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.     

Synergistic effect in anaerobic co-digestion of rice straw and dairy manure - a batch kinetic study

Methane yield of seven co-digestion mixture proportions (1:0, 5:1, 3:1, 1:1, 1:3, 1:5, and 0:1) of rice straw and dairy manure was investigated at a total solids (TS) loading of 8%. Methane yield was improved by 50–57% and 9–10% with co-digestion at mixture proportions of 1:1,1:3 and 1:5 compared to mono digestion of rice straw and dairy manure, respectively. The modified Gompertz model accounted well for the kinetic behavior of methane yield with an R² of 0.99 and Root Mean Square Error of 0.06–1.70. It was observed that the co-digestion caused a reduction in lag phase time and improvement in the maximum methane production rate. The positive synergistic effects are a result of nutrient balance with the co-digestion of dairy manure and rice straw.     

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.     

沼气微氧发酵过程硫转化及微生物群落

以水稻秸秆与猪粪为原料,探究微氧发酵过程中S元素的转化与微生物群落特征以及通氧量的影响。结果表明,厌氧发酵过程中原料的S元素约有65.7%转化为H2S进入沼气,19.0%进入发酵后的沼液,15.3%残留在沼渣中。微氧条件下,沼液中S2-的浓度(100 mg/L)远低于厌氧条件的250 mg/L,约71.8%的S元素转化为H2S然后被氧化成为S单质和少量SO42-。H2S去除效率随通氧量的增大而增大,当通氧量为11.85 L/m3沼气时,约96%的H2S被氧化脱除。根据高通量测序结果,与厌氧发酵相比,在微氧条件下,沼液中微生物多样性仅有轻微变化,比较稳定;硫氧化菌明显增多,而产甲烷菌无明显变化。较高浓度硫氧化菌的存在,有利于沼气中H2S的及时转化,可减轻H2S对产甲烷菌活性的抑制,从而促进厌氧发酵的进行。     

Hydrogen production performance from food waste using piggery anaerobic digested residues inoculum in long-term systems

The objective of this study was to investigate the hydrogen production performance from food waste using piggery anaerobic digested residues (PADRs) inoculum. Multiple parameters were evaluated such as organic load rate (OLR), pH, and hydraulic retention time (HRT), over a wide range of values in long-term dark fermentation systems. Results showed that a value of 126.50 mL/gVS·d hydrogen yield was achieved at OLR 6 g VS/L·d under thermophilic condition. A relatively stable structural composition dominated by Thermoanaerobacterium was maintained even suffering from OLR and acid shock. On the contrary, mesophilic fermentation performed acetic acids accumulation and an average hydrogen yield of less than 80 mL/gVS·d. High OLR and low pH (range of 5.0–5.5) led to the establishment of Lactobacillus. Beyond this range, the relative abundance of Olsenella, Streptococcus, and other bacteria showed a significant difference under different operating conditions, which caused weak resistance to external shocks during mesophilic fermentation. It showed that PADRs was capable of obtaining optimal hydrogen production performance under thermophilic condition from food waste with a stable microbial community structure.     

Characterization of microbial community in the two-stage process for hydrogen and methane production from food waste

The structure of a microbial community in the two-stage process for H₂ and CH₄ production from food waste was investigated by a molecular biological approach. The process was a continuous combined thermophilic acidogenic hydrogenesis and mesophilic (RUN1) or thermophilic (RUN2) methanogenesis with recirculation of the digested sludge. A two-phase process suggested in this study effectively separate H₂-producing bacteria from methanogenic archaea by optimization of design parameters such as pH, hydraulic retention time (HRT) and temperature. Galore microbial diversity was found in the thermophilic acidogenic hydrogenesis, Clostridium sp. strain Z6 and Thermoanaerobacterium thermosaccharolyticum were considered to be the dominant thermophilic H₂-producing bacteria. The hydrogenotrophic methanogens were inhibited in thermophilic methanogenesis, whereas archaeal rDNAs were higher in the thermophilic methanogenesis than those in mesophilic methanogenesis. The yields of H₂ and CH₄ were in equal range depending on the characteristics of food waste, whereas effluent water quality indicators were different obviously in RUN1 and RUN2. The results indicated that hydrolysis and removal of food waste were higher in RUN2 than RUN1.     

Waste activated sludge treatment in an anaerobic dynamic membrane bioreactor at varying hydraulic retention time: Performance monitoring and microbial community analysis

In this study, the variations in system performance and microbial community composition when treating waste activated sludge without prior chemical or physical pretreatment in anaerobic systems is examined. Two lab-scale digesters, namely anaerobic dynamic membrane bioreactor (AnDMBR) and continuously stirred tank reactor (CSTR), were operated and maintained under mesophilic conditions at varying hydraulic retention times (10-25 days). Decreasing the hydraulic retention time (HRT) affected the methane yield (MY) and methane production rate (MPR) proportionally in both systems. The AnDMBR's maximum MY of 252 mL CH₄/g-VS and MPR of 0.73 L/L/d were 25% and 34% higher than those obtained using the CSTR, respectively. Moreover, a decrease in HRT was accompanied by accumulation of butyric acid in the CSTR, which caused further performance deterioration. In both systems, AnDMBR's dynamic membrane acted as an added layer preventing methanogen wash-out and retaining the essential microorganisms for stable sludge treatment. Dominance in the microbial composition shifted from a strict acetoclastic to a mixed acetoclastic and hydrogenotrophic methanogenic community and that a decrease in the ration of Bacteroidetes to Firmicutes was associated with the increased MY.     

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.     

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。     

Thermophilic hydrogen production from starch wastewater using two-phase sequencing batch fermentation coupled with UASB methanogenic effluent recycling

The aim of this study was to evaluate the performance of thermophilic hydrogenesis coupled with mesophilic methanogenesis in which the effluent was recycled to the hydrogen reactor for starch wastewater treatment. With this system, the hydrogen production rate and yield were 3.45 ± 0.25 L H₂/(L·d) and 5.79 ± 0.41 mmol H₂/g COD_added respectively, and thus higher than the values of the control group without methanogenic effluent recycling. In addition, relatively higher contents of acetate and butyrate were obtained in the hydrogen reactor with recirculation. The methane reactors were operated with the effluent from the hydrogen reactor, and methane yield was stabilized at 0.21–0.23 L/g COD_removal in both. Analysis of the microbial communities further showed that methanogenic effluent recirculation enriched microbial communities in the hydrogen reactor. Two species of bacteria effective in hydrogenesis, Thermoanaerobacterium thermosaccharolyticum and Clostridium thermosaccharolyticum, dominated during hydrogen production, whereas archaea belonging to Euryarchaeota were detected and cultured in the methane reactor. The recycled effluent supplied alkaline substrates for the hydrogen producing bacteria. Alkali balance calculations showed that the amount of added alkali was reduced by 88%. This amount, required for hydrogen production from starch wastewater, was contributed by alkali in the methanogenic effluent, (2225 ± 140 mg CaCO₃/L), resulting in lower operational costs.     

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.     

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.     

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.     

Co-digestion of poultry manure and residues from enzymatic saccharification and dewatering of sugar beet pulp

This study investigates the co-digestion of poultry manure (PM) with sugar beet pulp residues (SBPR) obtained from saccharification and dewatering of sugar beet pulp. The laboratory-scale experiments were conducted under batch and semi-continuous conditions at mesophilic temperatures (35 °C). Batch tests gave specific biogas and methane yields of 590 dm³/kgVS_fed and 423 dm³CH₄/kgVS_fed, respectively for SBPR, whereas the corresponding values for PM were 434 dm³/kgVS_fed and 300 dm³CH₄/kgVS_fed. The co-digestion of PM with SBPR was found to increase biogas and methane yields compared to the manure alone. In semi-continuous reactor experiments, the highest methane yield of 346 dm³ CH₄/kgVS_fed was achieved for the mixture containing poultry manure with 50% SBPR (weight basis) and a solids retention time (SRT) of 20 days. However, when poultry manure was digested as a sole feedstock, the biogas production was inhibited by ammonia, whereas the co-digestion of PM with 25% SBPR was slightly affected by volatile fatty acids, which concentrations exceeded 4000 g/m³.     

Hydrogen-methane production from pulp & paper sludge and food waste by mesophilic–thermophilic anaerobic co-digestion

The present study focused on the mesophilic anaerobic bio-hydrogen production from PPS (pulp & paper sludge) and FW (food waste), and the subsequent anaerobic digestion of the effluent for the methane production under thermophilic conditions by a two-stage process. The maximum hydrogen yield of 64.48 mL g⁻¹ VS_fed and methane yield of 432.3 mL g⁻¹ VS_fed were obtained when PPS and FW were applied with 1: 1 VS ratio as the feedstock. No VFA were cumulated in the reactor during the period of hydrogen - methane fermentation, as well as no NH₃–N and Na⁺ inhibition were found in the process. 71%–87% removal efficiencies of SCOD were attained for hydrogen and methane co-production. pH 4.8–6.4 and alkalinity 794–3316 mg CaCO₃ L⁻¹ for H₂ fermentation, as well as pH 6.5–8.8 and alkalinity 4165–4679 mg CaCO₃ L⁻¹ for CH₄ fermentation, were achieved without any adjustment. This work showed that anaerobic co-digestion of PPS and FW for hydrogen-methane co-production was a stable, reliable and effective way for energy recovery and bio-solid waste stabilization by the two-stage mesophilic–thermophilic process.     

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.     

Enhancement of biohythane production from solid waste by co-digestion with palm oil mill effluent in two-stage thermophilic fermentation

Improvement of biohythane production from oil palm industry solid waste residues by co-digestion with palm oil mill effluent (POME) in two-stage thermophilic fermentation was investigated. A two-stage co-digestion of solid waste with POME has biohythane production of 26.5–34 m³/ton waste. The co-digestion of solid waste with POME increased biohythane production of 67–114% compared to digestion POME alone. Co-digestion of solid waste with POME enhanced hydrolysis constant (k_h) from 0.07 to 0.113 to 0.120–0.223 d⁻¹. The hydrolysis constant (k_h) of co-digestion was 10 times higher than the single digestion of solid waste. Clostridium sp. was predominated in the hydrogen stage, while Methanosphaera sp. was predominant in methane stage. The co-digestion of solid waste with readily biodegradable organic matter (POME) could significantly increase biohythane production with achieving the significant cost reduction for pretreatment of solid wastes.     

Hydrogen production from alcohol wastewater by an anaerobic sequencing batch reactor under thermophilic operation: Nitrogen and phosphorous uptakes and transformation

The objective of this study was to investigate hydrogen production from alcohol wastewater using an anaerobic sequencing batch reactor (ASBR) under thermophilic operation and at a constant pH of 5.5. Under the optimum COD loading rate of 68 kg/m³d, the produced gas contained 43% H₂ without methane and the system provided a hydrogen yield and specific hydrogen production rate of 130 ml H₂/g COD removed and 2100 ml H₂/l d, respectively, which were much higher than those obtained under the mesophilic operation. Under thermophilic operation, both nitrogen and phosphate uptakes were minimal at the optimum COD loading rate for hydrogen production and most nitrogen uptake was derived from organic nitrogen. Under the thermophilic operation for hydrogen production, the nutrient requirement in terms of COD:N:P was found to be 100:6:0.5, which was much higher than that for the methenogenic step for methane production under both thermophilic and mesophilic operations and for the acidogenic step for hydrogen production under mesophilic operation.     

“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.     

Energy valorization of crude glycerol and sanitary sewage in hydrogen generation by biological processes

Biohydrogen production was studied with increased concentrations of crude glycerol (CG) co-digested with sanitary sewage by anaerobic consortium bacteria in anaerobic batch reactors, at 30 °C and initial pH 7.0. The CG was obtained during the biodiesel production from waste cooking oils (WCO). The anaerobic consortium was from a granular sludge of UASB reactor used in the treatment of poultry wastes heat treated to inhibit methanogenic activity previously. The higher H₂ generation was observed with 240.0 g COD L⁻¹ (35.82 mmol L⁻¹), being consumed 63.9% of CG. The co-digestion associated with sanitary sewage facilitated the CG consumption with the increase of organic load, favoring the acetic acid and 1,3-propanediol production in a liquid phase of the reactors. These results are promising, contributing effectively to the treatment of both wastes with concomitant generation of bioenergy.