Average Biogas Yield Research Articles

Anaerobic dynamic membrane bioreactor for the co-digestion of toilet blackwater and kitchen waste.

Anaerobic co-digestion using an anaerobic dynamic membrane bioreactor (AnDMBR) can separate the sludge retention time and hydraulic retention time, retaining the biomass for efficient degradation and the use of less expensive large pore-size membrane materials and more sustainable dynamic membranes (DMs). Therefore, anaerobic co-digestion of toilet blackwater (BW) and kitchen waste (KW) using an AnDMBR was hypothesized to increase the potential for co-digestion. Here, the efficiency and stability of AnDMBR in anaerobic co-digestion of toilet BW and KW were investigated. DM morphology and structural characteristics, filtration properties, and composition, as well as membrane contamination and membrane regeneration mechanisms, were investigated. Average daily biogas yields of the reactor in two membrane cycles before and after cleaning were 788.67 and 746.09 ml/g volatile solids, with average methane content of 66.64% and 67.27% and average COD removal efficiencies of 82.03% and 80.96%, respectively. The results showed that the bioreactor obtained good performance and stability. During the stabilization phase of the DM operation, the flux was maintained between 43.65 and 65.15L/m2/h. DM was mainly composed of organic and inorganic elements. Off-line cleaning facilitated DM regulation and regeneration, restoring new Anaerobic morphology and structure. PRACTITIONER POINTS: High efficiency co-digestion of BW and KW was realized in the DMBR system. Average daily biogas yields before and after membrane cleaning were 788.67 and 746.09 ml/g volatile solids. Off-line cleaning facilitated DM regulation and regeneration as well as system stability. The flux was maintained between 43.65 and 65.15L/m2/h during operation.

Evaluation of biogas production and bacterial load from co‐digestion of chicken manure with different types of household waste

AbstractBackgroundThe aim of this study was to evaluate the biogas production of chicken manure (CM) co‐digestion with different types of household waste (soft organic [SO] and food waste [FW]), as well as to evaluate the bacterial load of feeding stock and digested slurry samples before and after anaerobic digestion (AD). The experiment was carried out using lab‐based prototype digesters for co‐digestion of CM with different household wastes (5%). Three experimental groups (T1, T2, and T3) were designed using mixing ratios of SO:CM:H2O:inoculum (5:22.5:22.5:50), FW:CM:H2O:inoculum (5:22.5:22.5:50), and (SO + FW):CM:H2O:inoculum (2.5 + 2.5:22.5:22.5:50). The digesters were set at 28–34°C for 30 days for hydraulic retention time (HRT). Total viable count (TVC), Escherichia coli, and Salmonella spp. counts were determined using the spread plate technique.ResultsThe study revealed that the highest average cumulative biogas yield was achieved from T1 > T3 > T2, but the concentration of CH4 was found in T3 > T2 > T1. The biogas production between the three groups was statistically nonsignificant (p > 0.05) but the daily concentration of CH4 was found statistically significant (p < 0.05). The average concentration of CH4 and CO2 in biogas was found to be 30% and 68% for T1, 60% and 37% for T2, and 69% and 27% for T3. However, the H2S content was within the acceptable range. The bacterial load was decreased by 2–3 logs before and after AD, and this reduction was statistically significant (p < 0.05).ConclusionThe research found that the co‐digestion of CM with combined household wastes increased the methane concentration in biogas.

Anaerobic Digestion of Maize Husk in Co-Digestion with Goat and Cow Dung for Enhanced Biogas Production

In recent investigations, Anaerobic co-digestion has been superior to traditional anaerobic digestion (AD). The advantages of employing co-substrates for improved bioenergy generation and solids reduction have drawn researchers to investigate the co-digestion technology and understand the impact of multiple substrates on digester performance. This study aimed to generate biogas by co-digestion of maize husk with cow and goat dung as substrates, isolate the bacteria involved in the process, and assess the quantity and makeup of the biogas generated by the substrates. The substrates were fed to mini-digesters fabricated in the laboratory using 1L bottles for 49 days’ retention time. It assessed the production potential of the substrates for biogas yield in mono-digestion and co-digestion. The average biogas yield (cm3) and methane content (%) in the D1, D2, D3, D4, D5, and D6 were 9135 (58%), 8660 (71%), 9820 (69%), 6545 (65%), 5915 (48%) and 1965 (21%) respectively. The highest gas yield was observed in digesters with co-digestion of the substrates (D1 and D2) than the mono-digestion of the GD and CD by 35.2% and 24.4%, respectively, with an improvement in methane content. The process was carried out in a mesophilic condition and a pH range of 6.8-8.2. The study's findings showed that the most frequently isolated and identified bacteria were Klebsiella pneumoniae and Bacillus species, indicating that these species are essential to the microbial activities involved in biogas production. The investigation additionally showed that maize husk in co-digestion with cow dung and goat dung had great potential for generating and producing large quantities of biogas within 49 days’ retention time.

Effect of acclimatization rate on biogas production from anaerobic digestion of biodiesel waste products

AbstractDigester acclimatization can improve the efficiency of anaerobic digestion (AD), a potentially sustainable process for generating biogas from the biological decomposition of organic byproducts from biodiesel production. This study examined the impact of acclimatization rate on biogas production and conversion efficiency in laboratory digesters using inocula from a wastewater treatment plant digester and from an agro‐industrial waste digester. The results showed that co‐digestion of crude glycerol and biodiesel wastewater at high organic loading rates, up to 6.8 g chemical oxygen demand (COD) L−1 day−1, is possible without the addition of other substrates or pretreatment. Higher organic loading rates were achieved in the digesters using inocula from the agro‐industrial waste digester than in the digesters using the wastewater treatment plant digester, indicating that an inoculum with similar physical characteristics may be most appropriate for the AD of biodiesel waste. Of the two acclimatization rates studied, the slower rate improved the cumulative biogas production for both inocula. Both inocula also exhibited higher maximum daily efficiencies with a slower rate of acclimatization, up to a maximum average daily biogas yield of 621 mL biogas g−1 COD added. This implied that the rate of acclimatization can impact the ability of the digester to adapt efficiently to a new substrate.

Biogas Production from Kitchen Wastes by Anaerobic Digestion

Abstract: This paper aimed to study the biogas production from kitchen wastes mixed with cattle dung. A vertical bench scale biogas digesters were constructed. Each three of them were replicates and their average biogas yields were recorded. The mixing ratios were 75%, 50% and 25% of kitchen wastes to the total slurry. The pH, alkalinity and temperature were measured during the experiments. It was found that digestion process was sensitive to temperature changes. Also, the pH and alkalinity were increasing over time. Moreover, it was found that the mixing ratio of 75% kitchen wastes to the total slurry enhanced the biogas production by 17.3% in comparison to the ratio of 25% kitchen wastes.

Research on Biogas Yield from Macroalgae with Inoculants at Different Organic Loading Rates in a Three-Stage Bioreactor.

Macroalgae can be a viable alternative to replace fossil fuels that have a negative impact on the environment. By mixing macroalgae with other substrates, higher quality biogas can be obtained. Such biogas is considered one of the most promising solutions for reducing climate change. In the work, new studies were conducted, during which biogas yield was investigated in a three-stage bioreactor (TSB) during the anaerobic digestion of Cladophora glomerata macroalgae with inoculants from cattle manure and sewage sludge at different organic loading rates (OLR). By choosing the optimal OLR in this way, the goal was to increase the energy potential of biomass. The research was performed at OLRs of 2.87, 4.06, and 8.13 Kg VS/m3 d. After conducting research, the highest biogas yield was determined when OLR was 2.87 Kg VS/m3 d. With this OLR, the average biogas yield was 439.0 ± 4.0 L/Kg VSadded, and the methane yield was 306.5 ± 9.2 L CH4/Kg VSadded. After increasing the OLR to 4.06 and 8.13 Kg VS/m3 d, the yield of biogas and methane decreased by 1.55 times. The higher yield was due to better decomposition of elements C, N, H, and S during the fermentation process when OLR was 2.87 Kg VS/m3 d. At different OLRs, the methane concentration remained high and varied from 68% to 80%. The highest biomass energy potential with a value of 3.05 kWh/Kg VSadded was determined when the OLR was 2.87 Kg VS/m3 d. This biomass energy potential was determined by the high yield of biogas and methane in TSB.

Onsite anaerobic treatment of tomato plant waste as a renewable source of energy and biofertilizer under desert conditions

Crop residues, such as toxic tomato plant wastes, often cause environmental and economic burdens. Anaerobic digestion of these residues, which contain hardly biodegradable lignocellulosic content and low C/N (~10), was not thoroughly studied or practiced. This study investigated the impacts of temperature and particle size on anaerobic degradation performance of tomato plant waste in both laboratory and field scales (the latter was studied for one year under desert conditions). The highest batch degradation rate was observed for the smallest particles <0.15 mm and highest temperature (35 °C). In the field reactor, 89 % of the organic carbon was recovered as biogas containing 62 % CH4. The average biogas yield was 0.55 m3/kg-VS. The digestor supernatant contained N and P of 657 mg/L and 76 mg/L, respectively, mostly as ammonia and soluble reactive-P. Onsite anaerobic digestion of tomato plant waste can efficiently reduce pollution burden, produce biogas, and recover nutrients under desert conditions.

Anaerobic digestion of abattoir wastes for biogas production: optimization via performance evaluation comparison

Anaerobic digestion of abattoir wastes under mesophilic conditions was carried out to investigate how different modeling tools affect biogas yield in order to be subsequently used for process optimization. Response Surface Methodology (RSM) and Artificial Neural Networks (ANNs) were employed to optimize the process, and to assess the individual and interactive effect of incubation time, temperature, and pH on biogas yield. The digester used in this study produced an average biogas yield of 0.00103 m3/kg VS daily from cow-dung. Gas chromatographic analysis of the produced biogas showed the methane content to be 66.8%. The conditions for optimum biogas yield as predicted by RSM were incubation time of 28.98 days, temperature and pH of 30.16°C, and 7.43, respectively. For ANNs, the incubation time, temperature, and pH for optimum biogas yield were 26.76 days, 30.94°C, and 7.27, respectively. With these conditions, biogas yield by RSM was Olayomi Abiodun Falowo m3/kg VS while that of ANNs was Olayomi Abiodun Falowo m3/kg VS. Model validation by experimental tests showed that ANN is better in terms of prediction and accuracy than the RSM, though, the two techniques complemented each other in interpreting the interactive effects of the input variables on the biogas production. Anaerobic digestion of abattoir wastes for biogas production: optimization via performance evaluation comparisonAll authorsOludare Johnson Odejobi, Ebenezer Leke Odekanle, Ayorinde Bamimore, Olayomi Abiodun Falowo & Funso Akeredoluhttps://doi.org/10.1080/23311916.2022.2122150Published online:20 September 2022Display full size

Assessment of biogas production and bacterial load from manure of layer chicken fed with two different types of feed

Assessment of biogas production and bacterial load from manure of layer chicken fed with two different types of feed

Application fuzzy DEMATEL methodology to investigate some technical parameters of biochemical methane potential (BMP) test produced vegetable waste anaerobic biogas.

As the transition to renewable energy systems is accelerating, anaerobic digestion, which is one of the methods of energy recovery from organic substrates, continues to be studied with great interest by scientists. Anaerobic digestion research and applications are mostly carried out with biochemical methane potential (BMP) tests to decide the methane potency of sewage sludge, energy crops, and organic wastes. Unlike long and costly continually reactor experiments, actually, BMP tests are cumulative and can be performed with a relatively low investment of materials, technical labor, and also time. For the BMP to give accurate results, the effect of all the tools and technical parameters used in the implementation of the BMP should be well understood. In such situations, it is very useful to apply fuzzy logic methods in multi-criteria decision-making stages when more than one parameter changes at the same time. Therefore, in this study, fifteen parameters were determined and analyzed with the fuzzy DEMATEL (decision-making trial and evaluation laboratory) method to understand the cause-effect mechanism of the technical parameters of BMP. As a result of these analyses, it was seen that the material of the reactor (ri-cj value of 0.55), the particle size (ri-cj value of 0.43), the effect of mixing (ri-cj value of 0.32), and the amount of the total solids (TSA) (ri-cj value of 0.25) had a high effect in the causal sense. It was observed that the first-order parameter (material of reactor) was 27% stronger than the second-order (the particle size) parameter in terms of causality. Likewise, the second-order parameter is 34% stronger than the third-order parameter (the effect of mixing) in terms of cause effect. In addition, it was understood that the most effective parameters in the mechanism of effect were pH (ri + cj value of 3.41), C/N ratio (ri + cj value of 3.26), and temperature (ri + cj value of 3.07), respectively. Besides, high methane yield is seen in mesophilic conditions. The average cumulative biogas yield of the reactor is 282.1 NmL/g VS. The highest percentage of methane formed in the biogas occurred on the 21st day. Briefly, this study is important to provide a facilitating way for researchers working on BMP to understand the cause-effect mechanism of system technical requirements.

Thermophilic anaerobic membrane bioreactor for pulp and paper primary sludge treatment: Effect of solids retention time on the biological performance

Lignocellulosic biomass is a promising renewable feedstock for the production of bioenergy and platform chemicals; however, its use would not be economically viable without adopting effective transformation technologies. In this work, long-term anaerobic treatment (370 days) of pulp and paper primary sludge (PS) was performed by a thermophilic anaerobic membrane bioreactor (AnMBR) for the first time to investigate the effect of various solid retention times (SRTs) on biogas production and solids reduction ratios. The tested STRs (32–55 days) have shown varying biogas productivity, and it can be concluded that the longer the SRT, the higher is the biogas yield. At the optimum solids retention time of 55 d, an organic loading rate of 2.15 ± 0.10 kg-TSS/L.d, and hydraulic retention time of 5 d, average biogas yield of 106.4 ± 8.5 m3 biogas/tonne TSS added (approximately 72.7 m3 CH4/t VSadded) was achieved with an average methane content of 56 ± 4% and the solids reduction ratio ranged between 47% and 54.9%. Besides biogas yield, the quality of the permeates, solids reduction, and digestates characteristic/dewaterability changed by changing the SRT. The mixed liquor suspended solids concentrations and solids reduction increased with increasing SRT, while the effluent COD concentration and sludge dewaterability decreased. The Fourier Transform Infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) findings exhibited that the digestate contains more lignin and cellulose than the other substances, while the nitrogen and carbon concentration decreased with increasing SRT.

Оценка энергетического потенциала свалочного газа

The purpose of the work was to compare the potential of biogas generation at MSW landfills, determined by the most commonly used methods, and to determine the energy potential of landfill gas in the country's energy system, provided that it is fully used to generate electricity. Based on the equation of the chemical reaction of biogas formation, equations are proposed for calculating the specific yield of biogas components from 1 kg of waste and their shares in volume percent. Calculations according to the proposed formulas showed that the yield of biogas from a ton of waste for Russian MSW, the composition of which is accepted from different sources, varies significantly, from 312 to 433 m3. The composition of biogas changes little, and the theoretical content of methane in it ranges from 53% to 57%. The yield and composition of biogas was estimated using the Tabasaran-Rettenberger equation, LandGEM, DOD (IPCC), CLEEN models and Russian regulatory methods. The average total biogas yield was 195 m3/t waste with a variation coefficient of 38%, the average methane yield was 95 m3/t waste with a variation coefficient of 46%, and the average calorific value of biogas, related to 1 ton of waste from which it was formed, was 3 400 MJ/t of waste with a coefficient of variation of 44%. With a conversion efficiency of 39%, landfill gas from 1 ton of waste can generate 368 kWh of electricity. The total volume of municipal solid waste in Russia, subject to the full collection and use of biogas, makes it possible to generate 22.1 billion kWh of electricity, which is about 2% of the total energy consumption in the country. For a number of countries, the energy potential of landfill gas ranged from 0.05% (China) to 4.5% (Spain). Thus, landfill gas is a significant source of electricity in the overall energy balance.

A combined anaerobic digestion system for energetic brewery spent grain application in co-digestion with a sewage sludge.

In the present study, a combined technology for energetic brewery spent grain (BSG) use in co-digestion with sewage sludge (SS) was presented. A holistic approach that includes the impact of co-substrates and their carriers on the anaerobic digestion (AD) process, and the energetic aspects, was involved. Prior to AD, BSG was pretreated involving the hydrodynamic cavitation (HC); two different carriers were applied: MPW (municipal pre-settled wastewater) and mature landfill leachate (MLL). An orifice plate with a conical concentric hole of 3/10mm (inlet/outlet diameter) was applied as cavitation device. The initial pressure was 7bar and the number of recirculation passes through the cavitation zone was 30. The AD experiments were performed in semi-flow reactors, under mesophilic conditions at HRT of 20 and 21 d. In both co-digestion series, the constant co-substrate dose of 6% v/v was adopted. In the presence of cavitated BSG and MPW, a significant increase in biogas/methane production was provided as compared to SS mono-digestion, with the related improvement in kinetic constant by 3.5%. The average biogas yield was 0.48±0.03m3 kg-1 VS added, while in the control run 0.41±0.03m3 kg-1 VS added. Using cavitated BSG and MLL, such a beneficial effect was not observed. In both co-digestion series, slightly lower VS removal (as for the control) and stable process performance occurred. Moreover, the improved energy balance was provided. Due to the technological aspects, only co-digestion of cavitated BSG and MPW with SS is recommended for implementation into a full-scale.

In-situ microaeration of anaerobic digester treating buffalo manure for enhanced biogas yield

Microaeration pretreatment can enhance lignin degradation of lignocellulosic biomass and subsequent biogas production during anaerobic digestion (AD). However, the reported values of effective aeration dose, aeration contact time, and aeration frequency differ with substrates riddling the selection of a suitable combination. A serial approach was adopted to identify the suitable combination for the degradation of lignin in the buffalo manure and improvement of the biogas production. Single and Multiple injections of three aeration doses of 5.3, 7.3, and 9.3 mL O2/g VS were tested at 5 different contact times– 6, 12, 24, 36, and 47 h. Results for acid-soluble lignin (% ASL) indicated the suitability of 12 h contact time with a single injection of 7.3 mL O2/g VS for lignin degradation and biogas enhancement for AD of buffalo manure. This combination achieved 78% higher ASL content and a 32% increase in average daily biogas yield than the control. Finally, the kinetic parameters obtained through the modified Gompertz model accurately predicted the biogas potential of the process (R2 > 0.93). The results of this study can be referenced for improving the yield of similar biomass to bioenergy initiatives by employing a low-cost pretreatment strategy of in-situ microaeration.

Recycling anaerobic digestate enhances the co-digestion potential of agro-industrial residues: Influence of different digestates as sources of microbial inoculum

Anaerobic codigestion (AcD) of agroindustrial residues was investigated. Granular sludge from bench-scale bioreactors digesting different manure were acclimated and recycled as microbial seed sludge to demonstrate inoculum-type influence on digestion performance. The biomethane potential (BMP) assay was operated for 30 days at 40 ± 2 °C in batch-type laboratory-scale reactors (100 mL). In inoculum amended reactors, codigestion showed significant, yet distinctive, biomethanation than monodigestion with a 5-fold increase (p < 0.05) in average biogas (248.3 ± 5.30 mL gVS-1) and CH4 yield (207.5 ± 4.15 mL gVS-1). The pH, soluble chemical oxygen demand (sCOD) and volatile fatty acids (VFAs) concentrations were within limits for stable AcD process with elevated total solids (TS) and volatile solids (VS) removal efficiencies. This study reinforces advancements in the recycling of digestate in biodigesters and suggests the appropriate selection of inoculum, preferably cow manure, to essentially boost methane production from these wastes.

Effect of Semi-Continuous Anaerobic Digestion on the Substrate Solubilisation of Lignin-Rich Steam-Exploded Ludwigia grandiflora

In this study, semi-continuous anaerobic digestion of lignin-rich steam-exploded Ludwigia grandiflora (Lignin = 25.22% ± 4.6% total solids) was performed to understand better the effect of steam explosion on the substrate solubilisation and inhibitors formation during the process. Steam explosion pretreatment was performed at 180 °C for 30 min at a severity factor of 3.8 to enhance the biogas yield of the lignocellulosic biomass. The semi-continuous anaerobic digestion was performed in a continuously stirred tank reactor for 98 days at an initial hydraulic retention time of 30 days and an organic loading rate of 0.9 g-VS L−1 day−1. The performed steam explosion pretreatment caused biomass solubilisation, resulting in enhanced biogas production during the process. During the anaerobic digestion process, the average biogas yield was 265 mL g-VS−1, and the pH throughout the operation was in the optimum range of 6.5–8.2. Due to fluctuations in the biogas yield, the hydraulic retention time and organic loading rate were changed on day 42 (50 days and 0.5 g-VS L−1 day−1) and on day 49 (40 days and 0.7 g-VS L−1 day−1), and 1 M of NaOH was added to the liquid fraction of the steam-exploded L. grandiflora during the latter part of the operation to maintain the stability in the reactor. Therefore, the steam explosion pretreatment helped in the degradation of L. grandiflora by breaking the lignocellulose structure. In addition, changes in the operating conditions of the anaerobic digestion led to an increase in the biogas production towards the end of the process, leading to the stability in the CSTR.

Study on interchangeability of seed based feedstocks for biogas production in multi-feeding mode

Biogas is an excellent renewable fuel providing gas for clean energy applications and fertilizers for organic farming. In the present study, seeds from four tree species of Acacia nilotica , Albizia lebbeck , Prosopis juliflora , and Leucaena leucocephala have been utilized for biogas production as alternative feedstocks. They have been investigated in a mixed-feeding mode in a single digester to tackle the feedstock availability and seasonality challenges. The investigations were conducted in a 300 ​L anaerobic digester for 120 days under daily feeding mode. The average specific biogas yield and specific methane yield was found to be 0.425 ​m 3 /kg of volatile solids and 0.228 ​m 3 /kg of volatile solids, respectively. The average volumetric methane content in biogas was 54.7%. This paper presents a unique study on anaerobic digestion of selected seeds in a mixed-feeding mode to provide broad opportunities for their efficient and sustainable utilization. • Interchangeability of tree species seeds explored for 120 days in the mixed-feeding mode for biogas production. • Anaerobic digestion parameters for the utilization of these seeds are investigated in detail. • An amount of 3.0–3.5 ​kg of seeds is required to produce one cubic metre of biogas. • Specific biogas yield of 0.425 ​m 3 /kg VS with methane of 54.7% and TVSMRE as 46.0% were found.

Utilization of de-oiled rice bran as a feedstock for renewable biomethane production

This research aims to study biogas production using de-oiled rice bran as a renewable source of energy. The measured volatile solids content of de-oiled rice bran revealed its significant potential for biogas production. In the first phase of the experimentation, the hydrolytic behavior was studied to determine the optimal total solids (TS) concentration of the substrate, required for maintaining the favourable environmental condition for efficient anaerobic digestion. Out of four TS concentration taken (5%, 7.5%, 10%, and 15%), the most significant result was found for the substrate maintained at 5% TS. As per the finding of the hydrolysis experiment, further investigation was conducted using 60 L plastic made digester under continuous feed mode and at mesophilic temperature condition in three replicates. The results revealed average specific biogas yield of 0.470 L/g TS and 0.547 L/g VS with an average specific methane production yield of 0.232 L/g TS and 0.270 L/g VS. The most encouraging finding of this study was the high material conversion efficiency (maximum 67.54%), which makes de-oiled rice bran more potential feedstock than other conventional biomass. The novelty of the present study lies in the development of efficient ‘secondary inoculum’ through a continuous system. The inoculum developed through continuous mode gives a higher degree of control than batch mode. Along with the microbial growth, the secondary metabolites produced during the anaerobic digestion process, (which plays a crucial role in process continuation) can also be sustained simultaneously in the developed continuous system.

Bioaugmentation of anaerobic fungus Orpinomyces joyonii boosts sustainable biomethanation of rice straw without pretreatment

Rice straw is an abundant, renewable and energy rich agricultural biomass. Energy recovery in the form of biomethane from rice straw can be a sustainable process. However, one of the drawbacks associated with this process is the recalcitrant nature of rice straw which necessitates energy intensive, expensive and polluting thermochemical pretreatment of the substrate. Fiber digesting anaerobic fungi have the ability to degrade the plant biomass. Hence, the present investigation was undertaken to enhance the biodegradation and subsequently the biomethanation of rice straw by supplementing the startup inoculum with anaerobic fiber digesting fungus, Orpinomyces joyonii. The average daily biogas and methane yield increased by 25.04% and 38.41% respectively over control reactor when the startup inoculum was supplemented with O. joyonii in the test reactor. The reduction in volatile solids, cellulose and hemicellulose components of rice straw during biomethanation process was observed to be 68%, 82%, and 97%, respectively. Orpinomyces joyonii supplementation of startup inoculum enhanced the biodegradation of lignocellulosic component and biomethane yield by anaerobic digestion of rice straw without thermochemical pretreatment.

Improved Mixing System for Anaerobic Sequencing Batch Reactors

HighlightsA novel single-jet mixing system was designed for ASBR digesters.Mixing energy was reduced to the point that solids were only partially suspended in the reactor vessel.The partial mixing system increased effluent quality as measured by suspended solids content.The partial mixing system increased solids retention, allowing hydraulic retention time (HRT) to be reduced to at least 7.5 days while maintaining solids retention time (SRT) above 100 days.The partial mixing system did not reduce biogas production rate nor biogas yield.Abstract. An anaerobic sequencing batch reactor (ASBR) is a high-rate anaerobic digestion system ideally suited for the treatment of liquids with high organic strength and low solids content. Biota are retained in an ASBR by settling solids prior to decanting effluent from the top of the reactor. Solids retention time (SRT) can be managed separately from hydraulic retention time (HRT) in an ASBR. One problem encountered with ASBRs is poor solids retention due to inefficient solids settling. A novel mixing system in which solids are only partially mixed in the reactor prior to decanting was investigated in a series of three experiments. A battery of six 30 L ASBR reactors were fed a mixture of dilute swine manure (0.30% TS, 0.20% VS) and raw glycerol. In a side-by-side comparison of two reactors operated at an organic loading rate (OLR) of 0.30 g COD L-1 d-1 with 15-day HRT and two feeding cycles per day, the partially mixed reactor outperformed the fully mixed reactor as measured by effluent quality (130 vs. 350 mg VSS L-1), SRT (354 vs. 52 days), and VS removal efficiency (88% vs. 79%). In a replicated study of five reactors operated at 0.31 g COD L-1 d-1 OLR, 15-day HRT, and two feeding cycles per day before and after switching from full to partial mixing, the partially mixed reactors showed significantly (p = 0.05) better performance as measured by effluent quality (100 vs. 382 mg VSS L-1), SRT (760 vs. 72 days), and VS removal efficiency (85% vs. 71%). Biogas production did not significantly change with the change from full to partial mixing in the five replicated reactors, i.e., average biogas yield was 0.81 and 0.77 L biogas g-1 COD with partial and full mixing, respectively. Effluent quality, SRT, VS removal efficiency, and biogas yield did not significantly change when the OLR was increased from 0.31 to 0.62 g COD L-1 d-1 and HRT was reduced from 15 to 7.5 days in a replicated study of six partially mixed reactors. A mass balance of COD across the six partially mixed reactors showed that endogenous respiration of retained biomass accounted for approximately 50% of the biogas produced by an ASBR with SRT exceeding 400 days. Keywords: Anaerobic digestion, Anaerobic sequencing batch reactor, ASBR, Biogas, Glycerol, Hydraulic retention time, Mixing, Operation, Performance, Solids retention time, Swine manure.