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%。     

Mesophilic and thermophilic anaerobic co-digestion of waste activated sludge and source sorted biowaste in pilot- and full-scale reactors

The paper presents the results of a pilot- and full-scale experimental campaign on the anaerobic co-digestion of waste activated sludge and biowaste both in mesophilic and thermophilic conditions. The study demonstrated the possibility to increase the specific biogas production from 0.34 to 0.49 m³/kgTVS and the gas production rate from 0.53 to 0.78 m³per m³ of reactor per day changing the reactor temperature from the mesophilic (37 °C) to the thermophilic (55 °C) range. The experimental work was carried out at pilot-scale, and the results match the full-scale behaviour. Ammonia nitrogen recycled from the anaerobic digestion section to the wastewater treatment plant accounted for about 4% of the total nitrogen loading. Digestate characteristics in terms of biological stability and heavy metals content suggested the opportunity of a short time post-aerobic stabilisation, leading to a high quality compost product.     

Methanogenic activity optimization using the response surface methodology,during the anaerobic co-digestion of agriculture and industrial wastes. Microbial community diversity

The anaerobic co-digestion of manure, agriculture and industrial wastes for methane production depends on the nutritional condition to develop the microbial community. The effect of each substrate concentrations, as well as their interactive effects on specific methanogenic activity and microbial community diversity were investigated in this work. A central composite design and the response surface methodology were applied for designing the anaerobic co-digestion batch test at 35 and 55 °C. It was analyzed the anaerobic sludge by specific methanogenic activity (SMA) and using molecular techniques (terminal restriction fragment length polymorphism, TRFLP). The results showed a significant interaction among the substrates and an enhancement of the methane production and SMA response caused by the three components. Rice straw had lower influence on SMA than clay residues, due to the mineral content and the beneficial ammonia nitrogen adsorbent properties of the latter. The optimum condition for mesophilic and thermophilic anaerobic co-digestion of pig manure, rice straw and clay mixture allowed SMA values of 1.31 and 1.38 gCH₄-COD/gVSSd⁻¹, respectively. The TRFLP analysis showed the effect of rice straw and clay addition on microbial community diversity at both temperatures. The acetotrophic methanogens belonging to the order Methanosarcinales (genera Methanosarcina and Methanosaeta) dominated in mesophilic condition, whereas at thermophilic conditions dominated Methanomicrobiales and Methanobacteriales order. The optimization allowed identifying the substrate interaction effects in a concentration range with a reduced number of experiments. Besides, the model validation proved to be useful for defining optimal combination of wastes in anaerobic system.     

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.     

Study on optimization of co-digestion process parameters for enhancing biohydrogen production using response surface methodology

In the present study, batch anaerobic co-digestion experiment was conducted with dairy secondary clarifier waste activated sludge as substrate and anaerobic digested municipal waste activated sludge as seed sludge for enhancing biohydrogen rate. The statistical tools were used to study the effect of co-digestion process parameters (pH, seed sludge, temperature, and digestion time) on mixed liquor suspended soils (MLSS) reduction % and chemical oxygen demand (COD) solubilization %. The maximum of MLSS reduction and COD solubilization obtained at global optimal condition (pH 6, temperature 40°C, seed sludge 35 ml, and digestion time 30 days) determined, respectively, were 22.7 and 28.02%. Subsequently, the production data of cumulative biohydrogen were fitted with modified Gompertz equation and the biohydrogen kinetic parameters were determined.     

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.     

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.     

Influence of the temperature and hydraulic retention time in bioelectrochemical anaerobic digestion of sewage sludge

At ambient temperature (25 °C), bioelectrochemical anaerobic digestion of sewage sludge was investigated with a hydraulic retention time (HRT) of 10 days and compared to that at a mesophilic condition (35 °C). The methane production and methane content in the biogas at ambient temperature were 612.8 mL/L·d and 73.3%, respectively, which were not significantly lower than that of the mesophilic condition. Additionally, the VS removal was 54.5% which was similar for both temperature conditions. However, for a HRT of 20 days, the bioelectrochemical anaerobic digestion at ambient temperature became more stable, and the VS removal improved up to 65.0%. For the HRT of 10 days, the net energy production at ambient temperature was about 168 kJ/L·d, which was similar to the mesophilic condition; however, the apparent energy efficiency at ambient temperature was 249.2% which was significantly higher than 197.7% at the mesophilic condition. The bioelectrochemical anaerobic digestion that can save the thermal energy input at ambient temperature is recommended for the treatment of organic waste including sewage sludge in moderate and cold climate regions.     

Production of bio‐energy from organic waste: effect of temperature and substrate composition

This article presents the influence of temperature and influent substrate composition on the produced biogas volume in an anaerobic co‐digestion process. Four cases of anaerobic digestion were considered. Digestion of waste sludge only and anaerobic co‐digestion of sludge mixed with solid waste in mesophilic (T = 35 °C) and thermophilic (T = 55 °C) phases. The obtained results show that thermophilic co‐digestion gives the best results; although the temperature has an effect on biogas production, it remains however quite relative compared to the effect of solid waste. They confirm, surely, that the combined effect of temperature and solid waste improves considerably the biogas production rate (GPR). Changing conditions from mesophilic to thermophilic ones for waste sludge alone and for waste sludge mixed with solid waste results in an increase of the GPR from 0.18 to 0.39 m³/m³.d and from 0.29 to 0.96 m³/m³.d, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

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.     

The efficacy of an anaerobic digester-based power production from various feedstocks

Biogas is one of the most promising renewable energy fuel sources obtained from various organic matters and used for energy requirements. This work is focused on the usage of biogas in power production. The main aim of this study was to evaluate the different factors that affect the power production during anaerobic digestion. This study examines the usage of Organic Fraction Municipal Solid Waste (OF-MSW), wastewater sludge, and co-digestion of both OF-MSW and wastewater sludge for power production. The digestions are performed under mesophilic conditions at an optimum temperature of 36°C. The maximum power produced is 128 kW when using OF-MSW alone and 48.9 kW for co-digestion (50% OF-MSW + 50% wastewater sludge) and 35.5 kW for wastewater sludge. The paper also focuses on various factors such as pH, temperature, and nitrogen concentration and its influence on power production.     

餐厨垃圾与污泥厌氧发酵产气动力学特性研究

对餐厨垃圾、污水厂污泥以及餐厨垃圾与污泥混合甲烷发酵的产气能力与动力学特性进行了实验分析,餐厨垃圾在中温和高温发酵的产甲烷潜能分别是400和426 mL CH4?gVS−1,经过120℃、20 min蒸煮除油后的餐厨垃圾在中温和高温发酵的产甲烷潜能分别是418和531 mL CH4?gVS−1。经Gompertz模型计算,除油后餐厨垃圾的最大产甲烷速率Rmax比除油前提高了49.8%（中温）和19.0%（高温）,但餐厨垃圾中固体有机物的产甲烷速率变化不明显。在餐厨垃圾机械破碎匀浆过程中,部分固体有机物被液化,中、高温发酵产气过程的一级动力学呈现两阶段特征,液相有机物在中温发酵的产甲烷速率（速率常数k = 0.1955 d−1）略快于高温（k = 0.1543 d−1）;而固体有机物在高温条件下的产甲烷速率（k = 0.0804 d−1）快于中温（k = 0.0388 d−1）。除油后餐厨垃圾中的固体有机物和污泥高温发酵的产甲烷速率也快于中温发酵,表明高温发酵有利于提高固体有机物的产气速率。污泥的产气潜能较低,产气速率慢,与餐厨垃圾共发酵有助于调节碱度和防止发酵体系的酸化。     

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.     

Evaluation of anaerobic co-digestion of spent brewery grains and an azo dye

Anaerobic batch biodegradation of spent brewery grains (SBG) was investigated in the presence of co-substrates and a monoazo dye (Acid Orange 7 – AO7) under mesophilic and thermophilic regimes. The highest values for the yield coefficient of biogas (STP) on substrate (Y_bs) were obtained under mesophilic conditions (0.381–0.516 Lbiogas/g COD_removed and 0.147 to 0.475 L_biogas/g COD_removed for mesophilic and thermophilic regimes, respectively). A stimulation of the degradation of SBG associated with microbial growth was observed in the presence of co-substrates (glucose and acetate). Supplemented co-substrates also lowered the residual COD leading to an increase in the COD removal efficiency, particularly under thermophilic regime (from 41% to 70%). Although biogas yield (Y_bs) indicates a decrease in the presence of the dye, suggesting that it has inhibitory effects, the overall COD removal was not significantly altered. An increase of colour removal was observed when the temperature of the operation was increased (87 ± 2% and 93 ± 1% for mesophilic and thermophilic reactors, respectively), which could be explained by both faster adsorption and biotic reductive cleavage of azo dye bond mechanisms. These results indicate that raw SBG is more prone to biodegradation under an anaerobic mesophilic regime; hence its bio-energetic valorisation is possible.     

Production of methane by co-digestion of cassava pulp with various concentrations of pig manure

Cassava pulp is a major by-product produced in a cassava starch factory, containing 50–60% of starch (dry basis). Therefore, in this study we are considering its potential as a raw material substrate for the production of methane. To ensure sufficient amounts of nutrients for the anaerobic digestion process, the potential of co-digestion of cassava pulp (CP) with pig manure (PM) was further examined. The effect of the co-substrate mixture ratio was carried out in a semi-continuously fed stirred tank reactor (CSTR) operated under mesophilic condition (37 °C) and at a constant OLR of 3.5 kg VS m^?3 d^?1 and a HRT of 15 days. The results showed that co-digestion resulted in higher methane production and reduction of volatile solids (VS) but lower buffering capacity. Compared to the digestion of PM alone, the specific methane yield increased 41% higher when co-digested with CP in concentrations up to 60% of the incoming VS. This was probably due to an increase in available easily degradable carbohydrates as the CP ratio in feedstock increased. The highest methane yield and VS removal of 306 mL g^?1 VS_added and 61%, respectively, were achieved with good process stability (VFA:Alkalinity ratio < 0.1) when CP accounted for 60% of the feedstock VS. A further increase of CP of the feedstock led to a decrease in methane yield and solid reductions. This appeared to be caused by an extremely high C:N ratio of the feedstock resulting in a deficiency of ammonium nitrogen for microbial growth and buffering capacity.     

Biogas production from sewage sludge and microalgae co-digestion under mesophilic and thermophilic conditions

Isochrysis galbana and Selenastrum capricornutum, marine and freshwater microalgae species respectively, were co-digested with sewage sludge under mesophilic and thermophilic conditions. The substrates and the temperatures significantly influenced biogas production.Under mesophilic conditions, the sewage sludge digestion produced 451 ± 12 mL_Biogas/g_SV. Furthermore, all digesters were fed with I. galbana, or mixed with sludge, resulting in an average of 440 ± 25 mL_Biogas/g_SV. On the contrary, S. capricornutum produced 271 ± 6 mL_Biogas/g_SV and in the mixtures containing sludge produced intermediate values between sludge and microalgae production.Under thermophilic conditions, the sewage sludge digestion achieved yet the highest biogas yield, 566 ± 5 mL_Biogas/g_SV. During co-digestion, biogas production decreased when the microalgae content increased, and for I. galbana and for S. capricornutum it reached minimum values, 261 ± 11 and 185 ± 7 mL_Biogas/g_SV, respectively. However, no evidence of inhibition was found and the low yields were attributed to microalgae species characteristics.The methane content in biogas showed similar values, independently from the digested substrate, although this increased by approximately 5% under thermophilic condition.     

“Methano-compost”, a booster and restoring agent for thermophilic anaerobic digestion of energy crops

The influence of plant litter-compost of the hot rotten-phase as additional inoculum for anaerobic batch digestion of sugar beet silage (SBS) was studied. Four simultaneously driven batch-fermenters were inoculated with sewage sludge. Two of the fermenters were inoculated additionally with the same amount of organics by compost of the hot rotten-phase. Two of the fermenters were mesophilic (40 °C) and the other two were thermophilic (60 °C). The impact on the gas production rate and gas yield was observed to be boosted for thermophilic (60 °C) and only a minor effect of 6–13% for mesophilic (40 °C) digestion. The gas yield increased considerably up to 26.5% at 60 °C (batch). Also the methane content increased from 57.4% to 62.3% by adding compost (continuously run mesophilic digestion). Fluorescence In Situ Hybridization (FISH) indicated that a microbial effect was responsible for the observed stimulation of gas production rates, but not simply by increasing the bacterial counts. By analysing each fermenter for its mineral and trace element content a mineralic effect could be excluded. However, the bacterial counts by FISH of 10 different groups were somewhat ambiguous. But an effect on the presence of Chloroflexi could be demonstrated. They nearly doubled to 15–16% by supplementation with compost. Furthermore, under thermophilic conditions, the added compost induced a significant shift in the microbial composition towards hydrogenotrophic Methanobacteriales. The suggestive conclusion drawn is that this explicitly increase in hydrogenotrophic activity could alone or in combination with accompanying fermentative bacteria forces the microbial food chain towards stimulation of methane generation.     

Use of organic waste for biohydrogen production and volatile fatty acids via dark fermentation and further processing to methane

Despite the suitability of organic waste for dark fermentation (DF), anaerobic digestion (AD) counteracts its large-scale use for biohydrogen production. Therefore, 12 types of organic waste obtained from sugar, textile, food, and milk industries are investigated in batch single-stage AD and compared energetically to batch two-stage DF with subsequent AD. From the viewpoint of DF, a parametric study of mesophilic and thermophilic conditions, different substrate concentrations, and mixed cultures, i.e., granular and digested sludge, is conducted. Hydrogen yields of 90–160 L_N/kg_oDM (mean) and maximum yields of 199–291 L_N/kg_oDM are achieved with starchy and sugary wastes. Concentrations of volatile fatty acids of 9.7–14.5 g/L (mean) show the possible material uses. Thermophilic conditions are more suitable than mesophilic ones. Furthermore granular sludge is applicable for DF. The energetic comparison of the procedures demonstrates a method for assessing the applicability of waste and allows preliminary economic estimations.     

Anaerobic co-digestion technology in solid wastes treatment for biomethane generation

Anaerobic co-digestion is considered to be an efficient way of disposing solid wastes which can not only reduce environmental burden, but also produce bioenergy. Co-digestion of solid wastes in the absence of bacteria inoculums with variable mixing ratios of three wastes has been experimentally tested for 35 days digestion time to determine the biogas potential. The temperature remained relatively constant at a mesophilic range of 29–36°C throughout the study. An average pH of 7.4 was recorded from all digesters. The average biogas yields obtained from the four digesters (D1, D2, D3 and D4) were 13.31, 15.67, 16.52 and 19.12 L/day, respectively. The cumulative result showed that from co-digestion of D4 43.67%, 22.02% and 15.71% more biogas was produced, respectively, than others. The maximum and average COD reduction was 57% and 31%, respectively, in co-digestion wastes. The biogas comprised average of 61% CH₄, 33.5% CO₂, 222 ppm H₂S, and 4.7% H₂O, respectively.