Biogas Production Performance Research Articles

Biogas production performance using soybean residue and hydrothermal pretreated food waste hydrolysate in a continuously anaerobic two-stage pilot plant

In this study, a continuously anaerobic two-stage pilot plant was established for bioenergy production, comprising 5 major pieces of equipment: a mixing tank, 1st anaerobic digester (AD), 2nd AD, sediment tank, aeration tank, and final sediment tank, all operating at ambient conditions. The operation of the continuously anaerobic two-stage pilot plant was automatically controlled by a programmable logic controller (PLC) using a designed control logic concept to set the hydraulic retention time (HRT) and inlet substrate concentration. The organic loading rate, pretreatment of hydrolysis pressure, and microbial community analysis were investigated for their effects on biogas production performance using different substrates: soybean residue (SR) and food waste hydrolysate (FWH), respectively. It was found that the peaks of biogas production rate on daily volumetric feeding were 1.20 m³·m⁻³·d⁻1, and the biogas yield on VS added was 760 dm³·kg⁻1 from food waste hydrolysate with a pretreatment hydrolysis pressure of 10 kg cm⁻2, at an OLR in COD concentration of 3.56 kg m⁻³·d⁻1, and an HRT of 11 days, respectively. The Methanobrevibacter genus was found to be abundant in the 1st AD, approximately 6.7 times more abundant than in the 2nd AD. The continuous anaerobic two-stage pilot plant was properly examined for its application in treating food waste and soybean residue with the goal of obtaining renewable bioenergy.

Mathematical modelling of biodigestion in an Indian biodigester and its stability analysis via Lyapunov technique

Biodigesters are vessels in which a microbiological consortium converts an organic residue into biogas and biofertilizer. This bioprocess, anaerobic biodigestion, plays an important environmental role since the residue at the end of the reaction has a reduced organic load, in addition to lower toxicity, and can therefore be disposed of with less impact on the environment. Moreover, biodigestion produces biogas, which is of great interest in view of the current shortage of fossil fuels. In this sense, this work proposes a nonlinear mathematical model based on the mass flux balance of an Indian biodigester and it also analyses its properties, in particular the Lyapunov stability of its equilibrium solutions, and verifies the non-negativity of its solutions to be consistent with the biology of the issue. The proposed model represents an important tool to describe anaerobic biodigestion in an Indian biodigester, providing information for further planning, scenario prediction and control of the bioprocess. Simulations of the model in different scenarios showed that lower initial bacteria/substrate concentration ratios (≈0.14) can promote better biogas production performance.

Preparation of iron oxide-modified digestate biochar and effect on anaerobic digestion of kitchen waste

Two kinds of Fe2O3-modified digestate-derived biochar (BC) were prepared and their effects on anaerobic digestion (AD) of kitchen waste (40.0 g VS/L) were investigated, with BC and Fe2O3 addition used as a comparison. The results showed that Fe2O3-modified BC (Fe2O3-BC1 prepared by co-precipitation and Fe2O3-BC2 by impregnation) significantly increased methane yield (20.8 % and 16.4 %, respectively) and reduced volatile fatty acid concentration (35.6 % and 29.6 %, respectively). Microbial high-throughput analysis revealed that Fe2O3-modified BC selectively enriched Clostridium (47.3 %) and Methanosarcina (72.2 %), suggesting that direct interspecies electron transfer contributing to improved biogas production performance was established and enhanced. Correlation analysis indicated that biogas production performance was improved by the larger specific surface area (83.4 m2/g), pore volume (0.101 cm3/g), and iron content (97.4 g/Kg) of the BC. These results offer insights for enhancing the efficacy of AD processes using Fe2O3-modified BCs as additives.

Co-digestion approach for enhancement of biogas production by mixture of untreated napier grass and industrial hydrolyzed food waste.

The co-digestion of untreated Napier grass (NG) and industrial hydrolyzed food waste (FW) was carried out in the batch reactor to investigate the effect of substrate ratios on biogas production performance. Two-stage anaerobic digestion was performed with an initial substrate concentration of 5g VSadded/L and a Food to Microorganism Ratio (F/M) of 0.84. The 1:1 ratio of the NG and FW showed the optimum performances on biogas production yield with a value of 1,161.33mL/g VSadded after 60 days of digestion. This was followed by the data on methane yield and concentration were 614.37mL/g VSadded and 67.29%, respectively. The results were similar to the simulation results using a modified Gompertz model, which had a higher potential methane production and maximum production rate, as well as a shorter lag phase and a coefficient of determination of 0.9945. These findings indicated that the co-digestion of Napier grass and hydrolyzed food waste can enhance biogas production in two-stage anaerobic digestion.

Additives to Enhance the Performance and Mechanism of Biogas Production from Agricultural Wastes: A Mini-review

Additives to Enhance the Performance and Mechanism of Biogas Production from Agricultural Wastes: A Mini-review

Determine the Optimal Parameters for Biogas Production from Common Reed (Phragmites australis)

A series of batch assays have been conducted to investigate the optimal factors that can be adopted to improve the anaerobic digestion (AD) performance of Phragmites australis and increase biogas production. The assays were carried out using 125 mL microcosm reactors with a working volume of 80 mL and incubated at mesophilic conditions (37 ± 1ºC). The effect of particle size (10, 5, 2, and < 1 mm) and alkaline pre-treatment of P. australis using various concentrations of sodium hydroxide (0.5, 1, 2, and 4%) on biogas production was examined. Furthermore, the best pre-treatment incubation time (12, 24, 48, 72, 96, and 120 h) and the optimal inoculum to substrate ratio (ISR: 4:1, 2:1, 1:1, 1:2 and 1:4) were also assessed. The results revealed that the highest biogas production from P. australis was achieved at particle size < 1 mm (27.97 ± 0.07 and 16.67 ± 0.09 mL/g VS added, for pre-treated and untreated P. australis respectively); 2% and 4% NaOH concentration for pre-treatment (70.01 ± 3.75 and 76.14 ± 2.62 mL/g VS added, respectively); pre-treatment incubation time of 72, 96, and 120 h (71.18 ± 1.79, 72.46 ± 1.08, and 73.78 ± 1.87 mL/g VS added, respectively); and ISR of 1:2 for pre-treated P. australis (78.21 ± 0.36 mL/g VS added) and ISR 1:4 for untreated P. australis (28.93 ± 1.55 mL/g VS added). Determining optimal parameters in this work would guide further development of process configurations, such as continuous AD systems.

Multiple-layer statistical methodology for developing data-driven models of anaerobic digestion process

When modelling anaerobic digestion, ineffective data handling and inadequate designation of modelling parameters can undermine the model reliability. In this study, a multilayer statistical technique, which employed a machine learning technique using regression models, was introduced to systematically support the development of anaerobic digestion models. Layer-by-layer statistical techniques including cubic smoothing splines (missing data reconstruction), principal component analysis (identifying correlated parameters), analysis of variance (analysing differences among datasets), and linear regression (developing data-driven models) were used to develop and validate anaerobic digestion models. Experimental data collected from the long-term operation of lab-scale (operated for 350 days), pilot-scale (operated for 150 days), and full-scale reactors (operated for 750 days) were used to demonstrate the modelling process. The multivariate models based on a data-driven modelling technique were developed by subjecting the experimental and monitored data to a modelling process. The developed models could predict the biogas production and effluent chemical oxygen demand during anaerobic digestion. Statistical analyses verified the modelling hypotheses, evaded invalid model development, and ensured data integrity and parameter validity. Multiple linear regression of principal components demonstrated that the performance of biogas production using food waste was influenced by the variances of the nitrogen and organic concentrations, but not by the chemical oxygen demand to total nitrogen (C/N) ratio. In the validation process, the model developed with lab-scale reactor data showed relatively high accuracy with R2, SSE, and RMSE values of 0.86, 34.45, and 0.72.

Biogas production from food waste hydrolysate using a subcritical water pretreated process and pulp wastewater seed sludge

This study was investigated the biogas production performance from subcritical water hydrolysate (SCWH) using a pretreated food waste (FW) process, and pulp wastewater (PW) as seed sludge according to different volatile solid (VS) ratio of PW to SCWH, and different substrate concentration. The subcritical water hydrolysis was acted for 30 mins in a 70 ml Teflon reactor under different temperatures varied from 119, 129, 139, 159, and 195 ℃, respectively. A batch system for optimal biogas and methane production yields examination were fermented in a 60 ml flask under 37 °C and 120 rpm. A maximum biogas yield of 807.0 ml/g VSre and methane yield of 329.5 ml/g VSre were achieved at a VS ratio of PW to SCWH 1:3 and substrate concentration of 25 g/L with a hydrolysate under 159 ℃ and the volatile solids (VS) removal efficiency of 80%. These results indicated that the food waste pretreated by subcritical water hydrolysis can efficiently increase the biogas production under optimal conditions.

Improvement of Biogas Production Using Biochar from Digestate at Different Pyrolysis Temperatures during OFMSW Anaerobic Digestion

Anaerobic digestion (AD) was utilized to treat the ever-growing amount of organic fraction of municipal solid waste (OFMSW) generated due to population growth and the expansion of the global economy. The widespread application of AD has led to a continuous increase in residual solid digestate that necessarily requires further disposal. Improving AD efficiency and reducing the large amount of digestate is necessary. This study investigated the chemical and physical characteristics of biochar derived from digestate at different pyrolysis temperatures (300 °C, 500 °C, and 700 °C), as well as corn stover biochar at 500 °C, and their effects on AD performance. The pH value of the biochar increased with an increase in pyrolysis temperature while the electrical conductivity decreased. Macropores dominated the biochar’s pore size, and decreased with an increased pyrolysis temperature. The biochar preparation temperature significantly influenced the AD efficiency. Biochar prepared at 700 °C outperformed the other groups, improving the biogas production yields by 10.0%, effectively shortening the lag time, and increasing the average chemical oxygen demand (COD) degradation rate by 14.0%. The addition of biochar (700 °C) and corn stover biochar increased the relative abundance of the volatile fatty acid (VFAs)-oxidizing bacteria Syntrophomonadaceae, which expedited the acid conversion in AD systems. Biochar facilitated direct interspecies electron transfer between DMER64 and Trichococcus with Methanosaeta, enhancing the biogas production performance. These findings confirmed that the biochar derived from digestate promoted biogas production and acid conversion in the AD system of OFMSW. Furthermore, biochar has an improved AD stability, which represents a promising approach to recycling digestate.

Effects of Temperature Shifts on Microbial Communities and Biogas Production: An In-Depth Comparison

Temperature plays a significant role in anaerobic digestion (AD) as it affects the microbial communities and ultimately controls the efficiency of the process. Few studies have looked at temperature-adjusted AD, but it is unclear how the temperature shifts affect biogas production and the dynamics of microorganisms involved in methanogenesis. This study tested two temperature shift scenarios in fed-batch mode using anaerobically digested sewage sludge and glucose-based substrate. The first scenario was acclimatized to upshifting temperatures from 42 °C to 48 °C while the second was acclimatized to downshifting temperatures from 55 °C to 45 °C. Both temperature shift scenarios resulted in a decrease in biogas production, especially at 45 °C. The upshifted scenario experienced a maximum decrease of 83%, and the downshifted scenario experienced a 16–33% decrease in methane production. Next-generation 16S rRNA sequencing revealed the domination of Methanoculleus in the upshifted scenario. However, a low correlation between the number of Methanoculleus and the other hydrogenotrophic methanogens to biogas production indicates inhibition in the hydrogenotrophic pathway. The downshifted scenario showed better biogas production due to the substantial domination of acetoclastic Methanosaeta and the low abundance of sulfate-reducing bacteria. Hence, the temperature shift affects the microbial communities, significantly affecting biogas production performance.

Effects of biochar addition on anaerobic co‐digestion of sewage sludge and swine manure: copper immobilization and digestion performance

AbstractBACKGROUNDA significant concentration of the heavy metal Cu is found in sludge and swine manure, and excessive agricultural use of Cu can seriously inhibit plant growth. There is a critical need for an effective technology to address the issue of biotoxicity.RESULTSThis study aimed to immobilize heavy metal Cu and decrease its bioavailability by adding biochar for anaerobic co‐digestion (AcoD) with swine manure and sludge. Coconut shell biochar (CSB), bamboo biochar (BC) and fruit shell biochar (FSB) were prepared by pyrolysis based on coconut shell, bamboo and fruit shell as precursors. Anaerobic co‐digestion experiments were designed (sludge inoculation ratio: 20% of working volume), a biochar dosing ratio of 5% (dry weight of swine manure) and the effects on Cu immobilization and biogas production performance were investigated. CSB had a larger specific surface area (765.2 m2 g−1) and more abundant surface functional groups (CO, CO, OCO, OH) than BC and FSB. CSB treatment demonstrated that the ultimate cumulative biogas production was 360.27 mL g−1 volatile solid – 76.30% higher than the control (no addition). CSB addition decreased the amount of diethylenetriamine pentaacetic acid‐extractable Cu to 19.75 mg kg−1 (immobilizing 75%). The correlation between environmental factors (pH, total nitrogen, total phosphorus, total organic carbon) and Cu immobilization was verified by redundancy analysis, and a positive correlation was revealed between phosphorus content and the Cu immobilization effect.CONCLUSIONThis article presented comparative biochar research and contributed to assessing the environmental risk of Cu in anaerobic digestion. It guided the application of biochar for the treatment of heavy metal pollution. © 2023 Society of Chemical Industry (SCI).

The effects of catalyst and co-digestion on the performance of biogas yield

This study presented the effects of catalyst and co-digestion on the performance of biogas production. Rabbit dung and plantain peels were used as feedstock materials while clay, KOH and NaOH were used as catalysts. The experiment was divided into five setups. The slurry stayed in the digester for 45days. The digester temperature fluctuated around 35-47°C while the pH varied from 6.8-7.8. The result of the analysis revealed that the gas produced has high methane content values from 69.75 – 72.38% with low CO2 concentration values from 7.16 - 15.41%. Total volume of biogas were noted to be 74L, 31.9L, 125.5L, 112.4L and 55.8L for each sample. The physicochemical properties revealed that the TS varied from 3.63% - 4.20%, while VS varied from 3.17% - 3.78%. The TOC ranged from 2.18% - 4.79% while the nitrogen content ranged within 0.195% - 0.352%, Crude fibre ranged from 3.15 – 3.81%. Ash content ranged within 3.21 – 4.50% and moisture content varied between 82.47 – 90.05%. The COD and BOD were also obtained. The calorific values of the samples obtained ranged from 17,600 – 20,184KJ/kg. The phosphorus content was between 0.25% and 0.40% while potassium was between 0.15 and 0.37% on average.

Effects of biogas slurry reflux mode and reflux rate on methane production by mixed anaerobic digestion of corn straw and pig manure

Biogas slurry reflux is a promising method to realize biogas slurry reduction and improve biogas production performance of anaerobic digestion. The purpose of this study was to investigate the effects of reflux mode and reflux ratio on mixed anaerobic digestion of corn straw and pig manure to obtain the best biogas slurry reflux process. The influence of reflux mode and reflux ratio on the internal environment during anaerobic digestion were clarified by kinetic analysis. The results showed that compared with the control group, the degree of substrate hydrolysis in the hydrolysis phase reflux (HPR) and two-phase synergistic reflux (TPSR) treatment groups increased, and the initial concentration and peak value of volatile fatty acids (VFAs) increased by 20.35%–85.81% and 24.72%–74.37%, respectively. The modified Gompertz model fitting results that the three biogas slurry reflux modes all significantly shortened the lag period of anaerobic digestion (17.29%–48.32%) and increased the peak gas production (7.54%–88.07%). And the maximum daily gas production (65.82 mL/(g VS∙d)), methane production (422.86 mL/g VS) and biodegradation rate (83.65%) were obtained under the TPSR mode with reflux ratios of 75% and 100%. This study provides a theoretical basis for the development of biogas slurry reflux technology in the mixed anaerobic digestion of corn straw and pig manure, and realizes the reduction and resource utilization of biogas slurry.

Mango Peel Nanofiltration Concentrates to Enhance Anaerobic Digestion of Slurry from Piglets Fed with Laminaria.

The environmental impact of biowaste generated during animal production can be mitigated by applying a circular economy model: recycling, reinventing the life cycle of biowaste, and developing it for a new use. The aim of this study was to evaluate the effect of adding sugar concentrate solutions obtained from the nanofiltration of fruit biowaste (mango peel) to slurry from piglets fed with diets incorporating macroalgae on biogas production performance. The nanofiltration of ultrafiltration permeates from aqueous extracts of mango peel was carried out using membranes with a molecular weight cut-off of 130 Da until a volume concentration factor of 2.0 was reached. A slurry resulting from piglets fed with an alternative diet with the incorporation of 10% Laminaria was used as a substrate. Three different trials were performed sequentially: (i) a control trial (AD0) with faeces resulting from a cereal and soybean-meal-based diet (S0); (ii) a trial with S1 (10% L. digitata) (AD1), and (iii) an AcoD trial to assess the effect of the addition of a co-substrate (20%) to S1 (80%). The trials were performed in a continuous-stirred tank reactor (CSTR) under mesophilic conditions (37.0 ± 0.4 °C), with a hydraulic retention time (HRT) of 13 days. The specific methane production (SMP) increased by 29% during the anaerobic co-digestion process. These results can support the design of alternative valorisation routes for these biowastes, contributing to sustainable development goals.

Effects of Magnetic Biochar Addition on Mesophilic Anaerobic Digestion of Sewage Sludge.

As a low-cost additive to anaerobic digestion (AD), magnetic biochar (MBC) can act as an electron conductor to promote electron transfer to enhance biogas production performance in the AD process of sewage sludge and has thus attracted much attention in research and industrial applications. In the present work, Camellia oleifera shell (COS) was used to produce MBC as an additive for mesophilic AD of sewage sludge, in order to explore the effect of MBC on the mesophilic AD process and its enhancement mechanism. Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectrometry (FTIR), and X-ray diffraction (XRD) further confirmed that biochar was successfully magnetized. The yield of biogas from sewage sludge was enhanced by 14.68-39.24% with the addition of MBC, and the removal efficiency of total solid (TS), volatile solids (VS), and soluble chemical oxygen demand (sCOD) were 28.99-46.13%, 32.22-48.62%, and 84.18-86.71%, respectively. According to the Modified Gompertz Model and Cone Model, the optimum dosage of MBC was 20 mg/g TS. The maximum methane production rate (Rm) was 15.58% higher than that of the control reactor, while the lag-phase (λ) was 43.78% shorter than the control group. The concentration of soluble Fe2+ and Fe3+ were also detected in this study to analyze the function of MBC for improving biogas production performance from sewage sludge. The biogas production was increased when soluble Fe3+ was reduced to soluble Fe2+. Overall, the MBC was beneficial to the resource utilization of COS and showed a good prospect for improving mesophilic AD performance.

Long-Term Pre-Treatment of Municipal Sewage Sludge with Solidified Carbon Dioxide (SCO2)—Effect on Anaerobic Digestion Efficiency

Studies on harnessing solidified carbon dioxide (SCO2) for municipal sewage sludge (MSS) pre-treatment have been conducted exclusively in batch reactors. This makes it difficult to accurately assess how long-term SCO2 treatment affects anaerobic digestion (AD) conditions and performance. The aim of our study was to evaluate the effect of long-term MSS pre-treatment with SCO2 on AD conditions, anaerobic bacterial community, and biogas composition and yields. The presented experiments are the first studies on the effect of pre-treatment with SCO2 on the efficiency of AD of MSS in continuous reactors. So far, the impact of the organic load rate (OLR) on the efficiency of MSS methane fermentation has not been assessed, which is also a novelty of the conducted research. The AD process was conducted in continuous-stirred, continuous-flow anaerobic with an active volume of 20 dm3. The digestion process was run at 38 ± 1 °C. The experiment was divided into two stages. Raw (non-pretreated) MSS was used in stage 1, whereas the MSS used in stage 2 was pre-treated with SCO2. The SCO2/MSS ratio was 1:3. Each stage was sub-divided into four variants, with different levels of the OLR ranging from 2.0 to 5.0 gCOD/dm3·day. Pre-treatment with SCO2 was found to improve AD performance at an OLR of 3.0–4.0 gVS/dm3·day. The 3.0 gVS/dm3·day variant offered the best biogas production performance—both daily (29 ± 1.3 dm3/day) and per VS added (0.49 ± 0.02 dm3/gVS)—as well as the highest CH4 content in the biogas (70.1 ± 1.0%). In this variant, the highest energy output effect of 187.07 ± 1.5 Wh/day was obtained. The SCO2 pre-treatment was not found to change the pH, FOS/TAC, or the anaerobic bacterial community composition. Instead, these variables were mainly affected by the OLR. Our study shows that MSS pre-treatment with SCO2 at a SCO2/MSS ratio of 0.3 (by volume) significantly improves AD performance in terms of methane production and feedstock mineralization. The pre-treatment was found to have no negative effect on the long-term continuous operation of the reactor.

Effect of Ammonia–Autoclave Pretreatment on the Performance of Corn Straw and Cow Manure Batch Anaerobic Digestion

Biomass pretreatment is a critical method for improving the anaerobic digestion (AD) performance of lignocellulosic feedstocks. In this study, an effective combined ammonia–autoclave pretreatment method was selected for the pretreatment of corn straw at 90 °C using four ammonia concentrations (7%, 9%, 11%, and 13%). The results showed that the combined pretreatment improved the substrate’s degradation efficiency and the system’s buffer capacity, and significantly improved the hydrolysis and biogas production performance of corn straw. After pretreatment, the lignin removal rate increased by 11.28–39.69%, and the hemicellulose degradation rate increased from 10.12% to 21.23%. Pretreatment of corn straw with 9% ammonia and an autoclave gave the highest methane yield of 257.11 mL/gVS, which was 2.32-fold higher than that of untreated corn straw, making it the optimal pretreatment condition for corn straw. Therefore, the combined ammonia–autoclave pretreatment technology can further improve the AD performance of corn straw.

Economic performance of biogas production and use from residues co-digestion in integrated 1G2G sugarcane biorefineries: Better electricity or biomethane?

Recovering bioenergy through anaerobic digestion (AD) has become the most attractive waste management approach in modern industrial plants, because both the environmental adequacy and the provision of clean biogas-derived energy can be successfully met. Recent investigations have particularly shown the energetic benefits of residue co-digestion in sugarcane biorefineries, which significantly enhances biogas production compared to mono-digestion schemes. This work carried out an economic analysis to assess the feasibility of producing biogas from residues co-digestion in an integrated 1G2G (first and second generation) ethanol biorefinery and its application in electricity and biomethane (BioCH4) production. Scenarios considered the mono-digestion of 1G vinasse in the season (MD1-base scenario), the mono-digestion of 1G vinasse in the season followed by the mono-digestion of 2G vinasse in the off-season (MD2), the co-digestion of 1G vinasse, filter cake and deacetylation liquor in the season followed by the co-digestion of filter cake and deacetylation liquor in the off-season (CD1), and finally the co-digestion of 1G vinasse, filter cake and deacetylation liquor in the season followed by the mono-digestion of 2G vinasse in the off-season (CD2). The scenarios comparison aimed to investigate the potential to implement year-round biogas production in sugarcane processing plants. The results showed that co-digestion-based scenarios (CD1 and CD2) had the best performance for producing both electricity and BioCH4 from biogas, with the higher profitability related to the latter. Scenario MD1 scenario presented a negative net present value (NPV) for both electricity and BioCH4 production, whilst only BioCH4 production would be profitable in scenario MD2. The NPV for electricity production in scenario CD2 reached USD 9 million (4-fold higher than mono-digestion of 1G vinasse reported in the literature), whilst a peak of USD 45 million was calculated for BioCH4 production. In addition, the current bioelectricity production from bagasse burning showed to be much more economically unfavorable compared to biogas production and use. Biogas recovery from residue co-digestion has been increasingly confirmed as an attractive alternative for energy generation within 1G2G ethanol biorefineries, maintaining year-round production and consisting of a robust BioCH4 source, with great potential to be used both as a biofuel to supply the plant’s fleet and to replace natural gas via injection into the grid.

Degradation Kinetics of Lignocellulolytic Enzymes in a Biogas Reactor Using Quantitative Mass Spectrometry

The supplementation of lignocellulose-degrading enzymes can be used to enhance the performance of biogas production in industrial biogas plants. Since the structural stability of these enzyme preparations is essential for efficient application, reliable methods for the assessment of enzyme stability are crucial. Here, a mass-spectrometric-based assay was established to monitor the structural stability of enzymes, i.e., the structural integrity of these proteins, in anaerobic digestion (AD). The analysis of extracts of Lentinula edodes revealed the rapid degradation of lignocellulose-degrading enzymes, with an approximate half-life of 1.5 h. The observed low structural stability of lignocellulose-degrading enzymes in AD corresponded with previous results obtained for biogas content. The established workflow can be easily adapted for the monitoring of other enzyme formulations and provides a platform for evaluating the effects of enzyme additions in AD, together with a characterization of the biochemical methane potential used in order to determine the biodegradability of organic substrates.

Improvement of biogas production and quality by addition of struvite precipitates derived from liquid anaerobic digestion effluents of palm oil wastes

When biogas is produced, the liquid anaerobic digestion effluents (LADE) still contain pollutants. Struvite precipitation is a technique for reducing pollutants as well as recovering useful elements such as nitrogen, phosphorus, and magnesium. This study aims to precipitate struvite from LADE and use it as an additive to palm oil mill effluent (POME) feedstocks in subsequent biogas production systems (batch and continuous operational modes). Struvite precipitation was simply performed using NaOH at a pH range of 8–10 without external sources of magnesium and phosphorus. The result showed that the optimum pH for struvite precipitation was 9, giving the highest yield and purity of struvite. The addition of 5% struvite to POME feedstock improved the performance of biogas production in the continuous stirred tank reactor (CSTR) in terms of stability, high COD removal efficiencies, increased methane yields, and decreased H2S concentrations. The greatest methane yield of 509.8 mL/g-VS and the methane concentration of 65.10% were obtained in the CSTR. The significant decrease in H2S concentration in biogas can increase the energy content of biogas, save on the cost of H2S removal, reduce corrosion, and extend the operating time of gas turbines used for electricity production. The results of this study emphasize the role of integrating struvite precipitation with continuous biogas production in improving the process sustainability and economy. Struvite precipitation from LADE diminishes the polluted wastewater, decreases the long-term process problems of fouling and clogging caused by struvite, and improves the performance of the biogas production.