Batch Anaerobic Digestion Research Articles

Use of Inoculum, Water and Percolate as Strategy to Avoid Inhibition on Dry-Batch Anaerobic Digestion of Organic Fraction of Municipal Solid Waste

The impact of inoculum to substrate ratio (I:S) and the addition of water and percolate on stopping inhibition in dry batch anaerobic digestion of organic fraction municipal solid waste (OFMSW) was investigated. In particular, ratios of I:S from 1:2 to 1:16 and total solid contents from 40 to 25% with water and percolate addition were analysed. Tested I:S did not avoid acidification of the anaerobic digesters (ADs), and the highest biogas and methane production (16.2 and 1.7 L/kg VSadded, respectively) was achieved with the 1:4 ratio. Water addition was also insufficient to avoid acidification, and while biogas increased as TS decreased, 40.9 L/kg VSadded for 25% TS, methane yield remained low at 1.2 L/kg VSadded due to the inhibition of methanogenic archaea. Percolate addition proved a suitable strategy to increase pH buffering, with an increased methane production of 199.4 L/kg VSadded at similar TS ranges (27%). Impact on kinetics of methane formation was assessed by kinetic modelling with logistic model identified as the better fit for most of the ADs. Shorter lag phases were observed as TS were reduced, regardless of the acidification, as mass transfer limitations were reduced at the beginning of the batch, but an increase was observed when percolate was used instead of water. Increases of the maximum methane rate (Rmax) was also achieved with TS reduction, but only when acidification was avoided. This study has highlighted the need to profile percolate composition during batch digestion in order to balance recirculation of nutrients, microbial communities and toxic compounds.Graphic

LiqTech International Inc, Denmark

The role of extracellular polymeric substances (EPS) in the minimization of the excess sludge yield underlying hybrid activated sludge treatment (as MANODOX system) for tannery wastewater was experimentally elucidated. The operational strategies designed for the MANODOX system configuration and a parallel-run conventional aerobic activated sludge (p-CAS) treatment were tested throughout the study period of 320 days. In comparison with the p-CAS system, MANODOX experimentation received prominently lowered sludge yield (averaged around 0.36 gVSS/gCOD). The experimental observation further affirmed that the sludge generation found influenced by the variation in the sludge characteristics like protein to polysaccharides ratio (ranged around 0.62–0.73), food to microorganism ratio (0.41 ± 0.04), dissolved oxygen (2.23 ± 0.30 mg/L) and bioflocculation ability (71.8–73.8%). Here, MANODOX implementation exhibited three times lowered EPS accumulation and around 70% less sludge generation compared with the p-CAS system. However, the ascertained was positively attributed to the purposeful nourishment of cell-lysis in the MANODOX system. Importantly, the strict maintenance of desired sludge retention time of 23–26 days imposed a profound effect on the aforementioned floc characteristics and EPS degradation. Furthermore, the Fourier transform infrared spectroscopy and specific ultra-violet absorbance analysis reveals, the facultative microbiota had a prominent influence on organic functional groups that presumed to be originated from the disintegration of EPS in the sludge. The corroborated has further been supported by thermogravimetric analysis and batch anaerobic and aerobic digestion test of the volatile sludge pool performed at end of the mainstream operation.

Hydrolysate recycling improves economic feasibility of alkaline pretreatment for bioenergy production

More sustainable processes capable to minimize the demand for chemical inputs and the generation of toxic wastes are essential to scale up the pretreatment strategies applied to lignocellulosic biomass for bioenergy production. This study aimed to evaluate the reuse of the black liquor (hydrolysate) generated after alkaline pretreatment as a sustainable and cheaper strategy to increase biodegradability of grass clippings (GC) and enhance process economic feasibility. Batch anaerobic digestion experiments were carried out at mesophilic temperature (37 °C) using KOH and NaOH solutions at a concentration of 5% (w/v). The methane yield of the untreated substrate was 227 LN CH4 kg−1 VS. Methane yields obtained from pretreated grass clippings using KOH and NaOH at 5% were increased to 30.5% and 34.5% and the hydrolysate generated after the pretreatments showed statistical (p < 0.05) good capacity to be reused up to five sequential batches (fours reuse cycles). The conversion of biomethane to electricity with NaOH hydrolysate recycling was economically feasible, generating a profit of 0.11 USD kg-1VS while the reuse of KOH hydrolysate resulted in a loss −0.66 USD kg-1VS due to the different acquisition costs of chemical reagents. Encouraging hydrolyzate recycling after alkaline pretreatment of lignocellulosic biowaste through the creation of a zero discharge system cooperate with the circular economy of wastes. In addition, this sustainable strategy proved to promote a positive economic scenario when less expensive chemical reagents such as NaOH is applied.

Multicomponent nanoparticles as means to improve anaerobic digestion performance

Sufficient quantity of trace metals is essential for a well performing anaerobic digestion (AD) process. Among the essential trace elements in active sites of multiple important enzymes for AD are iron and nickel ions. In the present study, iron and nickel in the form of Fe2O3 and NiO were coated on TiO2 nanoparticles to be used in batch and continuous operation mode. The effect of TiO2, Fe2O3–TiO2, and NiO–TiO2 nanoparticles on each step of AD process was assessed utilizing simple substrates (i.e. cellulose, glucose, acetic acid, and mixture of H2–CO2) as well as complex ones (i.e. municipal biopulp). The hydrolysis rate of cellulose substrate increased with higher dosages of the coated TiO2 with both metals. For instance, the hydrolysis rate was increased up to 54% at Fe2O3–TiO2 and at a concentration of 23.5 mg/L for NiO–TiO2 it was increased up to 58%, while higher dosage suppressed the hydrolytic activity. Experimental results revealed that low dosages of NiO–TiO2 increased the accumulated methane production up to 24% probably by increasing the enzymatic activity of acetoclastic methanogenesis. NiO–TiO2 showed positive effect on batch and continuous AD of biopulp and improved methane yield up to 8%.

Batch optimization of biogas yield from pasteurized slaughterhouse by-products incorporating residues from corn sieving

Batch anaerobic digestion of pasteurized pig slaughterhouse waste (SW) and corn sieving waste (CSW), and anaerobic co-digestion of CSW/SW were studied at lab scale employing several carbon to nitrogen ratio (C/N) and total solids (TS) content. The mixtures with highest biogas yield and suitable process inhibition parameter values were used to scale up to pilot scale. The results showed that SW and CSW co-digestion improved biogas yield in comparison with that obtained from mono-digestion of both substrates. Thus, it is possible to ensure that the CSW is a proper substrate to balance C/N and improve biogas yield. Moreover, this study reveals that the best biogas yield for each C/N mixture is achieved using the lowest TS content. Also, the SW/CSW mixture with C/N 15 and 5% TS achieved the highest biogas yield and the best inhibition parameters values. The pilot scale assay demonstrates that biogas yield, methane yield and Organic Matter Removal for C/N 15 mixture were 41%, 25%, and 24% higher than those using C/N 20, respectively, and the H2, CO2 gasses composition presented variations. However, the methane content was similar for both C/N 15 and C/N 20 at pilot scale.

Comparative Assessment of Biogas Production Potential of the Most Abundant Agro-residues in Turkey

Recent energy policies promote energy generations from green resources to meet sustainability criteria. Since Turkey is one of the largest agricultural producers globally, it has great biogas production potential. This study aims to evaluate the biomethane yields of the most abundant agro-residues in Turkey and to assess their potentials for contribution to biogas production. Within this scope, sunflower heads, tea residues, cotton stalks, and crop residues; wheat, rye, and triticale straws were collected from different regions of Turkey. Anaerobic batch digesters were conducted to investigate the biomethane production of the selected feedstock and operated for 30 days at 37°C. Each setup was conducted in triplicates and methane productions were monitored online. The main methane production route of the inoculum was determined as acetoclastic methanogenesis while Cloacimonetes, Firmicutes, and Bacteroidetes composed the core bacterial phyla. The greatest methane yield was observed in the digesters operated with the wheat straw followed (164 NmL/gVSinfluent) by triticale straw and sunflower head. The lowest yields were calculated for the digesters fed with the cotton stalks (71 NmL/gVSinfluent). To increase the biomethane potential yields in the anaerobic digesters operated with agro-residues and to make the anaerobic digesters more feasible, operational conditions should be optimized and physico-chemical and biological pre-treatment techniques and/or bioaugmentation applications should be integrated into the systems.

Shift in methanogenic community in protein degradation using different inocula

Anaerobic digestion (AD) of protein-rich wastes is problematic due to production of ammonia and hydrogen sulfide. In this work, eight inocula were used in batch AD of solutions of gelatin and gluten at 3 g COD substrate/1g VSS inoculum. AD plants from which inocula originated were treating food waste or food wastewater, wastewater sludge, or a combination of them. Inocula were evaluated by fitting methane production data using the modified Gompertz model. Sequencing of 16 s rRNA of microorganisms showed that Methanoculleus was dominant in inocula from plants that were treating food waste, and Methanosaeta was dominant in the others. The maximum methane production rate varied by a factor of three for each substrate: 2.734–7.438 mLCH4 gCOD-1 d-1 for gelatin, and 1.950 to 5.532 mLCH4 gCOD–1 d-1 for gluten. This study demonstrates that inoculum must be chosen appropriately when treating proteinaceous waste by AD.

Biomethane potential from herbivorous animal’s manures: Cuban case study

Anaerobic digestion technology is a feasible alternative for wastes environmental treatment, nutrients recovery (as biofertilizer) and biomethane production. In Cuba, several wastes energy potentials have been evaluated, however, other biomass like horse manure (HM), rabbit manure (RM), and goat manure (GM) has been little studied. This study aims to determine the biochemical methane potential contained in herbivorous animal manures (horse, rabbit and goat) for energy purposes in Cuban context. Anaerobic digestion batch assay in 0.5 L reactors, using a mixture of pig and cow manure anaerobic sludge as inoculum, was performed under mesophilic conditions (35 ± 2 °C) during 40 days. The methane yield potentials of 245, 326 and 112 L CH4 kg/VS were obtained for horse, rabbit and goat manures, respectively, influenced by the difference in their digestive system to digest the grass feedstock. The highest rabbit manure methane potential results attractive for domestic digesters, in which experience is very limited. In addition, due to the availability of horse manure in many municipalities of Cuba, the generation of electricity from this manure (128 GWh/year) could replace 1.4% of the electricity consumed by households, making it promising to further exploitation considering the expected 2030 energetic matrix changes using renewable energy.

Experimental characterization and assessment of bio- and thermo-chemical energy potential of dromedary manure

The aim of this study was to determine the bio- and thermo-chemical characteristics of dromedary (Camelus dromedaruis) manure to be used for renewable energy generation and greenhouse gas (GHG) mitigation. Lactating and pregnant dromedary manure samples were collected from a dromedary milk production farm and were tested. A comprehensive experimental analysis was conducted for the sampled manure to determine key parameters, including organic and nutrients content, ions, heavy metals, in addition to X-ray diffraction and fluorescence characterization. The bio-methane potential was measured in batch anaerobic digestion (AD) assays, while the energy content was determined through a bomb calorimeter. The experimental results showed that the bio-methane production ranged between 129 and 160 mL of CH4 per gram of volatile solids (VS) of dromedary manure. On the other hand, the measured calorific values of dromedary manure ranged between 12.18 and 13.60 MJ kg−1. A feasibility study was carried out for bio- and thermo-chemical waste-to-energy systems for dromedary manure management. The assessment showed that an AD-based manure management system could potentially mitigate GHG emissions; with a unit emission of 0.52 kg kWh−1 of CO2 eq compared to 0.61–0.91 kg kWh−1 of CO2 eq from conventional fossil fuel combustion. Results showed that, compared to AD, incineration would be more viable for dromedary manure management, in terms of economic revenue and energy recovery.

Evaluation of Methane Production From Dairy Cow Manure and Vegetable Waste

Dairy cow manure has high buffering capacity hence a substrate for anaerobic digestion, however the process is not optimised in mono-digestion system due to limited substrate. The aim of the study was to assess the effect of co-digesting animal waste and vegetable waste on methane production. Two systems were applied- batch and continuous anaerobic digestion system to determine effect on methane yield. The experiments were conducted with treatments as: manure alone (M), composite of manure with cabbage (MC), manure with potatoes (MP), manure with cabbage and potatoes (MCP), faecal alone (F), faecal with cabbage (FC), faecal with potatoes (FP) and faecal with cabbage and potatoes (FCP). Rectal grab samples were collected prior to incubation and manure was collected from the pens. All treatments were in replicates. Composite of manure or faecal with cabbage and potatoes produced the highest biogas (FCP: 32.1 mL/g DM, MCP: 29.5 mL/g DM) and methane (FCP: 3.13 mL/g DM, MCP: 2.36 mL/g DM) compared to manure alone or faecal alone (F: 27.0 biogas mL/g DM, M: 26.6 biogas mL/g DM) (F: 1.36 methane mL/g DM, M: 1.18 methane mL/g DM). Co-digesting dairy excreta with cabbage as only vegetable substrate affected anaerobic digestion (FC: 24.8 mL/g DM, MC: 24.9 mL/g DM), since it was the lowest in biogas production compared to all treatments. The anaerobic digestion system had an effect in methane production since continuous anaerobic digestion system produced the highest methane compared to batch anaerobic digestion system in all treatments. The results obtained in this study suggest that composite of manure with both cabbage and potatoes results in the highest biogas and methane production.

Simultaneous phosphorus recovery, sulfide removal, and biogas production improvement in electrochemically assisted anaerobic digestion of dairy manure

Anaerobic digestion (AD) produces renewable biogas from organic-rich waste streams, but the resultant digestate has to be subject to further nutrient recovery processes for better valorization. In this study, an electrochemical treatment unit using stainless steel mesh electrodes was integrated with an up-flow anaerobic sludge blanket (UASB) reactor to treat liquid dairy manure for simultaneous phosphorus (P) recovery, methane production improvement, and hydrogen sulfide (H2S) removal. The 36-d batch AD trial showed that a large portion of total P and reactive P were removed from the liquid dairy manure and were recovered mainly on the cathode deposits in the form of phosphate-bearing minerals. In the continuous USAB trial with an applied voltage of 1.0 V, 65.1% of the total P in the feeding manure was removed, of which 96.7% was achieved by sludge bed accumulation and 3.3% in the cathode deposit. Increases in both biogas production rate (13.0%) and methane yield (10.9%) were observed in the electrochemically assisted UASB system as compared to the one without electrochemical treatment. The electrochemical assistance helped decrease the H2S concentration in biogas by 20.8% at an applied voltage of 0.5 V and by 50.3% at 1.0 V. This electrochemically assisted UASB system can produce more biogas with less H2S content and recover P-enriched sludge in the sludge bed and the cathode deposit.

Sugarcane Bagasse as a Co-Substrate with Oil-Refinery Biological Sludge for Biogas Production Using Batch Mesophilic Anaerobic Co-Digestion Technology: Effect of Carbon/Nitrogen Ratio

Man-made organic waste leads to the rapid proliferation of pollution around the globe. Effective bio-waste management can help to reduce the adverse effects of organic waste while contributing to the circular economy at the same time. The toxic oily-biological sludge generated from oil refineries’ wastewater treatment plants is a potential source for biogas energy recovery via anaerobic digestion. However, the oily-biological sludge’s carbon/nitrogen (C/N) ratio is lower than the ideal 20–30 ratio required by anaerobic digestion technology for biogas production. Sugarcane bagasse can be digested as a high C/N co-substrate while the oily-biological sludge acts as a substrate and inoculum to improve biogas production. In this study, the best C/N with co-substrate volatile solids (VS)/inoculum VS ratios for the co-digestion process of mixtures were determined empirically through batch experiments at temperatures of 35–37 °C, pH (6–8) and 60 rpm mixing. The raw materials were pre-treated mechanically and thermo-chemically to further enhance the digestibility. The best condition for the sugarcane bagasse delignification process was 1% (w/v) sodium hydroxide, 1:10 solid-liquid ratio, at 100 °C, and 150 rpm for 1 h. The results from a 33-day batch anaerobic digestion experiment indicate that the production of biogas and methane yield were concurrent with the increasing C/N and co-substrate VS/inoculum VS ratios. The total biogas yields from C/N 20.0 with co-substrate VS/inoculum VS 0.06 and C/N 30.0 with co-substrate VS/inoculum VS 0.18 ratios were 2777.0 and 9268.0 mL, respectively, including a methane yield of 980.0 and 3009.3 mL, respectively. The biogas and methane yield from C/N 30.0 were higher than the biogas and methane yields from C/N 20.0 by 70.04 and 67.44%, respectively. The highest biogas and methane yields corresponded with the highest C/N with co-substrate VS/inoculum VS ratios (30.0 and 0.18), being 200.6 mL/g VSremoved and 65.1 mL CH4/g VSremoved, respectively.

Granular activated carbon supplementation enhances anaerobic digestion of lipid-rich wastewaters

This study investigated the application of a conductive material, granular activated carbon (GAC), as an approach to improve anaerobic lipid degradation and methane production. Anaerobic biomethane potential (BMP) assays were performed in 120 ml batch anaerobic digestion (AD) vials using 5 gVS/L anaerobic sludge as inoculum. Different BMP assays were carried out testing the impact of increasing GAC concentrations (0–33 g/L), use of different sludge types (granular vs. crushed), different substrates (oleate C18:1, butter and dairy wastewaters) and different temperatures (15, 37 and 55 °C). Experimental results and model fitting showed that addition of GAC supports faster methane production, i.e. the lag-phase decreased by 2–1000% depending on the GAC concentration and AD temperature. GAC addition also showed faster consumption of both volatile fatty acid and long-chain fatty acid, particularly palmitate (C16:0). Thermodynamic modelling suggested that GAC-induced direct interspecies electron transfer is kinetically superior to conventional indirect hydrogen transfer during AD of oleate. However, when the GAC concentration exceeded 8.0 g/L, there was a 20–50% decrease in the maximum methane production compared to the control. Overall, GAC supplementation has a significant potential to improve the digestion of lipid-rich wastewater which benefits design of modern bioenergy systems.

Effect of gentamicin mycelial residues disintegration by microwave-alkaline pretreatment on methane production and gentamicin degradation during anaerobic digestion

Gentamicin mycelial residues (GMRs) are microbial fermentation residues of the pharmaceutical industry. In this study, anaerobic digestion of GMRs in combination with microwave-alkaline pretreatment (MAPT) was first employed to enhance methane production and the efficiency of gentamicin degradation. The anaerobic digestion batch tests were conducted to optimize the MAPT conditions, and semi-continuous tests of three-month duration were carried out to investigate the anaerobic digestion performance and fate of gentamicin. The results indicated that the GMRs flocs were substantially disintegrated after MAPT, and the average particle size was significantly related to methane production (p < 0.05). Meanwhile, the solubilization of proteins after MAPT demonstrated a prominently positive effect on the anaerobic digestion performance of GMRs (p < 0.05), including biochemical methane potential, lag phase and maximum methane production rate fitted by modified Gompertz model. The results of the batch tests of MAPT pretreated GMRs (pH > 12) suggested that the excessive alkali dosage in the pretreatment process adversely affected the anaerobic digestion performance due to the solubilization or generation of the refractory compounds (e.g. melanoidin). An increase of 58.05% in methane production (323.33 ± 11.88 mL gVS−1) was accomplished by MAPT in the sable running stage of the semi-continuous stirring tank reactor. The analysis of gentamicin mass balance in anaerobic digestion process demonstrated that the degradation was a preponderant mechanism for gentamicin removal. Simultaneously, MAPT facilitated the release of gentamicin trapped in flocs, thus, effectively improving the average degradation efficiency of gentamicin in anaerobic digestion process (degradation efficiency: 97.70 ± 0.63%).

Consistency of batch anaerobic digestion process of high and low activated sludge concentrations to the interference of sodium benzoate as preservative material

Anaerobic digestion resulted best performance in degradation of organic materials. Degradation of the organic materials was stated as complete by the formation of methane, carbon dioxide etc. (or biogas) as the final product of degradation. Food or beverages products utilized preservative agents in order to prolong the expired date. Sodium benzoate is the most common of preservative agent which can be used for both food and beverages. This experiments were pointed out to observe the effect of high and low activated sludge to the formation of biogas. Research was conducted in some batch mode reactor systems employing high and low of activated sludge (80% and 20% of volume) and solution concentration of sodium benzoate volume. The activated sludge used was 12 g MLSS/L. Concentrations of sodium benzoate used were 400, 600, and 800 mg/L. Product of biogas samples was measured every two days for 60 days of experiment. The results showed that the volume ratio of activated sludge and sodium benzoate of 80% able to reduce the interference of sodium benzoate and for 20% was not able to produce biogas where the load of sodium benzoate influenced the production of biogas.

Evaluation of biomethane potential and kinetics modelling of green macroalgae from the South Atlantic Sea:

Environmental context The east coast of the Argentine Sea is frequently impacted by seasonal macroalgal blooms, resulting from anthropogenic activities such as the discharge of untreated wastewater. The use of these macroalgae for energy purposes through the anaerobic digestion process provides an opportunity to convert a biomass, currently considered as a waste, into a renewable energy source. Bioenergy potential and the process kinetics of two macroalgae were studied and the results suggest this is a potentially useful novel energy source. Abstract Several uses for macroalgae have been reported in the literature, including in agriculture, pharmaceuticals, and human and animal feed. While many authors have recognised the potential use of algae biomass for bioenergy, specific research on their energy potential is less abundant. The wide east coast of the Argentine Sea is frequently impacted by seasonal macroalgal blooms that nowadays are managed as a residue of land disposal. The feasibility of bioenergy production from two species of macroalgae from the South Atlantic Sea was evaluated through the analysis of the biomethane potential determined according to a standard protocol. Fresh, washed and chopped samples of Codium sp. (Codiaceae) and Ulva sp. (Ulvaceae) were studied in anaerobic batch digestion under the mesophilic regime and with an inoculum : substrate ratio of 3 : 1. The results showed 35 % higher methane production of Codium sp. (205.2 mL CH4/g volatile solids), which revealed that the composition of Ulva sp., rich in sulfated anionic polysaccharide (Ulvan), reduces the activity of methanogenic bacteria. The kinetics of methane production was studied through the first-order kinetic, the modified Gompertz and the Cone models, which all showed an adequate adjustment of the experimental data (R2 &gt; 96 %) but the Cone model yielded the best performance (R2 &gt; 98.6 %). The potential methane production L0 and the hydrolysis rate constant k were respectively 30 % and 124 % higher for Codium sp. than Ulva sp., which demonstrated a higher biodegradability of this algae. Despite the differences observed, the results obtained revealed an interesting bioenergy potential of the studied species of seaweed from the Argentine Sea.

Enhancement of methane yield from cotton stalks by mechanical pre-treatment

Cotton stalks (CS) are lignocellulosic agricultural by-products, a potential source for biogas production, but pretreatment must be considered since hydrolysis is the rate-limiting stage for lignocellulosic biomass substrates. This study investigates the feasibility of mechanical pretreatment of CS to enhance methane production. Batch anaerobic digestion of CS samples with particle sizes ranging from 0.5 to 65 mm was carried out in 1 L eudiometer batch digesters for 48 days at 37°C. Results showed that methane yield was inversely proportional to particle size, and the quality of biogas was good (54.0–55.2% CH4). Significant increases in methane yield were observed with 20.3% and 26% for samples with a particle size of 3 mm and 0.5 mm, respectively, compared to untreated CS. The coefficient of anaerobic energy turnover was relatively low (20.2–25.5%). Reduction of the CS particle size to 3 mm or less is recommended to achieve effective methane conversion and decrease the retention time in an anaerobic digester from 31 to about 25 days. However, to offset the high energy demand required for grinding, further research should be conducted in combining size reduction with chemical and physicochemical pretreatment.

Anaerobic digestion of dissolved air floatation slurries: Effect of substrate concentration and pH

Dissolved air floatation (DAF) slurries are an unconventional substrate for anaerobic digestion owing to their high COD concentrations, mainly consisting of lipids. Batch anaerobic digestion of DAF slurry was conducted to investigate the methane production through dilution of the slurry (with mineral salt medium, MSM) and by adjusting the initial pH (to 6.0, 5.5, 5.0 and 4.5) The performance of two different inocula, namely waste activated sludge (WAS) treating domestic wastewater and anaerobic granular sludge (AGS) treating dairy wastewater, was compared. The DAF slurry had a pH of 7.03 ( ± 0.07), conductivity of 6.69 ( ± 0.54) mS/cm, and a COD and ammonium concentration of 85.96 ( ± 8.32) g/L and 168.49 ( ± 1.79) mg N/L, respectively. DAF slurry without dilution produced a maximum methane yield of 58.60 ( ± 1.97) mL/g COD after 30 days of incubation. Dilution with MSM up to three folds, improved the methane yield by about 67%–105% and 67%–177% with WAS and AGS as the inoculum, respectively. Higher methane productivity was achieved at an inoculum to substrate ratio of at least 1.5 for WAS and 2.0 for AGS, respectively. AGS was more effective with a 20% increase in methane production from 3-fold diluted DAF slurry when compared with WAS. Adjustment of the initial pH of the DAF slurry to 6.0 resulted in a methane yield of 359.71 ( ± 32.72) mL/g COD, which was 23% higher than the control without pH adjustment. This study demonstrated that the methane yield from DAF slurries can be enhanced through substrate dilution and initial pH adjustment. • Methane yield enhanced by 23% upon adjustment of initial pH of the DAF slurry to 6.0. • 3-fold dilution increased methane production rate by 275% with granular sludge. • Anaerobic granular sludge is an efficient inoculum for methanogenesis of DAF slurry. • Lag phase duration was not shortened by dilution or pH adjustment of the DAF slurry. • Optimal inoculum to substrate ratio at least 1.5 and 2.0 for WAS and AGS, respectively.

Kinetic of Biogas Production in a Batch Anaerobic Digestion Process with Interference of Preservative Material of Sodium Benzoate

Sodium benzoate is a preservative compounds which are widely used for both food and beverage products. The treatment of waste water containing this compound was normally conducted in a anaerobic digestion (AD) using a batch reactor system at a room temperature. The anaerobic process eventually produced biogas which can be used for bioenergy. This research was aimed to evaluate the production of biogas from by synthetic solution models containing sodium benzoate (SB). The experiment was performed in a variation of Mixed Liquor Suspended Solid (MLSS) of 4.8 and 7.2 g/L, and initial sodium benzoate concentration of 400, 600, and 800 mg/L. The digestion was performed at 60 days, while the biogas content was measured every 2 days. The results indicated a reduction in the cumulative biogas by the addition of sodium benzoate, compared to the control condition. Moreover, the decrease in organic loading rate (OLR) of SB in wastewater follows the first order kinetic with kinetic rate constant (k) was 0.0432 to 0.1254 (day−1) for MLSS of 4.8 g/L and 0.0276 to 0.0372 (day−1) for 7.2 g/L MLSS. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Improved anaerobic digestion of swine manure by simultaneous ammonia recovery using gas-permeable membranes

In feedstocks containing high ammonia (NH3) concentration, removal of the NH3 during the anaerobic digestion (AD) process can improve AD process performance. In the present study, the effect of NH3 removal using gas-permeable membrane (GPM) technology on AD process performance and biogas production was investigated using swine manure feedstock. Batch and semi-continuous AD experiments were carried out under mesophilic conditions. In the reactor with NH3 recovery, total ammonia nitrogen (TAN) concentration was reduced 28% in batch experiments and 23% on average in the semicontinuous experiment compared with the reactor without NH3 recovery. Free ammonia (FA) concentrations were also decreased by 23% and 4% on average in batch and semicontinuous experiments, respectively. These reductions in TAN and FA by GPM system positively impacted both the quality and quantity of the biogas produced by AD of swine manure. Specifically, the specific methane yield increased 9% in the batch experiment and 17% on average in the semicontinuous experiment. Furthermore, higher percentages of methane in biogas were obtained during AD retrofitted with GPM system, 24% increase in the batch experiment and 11% on average in the semicontinuous experiment (range 8.3-13.6%). Simultaneously, a uniform TAN recovery rate of 6.7 g N TAN per m2 of membrane and per day was obtained for the 205 days of semicontinuous operation; ammonia nitrogen was recovered in the form of ammonium sulphate solution. Therefore, the AD-GPM configuration produces beneficial results on biogas quantity and quality while recovering ammonia nitrogen in form of ammonium sulphate.