Methane enhancement through co-digestion of chicken manure and thermo-oxidative cleaved wheat straw with waste activated sludge: A C/N optimization case

Plug-flow hydrolysis with lignocellulosic residues: effect of hydraulic retention time and thin-sludge recirculation

BACKGROUND

Two parallel plug-flow reactors were successfully applied as a hydrolysis stage for the anaerobic pre-digestion of maize silage and recalcitrant bedding straw (30% and 66% w/w) under variations of the hydraulic retention time (HRT) and thin-sludge recirculation.

RESULTS

The study proved that the hydrolysis rate profits from shorter HRTs while the hydrolysis yield remained similar and was limited by a low pH-value with values of 264-310 and 180-200 g_O2 kg_VS^-1 for 30% and 66% of bedding straw correspondingly. Longer HRT led to metabolite accumulation, significantly increased gas production, a higher acid production rate and a 10-18% higher acid yield of 78 g_SCCA kg_VS^-1 for 66% of straw. Thin-sludge recirculation increased the acid yield and stabilized the process, especially at a short HRT. Hydrolysis efficiency can thus be improved by shorter HRT, whereas the acidogenic process performance is increased by longer HRT and thin-sludge recirculation. Two main fermentation patterns of the acidogenic community were found: above a pH-value of 3.8, butyric and acetic acid were the main products, while below a pH-value of 3.5, lactic, acetic and succinic acid were mainly accumulating. During plug-flow digestion with recirculation, at low pH-values, butyric acid remained high compared to all other acids. Both fermentation patterns had virtually equal yields of hydrolysis and acidogenesis and showed good reproducibility among the parallel reactor operation.

CONCLUSIONS

The suitable combination of HRT and thin-sludge recirculation proved to be useful in a plug-flow hydrolysis as primary stage in biorefinery systems with the benefits of a wider feedstock spectrum including feedstock with cellulolytic components at an increased process robustness against changes in the feedstock composition.

Start-up of co-digestion of poultry litter and wheat straw in anaerobic sequencing batch reactor by gradually increasing organic loading rate: Methane production and microbial community analysis

Anaerobic co-digestion (ACoD) of poultry litter (PL) and wheat straw (WS) in an anaerobic sequencing batch reactor (ASBR) for continuous bio-energy generation was started up for the first time by gradually increasing the organic loading rate (OLR). A steady-state was reached with a daily biogas production of (13.06 ± 0.21) L and methane content of (54.38 ± 0.53) %. The subsequent regular operation achieved a daily methane yield of (100.41-188.65) mL CH₄/g VS added and a total chemical oxygen demand (tCOD) removal rate of (70.3-85.9) % in the effluent under different operating parameters. The overall microbial community became more uniform, and the dominant aceticlastic methanogen of Methanosaeta was enriched after the start-up. While the microbial community was largely stable in the overall structure since the regular operation. Therefore, the start-up of the ACoD of PL and WS was successful with stable and continuous methane production.

Impact of temperature, inoculum flow pattern, inoculum type, and their ratio on dry anaerobic digestion for biogas production

This study is aimed to apply dry anaerobic digestion (DAD) for methane (CH₄) enriched biogas production from unsorted organic municipal solid waste (MSW). Cumulative biogas production was monitored for 35 days of operation in batch digesters at fixed feedstock to inoculum (F/I) ratio 2. Anaerobic sludge (AS) and cow manure (CM) were used as inoculum in single and mixed modes. Several process parameters such as inoculum flow pattern (single layer, multilayer, and spiral), digestion temperature (25 to 40 °C), inoculation modes (single and mixed mode), and inoculation proportion (AS:CM = 1:1, 1:2, 1:3, and 2:1) were investigated to determine the optimum DAD conditions to maximize the CH₄ laden biogas yield. The study of inoculum flow pattern showed that digester with multilayer inoculum configuration generated the maximum 555 mL cumulative biogas with the production rate of 195 mL/day (at 25 °C). Biogas production rate and cumulative biogas production were found to increase with a rise in temperature and the maximum values of 380 mL/day and 1515 mL respectively were observed at 37 °C. The mixed mode of inoculation containing AS and CM augmented the biogas yield at previously optimized conditions. Final results showed that digester with multilayer inoculum flow pattern at 37 °C produced 1850 mL cumulative biogas with 1256.58 mL CH₄/kg volatile solid (VS) when the mixed inoculum was used at the AS:CM—1:2 ratio. Biogas production with this significant amount of CH₄ justifies the use of the DAD process for energy (biogas) generation from widely available biomass feedstock (MSW), offering various advantages to the environment.

Efficient methane production from waste activated sludge and Fenton-like pretreated rice straw in an integrated bio-electrochemical system

Integrated microbial electrolysis cell-anaerobic digestion (MEC-AD) systems have demonstrated potential advantages for methane production in the presence of small amounts of residual inhibitors. In this study, a series of tests were conducted to analyse the acidification and methanogenesis performance of pretreated rice straw (RS) in anaerobic digestion (AD) and MEC-AD systems after the addition of Fenton-like reagents. The results indicated that the short-chain acids (SCFAs) accumulations reached 2284.64 ± 21.57 mg COD/L with a dosage ratio of 1/4 (g RS/g VSS sludge) in the MEC-AD system and that methane production increased by 63.8% compared with that of an individual AD system. In the interim, the net energy output reached 1.09 × 10³ J/g TCOD, which was 1.23 times higher than that of the AD system. The residual Fe³⁺/Fe²⁺ in the pretreatment reagent was capable of promoting acidification and methanogenesis in sludge and RS fermentation. The RS hydrolysis products could constrain methanogenesis, which can be mitigated by introducing an MEC. The microbiological analyses revealed that the MEC strongly increased the enrichment of hydrogenotrophic methanogens, especially Methanobacterium (61.16%). Meanwhile, the Syntrophomonas and Acetobacterium abundances increased to 2.81% and 2.65%, respectively, which suggested the reinforcement of acetogenesis and methanogenesis. Therefore, the enhanced hydrogenotrophic methanogens might have served as the key for enhancing the efficiency of methanogenesis due to the introduction of an MEC.

Surfactant rhamnolipid promotes anaerobic codigestion of excess sludge and plant waste

In order to solve the bottleneck of low methane production in anaerobic codigestion of excess sludge (ES) and plant waste (PW), a new strategy of enhancing hydrolysis and acidification by rhamnolipid (RL) was proposed under thermophilic condition. The results showed that the optimal dosage of RL was 50 g/kg total suspended solids, and the maximum yield of methane was 198.5 mL/g volatile suspended solids (VSS), which was 2.3 times of that in the control. RL promoted the dissolution of organic matter in the codigestion process of ES and PW, and the higher the dosage of RL, the higher the concentration of soluble chemical oxygen demand (SCOD) in the fermentation broth. When RL was 100 g/kg, the maximum content of SCOD in fermentation broth was 2,451 mg/L, and the contents of soluble protein and polysaccharide were 593 mg/L and 419 mg/L on 10 d, respectively, which were significantly higher than other groups. In addition, the yield of VFA in RL group was also significantly increased, and acetate and propionate were the main components of VFAs. This research work provides data support for the resource utilization of ES and PW, and expands the application field of RL.

Enhanced Methane Production from Anaerobic Co-Digestion of Wheat Straw Rice Straw and Sugarcane Bagasse: A Kinetic Analysis

Future energy and environmental issues are the major driving force towards increased global utilization of biomass, especially in developing countries like Pakistan. Lignocellulosic residues are abundant in Pakistan. The present study investigated the best-mixed proportion of mechanically pretreated lignocellulosic residues i.e., wheat straw and rice straw (WSRS), bagasse and wheat straw (BAWS), bagasse, and rice straw (BARS), bagasse, wheat straw, and rice straw (BAWSRS) through anaerobic co-digestion. Anaerobic batch mode bioreactors comprising of lignocellulosic proportions and control bioreactors were run in parallel at mesophilic temperature (35 °C) for the substrate to inoculum (S/I) ratio of 1.5 and 2.5. Maximum and stable biomethane production was observed at the substrate to inoculum (S/I) ratio of 1.5, and the highest biomethane yield 339.0089123 NmLCH4/gVS was achieved by co-digestion of wheat straw and rice straw (WSRS) and lowest 15.74 NmLCH4/gVS from bagasse and rice straw (BARS) at 2.5 substrates to inoculum ratio. Furthermore, anaerobic reactor performance was determined by using bio-kinetic parameters i.e., production rate (Rm), lag phase (λ), and coefficient of determination (R2). The bio-kinetic parameters were evaluated by using kinetic models; first-order kinetics, Logistic function model, Modified Gompertz Model, and Transference function model. Among all kinetic models, the Logistic function model provided the best fit with experimental data followed by Modified Gompertz Model. The study suggests that a decrease in methane production was due to lower hydrolysis rate and higher lignin content of the co-digested substrates, and mechanical pretreatment leads to the breakage of complex lignocellulosic structure. The organic matter degradation evidence will be utilized by the biogas digesters developed in rural areas of Pakistan, where these agricultural residues are ample waste and need a technological solution to manage and produce renewable energy.

Anaerobic co-digestion of chicken manure and cardboard waste: Focusing on methane production, microbial community analysis and energy evaluation

This study aimed to investigate the synergistic effect and microbial community changes between chicken manure (CM) and cardboard (CB) during anaerobic co-digestion. Meanwhile, the energy balance of biogas engineering was extrapolated based on the batch tests. In batch tests, co-digestion system achieved the highest improvement (14.2%) and produced 319.62 mL CH₄/gVS with a 65:35 ratio of CB: CM. More extracellular polymeric substance secretion promoted the electron transfer for acidogenesis and more hydrolase was provided with 31.6% improvement. The microbial analysis illustrated that higher acetoclastic Methanosaeta abundance was achieved, leading to 211% enhancement of acetoclastic pathway. Moreover, associated network illustrated that the higher methane production was mainly achieved through matching of hydrolytic bacteria and acidogenesis bacteria. As for energy balance, the synergistic effect increased the energy output by 38% and energy recovery to 46.4%.

Anaerobic Digestion of Steam-Exploded Wheat Straw and Co-Digestion Strategies for Enhanced Biogas Production

Wheat straw (WS) is considered a favourable substrate for biogas production. However, due to its rigid structure and high carbon to nitrogen (C/N ratio), its biodegradability during anaerobic digestion (AD) is usually low. In the present study, the effect of steam explosion pre-treatment on WS, combined with C/N adjustment with inorganic nitrogen, on biogas production was evaluated. Additionally, co-digestion of WS with protein-rich agri-industrial by-products (dried distillers’ grains with solubles (DDGS) and rapeseed meal (RM)) was assessed. Steam explosion enhanced biogas production from WS, whereas the addition of NH4Cl was beneficial (p < 0.05) for the digestion of steam-exploded wheat straw (SE). Furthermore, mono-digestion of the four different substrates seemed to be efficient in both inoculum to substrate ratios (I/S) tested (3.5 and 1.75 (w/w)). Finally, during co-digestion of WS and SE with DDGS and RM, an increase in the cumulative methane production was noted when higher amounts of DDGS and RM were co-digested. This study demonstrated that DDGS and RM can be used as an AD supplement to stimulate gas production and improve wheat straw biodegradability, while their addition at 10% on an AD system operating with WS can enhance gas yields at levels similar to those achieved by steam-exploded straw.

Trace Element Supplementation and Enzyme Addition to Enhance Biogas Production by Anaerobic Digestion of Chicken Litter

Anaerobic digestion (AD) of chicken litter (CL) is a viable alternative to disposal. However, methane yields from this primarily organic waste are quite low when mono-digested. This paper discusses the effect of an enzyme cocktail, trace element (TE) supplementation and selenium (Se) addition in small-scale batch biomethane potential (BMP) assays to enhance the AD of CL. Eleven different assays were set up in triplicate including assays containing only inoculum (blank), only CL (negative control) and cellulose and inoculum (positive control). The results indicate that both enzyme treatment and trace element supplementation enhanced the biogas and methane yield. The highest specific biogas and methane yields were noted for 1% enzyme-treated CL of 835.2 L/kg volatile solids (VS) and 460.8 L/kg VS, respectively. Usually, mono-digestion of CL is low due to high nitrogen content and the presence of recalcitrant lignocellulosic material from the bedding material. Enzyme treatment performed better than the addition of the TE mix and Se.

Enhanced mesophilic anaerobic digestion of waste sludge with the iron nanoparticles addition and kinetic analysis

As the functional material, iron nanoparticles effectively promote anaerobic digestion (AD) process, including the hydrolysis-acidification process and the biogas production. In this study, nano zero-valent iron (nZVI) and Fe₃O₄ nanoparticles (Fe₃O₄ NPs) were added to AD reactors respectively. The AD process was evaluated by the reactors performances, including pH, biogas yields and compositions, as well as the removal ratio of total solids (TS), volatile solids (VS) and soluble chemical oxygen demand (sCOD). Three models (first-order kinetic model, transfer function model and Cone model) were used to explore the kinetics of AD biogas production. The results showed that adding appropriate dose of nZVI or Fe₃O₄ NPs enhanced anaerobic digestibility of sludge. The highest cumulative biogas yield of 140.34 L with 0.5 g L^-1 nZVI and 137.13 L with 1 g L^-1 Fe₃O₄ NPs were obtained by the 80 days of mesophilic operation, respectively. Cumulative biogas productions of these two reactors were significantly enhanced up to 15.70% and 13.44%. TS removal rates reached >70% in all AD reactors with iron nanoparticles, and the highest sCOD removal rates of nZVI and Fe₃O₄ NPs digesters on the 80th day were 88.22% and 77.63%, respectively. The results of the three-day fermentation experiment and the kinetic parameters showed that the nZVI or Fe₃O₄ NPs enhanced the hydrolysis-acidification process of the AD, which eventually promoted biogas production. The Cone model was satisfied with the experimental results, which could be used to evaluate the kinetics of AD with iron nanoparticles more reasonably.

The effects of temperature and duration of thermal pretreatment on the solid-state anaerobic digestion of dairy cow manure

Cellulosic substrates such as dairy cow manure often yield low volumes of biogas and low concentrations of methane when digested anaerobically. Thermal pretreatment of dairy cow manure was investigated to determine if pretreatment temperature and duration can be optimized to maximize biogas yield and methane concentration. A central composite rotatable design was used to select combinations of temperature and duration. Based on measured data, statistical models were generated to estimate the biogas yield and methane concentration during digestion. The highest biogas yields were from the untreated samples and samples treated at the center temperature and duration of the statistical model (125 °C, 37.5 min). The model predicted the optimum pretreatment conditions of 140 °C for 30 minutes. Under the conditions of this experiment, temperature and duration had no significant effect on the biogas yield and methane concentration. This lack of significance may indicate that thermal pretreatment may be an unnecessary step in the anaerobic digestion of dairy cow manure, which could reduce capital and operating costs for the industry.

Revealing the correlation of biomethane generation, DOM fluorescence, and microbial community in the mesophilic co-digestion of chicken manure and sheep manure at different mixture ratio

Batch co-digestion tests of chicken manure (CM) and sheep manure (SM) at different ratio (R_s/c) were conducted under mesophilic condition (35 °C). Batch kinetic analysis of bioCH₄ production, excitation-emission matrix (EEM) fluorescence of dissolved organic matter (DOM), and microbial community were investigated. The well-fitted modified Gompertz model (R², 0.98-0.99) resulted that the co-digestion markedly improved the methane production rate and shortened the lag phase time. The highest bioCH₄ yield of 219.67 mL/gVS_add and maximum production rate of 0.378 mL/gVS_add/h were obtained at an optimum R_s/c of 0.4. Additionally, a significant variation of DOM was detected at the R_s/c of 0.4 with a consistent degradation of soluble microbial byproduct-like and protein-like organics. The positive synergy effects of co-digestion conspicuously enhanced the bioCH₄ production efficiency. FI₃₇₀ and NADH were significantly correlated to R_s/c (p < 0.05). Moreover, the correlations among process indicator, EEM-peaks and different environmental parameters were evaluated by Pearson correlation analysis. The high diversity of acetoclastic methanogens and hydrogenotrophic methanogens in the co-digestion improved the stability of process. Graphical Abstract.

Ammonia removal from chicken manure digestate through vapor pressure membrane contactor (VPMC) and phytoremediation

Ammonia removal from synthetic ammonia solutions and chicken manure digestate via vapor pressure membrane contactor through Polytetrafluoroethylene (PTFE) membrane was investigated. The highest ammonia mass flux, separation factor, and removal efficiencies of 28.6 ± 0.2 g N/m² h, 53.9 ± 10.7, and 97.6 ± 0.7% were observed for synthetic solutions, respectively. Ammonia removal efficiency of 93.6 ± 1.9% through membrane contactor was observed for chicken manure digestate decreasing the total ammonia concentration from 3643.5 ± 67.2 to 230.9 ± 46.2 mg N/L. Phytoremediation via Lemna minor species was used as a polishing step to remove remaining ammonia from the membrane contactor effluent. Total ammonia concentration was then decreased below 2 mg N/L through evaporation, nitrification, and plant uptake processes occurring in the phytoremediation containers. This study reveals that ammonia can be successfully removed via VPMC and phytoremediation systems and the process is implementable as it can be coupled to anaerobic digestion processes to recover ammonia and to prevent ammonia inhibition.

Biogas Production by Co-Digestion of Canteen Food Waste and Domestic Wastewater under Organic Loading Rate and Temperature Optimization

The objective of this study was to characterize biogas production performance from the co-digestion of food waste and domestic wastewater under mesophilic (35 ± 1 °C) and thermophilic (55 ± 1 °C) conditions. The food waste used as a co-substrate in this study was collected from a main canteen at the Hatyai campus of Prince of Songkla University, Songkhla Province, Thailand. The optimum co-digestion ratio and temperature conditions in a batch experiment were selected for a semi-continuous experiment. Organic loading rates (OLRs) of 0.66, 0.33, and 0.22 g volatile solid (VS) L−1 d−1 were investigated in a semi-continuous experiment by continuously stirring a tank reactor (CSTR) for biogas production. The highest biomethane potential (BMP, 0.78 ml CH4 mg−1 VS removal) was achieved with a ratio of food waste to domestic wastewater of 10:90 w/v at a mesophilic temperature. An OLR of 0.22 g VS L−1 d−1 of co-digestion yielded positive biogas production and organic removal. The findings of this study illustrate how biogas production can be used for operating feed conditions and control for anaerobic co-digestion of domestic wastewater and food waste from a university canteen.

Semi-continuous anaerobic co-digestion of chicken litter with agricultural and food wastes: A case study on the effect of carbon/nitrogen ratio, substrates mixing ratio and organic loading

In this study, four agro-industrial substrates, chicken litter (CL), food waste (FW), wheat straw (WS) and hay grass (HG) were assessed as feedstock for anaerobic digestion (AD) under semi-continuous conditions at organic loading rates (OLRs) of 2.0-3.0 g TS/L.d and hydraulic retention time (HRT) of 20 days. Six different substrate mixtures were prepared such that the C/N ratio of each was 20 or more. Using principal component analysis 68.1% of data variability was explained. Biogas production from CL, as a single substrate, was 181.3 ± 9.8mL_N biogas/g VS_added at OLR of 2.0gTS/L.d. The optimum substrates mixture was CL:FW:WS 60:20:20, where 73.0%, 167.2% and 116.9% increase in total biogas production at OLR of 2.0, 2.5, 3.0gTS/L.d, respectively, compared to that from CL, was obtained. Digestate sequential fractionation revealed carbohydrate degradation is an important factor that can explain the variation in performance and production of biogas for feedstocks of balanced C/N ratio.

Valuable Compound Extraction, Anaerobic Digestion, and Composting: A Leading Biorefinery Approach for Agricultural Wastes

In a society where the environmental conscience is gaining attention, it is necessary to evaluate the potential valorization options for agricultural biomass to create a change in the perception of the waste agricultural biomass from waste to resource. In that sense, the biorefinery approach has been proposed as the roadway to increase profit of the agricultural sector and, at the same time, ensure environmental sustainability. The biorefinery approach integrates biomass conversion processes to produce fuels, power, and chemicals from biomass. The present review is focused on the extraction of value-added compounds, anaerobic digestion, and composting of agricultural waste as the biorefinery approach. This biorefinery approach is, nevertheless, seen as a less innovative configuration compared to other biorefinery configurations, such as bioethanol production or white biotechnology. However, any of these processes has been widely proposed as a single operation unit for agricultural waste valorization, and a thoughtful review on possible single or joint application has not been available in the literature up to now. The aim is to review the previous and current literature about the potential valorization of agricultural waste biomass, focusing on valuable compound extraction, anaerobic digestion, and composting of agricultural waste, whether they are not, partially, or fully integrated.

Performance Evaluation of Mesophilic Anaerobic Digestion of Chicken Manure with Algal Digestate

Dilution is considered to be a fast and easily applicable pretreatment for anaerobic digestion (AD) of chicken manure (CM), however, dilution with fresh water is uneconomical because of the water consumption. The present investigation was targeted at evaluating the feasibility and process performance of AD of CM diluted with algal digestate water (AW) for methane production to replace tap water (TW). Moreover, the kinetics parameters and mass flow of the AD process were also comparatively analyzed. The highest methane production of diluted CM (104.39 mL/g volatile solid (VS)) was achieved with AW under a substrate concentration of 8% total solid (TS). The result was markedly higher in comparison with the group with TW (79.54–93.82 mL/gVS). Apart from the methane production, considering its energy and resource saving, nearly 20% of TW replaced by AW, it was promising substitution to use AW for TW to dilute CM. However, the process was susceptible to substrate concentration, inoculum, as well as total ammonia and free ammonia concentration.

Thermophilic Alkaline Fermentation Followed by Mesophilic Anaerobic Digestion for Efficient Hydrogen and Methane Production from Waste-Activated Sludge: Dynamics of Bacterial Pathogens as Revealed by the Combination of Metagenomic and Quantitative PCR Analyses

Thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM) for hydrogen and methane production from waste-activated sludge (WAS) was investigated. The TM process was also compared to a process with mesophilic alkaline fermentation followed by a mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The results showed that both hydrogen yield (74.5 ml H₂/g volatile solids [VS]) and methane yield (150.7 ml CH₄/g VS) in the TM process were higher than those (6.7 ml H₂/g VS and 127.8 ml CH₄/g VS, respectively) in the MM process. The lowest methane yield (101.2 ml CH₄/g VS) was obtained with the M process. Taxonomic results obtained from metagenomic analysis showed that different microbial community compositions were established in the hydrogen reactors of the TM and MM processes, which also significantly changed the microbial community compositions in the following methane reactors compared to that with the M process. The dynamics of bacterial pathogens were also evaluated. For the TM process, the reduced diversity and total abundance of bacterial pathogens in WAS were observed in the hydrogen reactor and were further reduced in the methane reactor, as revealed by metagenomic analysis. The results also showed not all bacterial pathogens were reduced in the reactors. For example, Collinsella aerofaciens was enriched in the hydrogen reactor, which was also confirmed by quantitative PCR (qPCR) analysis. The study further showed that qPCR was more sensitive for detecting bacterial pathogens than metagenomic analysis. Although there were some differences in the relative abundances of bacterial pathogens calculated by metagenomic and qPCR approaches, both approaches demonstrated that the TM process was more efficient for the removal of bacterial pathogens than the MM and M processes.IMPORTANCE This study developed an efficient process for bioenergy (H₂ and CH₄) production from WAS and elucidates the dynamics of bacterial pathogens in the process, which is important for the utilization and safe application of WAS. The study also made an attempt to combine metagenomic and qPCR analyses to reveal the dynamics of bacterial pathogens in anaerobic processes, which could overcome the limitations of each method and provide new insights regarding bacterial pathogens in environmental samples.

Influence on anaerobic digestion by intermediate thermal hydrolysis of waste activated sludge and co-digested wheat straw

This paper analyses time (30 and 60 min) and temperature (120-190 °C) effects of intermediate thermal hydrolysis (ITHP) in a two-step anaerobic digestion of waste activated sludge (WAS) with and without wheat straw as a co-substrate. Effects were analyzed by measuring biochemical methane potential for 60 days and assessing associated kinetic and chemical data. Compared to non-treatment, ITHP increased the secondary step methane yield from 52 to 222 L CH₄ kg VS^-1 and from 147 to 224 L CH₄ kg VS^-1 for pre-digested WAS and pre-co-digested WAS respectively at an optimum of 170 °C and 30 min. The hydrolysis coefficients (k_hyd) increased by up to 127% following treatment. Increasing ITHP time from 30 to 60 min showed ambiguous results regarding methane yields, whilst temperature had a clear and proportional effect on the concentrations of acetic acid. The energy balances were found to be poor and dewatering to increase total solids above the values tested here is necessary for this process to be energetically feasible.

Anaerobic digestion/co-digestion kinetic potentials of different agro-industrial wastes: A comparative batch study for C/N optimisation

Anaerobic digestion (AD) of different agro-industrial wastes and their co-digestion potential has been exhaustively studied in this research. It explores variation of feedstock characteristics such as biodegradability and methane potential during AD and anaerobic co-digestion (ACoD) of chicken litter (CL) with yoghurt whey (YW), organic fraction of municipal solid waste (OFMSW), hay grass (HG) and wheat straw (WS) under mesophilic conditions. Comparative performance was made at different loading concentrations (2%, 3% and 4% VS) with 1:2g/g VS of substrate to inoculum and carrying C/N ratio. Among different kinetic models, the AD of single substrates showed better fit to the modified Gompertz model (R²: 0.93-0.997) indicating variation in lag phase and methane production rate depend on the substrate characteristics. During ACoD, the methane yield improved by 9-85% through the addition of two, three or four substrates due to the synergistic effect asa result of increased biodegradability and optimum conditions (such asC/N ratio). A surface (optimisation) model indicated that maximum methane production can be achieved by blending chicken litter (30-35%) and a (65-70%) mixture of yoghurt whey, hay and wheat straw with aC/N ratio of (26-27.5).

Anaerobic co-digestion of microalgal biomass and wheat straw with and without thermo-alkaline pretreatment

This study aimed at analyzing the anaerobic co-digestion of microalgal biomass grown in wastewater and wheat straw. To this end, Biochemical Methane Potential (BMP) tests were carried out testing different substrate proportions (20-80, 50-50 and 80-20%, on a volatile solid basis). In order to improve their biodegradability, the co-digestion of both substrates was also evaluated after applying a thermo-alkaline pretreatment (10% CaO at 75°C for 24h). The highest synergies in degradation rates were observed by adding at least 50% of wheat straw. Therefore, the co-digestion of 50% microalgae - 50% wheat straw was investigated in mesophilic lab-scale reactors. The results showed that the methane yield was increased by 77% with the co-digestion as compared to microalgae mono-digestion, while the pretreatment only increased the methane yield by 15% compared to the untreated mixture. Thus, the anaerobic co-digestion of microalgae and wheat straw was successful even without applying a thermo-alkaline pretreatment.

Batch and semi-continuous anaerobic co-digestion of goose manure with alkali solubilized wheat straw: A case of carbon to nitrogen ratio and organic loading rate regression optimization

The present study focused on carbon to nitrogen ratio (C/N) and organic loading rate (OLR) optimization of goose manure (GM) and wheat straw (WS). Dealing the anaerobic digestion of poultry manure on industrial scale; the question of optimum C/N (mixing ratio) and OLR (daily feeding concentration) have significant importance still lack in literature. Therefore, Batch and CSTR co-digestion experiments of the GM and WS were carried out at mesophilic condition. The alkali (NaOH) solubilization pretreatment for the WS had greatly enhanced its anaerobic digestibility. The highest methane production was evaluated between the C/N of 20-30 during Batch experimentation while for CSTRs; the second applied OLR of (3g.VS/L.d) was proved as the optimum with maximum methane production capability of 254.65ml/g.VS for reactor B at C/N of 25. The C/N and OLR regression optimization models were developed for their commercial scale usefulness.