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The composition of waste-activated sludge (WAS) is complex, containing a large amount of harmful substances, which pose a threat to the environment and human health. The reduction and resource utilization of sludge has become a development demand in sludge treatment and disposal. Based on the technical bottlenecks in the practical application of direct anaerobic digestion technology, this study adopted two different thermal and thermal–alkali hydrolysis technologies to pretreat sludge. A pilot-scale experiment was conducted to investigate the experimental conditions, parameters, and effects of two hydrolysis technologies. This study showed that the optimal hydrolysis temperature was 70 °C, the hydrolysis effect and pH can reach equilibrium with the hydrolysis retention time was 4–8 h, and the optimal alkali concentration range was 0.0125–0.015 kg NaOH/kg dry-sludge. Thermal–alkali combination treatment greatly improved the performance of methane production, the addition of NaOH increased methane yield by 31.2% than that of 70 °C thermal hydrolysis. The average energy consumption is 75 kWh/m3 80% water-content sludge during the experiment. This study provides a better pretreatment strategy for exploring efficient anaerobic digestion treatment technologies suitable for southern characteristic sewage sludge. HIGHLIGHTS Enhanced anaerobic digestion of WAS by thermal–alkali pretreatment was studied at a pilot-scale level.; Optimal thermal temperature and retention time were confirmed for a pilot-scale study.; Energy demand can be basically met based on biogas production.;

Biochar (BC) is often used as an additive in anaerobic digestion (AD) to increase yield and/or to stabilise the process when the manure content is increased. Unfortunately, BC is rarely described in detail in terms of its raw material sources, production processes, and structural, physical and chemical properties to allow correlation with its effects on AD. It is an open question whether microorganisms from AD can penetrate into different biochar pore types, depending on their wood origin. In this paper, we describe the preparation (temperatures, treatment times, yields) and characterisation shrinkage, density, pore sizes, pore size distribution, specific surface area, ash, volatiles, fixed carbon, elemental composition, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), benzene, toluene, ethyl-toluene, xylene (BTEX) and volatile halogenated hydrocarbons (VHH) of BC cubes of Scots pine (Pinus sylvestris) and common beech (Fagus sylvatica) powder made from this BC in addition to commercial charcoal powder. The pore size distribution determined by mercury porosimetry differs from that determined by 3D-reflected light microscopy. After incubating BC cubes in AD, the cubes were mechanically cleaned and cut into two pieces. Microorganisms were detected inside the cubes by fluorescence microscopy. Particle size and wood source determine the influence of BC on AD. [ABSTRACT FROM AUTHOR]

Anaerobic Digestion (AD) of organic waste is one of the most promising processes and is the ideal solution for the disposal of organic waste (OW) and at the same time, the production of methane gas which may be used as a sustainable energy resource. An anaerobic biodigester with a volume of (20) liters has been used to digest organic waste and to trace the changes that occur during the AD process. Operating parameters such as temperature, pH, total solids, and volatile solids (TS, VS) have been measured which have a significant impact on the rate and quality of biogas production. Experiments on anaerobic biodegradation of OW-SS were monitored under mesophilic conditions (temperature 37 °C, retention time 30–31 days). The pH value varied between (4.2–5.8) for OW-SS. During 30 days of the detection period, the maximum methane production (corrected) occurred on day 21 which was equal to 254.3-ml. The cumulative volume of the produced methane was recorded as (3409 ml), OW-SS, and these results were corrected to the standard conditions, where after correction, it became (2929 ml). The highest rate of methane concentration was estimated at (52 %) for OW-SS, while the rate of decrease in the TS and VS was (54 %, and 45 %), respectively. It is recommended to examine the changes that occur if a larger digester is used than the one used in the current study, such as 50 L, 100 L …. Etc. To compare the data obtained in this study with the results of larger digestions to allow for the opportunity to build anaerobic digesters at the plant level with the benefit of renewable energy production. It is also recommended to investigate the impact of some types of pretreatments on biogas production such as the use of alkali, enzymatic, ultrasonic treatment or acid ton the solid waste feed.

A cross-flow ultrafiltration harvesting system for a pre-concentrated microalgae culture was tested in an innovative anaerobic-based WRRF. The microalgae culture was cultivated in a membrane photobioreactor fed with effluent from an anaerobic membrane bioreactor treating sewage. These harvested microalgae biomasses were then anaerobically co-digested with primary and secondary sludge from the water line. Depending on the needs of this anaerobic co-digestion, the filtration harvesting process was evaluated intermittently over a period of 212 days for different operating conditions, mainly the total amount of microalgae biomass harvested and the desired final total solids concentration (up to 15.9 g·L−1 with an average of 9.7 g·L−1). Concentration ratios of 15–27 were obtained with average transmembrane fluxes ranging from 5 to 28 L·m−2·h−1. Regarding membrane cleaning, both backflushing and chemical cleaning resulted in transmembrane flux recoveries that were, on average, 21% higher than those achieved with backflushing alone. The carbon footprint assessment shows promising results, as the GHG emissions associated with the cross-flow ultrafiltration harvesting process could be less than the emissions savings associated with the energy recovered from biogas production from the anaerobic valorisation of the harvested microalgae. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion offers a promising approach to enhancing biogas production from surplus by-products of wastewater treatment plants (WWTPs) and agricultural waste while reducing environmental negative impact. This study investigated the co-digestion of anaerobic thickened sewage sludge (ATSS) and rice straw (RS) under mesophilic conditions (35 ± 1 °C). In phase 1 of the experiment, lab-scale reactors with varying MRs of RS (0 %, 4 %, 8 %, and 16 % based on sludge weight) were employed to determine the optimal MR for maximizing biogas quantity and methane content. Phase 2 examined the impact of mechanical mixing (MM) on biogas production, pathogen and trace element reduction, and the calorific value (CV) of the co-digested mixture compared to the digested thickened sludge (DTS) and RS individually to assess the potential energy of co-digestion. Results revealed that the 8 % MR yielded the highest biogas volume, approximately 2.5 times that of the DTS alone, with methane and carbon dioxide contents within the typical ranges. MM in phase 2 further increased biogas volume by 2.8 times compared to DTS. The CV of the co-digested mixture was 24,937 kJ/kg and 21,929 kJ/kg for the DTS. Pathogens were effectively eliminated, and trace elements remained below the permissible limits. The 8 % MR with MM was identified as the optimal MR that produces the highest biogas quantity before reaching the turning point. Moreover, co-digestion at this MR enhanced the CV of ATSS by 14 %.

Biochar (BC) is often used as an additive in anaerobic digestion (AD) to increase yield and/or to stabilise the process when the manure content is increased. Unfortunately, BC is rarely described in detail in terms of its raw material sources, production processes, and structural, physical and chemical properties to allow correlation with its effects on AD. It is an open question whether microorganisms from AD can penetrate into different biochar pore types, depending on their wood origin. In this paper, we describe the preparation (temperatures, treatment times, yields) and characterisation shrinkage, density, pore sizes, pore size distribution, specific surface area, ash, volatiles, fixed carbon, elemental composition, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), benzene, toluene, ethyl-toluene, xylene (BTEX) and volatile halogenated hydrocarbons (VHH) of BC cubes of Scots pine (Pinus sylvestris) and common beech (Fagus sylvatica) powder made from this BC in addition to commercial charcoal powder. The pore size distribution determined by mercury porosimetry differs from that determined by 3D-reflected light microscopy. After incubating BC cubes in AD, the cubes were mechanically cleaned and cut into two pieces. Microorganisms were detected inside the cubes by fluorescence microscopy. Particle size and wood source determine the influence of BC on AD.

Slaughterhouse wastewater (SWW) is one of the most harmful agriculture and food industrial wastewaters because of rich impurities, particularly organic matter, suspended solids, oil, grease, and nitrogen (N) nutrients. This study investigated organics and N nutrients removal performance in the developed upgraded anaerobic-aerobic slaughterhouse wastewater treatment process (U-AASWWTP). The supernatant reflux position, ratio and dissolved oxygen (DO) in the aerobic units play key roles, and the optimized solutions were 300% reflux to the second compartment at DO of 4.64-4.90 mg/L. Under such conditions, chemical oxygen demand (COD) removal efficiency only decreased from 98.14% to 95.94% when the loading rates increased from 500 to 2,000 g·COD/(m³·d) gradually, whereas total nitrogen (TN) showed a different removal trend. Effluent TN was the lowest at 1,500 g·COD/(m³·d) and the corresponding effluent COD, TN and NH4+-N all satisfied with the Chinese upcoming discharge standard. Therefore, U-AASWWTP can effectively remove COD and N from SWW and would become the main direction of traditional treatment processes upgrading to addressing the issue of upcoming stricter effluent standard. This study holds significant importance in ensuring the sustainable development of slaughtering industry in China. Additionally, this study enhances the understanding of the synergy relationship between anaerobic digestion and Anammox microorganisms, thereby promoting the intelligent application in SWW treatment processes. [ABSTRACT FROM AUTHOR]

Wasted tofu rich in protein was subject to hydrothermal pretreatment (HTPT) under different conditions (at 120, 140, 160 and 180 ℃; for 0, 30, 60 and 90 min) followed by biochemical methane potential (BMP) tests, and 140 ℃ and 0 min were found to be respectively the best temperature and duration for HTPT of tofu in terms of its biogas production. Under the under the optimal conditions (140 ℃, 0 min) the accumulative methane yield reached up to 510.9 mL·(gVS)-1, which was 26.98 % higher than that without HTPT (402.3 mL·(gVS)-1). The start-up process of continuous anerobic digestion (AD) of the tofu before and after hydrothermal treated (HT) at the optimal HTPT conditions (140 ℃, 0 min) was examined, to investigate and compare how their consequent AD responded to HTPT. It was found that, for start-up of continuous AD, the HT tofu delivered more balanced nutrients and thus led to more stable AD and quicker biogas production. Unavoidably, HTPT generated products refractory to biodegradation, to slightly decrease the total biogas production. During AD of HT tofu some weak ammonia-tolerant microbes, such as methylotrophic methanogens, survived and played indispensable roles. Analyses of living microbial community structure indicated that, some hydrolytic acidification bacteria intolerant to ammonia nitrogen (such as Proteobacteria) were always active and appeared at high proportion. The viable methylotrophic methanogens, e. g. RumEn M2, took obvious responsibilities in start-up of the AD for HT tofu.

Sugarcane ethanol production generates about 360 billion liters of vinasse, a liquid effluent with an average chemical oxygen demand of 46,000 mg/L. Vinasse still contains about 11% of the original energy from sugarcane juice, but this chemical energy is diluted. This residue, usually discarded or applied in fertigation, is a suitable substrate for anaerobic digestion (AD). Although the technology is not yet widespread—only 3% of bioethanol plants used it in Brazil in the past, most discontinuing the process—the research continues. With a biomethane potential ranging from 215 to 324 L of methane produced by kilogram of organic matter in vinasse, AD could improve the energy output of sugarcane biorefineries. At the same time, the residual digestate could still be used as an agricultural amendment or for microalgal production for further stream valorization. This review presents the current technology for ethanol production from sugarcane and describes the state of the art in vinasse AD, including technological trends, through a recent patent evaluation. It also appraises the integration of vinasse AD in an ideal sugarcane biorefinery approach. It finally discusses bottlenecks and presents possible directions for technology development and widespread adoption of this simple yet powerful approach for bioresource recovery. [ABSTRACT FROM AUTHOR]

The anaerobic digestion (AD) study for the valorization of poultry slaughterhouse waste (PSHW) was assessed at laboratory scale and in mesophilic conditions. Different loads, given gradually from 0.5 g VS/L to 3 g VS/L, were used to evaluate the methane production from PSHW via AD. The highest cumulative methane production (CMP) and methane yield (YCH4) were observed for the 2 g VS/L and 1 g VS/L added loads, with values of 566 Nml and 378 Nml/g VS, respectively, in a HRT of 140 h. The efficiency of the process was examined using a response surface method-central composite design (RSM-CCD) to examine the impact of independent variables such as load and HRT on CMP and YCH4. A statistical analysis of variance (ANOVA) was carried out to evaluate the suitability of the developed model. The YCH4 results showed a probability value (P-value)

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. [ABSTRACT FROM AUTHOR]

Inadequate methane production and insufficient hydrolysis-acidification activity impede the practical application of anaerobic digestion (AD) of waste activated sludge (WAS). Recently, metal-organic framework (MOF) materials attains promising capability of controlling proton/electron transfer in AD processes. This study used a typical iron-based MOF and MIL-88A(Fe) to improve the methane production via digesting WAS. These materials were prepared via a one-step hydrothermal method. The findings indicated that the addition of 150 mg MIL-88A(Fe)/g WAS VS resulted in a 57.23% increase in accumulated methane production and a 43.84% increase in daily maximum methane production. The methane production rate (R max) also increased from 22.25 to 29.14 mL/g VS/d. The enhanced electron transfer capacity, improved hydrolysis of WAS, boosted acetate generation, and mitigated accumulation of volatile fatty acids (VFAs) collectively contributed to the better methane yield in the MIL-88A(Fe)-added system. The significant enrichment of Methanobacterium and Methanosaeta along with the up-regulation of key methanogenesis enzyme-encoding genes jointly suggested that the CO 2 reduction and methanogenesis were strengthened. Moreover, MIL-88A(Fe) stimulated the production of c-type cytochrome and e-pili, facilitating direct interspecies electron transfer (DIET) between norank-f-SC-I-84 and Methanobacterium. This study provided new solutions for improving methane production and offered insights into the mechanism of enhanced methanogenesis of AD in the presence of MIL-88A(Fe). [Display omitted] • MIL-88A(Fe) is a promising Fe-MOF to enhance methanogenic activities. • MIL-88A(Fe) increased Cyt-C and e-pili levels and facilitated electron transfer. • MIL-88A(Fe) stimulated gene expression for acetate-oxidation and CO 2 -reduction. • MIL-88A(Fe) mediated DIET and optimized the electron transfer metabolic pathway. [ABSTRACT FROM AUTHOR]

This study carried out the anaerobic digestion of recycled paper mill wastewater (RPMW) in a high-rate novel anaerobic baffled reactor. The parametric interaction between influent chemical oxygen demand (CODin) and hydraulic retention time (HRT) was modeled, and process responses were optimized by the response surface methodology (RSM) using a three-level factorial design. The results showed that the optimal condition was determined at CODin of 4,000 mg/L and HRT of 2 days and predicted values for COD removal, biochemical oxygen demand (BOD) removal, lignin removal, CH4 content, and CH4 production were found to be 94%, 98%, 68%, 85%, and 20.8 L CH4/d, respectively. According to the statistical analysis of the RSM, all models were significant with very low probability values (from 0.0045 to

Forty percent of the food generated in Canada is wasted, making it the most significant component of municipal solid waste. Food waste characteristics, such as high moisture and oil content, and variable composition, make it difficult to manage with conventional waste treatment methods. Part of food waste is disposed of in landfills, generating greenhouse gases and significantly increasing the carbon footprint. Various treatment methods such as composting and anaerobic digestion have been employed to treat and manage the remaining waste efficiently. This study provides an overview of the impact of composting as a food waste treatment method in Canada and paves way for the research of the usefulness of composting in addition to other food waste treatment methods such as anaerobic digestion. Average composting data for Canada was used to determine the change in the carbon footprint by the diversion of food waste using CCaLC2 software. It was determined that the overall carbon footprint of 1.38 and 1.33 mega-tons of CO2 was reduced from the composting of food waste in the years 2014 and 2016, which were approximately 18% and 20% of the total footprint of Canada municipal solid waste, respectively. The carbon footprint data collected herein were compared to the data from England, Sweden, and the USA to reveal the high effectiveness of composting in Canada. [ABSTRACT FROM AUTHOR]

The profile of microbial diversity in a NABR digesting RPMW was investigated using phylogeneticanalysis of partial 16S rRNA sequences by a neighbor-joining-tree, supported by microbial morphology analysis by SEM. The results showed that microorganism inside NABR consisted of dominant Bacillus (25 strains) and Bacterium (1 strain) which were isolated from the settled sludge at the bottom of the reactor, whilst Bacillus (2 strains), Pseudomonas (2 strain) and Chryseobacterium (2 strain) were isolated from the biofilm formed on the packing material. It revealed that the microbial community strains, function, and structure changed simultaneously throughout the reactor system. The microscopic results showed rich biofacies, while the dominant microorganisms have various morphologies in every compartment of the system. It consisted of a long rod-shaped and filamentous bacterium composed majorly of bacilli of different sizes. Although the study successfully analyzed the microbial diversity and morphology in the system, the microbial communities reported in this study were different from other similar studies. This may be caused by the application of a culture-based technique that usually provides limited information due to the number of barely cultivated or uncultured strains

Perfluorooctanoic acid (PFOA) that accumulates in wastewater and excess sludge interact with the anaerobes and deteriorate the energy recovery and pollutants removal performance in the anaerobic digestion (AD) system. However, the interaction between PFOA and microbial metabolism in the AD systems remains unclear. This study aimed to clarify the effects and mechanism of PFOA on the AD process as well as the removal pathways of PFOA in an AD system. The results showed that the methane recovery efficiency was inhibited by 7.6–19.7% with the increased PFOA concentration of 0.5–3.0 mg/L, and the specific methanogenesis activity (SMA) was inhibited by 8.6–22.3%. The electron transfer system (ETS) was inhibited by 22.1–37.3% in the PFOA-containing groups. However, extracellular polymeric substance (EPS) gradually increased due to the toxicity of PFOA, and the ratio of protein to polysaccharide shows an upward trend, which led to the formation of sludge aggregates and resistance to the toxic of PFOA. The PFOA mass balance analysis indicated that 64.2–71.6% of PFOA was removed in the AD system, and sludge adsorption was the main removal pathway, accounting for 36.1–61.2% of the removed PFOA. In addition, the anaerobes are proposed to have the potential to reduce PFOA through biochemical degradation since 10.4–28.2% of PFOA was missing in the AD system. This study provides a significant reference for the treatment of high-strength PFOA-containing wastes. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is an essential technology for wastewater management, resource recovery and biogas production, and it is considered as an efficient and reliable treatment method for many wastewaters. Operating parameters have been shown to directly affect the stability and treatment performance of AD, especially temperature. For 180 days, the AD of recycled paper mill wastewater (RPMW) was carried out in a modified anaerobic inclining-baffled (MAIB) reactor under various temperature conditions, i.e. 29 °C (low mesophilic), 37 °C (mesophilic) and 55 °C (thermophilic). It was found that total COD removal of 94, 96 and 76%, and methane yields of 0.125, 0.196 and 0.256 L CH4/g CODremoved were attained at temperatures of 29, 37 and 55 °C, respectively. Throughout the three transition periods, the pH level in the MAIB reactor fluctuated slightly within the range of 5.8–6.5 without affecting the system stability. The results concluded that thermophilic condition strongly influenced the MAIB reactor performance, leading to lower COD removal, higher methane yield and gradually recovered pH level. Highlights Novel modified anaerobic inclining-baffled (MAIB) reactor, which combines the development of attached and settled microorganisms, was operated for the treatment of recycled paper mill wastewater (RPMW).; The operational temperature intensive analysis of MAIB was investigated at thermophilic and mesophilic conditions.; The system compartmental characteristics were also analyzed and discussed.;

[Display omitted] • AD patterns in different CMs-mediated AD systems were evaluated at high pH 2. • Abundant electron-exchanging functional groups in biochar promoted maximum DIET flux. • DIET interaction types between acetate oxidizers and Methanothrix relied on added CMs. • CMs selectively induced metabolic coordination from aspect of energy/electron flux. • Functional characteristics of different CMs-mediated DIET optimized CMs selection. In this study, different carbon/metal-based conductive materials (CMs) were amended in traditional anaerobic digestion (AD) system with high hydrogen partial pressure (pH 2) to verify the operational feasibility of CMs-mediated direct interspecies electron transfer (DIET). Operational performances revealed that SCOD removal efficiencies and CH 4 production of CMs-mediated groups including GS (graphene), CTS (carbon nanotube), BS (biochar), IS (magnetite) and MS (MnO 2) were increased by 34.7 %-157.3 %, 33.0 %-154.4 %, 41.2–169.6 %, 30.7 %-146.7 % and 28.1 %-139.5 % when compared with those of control group (54.5 ± 4.1 % and 184.9 ± 12.5 mL/g·VSS). Additionally, electron transfer capacity measurement showed that the equivalent current of biochar-mediated DIET flux (7 × 10-3 A) was 102 and 109 times higher than those in magnetite-mediated and interspecies H 2 transfer (IHT) conditions due to presence of abundant electron-exchanging functional groups. Furthermore, dynamic microbiome distribution and anaerobic metabolism analysis proved that genes encoding syntrophic enzymes were highly stimulated in GS, CTS and BS while genes encoding acidogenic enzymes were more expressed in IS and MS with acetate oxidizers and Methanothrix as CMs-mediated DIET participants, suggesting that metabolic coordination of fermentative bacteria could be selectively induced to cooperate with DIETers for maintaining stable operation of each CMs-mediated AD systems in high pH 2 condition. Overall, this study could offer better understand on application strategies of carbon-based and metal-based CMs for inducing the distinct CMs-mediated DIET process, which further optimized selection basis of CMs and widened real application of CMs-mediated DIET. [ABSTRACT FROM AUTHOR]

Sugarcane ethanol production generates about 360 billion liters of vinasse, a liquid effluent with an average chemical oxygen demand of 46,000 mg/L. Vinasse still contains about 11% of the original energy from sugarcane juice, but this chemical energy is diluted. This residue, usually discarded or applied in fertigation, is a suitable substrate for anaerobic digestion (AD). Although the technology is not yet widespread—only 3% of bioethanol plants used it in Brazil in the past, most discontinuing the process—the research continues. With a biomethane potential ranging from 215 to 324 L of methane produced by kilogram of organic matter in vinasse, AD could improve the energy output of sugarcane biorefineries. At the same time, the residual digestate could still be used as an agricultural amendment or for microalgal production for further stream valorization. This review presents the current technology for ethanol production from sugarcane and describes the state of the art in vinasse AD, including technological trends, through a recent patent evaluation. It also appraises the integration of vinasse AD in an ideal sugarcane biorefinery approach. It finally discusses bottlenecks and presents possible directions for technology development and widespread adoption of this simple yet powerful approach for bioresource recovery.

Paunch contents are the recalcitrant, lignocellulose-rich, partially-digested feed present in the rumen of ruminant animals. Cattle forage in Europe is primarily from perennial and Italian ryegrasses and/or white clover, so paunch contents from forage-fed cattle in Europe is enriched in these feedstuffs. Globally, due to its underutilisation, the potential energy in cattle paunch contents annually represents an energy loss of 23,216,548,750–27,804,250,000 Megajoules (MJ) and financial loss of up to ~€800,000,000. Therefore, this review aims to describe progress made to-date in optimising sustainable energy recovery from paunch contents. Furthermore, analyses to determine the economic feasibility/potential of recovering sustainable energy from paunch contents was carried out. The primary method used to recover sustainable energy from paunch contents to-date has involved biomethane production through anaerobic digestion (AD). The major bottleneck in its utilisation through AD is its recalcitrance, resulting in build-up of fibrous material. Pre-treatments partially degrade the lignocellulose in lignocellulose-rich wastes, reducing their recalcitrance. Enzyme systems could be inexpensive and more environmentally compatible than conventional solvent pre-treatments. A potential source of enzyme systems is the rumen microbiome, whose efficiency in lignocellulose degradation is attracting significant research interest. Therefore, the application of rumen fluid (liquid derived from dewatering of paunch contents) to improve biomethane production from AD of lignocellulosic wastes is included in this review. Analysis of a study where rumen fluid was used to pre-treat paper sludge from a paper mill prior to AD for biomethane production suggested economic feasibility for CHP combustion, with potential savings of ~€11,000 annually. Meta-genomic studies of bacterial/archaeal populations have been carried out to understand their ruminal functions. However, despite their importance in degrading lignocellulose in nature, rumen fungi remain comparatively under-investigated. Further investigation of rumen microbes, their cultivation and their enzyme systems, and the role of rumen fluid in degrading lignocellulosic wastes, could provide efficient pre-treatments and co-digestion strategies to maximise biomethane yield from a range of lignocellulosic wastes. This review describes current progress in optimising sustainable energy recovery from paunch contents, and the potential of rumen fluid as a pre-treatment and co-substrate to recover sustainable energy from lignocellulosic wastes using AD.

Application of anaerobic digestion (AD) has become common in treating palm oil mill effluent in Malaysia; however, employing AD in treating the organic fraction of municipal solid waste (OFMSW), especially food waste, is still scarce. This study aims to characterize the commercial Malaysian food waste (CMFW) and determine its potential as sustainable bioenergy feedstock through biogas production. The sample was digested via the biomethane potential (BMP) test with the variation of organic loading rates (OLRs), ranging from 0.38 to 3.83 gCOD/L. day, under mesophilic conditions. The digestion process was further evaluated in continuous operation using a 6-L continuous stirred-tank reactor (CSTR). The kinetic properties of the process were also determined. It was found that the CMFW had a significant amount of chemical oxygen demand of 230 g/L and an acidic pH of 4.5 with the carbon to nitrogen (C/N) ratio at 121:1. A maximum methane composition of 81% was obtained at 1.92 gCOD/L in the BMP test with specific methane production (SMP) at 0.952 L. CH4/L.COD fed. The biogas production was well-fitted with the modified Gompertz model with R2 at 0.9983 and the maximum biogas potential production rate at Rm 0.1573 L/day, whereas in the CSTR operation, a maximum methane composition of 85% was produced at OLR 6 gCOD/L. day with the SMP of 1.13 L. CH4/L.COD fed. The CSTR system was in high stability as the pH was maintained in a range of 6.6–6.7, with an alkalinity ratio of 0.28. This study indicates the CMFW is a sustainable feedstock for biogas production in Malaysia. Toward a circular economy approach, the authorities shall introduce commercial scale CMFW AD as part of managing municipal solid waste issues in Malaysia.

The composition of waste-activated sludge (WAS) is complex, containing a large amount of harmful substances, which pose a threat to the environment and human health. The reduction and resource utilization of sludge has become a development demand in sludge treatment and disposal. Based on the technical bottlenecks in the practical application of direct anaerobic digestion technology, this study adopted two different thermal and thermal-alkali hydrolysis technologies to pretreat sludge. A pilot-scale experiment was conducted to investigate the experimental conditions, parameters, and effects of two hydrolysis technologies. This study showed that the optimal hydrolysis temperature was 70 °C, the hydrolysis effect and pH can reach equilibrium with the hydrolysis retention time was 4-8 h, and the optimal alkali concentration range was 0.0125-0.015 kg NaOH/kg dry-sludge. Thermal-alkali combination treatment greatly improved the performance of methane production, the addition of NaOH increased methane yield by 31.2% than that of 70 °C thermal hydrolysis. The average energy consumption is 75 kWh/m 3 80% water-content sludge during the experiment. This study provides a better pretreatment strategy for exploring efficient anaerobic digestion treatment technologies suitable for southern characteristic sewage sludge., Competing Interests: The authors declare there is no conflict., (© 2024 The Authors This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY-NC-ND 4.0), which permits copying and redistribution for non-commercial purposes with no derivatives, provided the original work is properly cited (http://creativecommons.org/licenses/by-nc-nd/4.0/).)

Anaerobic Digestion (AD) is one of the most widely used methods in the field of sustainable bioenergy production from various feedstock. One such feedstock is algae waste which has become an increasingly serious environmental problem. AD of algal biomass is hindered by the presence of resistant cell walls; hence a pretreatment step is usually required to decompose the cell wall structure. This study uses green algae (Enteromorpha) and anaerobic sludge as raw materials to explore the impact of autoclave (AC) pretreatment on biogas production. AC pretreatment was performed at 120 °C and 80 °C. The cumulative biogas production of the 120 °C AC pretreatment, 80 °C AC pretreatment and control group were 600 mL, 450 mL and 400 mL, respectively. The results showed that AC pretreatment improved the biodegradability of biomass as 120 °C AC pretreatment group achieved higher degradation rate of cells (95.99 %). The energy evaluation showed that the net energy ratio of the 120 °C AC pretreatment group was 1.07, indicating high overall energy gain via AD process. The experimental data is further modeled by using Modified Gompertz Model (MGM) and Logistic Function Model (LFM). To check the applicability of better model for this AD process, an Akaike Information Criteria (AIC) test was performed. AIC showed that the MGM is basically consistent with the experimental data and more reliable for prediction modeling of Enteromorpha AD. [ABSTRACT FROM AUTHOR]

Forty percent of the food generated in Canada is wasted, making it the most significant component of municipal solid waste. Food waste characteristics, such as high moisture and oil content, and variable composition, make it difficult to manage with conventional waste treatment methods. Part of food waste is disposed of in landfills, generating greenhouse gases and significantly increasing the carbon footprint. Various treatment methods such as composting and anaerobic digestion have been employed to treat and manage the remaining waste efficiently. This study provides an overview of the impact of composting as a food waste treatment method in Canada and paves way for the research of the usefulness of composting in addition to other food waste treatment methods such as anaerobic digestion. Average composting data for Canada was used to determine the change in the carbon footprint by the diversion of food waste using CCaLC2 software. It was determined that the overall carbon footprint of 1.38 and 1.33 mega-tons of CO2 was reduced from the composting of food waste in the years 2014 and 2016, which were approximately 18% and 20% of the total footprint of Canada municipal solid waste, respectively. The carbon footprint data collected herein were compared to the data from England, Sweden, and the USA to reveal the high effectiveness of composting in Canada.

Anaerobic co-digestion offers a promising approach to enhancing biogas production from surplus by-products of wastewater treatment plants (WWTPs) and agricultural waste while reducing environmental negative impact. This study investigated the co-digestion of anaerobic thickened sewage sludge (ATSS) and rice straw (RS) under mesophilic conditions (35 ± 1 °C). In phase 1 of the experiment, lab-scale reactors with varying MRs of RS (0 %, 4 %, 8 %, and 16 % based on sludge weight) were employed to determine the optimal MR for maximizing biogas quantity and methane content. Phase 2 examined the impact of mechanical mixing (MM) on biogas production, pathogen and trace element reduction, and the calorific value (CV) of the co-digested mixture compared to the digested thickened sludge (DTS) and RS individually to assess the potential energy of co-digestion. Results revealed that the 8 % MR yielded the highest biogas volume, approximately 2.5 times that of the DTS alone, with methane and carbon dioxide contents within the typical ranges. MM in phase 2 further increased biogas volume by 2.8 times compared to DTS. The CV of the co-digested mixture was 24,937 kJ/kg and 21,929 kJ/kg for the DTS. Pathogens were effectively eliminated, and trace elements remained below the permissible limits. The 8 % MR with MM was identified as the optimal MR that produces the highest biogas quantity before reaching the turning point. Moreover, co-digestion at this MR enhanced the CV of ATSS by 14 %. [ABSTRACT FROM AUTHOR]

Anaerobic digestion of kitchen waste faces the challenge of frequent composition variation and rapid digester acidification due to its highly degradable nature. Considering this challenge, one year long pilot scale anaerobic digestion study was conducted in the anaerobic digester of 25 ​m3/day capacity with seasonal kitchen waste (fruits and vegetable waste). The seasonal variation in kitchen waste content was studied by dividing a year into six seasons (each season comprising 60 days), namely, spring, summer, monsoon, autumn, early winter, and prevernal winter. Considering all the properties of kitchen waste, the anaerobic digestion experiment was conducted with the organic loading rate (OLR) of 0.60–0.72 ​kg VS/m3/day. The specific biogas production for all the seasons was found to be 0.56–0.68 ​m3/kg VS, with the volumetric methane content of 54.3–62.8%. The average seasonal specific methane production was observed in the range of 0.30–0.41 ​m3/kg VS. The anaerobic digestion conversion efficiency of 55.3–67.0% was found for the anaerobic digestion of the wastes. The problem of the rapid acidification of kitchen waste has been rectified with the addition of protein-rich de-oiled pongamia cake in place of alkali chemicals. The economic analysis of kitchen waste based anaerobic digestion showed the maximum economic benefits of biogas production as INR 30,783 for its utilization as LPG and INR 37,777 for its utilization as electricity for the summer season compared to all other seasons. The extra economic benefits earned by the utilization of the digested slurry as organic manure, as it contains a good amount of nitrogen (N) 2.3–2.6%, phosphorus (P) 0.6–0.9%, and potassium (K) 0.7–1.1%.

Hydrothermal carbonisation (HTC) can be integrated with anaerobic digestion (AD) for the treatment of digestate, resulting in a solid hydrochar or bio-coal and a process water, which can be recirculated back into AD to produce biogas. The properties of digestate-derived hydrochars do not lend themselves to producing high quality bio-coal and blending with lignocellulosic feedstocks can improve its properties. This study investigates the co-processing of sewage sludge (SS) digestate with three lignocellulosic biomass (grass, privet hedge, and woodchip). The calorific value of the resulting bio-coal is increased following co-processing, although feedstock interactions result in non-additive behaviour. The largest increase in calorific value was observed for co-processing with woodchip. There is evidence for non-additive partitioning of metals during co-processing resulting in only moderate improvements in ash chemistry during combustion. Co-processing also effects the composition of process waters, influencing the potential for biogas production. Experimental biomethane potential (BMP) tests indicate that grass clippings are the most suitable co-feedstock for maintaining both calorific value and biogas production. However, above 200 °C, BMP yields appear to decrease, suggesting the process water may become more inhibitory. Co-processing with wood waste and privet hedge produce the higher CV bio-coal but significantly reduced BMP.

Kinetic models which can express the behaviors of hydrolysis and biogas generation more precisely than the conventional models were developed. The developed models were evaluated based on the experimental data of six batch reactors. Anaerobic digestion test was co-digestion of food and vegetable waste with inoculating horse dung by 15% of the total wet weight, at the temperature of 37oC. For hydrolysis, the modified model was developed from an original first-order kinetic model. The modified first-order kinetic model was proved to be better than the original one with the hydrolysis rate constant in the range of 0.22-0.34/day and hydrolyzable rate of 0.80 to 0.84. Kinetics of carbon dioxide and methane were developed from a current potential model. The comparison between experimental data and modeling values had the high correlation of determination (0.9918-0.9998) and low root mean square errors (0.08-4.51) indicating the feasibility of the developed model. In which, the evolution of methane showed the rate constant in the range of 0.031-0.039/day. The carbon dioxide from fermentation accounted for 12-44% of the total observed carbon dioxide. Thus, separation of fermentation and methanogenesis by various reactors may reduce the price of methane enrichment significantly. There was a lag time between methanogenesis and fermentation in reactors (λ = 7-11 days). Also, the biogas yield was in the range of 431.6-596.9 Nml/g-VS with the CH4 concentration of 56.2-67.5%. The best methane yield (393.7 Nml/g-VS) was in a reactor with food waste to the vegetable waste ratio by 1.8:1 (wet basis) and C/N ratio by 25.4.

Organic waste mostly comes from food waste, which has characteristics of high concentrations of nitrogen and fat, and high humidity. Domestic waste in Indonesia has a high organic content, which is suitable for anaerobic conditions. Waste oil and fat can be used as co-substrates and are helpful in yielding biogas in an anaerobic digestion (AD) process. The aim of this research is to analyze the performance of a food waste dry anaerobic digestion reactor after the addition of fat oil and grease (FOG) waste. The research was conducted using a semi-continuous stirred tank reactor (SCSTR) with an active volume of 400 L, operated at an average temperature of 27.8±1.07oC. Two experimental scenarios were performed, using varying types of food waste, food waste with cow dung as substrate, and FOG waste as co-substrate. The experiment was conducted using an Organic Loading Rate (OLR) of approximately 10 kg VS/m3, with a constant mixing intensity of 30 rpm. The results show that there was a significant difference between the input of food waste substrate with and without the addition of FOG (p

Anaerobic digestion (AD) is an economical and effective method to treat sludge. AD with several pretreatments is the prior process to treat surplus sludge for a wastewater treatment plant. During a sludge-treatment process, various methanogens play their specific role in each sludge-processing stage where different methanogens predominate. Therefore, an expert in the shift of methanogen community could facilitate the workers in a plant to understand the efficiency of the sludge-treatment process. In this paper, a membership-fusing model is established to characterize the shift of methanogen community in a three-stage sludge-treatment process. The introduction of fuzzy sets clarifies the vagueness of the methanogen community structure between two processing stages. Dempster–Shafer (DS) evidence theory effectively alleviates the data error generated among paralleling samples. The accuracy of the model was verified, and the result shows the model could clearly distinguish the methanogen community structure of the three stages and make accurate judgment on the processing stage affiliation. The reliability of the model in dealing with different numbers of conflict data was proved and the experiment indicates the model could make a reliable judgment on the processing stage affiliation by reasonably fusing the interference data. [ABSTRACT FROM AUTHOR]

The anaerobic digestion plant studied in this paper is one of the first full-scale plants using olive oil by-products. This is a two-stage plant with a power of 100 kWe. Two tests were performed: the first on olive pulp and pitted pomace and the second on biomass consisting of 10% crushed cereal. In both cycles, the retention time was 40 days. The production of biogas was between 51 and 52 m3/h, with limited fluctuations. The specific production values of biogas indicate that a volume of biogas greater than 1 m3/kg was produced in both tests. The produced biogas had a methane percentage of about 60% and the specific production (over total volatile solids, TVS) of methane was of the order of 0.70 m3methane/kgTVS. FOS/Alk (ratio between volatile organic acids and alkalinity) was always lower than 1 and tended to decrease in the second digester, indicating a stable methanogenic phase and the proper working of the methanogenic bacteria in the second reactor. The concentration of incoming biomass TPC (total polyphenols content) can vary significantly, due to the seasonality of production or inadequate storage conditions, but all measured values of TPC, between 1840 and 3040 mg gallic acid kg−1, are considered toxic both for acidogenic and methanogenic bacteria. By contrast, during the process the polyphenols decreased to the minimum value at the end of the acidogenic phase, biogas production did not stop, and the methane percentage was high.

The increasing demand on energy and the constraints on environmental aspects motivate the research on municipal solid waste to be an environmentally friendly source of renewable energy. Therefor using the organic fraction of municipal solid household waste in an aerobic digester to produce biogas and a digestate which can be used safely as fertilizer. In this study three reactors of two liter volume are used to investigate the effect of total solid content (10%, 15%, 20%) and pH on the produced amount of biogas. The results revealed that lower percentage of solid content yields the highest amount of biogas and the pH below 6.0 will inhibit the biogas production. The percentage of methane from the 10% reactor was 50.2 % of the gas production.

The effect of biochar addition on the anaerobic digestion (AD) of food waste was evaluated. From the five biochars tested, Fe, Co, Ni, and Mn were leached in very small quantities (

Anaerobic digestion (AD) can bring benefits in terms of effective management of organic waste, recovery of nutrients and energy recovery, and is consistent with circular economy principles. AD has been promoted and implemented worldwide, but at widely differing scales, influenced by the availability and location of feedstocks. In developing countries, feedstock arises from small- to medium-scale agriculture and agro-processing operations, as well as from household and municipal waste. Biogas produced from residues from agro-processing facilities may be used for on-site heat and power, but the lack of a gas and electricity grid infrastructure can limit opportunities to distribute gas or generated electricity to wider users. This paper presents the findings of the first study to consider novel technologies for small-scale and low-cost biogas clean-up into biomethane, and compression into small bottles, suitable as a clean cooking fuel. The paper reports on the initial evaluation of biomethane for cooking in Ghana and Uganda.

Changes in chemical composition and structure of corncob lignocellulosic biomass were investigated relative to pretreatment and anaerobic digestion. The pretreatment involved 1% and 3% sodium hydroxide, 3% and 7% sulphuric acid, as well as medium and high temperature extrusion (in 110°C and in the range from 140°C to 160°C). The chemical components content was studied using a gravimetric method, whereas structure and relations between the carbohydrate and lignin participation were investigated using Fourier transform infrared spectroscopy. It was determined that the chemical treatment, both acidic and alkaline, changed the chemical composition of corncob more significantly than the extrusion. Alkaline pretreatment contributed to significant delignification, while acidic pretreatment reduced the share of hemicelluloses and increased the proportion of lignin, the so-called "pseudolignin". The composition of corncob (control and after pre-treatment) was changed after anaerobic digestion, i.e., a decreased carbohydrate substance content and a significantly increased lignin content. FTIR analysis showed changes in their structure. Although the control corncob differed from that processed by various pretreatment methods, the chemical composition of the digested pulp obtained from them was similar. The NaOH pretreatment was judged to be the preferred method for delignification of the raw material. [ABSTRACT FROM AUTHOR]

• CNT worsened ammonia inhibition when TAN was above 2500 mg N/L. • Potassium transport was interrupted by the interactive effects of CNT and ammonia. • CNT formed potassium channel and dispatched proton motivate force. • CNT affected intercellular ATP level and reduced microbial detoxification activity. • Enhanced secretion of bound EPS was related to the presence of ammonia and CNT. Carbon-based materials are promising in improving the performance and stability of anaerobic digestion (AD). However, it is not clear if carbon-based materials would have any interaction with ammonia on AD performance, especially when ammonia is above inhibition level. This study aims to explore the effects of ammonia on carbon nanotube assisted AD reactors. Methanogenic performance, intracellular energy production, potassium transport activity as well as extracellular polymeric substance (EPS) changes were investigated. The results show that the presence of CNT may mitigate or worsen the ammonia inhibition depending on the total ammonia nitrogen (TAN) concentration. Further investigation found that potassium transportation process of the culture was disturbed with the presence of CNT, which dispatched the proton motive force. As a result, the intracellular energy level reduced, and the microbial detoxification capability decreased. TAN exhibited a strong positive correlation with microbes' detoxification activity, and CNT concentration was positively correlated with polysaccharide which created a physical structure to protect cell membrane. [ABSTRACT FROM AUTHOR]

Potential of nutrient recovery as struvite (NH 4 MgPO 4 ·6H 2 O) with sole waste activated sludge (WAS) of a conventional activated sludge treatment plant has been investigated using computational modelling supported by laboratory experiments. Predicted key outcomes using Bio-Win modelling tool indicated that anaerobic digestion of WAS could produce a supernatant consisting of 300–420 mg/L ammonia , 100–200 mg/L phosphate and 12–30 mg/L magnesium and laboratory experiments confirmed that struvite can be precipitated using these nutrient concentrations. Study of sludge retention time (SRT 15–30 days) and temperature (34–38 °C) on the nutrient concentrations of digester supernatant revealed that ammonia and phosphate concentrations of supernatant increased with SRT and temperature. The removal efficiencies of magnesium and phosphate in struvite precipitation reactions were 91% and 50% respectively, indicating that magnesium addition is required for extra phosphate removal in the digester supernatant. It was found that a substantial excess ammoniac nitrogen would remain and need alternative method to remove and recover, if sustainability is to be achieved. The outcome of this study confirms that WAS from conventional wastewater treatment plants such as Loganholme can be successfully upgraded towards a nutrient recovery facility by optimizing anaerobic digester parameters. Modelling is a suitable first approach for planning and decision-making. [ABSTRACT FROM AUTHOR]

The present study aimed to determine the effect of a 17.6 mT static magnetic field (SMF) on the efficiency of anaerobic digestion (AD) of municipal sewage sludge (MSS). The SMF had a significant impact on methane (CH4) production efficiency, the levels of fermentation rate (ηFMSS) vs. removal rate (ηVS), and the structure of the anaerobic bacteria consortium, but it did not affect cumulative biogas production. The highest CH4 yield (431 ± 22 dm3CH4/kgVS) and the highest methane content in the biogas (66.1% ± 1.9%) were found in the variant in which the SMF exposure time was 144 min/day. This variant also produced the highest ηFMSS and ηVS values, reaching 73.8% ± 2.3% and ηVS 36.9% ± 1.6%, respectively. Longer anaerobic sludge retention time in the SMF area significantly decreased AD efficiency and caused a significant reduction in the number of methanogens in the anaerobic bacteria community. The lowest values were observed for SMF exposure time of 432 min/day, which produced only 54.8 ± 1.9% CH4 in the biogas. A pronounced reduction was recorded in the Archaea (ARC915) and Methanosaeta (MX825) populations in the anaerobic sludge, i.e., to 20% ± 11% and 6% ± 2%, respectively.

Conductive materials have been demonstrated to enhance sludge methanogenesis, but few researches have concentrated on the interaction among conductive materials, microorganisms and their immediate living environment. In this study, Fenton iron mud with a high abundance of Fe(III) was recycled and applied in anaerobic reactors to promote anaerobic digestion (AD) process. The results show that the primary content of extracellular polymeric substances (EPS) such as polysaccharides and proteins increased significantly, possibly promoting microbial aggregation. Furthermore, with the increment of redox mediators including humic substances in EPS and Fe(III) introduced by Fenton iron mud, the direct interspecies electron transfer (DIET) between methanogens and interacting bacteria could be accelerated, which enhanced the rate of methanogenesis in anaerobic digestion (35.21 ± 4.53% increase compared to the control). The further analysis of the anaerobic microbial community confirmed the fact that Fenton iron mud enriched functional microorganisms, such as the abundance of CO 2 -reducing (e.g. Chloroflexi) and Fe(III)-reducing bacteria (e.g., Tepidimicrobium), thereby expediting the electron transfer reaction in the AD process via microbial DIET and dissimilatory iron reduction (DIR). This work will make it possible for using the recycled hazardous material – Fenton iron mud to improve the performance of anaerobic granular sludge during methanogenesis. A sustainable strategy for reusing Fenton iron mud environmentally friendly and the potential mechanisms on the immediate living environment of anaerobic microorganisms. [Display omitted] • Using recycled hazardous material – Fenton iron mud to improve the AD process. • Fenton iron mud increased the methane production efficiency. • More electroactive substance in EPS with Fenton iron mud dosing. • Fenton iron mud possibly expedited electron transfer through microbial DIET. • Fenton iron mud might promote DIR among the Fe(III)-reducing microorganisms. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrothermal carbonization (HTC) enhances fuel ratio and calorific value in hydrochar. • Hydrolysis reactions during HTC differentiate it from other thermochemical processes. • Microalgal hydrochar has applications in energy, environment and agricultural fields. • CEC and oxygenated functional groups promote adsorption capacity of algal hydrochar. • Integrating HTC with AD can lead to self-sustaining energy generation strategy. Exploitation of microalgal biomass as a valuable resource is hindered by the challenges associated with high downstream processing costs, including biomass harvesting, drying, and product extraction. Direct utilization of microalgae as a solid fuel source, soil conditioner, capacitor or adsorbent material raises environmental concerns. Hydrothermal carbonization (HTC) is a highly efficient and promising technology for microalgal biomass conversion. This comprehensive review provides an in-depth understanding of the HTC reaction mechanisms involved in microalgal hydrochar production, shedding light on the underlying processes and factors affecting the quality of hydrochar. HTC has the potential to improve fixed carbon content, thermal stability and nutrient availability in the resulting hydrochar. Furthermore, this review explores the integration of HTC with anaerobic digestion (AD) to establish a circular bioeconomy, thereby promoting sustainability in energy generation. The synergistic combination offers a promising approach for the efficient utilization of microalgal biomass, where hydrochar can serve as a renewable energy source while the aqueous fraction can be utilized as a nutrient-rich feedstock for biogas production. By highlighting the potential benefits and futuristic directives associated with microalgal biomass valorisation through HTC, this review aims to contribute to the development of sustainable waste management strategies for recovery of value-added compounds from microalgae. Ultimately, this review strives to foster the transition towards a more environmentally friendly and resource-efficient bioeconomy. [ABSTRACT FROM AUTHOR]

One of the greatest challenges facing the societies now and in the future is the reduction of green house gas emissions and thus preventing the climate change. It is therefore important to replace fossil fuels with renewable sources, such as biogas. Biogas can be produced from various organic waste streams or as a byproduct from industrial processes. Beside energy production, the degradation of organic waste through anaerobic digestion offers other advantages, such as the prevention of odor release and the decrease of pathogens. Moreover, the nutrient rich digested residues can be utilized as fertilizer for recycling the nutrients back to the fields. However, the amount of organic materials currently available for biogas production is limited and new substrates as well as new effective technologies are therefore needed to facilitate the growth of the biogas industry all over the world. Hence, major developments have been made during the last decades regarding the utilization of lignocellulosic biomass, the development of high rate systems, and the application of membrane technologies within the anaerobic digestion process in order to overcome the shortcomings encountered. The degradation of organic material requires a synchronized action of different groups of microorganisms with different metabolic capacities. Recent developments in molecular biology techniques have provided the research community with a valuable tool for improved understanding of this complex microbiological system, which in turn could help optimize and control the process in an effective way in the future.

Anaerobic digestion (AD) is an economical and effective method to treat sludge. AD with several pretreatments is the prior process to treat surplus sludge for a wastewater treatment plant. During a sludge-treatment process, various methanogens play their specific role in each sludge-processing stage where different methanogens predominate. Therefore, an expert in the shift of methanogen community could facilitate the workers in a plant to understand the efficiency of the sludge-treatment process. In this paper, a membership-fusing model is established to characterize the shift of methanogen community in a three-stage sludge-treatment process. The introduction of fuzzy sets clarifies the vagueness of the methanogen community structure between two processing stages. Dempster–Shafer (DS) evidence theory effectively alleviates the data error generated among paralleling samples. The accuracy of the model was verified, and the result shows the model could clearly distinguish the methanogen community structure of the three stages and make accurate judgment on the processing stage affiliation. The reliability of the model in dealing with different numbers of conflict data was proved and the experiment indicates the model could make a reliable judgment on the processing stage affiliation by reasonably fusing the interference data.

The growing global energy demand pushes towards higher share of renewable energy sources. Biomass energy is one of the alternative renewable sources, whereas municipal solid waste (MSW) is one of the important renewable resources estimated in millions of tons per year, about 50% of it is organic. This amount can be treated and used for methane production in anaerobic digesters. The objective of this study is to figure out the effect of temperature and pH on the methane production in laboratory scale batch reactor of 2L size. Experiments were conducted at 35°C, 45°C, 55°C, 65°C, and pH was controlled to be close to 7.0. It was found that mesophilic conditions at 35°C, yielded the highest biogas production, and the lowest production was at 65°C. pH below 6.0 inhibited production. The biogas share was about 45%, which is encouraging compared to other published results.

In this study, a simulation was carried out using BioWin 3.1 to test the capability of the software to predict the biogas potential for two different anaerobic systems. The two scenarios included: (1) a laboratory-scale batch reactor; and (2) an industrial-scale anaerobic continuous lagoon digester. The measured data related to the operating conditions, the reactor design parameters and the chemical properties of influent wastewater were entered into BioWin. A sensitivity analysis was carried out to identify the sensitivity of the most important default parameters in the software’s models. BioWin was then calibrated by matching the predicted data with measured data and used to simulate other parameters that were unmeasured or deemed uncertain. In addition, statistical analyses were carried out using evaluation indices, such as the coefficient of determination (R-squared), the correlation coefficient (r) and its significance (p-value), the general standard deviation (SD) and the Willmott index of agreement, to evaluate the agreement between the software prediction and the measured data. The results have shown that after calibration, BioWin can be used reliably to simulate both small-scale batch reactors and industrial-scale digesters with a mean absolute percentage error (MAPE) of less than 10% and very good values of the indexes. Furthermore, by changing the default parameters in BioWin, which is a way of calibrating the models in the software, as well, this may provide information about the performance of the digester. Furthermore, the results of this study showed there may be an over estimation for biogas generated from industrial-scale digesters. More sophisticated analytical devices may be required for reliable measurements of biogas quality and quantity.

Abstract In this paper, biogas recovery from organic fraction of municipal solid waste for the purpose of electricity generation is presented with the objective of determining its economic and environmental benefits for the city of Ibadan, Nigeria. Two methods of biogas recovery technologies (i.e., anaerobic digestion and landfill gas recovery technologies) were considered. The environmental impact was performed using life cycle assessment technique while the economic assessment was determined using total life cycle cost, levelised cost of energy, net present value, internal rate of return and payback period. Sensitivity analysis was conducted to investigate the influence electricity generation efficiency, capacity factor, per capita waste generation rate, discount rate, population growth rate and waste collection efficiency on the economic viability of the two technologies. Some of the results indicated that in a span of 20 years (i.e., 2017–2036), the waste generation potential of the city of Ibadan was estimated between 477,001 and 966,897 tons. The methane yield for anaerobic digestion and landfill gas recovery technologies were determined to be about (104.66–212.15) x 106 m3/yr and (22.65–127.65) x 106 m3/yr, respectively. Also, the electricity generation potential ranged between 321.73 and 652.15 Gigawatt-hour for anaerobic digestion and 63.25–436.18 Gigawatt-hour for landfill gas recovery technologies. The economic indicators showed that both technologies are economically viable as they presented positive net present values. The net present value for anaerobic digestion was 834.12 million US dollar while that of landfill gas recovery was 489.26 million US dollar. The levelised cost of electricity generation was between 0.0681 and 0.0336 US dollar per kilowatt-hour for anaerobic digestion technology while it ranged from 0.2411 to 0.0350 US dollar per kilowatt hour for landfill gas recovery technology. The payback period, internal return and the total life cycle cost were 5 years, 19.3% and 413.68 million US dollar for the anaerobic digestion and 7 years, 23.4% and 288.05 million US dollar for landfill gas recovery technology. This paper intends to serve as first-hand technical information to potential investors, government agencies, policy makers and potential non-governmental organisations to enhance optimal investment in biogas to energy technologies in Nigeria. Highlights • Economic & environmental benefits of biogas recovery are conducted for Ibadan city. • Sensitivity analysis are conducted on some parameters to understand biogas recovery. • The results reveal that the technologies are technically and economically viable. • The LCOE from waste ranges between 0.0681 and 0.0336 USD/kWh for AD technology. • Also the cost ranges from 0.2411 to 0.0350 USD/kWh for LFGR technology. [ABSTRACT FROM AUTHOR]