Potential for methane production from anaerobic co-digestion of swine manure with winery wastewater

This work examines the methane production potential for the anaerobic co-digestion of swine manure (SM) with winery wastewater (WW). Batch and semi-continuous experiments were carried out under mesophilic conditions. Batch experiments revealed that the highest specific methane yield was 348 mL CH₄ g⁻¹ COD added, obtained at 85.4% of WW and 0.7 g COD g⁻¹ VS. Specific methane yield from SM alone was 27 mL CH₄ g⁻¹ COD added d⁻¹. Furthermore, specific methane yields were 49, 87 and 107 mL CH₄ g⁻¹ COD added d⁻¹ for the reactors co-digesting mixtures with 10% WW, 25% WW and 40% WW, respectively. Co-digestion with 40% WW improved the removal efficiencies up to 52% (TCOD), 132% (SCOD) and 61% (VSS) compared to SM alone. These results suggest that methane can be produced very efficiently by the co-digestion of swine manure with winery wastewater.     

Pathogen removal in farm-scale psychrophilic anaerobic digesters processing swine manure

This study assessed the efficiency of commercial-scale psychrophilic anaerobic digestion in sequencing batch reactors (PADSBRs) for pathogen removal from pig manure. The impact of treatment cycle length and of hydraulic flow regimes on pathogen removal efficiency was investigated. Two conventionally operated SBRs (BR1 and BR2) and two SBRs simultaneously fed during the draw step (BR3 and BR4) were monitored over a two-year period. PADSBRs significantly decreased the concentration of coliforms, Salmonella, Campylobacter spp., and Y. enterocolitica, respectively from about 10⁶, 10³ CFU g⁻¹, 10³, and 10⁴ CFU g⁻¹ to undetectable levels in most samples. Densities of the gram-positive Clostridium perfringens and Enterococcus spp. remained high (10⁵ CFU g⁻¹) in the digesters throughout treatment. The PADSBRs maintained the same level of pathogen removal when the treatment cycle length was reduced from 2 to 1 week. Mass balances on volatile fatty acids (VFAs) revealed short-circuits of inlet flow respectively averaging 6.3% and 6.4% for BR3 and BR4, significantly reducing the overall performance of these reactors regarding pathogens removal. The results obtained in this study show the ability of low temperature anaerobic digestion to remove or significantly reduce indicator and pathogen concentration from raw pig manure.     

Optimization of biogas production from cattle manure by pre-treatment with ultrasound and co-digestion with crude glycerin

Biogas production by co-digestion of cattle manure with crude glycerin obtained from biodiesel production was studied after pre-treatment of the cattle manure or mixtures of cattle manure with different amounts of added glycerin with ultrasound. Batch experiments with 1750 mL of medium containing 1760 g of screened cattle manure or mixtures of cattle manure (screened or ground) and 70-140 mL or crude glycerin were incubated under mesophilic and thermophilic condition in stirred tank reactors. Under mesophilic conditions, the addition of 4% glycerin to screened manure increased biogas production by up to 400%. Application of sonication (20 kHz, 0.1 kW, and 4 min) to a mixture of manure + 4% glycerin increased production of biogas by up to 800% compared to untreated manure. The best results were obtained under thermophilic conditions using sonicated mixtures of ground cattle manure with 6% added glycerin (348 L methane/kg COD removed were obtained).     

Comparative evaluation of biogas production from dairy manure and co‐digestion with maize silage by CSTR and new anaerobic hybrid reactor

This study aimed to investigate potential methane production through anaerobic digestion of dairy manure and co‐digestion with maize silage. Two different anaerobic reactor configurations (single‐stage continuously stirred tank reactor [CSTR] and hybrid anaerobic digester) were used and biogas production performances for each reactor were compared. The HR was planned to enable phase separation in order to improve process stability and biogas production under higher total solids loadings (≥4%). The systems were tested under six different organic loading rates increased steadily from 1.1 to 5.4 g VS/L.d. The CSTR exhibited lower system stability and biomass conversion efficiency than the HR. The specific biogas production of the hybrid system was between 440 and 320 mL/gVS with 81–65% volatile solids (VS) destruction. The hybrid system provided 116% increase in specific biogas production and VS destruction improved by more than 14%. When MS was co‐digested together with dairy manure, specific biogas production rates increased about 1.2‐fold. Co‐digestion was more beneficial than mono‐material digestion. The hybrid system allowed for generating methane enriched biogas (>75% methane) by enabling phase separation in the reactor. It was observed that acidogenic conditions prevailed in the first two compartments and the following two segments as methanogenic conditions were observed. The pH of the acidogenic part ranged between 4.7 and 5.5 and the methanogenic part was between 6.8 and 7.2.     

Sulfide removal from livestock biogas by Azospirillum-like anaerobic phototrophic bacteria consortium

Biogas production from anaerobic biodegradation of livestock waste is a potential source of renewable energy. In addition to methane, biodegradation of this high-strength waste also produces sulfide that must be removed in order to prevent costly corrosive impacts on infrastructure. In this work, an anaerobic, phototrophic microbial community enriched from the native population in a swine waste lagoon was evaluated for its potential to remove sulfide from swine waste biogas. Batch experiments with the consortium attained removal efficiencies greater than 97% for sulfide concentrations above 1200 ppm. 16S rRNA gene sequencing revealed that the dominant population was most closely related to the isolate Azospirillum strain C5 (similarity index of 99%). Photomicrograph of the enriched consortium revealed the presence of cells with intracellular globules resembling sulfur storage. The enrichment of Azospirillum-like and the concomitant sulfide consumption suggest that this microorganism played an important role in sulfide removal in the bioreactor.     

The future of anaerobic digestion and biogas utilization

One of the common tendencies of animal production activities in Europe and in developed countries in general is to intensify the animal production and to increase the size of the animal production units. High livestock density is always accompanied by production of a surplus of animal manure, representing a considerable pollution threat for the environment in these areas. Avoiding over-fertilization is not only important for environmental protection reasons but also for economical reasons. Intensive animal production areas need therefore suitable manure management, aiming to export and to redistribute the excess of nutrients from manure and to optimize their recycling.     

Development of a pilot scale anaerobic digester for biogas production from cow manure and whey mix

This paper presents results from anaerobic digestion of cow manure and whey mix. A pilot scale anaerobic digester, 128 l in volume, has been developed, to operate under batch and fed-batch conditions. The versatile and unique characteristics of the instrument allowed testing the methane production directly in the farm. The digester performance was evaluated with two calibration tests, the main for a period of 56 days. The study test was divided into three phases, one for each type of feeding operation (batch, fed-batch, batch). The initial phase of digestion resulted in 57 l-CH₄/kg-VS, the second phase had a yield of 86.6 l-CH₄/kg-VS and the third one had a production of 67 l-CH₄/kg-VS. The total methane yield was equal to 211.4 l-CH₄/kg-VS. Using the obtained pilot plant results to a real scale diary production cycle, it was possible to evaluate an electricity production equal to 8.86 kwh per 1 t/d. The conducted tests did show that there is a good potential to the use of a cow manure and whey biomass mix for biogas production.     

Mesophilic and thermophilic anaerobic co-digestion of abattoir wastewater and fruit and vegetable waste in anaerobic sequencing batch reactors

Anaerobic co-digestion of fruit and vegetable waste (FVW) and abattoir wastewater (AW) was investigated using anaerobic sequencing batch reactors (ASBRs). The effects of hydraulic retention time (HRT) and temperature variations on digesters performances were examined. At both 20 and 10 days biogas production for co-digestion was greater thanks to the improved balance of nutrients. The high specific gas productions for the different digestion processes were 0.56, 0.61 and 0.85 l g⁻¹ total volatile solids (TVS) removal for digesters treating AW, FVW and AW + FVW, respectively. At an HRT of 20 days, biogas production rates from thermophilic digesters were higher on average than from mesophilic AW, FVW and AW + FVW digestion by 28.5, 44.5 and 25%, respectively. However, at 10 days of HRT results showed a decrease of biogas production rate for AW and AW + FVW digestion processes due to the high amount of free ammonia at high organic loading rate (OLR).     

Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant

The effect of mixing on biogas production of a 1.5‐m³ pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.     

Biogas manufacture from co-digestion of untreated primary sludge with raw chicken manure under anaerobic mesophilic environmental conditions

This work aimed to co-digest various wastes to assess the best combination of all mixing ratio, also at choosing the best ratio between untreated primary sludge (UPS) singly from two sources, (South valley University (SUPS) and Abu tesht wastewater station (AUPS) and raw chicken manure (RCM) and comparing the results in either case. The co-digestions of untreated primary sludge from Abu tesht wastewater treatment stations with different levels of raw chicken manure (0:100, 10:90, 30:70, 50:50, 90:10, and 100:0) to obtain the best mixtures. Also, co-digestion of untreated primary sludge from south valley university with different levels of raw chicken manure at the same ratios, to obtain the best mixtures. Batch digestion tests were applied in 2.5 L digester with a working volume of 2.0 L. The samples in triplicates were separately loaded into the digesters locally fabricated and kept for 20 days as a retention period and diluted with the same amount of water. Mesophilic under 35 °C was adopted for untreated primary sludge as well as mixtures with raw chicken manure based on total solids (TS) and volatile solid (VS) proportions. The average biogas yields from AUPS/RCM mixture obtained ranged from 8570 to 5600 ml, by the following descending order, 10: 90 > 90:10 and so on >100:0, and the average biogas yields from SUPS/RCM obtained ranged from 6330 to 5635 ml, in the order of 90: 10 > 10:90 and so on >100:0. The results showed highest biogas yield from AUPS/RCM and SUPS/RCM mixtures with mixing ratio of 10:90 and 90:10, respectively, however, the lowest biogas production detected in separate digestion of AUPS and SUPS. The results indicated that co-digestion between the sludge and raw chicken manure could increase total biogas production volume, enhance sludge treatment process, and produce eco-friendly sludge because of co-digestion process than separate processing of each feedstock.     

Impact of chlortetracycline on sequencing batch reactor performance for swine manure treatment

Treatment of aged (500 day, 4 °C stored) chlortetracycline (CTC; 0, 20, 40, 80 mg/L CTC)-amended swine manure using two cycle, 22 day stage anaerobic sequencing batch reactors (SBR) was assessed. Eighty milligrams per liter CTC treatment inhibited SBR treatment efficiencies, although total gas production was enhanced compared to the no-CTC treatment. The 20 and 40 mg/L CTC treatments resulted in either slight or no differences to SBR treatment efficiencies and microbial diversities compared to the no-CTC treatment, and were generally similar to no-CTC treatments upon completion of the first 22 day SBR cycle. All CTC treatments enhanced SBR gas generation, however CH₄ yields were lowest for the 80 mg/L CTC treatment (0.111 L CH₄/g tCOD) upon completion of the second SBR react cycle. After a 22 day acclimation period, the 80 mg/L CTC treatment inhibited methanogenesis due to acetate accumulation, and decreased microbial diversity and CH₄ yield compared to the no-CTC treatment.     

Stirring and biomass starter influences the anaerobic digestion of different substrates for biogas production

Here, we present the results of lab‐scale experiments conducted in a batch mode to determine the biogas yield of lipid‐rich waste and corn silage under the effect of stirring. Further semi‐continuous experiments were carried out for the lipid‐rich waste with/without stirring. Additionally, it was analyzed how the starter used for the batch experiment influences the digestion process. The results showed a significant stirring effect on the anaerobic digestion only when seed sludge from a biogas plant was used as a starter. In this case, the experiments without stirring yielded only about 50% of the expected biogas for the investigated substrates. The addition of manure slurry to the batch reactor as part of the starter improved the biogas production. The more diluted media in the reactor allowed a better contact between the bacteria and the substrates making stirring not necessary.     

Anaerobic co-digestion of swine manure with energy crop residues

Anaerobic co-digestion involves the treatment of different substrates with the aim of improving the production of biogas and the stability of the process. In this research, co-digestion of swine manure (SM) and energy crop residues (ECRs) was studied. The mixtures evaluated contained SM combined with maize (Mz), rapeseed (Rs) or sunflower (Sf) residues. Batch and semi-continuous experiments were performed to determine methane (CH₄) yields and the behavior of reactors while co-digesting agricultural wastes. Three different proportions of ECRs were tested in batch experiments for co-digestion with SM: 25, 50, and 75% volatile solids (VS). On the basis of the results obtained from batch tests, a mixture with a 50% ECR content was selected for the second stage of the study. Mesophilic reactors with a 3 L working volume were used for semi-continuous experiments. The hydraulic retention time (HRT) was set at 30 days and the reactors were kept under these operational conditions over four HRTs. The addition of ECR to the co-digestion system resulted in a major increase in the amount of biogas produced daily. The highest biogas yield was obtained when co-digesting Rs (3.5 L/day), although no improvement was observed in specific gas production from the addition of the co-substrate.     

Optimising the biogas production from leather fleshing waste by co-digestion with MSW

Waste from the leather industry, known as limed leather fleshing (LF), has a low C:N (3.2) and an alkaline pH of 11.4. This is a major disadvantage for anaerobic digestion due to ammonia toxicity for methanogenesis. This study describes co-digestion of LF with biodegradable fraction of municipal solids waste optimised over a range of C:N and pH to minimise ammonia and to maximise biogas yield. The optimum conditions were found with a blend that provided C:N of 15 and pH of 6.5 and the cumulative biogas yield increased from 560 mL using LF fraction alone, to 6518 mL with optimum blend. At higher pH of 8.5, unionised ammonia was high (2473 mg L⁻¹) coincided with poor biogas yield (47 mL d⁻¹) that confirms ammonia toxicity. By contrast at a pH of 4.5 the ammonia was minimum (510 mg L⁻¹), but high VFA (26,803 mg L⁻¹) inhibited the methanogens. Biomass activity measured using ATP correlated well with biogas yield as reported previously.     

Potential errors in the quantitative evaluation of biogas production in anaerobic digestion processes

Errors that are commonly made in the quantification of biogas from anaerobic digestion experiments were investigated.For liquid displacement gasometers where a barrier solution separates the biogas and the atmosphere, inaccuracy due to gas diffusion was examined experimentally. Acidified saturated saline solution was the most suitable barrier solution, as biogas characteristics changed least with time. Using acidified or tap water caused considerable biogas losses and should therefore be avoided where biogas is stored before measurement.Errors associated with volume calculation from three common liquid displacement gasometer types were investigated theoretically. Corrections that must be made to obtain gas volumes at standard temperature and pressure when using this equipment are discussed. Regarding experimental errors, gasometer designs where displaced liquid is weighed to determine the volume are the most versatile since errors depend mainly upon balance sensitivity. Using liquid heights to calculate volume requires appropriate sizing of the gasometer relative to the volume of gas measured.The calibration of a low flow gas meter was investigated and an approximately linear variation with flow rate was found; hence in situ calibration is advised for this type of instrument. Correction for atmospheric conditions should be performed in real time to reduce errors.     

Optimization of biogas production from co-digestion of whey and cow manure

Anaerobic co-digestion is effective and environmentally attractive technology for energy recovery from organic waste. Organic, agricultural and industrial wastes are good substrates for anaerobic co-digestion because they contain high levels of easily biodegradable materials. In this paper enhancement of biogas production from codigestion of whey and cow manure was investigated in a series of batch experiments. The influence of whey ratio on specific biogas production in a mixture with cow manure was analyzed at 35 and 55°C, for different initial pH values and for different concentrations of supplemental bicarbonate in experiments carried out over 12 days. Good biogas production (6.6 dm³/dm³), methane content (79.4%) in a biogas mixture and removal efficiencies for total solids (16%) were achieved at optimum process conditions (temperature of 55°C, 10% v/v of whey and 5 g/dm³ NaHCO₃ in the initial mixture). In order to validate optimized conditions for co-digestion of whey and cow manure in the one-stage batch process, the experiments were performed within 45 days. The high biogas production (21.8 dm³/dm³), a good methane content (78.7%) in a biogas mixture as well as maximum removal efficiencies for total solids (32.3%), and chemical oxygen demand (56.3%), respectively indicate that whey could be efficiently degraded to biogas in a onestage batch process when co-digested with cow manure.     

Utilization of by-products from ethanol production as substrate for biogas production

The aims of this work were to determine the specific biogas yields of steam-exploded sugarcane straw and bagasse as well as to estimate their energy potential under Brazilian conditions. Steam-explosion was carried out under different time and temperature conditions. The specific biogas yields were analyzed in batch-tests according to VDI 4630.Results have shown that steam-explosion pre-treatment increased the specific biogas yields of straw and bagasse significantly compared to the untreated material. The utilization of these by-products can contribute to 5% of the total energy consumption and thereby higher energy independence in Brazil. Further efforts in defining the optimum pretreatment conditions with steam-explosion as well as implementing this technology in large scale plants should be made.     

Microbial communities involved in biogas production from wheat straw as the sole substrate within a two-phase solid-state anaerobic digestion

Microbial communities involved in biogas production from wheat straw as the sole substrate were investigated. Anaerobic digestion was carried out within an up-flow anaerobic solid-state (UASS) reactor connected to an anaerobic filter (AF) by liquor recirculation. Two lab-scale reactor systems were operated simultaneously at 37 °C and 55 °C. The UASS reactors were fed at a fixed organic loading rate of 2.5 g L⁻¹ d⁻¹, based on volatile solids. Molecular genetic analyses of the bacterial and archaeal communities within the UASS reactors (digestate and effluent liquor) and the AFs (biofilm carrier and effluent liquor) were conducted under steady-state conditions. The thermophilic UASS reactor had a considerably higher biogas and methane yield in comparison to the mesophilic UASS, while the mesophilic AF was slightly more productive than the thermophilic AF. When the thermophilic and mesophilic community structures were compared, the thermophilic system was characterized by a higher Firmicutes to Bacteroidetes ratio, as revealed by 16S rRNA gene (rrs) sequence analysis. The composition of the archaeal communities was phase-separated under thermophilic conditions, but rather stage-specific under mesophilic conditions. Family- and order-specific real-time PCR of methanogenic Archaea supported the taxonomic distribution obtained by rrs sequence analysis. The higher anaerobic digestion efficiency of the thermophilic compared to the mesophilic UASS reactor was accompanied by a high abundance of Firmicutes and Methanosarcina sp. in the thermophilic UASS biofilm.     

Biohydrogen from thermophilic co-fermentation of swine manure with fruit and vegetable waste: maximizing stable production without pH control

Hydrogen production by dark fermentation may suffer of inhibition or instability due to pH deviations from optimality. The co-fermentation of promptly degradable feedstock with alkali-rich materials, such as livestock wastes, may represent a feasible and easy to implement approach to avoid external adjustments of pH.Experiments were designed to investigate the effect of the mixing ratio of fruit-vegetable waste with swine manure with the aim of maximizing biohydrogen production while obtaining process stability through the endogenous alkalinity of manure.Fruit-vegetable/swine manure ratio of 35/65 and HRT of 2 d resulted to give the highest production rate of 3.27 ± 0.51 L_H2 L⁻¹ d⁻¹, with a corresponding hydrogen yield of 126 ± 22 mL_H2 g⁻¹_VS-added and H₂ content in the biogas of 42 ± 5%. At these operating conditions the process exhibited also one of the highest measured stability, with daily productions deviating for less than 14% from the average.     

Improvement of the anaerobic treatment of potato processing wastewater in a UASB reactor by co-digestion with glycerol

The effect of three different types of glycerol on the performance of up-flow anaerobic sludge blanket (UASB) reactors treating potato processing wastewater was investigated. High COD removal efficiencies were obtained in both control and supplemented UASB reactors (around 85%). By adding 2 ml glycerol product per liter of raw wastewater, the biogas production could be increased by 0.74 l biogas ml⁻¹ glycerol product, which leads to energy values in the range of 810–1270 kWh_electric per m³ product. Moreover, a better in-reactor biomass yield was observed for the supplemented UASB reactor (0.012 g VSS g⁻¹ COD_removed) compared to the UASB control (0.002 g VSS g⁻¹ COD_removed), which suggests a positive effect of glycerol on the sludge blanket growth.