Co-digestion of poultry manure and residues from enzymatic saccharification and dewatering of sugar beet pulp

This study investigates the co-digestion of poultry manure (PM) with sugar beet pulp residues (SBPR) obtained from saccharification and dewatering of sugar beet pulp. The laboratory-scale experiments were conducted under batch and semi-continuous conditions at mesophilic temperatures (35 °C). Batch tests gave specific biogas and methane yields of 590 dm³/kgVS_fed and 423 dm³CH₄/kgVS_fed, respectively for SBPR, whereas the corresponding values for PM were 434 dm³/kgVS_fed and 300 dm³CH₄/kgVS_fed. The co-digestion of PM with SBPR was found to increase biogas and methane yields compared to the manure alone. In semi-continuous reactor experiments, the highest methane yield of 346 dm³ CH₄/kgVS_fed was achieved for the mixture containing poultry manure with 50% SBPR (weight basis) and a solids retention time (SRT) of 20 days. However, when poultry manure was digested as a sole feedstock, the biogas production was inhibited by ammonia, whereas the co-digestion of PM with 25% SBPR was slightly affected by volatile fatty acids, which concentrations exceeded 4000 g/m³.     

Anaerobic co-digestion technology in solid wastes treatment for biomethane generation

Anaerobic co-digestion is considered to be an efficient way of disposing solid wastes which can not only reduce environmental burden, but also produce bioenergy. Co-digestion of solid wastes in the absence of bacteria inoculums with variable mixing ratios of three wastes has been experimentally tested for 35 days digestion time to determine the biogas potential. The temperature remained relatively constant at a mesophilic range of 29–36°C throughout the study. An average pH of 7.4 was recorded from all digesters. The average biogas yields obtained from the four digesters (D1, D2, D3 and D4) were 13.31, 15.67, 16.52 and 19.12 L/day, respectively. The cumulative result showed that from co-digestion of D4 43.67%, 22.02% and 15.71% more biogas was produced, respectively, than others. The maximum and average COD reduction was 57% and 31%, respectively, in co-digestion wastes. The biogas comprised average of 61% CH₄, 33.5% CO₂, 222 ppm H₂S, and 4.7% H₂O, respectively.     

Methane yield of oat husks

The biogas yield of solid manure from dairy cattle depends on its quality and the proportion of excreta and organic litter material contained within. The biogas yield of both faeces and straw is available in literature. Straw is a common litter material of mixed farms. However, straw is scarcely available on dairy farms. Oat husks are appropriate to replace or supplement straw for use as litter material. In this study, the actual methane yield and the total methane potential of oat husks were determined. Based on an optimized test with ground oat husks, the total methane potential resulted from regression and extrapolation of the experimental data. The total methane potential was determined with 242 L_N CH₄ kg⁻¹ VS added. Additionally, the actual methane yield over retention time at a digestion temperature of 37 °C was determined, using untreated oat husks. For 42 days of retention, the methane yield was 202 L_N CH₄ kg⁻¹ VS added at 52% CH₄ content. Results indicate that the methane yield of oat husks reaches the same level as that of straw. The total methane potential is not higher, but digestion of oat husks may proceed faster. Verification of the laboratory results on-farm revealed that the contribution of oat husks to overall methane production of a prototype biogas plant for solid manure might reach up to 80%.     

Enhancement of biogas production from sunnhemp using alkaline pretreatment

This study investigates enhancing the biogas production of sunnhemp by pretreatment, before the anaerobic digestion and co-digestion processes, to address the complex and recalcitrant structure of the plant. Fresh sunnhemp harvested at a cutting interval of 50 days is used in the study. Five systems (each with a 5 litre useable volume) are operated semi-continuously with five different ratios of the feedstock by feeding separate feedstocks every five days with a hydraulic retention time (HRT) of 40 days. The system operates at room temperature (30 °C). The study uses sunnhemp as 20% of the feedstock and also considers sunnhemp mixed with cow manure at different ratios, with the weighed sunnhemp being pretreated with dilute sodium hydroxide. Pretreatment of sunnhemp before digestion produces a methane (CH₄) yield 89% greater than that of the untreated sunnhemp. It requires 3.597 kg of dry sunnhemp to produce 1 m³ of CH₄ and the annual CH₄ yield per hectare is 19,015 m³. In the pretreatment of sunnhemp before co-digestion, the increased CH₄ yield depends on the amount of pretreated sunnhemp in the feedstocks. However, the %CH₄, the CH₄ production level and the system stability depend on the optimal ratio of the sunnhemp to cow manure. The initially prepared sunnhemp to cow manure ratio is recommended at 10 g:10 g in 80 mL of water. At this ratio, the %CH₄ and the CH₄ yield are 53.84% and 313 kg chemical oxygen demand (COD) removed, respectively, and the COD removal efficiency is 56.4%. Sunnhemp has high potential and it is worth pretreating before producing biogas. Using sunnhemp to produce biogas is recommended to decrease greenhouse gas emissions and mitigate global warming.     

Methane production for sanitation improvement in Haiti

There is a great need for decentralized anaerobic digestion (AD) that utilizes wastewater for energy generation. The biochemical methane potential (BMP) of Haitian latrine waste was determined and compared to other waste streams, such as grey water, septage, and dairy manure. Average methane (CH₄) production for the latrine waste (13.6 ml ml⁻¹ substrate) was 23 times greater than septage (0.58 ml ml⁻¹ substrate), and 151 times greater than grey water (0.09 ml ml⁻¹ substrate), illustrating the larger potential when waste is source separated using the decentralized sanitation and reuse (DESAR) concept for more appropriate treatment of each waste stream. Using the BMP results, methane production based on various AD configurations was calculated, and compared with the full-scale field AD design. Methane potential from the BMP testing was calculated as 0.006–0.017 m³ person⁻¹ day⁻¹ using the lowest and highest latrine BMP results, which was similar to the values from the full-scale system (0.011 m³ person⁻¹ day⁻¹), illustrating the ability of BMPs to be used to predict biogas production from sanitation digesters in a smaller-scale setting.     

Grass as a high potential by-product: Buffalo grass to biogas and the increase of system performance and stability

Buffalo grass and alkaline-pretreated buffalo grass samples were co-digested with cow manure separately to generate biogas in anaerobic reactors. The study considered a solid content of 20% (10% buffalo grass and 10% cow manure). The methane (CH₄) content and CH₄ yield of the distinct experiments were compared. For the untreated buffalo grass, the weighed buffalo grass was mixed with cow manure and water. For the alkaline-pretreated buffalo grass, the weighed buffalo grass was soaked in 1% sodium hydroxide for 1 day prior to being mixed with cow manure and water. The untreated and pretreated buffalo grass-manure were fed semi-continuously at the rate of 125 mL/day for five days feeding in a 5 L reactor, with 40 days hydraulic retention time. The experiments were conducted for approximately 100 days. Results were reported when the systems were in steady-state conditions. The chemical oxygen demand (COD) conversion efficiency of co-digestion of the untreated and pretreated buffalo grass-manure were 46.21 and 62.76%, respectively, and for the total volatile solids (TVS) were 68.50 and 71.80%, respectively. The CH₄ contents generated from co-digestion of the untreated and pretreated buffalo grass-manure were 48.32% and 50.36%, respectively. The CH₄ yields generated from co-digestion of the untreated and pretreated buffalo grass-manure were 328 and 385 L/kgTVS conversion, respectively. It was observed from the experiments that pretreatment of the buffalo grass prior to co-digestion provided system stability during biogas production.     

Biogas production in low-cost household digesters at the Peruvian Andes

Low-cost tubular digesters originally developed in tropical regions have been adapted to the extreme weather conditions of the Andean Plateau (3000-4000 m.a.s.l.). The aim of this study was to characterise biogas production in household digesters located at high altitude, operating under psychrophilic conditions. To this end, two pilot digesters were monitored and field campaigns were carried out in two representative digesters of rural communities. Digesters’ useful volume ranged between 2.4 and 7.5 m³, and hydraulic residence time (HRT) between 60 and 90 days. The temperature inside the digester’s greenhouse ranged between 20 and 25 °C. Treating cow manure, a specific biogas production around 0.35 m³ kg_VS⁻¹ was obtained, with some 65% CH₄ in biogas. In order to fulfil daily requirements for cooking and lighting, biogas production should be enhanced without increasing implementation costs as not to impede the expansion of this technology at household scale. In this sense, HRT below 60 days and OLR above 1 kg_VS m⁻³ day⁻¹ should be investigated to decrease digesters’ volume (i.e. costs) and increase biogas production rate. The adaptation of conventional gas burners to biogas characteristics can also contribute in improving the efficiency of the system.     

The effect of waste paper on the kinetics of biogas yield from the co-digestion of cow dung and water hyacinth

The effect of waste paper on biogas yield produced by co-digesting fixed amount of cow dung and water hyacinth in five digesters A-E was studied at room temperature. Waste paper was observed to improve biogas yield in digesters B-E with digester A acting as the control. However, as the amount of waste paper increased the biogas yield was observed to decrease. Kinetic model based on first order kinetic was derived to estimate the maximum, ultimate, biogas yield and also the ultimate methane yield from these biomass mixtures. The maximum biogas yield estimated using this model for digesters B-E were 0.282, 0.262, 0.233, and 0.217 lg⁻¹ VS fed with goodness of fit (R²) of 0.995, 0.99, 0.889, and 0.925 respectively, which were obtained by fitting the experimental biogas yield (y_t) against (exp(kt)−1)/exp(kt). The ultimate biogas and methane yield at very low batch solid load were extrapolated to be 0.34 and 0.204 lg⁻¹ VS fed respectively. In essence, the addition of waste paper in the co-digestion of cow dung and water hyacinth can be a feasible means of improving biogas yield and also alternative means of recycling waste paper. Furthermore, the kinetic model developed can compliment other models used in anaerobic digestion of agricultural and solid waste.     

Anaerobic co-digestion of primary sludge and the fruit and vegetable fraction of the municipal solid wastes: Conditions for mixing and evaluation of the organic loading rate

This paper presents the results obtained for the digestion of primary sludge (PS) and co-digestion of this sludge with the fruit and vegetable fraction of municipal solid wastes (FVFMSW) under mesophilic conditions. This mixture was prepared with a PS content of 22%. The anaerobic digestion process was evaluated under static conditions and with different mixing conditions, with good results being found for the digesters with limited mixing, this representing an energy saving. The results for co-digestion of mixtures of PS+FVFMSW are better than those obtained from digestion of PS on its own. Biogas production for co-digestion is much greater thanks to the larger volatile-solid (VS) content of this feedstock. Nevertheless, biogas yield and specific gas production for the two digestion processes are similar, with values in the range 0.6–0.8 l g⁻¹ VS destroyed for the first parameter and in the range 0.4–0.6 l g⁻¹ VS fed for the second. The co-digestion process was also evaluated at different organic loading rates (OLR) under low mixing conditions, with stable performance being obtained even when the systems were overloaded.     

Semi-continuous co-digestion of solid slaughterhouse waste, manure, and fruit and vegetable waste

The potential of semi-continuous mesophilic anaerobic digestion (AD) for the treatment of solid slaughterhouse waste, fruit-vegetable wastes, and manure in a co-digestion process has been experimentally evaluated. A study was made at laboratory scale using four 2 L reactors working semi-continuously at 35 °C. The effect of the organic loading rate (OLR) was initially examined (using equal proportion of the three components on a volatile solids, VS, basis). Anaerobic co-digestion with OLRs in the range 0.3–1.3 kg VS m⁻³ d⁻¹ resulted in methane yields of 0.3 m³ kg⁻¹ VS added, with a methane content in the biogas of 54–56%. However, at a further increased loading, the biogas production decreased and there was a reduction in the methane yield indicating organic overload or insufficient buffering capacity in the digester.In the second part of the investigation, co-digestion was studied in a mixture experiment using 10 different feed compositions. The digestion of mixed substrates was in all cases better than that of the pure substrates, with the exception of the mixture of equal amounts of (VS/VS) solid cattle–swine slaughterhouse waste (SCSSW) with fruit and vegetable waste (FVW). For all other mixtures, the steady-state biogas production for the mixture was in the range 1.1–1.6 L d⁻¹, with a methane content of 50–57% after 60 days of operation. The methane yields were in the range 0.27–0.35 m³ kg⁻¹ VS added and VS reductions of more than 50% and up to 67% were obtained.     

Using sugarcane leaves and tops for exploiting higher methane yields: An assessment study

Sugarcane leaves and tops are lignocellulosic agricultural by-products which are considered a significant input for biogas production. Their potential pretreatment by sodium hydroxide prior to co-digestion with cow manure helps increase the methane (CH₄) content, biodegradation efficiency of the lignocellulosic materials and CH₄ yield. The untreated and pretreated sugarcane leaves and tops to cow manure and water of different ratios were digested and co-digested in the 5 L reactors by semi-continuous operation with hydraulic retention time of 40 days. The pretreated sugarcane leaves and tops to cow manure at the initial prepared ratio of 100 g:100 g, in 800 mL water which was corresponding to the organic loading rate (OLR) of 0.61 kg COD/m³·day was recommended. At this ratio, the chemical oxygen demand and total volatile solids degradation efficiency was 68.80 and 72.52%, respectively, the CH₄ content was 44.52% and the CH₄ yield was 331 L/kg COD degraded. According to the results, there is an average of 3.7% deviation between the practical model based on the thermodynamic balance equations carried out using the Aspen Plus and the experimental study. The highest exergy destruction rate is found at 21 kW where the sugarcane leaves and tops, and cow manure ratio is 100 g:100 g, in 800 mL water. The highest energy and exergy efficiencies of the overall system are calculated as 45.53% and 46.02%, respectively.     

Green biohydrogen production in a Co-digestion process from mixture of high carbohydrate food waste and cattle/chicken manure digestate

This study was investigated biohydrogen production on the effects of different ratio of food waste to seed digestate and pH value from co-digestion process in anaerobic reactor. The seed digestate was mixture of cattle manure 45%, corn silage 25%, chicken manure 15%, and olive pomace 15% which was collected from the biogas plant in central Italy. It was found that the peaks of total biogas and the biohydrogen productions were 1355 ± 26 and 436 ± 10 mL whereas the biohydrogen yield was 50.4 mL/g-VS (45.8 mL/g-COD) with 43.33% COD removal rate, the bacteria to substrate volatile solids (VS) ratio was 2:1 where seed digestate to food waste was 6:4 under pH 6.5. As a consequence, food waste with a high COD concentration can be adapted C/N ratio by the cattle manure and chicken manure in the seed digestate which resulted in a high biohydrogen production. The food waste co-digestion system mixed with biogas plant digestate is one of approach to increase total biogas production.     

Transient performance during start-up of a two-phase anaerobic digestion process demonstration unit treating carbohydrate-rich waste with biochar addition

The paper reports an experimental investigation into the transient performance during the start-up of a pilot-scale two-phase anaerobic digestion (TPAD) process demonstration unit (PDU) treating food waste with biochar addition. Hydrogen (H₂) was produced in the first phase (R1) and methane (CH₄) was produced in the second phase (R2). A fed-batch operation strategy was applied to the start-up of both phases, followed by semi-continuous operation. Production rates and yields of H₂ and CH₄ and volatile fatty acids (VFA) were measured while the pH and temperature were monitored throughout the process. Fed-batch operation allowed microbe enrichment and gradual VFA production in both phases, which was observed to be efficient in starting up the TPAD PDU. Under semi-continuous operation, R1 produced biogas with composition up to 49% of H₂ and at a yield of 46 L H₂.kg ⁻¹ VS. CH₄ composition and yield reached up to 59% and 301 L CH₄.kg⁻¹ VS in the R2.     

Hydrogen and methane production from untreated rice straw and raw sewage sludge under thermophilic anaerobic conditions

Bioenergy produced from co-digestion of sewage sludge (SS) and rice straw (RS) as raw materials, without pretreatment and additional nutrients, was compared for the one-stage system for producing methane (CH₄) and the two-stage system for combined production of hydrogen (H₂) and CH₄ in batch experiments under thermophilic conditions. In the first stage H₂ fermentation process using untreated RS with raw SS, we obtained a high H₂ yield (21 ml/g-VS) and stable H₂ content (60.9%). Direct utilization of post-H₂ fermentation residues readily produced biogas, and significantly enhanced the CH₄ yield (266 ml/g-VS) with stable CH₄ content (75–80%) during the second stage CH₄ fermentation process. Overall, volatile solids removal (60.4%) and total bioenergy yield (8804 J/g-VS) for the two-stage system were 37.9% and 59.6% higher, respectively, than the one-stage system. The efficient production of bioenergy is believed to be due to a synergistically improved second stage process exploiting the well-digested post-H₂ generation residues over the one-stage system.     

Popularizing household-scale biogas digesters for rural sustainable energy development and greenhouse gas mitigation

Biogas utilization has undergone great development in rural China since the government systematically popularized household-scale biogas digesters for meeting the rural energy needs in the 1970s. In order to comprehensively estimate the significance of biogas utilization on rural energy development and greenhouse gas emission reduction, all types of energy sources, including straw, fuelwood, coal, refined oil, electricity, LPG, natural gas, and coal gas, which were substituted by biogas, were analyzed based on the amount of consumption for the years from 1991 to 2005. It was found that biogas provided 832749.13 TJ of energy for millions of households. By the employment of biogas digesters, reduction of greenhouse gases (GHG) was estimated to be 73157.59 Gg CO₂ equivalents (CO₂-eq), and the emission by the biogas combustion was only 36372.75 Gg CO₂-eq of GHG. Energy substitution and manure management, working in combination, had reduced the GHG emission efficiently. The majority of the emission reduction was achieved by energy substitution that reduced 84243.94 Gg CO₂, 3560.01 Gg CO₂-eq of CH₄ and 260.08 Gg CO₂-eq of N₂O emission. It was also predicted that the total production of biogas would reach to 15.6 billion m³ in the year 2010 and 38.5 billion m³ in the year 2020, respectively. As a result, the GHG emission reductions are expected to reach 28991.04 and 46794.90 Gg CO₂-eq, respectively.     

Hydrogen–methane production from swine manure: Effect of pretreatment and VFAs accumulation on gas yield

A two-phase anaerobic process to produce hydrogen and methane from swine manure was investigated, using pretreated sludge with heat, acid and alkali treatment as inoculum. The relative order of pretreatment methods of H₂ productivity effectiveness and CH₄ productivity effectiveness produced by the residua of the first phase was heat treatment > alkali treatment > acid treatment. When the inoculum sludge was heat-treated at 80°C for 30 min, the H₂ and CH₄ production rate was the highest of 36.6, 201.7 ml (g TS)_added⁻¹. There were significant correlations between biogas production and accumulation of acetic acid and butyric acids. When propionic acid and total VFA concentrations reached about 2850 mg L⁻¹ and 10.0 g L⁻¹, respectively, the average H₂ production rate and H₂ content decreased from 7.6 ml d⁻¹(g VS)_added⁻¹ and 55.3% to 1.4 ml d⁻¹(g VS)_added⁻¹ and 43.2%, respectively. The activity of methanogenic bacteria was inhibited to a significant extent when the total VFA concentration was above 10.0 g L⁻¹, but this inhibitory effect weakened when the VFA concentration fell to 6200–8500 mg L⁻¹. Correspondingly, average CH₄ production rate increased from 4.0 ml d⁻¹(g TS)_added⁻¹ to 12.5 ml d⁻¹(g TS)_added⁻¹. Propionic acid was degraded rapidly only when acetic and butyric acid concentrations dropped to 2500 mg L⁻¹ and 1000 mg L⁻¹, respectively.     

Bio-methane potential test (BMP) using inert gas sampling bags with macroalgae feedstock

An approach to Bio-methane potential test (BMP) was carried out at mesophilic temperature of 35 °C with Supel™ inert gas sampling bags as biogas collection and storage bags, using selected seaweed (macroalgae) as substrate. Samples were given a range of pre-treatments from washing, drying and macerating. Dried laminaria digitata (DD) with 68.14% VS (%TS) produced the highest BMP of 141 ± 5.77 L CH₄/kg VS, with methane content increasing to about 70%, while the lowest BMP of 93.35 ± 5.03 L CH₄/kg VS with methane content of about 65% was obtained for fresh laminaria digitata (FD) with 72.03% VS (%TS). Methane yields of 97.66 and 67.24 m³ CH₄/t wet weight based on BMP results were obtained for DD and FD. Both DD and FD achieved within 28% and 38% of the theoretical BMP value based on the Buswell equation, respectively. The total methane (V) produced was computed based on;V = X₁ + X₂ – X₃ corrected to Standard temperature and pressure (STP).where X₁ = daily calculated headspace methane volume, X₂ = daily measured volume of methane in gas bags, X₃ = previous day headspace methane volume. An advantage of this approach is the volumetric measurement of gas produced directly from the gas bags, hence it does not require liquid displacement or pressure transducers. Results from a second set of freshly collected sample seaweed sample showed it was in agreement with published BMP values. All analysis were carried out without mineral supplementation.     

Nymphoides peltatum as a novel feedstock for biomethane production via anaerobic co-digestion with waste sludge

Nymphoides peltatum (NP) is exploited as a novel feedstock for biomethane production via anaerobic co-digestion with waste sludge (WS). Batch experiments are conducted under mesophilic condition at NP/WS of 1/3, 2/2, 3/1, 0/4 and 4/0 based on volatile solids (VS). Prior to anaerobic digestion (AD), NP undergoes only natural drying and grinding. The maximum net cumulative methane yield (265.16 mL CH₄·g VS_added^?1) and the highest gross VS removal rate (56.12%) are obtained at NP/WS of 1/3. The kinetic analysis by the modified Gompertz model fit hinted that 28 days is adequate for methane recovery and co-digestion significantly accelerates the digestion rate. Synergetic effect is corroborated to exist in co-digestion due to amiable conditions in term of total ammonia nitrogen, free ammonia, pH, volatile fatty acids and total alkalinity. High-throughput 16S rRNA pyrosequencing reveals that Bacteroidetes, Firmicutes, Methanosarcina and Methanosaeta are conducive to AD of NP.     

Simultaneous production of hydrogen and carbon nanotubes from biogas: On the design of combined process

We introduced a novel combined process of CO₂ methanation (METH) and catalytic decomposition of methane (CDM) for simultaneous production of hydrogen (H₂) and carbon nanotubes (CNTs) from biogas. In this process, biogas is catalytically upgraded into CH₄-rich gas in METH reactor using Ni/CeO₂ catalyst, and the obtained CH₄-rich gas is subsequently decomposed into H₂ and CNTs in CDM reactor over CoMo/MgO catalyst. Among the three different process scenarios proposed, the combined process with a steam condenser equipped between METH and CDM reactors could greatly improve a CNTs productivity. The CNTs production yield increased by more than 2.5-fold, maximizing at 9.08 gCNTs/gCat with a CNTs purity of 90%. The deposited carbon product was characterized as multi-walled carbon nanotubes (MWCNTs) with a surface area of 136.0 m²/g, comparable with commercial CNTs of 199.8 m²/g. The remarkable I_G/I_D ratio of 2.18 confirms a superior portion of graphitic carbon in the synthesized CNTs upon the commercial CNTs with I_G/I_D = 0.74. Notably, the CH₄ conversion reached 94.5%, while the CO₂ conversion achieved 100%, resulting in the H₂ yield and H₂ purity higher than 90%. This combined process demonstrates a promising route for production of high quality CNTs and high purity H₂ with complete CO₂ conversion using biogas as abundant renewable energy resources. In addition, the test of raw biogas showed no deactivation of catalyst, justifying the implementation of the developed process for real biogas without purification.     

Biogas production from co-digestion of a mixture of cheese whey and dairy manure

In this study, daily amount of biogas of different mixtures of cheese whey and dairy manure, rates of production of methane, removal efficiencies of chemical oxygen demand (COD), total solid (TS) matter and volatile solid (VS) matter from the mixtures were investigated at 25 and 34 °C. In the experimental studies, two different solid matter rates (8% and 10%) were studied. The hydraulic retention times (HRTs) were 5, 10 and 20 days. Removal efficiencies and amount of biogas produced in each HRT were determined. Maximum daily biogas production was obtained as 1.510 m³ m^?3 d^?1 at HRT of 5 days in the mixture containing 8% total solid matters at 34 °C and the methane production rate was around 60 ± 1% in all experiments. Maximum removal efficiencies for TS, VS and COD were found as 49.5%, 49.4% and 54%, respectively at HRT of 10 days in the mixture containing 8% total solid matters at 34 °C.