Cumulative Biogas Yield Research Articles

Biogas production from wastewater treatment: Evaluating anaerobic and biomagnetic systems

Biogas, a green and sustainable form of energy produced during the degradation of organic waste anaerobically comes with ecological and economic paybacks when compared to a comprehensive fossil fuel-based energy system. However, the biodiversity of microorganisms and chemical loads for enzymatic and bioconversion reactions impedes the anaerobic digester’s (AD) practicality for commercialization. Hence, this study examined the application of titanium dioxide magnetite (Fe-TiO2) (F) via a synthetic route in AD + F and a biomagnetic system (BMs) as a collective pathway to maximize methane potentials, wastewater treatment, and improve biogas production. The AD + F and BM systems were operated at a working volume of 0.8 L (inoculum to wastewater ratio of 0.6), the mesophilic temperature of 35 °C for an incubation period of 30 days. The results showed in-situ Fe-TiO2 facilitated the bio-electrolysis and bio-methanation reactions in the AD process which improved its performance as compared to the control (AD only). Above 75% of chemical oxygen demand (1600 ± 16.2 mg/L), Total Kjeldahl Nitrogen (76 ± 6.4 mg/L), total solids (135 ± 12 mg VS/L), volatile solids (94 ± 6.8 mg VS/L), and other inorganic contaminants (28 elementals) contained in the wastewater were removed by the BMs at a pH of 6.5 followed by the AD + F (65–75%) and the AD only (50–65%). On the 20th day, the control system (AD only) had a maximum daily biogas yield of 50 mL/COD.d, whereas the AD + F gave 90 mL/d and BMs 120 mL/d. Compared to the control with a methane yield of 66%, the addition of the Fe-TiO2 to AD + F and BMs increased the methane yield to 100%. Synergistically, the catalytic and biomagnetic activity of Fe-TiO2 in the BMs heightened the adsorption and reaction pathway of the contaminant’s transformations and degradation. Amidst two kinetic models investigated, the cumulative biogas yield followed the Gompertz kinetic model. In conclusion, combining the magnetic effect with green magnetic catalyst (Fe-TiO2) in AD and adsorption–based wastewater settings have viable prospects towards environmental purification.

Application of biomagnetic nanoparticles for biostimulation of biogas production from wastewater treatment

This study presents biomagnetic nanoparticles (BMNPs) as a biostimulant for wastewater treatment and biogas upgrading to natural quality (>90% CH4). Notwithstanding, application of anaerobic digestion (AD) in wastewater settings is still limited with slow kinetics and low methanation yield. Here, four BMNPs (CuO, Fe2O3, TiO2, Cu/Fe-TiO2) were investigated to enhance the high-rate anaerobic system for complete degradation of organic waste to value – added products (water and biogas). Sugar refinery wastewater was used as a substrate and activated sludge as inoculum. This was carried out in 800 mL working volume bioreactors at a mesophilic temperature of 35 °C and hydraulic retention time of 30 days. Results showed the substrate – inoculum degradation in the control system, when induced with the BMNPs increased the methane (CH4) potential from 63% to 100%. Likewise over 75% water index of chemical oxygen demand, total suspended solids, and volatile solids were removed. Stimulatingly, the biogas production and wastewater treatability was significantly improved upon adding the BMNPs to the bioreactors which enriched the methanogenic activities. The post-sludge analysis showed the morphological and elemental distribution of the BMNPs, and their biomagnetic interactions with the micobes which enhanced the adsorptive removal of the contaminants and the biogas production yield. The Gompertz modified kinetic model significantly (P < 0.05) favoured the cumulative biogas yield obtained for all the bioreactors with a kinetic rate constant within the range of 0.182504–0.203027 d-1. The performance of Cu/Fe-TiO2 additives superseded the rest of the BMNPs. In conclusion, BMNPs revealed economic prospects of regeneration and reuse with external magnets for effective wastewater treatment.

Fungal pretreatment of non-sterile maize silage and solid digestate with a Cephalotrichum stemonitis strain selected from agricultural biogas plants to enhance anaerobic digestion

The enhancement of the yields of the anaerobic digestion process was the primary target of the present study, thanks to the development of an innovative fungal pretreatment. The fungal community of agrozootechnical biogas plant feedstocks and by-products (i.e., maize silage and stover, zootechnical slurry and manure, wheat and rice straw, and solid digestate) were studied, isolating and identifying 172 strains belonging to 89 taxa. The mycobiota was dependent on the biomass: maize and zootechnical samples showed a higher biodiversity than straw and solid digestate. During the preliminary screening, Cephalotrichum stemonitis extensively grew on both non-sterile maize silage and solid digestate and it was then selected for their pretreatment. The fungus did change the biomasses features: the total solids decreased (approximately 20%), while the volatile solids slightly changed (<1%). Lignin, cellulose and hemicellulose degradation rate in maize silage was higher (55.2%, 25.0% and 24.5%, respectively) than in solid digestate (8.7%, 0.6% and 10.9%, respectively), highlighting their different accessibility and recalcitrance. During the anaerobic digestion, fungal-pretreated maize silage produced lower cumulative biogas and methane than the control, probably due to an excessive degradation of easily accessible fibers. On the contrary, the pretreated solid digestate was less recalcitrant to the microbial transformation in the anaerobic digestion: as a result, cumulative biogas and methane yields were significantly enhanced (approximately 70%). By favoring the (re)use of digestate as a feedstock, the investigated fungal pretreatment could help the economic and environmental sustainability of the anaerobic digestion.

Biodegradation of creosote-treated wood by two novel constructed microbial consortia for the enhancement of methane production

Lignocellulose biodegradation is limited because of its recalcitrant structure particularly when polluted by toxic and carcinogenic compounds such as creosote oil (CRO). As far as we know, this might be the first report that explores the biodegradation of creosote treated wood (CTW) to serve biomethane production. Two novel CTW-degrading microbial consortia, designated as CTW-1 and CTW-2, were screened and constructed to enhance methane production from CRO-treated pine sawdust. After 12 days of biological pretreatment by CTW-1 and CTW-2, a significant reduction in lignocellulosic content of CTW was recorded; estimated as 49 and 43%, respectively. More than 64 and 91% of cumulative biogas and methane yields were obtained from biodegraded CTW over control. Ecotoxicity of treated and untreated CTW was compared by Microtox test. The biodegraded CTW hydrolysates showed a toxicity decrease of more than 80%, suggesting the promising role of constructed microbial consortia for biofuel production and bioremediation.

Parametric optimization of biogas potential in anaerobic co-digestion of biomass wastes

The effect of anaerobic co-digestion of Prosopis juliflora seeds, water hyacinth, dry leaves, and cow manure on the biogas production performance was assessed in the present study. The research was optimized by central-composite design and methodology of the response surface to optimize the operating parameters of pH and temperature. Average biogas production, cumulative biogas yield, and methane content had a significant impact on pH and T variation results. Good linear regressions were observed between the predicted and experimented responses. We found a unique operating condition (pH = 7.034, and T = 35.557 °C) to achieve the maximum value of each responses. In all tests, the anaerobic biodegradability was observed within the range of 14.7–72.6%. The experiment conducted on the predicted operating condition resulted in actual methane yield (AMY) of 396.0 ± 6 L/kgVS, anaerobic biodegradability of 76.6%, and the TS reduction of 41.1%.

Renewable energy from the solid-state anaerobic digestion of grape marc and cheese whey at high treatment capacity

Globally, wine production annually generates some 11 million metric tonnes of grape marc (GM) while the cheese-making industry releases over 200 million m3 y−1 of effluent. Where value-creation mechanisms are absent, such wastes may be channelled to landfills. The study aimed to evaluate the bioenergy potential of the combined treatment of such wastes. Digestion of feedstock at a ratio 3/1 GM/CW (w/w) was conducted in unstirred conditions at 45 °C, following optimisation through the Taguchi Method. Cumulative biogas and methane yields were 0.601 m3 gas kg−1 VS and 0.363 m3 CH4 kg−1 VS, respectively. Firmicutes and Bacteroides mediated hydrolysis and acidogenesis, thus providing metabolites to Methanosarcina. Co-digestion can potentially generate 1330 GW h and 482,000 Mt CO2-equivalents avoidance. Wine and dairy industries jointly present a case for value-creation through a circular economy, thereby reducing the dependency on non-renewables, renewing commitment to the Paris Agreement.

Kinetics and Nanoparticle Catalytic Enhancement of Biogas Production from Wastewater Using a Magnetized Biochemical Methane Potential (MBMP) System

This study presents magnetized nanoparticles (NPs) as a catalyst to accelerate anaerobic digestion (AD) potential for clean and ecofriendly energy (biogas) from wastewater settings. The effects of iron oxides (Ms) and aluminum sulphate (Alum) were investigated using two chronological experiments: (i) the Jar test technique to generate residue slurry as organic fertilizer potential and (ii) a magnetized biochemical methane potential (MBMP) system for biogas production at mesophilic conditions for 21 days. X-ray diffraction and Fourier Transform Infrared spectroscopy were carried out to establish the Ms Crystallite and active functional groups respectively. Scanning electronic microscopy coupled with energy dispersive X-ray spectrometer and elemental analysis were used to track and confirm NPs inclusion after the post-AD process. Coagulation at 50 mg/L and magnetic exposure time of 30 min showed above 85% treatability performance by Ms as compared to 70% for Alum. Owing to the slow kinetics of the AD process, additional NPs content in the digesters coupled with an external magnetic field improved their performance. Cumulative biogas yields of 1460 mL/d &gt; 610 mL/d &gt; 505 mL/d for Ms &gt; Control &gt; Alum respectively representing 80% &gt; 61% &gt; 52% of CH4 were attained. The modified Gompertz model shows that the presence of NPs shortens the lag phase of the control system with kinetics rate constants of 0.285 1/d (control) to 0.127 1/d (Ms) &lt; 0.195 1/d (Alum).

Energy generation from anaerobic co-digestion of food waste, cow dung and piggery dung

The study investigated bioenergy generation from anaerobic co-digestion of food wastes (FW), cow dung (CD) and piggery dung (PD). The physicochemical parameters of the substrates were determined before and after digestion following standard procedures after mechanical pretreatment. Throughout the study, pH remained slightly alkaline while temperature varied between 26 and 32 °C. The highest cumulative biogas yield of 0.0488 L was recorded from the digestion of FW + CD + PD on the ninth day. After analyses, the highest methane content of 64.6 was obtained from the digestion of FW + PD while the lowest (54.0%) was from the digestion of FW only. Overall, cumulative biogas production for the four digestion regimes followed the order: FW + CD + PD, FW + PD, FW + CD and FW only respectively. Accumulation of VFAs was recorded at a slow rate during the digestions.

Datasets on chemical composition and anaerobic digestion of organic fraction of municipal solid waste (OFMSW), digested sewage sludge (inoculum) and ashes from incineration or gasification.

This article contains data on the chemical composition and anaerobic digestion of different residue streams including OFMSW, digested sewage sludge, low-carbon (LC) ashes from incineration subdivided into LC coarse and LC fly ash as well as high-carbon (HC) ashes from gasification subdivided into HC reactor and HC fly ash. All materials were collected in accordance to standard procedures in southern Germany. The data presented in this article include (1) dry matter (2) organic dry matter (3) elemental analysis (4) trace elements and (5) cumulative biogas and CH4 yields. Researchers and waste management companies on lab-/pilot-/industrial-scale can rely on the presented data for classification and comparison of biogenic waste streams. For further discussion, please refer to the scientific article entitled “Optimizing anaerobic digestion of organic fraction of municipal solid waste (OFMSW) by using biomass ashes as additives” [1].

An experimental approach to produce hydrogen and methane from food waste using catalyst

Anaerobic co-digestion of food waste, cow dung, and sludge solution is experimented in the presence of calcium peroxide (CaO2) as the catalyst to produce hydrogen and methane as a source of renewable energy. The substrate to inoculum ratios (v/v) of 1:1(S1), 1:2(S2), 1:3(S3), 1:4(S4) and 1:5(S5) are investigated in separate fermentative and methanogenic reactors. The result from the fermentative reactors indicate maximum hydrogen concentration of 26.34% with cumulative yield of 114.1 mL/g total solid (TS) in S3 compared to the other samples. Methanogenic reaction shows the highest methane concentration of 54.13% in S3. The highest daily (average) and cumulative biogas yield of 5.36 mL/g TS and 201.9 mL/g TS respectively are identified in S3. A maximum carbon dioxide concentration of 63.11% is found in S1. Overall, the substrate to inoculum ratio of 1:3 is spotted to be optimal for effective hydrogen and methane production during the anaerobic co-digestion process.

Enhancement of bioenergy recovery from agricultural wastes through recycling of cellulosic alcoholic fermentation vinasse for anaerobic co-digestion

Cellulosic alcoholic fermentation generates large amounts of vinasse, which was utilized in the present work to enhance the anaerobic digestion of rice straw and swine manure at different total solid (TS) contents. Straw fermentation resulted in bioethanol and vinasse yields of 95.2 g and 857.7 mL, respectively, per kg dry straw. Vinasse-straw co-digestion showed the highest cumulative biogas yield of 633.4 L kg−1 VS at 3% TS. Therefore, biogas productivity from co-digestion represented 92.1% higher than that of straw mono-digestion. Vinasse-manure co-digestion showed the highest cumulative biogas yield of 676.7 L kg−1 VS at 3% TS at a shorter technical digestion time, which resulted in 53.9% higher biomethane productivity than the corresponding vinasse-straw. Consequently, vinasse co-digestion at all studied TS ratios enhanced the total gross energy output rate (GEORtotal) over mono-digestion. Amongst, vinasse-manure co-digestion at 3% TS showed 7.9% higher GEORtotal than the highest recorded value from vinasse-straw co-digestion.

Role of biomass-derived carbon-based composite accelerants in enhanced anaerobic digestion: Focusing on biogas yield, fertilizer utilization, and density functional theory calculations

The performance of anaerobic digestion (AD) can be improved by the addition of accelerants. Three types of biomass-derived carbon-based composites (Co/C, CoO/C, and Co3O4/C) were used as accelerants to investigate the effect on AD systems in this work. These accelerants significantly improved the cumulative biogas yield (576–585 mL/g VS), and the total chemical oxygen demand degradation rate (68.48–71.11%) compared to the reference group (435.8 mL/g VS, 50.74%). The digestates with accelerants exhibited exceptional stability (59.24–63.67%) and superior fertilizer utilization (3.50–4.55%). In addition, first-principle density functional theory (DFT) calculations were conducted to provide the theoretical basis for the direct interspecies electron transfer (DIET), and a general strategy was proposed to help understand the enhanced methanogenesis pathway induced by the biomass-derived carbon-based composites. These important findings provide a novel avenue for the development of composite accelerants for AD systems.

Thermophilic Anaerobic Digestion of Arundo donax cv. Lvzhou No. 1 for Biogas Production: Structure and Functional Analysis of Microbial Communities

Thermophilic anaerobic digestion (TAD) is an efficient method for biogas production. In this study, the TAD of Arundo donax cv. Lvzhou No. 1 (ADL-1, a new kind of energy crop with high cold tolerance) at different growth stages was carried out, in order to investigate the relationship between microbial community structure and its function during the fermentation process. The results showed that the most optimal growth period of ADL-1 was 3 months, regarding the yield of biogas production. The TAD process lasted for 10 days with cumulative biogas and methane yields of 312.7 mL/g VS and 231 mL/g VS, respectively. The degradation rates of hemicellulose, cellulose, and lignin were 41.78%, 27.99%, and 14.46%, respectively. The high-throughput sequencing of 16S rRNA gene amplicons revealed that the most abundant bacterial phylum in TAD was Firmicutes with three dominant genera of Tepidiphilus, Sedimentibacter, and Gelria. Also, the main archaeal order was Methanomicrobiales, in which Methanoculleus and Methanosarcina were detected as dominant genera. Therefore, this article reveals the dynamic changes of structure and function of microbial communities during TAD of ADL-1, providing the theoretical basis for the development of energy crops with cold tolerance as potential biogas feedstock.

Renewable electricity generation from biogas of anaerobic co-digestion of sludge, cattle manure and water

This study reported the viability of energy supply from the energetic conversion of biogas generated by the anaerobic co-digestion in biodigester of rural properties with different sizes of the herd. Indian model benchtop biodigesters were filled with sewage sludge (SS), cattle manure (CM) and deionized water (DW). The energy conversion calculation was based on the cumulative biogas yield (CBY), amount of cattle manure and one cubic meter equivalence of gas with electricity. In the SS co-digestion biogas production was accelerated and 25:50:25 SS:CM:DW presented higher cumulative production. Experimental data on the cumulative production of this ratio fitted to the exponential model, in which 28.15 L were obtained. The efficiency of anaerobic co-digestion of SS and CM was proved with a higher cumulative biogas production than in the single substrate digestion of SS and the single substrate digestion of CM. High immediate production was only observed with SS. There was a long lag-phase for digestion of only CM. An intermediate production profile to the previous ones was noticed when balancing the three co-digesters. The CBY was 16.56 L kg -1 , 0.48 L gTS added -1 and 0.59 L gVS added -1 to 25:50:25 SS:CM:DW. The implement of biodigesters in rural properties for electricity generation provided monthly 2600 kWh and economy of US$ 7669.19. It was concluded that the implantation of biodigesters with 25:50:25 SS:CM:DW to produce electric energy from biogas allows energy self-sufficiency of the property, enabling the sustainable development of the activity through the proper disposal of waste and economic gains to the producer.

Comparative Biogas production by Anaerobic Digestion Using Sugarcane Bagasse, Cow Dung and Chicken Droppings Obtained from Katsina Metropolis as Substrates

The use of energy derived from fossil raw materials as conventional primary source of energy has led to environmental pollution climate changes. The need for other alternative sources such as energy derived from wind, solar and biofuel has become necessary. This research investigated the generation of biogas from three types of wastes: Sugarcane bagasse, Cow dung, and chicken droppings wastes using three different biogas plants. Batch operation was carried out and the daily gas produced from each digester was monitored for the retention period of four weeks at the ambient and slurry temperatures. The digesters were charged differently with these wastes in the ratio of 1:3 wastes to distilled water. The ambient temperature ranges within the retention period were 17-290C and a slurry temperature range of 19-320C. The result showed that chicken droppings had the highest cumulative biogas yield of 3228.3cm3; cow dung had 2816.6cm3 and sugarcane bagasse had the least cumulative production of 681.4cm3 within digestion period of 30 days. The qualitative test of the generated gas showed that, cow dung has superior quality for biogas production with the highest methane content of 61.3% over the sugarcane bagasse (57.2%) and chicken droppings (47.6%). The bacterial enumeration for chicken droppings was discovered to have highest count of 28.7 x 105cfu/g than cow dung and sugarcane bagasse with 21.2 x 105cfu/g and 2.1 x 105cfu/g respectively. Cow dung was discovered to have the highest total solid content of 84.74% while sugarcane bagasse had the least (8.67%). The utilization of these waste stockscould bean alternative option for energy source and wastes treatment.

ASSESSMENT OF BIODEGRADATION EFFECTS OF AGRO-WASTES (POULTRY DROPPINGS AND COW DUNG) ON SOME PHYSICO-CHEMICAL PROPERTIES OF THEIR EFFLUENTS

Purpose: The biodegradation effects of agro-wastes (poultry droppings and cow dung) on some physico-chemical properties of the effluents were assessed. Methodology: Triplicate slurries (1:3 w/v) of five ratios of poultry droppings and cow dung: (0:1, 1:3, 1:1, 3:1 and 1:0 as treatments A, B, C, D and E) were separately fed into 13.6L locally constructed digesters, under strict anaerobic condition. They were kept for eight weeks retention period. Separate fractions of the undigested and digested treatments were subjected to standard assay procedures to determine their C, N, heavy contents, chemical oxygen demand (COD). The average weekly temperature and the pH before and after digestion of the media were measured. Findings: The cumulative biogas yield was in the order of treatment C (2961.0ml) &gt;D(2241.7ml) &gt; E(2197.9ml) &gt; A(2079.0ml) &gt; B(2031.1ml), based on the following mixing ratios 1:1&gt;3:1&gt;0:1&gt;1:0&gt;1:3. The gas production was affected by weekly temperature variation, which peaked at the mesophilic range (40.5±0.3 ̶ 44.1±0.3OC). The resultant pH of the digestates was in the order of 1:3 &gt; 3:1 &gt; 1:1 &gt; 0:1 &gt; 1:0. There was a general reduction in heavy metal contents for all treatment digestates, except Cu, with 200.00, 35.82 and 7.34% as %increases in treatments A, E and C respectively. All treatments indicated reduction in C:N ratios, ranging from 7.93 ̶ 13.02, in the order of 3:1&gt;1:1&gt;1:3&gt;0:1&gt;1:0. Similarly, there was decrease in COD contents for all treatments due to AD. Consequently, the percentage COD reduction (%CODR) was in the order of treatment D(53.70%) &gt; E(34.15%) &gt; C(29.63%) &gt; A(25.81%) &gt; B(19.23%). Unique contribution to theory, practice and policy: The biodegradation process had provided an effective means of alternative energy production, agricultural waste management initiative, which would ensure bioremediation, sustainable public health and environmental management

Assessment of Anaerobic Co-Digestion Effects of Maize Cob and Poultry Manure on Biogas Yields and Their Digestate Characteristics

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.&#x0D; Place and Duration of Study: Department of Forestry Technology, Federal College of Forestry, Jos between March and April, 2018.&#x0D; 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.&#x0D; Results: The cumulative biogas yields was in the order of T3(2481.3 mL/kg) &gt;TI(2197.9 mL/kg) &gt; T4(2163.0 mL/kg) &gt; T2(2116.3 mL/kg) &gt;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%) &gt; T4(58.00%) &gt;T5(46.81%) &gt;T1(34.15%) &gt;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%) &gt;T3(270.97%) &gt;T2(268.10%) &gt;T4(43.66%) &gt;T1(35.82%).&#x0D; 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.

Effects of Substrate to Inoculum Ration on Biogas Production from Anaerobic Co-digestion of Office Paper and Cow Manure

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.

Biogas production from chicken manure at different organic loadings using a special zeolite additive (ZeoVit sorbent)

This work was aimed at investigating biogas production from chicken manure (common agricultural organic waste) using different organic loadings and a special zeolite additive (ZeoVit sorbent), by applying a small-sized batch-type bioreactor operating under mesophilic conditions (35 °C) with mechanical mixing of the substrate. The effect of the zeolite used in the amount of 10% (percent of dry organic matter) on the promotion of biogas production efficiency was investigated under different organic loadings (80, 120, and 180 g VS l−1) of the bioreactor. It was found that increasing the organic load also increased the promoting effect of the zeolite additive, for which the best results achieved were 10% and 14% for the cumulative biogas yield and total amount of methane, respectively. The obtained results show that the zeolite additive can greatly impact the biogas yield, whereas its promoting effect upon the methane concentration was much lower (4%). The methane concentration reached a maximal value of ∼70%, while the concentrations of the most important components of the cumulative produced biogas were 60%, 38%, and 0.03% for CH4, CO2, and H2S, respectively.

Impact of Fe and Ni Addition on the VFAs' Generation and Process Stability of Anaerobic Fermentation Containing Cd.

The effects of Cd, Cd + Fe, and Cd + Ni on the thermophilic anaerobic fermentation of corn stover and cow manure were studied in pilot experiments by investigating the biogas properties, process stability, substrate biodegradation, and microbial properties. The results showed that the addition of Fe and Ni into the Cd-containing fermentation system induced higher cumulative biogas yields and NH4+–N concentrations compared with the only Cd-added group. Ni together with Cd improved and brought forward the peak daily biogas yields, and increased the CH4 contents to 80.76%. Taking the whole fermentation process into consideration, the promoting impact of the Cd + Ni group was mainly attributed to better process stability, a higher average NH4+–N concentration, and increased utilization of acetate. Adding Fe into the Cd-containing fermentation system increased the absolute abundance of Methanobrevibacter on the 13th day, and Methanobrevibacter and Methanobacterium were found to be positively correlated with the daily biogas yield. This research was expected to provide a basis for the reuse of biological wastes contaminated by heavy metals and a reference for further studies on the influence of compound heavy metals on anaerobic fermentation.