Control of fermentation types in continuous-flow acidogenic reactors:effects of pH and redox potential

The experiments were carried out in continuous flow acidogenic reactors with molasses used as substrate to study the effects of pH and redox potential on fermentation types. The conditions for each fermentation type were investigated at different experimental stages of start up, pH regulating and redox potential regulating. The experiments confirmed that butyric acid type fermentation would occur at pH > 6, the propionic acid type fermentation at pH about 5.5 with E h> -278 mV, and the ethanol type fermentation at pH < 4.5. A higher redox potential will lead to propionic acid type fermentation because propionogens are facultative anaerobic bacteria.

Hydrogen energy recovery from high strength organic wastewater with ethanol type fermentation using acidogenic EGSB reactor

A lab-scale expanded granular sludge bed （EGSB） reactor was employed to evaluate the feasibility of the hydrogen energy recovery potential from high strength organic wastewater. The results showed that a maximum hydrogen production rate of 7.43 m^3 H2/m^3 reactor · d and an average hydrogen production rate of 6.44- ms H^2/ms reactor · d were achieved with the hydrogen content of 50% -56% in the biogas during the 90-day operation. At the acidogenic phase, COD removal rate was stable at about 15%. In the steady operation period, the main liquid end products were ethanol and acetic acid, which represented ethanol type fermentation. Among the liquid end products, the concentration percentage of ethanol and acetic acid amounted to 69.5% - 89. 8% and the concentration percentage of ethanol took prominent about 51.7% - 59. 1%, which is better than the utilization of substrate for the methanogenic bacteria. An ethanol type fermentation pathway was suggested in the operation of enlarged industrial continuous hydrogen bio-producing reactors.

Straw bio-degradation by acidogenic bacteria and composite fungi

A composite microbial system, including a strain of Candida tropicalis(W3), a strain of Lactobacillus plantarm(WY3) and three strains of basidiomycete pL104, pL113 and C33, was chosen to degrade corn straw. The final pH was acid owing to the inoculation of acidogenic bacteria, and under this condition the composite fungi system could produce complex enzyme to destroy the compact structure of corn straw. The experimental results showed that the biomass of composite fungi could reach up to maximum when the pH value was 4.5. Through the bio-degradation by combining acidogenic bacteria with the composite fungi system, the cellulose, hemi-cellulose and lignin degradation rates of corn straw powder were 26.36%, 43.30% and 26.96%, respectively. And the gross crude protein content increased 60.41%. This study provided the evidence for the feasibility of developing a composite microbial system with high capability of degrading straw lignocelluloses in order to make reasonable use of straw resource and protect rural eco-environment.

Quantification and control of restrictive ecological factors in acidogenic de-sulfate bioreactor

As an artificial microbial ecosystem, acidogenic de sulfate bioreactor has high efficiency of sulfate removal. The restrictive ecological factors, including causing ecological factors, such as COD/SO 4 2- ratio and sulfate loading rate (Ns), and following ecological factors, such as pH value, oxidation reduction potential (ORP) and alkalinity (ALK) have significant effect on the ability and stability of acidogenic de sulfate bio reactor. Continuous flow and batch test were carried out to investigate the quantification and control of COD/SO 4 2- ratio, Ns, pH value, ORP and ALK in acidogenic de sulfate bioreactor supplied with molasses wastewater as sole organic carbon source and sodium sulfate as electron donor. It was demonstrated that In order to maintain high sulfate removal rate (SRR) of 80% to 90%, the restrictive factors should meet all the requirement as follows: k COD/ SO 4 2-  ratio≥2.0, Ns≤7.5 kg (m 3·d) -1 ,pH=5.7～6.2,ORP=-320～-420 mV and  ALK= 1 500～2 000 mg/L.

The Microbial Metabolic Characteristics in the Course of Sulfate-Reduction

Acid-producing phase reactor of two-phase anaerobic treatment process has remarkable advantages treating sulfate-laden wastewater. In order to investigate SRB population's capability of utilizing substrate and the microbial acidification type formed during the course of sulfate reduction, continuous-flow and batch tests were conducted in a continuous stirred tank bio-film reactor supplied with sodium sulfate as electron acceptor. The experimental results demonstrated that the acidification type formed b...

Effect of pH and temperature on acidogenic and hydrogenic activities of glucose-degrading bio-granules

Series batch experiments were made to investigate the influences of pH and temperature on the activity of acidogenus and acidogenus in glucose-degrading bacteria cultured in an UASB(up-flow anaerobic sludge blanket) reactor for glucose fermentation and hydrogen production. The bacteria exhibited different capability to recover to produce hydrogen at different initial pH and temperature. Hydrogen production, VFA production, COD removal and COD balance were measured at different pH and 20, 37 ℃ respectively with the same glucose and VSS in vials. Results showed that there are different influences on the activity of acidogenic bacteria at varied pH and result in a variety of amount of hydrogen production, specific hydrogen production and VFA production, etc. Through the present study, when nonmalized to the weight of VSS, a maximal biogas and hydrogen production of 1 717 1 ml/g and 870 0 ml/g were obtained when pH equals 9 at 37 ℃ and 679 00 ml/g of biogas, 246 35 ml/g of hydrogen were also got when pH equals 5 at 20 ℃ respectively. The maximal specific hydrogen production (SHA) was 116 56 ml/h,g around 8 of pH value at 37 ℃ and 6 46 ml/h,g around 4 of pH value at 20 ℃, which were obtained by calculating the slope of the accumulated hydrogen gas via time. Butyric acid fermentation was important for hydrogen production. Large quantity of unknown COD was found in the vials when a small quantity of bio-gas was produced, but relative less unknown COD was determined when there was large quantity of hydrogen produced. This revealed a better engineering foreground for application of hydrogen bio-production.

Isolation of Dental Caries Bacteria from Dental Plaque and Effect of Tooth Pastes on Acidogenic Bacteria

Destruction of calcified tissue was caused by acids which are by product of carbohydrate metabolism of acidogenic bacteria consequent to dental caries. The purpose of this study was to assess the existence of acidogens potentially causing the dental caries and comparatively evaluation of efficacy of different toothpastes. The dental plaques of fifty persons belong to three age groups (1 - 20, 21 - 40, 41 - 60 year and above) were examined to identify microorganisms by the culture method. Thirty nine bacteria were isolated by spread plate method on BSMY I minimal media. Thirteen out of thirty nine, acidogens colonized in the dental plaques. Seven potentially acidogens CD17, CD26, CD27, CD28, CD29, CD34 and CD35 were treated with five different toothpastes. Inhibition effect of Triclosan and Fluoride containing tooth pastes were found more efficient. The results of the present study revealed that bacteria that commonly cause dental caries colonized in dental plaques of children and alcoholic person. Therefore, dental plaques must be considered a specific reservoir of colonization and subsequent dental caries. To reduce the dental problem triclosan and fluoride containing product should be recommended.

Valorisation of industrial hemp (Cannabis sativa L.) residues and cheese whey into volatile fatty acids for single cell protein production

The production of single cell protein(SCP)using lignocellulosic materials stands out as a promising route in the circular bioeconomy transition.However,multiple steps are necessary for lignocellulosics-to-SCP processes,involving chemical pretreatments and specific aerobic cultures.Whereas there are no studies that investigated the SCP production from lignocellulosics by using only biological processes and microbial biomass able to work both anaerobically and aerobically.In this view,the valorisation of industrial hemp(Cannabis sativa L.)biomass residues(HBRs),specifically hurds and a mix of leaves and inflorescences,combined with cheese whey(CW)was investigated through a semi-continuous acidogenic co-fermentation process(co-AF).The aim of this study was to maximise HBRs conversion into VFAs to be further used as carbon-rich substrates for SCP production.Different process conditions were tested by either removing CW or increasing the amount of HBRs in terms of VS(i.e.,two and four times)to evaluate the performance of the co-AF process.Increasing HBRs resulted in a proportional increase in VFA production up to 3115 mg HAc L^(-1),with experimental production nearly 40%higher than theoretical predictions.The synergy between HBRs and CW was demonstrated,proving the latter as essential to improve the biodegradability of the former.The produced VFAs were subsequently tested as substrates for SCP synthesis in batch aerobic tests.A biomass concentration of 2.43 g TSS L^(-1) was achieved with a C/N ratio of 5.0 and a pH of 9.0 after two days of aerobic fermentation,reaching a protein content of 42%(g protein per g TSS).These results demonstrate the overall feasibility of the VFA-mediated HBR-to-SCP valorisation process.

The role of lipids in fermentative propionate production from the co-fermentation of lipid and food waste

Food waste(FW)is a promising renewable low-cost biomass substrate for enhancing the economic feasibility of fermentative propionate production.Although lipids,a common component of food waste,can be used as a carbon source to enhance the production of volatile fatty acids(VFAs)during co-fermentation,few studies have evaluated the potential for directional propionate production from the co-fermentation of lipids and FW.In this study,co-fermentation experiments were conducted using different combinations of lipids and FW for VFA production.The contributions of lipids and FW to propionate production,hydrolysis of substrates,and microbial composition during.cofermentation were evaluated.The results revealed that lipids shifted the fermentation type of FW from butyric to propionic acid fermentation.Based on the estimated propionate production kinetic parameters,the maximum propionate productivity increased significantly with an increase in lipid content,reaching 6.23 g propionate/(L·d)at a lipid content of 50%.Propionate-producing bacteria Prevotella,Veillonella,and norank f Propionibacteriaceae were enriched in the presence of lipids,and the succinate pathway was identified as a prominent fermentation route for propionate production.Moreover,the Kyoto Encyclopedia of Genes and Genomes functional annotation revealed that the expression of functional genes associated with amino acid metabolism was enhanced by the presence of lipids.Collectively,these findings will contribute to gaining a better understanding of targeted propionate production from FW.

Mechanism and controlling strategy of the production and accumulation of propionic acid for anaerobic wastewater treatment

The production and accumulation of propionic acid affect significantly anaerobic wastewater treatment system, but the reasons are not approached until now. Based on the results of continuous-flow tests and the analysis of biochemistry and ecology, two mechanisms of producing propionic acid have been put forward. It is demonstrated that the reasons of propionic acid production and accumulation are not caused by higher hydrogen partial pressure. The combination of specific pH value and ORP is the ecological factor affecting propionic acid production, and the equilibrium regulation of NADH/NAD+ ratio in cells is the physiological factor. Meanwhile, it is put forward that using the two-phase anaerobic treatment process and the ethanol type fermentation in anaerobic reactor to avoid propionic acid accumulation are efficient methods.

Waste activated sludge treatment based on temperature staged and biologically phased anaerobic digestion system

The concept of temperature staged and biological phased （TSBP） was proposed to enhance the performance of waste-activated sludge anaerobic digestion. Semi-continuous experiments were used to investigate the effect of temperature （35 to 70℃） as well as the hydraulic retention time （HRT） （2, 4 and 6 days） on the acidogenic phase. The results showed that the solubilization degree of waste- activated sludge increased from 14.7% to 30.1% with temperature increasing from 35 to 70℃, while the acidification degree was highest at 45℃ （17.6%）, and this was quite different from the temperature impact on hydrolysis. Compared with HRT of 2 and 6 days, 4 days was chosen as the appropriate HRT because of its relatively high solubilization degree （24.6%） and acidification degree （20.1%） at 45℃. The TSBP system combined the acidogenic reactor （45℃, 4 days） with the methanogenic reactor （35℃, 16 days） and the results showed 84.8% and 11.4% higher methane yield and volatile solid reduction, respectively, compared with that of the single-stage anaerobic digestion system with HRT of 20 days at 35℃. Moreover, different microbial morphologies were observed in the acidogenic- and methanogenic-phase reactors, which resulted from the temperature control and HRT adjustment. All the above results indicated that 45℃ was the optimum temperature to inhibit the activity of methanogenic bacteria in the acidogenic phase, and temperature staging and phase separation was thus accomplished. The advantages of the TSBP process were also confirmed by a full-scale waste-activated sludge anaerobic digestion project which was an energy self-sufficient system.

The effect of decreasing alkalinity on microbial community dynamics in a sulfate-reducing bioreactor as analyzed by PCR-SSCP

PCR-single-strand conformation polymorphism (SSCP) and Southern blotting tech-niques were adopted to investigate microbial community dynamics in a sulfate-reducing bioreactor caused by decreasing influent alkalinity. Experimental results indicated that the sulfate-removal rate approached 87% in 25 d under the conditions of influent alkalinity of 4000 mg/L (as CaCO3) and sul-fate-loading rate of 4.8 g/(L·d), which indicated that the bioreactor started up successfully. The analy-sis of microbial community structure in this stage showed that Lactococcus sp., Anaerofilum sp. and Kluyvera sp. were dominant populations. It was found that when influent alkalinity reduced to 1000 mg/L, sulfate-removal rate decreased rapidly to 35% in 3 d. Then influent alkalinity was increased to 3000 mg/L, the sulfate-removal rate rose to 55%. Under these conditions, the populations of Dysgo-nomonas sp., Sporobacte sp., Obesumbacterium sp. and Clostridium sp. got to rich, which predomi-nated in the community together with Lactococcus sp., Anaerofilum sp. and Kluyvera sp. However, when the alkalinity was decreased to 1500 mg/L, the sulfate-removal rate rose to and kept stable at 70% and populations of Dysgonomonas sp., Sporobacter sp. and Obesumbacterium sp. died out, while some strains of Desulfovibrio sp. and Clostridium sp. increased in concentration. In order to determine the minimum alkalinity value that the system could tolerate, the influent alkalinity was de-creased from 1500 to 400 mg/L secondly. This resulted in the sulfate-removal rate, pH value and ef-fluent alkalinity dropping quickly. The amount of Petrotoga sp., Prevotella sp., Kluyvera sp. and Neisseria sp. reduced obviously. The result data from Southern blotting indicated that the amount of sulfate-reducing bacteria (SRBs) decreased with influent alkalinity dropping. Analysis of the microbial community structure and diversity showed that the SRBs populations were very abundant in the in-oculated activated sludge and the alkalinity decrease caused the reduction of the populations noted. Most of resident populations in the bioreactor were fermentative acidogenic bacteria (FABs), among which the phylum Firmicute was in the majority, but SRBs were very few. This community structure demonstrates the cooperation between SRBs and FABs, which sustains the system’s high sul-fate-removal and operation stability.

Potassium ferrate pretreatment promotes short chain fatty acids yield and antibiotics reduction in acidogenic fermentation of sewage sludge

During the acidogenic fermentation converting waste activated sludge (WAS) into shortchain fatty acids (SCFA), hydrolysis of complex organic polymers is a limiting step and the transformation of harmful substances (such as antibiotics) during acidogenic fermentation is unknown. In this study, potassium ferrate (KFeO) oxidation was used as a pretreatment strategy for WAS acidogenic fermentation to increase the hydrolysis of sludge and destruct the harmful antibiotics. Pretreatment with KFeOcan effectively increase the SCFA production during acidogenic fermentation and change the distribution of SCFA components.With the dosage of 0.2 g/g TS, the maximum SCFA yield was 4823 mg COD/L, which is 28.3times that of the control group;acetic acid accounts for more than 90% of the total SCFA. The higher dosage (0.5 g/g TS) can further increase the proportion of acetic acid, but inhibit the overall performance of SCFA production. Apart from the promotion of hydrolysis and acidogenesis, KFeOpretreatment can also simultaneously oxidizes and degrades part of the antibiotics in the sludge. When the dosage is 0.5 g/g TS, the degradation efficacy of antibiotics is the most significant, and the contents of ofloxacin, azithromycin, and tetracycline in the sludge are reduced by 69%, 42%, and 50%, respectively. In addition, KFeOpretreatment can also promote the release of antibiotics from sludge flocs, which is conducive to the simultaneous degradation of antibiotics in the subsequent biological treatment process.

New insights into the evaluation of anaerobic properties of sludge:Biodegradability and stabilization

Evaluating anaerobic biodegradability of sludge and then identifying the stabilization of digestate is necessary in sludge treatment and disposal.48 sludge samples from 24 typical waste water treatment plants(WWTPs)in 11 provinces in China were selected to investigate the relationship between Biochemical Acidogenic Potential(BAP)test and Biochemical Methane Potential(BMP)test.The volatile fatty acid(VFA)production obtained from BAP tests was found linearly related to the ultimate methane production from corresponding BMP tests.Satisfying results were obtained with Pearson correlation coefficient as 0.929 and R^2 value as 0.76.Furthermore,the physio-chemical characteristics(FCI,SUVA254,E 4/E 6)of supernatant,which were associated with humic-like substances(HS),were investigated before and after BMP tests.Through which a new criterion(FCI>1.50,SUVA 254>1.10,E 4/E 6<4.0)was proposed to evaluate the stabilization level of anaerobic digested sludge.

PICRUSt2 functionally predicts organic compounds degradation and sulfate reduction pathways in an acidogenic bioreactor

For comprehensive insights into the influences of sulfate on performance,microbial community and metabolic pathways in the acidification phase of a two-phase anaerobic system,a laboratory-scale acidogenic bioreactor was continuously operated to treat wastewater with elevated sulfate concentrations from 2000 to 14000 mg/L.The results showed that the acidogenic bioreactor could achieve sulfate reduction efficiency of greater than 70%for influent sulfate content less than 12000 mg/L.Increased sulfate induced the accumulation of volatile fatty acids(VPAs),especially propionate and butyrate,which was the primary negative effects to system performance under the high-sulfate environment.High-throughput sequencing coupled with PICRUSt2 uncovered that the accumulation of VFAs was triggered by the decreasing of genes encoding short-chain acyl-CoA dehydrogenase(EC:1.3.8.1),regulating the transformation of propanoyl-CoA to propenoyl-CoA and butanoyl-CoA to crotonyl-CoA of propionate and butyrate oxidation pathways,which made these two process hardly proceed.Besides,genes encoding(EC:1.3.8.1)were mainly carried by order Clostridiales.Desulfovibrio was the most abundant sulfate-reducing bacteria and identified as the primary host of dissimilatory sulfate reduction ftinctional genes.Functional analysis indicated the dissimilatory sulfate reduction process predominated under a low sulfate environment,but was not favored under the circumstance of high-sulfate.With the increase of sulfate,the assimilatory sulfate reduction process finally overwhelmed dissimilatory as the dominant sulfate reduction pathway in acidogenic bioreactor.

Acidogenic sludge fermentation to recover soluble organics as the carbon source for denitrification in wastewater treatment： Comparison of sludge types

For biological nitrogen （N） removal from wastewater, a sufficient organic carbon source is requested fbr denitrification. However. the organic carbon/nitrogen ratio in municipal wastcwatcr is becoming lower in recent years, which increases the demand for the addition of external organic carbon, e.g. methanol, in wastewater treatment. The volatile fatty acids （VFAs） produced by acidogenic fenncntation of sewage sludge can be an attractive alternative for methanol. Chemically enhanced primary sedimentation （CEPS} is an effective process that applies chemical coagulants to enhance the removal of organic pollutants and phosphorus from wastewater by sedimentation. In temls of the chemical and biological characteristics, the CEPS sludge is considerably different from the conventional primary and secondary sludge. In the present study, FeCI3 and PACI （polyalunfinum chloride） were used as the coagulants for CEPS treatment of raw sewage. The derived CEPS sludge （Fe-sludge and Al-sludge） was then processed with mcsophilic acidogenic fennentation to hydrolysc the solid organics and produce VFAs for organic carbon recovery, and the sludge acidogenesis efficiency was compared with that of the conventional primary sludge and secondary sludge. The results showed that the Fe-sludge exhibited the highest hydrolysis and acidogenesis efficiency, while the Al-sludge and secondary＇ sludge had lower hydrolysis efficiency than that of primary sludge. Utilizing ffie Fc-sludgc fermentation liquid as tbc carbon source for denitrificatiom more than 99%of nitrate removal was achieved in the main-stream wastewater treatment without any external carbon addition, instead of 35% obtained from the conventional process of primary sedimentation followed by the oxic/anoxic （O/A） treatment.

Efficient treatment of azo dye containing wastewater in a hybrid acidogenic bioreactor stimulated by biocatalyzed electrolysis

In this study, a novel scaled-up hybrid acidogenic bioreactor（HAB） was designed and adopted to evaluate the performance of azo dye（acid red G, ARG） containing wastewater treatment. Principally, HAB is an acidogenic bioreactor coupled with a biocatalyzed electrolysis module. The effects of hydraulic retention time（HRT） and ARG loading rate on the performance of HAB were investigated. In addition, the influent was switched from synthetic wastewater to domestic wastewater to examine the key parameters for the application of HAB. The results showed that the introduction of the biocatalyzed electrolysis module could enhance anoxic decolorization and COD（chemical oxygen demand） removal. The combined process of HAB-CASS presented superior performance compared to a control system without biocatalyzed electrolysis（AB-CASS）. When the influent was switched to domestic wastewater, with an environment having more balanced nutrients and diverse organic matters, the ARG, COD and nitrogen removal efficiencies of HAB-CASS were further improved, reaching 73.3% ± 2.5%, 86.2% ± 3.8% and 93.5% ± 1.6% at HRT of 6 hr, respectively, which were much higher than those of AB-CASS（61.1% ± 4.7%,75.4% ± 5.0% and 82.1% ± 2.1%, respectively）. Moreover, larger TCV/TV（total cathode volume/total volume） for HAB led to higher current and ARG removal. The ARG removal efficiency and current at TCV/TV of 0.15 were 39.2% ± 3.7% and 28.30 ± 1.48 mA,respectively. They were significantly increased to 62.1% ± 2.0% and 34.55 ± 0.83 mA at TCV/TV of 0.25. These results show that HAB system could be used to effectively treat real wastewater.