Acidogenesis Stage Research Articles

Explore the effect of Fe3O4 nanoparticles (NPs) on anaerobic digestion of sludge

ABSTRACT With their wide application, some nanomaterials entering into the environment and made effects in many ways. Different concentrations of Fe3O4 nanoparticles (NPs) were added (0, 100, 200, 400 and 600 mg/L) in this study, the changes of substance in three stages of anaerobic digestion (AD) were explored, the optimal dosage of Fe3O4 NPs was finally found. The results showed that the 200 mg/L Fe3O4 NPs could better promote the decomposition of organic matter than the other groups, the protein and polysaccharide degradation rate reached to 99.75% and 83.14%, respectively. In the acidogenesis stage, the acetic acid concentration reached up to 692.88 mg/L, increased by 31.8% compared with the control group. Fe3O4 NPs had also been proved to increase VFAs, finally made the methane content reach to 92.22%. The variation of coenzyme F420 had also been described in this research, the highest value was 1.83 Umol/g VS. These results showed that the different concentrations of Fe3O4 NPs had different effects on anaerobic digestion.

Characterization of water hyacinth (E. crassipes) from Lake Victoria and ruminal slaughterhouse waste as co-substrates in biogas production

Water hyacinth (Eichhornia crassipes), an invasive water weed with a large biomass, poses serious socioeconomic and environmental challenges in fresh water bodies. Efforts to control and remove water hyacinth (WH) can be complemented by biogas production, which, however, requires knowledge of its chemical and nutritional composition. Moreover, co-digestion with other substrates may compensate for possible limitations of its largely lignocellulosic biomass. This study carried out proximate, crude fiber, elemental and biochemical analysis of WH and a co-substrate, ruminal slaughterhouse waste (RSW). The WH had significant concentrations of cellulose, hemicellulose and carbohydrates of 331,200, 231,800 and 447,800 mg/L, respectively, and lesser concentration of lignin of 99,400 g/L that is desirable in biomass for biogas production. Concentrations of C, N, P and K in WH were 15,480, 1654, 51 and 137 mg/L compared to 26,220, 1390, 34 and 7475, respectively, for RSW, which indicated potential for biogas generation. The potassium concentration for WH of 137 mg/L was below the optimum range of 200–400 mg/L while that for RSW of 7476 mg/L was in the inhibitory range. Both biomass exhibited phosphorous deficiency at C/P of 310 and 656 for WH and RSW, respectively, against optimum ratio of 100 and 150 for hydrolysis and acidogenesis stages and methanogenesis stage, respectively. The C/N for WH of 9.4 was at the lower limit for optimal biogas production of 8 mg/L that demarcates potential ammonia toxicity while that for RSW of 18.8 was near the upper limit of 20 mg/L for nitrogen deficiency. Co-digesting the two substrates has the potential for balancing potassium concentrations and the C/N ratios. Trial co-digestion of WH with RSW improved WH gas production demonstrating complementary effect of the two substrates. However, commercialization of the co-digestion would need to establish the optimal mix proportions and methanogenic microbial communities involved in the digestion process.

A novel spatiotemporally anaerobic/semi-aerobic bioreactor for domestic solid waste treatment in rural areas

To meet the requirements of domestic solid waste treatment and technological upgrading of bioreactors, a spatiotemporally anaerobic/semi-aerobic bioreactor (STASAB) was designed. The STASAB took full advantages of anaerobic and semi-aerobic bioreactors by the sequential alternation of anaerobic and semi-aerobic operation and by recirculation of mixed leachate from different-stage bioreactors. Results indicated that after the start-up stage, the pH of leachate in the STASAB always remained higher than 6.88, even in the hydrolysis and acidogenesis stage. The maximum total nitrogen concentration in the STASAB was 1461 mg·L−1, which was merely half that of the sequentially anaerobic/semi-aerobic bioreactor (SASAB) and had no adverse effects on the anaerobic process. Nitrogen removal in the STASAB reached 92.3%–95.5% when operated in the semi-aerobic phase and even reached 49.4% when operated in the anaerobic phase. The peak concentration of chemical oxygen demand was much lower and the anaerobic digestion lag time was much shorter in the STASAB than in the SASAB. The period of rapid biogas production in the STASAB was double that of the SASAB, which resulted in a 70% increase in biogas generation. Moreover, leachate could be exhausted by evaporation in just 3–5 months during the semi-aerobic phase. Therefore, the STASAB can eliminate acidogenic and ammonia inhibition during solid waste treatment, enhance the rate and extent of organic waste decomposition, rapidly initiate methanogenesis, enhance methane generation, and achieve zero leachate discharge (excluding rainfall infiltration). The STASAB is an efficient and feasible technique for treating domestic solid waste in rural areas.

Enhancing syntrophic associations among Clostridium butyricum, Syntrophomonas and two types of methanogen by zero valent iron in an anaerobic assay with a high organic loading

The impacts of ZVI on microbial community diversity in an anaerobic assay with high organic loading were investigated. The relative abundance of bacteria, archaea, and the functional methyl coenzyme-M reductase (mcrA) gene were investigated using high-throughput sequencing, and variations in their quantity were determined by qPCR. The results showed that ZVI significantly increased both the relative abundance and quantity of Methanobacteriales and Methanosarcinales during hydrogenotrophic and acetoclastic methanogenesis. The relative abundance of syntrophic Methanobacteriales at the hydrolysis and acidogenesis stages resulted in H2 partial pressure decrease through an interspecies hydrogen transfer (IHT) network, which further induced butyric conversion to acetic by Syntrophomonas. The primary microbial metabolism then converted to acetoclastic methanogensis in the assay with ZVI addition. The short duration of this process and high relative abundance of Syntrophomonas, Clostridium butyricum and Methanosarcinales potentially indicated the existence of a novelty syntrophic mechanism for extracellular electron transfer, which promoted CH4 generation.

Effect of Agitation on Acidogenesis Stage of Two-Stage Anaerobic Digestion of Palm Oil Mill Effluent (POME) into Biogas

The acidogenesis stage in two-stage anaerobic digestion of palm oil mill effluent (POME) was studied in a continuous stirred tank reactor (CSTR). This research investigated the effect of agitation rate on the growth of microorganisms, the degradation of organic substances, and volatile fatty acids (VFA) production and composition. Initially, the suitable loading up was determined by varying the HRT 6.7, 5.0, and 4.0 days in a 2 L CSTR with agitation rate 50 rpm, pH 6.0 ± 0.2, at room temperature. Next, effect of agitation on the process was determined by varying agitation rate at 25, 50, 100, and 200 rpm. Analysis of total solids (TS), volatile solids (VS), total suspended solids (TSS), volatile suspended solids (VSS), chemical oxygen demand (COD), and volatile fatty acids (VFA) were conducted in order to study the growth of microorganisms and their abilities in converting organic compound to produce VFA. The highest growth of microorganisms was achieved at HRT 4.0 day with microorganism concentration was 20.62 mg VSS/L and COD reduction was 15.7%. The highest production of total VFA achieved was 5,766.61 mg/L mg/L at agitation rate 200 rpm, with concentration of acetic acid, propionic acid and butyric acid were 1,889.23; 1,161.43; and 2,725.95 mg/L, respectively. While degradation VS and COD were 16.61 and 38.79%.

Influence of Polyphosphate Hydrolysis on the Degradation of Volatile Fatty Acids (VFAs) in Anaerobic Digestion

The degradation rate of Volatile Fatty Acids (VFAs) produced predominantly in the acidogenesis stage is a key process parameter to be optimised to ensure a successful Anaerobic digestion (AD). Thermodynamically, the oxidation of the VFAs are energetically unfavourable, and as such external energy source apart from the energy derived from the hydrolysis of Adenosine Triphosphate (ATP) is needed for the initial activation of the VFAs, initial growth of the methanogens in AD process and improved degradation rate of the VFAs. Thus, this research investigated the influence of polyphosphate hydrolysis on the degradation rate of the VFAs at high concentration. Sodium-propionate, Sodium-butyrate and Sodium-acetate salts were added at the start of experiments in order to increase the concentration of the VFAs. The polyphosphate salts used were; Na-hexametaphosphate, Na-tripolyphosphate and potassium pyrophosphate. The control experiment was polyphosphate free and three process parameters (degradation rate, cumulative biogas production and specific methane content) of anaerobic digestion were investigated. The experiments were carried out at a mesophilic temperature of 37.5°C for 41 days. The results of the investigation showed that the treated reactors with the polyphosphate salt solution in low concentration performed better than the reactors with high concentration of the polyphosphate salts solution. All the treated reactors with poly-P salts performed better than reactor Nr-9 (control experiment), but reactor Nr-1 was outstanding with an improved degradation rate of 47%, cumulative biogas production of 21% and specific methane content of 23%.

Macromodelling of fermentation process of municipal solid organic waste at biogas plants on the acidogenesis stage

In this work the task of modeling processes of anaerobic microbiological fermentation with keeping the balance on the stages of hydrolysis and acidogenesis was considered. It was proposed and justified to build the model at the stage of acidogenesis in the form of interval difference operator (IDO). The structure identification method of IDO on the principles of honey bee colony functioning in the food search process, which provides the possibility of obtaining simple IDO structures with specified prognostic properties relative to existing methods, was substantiated.

Hydrolysis–acidogenesis of food waste in solid–liquid-separating continuous stirred tank reactor (SLS-CSTR) for volatile organic acid production

The use of conventional continuous stirred tank reactor (CSTR) can affect the methane (CH4) recovery in a two-stage anaerobic digestion of food waste (FW) due to carbon short circuiting in the hydrolysis–acidogenesis (Hy–Aci) stage. In this research, we have designed and tested a solid–liquid-separating CSTR (SLS-CSTR) for effective Hy–Aci of FW. The working conditions were pH 6 and 9 (SLS-CSTR-1 and -2, respectively); temperature-37°C; agitation-300rpm; and organic loading rate (OLR)-2gVSL−1day−1. The volatile fatty acids (VFA), enzyme activities and bacterial population (by qPCR) were determined as test parameters. Results showed that the Hy–Aci of FW at pH 9 produced ∼35% excess VFA as compared to that at pH 6, with acetic and butyric acids as major precursors, which correlated with the high enzyme activities and low lactic acid bacteria. The design provided efficient solid–liquid separation there by improved the organic acid yields from FW.

Acidogenesis of Palm Oil Mill Effluent to Produce Biogas: Effect of Hydraulic Retention Time and pH

Acidogenesis of palm oil mill effluent to produce biogas was conducted base on anaerobic digestion process. This process was consisted of four different stages using various types of microorganisms which came from various groups of bacteria. This research studied the effect of hydraulic retention time (HRT) and pH to the change of the organic compounds concentration and solids content of POME to the growth of microorganisms during acidogenesis stage. Initially, the suitable loading up was determined by varying the HRT 6.7; 5.0; and 4.0 days in the continuous stirred tank reactor (CSTR) with mixing rate 50rpm, pH 6.0 ± 0.2, and room temperature. Next, suitable pH was determined by varying the pH at 5.0; 5.5; and 6.0 with mixing rate 100-110rpm and temperature 55oC. Analysis of TS, VS, TSS, VSS, COD, and VFA were conducted in order to study the growth of microorganisms and their abilities in converting organic compound to produce VFA. The highest growth of microorganisms was achieved at HRT 4.0 day with microorganism concentration was 20.62mg VSS/L and COD reduction was 15.7%. The highest production of total VFA achieved was 5622.72mg/L at pH 6.0, with the concentration of acetic acid, propionic acid and butyric acid were 2257.34; 975.49; and 2389.90mg/L, respectively. While degradation VS and COD were 11 and 23%, respectively.

Performance assessment of two-stage anaerobic digestion of kitchen wastes

This study is aimed at investigating the performance of the two-phase anaerobic digestion of kitchen wastes in a lab-scale setup. The semi-continuous experiment showed that the two-phase anaerobic digestion of kitchen wastes had a bioconversion rate of 83%, biogas yield of 338 mL·(g chemical oxygen demand (COD))−1 and total solid conversion of 63% when the entire two-phase anaerobic digestion process was subjected to an organic loading rate (OLR) of 10.7 g·(L d)−1. In the hydrolysis–acidogenesis process, the efficiency of solubilization decreased from 72.6% to 41.1%, and the acidogenesis efficiency decreased from 31.8% to 17.8% with an increase in the COD loading rate. On the other hand, the performance of the subsequent methanogenic process was not susceptible to the increase in the feeding COD loading rate in the hydrolysis–acidogenesis stage. Lactic acid was one of the main fermentation products, accounting for over 40% of the total soluble COD in the fermentation liquid. The batch experiments indicated that the lactic acid was the earliest predominant fermentation product, and distributions of fermentation products were pH dependent. Results showed that increasing the feeding OLR of kitchen wastes made the two-stage anaerobic digestion process more effective. Moreover, there was a potential improvement in the performance of anaerobic digestion of kitchen wastes with a corresponding improvement in the hydrolysis process.

Two-Phase Anaerobic Digestion of Municipal Organic Solid Wastes

Two stages anaerobic digestion of the organic fraction of municipal solid wastes (OFMSW) is proposed using a batch anaerobic trickling bed (BATB) reactor in the first hydrolysis and acidogenesis stage. At total solids loading of 135 g/L and reaction times around 30 days, total solids (ηTS) and chemical oxygen demand (ηCOD) removal efficiencies above 46% were obtained independently of pH (between 4.1 and 6.4). Dependent on pH were methane production, four times more at pH 6.4 than at 4.8 and four times more volatile fatty acids (VFA) production at 6.4 than at 4.1 and twice than at 4.8. Leachates generated in the BATB reactor were diluted with municipal wastewater and fed to an upflow anaerobic sludge blanket (UASB) reactor at volumetric organic loading rates from 11 to 28 g/L.d where 90% COD removal efficiencies (ηCOD) and 11.4 g CODCH4./L.d were obtained. Two stages anaerobic digestion results in high rates of solids removal and methane production (0.63 kWhr/kg TS fed).

Spatial succession and metabolic properties of functional microbial communities in an anaerobic baffled reactor

The spatial successions of bacterial and archaeal communities in anaerobic digestion were investigated in a glucose-degrading five-compartment anaerobic baffled reactor (ABR). The distributions of H2-producing acetogens, H2-utilizing acetogens and methanogens in different anaerobic-digestion stages were quantitatively analyzed using functional probes. The results show that the acidogenesis stage and acetogenesis stage were located in the first two compartments, while the methanogenesis were located in the last two compartments. In acidogenesis/acetogenesis stage of anaerobic digestion, H2-producing acetogens (19.7%) and H2-utilizing acetogens (8.3%) were the dominant bacterial community. While in methanogenesis stage, methanogens became the dominant (40.2%) with H2-producing acetogens and H2-utilizing acetogens only accounting for 6.6% and 4.8%, respectively. With the bacterial population decreasing from 7.2 ± 0.5 × 1012 cells mL−1 to 0.6 ± 0.3 × 1012 cells mL−1 along water flowing direction, their diversity increased from 2.79 to 299. The acidogenic bacteria, such as Lactococcus sp., Uncultured Firmicutes bacterium, and Uncultured Clostridium sp., etc., dominated in the acidogenesis/acetogenesis stage, while Uncultured Desulfobacterales bacterium became dominant in the methanogenesis stage. A two-stage anaerobic process may be suitable for easily degradable organic matters removal.

Anaerobic fermentative system based scheme for green energy sustainable houses

The green energy sustainable house based on bio-hydrogen and bio-methane energy technologies proposed in this study employs dark fermentation technology to complete a scheme for green energy sustainable house that includes energy production, storage, distribution control, load applications, recycling, waste treatment, and reuse. In order to resolve the problem of wastewater discharge from hydrogen production in green energy sustainable houses, this study proposes wastewater chemical oxygen demand (COD) treatment research, and suggests the use of two-stage anaerobic treatment to produce two types of bio-energy i.e. hydrogen and methane, while simultaneously reducing COD levels. Methane production employed a condensed molasses fermentation solubles (CMS) and hydrogen fermentation tank effluent as a substrate to test the COD reducing efficiency and overall efficiency of methane production. It was found that if CMS is used during the hydrolysis and acidogenesis stages, the maximum carbohydrate degradation rate will be approximately 70% (F/M ratio of 1.9–2.3), and the COD removal rate will increase from 15 to 20% (F/M ratio of 1.9–2.3) to 68% (F/M ratio of 0.5). This study showed that the total gas (H 2 and CH 4) production yield from effluent of hydrogen fermentation tank (56.2 KJ/mol substrate) is greater than the value for CMS. In this study, a 3.2 m 3 anaerobic hydrogen reactor is evaluated to provide a family with 3–4 kW of power. When acclimatization is performed under conditions of 20 g COD/L substrate and hydraulic retention time (HRT) of 8 h, the COD removal rate can reach approximately 50%. If a methane-generating reactor with a 95% COD removal rate is used to degrade effluent from the hydrogen reaction tank, it will be possible to reduce the COD of organic effluent to under 500 mg/L. Since this water quality is not far from that of ordinary untreated household wastewater (approximately 300–500 mg COD/L), the effluent can be discharged into a community sewer system and treated in a community sewage treatment facility.

Enhanced solid-state anaerobic digestion of corn stover by alkaline pretreatment

Alkaline pretreatment was applied to enhance biogas production from corn stover through solid-state anaerobic digestion. Different NaOH loadings (1%, 2.5%, 5.0% and 7.5% (w/w)) were tested for solid-state pretreatment of corn stover. Lignin degradation during pretreatment increased from 9.1% to 46.2% when NaOH concentration increased from 1.0% to 7.5%. The NaOH-pretreated corn stover was digested using effluent of liquid anaerobic digestion as inoculum and nitrogen source. NaOH loading of 1% did not cause significant improvement on biogas yield. The highest biogas yield of 372.4 L/kg VS was obtained with 5% NaOH-pretreated corn stover, which was 37.0% higher than that of the untreated corn stover. However, a higher NaOH loading of 7.5% caused faster production of volatile fatty acids during the hydrolysis and acidogenesis stages, which inhibited the methanogenesis. Simultaneous NaOH treatment and anaerobic digestion did not significantly improve the biogas production ( P > 0.05).

Multiple response optimization analysis for pretreatments of Tequila’s stillages for VFAs and hydrogen production

The objective of this work was study the effect of three pretreatments (alkalinization, thermical treatment, and sonication) on Tequila’s stillages hydrolysis process in acidogenesis stage, through the following response variables: soluble chemical oxygen demand (CODs), total sugar and volatile fatty acids profile and the hydrogen production at the time. The stillages were subject to these pretreatments (according to a 2 3 factorial design); afterward they were transferred to a batch reactor at 35 °C and inoculated with an anaerobic digestor sludge. Multiple response optimization (MRO) analysis was done to find the global optimum for the response variables described above. This optimum is able to maximize simultaneously all these variables. It was found adequate to be useful hydrolyzing the organic matter present in Tequila’s stillages. Mathematical models were fitted to observe the estimated effects of pretreatments on each response variable, then the MRO was applied.

Nickel and cadmium inhibition in acidogenesis during anaerobic digestion

Abstract The inhibition of cadmium and nickel ions on the acidogenesis stage in anaerobic treatment was investigated in this study. The anaerobic culture was first acclimated to a glucose substrate in semi‐continuous anaerobic reactors. Inhibition of metal ions were investigated by batch experiments. Results were quantified by measuring the total volatile fatty acid (TVFA) production activity of samples. The relative toxicity in the acidogenesis stage was Cd > Ni. Mixtures of metal ions generally exhibited antagonistic effect on inhibition.