Anaerobic digestion of grain stillage at high organic loading rates in three different reactor systems

In this study the anaerobic digestion of grain stillage in three different reactor systems (continuous stirred tank reactor, anaerobic sequencing batch reactor, fixed bed reactor) with and without immobilization of microorganisms was investigated to evaluate the performance during increase of the organic loading rate (OLR) from 1 to 10 g of volatile solids (VS) per liter reactor volume and day and decrease of the hydraulic retention time (HRT) from 40 to 6 days. No significant differences have been observed between the performances of the three examined reactor systems. The changes in OLR and HRT caused a reduction of the specific biogas production (SBP) of about 25% from about 650 to 550 L kg⁻¹ of VS but would also diminish the necessary digester volume and investment costs of about 75% compared to the state of the art.     

Enhanced biogas production from anaerobic co-digestion of municipal wastewater treatment sludge and fat,oil and grease (FOG) by a modified two-stage thermophilic digester system with selected thermo-chemical pre-treatment

Anaerobic co-digestions with fat, oil and grease (FOG) were investigated in two-stage thermophilic (55 °C) semi-continuous flow co-digestion systems. One two-stage co-digestion system (System I) was modified to incorporate a thermo-chemical pre-treatment of pH = 10 at 55 °C, which was the best pre-treatment condition for FOG co-digestion identified during laboratory-scale biochemical methane potential (BMP) testing. The other two-stage co-digestion system (System II) was operated without a pre-treatment process. The anaerobic digester of each digestion system had a hydraulic retention time (HRT) of 24 days. An organic loading rate (OLR) of 1.83 ± 0.09 g TVS/L·d was applied to each digestion system. It was found that System I effectively enhanced biogas production as the thermo-chemical pre-treatment improved the substrate hydrolysis including increased COD solubilization and VFA concentrations. Overall, the modified System I yielded a 25.14 ± 2.14 L/d biogas production rate, which was substantially higher than the 18.73 ± 1.11 L/d obtained in the System II.     

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.     

Anaerobic mesophilic co-digestion of sewage sludge with glycerol: Enhanced biohydrogen production

Anaerobic mesophilic co-digestion of mixed sewage sludge from wastewater treatment plants, WWTP, with crude glycerol, the major byproduct of the biodiesel industry, has been examined using a two-phase digestion process in a semi-continuous CSTR at laboratory scale. The objective was to determine the operational conditions that enhanced biohydrogen and methane production and to evaluate the effect of the organic loading rate (OLR) applied to the process. It was concluded that the Hydraulic Retention Time HRT of the methanogenic stage did not have an important influence on the operational process of co-digestion of sewage sludge and glycerol in terms of efficiency of organic removal and biogas yield. Hence, the results obtained were 73–77% organic matter removal (as CODr) with 0.032 LH₂/gCODr and 0.16 LCH₄/gCODr when the system operated at OLRs in the range of 15.33–17.90 gCODs/L d with HRTs of 3 days in the acidogenic digester and 6, 8, and 10 days in the methanogenic digester. In terms of volatile solids, the results obtained were 92–88% organic matter removal (as VSr) with 0.20 LH₂/gVSr and 1.27 LCH₄/gVSr when the system operated at OLRs in the range of 1.94–2.79 gVS/L d.     

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.     

Anaerobic treatment of wastewater using an upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket (UASB) reactor of volume 0.03 m³ was designed and fabricated to treat wastewater. The initial organic loading rate (OLR) of the wastewater estimated to be 4.8 gVS/l.d was later reduced to 0.96 gVS/l.d to control the observed acidity in the medium while the reactor was operated continuously for 64 days. The percent biological oxygen demand (BOD) and volatile solid (VS) removal were calculated over a period of 5 weeks to measure the efficiency of the reactor. The mean VS, total solid (TS), and BOD for the influent substrate were 0.43 g/kg, 0.84 g/kg, and 0.020 mg/m³, respectively, while for the treated wastewater, the VS, TS, and BOD were 0.30 g/kg, 0.59 g/kg, and 0.013 mg/m³, respectively. The estimated energy produced by the biogas was 5.8 kWh and 0.001 m³ of the biogas raised the temperature of 20 ml of water by 11.8°C in 40 s. The study concluded that the UASB reactor designed could treat the wastewater and the biogas generated could also serve as a source of renewable energy for cooking. However, the start-up OLR should be monitored in the course of operation to prevent souring of the digester and to achieve optimum performance of the reactor.     

畜禽粪便、污泥、农村垃圾中温联合厌氧消化技术研究

利用中温厌氧消化工艺,在CSTR反应器内对畜禽粪便、污水处理厂污泥及农村生活垃圾3种原料进行联合厌氧消化试验研究,重点探讨了3种原料的配比问题。结果表明,在温度为37℃,停留时间为20 d,粪便、污泥、垃圾TS之比为6∶3∶1,容积负荷为3.61 g/(L.d)的条件下,系统稳定性和处理效果都比较理想,单位VS的产气率为0.36～0.39 L/g,VS去除率为45.1%～49.4%。     

Anaerobic co-digestion of sewage sludge with switchgrass: Experimental and kinetic evaluation

Sewage sludge removal via anaerobic digestion provides energy production in addition to waste minimization. Several strategies, such as anaerobic co-digestion, were developed to increase energy production from sewage sludge by improving C/N balance. In this study, anaerobic co-digestion of sewage sludge with an energy crop, namely switchgrass, was evaluated. As a result of studies implemented at different mixing ratios, maximum methane production was measured as 272.06 mLCH₄/gVS at the mixing ratio of 0.4:0.6 (sewage sludge:switchgrass). According to modified kinetic models used for interpretation of synergetic and/or antagonistic effects, anaerobic co-digestion has a synergetic effect on biogas production from both biomass.     

微量元素对蔬菜废弃物厌氧消化的促进效果

以蔬菜废弃物为原料的厌氧消化系统,由于原料的易酸化特性,在高负荷条件下易失稳,而低负荷的运行会导致较低的池容产气率。本研究采用自行设计的70-L厌氧发酵罐,在中温35℃条件下进行蔬菜废弃物厌氧消化的连续冲击负荷试验,根据气体成分（CH₄）的变化规律,添加微量元素（Fe, Co, Ni）以调控消化过程,使其由失稳状态恢复至稳定状态,旨在提高高负荷厌氧发酵的稳定性。研究结果表明,蔬菜废弃物中温厌氧消化系统的有机负荷率增大至2.0 g VS/(L•d)时,CH₄含量由50%降至40%,从第103天开始连续添加5天微量元素（Fe, Co, Ni）后,CH₄含量迅速恢复至50% ~ 55%的稳定状态,池容产甲烷率由0.38 L/(L•d) 增大至0.6 L/(L•d)左右并保持稳定。停止添加微量元素后,继续增大有机负荷率,厌氧消化系统稳定运行83天。当运行至第195天时（3.0 g VS/(L•d)）,CH₄含量再次出现下降趋势,由58.9%降至53.4%,添加3天微量元素后,CH₄含量再次恢复到55%以上的稳定状态。微量元素的添加可有效提高蔬菜废弃物厌氧消化的稳定性,能够快速恢复失稳的系统。     

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.     

Methane and hydrogen sulfide production during co-digestion of forage radish and dairy manure

Forage radish, a winter cover crop, was investigated as a co-substrate to increase biogas production from dairy manure-based anaerobic digestion. Batch digesters (300 cm³) were operated under mesophilic conditions during two experiments (BMP1; BMP2). In BMP1, the effect of co-digesting radish and manure on CH₄ and H₂S production was determined by increasing the mass fraction of fresh above-ground radish in the manure-based co-digestion mixture from 0 to 100%. Results showed that forage radish had 1.5-fold higher CH₄ potential than dairy manure on a volatile solids basis. While no synergistic effect on CH₄ production resulted from co-digestion, increasing the radish fraction in the co-digestion mixture significantly increased CH₄ production. Initial H₂S production increased as the radish fraction increased, but the sulfur-containing compounds were rapidly utilized, resulting in all treatments having similar H₂S concentrations (0.10–0.14%) and higher CH₄ content (48–70%) in the biogas over time. The 100% radish digester had the highest specific CH₄ yield (372 ± 12 L kg⁻¹ VS). The co-digestion mixture containing 40% radish had a lower specific CH₄ yield (345 ± 2 L kg⁻¹ VS) but also showed significantly less H₂S production at start-up and high quality biogas (58% CH₄). Results from BMP2 showed that the radish harvest date (October versus December) did not significantly influence radish C:N mass ratios or CH₄ production during co-digestion with dairy manure. These results suggest that dairy farmers could utilize forage radish, a readily available substrate that does not compete with food supply, to increase CH₄ production of manure digesters in the fall/winter.     

Biogas production from brown grease using a pilot-scale high-rate anaerobic digester

Food wastes are typically disposed of in landfills for convenience and economic reasons. However, landfilling food wastes increases the organic content of leachate and the risk of soil contamination. A sound alternative for managing food wastes is anaerobic digestion, which reduces organic pollution and produces biogas for energy recovery. In this study, anaerobic digestion of a common food waste, brown grease, was investigated using a pilot-scale, high-rate, completely-mixed digester (5.8 m³). The digestibility, biogas production and the impact of blending of liquid waste streams from a nearby pulp and paper mill were assessed. The 343-day evaluation was divided into 5 intensive evaluation stages. The organic removal efficiency was found to be 58 ± 9% in terms of COD and 55 ± 8% in terms of VS at a hydraulic retention time (HRT) of 11.6 ± 3.8 days. The removal was comparable to those found in organic solid digesters (45–60%), but at a much shorter HRT. Methane yield was estimated to be 0.40–0.77 m³-CH_4@STP kg-VS_removed⁻¹, higher than the typical range of other food wastes (0.11–0.42 m³-CH_4@STP kg-VS_removed⁻¹), with a mean methane content of 75% and <200 ppm of hydrogen sulfide in the biogas. The blending of selected liquid wastes from a paper mill at 10 vol% of brown grease slurry did not cause significant reduction in digester performance. Using a pseudo-first-order rate law, the observed degradation constant was estimated to be 0.10–0.19 d⁻¹ compared to 0.03–0.40 d⁻¹ for other organic solids. These results demonstrate that brown grease is a readily digestible substrate that has excellent potential for energy recovery through anaerobic digestion.     

Thermophilic and mesophilic temperature phase anaerobic co-digestion (TPAcD) compared with single-stage co-digestion of sewage sludge and sugar beet pulp lixiviation

The performance of temperature phase anaerobic co-digestion (TPAcD) for sewage sludge and sugar beet pulp lixiviation (using the process of exchanging the digesting substrate between spatially separated thermophilic and mesophilic digesters) was tested and compared to both single-stage mesophilic and thermophilic anaerobic co-digestion. Two Hydraulic Retention Times (HRT) were studied in the thermophilic stage of anaerobic digestion in two temperature phases, maintaining the optimum time of the mesophilic stage at 10 days, obtained as such in single-stage anaerobic co-digestion. In this way, we obtained the advantages of both temperature regimes.Volatile solids removal efficiency from the TPAcD system depended on the sludge exchange rate, but fell within the 72.6–64.6% range. This was higher than the value of 46.8% obtained with single-stage thermophilic digestion and that of 40.5% obtained with mesophilic digestion. The specific methane yield was 424–468 ml CH₄ per gram of volatile solids removed, similar to that of single-stage mesophilic anaerobic digestion. The increase in microbial activity inside the reactor was directly proportional to the organic loading rate (OLR) (or inversely proportional to the HRT) and inversely proportional to the size of the microbial population in single-stage anaerobic co-digestion systems.     

Co-digestion of waste glycerol and glucose to enhance biogas production

Co-digestion in anaerobic fermentation has been widely used to improve biogas production. The biogas production from co-digestion of glucose and glycerol was studied in laboratory-scale batch reactors under mesophilic temperatures, pH 7. The batch experiments involved a variation of glycerol/glucose ratios with initial chemical oxygen demand (COD) for all conditions was fixed at 5,200 mg L⁻¹. The highest yield of biogas production was obtained from glycerol/glucose with 5:5 ratio. The cumulative biogas production was 298.2 mL, and the maximum production rate was 8 mL hr⁻¹. The findings suggested that co-digestion is a potential method to achieve glycerol waste treatment and energy recovery at the same time.     

餐厨垃圾高温厌氧消化连续运行性能：有机物转化效率、发酵稳定性与代谢活性

在高温(50±1)℃条件下处理实际工程的餐厨垃圾,采用全混式厌氧反应器（CSTR）进行了80d的连续试验。试验以水力停留时间（HRT）20 d启动,HRT 15 d连续运行,研究了反应器启动和运行期间的发酵特性,解析了餐厨垃圾厌氧消化运行稳定性和代谢活性。试验结果表明,在HRT 15 d、有机负荷（OLR）为7.3 kgCOD/(m3·d)的条件下,容积产甲烷率为2.2L/(L·d),挥发性固体（VS）的甲烷产率达到480L/kgVS左右,有机物转化率约为95%。批次试验表明,高温产甲烷菌代谢乙酸能力较强,在适宜pH下可承受10000mg/L的乙酸浓度。餐厨垃圾的高温降解速率快,10 d达到90%的产气,有承受更高负荷的可能。系统pH稳定在7.6～7.7,总氨氮和自由氨浓度低于抑制水平。研究结果表明,餐厨垃圾的高温厌氧消化可实现较高的产气潜力和有机物去除率,系统稳定性好且有机物转化效率高,具有应用于工程高温餐厨垃圾厌氧处理的潜力。     

餐厨垃圾SBMR-ASBR两相厌氧消化产气性能研究

以学校食堂餐厨垃圾为原料,考察餐厨垃圾在SBMR-ASBR反应器中产酸和产甲烷性能。结果表明:高负荷下启动酸化相有利于系统快速形成稳定的乙醇型发酵,且可以避开丙酸型发酵,在10 g/(L.d)负荷(以VS计)下,稳定状态产酸率平均达到55 000 mg/L,VFA中乙醇和乙酸分别平均稳定在27 000 mg/L和23 000mg/L,两者共占总VFA的91%;甲烷相可以稳定运行的最高负荷为5 g/(L.d)(以VS计),此时,系统整体处理能力为3.3 g/(L.d),单位容积产气率达到2.3 L/(L.d),甲烷含量在65%～70%,TS,VS去除率分别达到77%,83%。在实际工程中可以高负荷启动酸化相,有利于系统形成稳定的乙醇型发酵和高负荷运行的甲烷相。     

Pre-treatment study on two-stage biohydrogen and biomethane productions in a continuous co-digestion process from a mixture of swine manure and pineapple waste

This study involves continuous co-digestion of swine manure and pineapple waste mixture using two-stage anaerobic reactors and examines hydraulic retention time (HRT) and substrate heat pre-treatment. The maximum hydrogen and methane production rates of 1488.62 and 991.57 mL/L/d, respectively, reached optimal HRTs of 4.5 h in the hydrogen production fermenter (HPF) and 9 d in the methane production fermenter (MPF) using heat pre-treatment. Acetic acid is a dominant volatile fatty acid of the soluble metabolites with values 70%–73% under all the tested conditions and increased values under heat pre-treatment and high HRT. Firmicutes and Euryarchaeota are the main bacteria species detected in HPF and MPF, respectively. The optimal total energy of 196.47 kJ/L/d and chemical oxygen demand (COD) removal efficiency of 90% were obtained by a complete anaerobic co-digestion process at a high substrate concentration of 105 g COD/L and low HRT of 4.5 h. This shows that the two-stage co-digestion process could increase the COD removal efficiency, hydrogen production rate, and net energy gains and produce high quality biogas and significantly reduce fermentation time.     

Laboratory investigations on continuous bio-methanization of energy crops as mono-substrate without supplementation

Continuous bio-methanization of an energy crop, namely the beet silage, was investigated in this laboratory-scale work as mono-substrate, using a mesophilic biogas digester controlled by a fuzzy logic control (FLC) technique and without using any supplementing or buffering agent, despite the low pH of the substrate around 3.80. The temperature, pH, redox potential (ORP), daily biogas production and composition of digester biogas were continuously measured online. During the operation, the hydraulic retention time (HRT) varied between 24.8 and 9 days, as the organic loading rate (OLR) ranged from 2.6 to 4.7 g L^?1 d^?1. The average pH, specific gas production rate (spec. GPR) and volumetric gas production rate (vol. GPR) were determined to be 7.12, 0.31 L g VS^?1 d^?1 and 1.084 L L^?1 d^?1, respectively. The average methane (CH₄) content of digester biogas was about 56%. The FLC technique, which was developed at HAW Hamburg for anaerobic conversion of acidic energy crops to methane, determined the daily feeding volume (～ OLR/HRT) for the biogas digester, depending on the feedback from online pH and methane measurements, and on the calculation of the spec. GPR. The spec. GPR was calculated by the corrected daily biogas production. Through online monitoring of pH, biogas production rate and composition, and by use of the FLC technique, the acidic beet silage could continuously be converted to biogas, without using manure or any other kind of buffering or supplementing agent(s). The lab-scale anaerobic biogas digester performed stable and safe, without encountering any problems of instability, as indicated by an adequate amount of buffering capacity, a VFA content below 0.5 g L^?1 and a neutral pH range throughout the study.     

鸡粪与NaOH预处理麦秸联合厌氧发酵产气性能与协同效果研究

试验研究了不同负荷下不同混合比例的鸡粪与NaOH预处理麦秸的厌氧发酵产气性能和协同作用效果。以鸡粪和2%NaOH预处理后的麦秸作为发酵原料,研究了混合物料在3种负荷和9种混合比例条件下的厌氧发酵产气情况。结果表明:在3种负荷(50,65,80 g/L)中,均是鸡粪和麦秸比例为1∶2时产气效果最佳,其累计产气量分别达到32 000,43 030 mL和50 370 mL;其TS产气率分别达到328.2,356.9,352.8 mL/g,比纯鸡粪相应负荷分别提高了27%,29%,23%。不同比例下,3种负荷中,均是65 g/L时产气效果最好,鸡粪与麦秸的协同作用使累计产气量提高了7%～17.7%。