Comparative performance of a UASB reactor and an anaerobic packed-bed reactor when treating potato waste leachate

The results presented in this paper are from studies on a laboratory-scale upflow anaerobic sludge blanket (UASB) reactor and an anaerobic packed-bed (APB) reactor treating potato leachate at increasing organic loading rates from 1.5 to 7.0 g COD/1/day. The hydraulic retention times ranged from 13.2 to 2.8 days for both reactors during the 100 days of the experiment. The maximum organic loading rates possible in the laboratory-scale UASB and APB reactors for stable operation were approximately 6.1 and 4.7 g COD/l day, respectively. The COD removal efficiencies of both reactors were greater than 90% based on the total COD of the effluent. The methane yield increased with increasing organic loading rate up to 0.23 l CH₄/g COD_degraded in the UASB reactor and 0.161 CH₄/g COD_degraded in the APB reactor. The UASB could be run at a higher organic loading rate than the APB reactor and achieved a higher methane yield. Signs of reactor instability were decreasing partial alkalinity and pH and increasing amounts of volatile fatty acids. The study demonstrated the suitability of the UASB and a packed-bed reactor for treating leachate from potato waste.     

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.     

Anaerobic digestion of molasses by means of a vibrating and non-vibrating submerged anaerobic membrane bioreactor

Bio-refineries produce large volumes of waste streams with high organic content, which are potentially interesting for further processing. Anaerobic digestion (AD) can be a key technology for treatment of these sidestreams, such as molasses. However, the high concentration of salts in molasses can cause inhibition of methanogenesis. In this research, concentrated and diluted molasses were subjected to biomethanation in two types of submerged anaerobic membrane bioreactors (AnMBRs): one with biogas recirculation and one with a vibrating membrane. Both reactors were compared in terms of methane production and membrane fouling. Biogas recirculation seemed to be a good way to avoid membrane fouling, while the trans membrane pressures in the vibrating MBR increased over time, due to cake layer formation and the absence of a mixing system. Stable methane production, up to 2.05 L L⁻¹ d⁻¹ and a concomitant COD removal of 94.4%, was obtained only when diluted molasses were used, since concentrated molasses caused a decrease in methane production and an increase in volatile fatty acids (VFA), indicating an inhibiting effect of concentrated molasses on AD. Real-time PCR results revealed a clear dominance of Methanosaetaceae over Methanosarcinaceae as the main acetoclastic methanogens in both AnMBRs.     

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.     

Optimization of the production and quality of biogas in the anaerobic digestion of different types of biomass in a batch laboratory biodigester and pilot plant: Numerical modeling,kinetic study and hydrogen potential

The study aims to evaluate the biogas production and quality from four biomasses (microalgae (MB), sorghum (S), corn stubble (CS), rapeseed oil (RO)) in a digestion process carried out in two batch reactor (6 L) and pilot plant (1.5 m³) agitated mechanically.The substrates were characterized and anaerobic digestion was carried out as batch tests in mesophilic conditions for 30–35 days. Inoculum/substrate ratio was 1:1–2:1. Gas composition and total gas volume produced were monitored. Methane yields of 306, 345, 419, and 740 NL kg VS^?1 were obtained for MB, CS, S, and RO, respectively, in laboratory tests, while in pilot plant tests were 182, 151, 397 and 655 NL kg VS^?1. CH₄ percentage in biogas was 49–60%. The yield of H₂ generated for the four biomasses in the two types of biodigesters has been estimated, obtaining values between 16 and 39 mL g VS^?1.First-order, Modified Gompertz, and Cone models have been applied to evaluate the kinetic parameters on the methane produced in the batch and pilot plant tests, obtaining an excellent fit. ADM1 model with 19 biological processes (disintegration of biomass composite, enzymatic hydrolysis, and digestion of soluble materials mediated by organisms), acid-base equilibria, kinetic study, and liquid-gas transference has been used to fit the cumulative methane volume.     

Pretreatment of energy crops with sodium hydroxide and cellulolytic enzymes to increase biogas production

This work presents the influence of alkali pretreatment on the enzymatic hydrolysis and efficiency of anaerobic digestion of lignocellulosic biomass pretreated both in a one- (chemical or enzymatic) and two-step (chemical and enzymatic) process. In this study two species of energy crops were used Miscanthus giganteus and Sida hermaphrodita. The aim of this work was to compare biogas production and methane yield during fermentation of pretreated and untreated energy crops. The results show that alkali pretreatment is necessary for the effective biogas generation from plant material due to high delignification level and significant hemicellulose degradation. The two-step hydrolysis process consisting on the alkali and enzymatic step leads to the release of high concentrations of glucose (about 20 g L⁻¹). The best results were achieved for M. giganteus with biogas production yield of 421.5 Ndm³ kg TS⁻¹ and with methane production yield of 257 Ndm³ kg TS⁻¹.     

Exploring the potential of fur farming wastes and byproducts as substrates to anaerobic digestion process

Mink farming is a well-established economic activity with a significant environmental footprint. In this work mink farming derived organic waste was assessed, for the first time, as substrate to anaerobic digestion plants. The substrates assessed were; (a)fresh mink manures, (b)weathered mink manures, (c)waste feed and (d)mink derived meat and bone meal. Substrates with in inoculum to substrate ratio of 2 offered specific methane productions ranging between 368 and 591 mLCH₄/gVS_added corresponding to 67.4 and 91.1% of their theoretical methane potential. In the second phase of the experiments three organic loading rates and three inoculum to substrate ratios were assessed. Substrate/inoculum ratios, in batch mode, lower than 1 seem to affect negatively the process, due to slow hydrolysis and acetogenesis of the macromolecules. In addition, initial organic loading rates of up to 50 gVS/L can be applied in batch systems when manure is utilized as substrate. In contrast to this, when mink derived byproducts are used the same loading rate will result into an irreversible process inhibition due to the accumulation of intermediate products.     

Effect of inoculum pre-treatment on mesophilic hydrogen and methane production from food waste using two-stage anaerobic digestion

Two-stage anaerobic digestion of food waste was performed using four different inoculum pre-treatment methods to enrich hydrogen (H₂) producing bacteria from sludge. The pretreatments used in this study included heat shock, alkaline treatment, aeration, and a novel pretreatment using waste frying oil (WFO). Alkaline pretreatment and aeration did not completely inhibit methanogens in the first stage while no methane (CH₄) was detected in the reactors cultivated either with heat shock or WFO-pretreated inocula. The highest H₂ and CH₄ yields (76.1 and 598.2 mL/gVS, respectively) were obtained using the inoculum pretreated with WFO. The highest total energy yield (21.96 kJ/gVS) and total organic carbon (TOC) removal efficiencies (95.77%) were obtained using inoculum pretreatment with WFO. The total energy yield trend obtained using the different pretreatments was as follows: WFO > alkaline > heat > aeration > control.     

Effect of sulfate on hydrogen production from the organic fraction of municipal solid waste using co-culture of E. coli and Enterobacter aerogenes

In the present study, the effect of sulfate on the hydrogen production from the organic fraction of municipal solid (OFMSW) waste using co-culture of Enterobacter aerogenes and E. coli has been studied under varying pH conditions. The presence of sulfate in the feedstock declines hydrogen production efficiency. To evaluate the effect of sulfate on hydrogen production from OFMSW, COD/sulfate ratio of 17.5, 15.0, 12.5, 10.0, 7.5, 5.0 and 2.5 were applied at different pH conditions (i.e. pH 5.5, 6.0 and 6.5). The hydrogen production continuously declined with the decreasing COD/sulfate ratio and increase in pH. The cumulative hydrogen production decreased from 220.8 ± 10.5 mL in control to a minimum of 98.3 ± 10.5 mL, 74.4 ± 10.4 mL, and 44.6 ± 2.6 mL at pH 5.5, 6.0 and 6.5 respectively. The major content of gaseous composition included hydrogen and CO₂ at higher COD/sulfate ratio and low pH, while H₂S formation started with the decrease in COD/sulfate ratio and increase in the pH. Similarly, sulfate removal efficiency was found to be influenced by COD/sulfate ratio and pH condition. Soluble metabolite analysis revealed that total volatile fatty acid concentration was not affected by sulfate addition. Thus, Sulfate removal is essential prior to fermentation in order to improve hydrogen yield.     

Optimization of hydrogen production from organic fraction of municipal solid waste (OFMSW) dry anaerobic digestion with analysis of microbial community

Effect of mixed culture bacteria (MCB) addition, initial substrate concentration to inoculum (S_o/X_o), carbon to nitrogen (C/N) ratio on the hydrogen production (HP) from organic fraction of municipal solid waste (OFMSW) via dry anaerobic digestion was investigated. The results showed that supplementation of OFMSW with MCB substantially improved hydrogen yield (HY) and HP. HYs were 306.2 ± 33.0, 149.8 ± 16.6, and 155.3 ± 22.9 ml_H2/gCOD_removed for OFMSW supplemented with MCB, OFMSW, and MCB, respectively. HP at S_o/X_o ratio of 9.2 g_COD/g_VSS was 3.1 times higher than those obtained at S_o/X_o ratio of 1.7 g_COD/g_VSS. The maximum HY of 338.4 ± 18.9 ml_H2/gCOD_removed was achieved at S_o/X_o ratio of 9.2 g_COD/g_VSS. The HP and HY were substantially increased from 169.7 ± 17.1 to 524.2 ± 34.4 ml and from 163.1 ± 23.6 to 338.4 ± 18.9 ml_H2/gCOD_removed with increasing the C/N from 16 to 25, respectively. However, HP and HY decreased at C/N ratio exceeding 26.6. The modified Gompertz equation model was highly fitted to the experimental data with correlation coefficient (R² > 0.984). The 16S rRNA sequences showed the dominance of Pseudomonas fulva with similarity of 99%. Copyright © 2015 John Wiley & Sons, Ltd.     

Integration of submersible microbial fuel cell in anaerobic digestion for enhanced production of methane and current at varying glucose levels

A submersible microbial fuel cell (SMFC) was coupled with anaerobic digestion (AD) system to establish synergy for enhancing the electricity and methane production at different glucose concentration of 2, 4 and 10 g/l. High amount of stable current generation of 0.35 mA was obtained at 4 g/l, which was about 1.5 times higher than the SMFC-AD operated at 10 g/l glucose. Methane production and yield were enhanced by 69% and 28%, respectively in SMFC-AD in comparison with AD operation at 2 g/l. Maximum methane yield of 0.32 l-CH₄/g COD was observed in SMFC-AD operation at 2 g/l, followed by 4 g/l (0.28 l-CH₄/g COD) and 10 g/l (0.18 l-CH₄/g COD). Furthermore, the SMFC-AD process increased COD removal and maintained proper pH of around 6.8–7.3 for efficient methane production. This study suggests that the SMFC-AD can achieve enhanced methane production compared to stand-alone AD with additional electricity generation.     

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.     

Mathematical modeling of the anaerobic digestion in two-stage system with production of hydrogen and methane including three intermediate products

Anaerobic digestion is a multi-step biotechnological process, in which H2 is not detected as it is consumed immediately e.g. by hydrogenotrophic methanogens to produce CH₄ and CO₂. Recently a two-stage AD concept consisting of hydrogenic process followed by methanogenic process was suggested. However, only few models of this process are known. In this study a mathematical model of a continuous process of AD with production of hydrogen and methane in a cascade of two bioreactors, including some intermediate products in the first bioreactor was developed and investigated.     

Biohydrogen production from food waste in batch and semi-continuous conditions: Evaluation of a two-phase approach with digestate recirculation for pH control

The research investigated the production of Biohythane in a two-phase anaerobic digestion process treating food waste as substrate. Preliminary batch assays were carried out at initial organic loadings of 15, 20, 25 and 30 kg TVS m⁻³, in stirred 1.5-l reactors at 55 °C. The results showed all hydrogen was produced within the first 24 h after feeding and the highest load tested gave the maximum hydrogen production (0.047 m³ H₂ kg⁻¹VS, H₂ 30%). Similar loadings were then tested in a two-phase system. Hydraulic retention times of 3 and 12 days were applied to the first and second reactor respectively. In order to keep the pH at ∼5.5, either supernatant or whole digestate from the methanogenic reactor was recirculated to the first phase. Results showed that hydrogen was produced (0.117 Nm³ kg⁻¹ VS, 47.7%) when recirculating whole digestate with an organic loading rate of 20 kg TVS m⁻³ day⁻¹.     

Investigation of anaerobic digestion of Chlorella sp. and Micractinium sp. grown in high-nitrogen wastewater and their co-digestion with waste activated sludge

This study investigated two wildtype green algae, Micractinium sp. and Chlorella sp., for their growth in high nitrogen wastewater (mixture of sludge centrate and primary effluent wastewater) and subsequent anaerobic digestion under mesophilic conditions. Extraction and analysis of extracellular polymeric substances (EPS) in both algal species during cultivation showed that Micractinium generated larger quantity of EPS-proteins than Chlorella. Anaerobic digestion of harvested algae showed the opposite trend that Chlorella allowed a higher CH₄ yield on the volatile solids fed the digester (VS_fed) of 230 dm³ kg⁻¹ than Micractinium (209 dm³ kg⁻¹). These results suggested that different growth patterns of two types of algae, with different quantity of EPS expressed, affected anaerobic digestibility and biogas yield. Co-digestion of algae with waste activated sludge (WAS) improved the volatile solids reduction, hydrolysis efficiency as well as the biogas yields of algae.     

Leachate valorization in anaerobic biosystems: Towards the realization of waste-to-energy concept via biohydrogen,biogas and bioelectrochemical processes

Leachate generated in landfills is considered as a hazardous waste stream due to its composition and needs adequate treatment for environmental protection purposes. Nonetheless, a contemporary technology should not only be able to deal with its degradation, but at the same time, recover energy in various forms. Such valorization approaches with priority on these dual-aims are potentially those that rely on anaerobic biosystems. In the literature, processes considered on that matter include fermentative, digestive and bioelectrochemical set-ups to deliver energy-carriers such as biohydrogen (DF), biogas (AD) and electricity (BES), respectively. Moreover, to enhance the global efficiency of leachate utilization, it has been recently trending to develop integrated options by combining these systems (DF, AD, BES) into a cascade scheme. In this review, it is intended to give an insight to the research activities realized in these fields and show possible directions towards the better exploitation of leachate feedstock under anaerobic conditions.