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Aim: The aim of the study was to assess the effects of anaerobic co-digestion of maize cob and poultry manure on biogas yields and their digestate characteristics. Place and Duration of Study: Department of Forestry Technology, Federal College of Forestry, Jos between March and April, 2018. Methodology: Slurries of five co-substrate treatment ratios viz 0:1(T1), 1:3(T2), 1:1(T3), 3:1(T4) and 1:0(T5) of these wastes (in three replicates) were separately fed to 13.6L locally made batch-digesters. The anaerobic reactors were monitored for a 56 day retention period. Weekly biogas yields and some digestate characteristics were measured by standard methods. Results: The cumulative biogas yields was in the order of T3(2481.3 mL/kg) >TI(2197.9 mL/kg) > T4(2163.0 mL/kg) > T2(2116.3 mL/kg) >T5(1713.2 mL/kg), in favor of the mixed substrates. While the percentage C:N reductions ranged from (12.94% - 81.80%), with T5 and T1 recording the highest and lowest values respectively. The chemical oxygen demand removal was in the order of T3(80.70%) > T4(58.00%) >T5(46.81%) >T1(34.15%) >T2(13.16%). The anaerobic digestion (AD) effected reductions in Mg, C, Ca, P, Mn, Zn, Fe, Pb and increase in Cu contents of the digestates across treatments. While the K contents increased in T2(36.72%), T3(229.79%) and T4(220.51%); %N in T3(9.94%), T4(113.19%) and T5(291.84%) and Na increased only in T4(4.55%). The Cu contents indicated % increase in the order of T5(487.5%) >T3(270.97%) >T2(268.10%) >T4(43.66%) >T1(35.82%). Conclusion: The anaerobic co-digestion of these organic wastes had unlocked the alternative energy potentials, enhanced the bioremediation tendency, while promoting sustainable public health and environmental management.

Anaerobic digestion can utilize renewable resources to produce energy in the form of biogas. Cow manure inoculum contains the microorganisms needed for this application and unrecycled paper waste can be used as a substrate. The use of these feedstocks together is not well studied. Finding ideal operating parameters and modelling biogas production is vital for future integration of anaerobic digestion. The use of various models when examining anaerobic digestion is important to ensure the best models are used for future research and industrial applications. Office paper and cow manure were combined at the different substrate to inoculum ratios with a total solids content of 6% at 38.4°C for 15 days. Four models (Time-Lag, No-Lag, Modified Gompertz, and Modified Logistic) were fitted to the experimental data to find which model best represented each biogas production process. Models varied in the accuracy of their fit to the data and no single model had the lowest RMSE values for each treatment. The digester containing a paper to manure ratio of 2:1 produced the most biogas (82 mL biogas/g VS), but the 5:1 reactor had the greatest biogas production potential over a longer period based on the model parameters (maximum cumulative biogas yield and biogas production potential). More biogas was produced in this study compared to other works reported in the literature, showing that this combination of co-digestion substrates could be expanded upon in the future. New models need to be examined or developed for these systems to better represent this co-digestion process for future research and commercial applications.

The study aims to evaluate two-stage anaerobic co-digestion of leachate and starch waste using anaerobic biofilm bioreactor to enhance methane production. The anaerobic digestion process was operated under the mesophilic condition at 35 ± 1 °C. Hydraulic retention time (HRT) applied to the acidogenesis and methanogenesis reactors were 5 and 25 days, respectively. The organic loading rate (OLR) used in the process of acidogenesis was 2.91 gram volatile solid /L.day, while methanogenesis was 0.58 gram volatile solid (VS) per liter per day. Results showed that two-stage process using biofilm was an effective method for operating anaerobic co-digestion of starch waste and landfill leachate in which the system produced higher methane yield at 125.11 mL methane (CH4) per gram volatile solid (VS) added (mL.CH4/g.VS.added) in comparison to the single-stage process (20.57 mL CH4/g.VS.added) and two-stage process (77.60 mL CH4/g.VS.added) without using biofilm. Two-stage process using biofilm also effectively reduced organic matters in the culture in which the system reached 61% BOD removal in comparison to the single-stage process and two-stage process without biofilm that only had 27.6 and 39.3% BOD removal, respectively. This study suggested that the two-stage process using biofilm would be the preferred technique for treating starch waste and landfill leachate.

In this study, biogas production from co-digestion of pig dung, water hyacinth, and poultry droppings was investigated. 500 ml bio-digesters were connected in series and water displacement method was used to estimate the amount of biogas produced. The ratio of the percentage weight distribution of pig dung to water hyacinth to poultry dropping was varied as: (0:40:60), (30:40:30), (15:40:45), (45:40:15), and (60:40:0) in digesters A1, B2, C3, D4 and E5, respectively. The highest biogas cumulative yield of 307 cm3 CH4/g was obtained in Digester C3. The gas chromatography analysis showed 22.50 wt% (CO2), 64.92 wt% (CH4) and 4.83 wt% (N2) which implied that the biogas produced can be used for cooking and heating of homes in rural and urban communities.

Anaerobic bio-digestibility of blend municipal sewage sludge (MSS), condensed waste activated sludge (CWAS) and petrochemical wastewater (PWW) has been evaluated utilizing semi-continuous operation, anaerobic reactors worked during mesophilic (37 ºC) and thermophilic (55 ºC) states. Supplementation of a significant PWW portion (49 % of VS) in an MSS + CWAS combination brought about 2.94 times more methane production, 153 versus 450 mL/g volatile solids (VS) under 37 ºC furthermore 2.59 times more methane production, 198 versus 513 mL/g VS under 55 ºC. The supplemented PWW portion might have been not inhibitory for the system. Those effects of this work show the profit from municipal sewage sludge, condensed waste activated sludge and petrochemical wastewater co-digestion.

This study examined the effectiveness of thermophilic sewage sludge co-digestion of and milled/non-milled brewery spent grain. In order to evaluate both the biogas potential and the biogas production rate, the experiments were conducted in batch-mode. Five runs were carried out, one of them concerned the anaerobic sewage sludge digestion (as control), whereas the others referred to the co-digestion of sewage sludge with addition of milled and non-milled brewery spent grain at doses of 5 and 10 g. The runs were conducted under thermophilic conditions (temperature 55±1°C) and lasted for 21 days. The effectiveness of the process was assessed on the basis of the volatile solids removal, biogas potential and the rate of biogas production. The physiochemical composition of reactor feed and digestate were characterized. The addition of the brewery spent grain resulted in increase of the biogas potential, but a decrease in the removal of volatile solids. In the case of biogas production rate, the highest value was recorded in the run with the addition of 10 g of milled and non-milled brewery spent grain (0.69 Ndm3dm-3d-1). There was no observed influence of milling on the thermophilic co-digestion effectiveness since the parameters specified revealed comparable values.

Anaerobic co-digestion of peanut hulls and swine manure was investigated. The interaction effects of the total solid percentage (TS%), carbon–nitrogen ratio (C/N ratio), and inoculum volume percent...

With the target of amplifying methane generation from sewage sludge (SS), co-digestion with petrochemical wastewater (PWW) was examined. In addition, the use of both 165 °C heat treatment and alkali pretreatment to mixed SS/PWW wastewater was assessed. Batch tests demonstrated that refractory materials were generated from pretreatment for petrochemical wastewater at the 165 °C heat and alkali pretreatments at the 75 or 115 °C and with pH value of 8, 9 or 10 producing enhanced preliminary methane generation percentage and a little effect for generation capacity of methane of the miscellaneous waste (+3–6 %). Anaerobic reactors which were operated more than four months semi-continuously with sewage sludge and petrochemical wastewater mix with the proportion of 85:15, 55:45 and 85:15 pretreated at alkaline environments maintaining the temperature of 75 °C and pH = 8. This pretreatment enhanced the production of methane at semi-continuous anaerobic reactors to + 59 %. Finally, this investigation demonstrated the viability of the co-digestion of sewage sludge with a higher ratio of petrochemical wastewater [45 % volume, 50 % volatile solid (VS) and 74 % COD, comparable with volatile fatty acids of 8 g L–1]. The system produced an exact methane of 363 mL CH4 g–1 VS while only sewage sludge generated 117 mL CH4 g–1 VS.

The confectionery wastewater with high organic content was explored for biogas production by anaerobic treatment. A study was conducted by pre-treating the wastewater by ultrasound technology for a...

Co-digestion of apple pomace (AP) and vegetable waste (VW) was a feasible proposal to simultaneously eliminate their potential pollution to the environment and produce alternative biogas energy, whereas, it can be easily interrupted by rapid acidogenesis and inhibition of methanogen. Additionally, the methane yield could not be maximization due to the recalcitrant cellulose substance of AP. The inoculum regulation was employed for overcoming the acidogenesis problem and enhancing methane yield when conducting high-solids (TS of 10%) co-digestion of AP and VW under mesophilic condition. The chosen inoculum was the special acclimated anaerobic granular sludge (AGS) from the upflow anaerobic sludge blanket reactor treating VW acidification liquid. The AGS inoculum was preferable to the conventional inoculum in view of the multitudinous and abundant methanogens. Under the optimum inoculation conditions, the anaerobic batch co-digestion of AP and VW at different mixing TS ratios of 5:0, 4:1, 3:2, 2:3, 1:4 and 0:5 were conducted to obtain a suitable substrate mixing ratio. Results showed that the optimal AP/VW ratio was 2:3, which gave the highest methane yield of 336 mL/g-VS. The excellent performance of the co-digestion was attributed to the balanced C/N, reduced accumulation of volatile fatty acids (VFAs), stable pH value, as well as the high quality and quantity of methanogens included in the inoculum.

Agricultural wastes have severely polluted the environment and obstruct the sustainable development of modern agriculture due to a lack of effective disposal methods. The present study conducted batch experiments in which rice straw (RS) and pig manure (PM) mixtures were pretreated with a previously developed cellulolytic microflora prior to their mesophilic anaerobic co-digestion. Optimal anaerobic digestion (AD) performance of RS and PM could be achieved after biological pretreatment with this specific cellulolytic microflora for 30 h. Under this condition, the filter paper cellulase (FPase) and carboxymethyl cellulase (CMCase) activities in RS and PM degradation broths reached maxima of 2.25 and 2.58 IU/mL, respectively, and the weight loss ratio reached 39.4%. After the subsequent AD process, the methane yield of RS and PM mixtures reached 263.69 mL/g-VS, which was 47.6% higher than that of the control group (CK) without biological pretreatment (178.66 mL/g-VS). In addition, the daily methane production peak duration (3 day) of the anaerobic co-digestion of RS and PM after 30 h of biological pretreatment with this microflora was longer than that of CK (1 day). The above results further indicated that pretreatment of RS and PM mixtures with microflora greatly enhanced the methane yield and prolonged the peak period of methane production in the subsequent anaerobic co-digestion.

Anaerobic digestion of dairy cattle manure is a common practice; however, the low biogas yield of manure can hamper the profitability of anaerobic digestion systems in small to medium dairy cattle farms . To make this technology more attractive to farmers, an increase in biogas yield per cubic meter of reactor could be achieved by co-digesting animal manure with co-substrates such as straw (in its raw form or pre-treated). A Techno-economic assessment of anaerobic co-digestion of cattle manure and raw and briquetted straw has been carried out. The results obtained from the techno-economic assessment showed that for a farm of 250 adult cattle heads the revenues generated in an anaerobic mono-digestion process are not able to offset the initial required investment. However, the co-digestion of manure with raw or briquetted straw showed better economic performance and positive returns (net present values > 0, internal rate of return > 9% and a RETURN of the investment in 11 years) for farmers willing to implement anaerobic digestion. Electricity selling price, and the price of the straw are the key parameters to determine the profitability of the system. Moreover, pre-treatments to increase the straw biogas production have been assessed and evaluated from a technic and economic perspective. Alkali and microwave-alkali straw pre-treatments showed the best results with an increase in biogas production of 156% and 92% compared to raw straw.

Mezcal is produced mostly from an Agave angustifolia Haw var. Espadin and generates large quantities of bagasse and vinasses that contaminate the environment. This paper presents a study on the co-digestion of Agave angustifolia Haw bagasse and vinasses for biogas production under minimal operation requirements (water and nutrients), typical in mezcal production facilities. Methane production results from Agave angustifolia Haw bagasse (AAHB) are compared to Agave tequilana Weber bagasse var. Azul (ATWB) from the Tequila industry at the same tested conditions. Small fibers of AAHB are more effective for producing methane than large fibers but adding high concentrations of vinasses stops the generation of methane. The resistance of fiber to biodegradation by microorganisms is partly observed in AAHB but not in ATWB. The type of inoculum had a strong effect on the methane yield. ATWB plus granular sludge gave rise to a potential methane production 65% more than AAHB plus granular sludge.

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.

The demand for uniformly sized and shaped produce that are aesthetically pleasing results in significant food waste throughout the world. Cucumber waste is a major agricultural waste product in a number of countries, especially areas with high pickle production. Opportunity exists for wastewater treatment plants containing anaerobic digesters to utilize cucumber agricultural and industrial waste for biogas production. The biomethane potential of cucumber waste as a substrate for co-digestion with sewage sludge was assessed. The impact of long-term co-digestion of cucumber was then evaluated using mesophilic continuously stirred tank reactors (CSTRs), in both single- and two-stage anaerobic co-digestion with sewage sludge. Ground cucumber waste was added to sewage sludge at 8% of the volume (4.5-4.6% of the organic load) and CSTRs were maintained for five hydraulic retention times (HRTs). One-stage co-digestion of cucumber waste produced comparable gas levels as CSTRs without cucumbers (averaging 219 and 221 m

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 study investigated the anaerobic co-digestion of different feed materials (FMs). The FMs of Prosopis juliflora pods (PJP), water hyacinth (WH), and dry leaves (DL) were anaerobically d...

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.

The anaerobic co-digestion of fruit and vegetable waste (FVW) and municipal sewage sludge (MSS) is investigated under mesophilic conditions. This was done at a constant hydraulic retention time (HRT) similar to that typically used at waste water treatment plant digesters, 20 days. The effects on digester performance of the FVW:MSS ratio and the organic loading rate (OLR) were examined. Initially the digester was fed with MSS from wastewater treatment plants (WWTP) with an average OLR of 1.03 kg

© 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 objective of this study was to evaluate the performance of the anaerobic co-digestion of different concentrations of industrial landfill leachate associated with crude residual glycerin, in relation to the methanogenic potential, COD removal, accumulated methane production, the effects of the factors (food/microorganism ratio and percentage of glycerin added to the leachate) and their interactions on kinetic parameters of methane production (CH

Sewage sludge and aqueous wastes are usually treated in separate facilities. Both may pose specific issues, mainly related to the uncertainty of the recovery/disposal route and costs, for the sludge, and to the extremely variable quantitative and qualitative properties, for the aqueous waste. In the present work, the co-digestion of thickened sludge and aqueous wastes in a Thermophilic Aerobic Membrane Reactor (TAMR) was studied in order to allow the almost complete reduction of sludge directly in wastewater treatment plants (WWTPs). Different conditions (aerobic and alternate aeration) were tested in a pilot plant, at the semi-industrial scale. The TAMR plant was operated at 48°C with constant organic load rate (5 kgCOD m

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.

Potential of co-digestion mixing thickened secondary sludge (TS) from extended aeration wastewater treatment plant and locally available substrates (whey, grease and septage) has been studied using three steps. The first step was a batch test to determine biological methane potential (BMP) of different mixtures of the three co-substrates with TS. The second step has been carried out with lab-scale reactors (20 L) simulating anaerobic continuous stirred tank reactors fed by three mixtures of co-substrates determined according to previous step results. Modelling using ADM1 as a mechanistic model was applied in the third step to help understanding the co-digestion process. According to BMP step, septage used as co-substrate has a negative effect on performance and addition of 10 to 30% grease or 10% whey would lead to a higher production of biogas and with an increase of the methane content. The results from the reactor showed less evi-dence of the positive effects observed with the BMP assay. Protein and lipid fractions of particu-late biodegradable COD are important variables for digester stability and methane production as predicted by modelling. Results of simulations with ADM1 model adapted to co-digestion confirmed that this model is a powerful tool to optimize the process of biogas production.

The dynamics of microbial communities involved in anaerobic digestion of mixed organic waste are notoriously complex and difficult to model, yet successful operation of anaerobic digestion is critical to the goals of diverting high-moisture organic waste from landfills. Machine learning (ML) is ideally suited to capturing complex and nonlinear behavior that cannot be modeled mechanistically. This study uses 8 years of data collected from an industrial-scale anaerobic co-digestion (AcoD) operation at a municipal wastewater treatment plant in Oakland, California, combined with a powerful automated ML method, Tree-based Pipeline Optimization Tool, to develop an improved understanding of how different waste inputs and operating conditions impact biogas yield. The model inputs included daily input volumes of 31 waste streams and 5 operating parameters. Because different wastes are broken down at varying rates, the model explored a range of time lags ascribed to each waste input ranging from 0 to 30 days. The results suggest that the waste types (including rendering waste, lactose, poultry waste, and fats, oils, and greases) differ considerably in their impact on biogas yield on both a per-gallon basis and a mass of volatile solids basis, while operating parameters are not useful predictors in a carefully operated facility.

Considerable amounts of slaughterhouse wastes (SHW) are generated in Indian urban centres causing serious environmental issues that demand effective treatment and disposal. The present study evaluates the effect of pasteurization (70 °C for 1 h) and extrusion pre-treatment on pathogen removal and methane production from SHW in anaerobic mono- and co-digestion with mixed vegetable, fruit and flower market wastes (VMW) under controlled batch anaerobic digestion (AD) tests. The complete destruction of pathogen was observed in post-pasteurized SHW, whereas the post-extruded SHW showed significant reduction (p

The synergism of food waste associated with swine manure can provide an increase in biogas production, besides promoting greater stability in the anaerobic co-digestion process. To verify this effect, co-digestion tests were performed in two reactors, one with agitation, and the other without agitation. In both systems, gasometers were used to measure biogas production in an experiment lasting two hydraulic retention times (HRT). On each feeding day, the temperatures of the ambient and of the effluent taken from the reactors were measured, and samples of the food waste and effluent were collected to perform analysis of pH, total solids (TS), volatile solids (VS), fixed solids (FS), volatile acidity (AV), and total alkalinity (TA). In addition, the chemical oxygen demand (COD) was determined every five days, and gas composition was determined at the beginning of the second HRT. As important results, in both reactors a decrease in pH was verified due to the weakening of the buffer effect of the medium. This was due to the low alkalinity found in the food waste, causing an increase in acidity in the contents of the reactors. The volume of biogas produced was higher in the reactor with agitation, which meant an increased efficiency of the process. Finally, a low methane content was verified through chromatographic analyses, indicating a reduction in the activity of the microorganisms present in the medium. Thus, it is concluded that agitation linked to anaerobic co-digestion of swine manure with food waste exerted a positive effect on biogas production.

The technology of anaerobic co-digestion to treat the excess biological sludge discharged from activated sludge systems in oil refineries was evaluated in bench scale experiments. Mixing food waste rich in fruits and vegetables with this sludge increased the reduction of volatile solids and biogas yield. An experimental design indicated that the best co-digestion condition was the use of waste activated sludge without previous dewatering (3.5% total solids) and food waste in an 80:20 ratio (% v/v), without the addition of inoculum. After 45 days at 35 °C, this condition resulted in volatile solid (VS) removal of 52% and biogas yield of 80.7 mL biogas/g VSadded, against only 19% and 38.5 mL biogas/g VSadded in mono-digestion of sludge alone. Anaerobic co-digestion demonstrates promising results and the potential for a simple and effective treatment method for excess biological sludge generated at refineries.

This study presents the effect of mechanical, chemical, thermal, and hybrid pretreatment on anaerobic digestion of fruit-juice industrial waste (FW) co-digested with municipal sewage sludge (MSS). The pretreatment of the substrates with ultrasonication, microwave, weak alkali-acid caused an increase in cumulative biogas production of approximately 20.9, 14.9, 8.1, and 5.2%, respectively. Beside this, thermal and strong acid-alkali pretreatment reduced biogas production. The highest cumulative biogas and methane yield was increased with hybrid pretreatment which contains ultrasonication (US) and alkali (AL) pretreatment by 36% and 49%, respectively. Also, compared to untreated mixture, the soluble COD, carbohydrate, and protein removal efficiencies were increased from 42.6% to 65.6%, 65.1% to 86.6%, and 17.3% to 62.4%, respectively for US-AL pretreatment. The kinetic parameters of cumulative biogas production for the selected reactors were further estimated with Monod, Cone, and Transference Function models.

Anaerobic digestion is a widely accepted method to treat wastes such as peanut shell. The energy and nutrients are simultaneously recovered by this method. The objective of this study was to elucidate the effect of TiO 2 nanoparticles in co-digestion of hybrid Pennisetum and peanut shell under mesophilic conditions. The results demonstrated the methane (CH 4 ) production was improved by adding the TiO 2 nanoparticles. The cumulative gas production is best (up to 11,133.3 mL) by adding 0.15% nano-TiO 2 particles. The microbial community analysis showed that Methanobacterium and Methanosarcina were enriched in the presence of TiO 2 nanoparticles indicating that TiO 2 can improve CH 4 production by stimulating the growth of methanogens.

Biomass is an attractive energy source that can be used for production of heat, power, and transport fuels, and when produced and used on a sustainable basis, can make a large contribution to reducing greenhouse gas (GHG) emissions. Anaerobic digestion (AD) is a suitable technology for reducing organic matter and generating bioenergy in the form of biogas. This study investigates the factors allowing the optimization of the process of biogas production from the co-digestion of wheat straw (WS) and bovine manure. The statistical analysis of the experiments carried out show that ultrasonic processing plays a fundamental role by sonication density and solids concentration leading to improved characteristics of WS by reducing particle size and increasing concentration of soluble chemical oxygen demand. The higher the sonicating power used, the more the waste particles are disrupted. The optimality obtained under mesophilic conditions for WS pretreated with 4% w/w (weight by weight) H2O2 at temperature 36 °C under 10 minutes of ultrasonication at 25 kHz improves the methane yield by 64%.

Plant waste (PW) and excess sludge (ES) are two main organic matters of municipal solid waste. However, there are few reports on their anaerobic co-digestion. In this work, the mixed proportion of PW and ES anaerobic co digestion was first optimized at mesophilic temperature, and then the anaerobic co-digestion of PW and ES was enhanced with strong oxidant calcium peroxide (CP). The results showed that the optimal mixing ratio of PW and ES was 1/1 (in terms of volatile solids), and the C/N of mixed digestion substrate was 23.5/1, the maximum methane production was 172.6 mL/g (in terms of volatile solids). CP could enhance methane production from anaerobic co-digestion of PW and ES. When the content of CP was 0.2 g/g (in terms of total suspended solids), the maximum methane production was 234.8 mL/g, about 1.4 times of the blank. The mechanism investigation showed that CP promoted the release of organic matter during the co-digestion, and the higher the content of CP, the greater the release of soluble chemical oxygen demand. The presence of appropriate amount of CP promoted the activities of key enzymes in anaerobic fermentation process, and then increased the efficiency of methane production. The results of this work provide an alternative strategy for the resource utilization of PW and ES.

Codigestion is an emerging approach to improve wastewater sludge biogas production and valorize food waste (FW). This study explores FW-derived biochar as a codigestion amendment for the first time and reports a matrix experiment using four diverse biochar amendments (mixed food waste, pinewood, bonechar, unamended control) across four FW types (vegetable, rice, chicken, mixed). It demonstrated that biochar derived from mixed FW can greatly improve the performance of biogas production and yield relative to unamended control and other biochars. The mixed food waste (MFW) biochar amendment led to 34.5%, 35.6%, and 47.5% increase in methane production from mixed FW compared to biochars made of wood, bone and non-amendment control, and the maximum methane production rate of MFW biochar reactors could be up to 6.7–9.9 times of the control. These results suggest that a more circular utilization of FW by integrating biochar production with codigestion can bring great benefits to FW management.

ABSTRACT Pretreatment of the fruit, food and vegetable waste materials could enhance the biogas generation in a shorter time along with waste reduction. The aim of the present work was to assess the effectiveness of alkaline, hydrothermal, thermal and ultrasonication pretreatment of fruit, food, and vegetable waste with cow dung for the mesophilic anaerobic co-digestion. The mesophilic anaerobic co-digestion of fruit food and vegetable waste as single substrate with cow dung were performed in a laboratory scale 1L batch digester for 30 days at 40 ± 2 oC temperature. Obtained result show that pretreatment process has enhanced the biogas and biomethane production by 35 % and 44.4 % with 19.89 % TS and 17.30 % VS removal in case of ultrasonication pretreatment (100.45 ml biogas/gVS and 27.92 ml CH4/gVS,), while slight increase is found with thermal and hydrothermal pretreatment as compared to untreated FFVW. The biogas production is enhanced by 35%, 20.4%, 5%, 6% and biomethane production are enhanced by 44.4%, 22%, 11%, 9.8% in the case of ultrasonication, alkaline, thermal and hydrothermal pretreatment process, respectively. The stable mesophilic anaerobic co-digestion operation was achieved and impacts of the different pretreatment methods on the biogas yield and net energy recovery along with viability of anaerobic co-digestion have been explored.

The agro-industry of tomato generates three types of residues: ripe rotten tomato (unfit for consumption) (RT), green (unripe) tomato (GT), and tomato branches including leaves and stems (TB). These materials are commonly wasted or used as feed for livestock. Energy production through anaerobic digestion is an alternative way to manage and simultaneously valorise these materials. Initially, the operating conditions of mono anaerobic digestion were investigated using RT. Thus, a design of experiments based on a two-level fractional factorial design with resolution V was performed to determine the factors that affect biochemical methane potential (BMP). The substrate to inoculum ratio (SIR), total volatile solids concentration (VSt), working volume (WV), presence of nutrients (Nu), and the pre-incubation of the inoculum (Inc) were investigated. The results showed that SIR is the most important factor. The maximum BMP for RT was 297 NmLCH4/gVS with SIR = 0.5, tVS = 20 g/L, WV = 20%, no pre-incubation and the presence of nutrients. Using these optimum operating conditions, co-digestion was investigated through a mixture design approach. The substrates RT and GT presented similar BMP values, whereas TB led to a significantly lower BMP. Indeed, when high concentrations of TB were used, a significant decrease in methane production was observed. Nonetheless, the highest BMP was achieved with a mixture of 63% RT + 20% GT + 17% TB, with a production of 324 NmLCH4/gVS, corresponding to a synergetic co-digestion performance index of about 1.20. In general, although the substrate RT generates the highest BMP, the mixture with GT did not impair the methane yield. Overall, the co-digestion of tomato residues must be conducted with SIR close to 0.5 and the content of tomato branches in the reaction mixture should be kept low (up to 20%).

BACKGROUND: Olive mill wastewater (OMW) represents an environmental problem due to its high organic load and relevant concentration of phenolic compounds (PCs). OMW treatment and disposal represents a relevant challenge and cost for olive mills and multi-utilities in charge of waste management in Mediterranean countries. The goal of this study was to develop an anaerobic co-digestion (co-AD) process of OMW and sewage sludge (SwS) from municipal wastewater treatment. RESULTS: Different volumetric OMW:SwS ratios up to 100% OMW were fed in continuous 1.7-L bioreactors. The reactors fed with raw OMW (rOMW) performed better than those fed with OMW dephenolized by adsorption (dOMW). At a 23-day hydraulic retention time, the best performances were obtained in the reactor fed with 25% rOMW, with a 105% increase in methane yield in comparison to the 100% SwS test. At a 40-day hydraulic retention time, the reactor fed with 40% rOMW attained a 268 NLCH4/kgvolatile solids methane yield. The conversion of phenolic compoundsreached 70% when the hydraulic retention time was increased from 23 to 40 days. A cost–benefit analysis indicated that both rOMW co-AD in existing digesters and phenolic compounds recovery from OMW followed by co-AD of dOMW can lead to relevant additional revenues for the multi-utilities in charge of wastewater management. CONCLUSION: This work proves that, using the existing network of SwS anaerobic digesters, it is feasible to co-digest the entire OMW production in regions characterized by intense olive oil production, thus attaining a relevant increase in methane production yield (a 144% increase in comparison to 100% SwS).

This study evaluated the effect of temperature on the anaerobic co-digestion of acerola agro-industry effluent (EAV) and domestic sewage (EDT). The assays were performed in triplicates of reactor flasks using treatments with different mixture compositions (T1= 5% EDT + 95% EAV; T2= 20% EDT + 80% EAV; T3= 30% EDT + 70% EAV) and anaerobic sludge as inoculum (5 g.L−1 ), at mesophilic (35 °C) and thermophilic (55 °C) temperatures. The analyses of soluble chemical oxygen demand (CODs) and volatile fatty acids (VFA) were performed by etermining the removal efficiency of the CODs, the decay rate constant of the COD (Kd), and the percentages of anaerobic biodegradability (%BD) and methanation (%M). The inoculum biomass of the treatments was observed through scanning electron microscopy (SEM) at the end of the degradation process (12 days). Regardless of the temperature, the anaerobic digestion was considered efficient, with biodegradability above 60%. The mesophilic temperature favored the anaerobic co-digestion for all mixture compositions, presenting more diversified and structured biomass at the end of the assays, as well as higher removal efficiencies of the CODs and methanization, especially for T3 at 35 °C (63% and 51%, respectively). Furthermore, the kinetics of the degradation process proved to be more accelerated at mesophilic conditions (Kd 0.1d−1 ) and in the treatments with a higher percentage of sewage (T2M and T3M). Made available in DSpace on 2022-03-10T12:02:52Z (GMT). No. of bitstreams: 1 Anaerobic-co-digestion-of-acerola-2021.pdf: 1147499 bytes, checksum: e73ae089b7e06eab14d5bdb104848265 (MD5) Previous issue date: 2021

The effects of pyrolysis pretreatment on biogas production during anaerobic co-digestion of corn stover were studied. The corn stover characteristics were investigated by performing thermogravimetric analysis using a heating rate of 10.0°C/min and an air atmosphere at atmospheric pressure. Corn stover aliquots pretreated in an electric furnace at 100°C for 360 min, 200°C for 15 min, and 300°C for 5 min were used. Untreated and pretreated corn stover samples were analyzed by scanning electron microscopy and other methods, and the bulk densities and component ratios were compared to identify changes caused by the pretreatments. The amounts of total solids, volatile solids, volatile fatty acids, and total ammonia nitrogen produced when the stover samples were anaerobically digested were measured. The biogas production rate and the methane concentration in the biogas were determined. The substrate-specific methane yields were determined, and the relationships between the yields and pretreatment conditions were assessed. The sample pretreated at 300°C for 5 min produced the most biogas. The corn stover total solid bulk density was directly related to the substrate-specific methane yield, the substratespecific methane yield decreasing as the total solid bulk density increased.

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.

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG [Abstract] The main aim of this work was to evaluate the efficiency of producing caproic acid and other volatile fatty acids using a co-digestion between cheese whey and sewage sludge in a continuous reactor. The effect of two different feeding regimes (one and two per day) and three hydraulic retention times (HRT) (15, 10 and 6 days) on the organic acids production were studied. The optimal conditions for the process were 10 days HRT, 2 feeding cycles per day, reaching a maximum degree of acidification of 44%. Under these conditions, the most abundant organic acid was caproic acid. The analysis of the microbial community dynamics in the reactor during the HRT changes revealed a microbiome enriched in organisms involved in caproic acid production. Additionally, the production of polyhydroxyalkanoates using the organic acids stream as feeding was verified in a fed-batch experiment obtaining a copolymer formed by hydroxybutyrate, hydroxyvalerate and hydroxyhexanoate. This study received funding from the European FEDER framework program CTQ2017-88292-R and from the Spanish Ministry of Economy and Competitiveness (MINECO), also by Xunta de Galicia under the grant agreement for Competitive Reference Research Groups (GRC) (ED431C 2017/66). The authors would like to thank the companies EMALCSA S.A., and INNOLACT S.L. for their contribution Xunta de Galicia; ED431C 2017/66

Dimitrios Komilis thanks TECNIOspring programme for the 2014-2016 incoming fellowship in UAB (no. TECSPR13-1-0006). Raquel Barrena thanks TECNIOspring programme for the outgoing + return fellowship (no. TECSPR15-1-0051). Goal of the work was to study the effect of mixing aerobically pretreated organic municipal solid wastes (OFMSW) with raw OFMSW in an anaerobic digestion process. The optimum time of aerobic pretreatment was found to be five days, as this was indicated via biological activity measurements (oxygen uptake rate, enzymatic activities, temperature). The aerobically pretreated wastes or a liquid extract from those pretreated wastes were, each separately, mixed with simulated OFMSW in various experiments. The mixtures were anaerobically digested for 28 days and five different treatments were performed including the blanks. The methane generation results were fitted to a typical anaerobic model to calculate theoretical maximum methane potential, maximum methane generation rate and theoretical lag time. Results indicated that the addition of 5-day aerobically pretreated OFMSW in solid form to raw OFMSW resulted in a 18 % net increase of the methane production. The Rmax was also increased by 39 % while no significant differences in the lag time of the methanogenic phase were observed. The addition of the liquid extract that was obtained from the 5-day pretreated OFMSW did not result in a statistically significant increase of the net methane production of the raw OFMSW.

Anaerobic mono- and co-digestion of fruits and vegetable waste (FVW), slaughterhouse waste (SHW), and cattle manure (CM) under mesophilic conditions (35°C) were conducted through biochemical methane potential tests to investigate how the FVW in a co-substrate formulation improves the methane yield, the degradative synergy between substrates, and especially the stability of the process. The co-digestion of FVW:SHW and FVW:CM were evaluated with volatile solids (VS) ratios of 1:2, 1:1, and 2:1. The results indicated that the highest synergistic effect was found in the co-digestion FVW:CM at 1:1 VS ratio. However, the co-digestion FWV:SHW at 1:2 VS ratio increased the methane yield by 74.2% compared to the mono-digestion of FVW (776.3 mL CH4 g VSadded−1). As a critical condition in these processes, the stability was evaluated using the early warning indicator VFA/TA (volatile fatty acids/total alkalinity). The co-substrate SHW promotes greater stability in methane production as the soluble carbohydrate content in FVW increases. It was proposed that the high protein (49.04 ± 0.96% VS) and ammonia content (693 ± 3 mg L−1) of SHW leads to the formation of a dampening system known as a carbonate-acetic buffer. It was concluded that balanced distribution between carbohydrates, proteins, and lipids is crucial to increase methane yields, and the low methane productions were associated with low N-NH4+ concentrations (FVW:CM co-digestions). The results obtained in this study can serve as a basis to design full-scale digesters under similar operating conditions and with the same substrate:co-substrate relationships. Implications: The production of methane from the anaerobic digestion process of food, and lose waste presents a viable alternative of valorization and could help to mitigate environmental impacts. However, anaerobic digestion from these substrates carries high instabilities and low methane yields. The need to increase these yields and contribute to process stability must be considered in the selection of a co-substrate. In this context, this work aims to evaluate the best fruits and vegetable waste: co-substrateformulation, that promotes higher methane yield, a synergy between substrates, and to improve the AD process stability in the presence of perturbations in the substrate composition. We believe that our results could be helpful for the design processes for methane production from fruit and vegetable waste, to contribute to competitiveness with conventional energies and promote the sustainability of these processes.