Starting-up low temperature dry anaerobic digestion of cow feces and wheat straw

Psychrophilic dry anaerobic digestion (PDAD) of animal manures and agriculture residues is of high interest in cold-climate regions. This paper reports the results of a start-up experiment (113 days) of PDAD of cow feces and wheat straw mixture (at two total solids (TS) of 18 and 21%) in laboratory scale sequence batch reactor (SBR) at 20 °C. An average specific methane yield (SMY) of 96.1 ± 5 L of CH₄ per kg of volatile solid (VS) corrected to standard pressure and temperature (101.3 kPa and 273 K) (_NL CH₄ kg⁻¹ VS) has been achieved for a feed with TS of 18% along with an organic loading rate (OLR) 4.0 g total chemical oxygen demand (TCOD) kg⁻¹ inoculum day⁻¹ and a treatment cycle length (TCL) of 21 days. An average SMY of 149.9 ± 14 _NL CH₄ kg⁻¹ VS with a maximum daily CH₄ production rate of 7.2 ± 0.7 _NL CH₄ kg⁻¹ VS day⁻¹ have been obtained for a feed with total solid of 21% along with an average daily inoculum OLR of 4.2 g TCOD kg⁻¹ inoculum day⁻¹ and TCL of 21 days. The rapid decrease in volatile fatty acids concentration after 7 days of treatment and their low concentration thereafter indicated that hydrolysis was the reaction limiting step. The results indicate that PDAD of cow feces and wheat straw is feasible at feed TS of 21%.     

Bioelectrochemical enhancement of methane production in anaerobic digestion of food waste

This study was conducted to optimize microbial electrolysis cells (MECs) + anaerobic digestion (AD) using integrated Taguchi method and response surface methodology (RSM). The MECSs were applied to enhance the efficiency of AD using food waste as substrate. Using Taguchi method and RSM, the optimum conditions of the MEC + AD were applied voltage (1.2 V), substrate (2.4 g COD/L) and ratio of reactor volume and electrode area (0.33 m3/m2), respectively. The results of the modified Gompertz and dual-pool 1st order showed that the maximum methane yield, maximum methane production rate, and rate constant for rapidly degradable substrate were 1.2, 1.3 and 1.5 fold higher than those of the AD, respectively. Microbial communities analyses indicated that acetoclastic methanogens were initially floating in MEC + AD reactor, but they became attached onto electrodes over time.     

Effective difference volumes of inoculum for methane production in anaerobic batch digestion by using casein

Anaerobic digestion is one the most efficient technologies in waste and wastewater management for producing renewable energy and reducing greenhouse gas emission from animal manure. In this experiment procedure was use duplicate samples and controls in different volumes of inoculum (10%, 20%, 30%, and 40%, respectively) were mixed with the same volume 10 g of casein, which the experimental results of the daily methane productions in duplicate samples were also slightly increased during the first day although out the final day of biodegradability process. The specific methane value in sample 40% was a highest methane volume about 86 ml/gVS when compared with the other samples (10%, 20% and 30%, respectively). However, the methane yield among samples was considerably lower than theoretical by comparison. Therefore, the differential volumes of inoculum used for a BMP test were influence the methane production of anaerobic batch digestion process, and these difference inoculum volumes were significantly effective or not were depending on the substrate used. This experimental study was to measure the methane production form different volumes of inoculum, and to evaluate the influence of inoculum by mixing 10g of casein as the substrate in BMP test processes.     

铜离子对猪粪厌氧消化性能的影响研究

在实验室条件下,研究了铜离子浓度为100⁶00μg/g时对猪粪厌氧消化性能的影响。结果表明:铜离子浓度为100～300μg/g时可提高甲烷产量,浓度为400～600μg/g时,则明显抑制甲烷产量;整个过程中,系统的pH值一直维持在6.5600μg/g时对猪粪厌氧消化性能的影响。结果表明:铜离子浓度为100～300μg/g时可提高甲烷产量,浓度为400～600μg/g时,则明显抑制甲烷产量;整个过程中,系统的pH值一直维持在6.5⁷.2,无明显酸化;当铜离子浓度为300μg/g时,COD去除率最大,达到68.23%。铜离子浓度对TS,VS去除率影响不明显,TS去除率为30%7.2,无明显酸化;当铜离子浓度为300μg/g时,COD去除率最大,达到68.23%。铜离子浓度对TS,VS去除率影响不明显,TS去除率为30%³5%,VS去除率为55%35%,VS去除率为55%⁶0%。不同重金属浓度的COD在前15 d内均达到较高值,这有利于反应高效进行,而氨氮(NH4+-N)一直处于升高状态,对反应中的产甲烷微生物造成抑制作用,最终导致消化系统氨中毒,使Cu400,Cu500,Cu600 3个处理的发酵罐产气提前结束。     

Integrated Taguchi method and response surface methodology to confirm hydrogen production by anaerobic fermentation of cow manure

In the present study, we evaluated the feasibility of integrating the Taguchi method and the response surface methodology (RSM) to predict and optimize fermentative hydrogen production of cow manure (CM) slurry, a mixture of CM and tap water that was equivalent to 6% of the volatile solid (VS) content. Batch vial tests were first conducted in accordance with an experimental design using the Taguchi method L₁₈ orthogonal array that selected the significant influencing factors (temperature and pH) of hydrogen production, and then the RSM with a central composite design was used for the following experiments based on the aforementioned factors. Finally, fermentation experiments in triplicate were carried out in a 2-L semi-continuously stirred tank reactor (semi-CSTR) with a fixed organic loading rate (OLR), solid retention time (SRT) and varying temperatures and pH under a steady-state operation. Through a series of investigations conducted in this study, our experimental data confirmed that the optimal conditions were 60 °C with pH 5.20 ± 0.21, resulting in hydrogen content (HC) of 54.64 ± 11.45%, volumetric hydrogen production (VHP) of 405.54 ± 193.61 ml-H₂/l/d, and specific hydrogen yield (SHY) of 10.25 ± 4.96 ml-H₂/g-VS. This study demonstrates a good performance of the Taguchi method with pretests and the prediction of the response surfaces methodology. The confirmed experimental results show the behavior of anaerobic fermenters’ treating in significant factors, which will comply with management strategies for treatment of relative organic wastes in the future.     

Effect of agitation pretreatment on anaerobic digestion of swine manure

This study evaluated the effect of mechanical agitation pretreatment on anaerobic digestion (AD) of swine manure (SM). The results showed a remarkable increase in soluble polysaccharides, soluble proteins, and soluble chemical oxygen demand (SCOD) by 82.42%, 121.17%, and 114.89%, respectively, after the SM being agitated for 22 h. No improvement in the volatile fatty acids (VFAs) yield was observed during the agitation pretreatment. Apparently, agitation significantly accelerated the hydrolysis of SM, while it did not seem to enhance the acidification step. Batch AD experiments showed an improved accumulative methane yield by 77.89% with the pretreated SM compared to raw SM.     

The effect of total solids concentration and temperature on biogas production by anaerobic digestion

This paper analyzed the effect of total solids (TS) concentration and temperature on biogas production from anaerobic digestion with dairy manure. Batch experiments were carried out for TS concentrations of 6%, 8%, and 10%, respectively, at five different temperatures (31, 34, 37, 40, and 43°C). Results showed that two factors both had significant effect on biogas production. The optimal condition for anaerobic digestion was 8% TS concentration at the temperature of 40°C. Under such condition, the biogas production is much better than the others and the yield peaked higher. Daily biogas production of 8% was more than those test groups which are 6% and 10% under the same temperature. When TS concentration was 8%, the rank of total biogas production of different digestion temperature test was 40 ＞ 37 ＞ 34 ＞ 43 ＞ 31°C, the biogas production of the 31, 34, 37, 40, and 43°C was 0.123, 0.159, 0.171, 0.205, and 0.153 L/g, respectively.     

Comprehensive study on a two-stage anaerobic digestion process for the sequential production of hydrogen and methane from cost-effective molasses

Two-stage anaerobic digestion process has been frequently applied to the sequential production of hydrogen and methane from various organic substrates/wastes. In this study, a cost-effective byproduct of food industry, molasses, was used as a sole carbon source for the two-stage biogas-producing process. The two-stage process consisted of two reactor parts named as the first-stage hydrogenic reactor (HR) operated at pH 5.5 and 35°C and the second-stage methanogenic reactor (MR) at pH 7.0 and 35°C. Microbial community analysis revealed that Clostridium butyricum was the major hydrogen-producing bacteria and methanogens consisted of hydrotrophic bacteria like Methanobacterium beijingense and acetotrophic bacteria like Methanothrix soehngenii. In the first-stage process, hydrogen could be efficiently produced from diluted molasses with the highest production rate of 2.8 (±0.22) L-H₂/L-reactor/d at the optimum HRT of 6 h. In the second-stage process, methane could be also produced from residual sugars and VFAs with a production rate of 1.48 (±0.09) L-CH₄/L-reactor/d at the optimum HRT of 6 d, at which overall COD removal efficiency of the two-stage process was determined to be 79.8%. Finally, economic assessment supported that cost-effective molasses was a potent carbon source for the sequential production of hydrogen and methane by two-stage anaerobic digestion process.     

Effect of inoculum pre-treatment on mesophilic hydrogen and methane production from food waste using two-stage anaerobic digestion

Two-stage anaerobic digestion of food waste was performed using four different inoculum pre-treatment methods to enrich hydrogen (H₂) producing bacteria from sludge. The pretreatments used in this study included heat shock, alkaline treatment, aeration, and a novel pretreatment using waste frying oil (WFO). Alkaline pretreatment and aeration did not completely inhibit methanogens in the first stage while no methane (CH₄) was detected in the reactors cultivated either with heat shock or WFO-pretreated inocula. The highest H₂ and CH₄ yields (76.1 and 598.2 mL/gVS, respectively) were obtained using the inoculum pretreated with WFO. The highest total energy yield (21.96 kJ/gVS) and total organic carbon (TOC) removal efficiencies (95.77%) were obtained using inoculum pretreatment with WFO. The total energy yield trend obtained using the different pretreatments was as follows: WFO > alkaline > heat > aeration > control.     

Mesophilic anaerobic co-digestion of cow manure with three-phase olive mill solid waste

The biogas production potential of different mixtures of cow manure (CM) and three-phase olive mill solid waste (3POMSW) at 37°C was evaluated. Results showed that 3POMSW produced more methane yield than CM. In the anaerobic co-digestion (AcoD) methane yield increased with increasing of 3POMSW content, the maximum methane yield was observed at 3POMSW:CM ratio of 3:1. Addition of an enzyme mixture (Celluclast, Pulpzyme HC, Sherazyme, Novozym 342, and Resinase A 2X) to the 1:1 mixture increased the quantity and quality of biogas production and reduced the retention time required to achieve a high rate of biodegradation. Therefore, AcoD with enzymes was an effective way to improve the methane yield of 3POMSW and CM.     

Integration of submersible microbial fuel cell in anaerobic digestion for enhanced production of methane and current at varying glucose levels

A submersible microbial fuel cell (SMFC) was coupled with anaerobic digestion (AD) system to establish synergy for enhancing the electricity and methane production at different glucose concentration of 2, 4 and 10 g/l. High amount of stable current generation of 0.35 mA was obtained at 4 g/l, which was about 1.5 times higher than the SMFC-AD operated at 10 g/l glucose. Methane production and yield were enhanced by 69% and 28%, respectively in SMFC-AD in comparison with AD operation at 2 g/l. Maximum methane yield of 0.32 l-CH₄/g COD was observed in SMFC-AD operation at 2 g/l, followed by 4 g/l (0.28 l-CH₄/g COD) and 10 g/l (0.18 l-CH₄/g COD). Furthermore, the SMFC-AD process increased COD removal and maintained proper pH of around 6.8–7.3 for efficient methane production. This study suggests that the SMFC-AD can achieve enhanced methane production compared to stand-alone AD with additional electricity generation.     

微量金属元素对餐厨垃圾与牛粪联合厌氧消化效率影响

为了提高餐厨垃圾(FW)与牛粪(CM)联合厌氧消化效率,试验通过向批式厌氧消化体系中加入微量金属元素(Fe,Co,Ni),研究其对FW与CM联合厌氧消化性能的影响。结果表明:添加微量金属元素有利于维持系统稳定,提高产气效率。T1~T5的沼气总产量均达到4 000mL以上,较不添加微量元素处理(CK)增加55%左右,平均甲烷含量均在60%以上,较不添加微量元素处理(CK)增加20%左右。T1~T5的有机酸(VFAs)及氨氮含量变化较平稳,未出现酸累积及氨抑制现象,而CK的VFAs及氨氮含量呈现不断上升的趋势。加入微量金属元素后辅酶F420的吸光值开始上升,15 d以后吸光值稳定在0.55~0.65,而CK的吸光值呈现下降趋势。因此,添加微量金属元素是提高FW与CM联合厌氧消化效率的有效途径。     

CSTR反应器鸡粪厌氧消化中试启动研究

在中温(37℃)条件下,利用全混式厌氧(CSTR)反应器进行鸡粪废水厌氧消化启动的实验室模拟,将试验分为4个阶段(Ⅰ,Ⅱ,Ⅲ,Ⅳ),逐级增加进料负荷量,研究分析各阶段影响因素。结果表明:CSTR反应器能够正常启动鸡粪废水厌氧消化,当试验各阶段(Ⅰ∶Ⅱ∶Ⅲ∶Ⅳ)进料比为1∶2∶2.67∶3.33时,相应的最高产气速率之比约为1∶1.76∶2.04∶2.46;在进料COD为25 496 mg/L,HRT为31 d时,氨氮最高浓度为2 122 mg/L左右,COD去除率为(57.5±1.93)%,每日甲烷产量(单位质量VS)为(301±6)mL/g。试验4 d后,CSTR反应器产生的沼气中CH4含量稳定在61.8%～70.1%。     

Promoting direct interspecies electron transfer for methane production in bioelectrochemical anaerobic digestion: Impact of electrode surface area and switching circuit

The bioelectrochemical enhancement of direct interspecies electron transfer (DIET) for methane production was investigated in a UASB reactor under different electrode surface areas. The specific methane production rate is stabilized at 316.7 mL/g COD in the bioelectrochemical UASB (BUASB) reactor with an electrode surface area of 10 m²/m³, which is significantly higher than the 216.8 mL/g COD of the UASB reactor. The electroactive bacteria, involved in the DIET for methane production, is signifianctly increased in the BUASB reactor. When the electrode surface area is expanded to (20 and 30) m²/m³, the specific methane production rates in the BUASB reactor are further increased to (358.4 and 361.0) mL/g COD, respectively (p-value > 0.05). The theoretical methane production from the electrode surface is approximate 3.1% of the total methane production in all BUASB reactors, and the bioelectrochemical methane production is mainly attributed to the biological DIET pathway (54%) in the bulk solution. The BUASB reactor at the electrode surface area of 20 m²/m³ showes better performance according to the methane production, process stability, and enrichment of electroactive microorganisms. The bioelectrochemical system provides a new platform that can dramatically improve the performance of UASB process for treating brewery wastewater.     

Mathematical modeling of the anaerobic digestion in two-stage system with production of hydrogen and methane including three intermediate products

Anaerobic digestion is a multi-step biotechnological process, in which H2 is not detected as it is consumed immediately e.g. by hydrogenotrophic methanogens to produce CH₄ and CO₂. Recently a two-stage AD concept consisting of hydrogenic process followed by methanogenic process was suggested. However, only few models of this process are known. In this study a mathematical model of a continuous process of AD with production of hydrogen and methane in a cascade of two bioreactors, including some intermediate products in the first bioreactor was developed and investigated.     

The effect of different acetic acid accumulation on the methanogenic population and methane production in dry mesophilic anaerobic digestion

In this article, the interaction between acetic acid and methanogenic bacteria activity was investigated. The dry anaerobic digestion was conducted with four lab-scale reactors (R1–R4) and acetic acid at different concentrations were fed as additional substrate to R1–R4. The results showed that the population of acetocastic-utilizing methanogens decreased along with the increasing of acetic acid, in which the concentration was above 120,000 mg·L^–1 during the stable stage with coefficient of 0.8984. The activity of methanogenic microorganisms in R2 was the best of all reactors. The maximal biogas production rate in R2 was 1.73 m³ m^–3 day^–1 with the methane content of 55%.     

In-storage psychrophilic anaerobic digestion of swine manure: Acclimation of the microbial community

Covering a concrete manure storage tank with an air-tight floating membrane should induce anaerobic digestion of the stored manure. If the microbial community in the manure can acclimate to the ambient conditions, then In-Storage Psychrophilic Anaerobic Digestion (ISPAD) could be used by Canadian livestock producers to produce methane and stabilize manure. The objective of this study was to determine whether the microbial community in swine manure can successfully acclimate to the psychrophilic operating conditions in ISPAD and develop robust anaerobic digestion. This was done in the laboratory by analyzing manure from a three-year old full-scale pilot ISPAD facility located in St. Francois Xavier, Quebec, Canada, along with fresh manure and manure from an uncovered storage tank. Biochemical methane production assays performed at the three temperatures were used to quantify the performance of the microbial community and its temperature dependence. The ISPAD microbial community produced methane, in terms of VS added, at rates of 44.6, 9.8 and 8.5 dm³ kg⁻¹ d⁻¹, at 35, 18 and 8 °C, respectively. The ISPAD process reduced the organic matter content of the manure by 24% while releasing 63% of the potential methane in the manure, as opposed to the open storage tank where no measurable reduction in solids occurred, and only 15% of the potential methane was released. These results indicate that a robust, acclimated microbial community actively digests manure in the pilot ISPAD installation.     

Bioelectrochemical enhancement of hydrogen and methane production from the anaerobic digestion of sewage sludge in single-chamber membrane-free microbial electrolysis cells

Batch tests were carried out to investigate the bioelectrochemical enhancement of hydrogen and methane production from the anaerobic digestion of sewage sludge in single-chamber membrane-free microbial electrolysis cells (MEC) and non-MECs. Hydrogen and methane were produced from the anaerobic digestion of sewage sludge in all reactors. Compared with controls, hydrogen production was enhanced 1.7–5.2-fold, and methane production 11.4–13.6-fold with Ti/Ru electrodes at applied voltages of 1.4 and 1.8 V, respectively. Most of hydrogen was produced in the first 5 days of digestion and most of methane was generated after 5 days. No oxygen was detected in the biogas and no hydrogen production was detected in the control test with water. The applied voltages can enhance the removal of suspended and volatile suspended solids, increase the transformation of soluble chemical oxygen demand, accelerate the conversion of volatile fatty acids and maintain an optimal pH range for methanogen growth.