Semi-continuous Digestion Research Articles

Novel bioaugmentation process to enhance anaerobic digestion of municipal sewage sludge

The imperative shift to a circular economy, driven by population growth, urbanization, and economic development, highlights the importance of recovering resources from waste streams. Anaerobic digestion (AD) is promising for stabilizing organic wastes and producing renewable methane-rich biogas. However, AD faces challenges, including operational instability, fatty acids accumulation, ammonium inhibition, and low yields. This study investigates the applicability of a novel Ydro Process® bioaugmentation on municipal sewage sludge anaerobic digestion. The process led to pre-hydrolysis of sewage sludge, as evidenced by an increase in volatile fatty acids (VFA), from 134 mg HAc/L in raw TWAS to 997 mg HAc/L in augmented sludge and improved soluble chemical oxygen demand (SCOD) yields. Additionally, the viscosity decreased by 41 % in the Ydro Process® bioaugmented sludge. Biogas production significantly increased from 732 mL/day to 1338 mL/day during semi-continuous digestion, with methane yield rising from 116 mL/g TCODadded to 218 mL/g TCODadded. Microbial analysis revealed an enhanced population of hydrogenotrophic methanogens.

Semi-continuous mesophilic anaerobic digestion of date palm (Phoenix dactelifyra L.) leaflets of the H'mira cultivar from the Adrar region of Southern Algeria using an alkaline pre-treatment

This research paper aim to investigate the enhancement potential of mesophilic Anaerobic Digestion (AD) of Algerian date palm (Phoenix dactylifera L.) leaflets from H'mira cultivars using an alkaline pretreatment approach. The experiment was conducted for the first time in semi-continuous digesters. NaOH was applied at various percentages (6 %, 12 % and 18 %) to chemically pretreat the substrate for 5 days at 37 °C. The chemical pretreatment results were interpreted for the first time with in-depth FTIR spectroscopic analyses. The Hydraulic Retention Time (HRT) was fixed at 15 days, and the Organic Loading Rate (OLR) at 2 g MO/L/day. The results showed that the methane (CH4) production values were stabilized with a clear distinction at averages of 211.85, 177.26, 143.36 and 123.07 ml of CH4/day, i.e. a CH4 yield of 105.92, 88.63, 71.68 and 61.53 ml of CH4/gVS/day for the reactors containing substrates pre-treated with 12 %, 6 %, 18 % NaOH and the substrate without pre-treatment respectively. Compared to the substrate without pre-treatment, the CH4 production rates were improved 1.72, 1.44 and 1.16 times for the reactors containing 12 %, 6 % and 18 % NaOH respectively. These findings were perfectly in accordance with FTIR spectroscopy results. These findings demonstrate that the semi-continuous AD process can be an attractive energy recovery solution from such waste compared to batch digesters, (on one day, it produce 77–105 % of the CH4 produced during 21–55 days in batch digesters), as well as the importance of adequate pre-treatment prior to the AD. FTIR Spectroscopic analysis technology can also be widely used to analyze pre-treatment data for lignocellulosic biomass, as it gives very encouraging results.

Reutilization of Brewer’s Spent Grain as Spent Mushroom Substrate for the Generation of Biogas in a Semi-Continuous Digester

Reutilization of Brewer’s Spent Grain as Spent Mushroom Substrate for the Generation of Biogas in a Semi-Continuous Digester

Advanced steam explosion as thermal hydrolysis process for high solids anaerobic digestion and enhanced methane yield: Proof of concept

Sewage sludge management is one of the major issues faced by wastewater treatment plant (WWTP) operators. Though anaerobic digestion (AD) is one of the most preferred sludge management techniques, the complex microbial floc structure of the sludge creates physical and chemical barriers that limit the rate of microbial degradation resulting in a longer hydraulic retention time (HRT) of 25–30 days. The thermal hydrolysis process (THP) can be used as a pretreatment technique to enhance the rate of biodegradation which results in reduced retention time and increased methane yields. This work investigated the effects of the THP on the semi-continuous anaerobic digestion of high solids sludge (15% total solids, TS) obtained from a municipal wastewater treatment plant (WWTP) operating at higher solids retention time (SRT) of 40 days. The thermal hydrolysis process achieved the effective release of organics into the liquid phase resulting in 37% chemical oxygen demand (COD) solubilization. Two semi-continuous digesters, one fed with untreated sludge (control digester, 5% TS) to mimic the conventional anaerobic digester and the other fed with THP sludge (160 °C, 30 min, 6 bar, 10% TS) were operated under a mesophilic regime and a hydraulic retention time (HRT) of 15 days. The methane yield from the THP digester (0.366 ± 0.010 m3/kg VSadded, 70 ± 1.13% CH4) was 47% higher than the control digester (0.248 ± 0.013 m3/kg VSadded). The volatile solids removal (VSR) was 51 ± 0.6% in the THP digester, i.e., 43% higher over control digester (35.7 ± 1.3%). The fecal coliforms concentration in the digestate of control and THP digesters were 9200 and 200 MPN/g, respectively. Thus, the THP sludge meets the Class A biosolids criteria (<1000MPN/g). THP integrated anaerobic digestion achieved higher solids reduction with enhanced energy recovery, high solids loading with shorter retention time, and generated Class A biosolids.

Pilot-Scale Anaerobic Co-Digestion of Wastewater Sludge with Lignocellulosic Waste: A Study of Performance and Limits

The effects of co-digesting sewage sludge (SS) and horse waste (HW), the composition of HW, and the ratio of HW:SS were studied using two semi-continuous digesters of 9.5 L of working volume. These digesters were operated in parallel with the mono-digestion of SS in digester 1 (D1) and the co-digestion of SS and HW in digester 2 (D2). In digester 2, there were two phases of digestion (durations of 40 and 43 weeks, respectively). The composition of HW in the first phase was 85% wheat straw (WS), 14% wood chips (WC), and 1% horse manure (HM), with 99% wheat straw (WS) and 1% horse manure (HM) in the second phase. Variable ratios of HW:SS were studied in the digesters. The co-digestion of sewage sludge (SS) and horse waste (HW) produced more biogas than the mono-digestion of SS alone, with a maximum of 15.8 L·d−1, compared to 9 L·d−1 at the end of the experiment. When comparing the results obtained in both phases, the production of methane in phase 2 was 18 NmL·gVS−1 higher than in phase 1. This slight increase in methane yield could be linked to the absence of wood chips (WC), which is considered to have a diluting effect on methane production. Therefore, this study shows that an organic loading rate (OLR) of 4.8 kgVS·m−3·d−1, a ratio of HW:SS of 3, and a composition of HW (99% WS, 1% HM) should be respected in the actual experimental conditions for a well-functioning anaerobic digestion.

Semi-continuous anaerobic co-digestion of thermal and thermal-alkali processed organic fraction of municipal solid waste: Methane yield, energy analysis, anaerobic microbiome

The semi-continuous anaerobic co-digestion (AcoD) of thermal and thermal-alkali pretreated organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) was studied under varying hydraulic retention times (HRT) and organic loading rates (OLR Three semi-continuous digesters were operated under control (non-pre-treated), thermally pretreated (125 °C), and thermal-alkali pretreated (125°C-3g/L NaOH) conditions at variable OLRs at 2.5, 4.0, 5.1, and 7.6 kgVS/m3.d and corresponding HRTs of 30, 20, 15, and 10 days. The 10 and 43% higher methane yield (0.445 m3/kgVS) and 11 and 57% higher VS removal (52%) was achieved for thermal-alkali pretreated digester at 5.1 kgVS/m3.d OLR over thermally pretreated (0.408 m3/kgVS, 45% VS removal) and control digesters (0.310 m3/kgVS, 33% VS removal), respectively. Thermal and thermal-alkali digesters failed on increasing the OLR to 7.6 kgVS/m3.d, whereas the control digester becomes upset at 5.1 kgVS/m3.d OLR. The metagenomic study revealed that Firmicutes, Bacteroidetes, Chloroflexi, Euryarchaeota, Proteobacteria, and Actinobacteria were the predominant bacterial population, whereas Methanosarcina and Methanothrix dominated the archaeal community. Energy balance analysis revealed that thermal alkali pretreatment showed the highest positive energy balance of 114.6 MJ/ton with an energy ratio of 1.25 compared with thermally pretreated (81.5 MJ/ton) and control samples (−46.9 MJ/ton). This work pave the way for scaleup of both thermal and thermal-alkali pre-treatment at 125 °C to realize the techno-economic and energy potential of the process.

Determination residence time distribution of the solid phase in a dry anaerobic semi-continuous horizontal reactor of 0.5 m3 using innovative 3D printed tracers

Solid residence time distribution (SRTD) analysis is important in the design, modeling, and operation of solid biomass in continuous dry anaerobic digestion (D-AD) reactors. SRTD analysis could allow the appropriately adjust of the applicable organic charge and the study of unusable volume due to solid accumulation and preferential pathways. The lack of sustainable, environmentally friendly, and cost-effective solid tracers limits the study of solid flow patterns in D-AD digesters. In this study, 3D printing enabled the fabrication of customized Poly Lactic Acid (PLA) tracers with a specific shape to perform SRTD analysis of the semi-continuous digestion of straw-cattle manure (SCM) in a horizontal reactor of 0.5 m3. The recovery of tracers at the reactor outlet allowed the determination of the average SRTD at 29.43 days. Solid convection was predominant over diffusion, indicating that the reactor behaves closer to a plug flow reactor (PFR) rather than a complete stirred tank reactor.

Production of Biogas from Food Waste Using the Anaerobic Digestion Process with Biofilm-Based Pretreatment

The production of biogas from food waste is a good approach to the minimization of food waste and increase in the production of renewable energy. However, the use of food waste as a feedstock for biogas production currently poses a difficulty due to an ineffective hydrolysis process, which is a pretreatment procedure and the initial step of the biogas conversion process. This restriction results from the food waste polymers’ solubilization and breakdown. This has an impact on the volume of biogas produced during the methanogenesis stage. It is essential to increase the biodegradation of organic compounds (OC) during the hydrolysis process to increase biogas generation. This study focuses on the enhancement of biogas production by the anaerobic digestion (AD) of food waste (FW). FW was hydrolyzed by the immobilized biofilm and digested anaerobically in a semi-continuous digester. Four different digesters including the control were prepared. The control digester composed of no hydrolyzed food waste had no immobilized biofilm while the other three digesters had immobilized biofilm-hydrolyzed food waste with inoculum concentrations of 10%, 30%, and 50%. The results showed that the 50% digester had the highest biogas yield of about 2000 mL/500 mL. The 10%, 30%, and control digesters had a biogas yield of 1523 mL, 753 mL, and 502 mL respectively. Thus, the analysis of total volatile solid (TVS) reduction in the digesters with 10%, 30%, and 50% inoculum and the control have increased to 43.4% for the digesters with 30% and 10%, 60% for the digester with 50% inoculum, and only 29% for the control. Total chemical demand (TCOD) removal increased to 29%, 33%, 43%, and 56% for the control, and 10%, 30%, and 50%, respectively for the inoculum-to-feed ratio. From these results, the 50% inoculum-to-feed ratio has shown the highest biogas production and highest degradation based on TVS reduction and TCOD reduction. Based on this study, the biofilm pretreatment method can be considered a promising method for the enhancement of biogas volume and biodegradation. Biogas production was high (2000 mL) for hydraulic retention time (HRT = 20) days but the HRT = 15 days was also able to produce a significant amount (1400 mL) of biogas and the 50% inoculum-to-feed ratio has shown the highest volume of biogas production.

Biogas Production from Residues of Industrial Insect Protein Production from Black Soldier Fly Larvae Hermetia illucens (L.): An Evaluation of Different Insect Frass Samples

Insect biomass shows promise as an alternative animal feedstuff with a low climate effect. Industrial insect rearing generates residual materials, such as feed remains and insect excrements, so-called insect frass, which exhibits a high organic content. Commonly, these residues are utilized as soil amendment. Information on the suitability of these residues for biogas production is rather scarce. The energetic utilization of insect frass as feedstock for anaerobic digestion (AD) would allow for the simultaneous residue material reduction and bioenergy production. Additionally, synergies in heat management could arise using the exhaust heat of the biogas plant in the insect farming process. In laboratory-scale anaerobic digestion trials, the specific methane yield (SMY) of six different insect frass samples from black soldier fly (Hermetia) rearing were tested in batch biochemical methane potential (BMP) tests. Further, semi continuous anaerobic digestion trials on a lab scale using continuously stirred tank reactors (CSTRs) were carried out with Hermetia insect frass from a pilot plant operation in order to determine the digestibility and process stability of the AD process. The BMP results showed SMY values of the different insect frass samples ranging from 201 ± 9 to 287 ± 37 mL/gVS that are similar to those of other animal excrements, such as cow or pig manure already been used as feedstock in agricultural biogas plants. Results of the semi-continuous digestion of insect frass from the pilot plant operation showed a SMY value of 167 ± 15 mL/gVS, suggesting no process-inhibiting effect caused by the feed material. Although, the high nitrogen content must be taken into account for stable AD performance.

Study of Different Parameters of Mixing on Biogas Production from Food Waste

Food waste generation is an increasing issue, and the disposal of it is controversial. It raises food prices, and the municipal solid waste contains 8.4% food waste by weight. The current study generates a pilot plant for converting food waste to biogas production as an energy source for tremendous paths. The present work deals with the study of the effect of mixing on biogas production from food waste in the pilot-scale digesters. A propeller agitator was employed for mixing in an anaerobic digester. Multiple experimental trials were addressed to optimize the parameters participating in the process of biogas production in semi-continuous operation at mesophilic conditions. Different mixing duration and mixing frequency was studied at the mixing speed of 5 rpm and a comparison was carried out with reference to the digester without a mixing facility. The highest biogas production of 0.12 m3/(kg dry mass) was observed at the mixing time of 5 min compared with the duration of 10 min and 15 min and without mixing conditions. Mixing once in a day obtained biogas production in the range 0.048 to 0.071 m3/(kg dry mass) while mixing at two times in a day obtained biogas production in the range of 0.019 to 0.0357 m3/(kg dry mass). Hence, mixing frequency once a day provided almost double biogas production. Effect of temperature and pH was also studied with different mixing duration and found that mixing duration of 5 min was the best for biogas production from food waste. Minimum mixing of 5 min is required once a day in semi-continuous digestion for stable biogas production. The study concluded to a point that mixing is important for stable processes and maximum biogas production.

Different microplastics distinctively enriched the antibiotic resistance genes in anaerobic sludge digestion through shifting specific hosts and promoting horizontal gene flow

Both microplastics (MPs) and antibiotic resistance genes (ARGs) are intensively detected in waste activated sludge (WAS). However, the distinctive impacts of different MPs on ARGs emergence, dissemination, and its potential mechanisms remain unclear. In this study, long-term semi-continuous digesters were performed to examine the profiles of ARGs and antibiotic-resistant bacteria (ARB) in response to two different typical MPs (polyethylene (PE) and polyvinyl chloride (PVC)) in anaerobic sludge digestion. Metagenomic results show that PE- and PVC-MPs increase ARGs abundance by 14.8% and 23.6% in digester, respectively. ARB are also enriched by PE- and PVC-MPs, Acinetobacter sp. and Salmonella sp. are the dominant ARB. Further exploration reveals that PVC-MPs stimulates the acquisition of ARGs by human pathogen bacteria (HPB) and functional microorganisms (FMs), but PE-MPs doesn't. Network analysis shows that more ARGs tend to co-occur with HBP and FMs after MPs exposure, and more importantly, new bacteria are observed to acquire ARGs possibly via horizontal gene flow (HGF) in MPs-stressed digester. The genes involved in the HGF process, including reactive oxygen species (ROS) production, cell membrane permeability, extracellular polymeric substances (EPS) secretion, and ATP synthesis, are also enhanced by MPs, thereby attributing to the promoted ARGs dissemination. These findings offer advanced insights into the distinctive contribution of MPs to fate, host, dissemination of ARGs in anaerobic sludge digestion.

Micro-Aerobic Pre-Treatment vs. Thermal Pre-Treatment of Waste Activated Sludge for Its Subsequent Anaerobic Digestion in Semi-Continuous Digesters: A Comparative Study

This article investigates methane production, organic matter removal, and energy by comparing micro-aerobic pre-treatment and thermal pre-treatment of waste-activated sludge (WAS). For micro-aerobic pre-treatment, WAS was pre-treated at 0.35 vvm (volume of air per volume of medium per minute) for 48 h. The data showed over a 30% increase in soluble Chemical Oxygen Demand (COD) and soluble proteins when this pre-treatment was applied. Then, the micro-aerobically pre-treated sludge was mixed with primary sludge and anaerobically digested in semi-continuous digesters with Hydraulic Retention Times (HRT) of 20, 15, and 10 days at 35 °C. We used two digesters as a control: one fed with a mixture of primary sludge (PS) and raw WAS; another fed with a mixture of PS and thermally pre-treated WAS. The results showed a better performance for the digester fed with micro-aerobically pre-treated sludge than the other two at all the HRT tested. The better performance is because of the solubilization of particulate organic matter, as shown at the reactor outlet. Energy consumption analysis showed that micro-aerobic pre-treatment required 32% more energy in a year than thermal pre-treatment. However, if sludge is pre-thickened in a similar way as performed for thermal pre-treatment, then the energy demand required by micro-aerobic pre-treatment is reduced by 41% concerning the thermal pre-treatment; nevertheless, more studies should be performed to verify that methane production and solid reduction advantages are maintained.

Semi-continuous anaerobic digestion of the organic fraction of municipal solid waste: digester performance and microbial population dynamics

Anaerobic digestion is an attractive approach for the management of organic fraction of municipal solid waste (OFMSW) and for the recovery of energy from this waste. A semi-continuous digestion of OFMSW was conducted on stirred reactor under mesophilic condition. Three organic loading rates (OLRs) were tested throughout the anaerobic process (1.36, 2.5 and 3.5 g VS/L.d). The achieved results showed that biogas yield decreased with the increase of OLR. Thus, the highest average of biogas yield, 0.51 L/g VS, was recorded at low OLR (OLR1:1.36 gVS/L.d). Likewise, optimal VS removal, pH, VFA and alkalinity were obtained at OLR1 compared to the other tested OLR. During the anaerobic digestion, the dynamic of microbial community was also assessed by the high-throughput sequencing technology. Firmicutes, Bacteroidetes and Proteobacteria were the dominant phyla during the digestion process. This could be related to their roles in hydrolysis of different OFMSW compounds, as well as in acidogenesis and acetogenesis steps. Regarding Archaeal population, the relative abundance of the Methanoculleus genus declined, while Methanosarcina increased over time. This indicated that acetotrophic and hydrogenotrophic pathways were used for methane production.

Effect of organic load regulation on anaerobic digestion performance and microbial community of solar-assisted system of food waste

Abstract The semi-continuous digestion experiment of food waste was carried out based on a solar-assisted heat anaerobic digestion reactor. The effects of organic load regulation (OLR of 2.0, 4.0, 6.0 and 7.0 kg m−3 d−1 VS (volatile solid)) on methane production, physical and chemical parameters, and microbial community structure were studied. The results showed that 6.0 kg m−3 d−1 VS could achieve the optimal methane production as the anaerobic digestion limit OLR of kitchen waste. At this stage, the accumulation of organic acids in the reactor led to a great fluctuation of pH. Artificial alkali regulation could restore the stable operation of the reactor, but the reactor could not withstand the OLR shock of 7.0 kg m−3 d−1 VS. In addition, Qualcomm sequencing results showed that microorganisms showed high functional concentration and poor community richness under low OLR, and increasing OLR could promote microbial richness. At the same time, the Methanosaeta of acetic acid methanogens was relatively abundant in the low OLR stage, while the hydrogen trophic methanogenic bacteria Methanoregula and Methanospirillum showed high activity in the high OLR stage, but the excessive reproduction of acidogenic bacteria in the digestive system would affect the stability of the archaea community when the OLR was too high.

Biochar assisted cellulose anaerobic digestion under the inhibition of dodecyl dimethyl benzyl ammonium chloride: Dose-response kinetic assays, performance variation, potential promotion mechanisms

This study evaluated the inhibitory effect and mitigation strategy of dodecyl dimethyl benzyl ammonium chloride (DDBAC) suppression on anaerobic digestion. With the 12 h-suppression, only 16.64% of anaerobes were alive, and acetotrophic methanogens were significantly inhibited. As for batch test, DDBAC suppression significantly prolonged the start-up of systems and decreased the biogas production. In cellulose semi-continuous digestion process, the DDBAC suppression induced volatile fatty acids accumulation and pH decrease. However, the biochar amended reactor effectively mitigated the DDBAC suppression and achieved 370.5 mL/d·g-chemical-oxygen-demand biogas production. Moreover, 17.8% more protein in extracellular polymeric substances was secreted as the bio-barrier to defense the DDBAC suppression. Furthermore, microbial analysis showed that biochar addition selectively enriched directed interspecies electron transfer (DIET) participant bacteria (Anaerolineaceae and Syntrophomonas) and methanogens (Methanosaeta and Methanobacterium). Meanwhile, the potential metabolic pathway analysis showed that the abundance of amino acids and energy metabolism were increased 28% and 8%, respectively. The abundance of encoding enzyme related to hydrogenotrophic and acetotrophic methanogenesis enriched 1.88 times and 1.48 times, respectively. These results showed the performance and mechanisms involved in DIET establishment with ethanol stimulation biochar addition.

Micro-Aerobic Pre-Treatment v/s Thermal Pre-Treatment of Waste Activated Sludge for its Subsequent Anaerobic Digestion in Semi-Continuous Digesters: A Comparative Study

Micro-Aerobic Pre-Treatment v/s Thermal Pre-Treatment of Waste Activated Sludge for its Subsequent Anaerobic Digestion in Semi-Continuous Digesters: A Comparative Study

Batch and semi–continuous experiments examining the sludge mesophilic anaerobic digestive performance with different varieties of rice straw

Anaerobic co–digestion of excess sludge (ES) and different varieties of rice straw including indica rice straw (IRS), japonica rice straw (JRS) and glutinous rice straw (GRS) was investigated in batch and semi–continuous experiments. The batch experiment results showed that the GRS addition presents the highest hydrolysis and methanogenesis rates, its cumulative methane yield (CMY) was 305.75 mL/g VS and its average methane content was 60.56%. After digestion, the structure of GRS was almost completely destroyed, which was beneficial to the degradation of lignocellulose. The digestive process is affected by the abundance of Actinobactereria, Proteobacteria, Methanosaetae and Methanosarcina. The results of semi–continuous digestion were similar to batch digestion. In addition, the addition of GRS increased TN concentration in biogas residue and TP concentration in biogas slurry, but was not conducive to the subsequent dehydration of sludge.

Hydrothermal Pretreatment of Rice Straw with Alkaline Addition for Enhancing Biogas Production in Semicontinuous Anaerobic Digester

This study presents the results of hydrothermal pretreatment of rice straw on its ability to improve the biogas production process in anaerobic digesters. Hydrothermal treatment on rice straw biomass was carried out with the addition of 0%, 3% and 5% NaOH (w/w rice straw) for one hour at a temperature of 140 °C. This study showed that hydrothermal and alkaline hydrothermal pretreatments were able to increase organic degradation of rice straw as indicated by an increase in the dissolution of lignin and hemicellulose from rice straw. Temperature and NaOH worked synergistically to dissolve lignocellulose in the hydrothermal pretreatment process. In the semicontinuous digester fed with pretreated rice straw, NaOH content in the pretreatment stage was found to give significant effect in enhancing biogas production. Average daily biogas production by the untreated rice straw, hydrothermal pretreated without NaOH addition, hydrothermally treated rice straw with 3% NaOH and 5% NaOH was 23.9, 57.1, 95.8 and 108.8 L/kg rice straw, respectively.

Biogas Production by Pilot-Scale Anaerobic Co-Digestion and Life Cycle Assessment Using a Real Scale Scenario: Independent Parameters and Co-Substrates Influence

This study evaluates the performance of different agricultural by-products to identify the potential effect of independent variables, using as the dependent variable the biogas production. A Box–Behnken experimental design was carried out in a pilot-scale plant of four stirred stainless-steel digesters under mesophilic semi-continuous digestion. The results obtained support the creation of a technical framework to scale up the process and further evaluation of the potential environmental impacts through life cycle assessment (LCA) methodology. A stable behaviour was achieved in 12 of the 13 experiments proposed. The highest value of daily biogas production was 2200.15 mL day−1 with a stabilization time of 14 days, an organic loading rate of 4 g VS feed daily, low C/N ratio and a 1:1 relation of nitrogen providers. The concentrations of CH4 remained stable after the production stabilization and an average biogas composition of 60.6% CH4, 40.1% CO2 and 0.3% O2 was obtained for the conditions mentioned above. Therefore, the real scale plant was estimated to manage 2.67 tonnes of residual biomass per day, generating 369.69 kWh day−1 of electricity. The LCA analysis confirms that the co-digestion process evaluated is a feasible and environmentally sustainable option for the diversification of the Colombian energy matrix and the development of the agro-industrial sector.

Biogas production from household food waste using homemade bio-activator in semi-continuous digester

This research aims to evaluate the performance of homemade bio-activator in processing household food waste through a semi-continuous process. It used a 214 litres capacity of an anaerobic digester that serve 8 households. Performance of digester with homemade bio-activator was compared to other commercial activators including Green Phosko (GP7), Effective Microorganisms 4 (EM4) and one digester control without activator. The pH of household food waste was set at a neutral using limestone, while the weight ratio of water and the waste was set at 2:1. There were 2 processes conducted, namely the preparation stage (batch process) and operational stage (semi-continuous process). The first stage means preparation for microbial activity in anaerobic conditions, while the latter stage means a biogas production process. Digester with homemade bio-activator displayed the best performance compared to other variations. The digester produced cumulative volume biogas of 335.7 L with methane gas production of 1.29 L/kg total solid or 1.52 L/kg of volatile solid.