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The capacity of a heat-treated sludge (HTS) to produce hydrogen from the mono- and co-digestion of corn (NW, pH 13.1) and brewery (BW, pH 3.8) wastewater was evaluated. The co-digestion of NW and BW was conducted with ratios (NW/BW) from 40/60 to 80/20 (vol/vol) at pH 6 and under different initial pH values (from 5.8 to 12.3) according to the substrates mixtures. With the initial pH adjusted to 6, the highest production (302 mL) occurred for the mono-digestion of NW, but hydrogen was produced in all incubations. For incubations under variable pH values, the highest hydrogen production was obtained with the ratio 60/40 (270 mL), followed by the ratio 65/35 (260 mL) with pH values of 10.8 and 10.4, respectively. The initial pH influenced the kinetic parameters, especially on maximum production and lag phase. For the ratio 60/40, with an alkaline pH value (10.4), the lag phase was delayed up to 122 h, but the highest volume of hydrogen was obtained with this condition. The Clostridium genus, present in all samples, could be associated as the main responsible for hydrogen production. Besides, the presence of Burkholderia genus, previously related to hydrogen production, was identified as the main involved in the culture at pH 10.8.

Anaerobic digestion (AD) under psychrophilic temperature has only recently garnered deserved attention. In major parts of Europe, USA, Canada and Australia, climatic conditions are more suited for psychrophilic (20 ℃) rather than mesophilic (35 - 37 ℃) and thermophilic (55 - 60 ℃) AD. Low temperature has adverse effects on important cellular processes which may render the cell biology inactive. Moreover, cold climate can also alter the physical and chemical properties of wastewater, thereby reducing the availability of substrate to microbes. Hence, the use of low temperature acclimated microbial biomass could overcome thermodynamic constraints and carry out flexible structural and conformational changes to proteins, membrane lipid composition, expression of cold-adapted enzymes through genotypic and phenotypic variations. Reduction in organic loading rate is beneficial to methane production under low temperatures. Moreover, modification in the design of existing reactors and the use of hybrid reactors have already demonstrated improved methane generation in the lab-scale. This review also discusses some novel strategies such as direct interspecies electron transfer (DIET), co-digestion of substrate, bioaugmentation, and bioelectrochemical system assisted AD which present promising prospects. While DIET can facilitate syntrophic electron exchange in diverse microbes, the addition of organic-rich co-substrate can help in maintaining suitable C/N ratio in the anaerobic digester which subsequently can enhance methane generation. Bioaugmentation with psychrophilic strains could reduce start-up time and ensure daily stable performance for wastewater treatment facilities at low temperatures. In addition to the technical discussion, the economic assessment and future outlook on psychrophilic AD are also highlighted.

Anaerobic digestion is a well-established technology for energy production and to diminish the environmental impact of different types of organic residues, which are mainly produced from human activities (processing food) but also from other recent activities related to energy generation processes (biofuel production). In the present study, mango organic residues: mango peel (MP) and mango seed (MS), and microalgal residue biomass (MRB) were co-digested in different proportions using a mixture design. The optimized mixture proportions of 60:20:20% of MP, MS and MRB, respectively, were determined by applying the simplex-centroid method to reach the highest biochemical methane potential (BMP); additionally, the mixture with the lowest BMP was selected (40:20:40%). The effects of thermal, physical and biological pretreatments of the selected mixtures were evaluated in order to improve its BMP. However, any pretreatment showed an improvement for the mixture 60:20:20, whereas the mixture 40:20:40 achieved an increment of 160.1, 72.5 and 96.4%, when the substrates were pretreated by thermal, physical and biological, respectively. The mixture optimization of these substrates shows an alternative way to reduce the environmental impact, due to their potential use in co-digestion process for biogas production.

Co-digestion is a well-established strategy to maximise the capacity of anaerobic digestion in wastewater treatment plants (WWTPs). Many tools have been developed to optimise the blend composition. However, the logistics associated with each component of the blend remain a relatively unexplored field, which can yield significant planning challenges. In this paper, an ant colony optimisation based approach is proposed to address these challenges. The proposed algorithm maximises an objective function composed of a first term related to the quality of the sludge and a second term related to the distance between the sludge generator and the anaerobic co-digester. The algorithm successfully optimises the blend composition by considering the related logistics, achieving an optimum blend with an approximately 18% volume of co-substrate. The approach presented here has been used to plan co-digestion using real data from an actual sanitation network composed of 13 WWTPs in the area of the Besos river basin in Catalonia, and an optimised co-digestion planning strategy with a waste management cost reduction of 77% was obtained

Anaerobic co-digestion (AcoD) of grease trap waste (GTW) and sewage sludge (SS) is an attractive management option for GTW valorisation and the transition to energy-neutral wastewater treatment plants (WWTPs). The main constraints that limit the direct use of GTW as a co-substrate in WWTP anaerobic digesters are the high content of non-disabled materials (floating plastics and fibres) and the low anaerobic biodegradability rates. This study assessed a single-step alkali and sieving pre-treatment of GTW at a low temperature (

This study investigated the performance of anaerobic co-digestion (AcoD) of pig manure and food waste on the reduction of antibiotic resistomes under wet and dry AcoD conditions. High-throughput quantitative PCR technology was utilized for a comprehensive assessment of the performances of the two processes. The results show that dry AcoD with a total solids (TS) content of 20% effectively reduced total antibiotic resistance genes (ARGs) by 1.24 log copies/g wet sample, while only 0.54 log copies/g wet sample was reduced in wet AcoD with a TS content of 5%. Dry AcoD was more efficient in reduction of aminoglycosides, multidrug and sulfonamide resistance genes compared with the reduction of other classes of ARGs. Dry AcoD caused a significant reduction of ARGs with resistance mechanisms of efflux pump and antibiotic deactivation. In contrast, there was no obvious difference in reductions of ARGs with different resistance mechanisms in wet AcoD. Network analysis showed that ARGs were significantly correlated with mobile genetic elements (MGEs) (Spearman's r 0.8, P 0.05), as well as microbial communities. Enrichment of ARGs and MGEs was found at the early period of AcoD processes, indicating some ARGs and MGEs increased during the hydrolysis and acidogenesis stages. But after a long retention time, their abundances were effectively reduced by dry AcoD in the subsequent stages.

The present work demonstrates the co-digestion of Used Disposable Nappies (DN) hydrolysate and Expired Food Products (EFP) at 60/40 (v/v) ratio in a two-stage pilot-scale mesophilic (37 °C) anaerobic system, in comparison with previously published data obtained from lab-scale experiments. The aim of the study was to validate the scale-up simulation of the lab experimentation and to evaluate the efficiency of the pilot-scale system. The operational conditions (acidogenic reactor: constant pH 5.5, HRT 2 d, and methanogenic reactor: HRT 20 d) were selected with respect to lab-scale results. The pilot-system succeeded a 75% COD removal, 0.63 ± 0.06 LCH4/LReactor.d and 0.37 ± 0.09 LH2/LReactor.d. The daily obtained gaseous biofuels’ yields correspond to 45.7 MJ of energy, which is 2.85 times higher than the energy needed for the operation of the equipment. It is estimated that the pilot-stage system converted 73% of the chemical energy of the feed materials to gaseous biofuels. Negligible differences between the two scales of the system were recorded, and the results are promising for the development of a full-scale process that would valorize these specific waste streams.

The disposal of large quantities of tobacco stalks and animal manures generated annually is among the serious challenges faced in China, especially the former, as its toxic composition (nicotine) can induce the risk of healthy impairment during tradition treatment process. Anaerobic digestion (AD) may be an efficient technique for tobacco stalks. Nevertheless, the impact of nicotine in tobacco stalks upon AD is still unclear so far. Thus, a simulated AD experiment using glucose with different nicotine concentrations was implemented, suggesting a nicotine concentration of more than 4% (w/w) could inhibit AD. The nicotine component in tobacco stalks would not be an inhibitor on AD because its content was far below 4%. Meanwhile, in order to efficiently treat abundant tobacco stalks and manure wastes at the same time, untreated and alkaline hydrogen peroxide (AHP)-pretreated tobacco stalks were co-digested with three typical manures, including pig manure (PM), chicken manure (CM), and dairy manure (DM), to investigate their digestion performance. Co-digestion of pretreated tobacco stalks and PM at 1:4 ratio exhibited the highest methane production of 397.2 mL/g VS and had a synergistic effect. This study provides valuable guidance for simultaneously converting these two wastes in future AD applications.

Dry anaerobic digestion (AD) has advantages over wet AD in treating high-solid organic wastes like livestock and food wastes, but an elevated total solids (TS) content would affect the AD performances. In this study, methane production of digesters co-digesting pig manure (PM) and food waste (FW) at different TS contents (R1, TS 5%; R2, TS 10%; R3, TS 15%; and R4, TS 20%) was assessed. The results showed the specific methane yield had no significant difference with the increase of TS contents from 5% to 15% (278.8-291.7 NmL/g VSadded), while it was reduced at a 20% TS content (259.8 NmL/g VSadded). Two peaks of total volatile fatty acids and daily methane production were observed in the high-solid digesters (R2-R4), while only one peak occurred in wet AD (R1). A new kinetics model was developed to describe the two-peak methane production behavior at high TS contents. The analysis on the microbial community structure clearly showed the different evolutions of methanogenic pathways in low and high solids content systems. In dry AD (R4), there was a general shifting from the acetoclastic pathway, to mixotrophic pathway and hydrogenotrophic pathway, with the dominance of mixotrophic and hydrogenotrophic methanogens.

Using high-strength wastes, such as grease trap waste mixture (GTWM) from multiple commercial facilities, as a co-substrate in anaerobic digestion can contribute to a significant increase in methane production. However, challenges such as long chain fatty acids (LCFAs) accumulation, sludge flotation, washout and scum formation can lead to digester failure. In this study, the optimal operating condition to achieve the highest methane production from an anaerobic, semi-continuous flow, mesophilic co-digester at a solids retention time of 20 days was determined. The ratio of GTWM/sludge was increased based on volatile solids (VS) concentration from 10% to 50% in 10% increments. A 40% GTWM/sludge ratio was determined to be optimum in which up to 22%, 200% and 68% improvements in VS removal, daily biogas production and specific methane production, respectively, were observed with respect to control utilizing sludge only. Beyond a 40% GTWM/sludge, the anaerobic co-digester experienced failure and addition of biochar to mitigate LCFA inhibition to failing co-digester could not recover the process. Digester LCFA concentrations were also measured during stable and unstable digester operations.

Process instability with consecutive low methane production are common challenges of the anaerobic digestion (AD) of municipal wastes. In the present study, the co-digestion of sewage sludge and municipal biopulp was investigated at batch and continuously fed digesters. At batch tests, the highest methane yield for co-digestion (467 ± 17 mLCH4/gVS) was achieved when biopulp contributed to 80% of organic matter content and sludge the remaining 20%. At continuous mode operation, co-digestion achieved 0.91 ± 0.11 L/(L·d) methane productivity, while mono-digestion of sludge achieved 0.62 ± 0.05 L/(L·d). Potassium inhibition was investigated at the most efficient co-digestion scenario and was found that the half maximal inhibitory concentration (IC50) occurred at 8 g-K+/L. Subsequently, the effect of K+ was investigated at different scenarios at continuous operation. Simulations based on BioModel described the inhibitory effect of K+ by introducing non-competitive inhibition of methanogens. Simulation results confirmed the strongly inhibitory effect of potassium to the AD process.

The effect of co-digesting slaughterhouse waste (SHW) with waste mixed sludge (WMS) for possible implementation in a full-scale digester in an existing wastewater treatment plant (WWTP) was investigated. Biomethane potential (BMP) runs were activated using SHW:WMS ratios from 0% to 60% at total solids (TS) of 4% and 7%. Higher values of BMP of about 735 NLCH4/kg volatile solids (VS) were obtained for the run with a SHW:WMS ratio of 40% and TS = 4%. Continuous runs were also performed using the same SHW:WMS ratio at different organic loading rates (OLR). The maximum biomethane generation of 550 NLCH4/kgVS was achieved for an OLR = 1.5 kgVS/m3.day. Stability monitored by FOS/TAC showed values

This work aims to enhance and optimize the methane production by anaerobic co-digestion of soybean straw (SS) and farm wastewater. Thermo oxidation and alkali pretreatments were applied during the present study. The effects of chemical composition were investigated and the influence of thermo-chemical pretreatment on methane production by SS with wastewater was evaluated by Batch and semi-continuous experiments. All pretreatments were found significant (P

Anaerobic co-digestion has been extensively applied in treating residual sludge (RS) and kitchen waste (KW). However, some problems still occur in co-digestive system. This study tries to add green waste (GW) as co-substrate into RS/KW co-digestive system to improve methane production and system stability. The results showed that K4 group (RS:KW:GW = 2:1:0.5, based on VS addition, similarly hereinafter) presented the highest specific methane yield (SMY) of 303.4 mL/g VS, as well as the highest acetic acid (HAc) concentration at the primary stage. An appropriate amount of GW addition into co-substrate mixture was conducive to guaranty continuous degradation and conversion of the organics, and it could also improve the stability of the digestive system and optimize volatile fatty acids (VFAs) composition structure. Buswell formula was used and showed that the highest biodegradability index (BI) was obtained in K4 (97.0%) and K5 (98.2%). Besides, the fitting results of kinetic models were used to analyze methane production and hydrolytic process. The enzymes activity and microbial diversity results of K4 group can also verify the results above.

This study evaluates the effect of mixing ratio (1, 1.5, 2 and 2.5) and hot air oven pretreatment on the anaerobic co-digestion of water hyacinth and banana peels. Two sets of bio-chemical methane potential (BMP) tests were performed concurrently. In set I, untreated water hyacinth was mixed with banana peels and in set II, water hyacinth was pretreated before co-digestion. Fixed amount of cow dung was added to each reactor as an inoculum. The anaerobic batch test revealed that set II, where pretreated water hyacinth and banana peels was co-digested, demonstrated higher biogas production and better quality of biogas than set I. Mixing ratio 2 and 1.5 were illustrated to be the optimal mixing ratio for set I and II respectively. Both the sets illustrated higher biogas generation than mono-digestion of the substrates. Thus, anaerobic co-digestion of water hyacinth and banana peels portrayed a synergistic action by balancing the overall process.

This work investigated the thermophilic (55 °C) co-digestion performance both in batch and continuous mode operation. The biochemical methane potentials of L. digitata and cattle manure were 308 ± 24 and 203 ± 33 mL CH4/g VS, respectively. The optimum co-digestion feedstock ratio was found to be 80% macroalgae: 20% manure on a volatile solids basis, which produced 290 ± 19 mL CH4/g VS under long-term and stable continuous operation at an organic loading rate of 2 g VS/L/d and hydraulic retention time of 15 days. Simulations of the batch and continuous experiments were, for the first time, carried out using an integrated anaerobic bioconversion model without structural modifications. Close fits between measured and simulated data provided mutual confirmation of experimental reliability and model robustness, and provided new perspectives for the use of the software tool.

© 2019 This study investigated changes in microbial community structure and composition in response to operational disturbance and subsequent process recovery by inoculum addition. Amplicon sequencing of 16S rRNA and mcrA marker genes on the Illumina Miseq platform was used for microbial community analysis. The results show that imbalance among core microbial groups caused volatile fatty acid accumulation and subsequent deteriorated biogas production (decreased by 45% of daily volume) and methane content (57% of the total abundance) and reduction of acetogenic and methanogenic microbes (they accounted for

The aim of this research was to develop a method for pretreatment of lignocellulose (LC) substrates (harvest residues (HR)) via electroporation (EP) for the purpose of improving the biogas production process. In addition, pretreated LC substrates were analyzed by scanning electron microscopy (SEM) and the energy balance of the total process was calculated. After the conducted pretreatment and anaerobic co-digestion with dairy cow manure (DCM), the statistical data analysis showed statistically significant differences in biogas and/or methane yield for all three LC substrates and their fractions. It was concluded that, after the pretreatment of LC substrates via EP, it is possible to improve the anaerobic co-digestion process and to achieve positive energy balance of the total process.

The high costs, health implications of energy derived from fossil fuel and its negative impact on environment has called for an alternative source of energy, among which biogas has been identified as eco-friendly. This study analyzed biogas production from digestion of cattle dung and co-digestion with Typha latifolia in Funtua, Katsina State Nigeria. The experiment was conducted batch wise in mixing ratio 1:1 of cattle dung: T. latifolia at mesophilic temperature under 38 days retention time. The quantity of cattle dung fed into digester was determined with a weighing balance. Descriptive statistics was used to analyse the rate of biogas production while the difference in the biogas produced by the substrates was analysed using inferential statistics. Total of 9,923 (Fresh T. latifolia - FTCD), 35 (Powdered T. latifolia - PTCD) and 8,418 seconds (Fresh cattle dung - FCD) worth of biogas was produced. There was no statistically significant difference (P < 0.084) in the biogas production between the substrates. The highest daily peak was 1008 (18.8 minutes) and 937 second (15.6 minutes) from FTCD and FCD respectively. On average 1kg of cattle dung co digested with T. latifolia produced biogas worth 1240 seconds (21minutes) while mono digestion of cattle dung produced 1052 seconds (16minutes). Co-digestion with fresh T. latifolia improves biogas production by 15%. T. latifolia does not significantly has potential in biogas production. It is recommended that an investigation on effect of additives in biogas production from cattle dung and co-digestion with powdered Typha latifolia be conducted.

Anaerobic digestion (AD) of wastewater sludge is an effective approach to produce biomethane and subsequently reduce the amount of sludge disposal to landfill generated from wastewater treatment plants (WWTPs). Recently, anaerobic co-digestion (ACD) of lipidic-waste such as fat, oil, and grease (FOG) has received much attention for the enhancement of biomethanation in WWTPs. However, there are several major challenges associated with ACD of FOG which includes inhibition by long chain fatty acids, sludge floatation and washout, and scum formation. This review summarizes the scientific and engineering aspects of the FOG supplementation as a co-substrate in AD as well provides appropriate solutions for challenges encountered during the anaerobic operation. The discussion on the existing pretreatment approaches (including mechanical, thermo-chemical, and biological) for rapid degradation of FOG was also highlighted. Metagenomic analysis elucidates the microbial community and the interspecies interactions which are responsible for the degradation of FOG and its biomethanation during ACD. Addition of FOG to AD was found be economically feasible in municipal WWTPs.

Fats, oil and grease (FOG) are energy-dense wastes that substantially increase biomethane recovery. Shifts in the microbial community during anaerobic co-digestion of FOG was assessed to understand relationships between substrate digestion and microbial adaptations. Excessive addition of FOG inhibited the methanogenic activity during initial phase; however, it enhanced the ultimate methane production by 217% compared to the control. The dominance of Proteobacteria was decreased with a simultaneous increase in Firmicutes, Bacteriodetes, Synergistetes and Euryarchaeota during the co-digestion. A significant increase in Syntrophomonas (0.18-11%), Sporanaerobacter (0.14-6%) and Propionispira (0.02-19%) was observed during co-digestion, which substantiated their importance in acetogenesis. Among methanogenic Archaea, the dominance of Methanosaeta (94%) at the beginning of co-digestion was gradually replaced by Methanosarcina (0.52-95%). The absence/relatively low abundance of syntrophic acetate oxidizers and hydrogenotrophic methanogens, and dominance of acetoclastic methanogens suggested that methane generation during co-digestion of FOG was predominantly conducted through acetoclastic pathway led by Methanosarcina.

The present study is a comparative evaluation of anaerobic co-digestion of water hyacinth and food waste with and without pretreatment. The novelty of this anaerobic co-digestion study is that it highlights the effect of pretreatment and mixing ratio. Two set up of bio-chemical methane potential (BMP) experiments for the same mixing ratios but with or without pretreatment were simultaneously conducted. In set I, untreated water hyacinth and food waste was co-digested whereas in set II, pretreated water hyacinth and food waste was co-digested. Higher biogas production in set I and II was witnessed by the mixing ratios 2 and 1.5 respectively indicating them to be the ideal mixing ratio. Considerably higher biogas production was observed for both the setup of anaerobic co-digestion than mono-digestion. Also, set II exhibited higher biogas production than set I. The results portrayed that pretreatment followed by co-digestion provided quicker and higher biogas production.

In municipal wastewater treatment plants (WWTPs), algae could be utilised for cleaning the water and, at thesame time, produce a biomass that can be used for energy. Through anaerobic digestion, microalgae can contributeto biogas production when co-digested with sewage sludge. In this paper, previous published results onthe co-digestion of sewage sludge and microalgae are summarised and reviewed, and any remaining knowledgegaps are identified. The batch tests currently documented in literature mostly concern digestion under mesophilicconditions, and studies investigating thermophilic conditions are less common. The average biochemicalmethane potential (BMP) for 29 different mixtures co-digested under mesophilic conditions is 317 ± 101 N cm3CH4 gVS−1 while the result for 12 different mixtures investigated under thermophilic conditions is a BMP of318 ± 60 N cm3 CH4 gVS−1. An evaluation of the heat required for increasing the temperature from mesophilicto thermophilic conditions shows that increased methane production under thermophilic conditions can beenough to create a positive energy balance. For a full-scale WWTP, using thermophilic digestion on sludge, or acombination of sludge and microalgae could therefore be of interest. This is dependent on the demands onsanitation of the sludge and the possibilities for heat recovery.Most of the mesophilic investigations indicate a synergetic effect for co-digestion, with enhancements of up toalmost 70%. However, the results are uncertain since the standard deviations for some of the BMP tests are in thesame order of magnitude as the identified enhancement. Neither of the presented publications provide an understandingof the basic mechanisms that led to higher or lower BMP when microalgae were mixed with wastewatersludge. We, therefore, call for care to be taken when assuming any effects related to the specification ofsubstrates. Microalgae and wastewater sludge have several similarities, and the specific results of BMP in themixtures relate more to the specifics of the respective materials than the materials themselves.Investigations into semi-continuous processes of co-digestion of microalgae and sludge are scarce. The yieldsfor three co-digestion studies show high variation, with an average of 293 ± 112 N cm3 gVSin−1. The availableresults show strong potential for co-digestion of sewage sludge and microalgae. Further investigations are requiredto identify optimal conditions for biogas production, and analysis of microalgae implementation onwastewater treatment at a system level is also needed to identify the total mass balance of substrate and nutrientrecovery. MAASICA

The world is now seeking sources of renewable energy that are both economical and environmentally friendly. Purified biogas is one essential source of renewable energy that can act as a substitute for fossil fuels. Anaerobic digestion has been recognised as a biochemical method of biogas generation that can convert organic compounds into a sustainable source of energy. Anaerobic co-digestion, AcoD is considered a pragmatic method to resolve the difficulties related to substrate properties and system optimisation in single-substrate digestion processes. The present manuscript studied the research prospects and challenges of anaerobic co-digestion, and the contributions of different methods in biogas generation studies. With the increased use of anaerobic co-digestion, the complexity of the process also increases. Several mathematical models had been established to optimise the anaerobic co-digestion technique. The biological methane potential test is a preferred technique for measuring the biodegradability and decomposition rate of organic substances. Furthermore, various additives are now used to maximise methane production. The improvement and optimisation processes of biogas production still need to be investigated in greater detail. In developing countries like Malaysia, biogas production may be more economically feasible if the latest simulation and characterisation methods are used at the industrial scale. Finally, this review describes a design and development framework to incorporate various aspects to enhance biogas production.

This study aimed to demonstrate the co-digestion of End-of-Life Dairy Products (EoL-DPs) with a typical mixture of Agroindustrial Wastes (AgW) in a pilot-scale two-stage mesophilic (37 °C) anaerobic system and compare its performance under single-stage operating conditions. The system was initially operated in the two-stage mode, with the fermentor fed exclusively with EoL-DPs which, after acidification, were co-digested with AgW in the methanogenic bioreactor. In the second operating scenario, the raw EoL-DPs and AgW were directly fed and co-digested in the digester. Both systems were operated at Hydraulic Retention Time of 37 days with the EoL-DPs mixture accounting for ∼20% (w/w) of the total feeding stream. At the two-stage mode, the digester exhibited 50% higher methane productivity (0.51 ± 0.27 L/L R /d) and 90% higher methane yield (448.3 ± 212.9 L CH 4 /kg VS add ) compared to the single-stage. The production of 1.84 m 3 H 2 /m 3 EoL-DPs added in the fermentor increases the overall energetic efficiency of the process.

This study has been conducted to optimise the dry-thermophilic anaerobic co-digestion of two different types of real waste (municipal solid waste and biodiesel waste) in a semi-continuous feeding regime, under high organic loading rates (OLRs) or low hydraulic retention times (HRTs). For this purpose, different high OLRs (from 10 to 34 g [VS] l−1 d−1) or low HRTs (from 10 to 4.4 d) were investigated in a continuously stirred tank reactor. Optimal conditions (257 ml [CH4] g−1 VS; 6.03 ± 0.43 l [CH4] l−1 d−1; 16.3 ± 2.3 × 10−12 l [CH4] cell−1 d−1) were obtained at 4.4 d HRT (OLR = 23 g [VS] l−1 d−1), in which the average values of the ratios of Eubacteria:Archaea and hydrolytic-acidogenic bacteria:acetogens were 95:5 and 87:8, respectively.

This study assessed the co-digestion of macro and microalgal biomass towards the improvement of hydrogen production. The red macroalgal biomass (Gelidium amansii) and green mixed microalgal biomass was mixed in a ratio of 8:2, with an initial substrate concentration of 10 g/L, and various amount of inoculum addition range from 3 to 15% (v/v) was evaluated to assess the feasible substrate to inoculum ratio for the effective co-digestion of the algal biomass. The results showed that the co-digestion with 6% inoculum addition provided the peak hydrogen yield of 45 mL/g dry biomass added with a high hydrogen content of 24% in the gas phase. The other tested conditions showed moderate hydrogen content in the range of 17–22%, respectively. These results suggest that anaerobic co-digestion of macro and microalgal biomass, with appropriate initial biomass loading (6%) is essential for enhanced hydrogen production.

Rice straw (RS) contains a high amount of lignocellulosic materials which are difficult to degrade without thermal pretreatment. In the present study, co-digestion of municipal solid waste (MSW) and RS was carried out in three different ratios i.e., 1:1, 2:1, and 3:1 to get the maximum biomethanation potential and methane generation rate constant (k). The biogas and methane (CH4) potential increased by 60% and 57%, respectively for MSW and RS in the ratio 2:1 as compared to other combination. The values of k, biochemical methane potential (µb) and sludge activity were measured as 0.1 d−1, 0.99 CH4-COD/CODfed and 0.50 g CH4-COD/g VSS, respectively. The sludge activity was found to be 100% for 2:1 ratio. Co-digestion of RS with MSW can also optimize the C/N ratio which is an essential parameter in the anaerobic digestion process.

The main objective of this paper is to examine the effect of the increase in organic loading rates (OLRs), by reducing the solids retention time (SRT) from 20 d to 5 d, in single-phase mesophilic anaerobic co-digestion of sewage sludge with glycerine (1% v/v). It was experimentally confirmed that anaerobic co-digestion of these biowastes under steady-state conditions can achieve an 85 ± 5% reduction in volatile fatty acids (VFA) at SRTs of between 20 and 9 d, with a methane production yield of around 0.8 l CH4/l/d. Decreases in the SRT not only allow the sludge stability and biogas production to be maintained, but also lead to an increase in the waste that could be treated and lower operating costs. Therefore, mesophilic anaerobic co-digestion of sewage sludge and glycerin at a SRT lower than 20 d is possible and preferable due to being more economical and environmentally friendly

The use of consecutive feeding was applied to investigate the response of the microbial biomass to a second addition of substrates in terms of biodegradation using batch tests as a promising alternative to predict the behavior of the process. Anaerobic digestion (AD) of the slaughterhouse waste (SB) and its co-digestion with manure (M), various crops (VC), and municipal solid waste were evaluated. The results were then correlated to previous findings obtained by the authors for similar mixtures in batch and semi-continuous operation modes. AD of the SB failed showing total inhibition after a second feeding. Co-digestion of the SB+M showed a significant improvement for all of the response variables investigated after the second feeding, while co-digestion of the SB+VC resulted in a decline in all of these response variables. Similar patterns were previously detected, during both the batch and the semi-continuous modes.

The status, recent trends and future perspectives in modelling and optimisation of anaerobic co-digestion is investigated. Areas that can be focused on and those which need further research towards enhancing biogas production are pointed out. Co-digestion, modelling and optimisation of anaerobic digestion as well as techno-economic aspects are reviewed in this paper. It was noted that co-digestion requires more research into a variety of bio-resources and their specific blend proportions. Modelling and optimisation of co-digestion with substrate seasonal fluctuations has not been addressed in previous studies. Controlling key process factors including temperature, pH, and carbon to nitrogen ratio is critical in improving biogas yield. Biogas hybridisation is yet to be explored in depth. The majority of researches are focused on mono-digestion, feedstock co-digestion, modelling, and optimisation of anaerobic digestion needs significant further investigations. A multi-objective approach taking all technical and economic parameters in the modelling and optimization is essential.

This study investigates the combined production of lipids and biogas via anaerobic mono- and co-digestion of microalgae biomass grown in municipal untreated wastewater. In the co-digestion assays, extracted microalgae and wastewater sludge were mixed at different ratios: 25–75, 50–50, and 75–25% total volatile solids (VS) of each substrate, respectively. The neutral and polar fatty acid methyl esters constituted approximately 13 and 1.5% of the total lipids, respectively. Mono-digestion of lipid-extracted microalgae had a lower biochemical methane potential (BMP) than of non-extracted microalgae. Organic solvents were shown to negatively impact both mono- and co-digestion of extracted microalgae. Co-digestion experiments showed synergy between sludge and microalgae residues, increasing the BMP from 91.4 Normalized mL (NmL) CH4/g VS in the mono-digestion of evaporated extracted microalgae up to 228.6 NmL CH4/g VS in the co-digestion of the mixture with 25% VS of microalgae biomass with 75% VS of sludge.

More than 400 papers in the last 5 years have been published on FW into energy. Food waste complexity and composition affects anaerobic conversion. Scaling up of the AD process is fundamental to assess the real methane potential. Methanogenesis is often rate limiting step leading to pH drop and instability. Strategies to improve AD performances and stability are here reviewed.

The effect of pre-fermentation of food waste (FW) for 48 h at 24 °C in anaerobic co-digestion with sewage sludge (SS) was studied in bench and pilot digesters (30 °C, HRT 30 d). The digesters fed with a mixture of SS and fresh or pre-fermented food waste (FW) (80:20% v/v) presented better performance (53% VSS reduction and 186–223 NmL biogas/g VSSadd) than the digester fed with only sludge (35% VSS reduction and 41 NmL biogas/g VSSadd). In both digesters, the pH quickly dropped in the first weeks of operation. However, the digester fed with SS and pre-fermented FW achieved 1.5 times faster pH recovery and relatively stable biogas production throughout the operation (186 ± 23 NmL biogas/g VSSadd). The pilot-scale results confirmed those obtained in bench-scale. Therefore, the pre-fermentation of FW did not affect long-term co-digestion but contributed to a better performance in the starting phase of the digesters.

A method for waste management and valorization of waste activated sludge (WAS) was developed using co-digestion. Biogas and methane production were used as indicators of efficiency for analyzing biochemical methane potential (BMP) of co-digestion of waste activated sludge with three agricultural wastes (i) wheat straw, (ii) rice straw, and (iii) soybean straw. Results infer that co-digestion system of waste activated sludge with wheat straw or rice straw or soybean straw gave higher cumulative specific methane production of 223, 218, and 197 ml/g VS, which produced 2.57, 2.52, and 2.27 times higher methane yield compared to the mono-digestion of WAS respectively. In addition, the use of rumen as inoculum was found to enhance biogas and methane production. The kinetic analysis further confirmed that the inclusion of agricultural straws could abbreviate the lag phase and increase the degradation of the substrates, which in turn enhances methane production potential.

Palm oil mill industry generates a large amount of palm oil mill effluent (POME) and empty fruit bunches (EFB) as byproducts. Biogas production from anaerobic co-digestion of POME with EFB was investigated under mesophilic condition. The amount of POME and EFB was varied from 2 to 10 gVS and size of EFB was varied from 0.5-6 centimeter. High methane yield and high biodegradability were achieved at the size of 0.2 mm with 63-70% biodegradability with a methane yield of 320 mL CH4/gVS. The POME:EFB ratio of 4.5-7.5 and size EFB of 3.3-6 centimeters shown acceptable biodegradability value of 40-50% with a methane yield of 282 mL CH4/gVS. The POME:EFB ratio of 4.5-7.5 and size EFB of 3.3-6 centimeters was more practical for biogas production due to reducing the cost of size reduction

This study explored two holistic approaches for co-digestion of activated sludge and food waste. In Approach 1, mixed activated sludge and food waste were first hydrolyzed with fungal mash, and produced hydrolysate without separation was directly subject to anaerobic digestion. In Approach 2, solid generated after hydrolysis of food waste by fungal mash was directly converted to biofertilizer, while separated liquid with high soluble COD concentration was further co-digested with activated sludge for biomethane production. Although the potential energy produced from Approach 1 was about 1.8-time higher than that from Approach 2, the total economic revenue generated from Approach 2 was about 1.9-fold of that from Approach 1 due to high market value of biofertilizer. It is expected that this study may lead to a paradigm shift in biosolid management towards environmental and economic sustainability.

Globally, there is increasing awareness that renewable energy and energy efficiency are vital for both creating new economic opportunities and controlling the environmental pollution. AD technology is the biochemical process of biogas production which can change the complex organic materials into a clean and renewable source of energy. AcoD process is a reliable alternative option to resolve the disadvantages of single substrate digestion system related to substrate characteristics and system optimization. This paper reviewed the research progress and challenges of AcoD technology, and the contribution of different techniques in biogas production engineering. As the applicability and demand of the AcoD technology increases, the complexity of the system becomes increased, and the characterization of organic materials becomes volatile which requires advanced methods for investigation. Numerous publications have been noted that ADM1 model and its modified version becomes the most powerful tool to optimize the AcoD process of biogas production, and indicating that the disintegration and hydrolysis steps are the limiting factors of co-digestion process. Biochemical methane potential (BMP) test is promising method to determine the biodegradability and decomposition rate of organic materials. The addition of different environmentally friendly nanoparticles can improve the stability and performance of the AcoD system. The process optimization and improvement of biogas production still seek further investigations. Furthermore, using advanced simulation approaches and characterization methods of organic wastes can accelerate the transformation to industrializations, and realize the significant improvement of biogas production as a renewable source and economically feasible energy in developing countries, like China. Finally, the review reveals, designing and developing a framework, including various aspects to improve the biogas production is essential.

In this study, anaerobic co-digestion of cattle manure (CM) and meadow grass (MG) with serial configurations of continuous stirred tank reactors (CSTRs) was investigated. Four laboratory-scale CSTRs were operated at thermophilic condition (55 °C), of which two CSTRs were connected serially with equal working volumes while the remaining two CSTRs were operated as single CSTRs as controls. Improvements on bio-methane yield, methane contents and solids reduction were observed with serial CSTR configurations. The results showed that co-digestion with 5% (w/w) MG with serial configurations of CSTRs produced 24% more bio-methane compared with single reactor, with the total hydraulic retention time (HRT) being the same. The volatile fatty acids (VFA) concentration was found higher in the 1st reactor, but was reduced by 40–50% in the 2nd reactor. The improved bio-methane yield with serial CSTR configuration with 100% CM was 8%, indicating that the serial CSTRs process is superior in a co-digestion set up with addition of MG.

This study investigated the possibility of using a model based on the anaerobic digestion model no. 1 (ADM1) on a full-scale 4000 m3 digester in order to understand how such theoretical models can ...

Acidogenic (ACIDO-DR) and methanogenic (METHA-DR) digesters were synchronously operated under the semi-continuous modes of mono-digestion (control) and co-digestion (mixture). The CH4 gas production rate was enhanced by 19.8% in co-digestion at an optimum ratio of 7:3 (food waste to sewage sludge). At this ratio, the maximum BMP of 620 ± 18 mL CH4 g−1 VS was attained in co-digestion but control showed lower BMP of 440 ± 14 mL CH4 g−1 VS. Co-digestion of food waste and sewage sludge was enhanced due to the adequate adjustment of C/N ratio for feed waste, improved buffer capacity and the necessary amounts of trace elements. Additionally, this system provided better buffering potential to high OLR than the one-phased system. As a result, the two-phased anaerobic co-digestion system suggested the alternatives for many struggling wastewater treatment plants, without any major remodeling of facilities, to enhance sustainable energy production that could be beneficial to public use.

This work investigates the combined influence of ultrasonic and microwave pre-treatment on bio-methane generation from anaerobic digestion of petrochemical wastewater and waste activated sludge. The results revealed that co-digestion of waste activated sludge with petrochemical wastewater produced approximately 0.22 L CH 4 /g VS added . However, the highest bio-methane generations from individual digestion of petrochemical wastewater and un-pretreated waste activated sludge were 0.19 and 0.17 L CH 4 /g VS added , respectively. In addition, co-digestion enhanced bio-methane generation by 18%–32% relative to individual digestion of the wastes. Using microwave and ultrasonic pre-treatments on the waste sludges before the co-digestion process resulted in supplementary enhancement of bio-methane generation by 53% and 25%, respectively, relative to co-digestion with un-pretreated waste activated sludges. The maximum biogas and bio-methane productions, 0.47 L/g VS added and 0.33 L CH 4 /g VS added , were attained from the co-digestion of 30-min microwave pre-treated waste activated sludge and petrochemical wastewater, respectively. The scientific contribution of the present work on the influence of microwave pre-treatment may play a role in the development of an energy-efficient strategy for waste management.

Anaerobic digestion is a long-established technology for the valorization of diverse organic wastes with concomitant generation of valuable resources. However, mono-digestion (i.e., anaerobic digestion using one feedstock) suffers from challenges associated with feedstock characteristics. Co-digestion using multiple feedstocks provides the potential to overcome these limitations. Significant research and development efforts have highlighted several inherent merits of co-digestion, including enhanced digestibility due to synergistic effects of co-substrates, better process stability, and higher nutrient value of the produced co-digestate. However, studies focused on the underlying effects of diverse co-feedstocks on digester performance and stability have not been synthesized so far. This review fills this gap by highlighting the limitations of mono-digestion and critically examining the benefits of co-digestion. Furthermore, this review discusses synergistic effect of co-substrates, characterization of microbial communities, the prediction of biogas production via different kinetic models, and highlights future research directions for the development of a sustainable biorefinery.

The energy potential of residue-derived biogas via electricity and biomethane production was assessed in an integrated 1G2G sugarcane biorefinery concept. The mono-digestion of 1G-vinasse (1G-VN) was compared with different co-digestion systems, namely, 1G-VN + filter cake (FC) + deacetylation liquor (DL) in the season and FC + DL in the off-season. Gross energy output values and the resulting sugarcane use efficiency were also assessed in different biorefinery schemes. Electricity production from 1G to VN (5.0 MW) could be increased by over 400% through its co-digestion with FC and DL (22.3 MW). Alternatively, biomethane could fully supply the diesel-powered fleet (1.8 × 106 Nm3 month−1) of a sugarcane plant processing 10 million tons of sugarcane per harvest, and the surplus biogas could flexibly provide 36 MW of extra electricity. Biomethane could enhance the energy output of 1G2G sugarcane biorefineries by 15%. However, 2G processes still require marked improvements to maximize energy production from sugarcane.

The aim of this study is to improve the management of different types of wastes using an anaerobic digestion process and CH4 production from the semi-continuous co-digestion of multi-substrates of fallen leaves (FL), grass (GR) and primary sludge (PS). As a first step, the co-digestion of FL, GR and PS was carried out using the BMP test based on C/N ratios. The results showed that the best CH4 production was at a C/N ratio of 13. Kinetic analysis of the methane produced showed no adaptation phase was needed for the methanogenic bacteria to stimulate their anaerobic digestion activity. The inflection point in the cumulative methane production curve is identified as the biological hydrolysis phase of the substrates by endogenous microorganisms. In the second step, semi-continuous co-digestion of FL, GR and PS was carried out. The performance of the reactor was monitored in particular for biodegradability of the feedstock and biogas production rate under different OLRs. The highest biogas production rate of 35 L/d was recorded at an OLR of 1 g VS/L·d. However, partial overloading occurred at an OLR of 1.5 g VS/L·d. The highest CH4 content of biogas produced was achieved at an OLR of 1.0 g VS/L·d.

In this study, the effects of adding different food waste proportions (volatile solids ratio of 3:7, 5:5, 7:3) to tylosin fermentation dreg on anaerobic digestion were investigated. The results showed that the co-digestion group (294–399 mL·g-VS−1) increased methane production by 14.8%–55.5% compared with tylosin fermentation dreg alone-digestion (256 mL·g-VS−1). The correlation analysis showed that pH, total volatile fatty acids and acetic acid were the most important factors affecting cumulative methane production. Tylosin in the solid and liquid phases decreased significantly after anaerobic digestion, indicating that tylosin could be effectively removed by co-digestion, and the total removal rate was 68.2%–83.7%. Therefore, due to the satisfactory methane yield and the tolerable tylosin removal rate, it is feasible to make the co-digestion of tylosin fermentation dreg and food waste.

This study focused on biochemical methane potential (BMP) from recalcitrant abattoir and winery solid wastes, to evaluate the effects of various input parameters on the overall anaerobic co-digestion (AcoD) performance. Standard BMP protocols were employed. The parameters evaluated were co-substrate-ratio of abattoir solid (As), winery solid (Ws) and cow blood (Cb) in binary and ternary combinations (1:1, 2:3 and 1:1:3), food-to-microorganism ratio (F/M) (0.5-2) and volatile solids (VS) concentration (5-20 gVSL-1). A combination of zebra dung and ruminal contents served as inoculum. Methane production was simulated by curve-fitting kinetic models. Highest methane yields of 369.56 and 354.13 NmLCH4/gVSadded were obtained from co-digested substrates AsWs and CbWs respectively. All models used showed methane production profiles with over 90% accuracy. An increase in F/M and VS concentration reduced the overall digestion performance. This suggests an improvement in the valorisation of abattoir and winery wastes for full-scale AD plants.