Kinetic and performance study of a batch two-phase anaerobic digestion of fruit and vegetable wastes

Anaerobic digestion of a simulated organic fraction of the waste of a central market selling fruit and vegetables was carried out in two-phase digesters in the mesophilic range of temperatures. Batch digestion was prolonged until no biogas was produced (33 days). With digested pig manure as inoculum, maximum biogas production was obtained around day 10, and within 3 weeks the digestion was almost complete. A kinetic analysis was carried out using first-order, Monod and Chen-Hashimoto models. The Chen-Hashimoto model represents the best fit, whereas a first-order model was not consistent with the experimental 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。     

餐厨垃圾厌氧消化的工艺比选研究

研究了餐厨垃圾两段法厌氧消化工艺与整体一段法的性能差异。两种工艺的累积产气量几乎不存在差异,产气率分别达到135．66L／kgVS和134．56L／kgVS。两种工艺相比,一段法的产气周期短,但是产气的稳定性不佳,在整个消化过程中产气量波动明显,规律性不明显。研究认为：对于餐厨垃圾的厌氧消化．整体一段法的产气周期短,工艺运行简单,应用到工业化生产上,一段法具有明显优势。     

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。     

预处理对秸秆废弃物沼气发酵的影响研究

研究了预处理对典型秸秆废弃物沼气发酵的影响。与豆秆和棉秆相比,木质素含量相对较低的玉米秆产气速率和沼气产率更高。碱处理缩短了产气高峰出现的时间,峰值也得到提高,这可能与预处理增加的可溶性组分的快速降解有关。经过几天的低产气期,又出现第二个小产气高峰。组分分析表明,碱处理去除大量木质素,纤维可及度得到提高,这是第二阶段产气得到加强的原因。最终,玉米秆、豆秆和棉秆的最高沼气产率分别达415,343 ml/g TS和298 ml/g TS,比未处理秸秆提高34%,54%和86%。结果表明,预处理豆秆和棉秆产气性能较好,可与玉米秆一样,作为沼气发酵的优良原料。     

Effects of solid retention time on anaerobic digestion of dewatered-sewage sludge in mesophilic and thermophilic conditions

Anaerobic digestion of dewatered-sewage sludge using continuous stirred tank reactors (CSTRs) in duplicates was evaluated under thermophilic (50 °C) and mesophilic (37 °C) conditions over a range of nine solid retention times (SRTs). The 35- and 30-day SRTs were designed to simulate a full-scale plant operation while 25-, 20-, 15- and 12-day SRTs were planned to evaluate process performance at the various SRTs. The 9-, 5- and 3-day SRTs were performed to push the reactors to extend their degradation capacity and test the threshold for process imbalance. The corresponding organic loading rates (OLR) varied from 1.6 to 20.5 kg VS m^?3 day^?1. Biogas production rate could be tripled when the SRT was shortened from 30 to 12 days and more than doubled from 35- to 15-day SRT because of a concomitant increase in OLR. In general, higher biogas productivity was realized under thermophilic, but methane yields were comparable due to the higher methane content in the biogas under mesophilic digestion. The methane content in biogas fluctuated between 55 and 65% and the methane yield ranged from 0.314 to 0.348 Nm³ CH₄ kg VS_added^?1 day^?1 for both thermophilic and mesophilic digestion. The VS-reduction at 12- and 15-day SRT ranged from 45 to 52% and there was no accumulation of VFAs. Increasing concentrations of VFAs, decreasing concentration of partial alkalinity and decrease in pH were noted as signs of reactor instability. Process imbalance started at 9-day SRT, souring of the reactors, cell wash-out and foaming was noted as the principal causes of process failure under both thermophilic and mesophilic conditions. This study projected the possibility of using CSTRs in treating dewatered-sewage sludge at a shorter SRT to achieve reasonable biogas production and VS-reduction without encountering adverse operation conditions as foaming and wash-out of cells.     

Pilot-scale high solids thermophilic anaerobic digestion of municipal solid waste with an emphasis on nutrient requirements

A pilot study was conducted to assess the biodegradable organic fraction of municipal solid waste (BOF/MSW) as a substrate in a high-solids anaerobic digestion process. Results obtained indicate that a typical BOF/MSW in the United States is deficient in most macro and micro-nutrients required for robust and stable digestion. The BOF/MSW was supplemented with nutrient-rich organic wastes such as wastewater treatment plant sludges, dairy manure, and synthetic chemical solutions to correct nutritional deficiencies. The combined addition of wastewater treatment plant sludge and dairy manure to a typical BOF/MSW significantly elevated the gas production rate and enhanced the process stability. Microbial nutrient requirements are identified and nutrient concentrations for stable operation are quantified.     

Heat and energy requirements in thermophilic anaerobic sludge digestion

The heating requirements of the thermophilic anaerobic digestion process were studied. Biogas production was studied in laboratory experiments at retention times from 1 to 10 days. The data gathered in the experiments was then used to perform a heat and energy analysis. The source of heat was a conventional CHP unit system. The results showed that thermophilic digestion is much faster than mesophilic digestion and therefore produces more biogas in a shorter time or at smaller digester volumes. The major part of the heating requirements consisted of sludge heating. The heat losses of the digester were only 2–8% of the sludge heating requirements. The heating requirements in thermophilic digestion are about twice those of mesophilic digestion. Therefore a CHP unit system cannot cover all of the needs for successful operation of thermophilic digestion. Heat regeneration was introduced as a solution. Heat is regenerated from the sludge outflow at a temperature of 50–55 °C and transferred to the cold inflow sludge at a temperature of 11 °C. Enough heat is regenerated in a conventional counter flow heat exchanger to bring the thermophilic process to the same level as the mesophilic one. Considering the smaller digester volumes and the relatively small investment in the regenerative equipment, the construction of thermophilic digestion systems may be a very good alternative to conventional mesophilic sludge digestion systems.     

Kinetic study of mesophilic anaerobic digestion of pulp & paper sludge

Anaerobic digestion of pulp and paper sludge (PPS) and monosodium glutamate waste liquor (MGWL) was studied in completely stirred tank reactors (CSTR) at 37 ± 2 °C. This work focused on the effect of increased organic loading rate (OLR) on the methane production in long-term experiments. For OLR in the range of (1.5-5.0) kg m⁻³ d⁻¹ based on VS fed, VFA and SCOD concentrations decreased for the first 10 days and then kept stable at about 2.3 kg m⁻³ and 4.0 kg m⁻³ respectively until to the critical OLR of 5.0 kg m⁻³ d⁻¹; and the methane generation rate enhanced to 0.838 m³ m⁻³ d⁻¹ during this period until to the reactor failure. Additionally, reaction rate constant k and sludge retention time (SRT) are described on the basis of a mass balance in a CSTR followed a first order kinetic equation. In the present study, values for y_m and k were obtained as 0.733 m³ kg⁻¹ of removed VS and 0.07 d⁻¹, respectively. The simple model can apply for dimensioning a CSTR digesting of organic wastes from pulp and paper industries, food processing industries, sewage treatment plants or biogas crops.     

Biogasification of solid wastes by two-phase anaerobic fermentation

Municipal, industrial and agricultural solid wastes, and biomass deposits cause large-scale pollution of land and water. Gaseous products of waste decomposition pollute the air and contribute to global warming. This paper describes the development of a two-phase fermentation system that alleviates methanogenic inhibition encountered with high-solids feeds, accelerates methane fermentation of solid bed, and captures methane (renewable energy) for captive use to reduce global warming. The innovative system consisted of a solid-bed reactor packed with simulated solid waste at a density of 160 kg/m³ and operated with recirculation of the percolated culture (bioleachate) through the bed. A rapid onset of solids hydrolysis, acidification, denitrification and hydrogen gas formation was observed under these operating conditions. However, these fermentative reactions stopped after about 2.5 months of solid-bed fermentation at which time total volatile fatty acids (VFA) concentration accumulated to 13,000 mg/l (as acetic) at pH 5, and the reactor head-gas consisted of 75% carbon dioxide, 20% nitrogen, 2% hydrogen and 3% methane. The VFA concentration and gas composition remained virtually constant for an additional 2.5 months of solid-bed fermentation indicating inhibition of the hydrolysis–acidification process. Inhibition of acidogenic fermentation was alleviated by moving the bioleachate to a separate methane-phase fermenter, and recycling methanogenic effluents at pH 7.5 to the solid bed. Coupled operation of the two reactors during the following 4.5 months of two-phase fermentation achieved methanogenic conversion of about 30% of the volatile solids (VS) content of the high-solids feed. Process operation was continuing.     

餐厨垃圾厌氧消化工艺研究

为了提高餐厨垃圾的厌氧消化效率,对餐厨垃圾序批式厌氧消化(BT)、半连续厌氧消化(SCT)、固液两相厌氧消化(SLT)进行了比选研究。研究结果表明,SLT生产系统有效提高了厌氧消化效率,单位沼气产量与甲烷含量也都显著提高,SLT,SCT及BT的单位VS最大沼气日产量分别为430,270 m L和150 m L,最高甲烷含量分别为68%,57%和50%;SLT的产酸效率及有机酸利用率均显著提高,有机负荷率较SCT提高50%,能够达到9 g/(L·d)。餐厨垃圾的SLT工艺有机负荷及消化效率较SCT及BT工艺均有大幅提高。     

Treatment of kitchen waste using a mobile thermophilic anaerobic digestion system

A mobile thermophilic anaerobic digestion (TAnD, 55 °C) system was developed to treat kitchen waste. A two-phase TAnD system was designed to fit in a 40 ft container (L × W × H = 1203 × 235 × 238 cm) with an initial designed capacity of 100 kg/d (assuming a solid content of 15%). During the grinding process, an equal amount of water was added to the kitchen waste (1:1 dilution) to maintain a manageable concentration and sludge flow conditions. The tested loading was up to 160 L/d. The system was operated at hydraulic retention times (HRT) of 5.6 and 25 days for hydrolysis and acidogenesis, respectively. The removal efficiencies of total COD (TCOD), suspended solids (SS), and volatile SS (VSS) were 72.5, 77.8, and 82.4%, respectively, with a specific gas production of 0.733 m³/m³d.     

Two-stage anaerobic process for bio-hydrogen and bio-methane combined production from biodegradable solid wastes

A two-stage anaerobic digestion process intended for biohydrogen and bio-methane combined production from organic fraction of municipal solid wastes was investigated. In thermophilic conditions blocking of methanogenesis at the first stage of the anaerobic fermentation was achieved at pH 9.0. Cumulative hydrogen production made 82.5 l/kg volatile solids. Pretreatment of organic fraction of municipal solid wastes and exploitation of mixed cultures of anaerobic thermophilic cellulolytic and saccharolytic bacteria of Clostridia sp resulted in the increase of hydrogen cumulative production up to 104 l/kg volatile solids. Content of methane in biohydrogen didn’t exceed 0.1%. Cumulative bio-methane production made 520 l/kg volatile solids. Methane percentage in produced biogas was 78.6%. Comparison of energy data for two-stage anaerobic digestion with those for solely methane production shows the increase in energy recovery from biodegradable fraction of municipal solid wastes. Results obtained make a foolproof basis for the development of cost-effective technological process providing hydrogen and methane combined production from solid organic wastes. Technology can be implemented at large scale biogas plants improving economical and ecological characteristics of the overall process.     

Continuous thermophilic hydrogen production and microbial community analysis from anaerobic digestion of diluted sugar cane stillage

The aim of this study was to promote biohydrogen production in an thermophilic anaerobic fluidized bed reactor (AFBR) at 55 °C using a mixture of sugar cane stillage and glucose at approximately 5000–5300 mg COD L⁻¹. During a reduction in the hydraulic retention time (HRT) from 8, 6, 4, 2 and 1 h, H₂ yields of 5.73 mmol g COD_added⁻¹ were achieved (at HRT of 4 h, with organic loading rate of 52.7 kg COD m⁻³ d⁻¹). The maximum volumetric H₂ production of 0.78 L H₂ h⁻¹ L⁻¹ was achieved using stillage as carbon source. In all operational phases, the H₂ average content in the biogas was between 31.4 and 52.0%. Butyric fermentation was the predominant metabolic pathway. The microbial community in accordance with the DGGE bands profile was found similarity coefficient between 91 and 95% without significant changes in bacterial populations after co-substrate removal. Bacteria like Thermoanaerobacterium sp. and Clostridium sp. were identified.     

Renewable energy from thermophilic anaerobic digestion of winery residue: Preliminary evidence from batch and continuous lab-scale trials

The winemaking process generates many by-products besides wastewater, mainly grape marcs, grape stalks, and wine lees. Anaerobic digestion is particularly suitable to treat winery waste because of its high content of nutrient-rich organic matter and for its noticeable energetic potential. To date, only results from mesophilic tests have been extensively reported. In this study, potential methane production and kinetic constants were determined by batch trials under thermophilic conditions and compared with mesophilic values already reported in literature. Grape marcs and wine lees appeared to be the most promising substrates with an estimated potential of 0.34 and 0.37 Nm³CH₄/kgVS_fed, respectively, while grape stalks generated only 0.13 Nm³CH₄/kgVS_fed. In order to assess the feasibility of a continuous anaerobic digestion process, a lab-scale semi-continuous reactor was constructed. Because of the consumption of buffer capacity, the biological process was difficult to control. On the other hand, biogas was produced when working with a hydraulic retention time of 40 d and with previously fermented grape marcs; a specific biogas production of 0.29 Nm³/kgVS_fed was observed. The results of the continuous tests were used to calculate the potential energy recovery from grape marcs produced in Italy (808 thousands of tons per year) in terms of heat and electricity; about 245 GWh of heat and 201 GWh of electricity per annum could be generated in Italian scenario.     

玉米秸秆两级CSTR厌氧消化工艺动力学性能研究

文章采用物料衡算模型、微生物衡算模型和一级动力学模型对两级CSTR厌氧消化系统的运行性能进行了研究。研究结果表明:两级厌氧消化系统HRT(20+20)d和HRT(30+10)d的产甲烷系数分别比单级厌氧消化系统HRT40d增加了5.38%和5.99%;HRT(20+20)d和HRT(30+10)d的第一级反应器的一级动力学常数高于HRT40d以及HRT(20+20)d和HRT(30+10)d的第二级反应器的一级动力学常数;HRT40d,HRT(20+20)d和HRT(30+10)d的微生物产率系数分别为0.003 8,0.016 6和0.020 4;在不同有机负荷率下,HRT(20+20)d,HRT30+10d和HRT40d的平均微生物浓度分别为0.221~0.350,0.275~0.447,0.047~0.076 g/L。     

Continuous hydrogen production from tofu processing waste using anaerobic mixed microflora under thermophilic conditions

We carried out continuous fermentative H₂ production from tofu (soybean curd)-processing waste (TPW) using anaerobic mixed microflora under thermophilic (60 °C) conditions and compared the rates and yields of H₂ production in a continuous stirred-tank reactor (CSTR) and a membrane bioreactor (MBR), wherein the membrane filtration unit was coupled to the CSTR. The TPW was diluted with tap water and then hydrolyzed by blending for 5 min in the presence of 0.5% HCl, and it was found that this protocol significantly increased the amount of soluble material in the mixture. The soluble chemical oxygen demand (SCOD)-to-total COD (TCOD) ratio jumped from 14% to 60%, and the soluble carbohydrate concentration was increased threefold, from 2.4 g/L to 7.2 g/L. Accordingly, H₂ production potential was increased 2.8-fold. In a CSTR operation using pretreated TPW as the substrate, a stable volumetric H₂ production rate (VHPR) of 8.17 ± 0.32 L H₂/L/d and a H₂ yield of 1.20 ± 0.05 mol H₂/mol hexose_added at 8-h HRT were achieved. Substantial increases in the VHPR and H₂ yield over those obtained with the CSTR were observed in the MBR operation. The role of the MBR was to increase the retention time of the solid substrate and the concentration of microorganisms, thereby enhancing the substrate utilization rate for H₂ production. Acetic and butyric acids were the main liquid-state metabolites produced during the fermentation process, thus indicating that the thermophilic operation provided favorable conditions for H₂ production from TPW. A maximum H₂ yield of 1.87 mol H₂/mol hexose_added was achieved at 8-h HRT and then gradually decreased to 1.00 mol H₂/mol hexose-equivalent at 2-h HRT. Meanwhile, the VHPR continuously increased to a maximum of 19.86 L H₂/L/d at 4-h HRT and then decreased with a high dilution rate as the HRT was lowered to 2 h (minimum). At 2-h HRT, the degradation of soluble carbohydrate was limited.     

Mesophilic and thermophilic co-fermentation of cattle excreta and olive mill wastes in pilot anaerobic digesters

Cattle excreta and two-phase olive mill wastes (TPOMW) were codigested at a 3:1 ratio in two 75 L continuous stirred tank reactors at 37 °C and 55 °C to analyse their biogas production. The contribution of each residue to the total gas production at 37 °C was evaluated in reactors digesting either 3:1 excreta:water or 3:1 water:TPOMW. The mesophilic co-fermentation of cattle excreta with TPOMW at an organic loading rate (OLR) of 5.5 g COD L^?1 d^?1 rendered 1096 mL biogas L^?1 sludge d^?1. This was 337% higher than that of excreta alone. The methane yield resulting from the codigestion was 179 L CH₄ kg^?1 VS loaded, of which 42% was attributed to the quarter of the reactor corresponding to TPOMW. Under thermophilic conditions, the codigestion yielded 17.3% more methane than mesophilically. In the reactor digesting TPOMW alone (OLR = 3.8 g COD L^?1 d^?1) the ratio VFA/alkalinity exceeded 0.8 after 21 d, leading to its acidification and inhibition of methanogenesis. Farm-scale digestion of animal excreta and TPOMW should be promoted in Mediterranean countries as an environmentally sound option for waste recycling and renewable energy production.     

Automatic process control for stable bio-hythane production in two-phase thermophilic anaerobic digestion of food waste

The paper reports the results of a long term (310 days) pilot-scale trial where food waste as sole substrate was treated in a two-phase thermophilic anaerobic digestion process. This was optimized for concurrent hydrogen and methane production. First phase's optimization for hydrogen production was obtained recirculating the effluent coming from the methanogenic phase and without the addition of external chemicals. A drawback of such approach is the recirculation of ammonia into the first phase reactor for hydrogen production with possibility of consequent inhibition.     

Anaerobic digestion of by-products of sugar beet and starch potato processing

Anaerobic digestion (AD) is a promising option for the environmentally friendly recycling of agricultural by-products. However, overloading of the digester with sugar, starch or protein might cause inhibition of the anaerobic processes. The aim of the present project was to investigate the AD of sugar beet, starch potato by-products and effect of pre-treatment by steam on methane yield of potatoes pulp. The investigated by-products have been: sugar beet pulp silage (SBP), sugar beet tail silage (SBT), potato pulp (PP), potato peel pulp (PPP) and potato fruit water (PFW). All by-products were digested in 1 l eudiometer-batch digesters at 37.5 °C during 28–38 days. The specific methane yields of SBP and SBT were 430 and 481 l_N kg^?1 volatile solids (VS), respectively. The specific methane yields of PP, PPP and PFW were 332, 377 and 323 l_N (kg VS)^?1. A steam pre-treatment significantly increased the specific methane yield of PP up to 373 l_N (kg VS)^?1.