFW-to-CD ratio, pH, and temperature. Accordingly, 17 experimental runs were conducted in triplicate, and the optimal conditions were determined to be a CFW-to-CD ratio of 3, pH 7.0°C, and 37.5°C, which resulted in the maximum biogas yield of 197 mL with 62.5% methane. These findings suggest that co-digestion of CFW and CD holds significant potential for enhancing the biogas yield and methane composition. Therefore, this approach offers an efficient and sustainable solution for renewable energy production, effectively transforming organic waste into a beneficial energy resource.

Rice husk is one of agricultural waste that is potentially converted to biogas. In this research, rice husk is used as the material to produce biogas by liquid anaerobic digestion (L-AD) with TS concentration below 15/5. The purposes of this research are finding the optimum value of total solid (TS), C/N ratio, and microbial consortium (MC) for biogas production and then analyzing the optimum biogas production rate from rice husk. Because of the high lignin content, rice husk must be through the pretreatment stage using NaOH 3%. The variations of the observed factor are 5%, 10%, 15% for TS concentration; 20, 35, 50 for C/N ratio; and 3%, 6%, 9% for MC concentration. There are 16 reactors in which the variation for each reactor was determined by Central Composite Design. Data obtained from the research will be optimized using Response Surface Methodology (RSM) in Statistica 10. The result shows that the optimum condition of biogas production from rice husk is TS in between 1%-2.5%, C/N ration 33.45, and MC in between 5.5%-7%. Reactor having a combination of value factors that close to the optimum value will be analyzed using Polymath 6.0, which is reactor 10. The kinetics constant of biogas production rate (u) is 3.625 ml/grTS.day, the maximum biogas production (A) is 277.374 ml/gr TS, and the minimum time needed to produce biogas (λ) is 3.878 days.

Biogas production is one of the renewable energy alternatives to fossil fuel consumption amidst a global rise in energy demand. In this study, goat manure was used as the substrate in batch-process anaerobic digesters, and the inoculum used was obtained from an existing biogas plant. The aim was to develop an empirical biomethane potential (BMP) of goat manure, develop a predictive model, and establish optimum process parameters for its anaerobic digestion using a response surface methodology. Proximate analysis of the substrates and inoculum was carried out according to American Public Health Association standards. An empirical BMP study was conducted on the substrate using the anaerobic biodegradation, activity, and inhibition protocol, and the effects of the process parameters on biogas yield from anaerobic digestion were investigated according to the central composite design generated by Design Expert 11 software (Stat-Ease Inc.). The results showed that goat manure has a dry matter content of 205.60 ± 12.64 g/kg and organic matter of 688.78 ± 18.02 g/kg of dry matter. The BMP was 0.49 ± 0.002 LCH<sub>4</sub>/gVS. Maximum biogas production of 650 mbar was recorded at a hydraulic retention time (HRT) of 60 days and a substrate-to-inoculum (S/I) ratio of 10:1. The significant mathematical model was linear, with a p-value < 0.0001. The optimum biogas yield was obtained at a S/I ratio of 0.5 and an HRT of 33.09 days at room temperature of 29 <sup>o</sup>C. The biogas composition was 58.53% CH<sub>4</sub> and 41.47% CO<sub>2</sub>. The study established goat manure as a good substrate for biogas production. It also established a mathematical model to predict process parameters for optimum yield.

Comparative evaluation of metal oxide nanoparticles (Mn3O4, NiO, Mn-doped NiO, and SnO2) on biogas and methane production from cow dung

Biohydrogen generation from jackfruit peel using anaerobic contact filter

The effects of hydraulic retention time (HRT), pH, and operating temperature (T OP) on the degradation of food waste-recycling wastewater (FRW) were investigated in laboratory-scale hydrolysis/acidogenesis reactors. Response surface analysis was used to approximate the production of volatile organic acids and degradation of volatile suspended solids (VSS), carbohydrate, protein, and lipid with regard to the independent variables (1 ≤ HRT ≤ 3days, 4 ≤ pH ≤ 6, 25 ≤ T OP ≤ 45°C). Partial cubic models adequately approximated the corresponding response surfaces at α < 5%. The physiological conditions for maximum acidification (0.4g TVFA + EtOH/gVSadded) and the maximal degradation of VSS (47.5%), carbohydrate (92.0%), protein (17.7%), and lipid (73.7%) were different. Analysis of variance suggested that pH had a great effect on the responses in most cases, while T OP and HRT, and their interaction, were significant in some cases. Denaturing gradient gel electrophoresis analysis revealed that Sporanaerobacter acetigenes, Lactobacillus sp., and Eubacterium pyruvivorans-like microorganisms might be main contributors to the hydrolysis and acidogenesis of FRW. Biochemical methane potential test confirmed higher methane yield (538.2mLCH4/g VSadded) from an acidogenic effluent than from raw FRW.

Biogas production from llama and cow manure at high altitude

Food waste (FW) valorization via lactic acid (LA) fermentation is a promising approach, yet most studies rely on surrogate substrates, limiting industrial applicability. This study investigated continuous LA fermentation of actual FW slurry from a Shenzhen treatment plant, focusing on the effects of hydraulic retention time (HRT: 1.33, 2.0, 3.0 days) and temperature (25, 30, 35, 40 °C) under open-culture conditions. Results showed that hydraulic retention time (HRT) and temperature jointly regulated fermentation performance and microbial communities. Short HRT (1.33 days) caused system instability with fluctuating LA concentrations, while extending the HRT to 2 days enhanced stability, achieving LA concentrations exceeding 14,000 mg/L across all temperatures. Further increasing the HRT to 3 days reduced LA yield and acidification rate, accompanied by acetic/propionic acid accumulation, especially at higher temperatures. Temperature affected the system’s hydrolysis rate, with higher temperatures promoting the hydrolysis of cellulose and hemicellulose. Metagenomic analysis revealed that Lactobacillaceae dominated (&gt;90% of bacteria). The phosphoketolase pathway was the most abundant LA-producing route, and temperature and HRT affected carbohydrate-active enzyme profiles. Balancing efficiency and cost, an HRT of 2 days at 30–35 °C is recommended for industrial LA fermentation of actual FW.

Effects of OLRs and HRTs on hydrogen production from high salinity substrate by halophilic hydrogen producing bacterium (HHPB)

Temperature-phased enhanced the single-stage anaerobic co-digestion of sewage sludge, wine vinasse and poultry manure: Perspetives for the circular economy

One-stage autothermal thermophilic aerobic digestion (ATAD) is a promising process for sewage sludge stabilization. This study investigated semicontinuous operation in simulated one-stage ATAD digesters and analyzed the effects of hydraulic retention time (HRT) on sludge stabilization. During semicontinuous operation, the average volatile solids (VS) removals at HRTs of 13 and 16 days were 40.1% and 41.8%, respectively. Because HRTs were 6 and 10 days, the maximum VS removal was no more than 33.2%, less than 38% required by Class A digested sludge, so a suitable HRT level is 13–16 days for a one-stage ATAD system. The digesters with 13- and 16-day HRTs maintained relatively low soluble chemical oxidation demand (SCOD), total nitrogen, NH4+-N, and total phosphate, whereas the digester at HRT 6 days had high SCOD concentration (<6,300 mg L−1) and low oxidation reduction potential (ORP), ranging between −335 and −245 mV. Volatile fatty acids (VFAs) accumulated rapidly at short HRTs, and acetic, pro...

This study investigated the potential of the continuous anaerobic co-digestion (AcoD) of Hura crepitans leaves and cow dung for biogas production under mesophilic conditions in a vertical plug-flow digester. The substrates were combined in ratio 1:1, mixed with water and allowed to acclimatize for 14 days before weekly feeding at organic loading rate (OLR) of 3.79 gVS/L d. AcoD was performed for a retention time of 7 weeks (49 days). Physicochemical analysis revealed Hura crepitans leaves had a high total solid (TS) content of 96% and volatile solid (VS) content of 83.85% while cow dung exhibited a TS of 26% and VS of 17.49%. The carbon-to-nitrogen (C/N) ratios of Hura crepitans and cow dung were 17.75 and 141.19 respectively Weekly biogas production measurements demonstrated a diauxic growth pattern, with initial production at 4.32 L in week 1, followed by a notable increase to 6.48 L in week 2, a significant drop to 1.40 L in week 3, and a recovery to higher production in weeks 4 through 7, culminating in a cumulative biogas production of 30.77 L at the end of the AD process. The biofertiliser potential of the digestate was evaluated, and the results indicated its potentials for agricultural purposes. The findings of this study suggest that the co-digestion of Hura crepitans leaves and cow dung in a vertical plug-flow digester could improve biogas production and promote sustainable waste management.

Anaerobic mesophilic co-digestion of ensiled sorghum, cheese whey and liquid cow manure in a two-stage CSTR system: Effect of hydraulic retention time

Three semicontinuous continuous stirred-tank reactors (CSTR) operating at mesophilic conditions (35°C) were used to investigate the effect of hydraulic retention time (HRT) on anaerobic digestion of wheat straw. The results showed that the average biogas production with HRT of 20, 40, and 60 days was 46.8, 79.9, and 89.1 mL/g total solid as well as 55.2, 94.3, and 105.2 mL/g volatile solids, respectively. The methane content with HRT of 20 days, from 14.2% to 28.5%, was the lowest among the three reactors. The pH values with HRT of 40 and 60 days were in the acceptable range compared to that with HRT of 20 days. The propionate was dominant in the reactor with HRT of 20 days, inhibiting the activities of methanogens and causing the lower methane content in biogas. The degradation of cellulose, hemicellulose, and crystalline cellulose based on XRD was also strongly influenced by HRTs.

Effect of hydraulic retention time on biohydrogen and volatile fatty acids production during acidogenic digestion of dephenolized olive mill wastewaters