厌氧消化菌群的筛选及其对高浓度玉米秸秆的厌氧消化

为了提高玉米秸秆类原料厌氧消化的产气率和底物利用率,从环境中筛选出了厌氧降解玉米秸秆产酸和产甲烷的优势菌群,该菌群的最高容积甲烷产率为0.73 m3/(m3.d),气体中的甲烷含量达到85%左右,底物产甲烷量为410 L/kg;以15%高浓度玉米秸秆为原料,该菌群的最大产酸能力为10 g/L,最高容积产气率为3.10m3/(m3.d),平均容积产气率为1.7 m3/(m3.d),平均甲烷含量为55%。研究结果明显高于报导过的相应数据。为高浓度玉米秸秆的高效厌氧消化利用提供了良好的微生物菌群应用基础。     

Thermogravimetric analysis and structure change of lime-pretreated Spartina alterniflora

The thermal behavior and structure change of Spartina alterniflora pretreated with lime were investigated with raw and water-soaked samples for comparisons. Pretreatment significantly changed thermal decomposition behavior and activation energy. The activation energy of S. alterniflora ranged from 100.7 to 128 kJ/mol at the main decomposition stage. FTIR and solid-state ¹³C NMR analyses revealed that pretreatment disrupted the carboxyl carbons attached to the lignin side chain. Compared with water soaking, lime pretreatment resulted in more modifications of structure and composition. Furthermore, structure breakage and composition removal change the pyrolysis characteristics of pretreated samples.     

Kinetics of anaerobic digestion

The basic chemical kinetic equations for anaerobic digestion have been solved to get closed form solutions for the substrate concentration and the concentration of anaerobes. Numerical calculations have been performed to obtain quantitative estimates for their time behaviour.     

高有机负荷下的稻草两级/单级CSTR厌氧消化工艺性能研究

文章以稻草为原料,采用两级和单级厌氧消化工艺,在较高有机负荷(100,120,140 g/L)下对稻草的消化性能进行了研究。研究结果表明:当有机负荷分别为100,120,140 g/L时,两级厌氧消化系统的产甲烷效率分别比单级厌氧消化系统提高了8.8%,11.5%,11.8%;两级厌氧消化系统的产甲烷量主要集中在第一级,随着有机负荷的提高,第二级的产甲烷量占比逐渐增加;两级厌氧消化系统的物质转化率比单级厌氧消化系统更高,并且两级厌氧消化系统中的大部分物质在第一级去除,与产气效率的结果相一致;两级和单级厌氧消化系统在3个高有机负荷条件下均可以稳定运行。     

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.     

Kinetics of anaerobic cowdung digestion

Expressions are presented for the concentration of substrate in the effluents of an anaerobic digestor for the Monod and Contois kinetic equations. The calculations are compared with experimental results of Morris. The comparison suggests that Contois' equation is the better relation for modelling cowdung digestors.     

Application of nano-scale transition metal carbides as accelerants in anaerobic digestion

Four types of nano-scale transition metal carbides (HfC, SiC, TiC, and WC), used as accelerants in anaerobic digestion (AD) with cattle manure, were investigated through batch experiments under mesophilic conditions (37 ± 1 °C). The AD system with four carbide accelerants showed a higher biogas yield (463–499 mL/g TS), chemical oxygen demand (COD) degradation rate (58.62–78.90%) and total Kjeldahl nitrogen (TKN) concentrations (905.0–1077.0 mg/L) as compared with control check (CK, 294 mL/g TS, 46.99%, 290 mg/L). All of the digestate samples from the AD systems using four carbide accelerants showed not only higher degradation of organic compounds during thermal analysis, but also stronger fertilizer values. The use of transition metal compounds (TMCs) as accelerants in AD can efficiently improve the conversion of waste resources into biogas and fertilizers, which can potentially open new avenues for the use of TMCs in upcoming research on biomass energy.     

Mathematical modeling of solid-state anaerobic digestion

Solid-state anaerobic digestion (SS-AD) technology for the conversion of solid organic wastes to renewable energy has been widely studied and applied during the past decades. Due to the nature of the solid medium, the SS-AD process is significantly different from the traditional liquid anaerobic digestion in many aspects, such as the distribution of microbes and substrates in the reactors, mass transfer, and reaction kinetics. Extensive efforts have been dedicated to developing mathematical models for understanding SS-AD mechanisms, predicting its performance, and improving process control. In this review, SS-AD mathematical models derived from theoretical, empirical, and statistical approaches are critically reviewed and discussed regarding their different assumptions, structures, applications, and limitations. Based on this review, it was concluded that significant efforts should be devoted to experimental verification of the model assumptions, measurement of important kinetic parameters specific for SS-AD, and generation of sufficient data for model validation. It is necessary to synergistically improve modeling and experimental approaches in order to gain deeper insight into the SS-AD mechanism. Several promising research directions for the future development of experimental and modeling approaches in SS-AD are proposed.     

Inclined-plug-flow type reactor for anaerobic digestion of semi-solid waste

Preliminary experimental results obtained from the treatment of semi-solid wastes generated from wholesale fruit and vegetable markets, supermarkets, etc. mixed together with sewage sludge, are reported.     

State-of-the-art of anaerobic digestion technology for industrial wastewater treatment

Anaerobic digestion is the most suitable option for the treatment of high strength organic effluents. The presence of biodegradable components in the effluents coupled with the advantages of anaerobic process over other treatment methods makes it an attractive option. This paper reviews the suitability and the status of development of anaerobic reactors for the digestion of selected organic effluents from sugar and distillery, pulp and paper, slaughterhouse and dairy units. In addition, modifications in the existing reactor designs for improving the efficiency of digestion has also been suggested.     

Characterization of paper mill sludge as a renewable feedstock for sustainable hydrogen and biofuels production

Paper and pulp mills generate substantial quantities of cellulose-rich sludge materials that are disposed in landfills at a large scale. For sustainability purposes, sludge materials can be bioprocessed to produce renewable fuels and useful chemicals. The enzymatic hydrolysis of cellulose is the process bottleneck that affects the conversion economics directly by using zero-cost raw materials. In order to study and optimize the process, the characteristics of the sludge raw materials should be first evaluated. In this work, sludge samples were obtained from paper mills located at different locations in Wisconsin and Minnesota. Part of the sludge samples was washed (de-ashed) with hydrochloric acid while the other part remained unwashed. The samples were subjected to multiple spectroscopic analyses techniques to evaluate the morphological properties of cellulose fibers and to estimate the total structural carbohydrate content. The results showed that the de-ashing process changed some fiber characteristics and cellulose crystallinity structure in all sludge samples. Sludge sample A (obtained from Kraft pulp and recycled paper mill region) showed a high percentage of fiber, with crystalline cellulose, compared to the other two sludge samples suggesting that sludge A is a valuable source to make value-added products. Aspen Plus mass and energy calculations performed in view of the ‘zero’ cost and the reliable supply of sludge raw materials producing 2 mol H₂/mol glucose. Moreover, the results showed that extracting crystalline cellulose from these sludge samples is more profitable than crystalline cellulose made from the other lignocellulosic feedstocks. The results reported here showed that the utilization of these sludge materials would be an economically attractive and promising alternative for the production of hydrogen.     

Batch and semi-continuous anaerobic digestion systems

A first order kinetic model, developed to predict the behaviour of both batch and semi-continuous anaerobic digestion systems, was tested under laboratory conditions. Two and a half litre glass reactors, using cattle-dung as a feedstock, were run in both batch and semi-continuous modes in temperature-controlled water baths at 35°C. The kinetic model defined constants which could be used to evaluate both systems. The daily gas production data from the batch systems suggested that two rate constants were required to explain them: a higher rate at shorter retention times and a lower rate for longer times. The values of the kinetic rate constant defined for the semi-continuous reactors were considerably higher than those defined for the batch reactors, while the gas production constant was lower. The model offers an effective way to predict the gas production from full-scale digesters running at 35°C, although constants derived from one mode of running should not be used for the other.     

A review of simple to scientific models for anaerobic digestion

To fully model the anaerobic digestion process, biological and physico-chemical background, the kinetics of bacterial growth, substrate degradation and product formation have to be taken into account. The presented approaches differ depending on the requirements and the developer of the model. Important parameters affecting the process such as temperature, which can cause great inaccuracy, are rarely included in the models. Simple calculators are also available that estimate the applicability of the process to a specific farm and provide information to a farmer or a decision maker. Six simple calculators are presented in this study: AD decision support software, Anaerobic Digestion Economic Assessment Tool, BEAT₂, BioGC, FarmWare and GasTheo. The simpler calculators mainly use the relation that exists between volatile solids and biogas production. A tested case of 100 dairy cows and 50 sows was applied to the simple calculators to compare the results.     

城市有机生活垃圾高温厌氧转化生物质能研究

在国内外已有的研究基础上,对城市有机生活垃圾的高温厌氧（批量）消化工艺实验进行了初步探索,研究了在55℃的高温条件下累积产气量与消化时间的关系,C／N比与产气量的关系,消化过程中pH值变化,并研究了垃圾高温发酵实验过程中沼气中的CH4和CO2的含量变化,其中甲烷含量最高可达75．3％。实验结果表明,城市生活垃圾高温消化的降解效果较好,产气量较高,启动时间短。     

我国城市生活垃圾厌氧消化处理的探讨

分析了我国城市生活垃圾处理现状及存在问题，探讨了以厌氧消化技术为主的城市生活垃圾处理方式，为解决我国的城市生活垃圾问题提供参考。     

Biohythane production in two-stage anaerobic digestion system

Hydrogen (H₂) and methane (CH₄) are the potential alternative energy carriers with autonomous extensive and viable importance. These fuels could complement the advantages, and discard the disadvantages of each other, if produced simultaneously. Considering their complementary properties, co-production of a mixture of H₂ and CH₄ in the form of biohythane in two-stage anaerobic digestion (AD) process is gaining more interest than their individual production. Biohythane is a better transportation fuel than compressed natural gas (CNG) in terms of high range of flammability, reduced ignition temperature as well as time, without nitrous oxide (NOx) emissions, improved engine performance without specific modification, etc. Other than production of biohythane, performing two-stage AD is advantageous over one-stage AD due to short HRT, high energy recovery, high COD removal, higher H₂ and CH₄ yields, and reduced carbon dioxide (CO₂) in biogas. For improved biohythane production, various aspects of two-stage AD need to be emphasized. Keeping the facts in mind, the process of two-stage AD along with microbial diversity in comparison to one-stage AD has been discussed in the previous sections of this review. For large scale commercial production, and utilization of biohythane in automobile sector, its execution needs evaluation of process parameters, and problems associated with two-stage AD. Hence, the later part of this review describes the production process of biohythane, concerned microbial diversity, operational process parameters, major challenges and their solutions, applications, and economic evaluation for enhanced production of biohythane.     

Whey waste as potential feedstock for biohydrogen production

In-house isolate Clostridium sp. IODB-O3 was exploited for biohydrogen production using cheese whey waste in batch fermentation. Analysis of cheese whey shows, it is enriched with lactose, lactic acid and protein components which were observed most favourable for biohydrogen production. Biohydrogen yield by IODB-O3 was compared with the cultures naturally occurring in waste solely or in combinations, and found that Clostridium sp. IODB-O3 was the best producer. The maximum biohydrogen yield obtained was 6.35 ± 0.2 mol-H₂/mol-lactose. The cumulative H₂ production (ml/L), 3330 ± 50, H₂ production rate (ml/L/h), 139 ± 5, and specific H₂ production (ml/g/h), 694 ± 10 were obtained. Clostridium sp. IODB-O3 exhibited better H₂ yield from cheese whey than the reported values in literature. Importantly, the enhancement of biohydrogen yield was observed possibly due to absence of inhibitory compounds, presence of essential nutrients, protein and lactic acid fractions which supported better cell growth than that of the lactose and glucose media. Carbon balance was carried out for the process which provided more insights in IODB-O3 metabolic pathway for biohydrogen production. This study may help for effective utilization of whey wastes for economic large scale biohydrogen production.     

稻壳中温厌氧消化产沼气试验研究

对稻壳厌氧消化产沼气进行了试验研究,采用中温发酵,用1%NaOH和2%NaOH分别对35g/L、50g/L、65g/L和80g/L四个负荷的稻壳进行预处理,并用相应负荷的未经NaOH预处理的稻壳作对比,结果发现:稻壳厌氧消化易酸化,酸化时间在8～11天左右,最长的一个为15天;经1%NaOH预处理的稻壳在不同负荷中日产气量均达到最高,分别为35g/L时1730mL、50g/L时2070mL、65g/L时2330mL和80g/L时2980mL;通过NaOH化学预处理,加快了稻壳的厌氧消化速度,厌氧消化周期明显缩短.     

Biohydrogen generation from anaerobic digestion of food waste

Biohydrogen generated from the anaerobic digestion of a synthetic food waste with constant composition and a real food waste collected in Hong Kong were studied. This study aims at using a monoculture to increase biohydrogen production and determining optimum conditions for maximum biohydrogen production. Among the nine bacteria screened for biohydrogen production, Escherichia cloacae and Enterobacter aerogenes produced the largest amount of biohydrogen from the anaerobic digestion of synthetic food waste. The optimum anaerobic digestion conditions were determined: initial pH of 7, a water to solids ratio of 5 (w/w), a mesophilic temperature (37 ± 1 °C), and in the presence of 40 mg/L FeSO₄·7H₂O. Anaerobic digestion at the optimum operating conditions using collected food waste with E. cloacae as the bacterial source was also performed. By adjusting the pH in the range of 5–6, a specific biohydrogen production of 155.2 mL/g of volatile solids (VS) in food waste was obtained.     

餐厨垃圾特性及其厌氧消化性能研究

以校园餐厨垃圾为原料,分析测定了早餐、午餐和晚餐餐厨垃圾的总固体(TS)、挥发性固体(VS)、碳水化合物、蛋白质、脂肪含量以及无机盐离子浓度,并通过批式厌氧发酵试验对3种餐厨垃圾的厌氧消化性能进行了对比研究。结果表明,早餐餐厨垃圾特性与午餐/晚餐餐厨垃圾差异较大,Na+,Ca2+和Cl-含量高于后两者。餐厨垃圾不同特性对其厌氧消化产气及有机物去除率都有一定影响,早餐、午餐和晚餐餐厨垃圾的累积甲烷产量分别为212.2,331.6和362.4 ml/g,早餐餐厨垃圾产气量比午餐和晚餐餐厨垃圾分别低36%和41.4%,其中Cl-含量高可能是造成其产气量低的主要原因。