Semi-continuous Stirred Tank Reactor Research Articles

A sustainable, zero-waste approach for production of biohydrogen from chicken manure slurry by hybrid recycling of digestate

This study provides a sustainable approach to produce biohydrogen through the long-term hydrogenic fermentation of chicken manure (CM) in a semi-continuous stirred tank reactor (CSTR) under different organic loading rates (OLRs). To ensure the zero-waste route and sustainability, the total digestate was mechanically separated into liquid and solid fractions. The solid digestate fraction was thermally treated to produce biochar, while the liquid digestate fraction was biologically treated through bioaugmentation with a novel heterotrophic nitrification-aerobic denitrification (HD-AN (bacterial strain (Alcaligenes sp. ME-1). The results showed that the high concentration of free ammonia nitrogen (FAN) contents of CM could inhibit methanogenesis and induce hydrogen production. The ORLs of 2.5, 3.5, 4.5, and 5.5 gVS/L.d imposed to the CSTR resulted in volumetric hydrogen production (VHP) of 643.3 ± 37, 908.8 ± 64.5, 1077.8 ± 95.17, and 1383.3 ± 156.8 mL/L.d, respectively. The microbial community structures indicated the long-term adaptation of hydrogen-producing bacteria and methanogenesis inhibition. The bioaugmentation process removed 83.3 % of total ammonia and 66.2 % of the chemical oxygen demand (COD) from the liquid digestate fraction. The characteristics of the biochar derived solid digestate is suitable for land applications as fertilizer. The hybrid approach combining biohydrogenation, pyrolysis, and bioaugmentation, maximizes the utilization of chicken manure slurry while conforming to the sustainable development goals.

Enhancing energy recovery from aquaculture residual materials: a focus on anaerobic digestion of African catfish (Clarias gariepinus) sediment sludge

In Germany, warm water Recirculating Aquaculture Systems (RAS) are generally integrated with biogas plants. The process sludge produced in aquaculture could be utilized to generate energy. This study investigates the potential of process sludge from commercial African catfish (Clarias gariepinus) warm water RAS, alongside associated plant production residues (whole plants and pruning residues) for energy generation through anaerobic digestion. Biogas tests, including batch, semi-Continuous Stirred Tank Reactor (CSTR), and Upflow Anaerobic Sludge Blanket Reactor (UASB) were conducted. In batch, methane yields were 229 L(N) / kg VS from the sludge and 173–184 L(N) / kg VS from the various plant substrates (cucumber, paprika, and tomato plants). During CSTR operation, mono-fermentation of sludge produced a methane yield of 265 L(N) / kg VS. Co-fermentation with 25% cucumber residues, based on VS, increased this value to 381 L(N) / kg VS. Mono-fermentation of sludge in the UASB reactor yielded a maximum of 329 L(N) /kg VS. The relatively low TS content and unfavorable C/N ratio in C. gariepinus sludge, along with the low energy density and occasional high sulfur content in the investigated plant substrates, present challenges for CSTR biogas production. These challenges can be partially mitigated through substrate combination. For mono-fermentation of African catfish RAS sludge, the UASB reactor is recommended. Improved solids separation, extraction, and concentration techniques at aquaculture operations are essential for the efficient utilization of aquaculture sludge, especially from African catfish, in biogas plants.

Advancing Energy Recovery from Sugarcane Leaf via Two-Stage Anaerobic Digestion for Hydrogen and Methane Production: Impacts on Greenhouse Gas Mitigation and Sustainable Energy Production

This study aims to enhance energy recovery from sugarcane leaf (SCL) through two-stage anaerobic digestion (TSAD) for hydrogen and methane production. The influence of hydraulic retention time (HRT) on this process was investigated. Optimal conditions established through batch experiments (5% total solids (TS) (w/v) and rice straw compost inoculum) were applied in semi-continuous stirred tank reactors (CSTR-H2 and CSTR-CH4). Remarkably, the highest production rates were achieved with HRTs of 5 days for CSTR-H2 (60.1 mL-H2/L·d) and 25 days for CSTR-CH4 (238.6 mL-CH4/L·d). Microbiological analysis by 16s rRNA sequencing identified Bacillus as predominant in CSTR-H2 followed by Lactobacillus and Clostridium. Utilizing SCL for TSAD could reduce greenhouse gas (GHG) emissions by 2.88 Mt-CO2 eq/year, compared to open-field burning, and mitigate emissions from fossil-fuel-based power plants by 228 kt-CO2 eq/year. This research underscores the potential of TSAD for efficient energy recovery and significant GHG emission reductions.

Synergistic interaction of tween 20 and magnesium@ functionalized graphene oxide nano-composite for dual productivity of biohydrogen and biochar from onion peel waste

This study aimed at developing a novel nano-composite enhancing fermentation/pyrolysis strategy for dual productivity of biohydrogen and biochar from onion peel waste (OPW). Biohydrogen productivity was maximized by adding tween 20 (T20) and magnesium@ functionalized graphene oxide (Mg@FGO) onto the fermentation of OPW. Three semi-continuous stirred tank reactors (CSTR1, CSTR2 and CSTR3) were respectively supplemented with OPW (control), OPW + T20, and OPW + T20+Mg@FGO and operated at constant retention time of 4.0 d. The hydrogen production rate (HPR) of 343.2 ± 36.2 mL/L/d and hydrogen yield (HY) of 30.30 ± 4.6 mL/g CODadded was obtained by CSTR2 which were greater than those achieved in the control (CSTR1) by 2-folds. Further improvement of H2 productivity >200% was achieved in CSTR3 supplemented with T20+Mg@FGO compared with CSTR1. The addition of T20+Mg@FGO in CSTR3 enhanced acetate fermentation pathway, the enzymatic activities and the biodegradation of phenolic compounds. Moreover, microbial diversity analysis of CSTR3 showed the dominance of the H2-producing bacteria related to Firmicutes, Planctomycetes, and Proteobacteria. Further, digestates collected from the CSTR3 were pyrolyzed at temperature of 550 °C, delivering biochar having multiple surface functional groups. Results confirm that adding T20+Mg@FGO onto the fermentation of OPW followed by digestate pyrolysis could be a sustainable strategy for fulfilling the renewable energy requirements.

Study on the role of the reaction time in the upcycling of HDPE by co-hydrocracking it with VGO

Pursuing the aim of improving the current waste plastics management strategy, we have investigated the co-hydrocracking of high-density polyethylene (HDPE) with vacuum gasoil (VGO) over a PtPd/HY catalyst for converting this blend into high-quality fuels. In particular, the work was focused on assessing the effects of the reaction time on the product yields and on the composition of the gas, naphtha and light cycle oil (LCO) fractions, which was determined by chromatographic means. The experimental runs were carried out in a 100 mL semi continuous stirred tank reactor varying the reaction time between 15 and 120 min and maintaining constant the rest of the variables at 420 °C (temperature reached using an electrical heating jacket and following a 5 °C min−1 heating ramp), 80 bar and a catalyst to oil mass ratio of 0.075 gcat goil−1. The results shown that at 120 min a naphtha fraction rich in 1-ring aromatics and with a RON value of 92.5 was obtained, while the LCO fraction was mainly iso-paraffinic with a cetane index of 43.8. Hence, these fractions could be used in the corresponding blending stages of commercial gasoline and diesel. Furthermore, the coke deposited on the catalyst was analyzed by means of TPO, obtaining that it was mainly formed at short contact times (< 15 min) and that its nature evolved with contact time being less condensed at long contact times.

A six-lump kinetic model for HDPE/VGO blend hydrocracking

A six lump-based kinetic model has been developed for the hydrocracking of high-density polyethylene (HDPE) blended with vacuum gas oil (VGO) over a PtPd/HY zeolite catalyst. The blend (20 wt% HDPE and 80 wt% VGO) has been hydrocracked in a semi-continuous stirred tank reactor under the following conditions: 400–440 °C; 80 H2 bar; catalyst to feed (C/F) weight ratio, 0.05–0.1 gcat gfeed−1; reaction time, 15–120 min; and stirring rate, 1300 rpm. The kinetic model, which is an approach to tackle the complex reaction mechanism behind the hydrocracking of a HDPE/VGO blend, predicts the evolution over time of product distribution (gas, naphtha, light cycle oil (LCO), heavy cycle oil (HCO), HDPE and coke). The kinetic model and its computed parameters have been used for the simulation of the HDPE/VGO hydrocracking establishing that a C/F ratio of 0.075 gcat gfeed−1 and temperature–time combinations of 430 °C–10 min and 440 °C–70 min are the optimal operating conditions. Under these conditions, a proper balance between the HCO conversion (>80 %), HDPE conversion (>60 %) and liquid fuel production index (>1.0) would be obtained. This kinetic model could serve as a basis for scaling-up in the valorization of waste plastics by co-feeding them to industrial hydrocracking units, within a Waste-Refinery strategy.

Effects of organic loading rates on the anaerobic co-digestion of fresh vinegar residue and pig manure: Focus on the performance and microbial communities

The 70 L mesophilic semi-continuous stirred tank reactor (semi-CSTR) for co-digestion of fresh vinegar residue (FVR) and pig manure (PM) was operated for 180 days to evaluate the behavior of process stability, inhibition and recovery, as well as the succession of microbial community structures with the increasing organic loading rates (OLRs). The maximum tolerable OLR for co-digestion was determined to be 5.0 g-VS/(L·d), achieving an average methane yield (MY) of 233.77 mL/g-VS. The feeding was paused for 7 days due to the accumulation of volatile fatty acids (VFAs), and then recovered at 5.5 g-VS/(L·d) with the maximum MY of 230.09 mL/g-VS. Meanwhile, the effect of OLRs on the microbial community was analyzed. It showed that there is a significant correlation between most of the major bacteria and VFA. PCA showed that stopping feeding and reducing OLR could change the bacterial community, but not archaeal community. The aceticlastic Methanosaeta was dominant at stable stage, and gradually replaced by the hydrogenotrophic methanogen, leading to the accumulation of acetate with increasing OLR. In the recovery stage, Methanosarcina became dominant to utilize the residual acetate. Due to the vigorous aceticlastic pathway of methanogenesis, the hydrogenotrophic pathway was depressed and the H2 pressure increased, causing the accumulation of propionate in a short time. With the relative abundance of Methanosarcina increasing constantly, the VFA except propionate decreased, suggesting that Methanosarcina transformed acetate and hydrogen into methane during the recovery stage.Supplementary Material_V4.doc

Enhancement of biogas production from cattle manure using glycerine phase as a co-substrate in anaerobic digestion

This study investigated the effect of glycerine phase on the anaerobic digestion of cattle manure under mesophilic conditions. The process was carried out in semi-continuous stirred tank reactors at a constant organic loading rate of 2.3 g VS/L·d and a hydraulic retention time of 30 days. It was found that the addition of 10% (as volatile solids) glycerine phase to cattle manure produced 3.1-times more biogas than cattle manure alone (237.5 L vs. 76.4 L) and a 10% higher methane content (69% vs. 59%). Biogas formation during co-digestion was strongly correlated with the concentrations of ammonium nitrogen (r = 0.89, p < 0.05) and volatile fatty acids (r = −0.71, p < 0.05), which resulted in a decrease in biogas production over time despite a stable pH value. The proposed use of glycerine phase could provide an advanced anaerobic digestion system that is technologically simple, has a positive energy balance, and produces upgraded biogas, although additional monitoring of the concentration of volatile acids and ammonium nitrogen is needed to maintain stable biogas production. These findings will be useful for reducing demand for non-renewable energy resources, and more broadly, they will assist in the shift from a traditional economy to a circular bioeconomy.

Anaerobic co-digestion of linen, sugar beet pulp, and wheat straw with cow manure: effects of mixing ratio and transient change of co-substrate

This study concerns the improvement and sustainability of producing methane (CH4) from the co-digestion of cow manure (CM), sugar beet pulp (SBP), linen (Ln), and wheat straw (WS). The first step involved co-digesting CM, Ln, and WS at various mixing ratios (CM/Ln/WS) in batch reactors to ascertain the best gas production. Biochemical methane potential (BMP) tests were carried out under mesophilic conditions using sludge from a wastewater treatment plant as an inoculum. The highest CH4 production (351 mL/g VSadd) and volatile solids removal rate (72.87%) were observed at the mixing ratio 50/25/25 and the lowest CH4 production (187 mL/g VSadd) was recorded at the ratio 25/25/50. A kinetic analysis was carried out to suggest the best strategy for methane production based on the ratio of substrates in the mix. The second step involved co-digesting CM, SBP, Ln, and WS in a semi-continuous stirred tank reactor to study the influence of a transient change in co-substrate on gas production and reactor performance. The rate of biogas production doubled with the transient change of co-substrate from WS to SBP, which may be due to the SBP being more easily biodegradable than WS.

Effects of organic loading rate on methane production from switchgrass in batch and semi-continuous stirred tank reactor system

Long-term anaerobic digestion of switchgrass (SG) was investigated in batch and semi-continuous reactors operating at different Substrate to Inoculum (S:I) ratios and organic loading rates (OLRs) by monitoring process stability, microbial community structure, and investigating kinetic modeling. The highest methane yield of 204 mLCH4/gVS was observed when the batch system was operated at the S:I ratio of 1.1. Methane yields in the semi-continuous configuration were around 148, 157, and 60 mLCH4/gVS at OLRs of 0.75, 1.0, and 1.5 gVS/(L.d), respectively. A drastic decrease in methane yields was observed at the highest OLR value of 1.5 gVS/(L.d). The optimum OLR in the semi-continuous configuration was decided as 1.0 gVS/(L.d) where 35% of the SG theoretical methane yield and 38% energy recovery were attained. Several methanogenic archaea, Methanosarcina, Methanosaeta, Methanothrix, and Methanomethylovorans, together with bacteria species, Chloroflexi, Firmicutes, Spirochaetes, and Actinobacteria were observed in the semi-continuous configuration after 270 days of operation. The dominant bacterial phyla of s-CSTR were mostly members of Spirochaetes phylum, which plays a considerable role in acetate oxidation under either mesophilic or thermophilic conditions.

Operational and biochemical aspects of co-digestion (co-AD) from sugarcane vinasse, filter cake, and deacetylation liquor.

This work performed co-AD from the vinasse and filter cake (from 1G ethanol production) and deacetylation liquor (from the pretreatment of sugarcane straw for 2G ethanol production) in a semi-Continuous Stirred Tank Reactor (s-CSTR) aiming to provide optimum operational parameters for continuous CH4 production. Using filter cake as co-substrate may allow the reactor to operate throughout the year, as it is available in the sugarcane off-season, unlike vinasse. A comparison was made from the microbial community of the seed sludge and the reactor sludge when CH4 production stabilized. Lactate, butyrate, and propionate fermentation routes were denoted at the start-up of the s-CSTR, characterizing the acidogenic phase: the oxidation-reduction potential (ORP) values ranged from -800 to -100 mV. Once the methanogenesis was initiated, alkalizing addition was no longer needed as its demand by the microorganisms was supplied by the alkali characteristics of the deacetylation liquor. The gradual increase of the applied organic load rates (OLR) allowed stabilization of the methanogenesis from 3.20 gVS L-1 day-1: the highest CH4 yield (230 mLNCH4 g-1VS) and average organic matter removal efficiency (83% ± 13) was achieved at ORL of 4.16 gVS L-1 day-1. The microbial community changed along with the reactor operation, presenting different metabolic routes mainly due to the used lignocellulosic substrates. Bacteria from the syntrophic acetate oxidation (SAO) process coupled to hydrogenotrophic methanogenesis were predominant (~ 90% Methanoculleus) during the CH4 production stability. The overall results are useful as preliminary drivers in terms of visualizing the co-AD process in a sugarcane biorefinery integrated to scale. KEY POINTS: • Integration of 1G2G sugarcane ethanol biorefinery from co-digestion of its residues. • Biogas production from vinasse, filter cake, and deacetylation liquor in a semi-CSTR. • Lignocellulosic substrates affected the biochemical routes and microbial community. • Biomol confirmed the establishment of the thermophilic community from mesophilic sludge.

The resource recovery potential of blackwater and foodwaste: anaerobic co-digestion in serial semi-continuous stirred tank reactors

The resource recovery potential of blackwater and foodwaste: anaerobic co-digestion in serial semi-continuous stirred tank reactors

Selecting fermentation products for food waste valorisation with HRT and OLR as the key operational parameters

Acidogenic fermentation is attractive for food waste valorisation. A better understanding is required on how operation affects product selectivity. This study demonstrated that the hydraulic retention time (HRT) and organic loading rate (OLR) selected fermentation pathways in a single-stage, semi-continuous stirred tank reactor. Three combinations of HRT and OLR were tested to distinguish the effect of each parameter. Three fermentation profiles with distinct microbial communities were obtained. Predominantly n-butyric acid (13 ± 2 gCOD L−1, 55 ± 14% of carboxylates) was produced at an HRT of 8.5 days and OLR around 12 gCOD L−1d−1. Operating at an HRT two days longer, yet with similar OLR, stimulated chain elongation (up to 13.6 gCOD L−1 of n-caproic acid). This was reflected by a microbial community twice as diverse at longer HRT as indicated by first and second order Hill number (1D = 24 ± 4, 2D = 12 ± 3) and by a higher relative abundance of genera related to secondary fermentation, such as the VFA-elongating Caproiciproducens spp., and secondary lactic acid fermenter Secundilactobacillus spp.. Operating at a higher OLR (20 gCOD L−1d−1) but HRT of 8.5 days, resulted in typical lactic acid fermentation (34 ± 5 gCOD L−1) harbouring a less diverse community (1D = 8.0 ± 0.7, 2D = 5.7 ± 0.9) rich in acid-resistant homofermentative Lactobacillus spp. These findings demonstrate that a flexible product portfolio can be achieved by small adjustments in two key operating conditions. This improves the economic potential of acidogenic fermentation for food waste valorisation.

A novel immobilization technique for the development of sustainable anammox gel beads for low nitrogen loadings

This study aimed to develop a sustainable anammox gel beads using sodium alginate (SA) mixed with three different support materials including sodium silicate (SS), polyvinyl alcohol (PVA), and colloidal silica (CS). A detailed characterization and comparison of anammox gel beads were conducted using four lab-scale semi-continuous stirred tank reactors (Semi-CSTRs) and SA–SS beads showed superior durability with better reactor performance. SA–SS (B2) beads showed the minimum reduction effective diameter of 24% in comparison to SA (B1) beads, SA–PVA​ (B3) beads, and SA–CS(B4) beads of 98%, 57%, and 96%, respectively indicating higher integrity of B2 beads. Moreover, R2 reactor containing B2 beads showed the maximum biomass retention after 30 days of operation, relative to the initial mass of 72% compared to R1, R3, and 3%, 44%, and 5%, in R1, R3, and R4, respectively. Total nitrogen removal efficiencies of 8%, 80%, 64%, and 10% were achieved by R1, R2, R3, and R4 reactors, respectively. The diffusion coefficients (De) of ammonium in anammox gel beads was maximum for B2 beads (26.2μm2/s) compared to B1 (18.8μm2/s), B3 (22.4μm2/s), and B4 (13.9μm2/s) beads indicating the enhanced internal mass transfer.

Co-digestion of Dairy Cattle Waste in a Pilot-Scale Thermophilic Digester Adapted to Poultry Litter Feedstock: Stress, Recovery, and Microbiome Response

The adaptability of a thermophilic anaerobic digester stabilized long-term with poultry litter as sole feedstock was measured with regard to co-digestion with dairy cattle manure. Both feedstocks have low C/N ratios but differ in carbohydrates, protein, and fiber content. The digester was a pilot-scale (40 m3) sCSTR (semi-continuously stirred tank reactor) with a 20-day hydraulic retention time (HRT). Dairy manure was added as three step-wise increases in concentration: 20, 40, and 80%. At 20% dairy manure, methane production was unchanged (17–19 m3 day−1). But as the fraction of dairy manure increased, methane, ammonia, sCOD, acetate, and propionate decreased. At 80% dairy manure, methane volume dropped by 60%. Acetate concentration decreased from an initial 878 ± 209 mg L−1 during poultry litter mono-digestion to 285 ± 169 mg L−1 with 80% dairy manure. Upon returning to mono-digestion, methane production was on a trajectory of recovery although acetate remained low. Bacterial community structure shifted during co-digestion, but community resilience was also underway following return to the original feedstock for one HRT. The dominant bacterial phylotypes belonged to the groups Thermotogales, Synergistales, Clostridiales, and Halanaerobiales, and three uncharacterized orders (MBA08, SHA-98, OPB54) in class Clostridia. Co-digestion led to a shift in dominance with reductions in Thermotogales and OPB54, and an increase in MBA08. This experiment provides guidance for digester operators who wish to mix livestock and poultry manures for thermophilic co-digestion.

Comparative genomics in \u201cCandidatus Kuenenia stuttgartiensis\u201d reveal high genomic plasticity in the overall genome structure, CRISPR loci and surface proteins

BackgroundAnaerobic ammonium oxidizing bacteria (anammox bacteria) are contributing significantly to the nitrogen cycle and are successfully used in wastewater treatment. Due to the lack of complete genomes in the databases, little is known about the stability and variability of their genomes and how the genomes evolve in response to changing environments.ResultsHere we report the complete genome of the anammox bacterium “Candidatus Kuenenia stuttgartiensis” strain CSTR1 which was enriched planktonically in a semi-continuous stirred-tank reactor. A comparison of the genome of strain CSTR1 with the genome of “Ca. Kuenenia stuttgartiensis” MBR1 and the draft genome of KUST showed > 99% average nucleotide identity among all. Rearrangements of large genomic regions were observed, most of which were associated with transposase genes. Phylogenetic analysis suggests that strain MBR1 is more distantly related to the other two strains. Proteomic analysis of actively growing cells of strain CSTR1 (growth rate ~ 0.33 d− 1) failed to detect the annotated cytochrome cd1-type nitrite reductase (NirS) although in total 1189 proteins were found in the proteome. Yet, this NirS was expressed when strain CSTR1 was under stress or starvation (growth rate < 0.06 d− 1). We also observed large sequence shifts in the strongly expressed S-layer protein compared to other “Ca. Kuenenia” strains, indicating the formation of hybrids of genes encoding the surface proteins.Conclusions“Ca. Kuenenia” strains appear to be relatively stable in their basic physiological traits, but show high variability in overall genome structure and surface proteins.

Co-digestión anaerobia en modo semi-continuo de residuos de vegetales y estiércol de vaca: un estudio de estabilidad de proceso

The anaerobic digestion of vegetable waste (VW) often shows the accumulation of fatty acids and low buffering capacity that promotes instability and low methane productivity. This work evaluated the anaerobic co-digestion of VW with cow manure (CM) as a strategy to improve the process stability. As a reaction system, a 4 L semi-continuous stirred tank reactor with an HRT of 20 days and fed with a substrate formulation of 40 g of VS was used in two periods: 34 days of VW mono-digestion and 26 days of VW:CM co-digestion. The mono and co-digestion processes were numerically evaluated through three analysis tools: a proposed co-digestion model embedded in the Anaerobic Digestion Model No. 1 structure, statistical process control theory, and modeling the pH dynamics as the response of a first-order linear system to an impulse manipulation. The mono-digestion process showed productivity of 0.381 L CH4 L digester-1 d-1, which increased by 14 % during co-digestion. The results also indicated that in VW:CM co-digestion, the pH dynamics presents a slower response to the daily feed induced by pulses, keeping the values of this parameter within the statistical stability range; as well as the early warning indicator IA/BA (ratio between intermediate and bicarbonate alkalinity) outside the failure thresholds. It was shown that the addition of CM to a mono-digestion of VW increases the buffer capacity of the system and the production of CH4, promoting a stable and efficient process.

Effect of solid-liquid separation on anaerobic digestion of dairy manure in semi-continuous stirred tank reactors: Process performance and digestate characteristics.

The objective of this study was to investigate the effect of solid-liquid separation on anaerobic digestion of dairy manure in semi-continuous stirred tank reactors. Reactors fed with liquid fraction of dairy manure (screened liquid manure) were kept in water baths at mesophilic (Run 1) and thermophilic (Run 3) temperatures, respectively, while reactors fed with water diluted manure and kept at mesophilic (Run 2) and thermophilic (Run 4) temperatures as control reactors. The performances of reactors were compared in terms of biogas and methane production, and digestate characteristics. The methane yields obtained from screened manure were higher than those from diluted manure at both mesophilic and thermophilic temperatures, while the highest methane yield was 185L/kg VSadded under thermophilic temperature. Solid-liquid separation also had improved the effect on digestate fertilizer characteristics. Among four digestates from reactors, the highest contents of nutrients, N (4.12g/kg) and P (2.36g/kg) were found in Run 3, while the highest content of K (3.42g/kg) was found in Run 1. These results showed the benefits of solid-liquid separation of dairy manure on process performance and digestate characteristics.

Enhanced methane production and syntrophic connection between microorganisms during semi-continuous anaerobic digestion of chicken manure by adding biochar

Abstract The synergetic inhibition of ammonia and organic acids during anaerobic digestion with high organic loading rate limits the methane yield and endangers process stability. Here, the anaerobic digestion of chicken manure was tested under three different experimental conditions (corresponding to organic loading rates of 0.625, 3.125, and 6.25 g VS/L•d) with and without biochar in a semi-continuously stirred tank reactor, operating within a mesophilic range (35 ± 1 °C). The results showed that methane yields were increased by 33%, 36%, and 32% with the addition of biochar at the three different organic loading rates, respectively. Investigating ammonia nitrogen concentrations, organic carbon transformation, and the 16S rRNA gene sequences together demonstrated that by streamlining the metabolic capability of methanogens for the most efficient utilization strategy, biochar facilitates the direct interspecies electron transfer between fermentative bacteria and electro-trophic methanogens. Results also revealed that biochar supplement can enhance the conversion efficiency of macromolecule organic matter into dissolved organic acids and to methane for energy recovery, and stimulate the denitrification process for nitrogen removal by activating Epsilonproteobacteria. This study offers a microbiological addition to the body of work focusing on the function and mechanism of biochar in AD.

Bio-hydrogen Production from Sewage Sludge: Screening for Pretreatments and Semi-continuous Reactor Operation

The high volumes of sewage sludge produced have raised interests for simultaneous treatment and clean energy production, e.g. in the form of hydrogen. Pretreatment of sewage sludge is required to enhance microbial degradation and in turn hydrogen yield from sewage sludge. The potential of five substrate pretreatments, individually and in combinations, to increase biohydrogen production from mixed primary and secondary sewage sludge at four incubation pH (5, 7, 9, and 11) was studied in batch assays. Alkali + ultrasonication pretreatment increased the hydrogen production almost seven times (0.35 mmol H2/g VS) compared to untreated sewage sludge at initial pH 11. In general, higher hydrogen yields and lower acetate concentrations were obtained under alkaline conditions (pH 9 and 11), being more favorable for protein degradation and not favorable for hydrogen consumption via homoacetogenesis. Subsequently, fermentation of alkali + ultrasonication pretreated sewage sludge in a semi-continuous stirred tank reactor (CSTR) produced a maximum hydrogen yield of 0.1 mmol H2/g VS, three times higher than the yield obtained from alkali pretreated sludge. The gas produced in the CSTRs contained a low concentration of CO2 (< 5%), and is thus easily upgradable to biohydrogen.