COD Conversion Research Articles

Uncovering the mechanisms of ethanol stimulation on magnetite-enhanced anaerobic process treating oxytetracycline contained wastewater

Magnetite has been proved to facilitate direct interspecies electron transfer (DIET)-based syntrophys and might alleviate inhibitory effects of antibiotics in anaerobic digestion (AD), while feeding ethanol was an effective approach to enrich the DIET partners. However, most of the existing studies were conducted at fixed ethanol concentration, few attentions were paid on the effects of differential ethanol proportion on AD, the underlying roles and mechanisms of ethanol stimulation remains unclear. This study systematically investigated the impact of ethanol stimulation on anaerobic processes treating oxytetracycline (OTC)-contaminated wastewater at varying proportions (20%, 50%, and 80%, based on equivalent COD value). In the presence of magnetite, ethanol stimulation promoted the methane production from 244.9 mL/g COD to a maximum 434.2 mL/g COD, with the most pronounced enhancement observed at high ethanol proportions. In particular, the average methane production obtained at 50% and 80% ethanol was 328.5 and 297.7 mL/g COD, respectively, whereas the enhancement of 20% ethanol stimulation was relatively limited. Concurrently, more stable COD removal and OTC reduction was noted in the existence of both magnetite and high ethanol proportions. Microbial analysis revealed the pivotal roles of Methanosaeta, alongside the predominance of Methanobacterium, in regulating COD conversion and driving methanogenesis through the CO2 reduction pathway. Notably, high ethanol proportions fostered the enrichment of exoelectrogens (Geobacter, Desulfovibrio) in the magnetite-amended system, accompanied by the up-regulation of genes involved in organic metabolism pathways. Further investigation of functional genes highlighted the prevalence of pilA enrichment in the magnetite-amended system at low ethanol proportions, whereas omcS became more abundant at high ethanol proportions.

Unlocking potential: Exploring the methane production potential in anaerobic co-digestion of cassava wastewater and glycerol

This study aimed at evaluating the feasibility of CH4 production in a mesophilic (30 °C) single-stage anaerobic co-digestion of cassava wastewater (CW) and glycerol in an anaerobic fluidized bed reactor (AFBR) with mixing ratio of 50 % / 50 % CW/Gly on a (chemical oxygen demand)COD basis. Thus, the following strategy was used: increasing the organic loading rate (OLR) (1–20 g COD.L−1.d−1) by increasing the substrate concentration (1–20 g COD.L−1) and applying a hydraulic detention time (HRT) of 24 h. The AFBR presented a maximum methane (CH4) content of 88.38±1.94 % and a CH4 yield (MY) of 293.48±18.37 mL of CH4.mL−1CODrem in the OLR of 1 g COD.L−1.d−1 and the maximum methane production rate (MPR) of 62.09±2.75 mL of CH4.L−1.h−1 in the OLR of 20 g COD.L−1.d−1. The conversion of glycerol and carbohydrates remained above 91±0.54 % and 82±2.79 %, respectively, and the COD conversion was above 80±0.65 %. The main metabolites were HAc, HPr, HBu, EtOH and HVa. The most abundant genera identified in the AFBR were Izemoplasmatales and Enterobacteriaceae for the bacteria domain, and Methanosaeta, Methanobacterium for the archaea domain. The single-stage system is robust and can operate with higher OLR without reducing the efficiency of wastewater treatment and CH4 production.

Bisphenol A affects microbial interactions and metabolic responses in sludge anaerobic digestion.

The widespread use of bisphenol A (BPA) has resulted in the emergence of new pollutants in various environments, particularly concentrated in sewage sludge. This study investigated the effects of BPA on sludge anaerobic digestion, focusing specifically on the interaction of microbial communities and their metabolic responses. While the influence of BPA on methane accumulation is not significant, BPA still enhanced the conversion of soluble COD, protein, and polysaccharides. BPA also positively influenced the hydrolysis-acidogenesis process, leading to 17% higher concentrations of volatile fatty acids (VFAs). Lower BPA levels (0.2-0.5mg/kg dw) led to decreased hydrolysis and acidogenesis gene abundance, indicating metabolic inhibition; conversely, higher concentrations (1-5mg/kg dw) increased gene abundance, signifying metabolic enhancement. Diverse methane metabolism was observed and exhibited alterations under BPA exposure. The presence of BPA impacted both the diversity and composition of microbial populations. Bacteroidetes, Proteobacteria, Firmicutes, and Chloroflexi dominated in BPA-treated groups and varied in abundance among different treatments. Changes of specific genera Sedimentibacter, Fervikobacterium, Blvii28, and Coprothermobacter in response to BPA, affecting hydrolysis and acetogenesis. Archaeal diversity declined while the hydrogenotrophic methanogen Methanospirillum thrived under BPA exposure. BPA exposure enabled microorganisms to form structured community interaction networks and boost their metabolic activities during anaerobic digestion. The study also observed the enrichment of BPA biodegradation pathways at high BPA concentrations, which could interact and overlap to ensure efficient BPA degradation. The study provides insights into the digestion performance and interactions of microbial communities to BPA stress and sheds light on the potential effect of BPA during anaerobic digestion.

Continuous flow degradation of Orange II by a dandelion-like NiCo2O4/NF activated peroxymonosulfate in a fixed-bed system

A novel dandelion-like catalyst, nickel foam supported NiCo2O4 (NiCo2O4/NF), was successfully synthesized and applied to the activation of peroxymonosulfate (PMS) in a fixed bed system for the degradation of Orange II (OII). The physicochemical properties of synthesis catalysts were identified by various characterization methods (SEM, EDS, XRD and XPS), revealing that the dandelion-like NiCo2O4 nanosheets were evenly distributed on the surface of NF. NiCo2O4/NF-250 showed excellent catalytic performance at a hydrothermal reaction time of 8 h, urea/metal ratio of 10:1, and Co/Ni concentration of 10 mM/5 mM. When PMS concentration was 5 mM, reaction temperature was 50 ℃, pH was 7.5, space velocity was 0.236 min−1, the conversion ratios of OII, PMS and COD were 99.8 %, 71.3 %, and 71.4 % at 240 min, respectively. In particular, NiCo2O4/NF still could reach 99.9 % OII conversion and 64.4 % COD conversion in the third cycle. DFT calculations implied that NiCo2O4/NF had excellent PMS activation performance.

Facile synthesis of NaA zeolite supported Co2Fe1 for highly efficient degradation of Acid Orange 7 by activation of peroxymonosulfate.

The development of heterogeneous Co-based catalysts with an effective combination mode of Co/Fe and supporter, a facile synthetic method, and a low treatment cost is an important environment challenge for azo dyes degradation by peroxymonosulfate (PMS) activation. In this study, NaA zeolite supported CoxFey with various molar ratio of Fe/Si and Co/Fe was synthesized by a facile hydrothermal process, and used to activate PMS for Acid Orange 7 (AO7) degradation. NaA zeolite supported Co2Fe1 with the Fe/Si molar ratio of 1:10 showed superior catalytic performance compared with other NaA zeolite supported CoxFey. In a system containing 0.6g/L catalysts, 4mM PMS, pH 5 and T = 30℃, 95.8% AO7 and 79.1% COD conversion could be achieved at 20 and 60min, respectively, and the first order kinetic rate constant reached 0.14795min-1. Moreover, NaA zeolite supported Co2Fe1/PMS system exhibited excellent catalytic effect in a wide pH range of 3-9. Temperature had an obvious effect on AO7 degradation, and the activation energy was 31.36kJ/mol. HCO3- demonstrated an obvious depression on AO7 degradation, while Cl-, SO42- and H2PO4- had a relatively poor impact. Quenching experiments showed that both sulfate radicals ([Formula: see text]) and hydroxyl radicals (·OH) were generated in the PMS reaction system, and the [Formula: see text] was the dominant active radical. During 3 cycles experiments, an acceptable AO7 conversion ratio (91.8%) within 30min arrived, suggesting the good stability of NaA zeolite supported Co2Fe1.

Study on Assessment and Feasibility of Hythane From POME to Improve Power Plant Performance

Biogas power plant from POME is getting trendier because Indonesia is the largest palm oil producer in the world as the amount of palm oil production produces more POME and has a high COD. COD is commonly used as a base stoichiometry calculation for CH4 conversion. Correction on COD conversion for biogas production was done by considering CO2 rather than CH4 only. Combining H2 with CH4 is a worthy breakthrough because it can increase by 15% of electricity output. Such H2 and CH4 mixing has some advantages on the unique combustion property of H2 in CH4 (hythane). Economic analysis comparison on this mixing of biogas and conventional biogas was assessed to see the improvement because of an increase in LHV value in biogas. Based on previous experiments conducted by cascading H2 and followed by CH4 production, with an H2 in CH4 ratio of 1:3, an economic analysis was calculated according to an industry capacity of 60 tonnes FFB/hour. A previous biogas power plant needed an investment of $1,502,000 for 1.35 MWe, but $400,000 was later invested for 1.59 MWe by hythane, increasing 15%. The investment performance of this power plant gave IRR 43.96%, 9.95% higher, and low BEP, 34%. The biogas power plant is economically safe, does not suffer from losses even produces only 34% capacity. The payback period was 2.6 years, seven months shorter. In conclusion, an additional one bioreactor on the existing power plant is economically feasible.

High-solid co-digestion performance of lipids and food waste by mesophilic hollow fiber anaerobic membrane bioreactor

The co-digestion performance of mesophilic (37℃) hollow fiber anaerobic membrane bioreactor (HF-AnMBR) in treating high-solid lipids and food waste (FW) for 180 days was investigated. The organic loading rate (OLR) was increased from 2.33 to 14.64 g-chemical oxygen demand (COD) /L/d by increasing the lipids/FW from 10%, 30%, and 50% on dry based. The COD conversion efficiency for methane was 83.13%, 84.85%, 82.63%, and 84.30%, and the sludge growth rate was 0.001, 0.097, 0.065, 0.016 g TS/g COD at OLR of 2.33, 9.36, 12.76 and 14.64 g-COD/L/d, respectively. The COD, proteins, and carbohydrates concentrations in permeate were stable, with an average of 2.25, 0.50, and 0.18 g/L, respectively. The long-term stable performance of the HF-AnMBR indicated that this study will help guide application of the co-digestion of lipids and food waste.

Treatment of beauty salon effluents using advanced oxidative electrochemical processes with boron-doped diamond anode

Beauty salons constitute a growing economic sector that is responsible for the release of effluents containing a diversity of pollutant compounds. This work proposes the local treatment of beauty salon effluent (BSE), with the aim of decentralizing the treatment process and avoiding increasing the organic load at municipal effluent treatment stations. The processes of electrochemical oxidation (EO) and simultaneous EO with electrogenerated H2O2 (EO/H2O2) were applied using different anode/cathode electrode pairs: BDD/stainless steel and BDD/GDE. Investigation was made of the influence of salts on the generation of oxidants in different support electrolytes, using the N,N-dimethyl-4-nitrosoaniline (pNDA) decoloration technique. The presence of active chlorine species was shown to influence the global oxidizing power. The BSE was characterized and the conversion rate of the organic load was monitored during 180 min of the processes. For the EO/H2O2 process, without adjustment of the initial pH, the COD conversions in 120 min were 43%, 63% and 69%; with the initial pH adjusted to 3.0 were 53%, 73%, and 78%, for the three different current densities evaluated. Regarding EO/H2O2 process, without pH adjustment, DOC have also a greater reduction reaching in 120 min 33%, 48%, and 73%, for 15, 38 and 62 mA cm−2, respectively. The lowest energy consumptions were 0.002, 0.005 and 0.006 kWh g COD−1, applying 15, 38, and 62 mA cm−2, respectively, with pH adjustment in the EO/H2O2 process. The results showed that the lowest energy consumption and the greatest reduction of the BSE organic load were achieved using the EO/H2O2 process.

Long term operation performance and membrane fouling mechanisms of anaerobic membrane bioreactor treating waste activated sludge at high solid concentration and high flux

High solid anaerobic membrane bioreactor (HSAnMBR) is widely applied in biomass treatment and energy regeneration, while membrane operation performance and membrane fouling control remain critical issues. In this study, a HSAnMBR was utilized for waste activated sludge (WAS) treatment at organic loading rates of 3.69–3.72 gCOD/L·d and biogas yield was ranged in 0.38–0.39 L/gVSfed with the COD conversion efficiency of 40 %. The membrane operated stably when the average flux was 9.6, 4.5 and 1.2 L/m2/h at mixed liquor total solid of 25, 30 and 40 g/L with a filtration: relaxation of 4:1, 1:1 and 1:2, respectively. The distinctive characteristics of membrane fouling at high solid condition were that the polysaccharides and proteins had high fouling propensity and were the main composition of the foulant layer. Furthermore, phosphorus and magnesium were the predominant causes of inorganic fouling. The minerals precipitated on the membrane and were embedded into membrane pores, contributing to cake layer formation and pore blocking. This research provided a comprehensive analysis of the membrane operation characterization and fouling mechanisms of HSAnMBR, which was expected to push forward HSAnMBR applications to WAS treatment.

Deactivation characteristics of Ce-modified Cu-based carbon materials for catalytic wet air oxidation of phenol wastewater

In this paper, Ce-modified Cu-based carbon materials (Cu-Ce/AC) were prepared by impregnation method using walnut shell as the carbon precursor, Cu-ammonia solution as Cu source and Ce as modifier. The catalytic wet air oxidation (CWAO) degradation of phenol wastewater was carried out in a self-assembled fixed-bed reactor. The stability of Cu-Ce/AC catalyst under different pH conditions was studied. This study combines XRD, BET, FT-IR, ICP-OES and XPS characterization techniques to study the main reasons for the deactivation of Cu-Ce/AC catalysts. The reaction mechanism of Cu-Ce/AC catalytic wet air oxidation degradation of phenol was clarified. The result indicates that although phenol was completely converted in the CWAO process, the acidic intermediate product produced were difficult to completely degraded. Therefore, the pH of the solution gradually decreased. In acidic environment, the interaction between active component Cu and carbon carrier is weak, resulting in a large amount of metal leaching into the solution. As a result, the COD conversion gradually decreases. The alkaline environment can effectively slow down the leaching of catalyst Cu while maintaining its high catalytic activity. In addition, the incompletely degraded intermediate products are easy to accumulate and deposit on the Cu-Ce/AC surface, block the micropores and cover the surface-active sites, which reduces the catalyst activity. The study also found that there is a redox cycle between Cu+, Cu2+ Ce3+ and Ce4+ during phenol degradation, which enables Cu and Ce to form a strong interaction. The redox cycle can also promote the formation of oxygen vacancy (h+), O2−·, and HO·, making the degradation of phenol more thorough. At the same time, the mutual conversion between metal lattice oxygen and surface chemisorbed oxygen can generate high concentration of oxygen defect sites, which can improve the oxygen storage capacity of Cu-Ce/AC. These oxygen vacancies also provide more reactive sites to further promote adsorption and catalytic oxidation degradation of phenol and intermediate products.

Preparation and testing of low-cost bioadsorbents for improving the anaerobic digestion of post-hydrothermal liquefaction wastewater (PHWW)

There are currently several promising technologies for the removal of toxic compounds from wastewater; most of them are expensive or require sophisticated equipment. Thus, this study proposes that peanut shells be used as low-cost bioadsorbents for the removal of organic matter (COD) and ammoniacal nitrogen (NH4+-N) from Spirulina hydrothermal liquefaction wastewater (PHWW). Additionally, anaerobic digestion (AD) was used as a biological treatment for pretreated PHWW (by adsorption) to promote additional organic matter removal while recovering energy in the form of methane. In this way, native (PB) and modified (APB) forms of peanut shell bioadsorbents were investigated. APB was activated using NaOH and HCl. For comparison, granular activated carbon (GAC) was chosen as the standard. The adsorbate-PHWW was obtained by using 20% solids (w/v) in the hydrothermal liquefaction (HTL) of Spirulina at 260 °C for 60 min. Response surface methodology (RSM) was used to explore and optimize the effect of various adsorption parameters, such as temperature, pH, and adsorbent dosage. Biochemical potential (BMP) tests were conducted under mesophilic conditions. In adsorption assays, PB was found to be more efficient at removing NH4+-N, while APB and GAC achieve higher COD removal percentages. In comparison to untreated PHWW, bioadsorption promoted higher efficiency phenol removal and COD conversion to methane during BMP tests. The anaerobic processes that followed APB and PB adsorption significantly removed more COD than the process fed with GAC-pretreated PHWW. These results established the feasibility of using peanut shells as bioadsorbents in the pretreatment of PHWW, which resulted in an increase in biogas/methane yield.

Production of caproic acid from acetate and ethanol through microbial chain elongation: A techno-economic assessment

Over the past years, microbial chain elongation has received increased attention as a way to produce high value products. This study investigates the economic feasibility of converting ethanol and acetate into caproic acid, using pertraction-based continuous product removal. Feedstock cost, CAPEX and electricity consumption were identified as being the most important cost factors. It was found that the system performance achieved at pilot scale (productivity of 2.5 g/L·d, COD conversion efficiency of 50%) is insufficient to make the process competitive with current market prices. Higher productivity levels could not be achieved experimentally, as when additional inputs were fed to the system these remained largely unconverted. This suggests that the main constraint lies at the fermentation side.

Biohydrogen production from diluted-acid hydrolysate of rice straw in a continuous anaerobic packed bed biofilm reactor

Bio-hydrogen production in a continuously operated anaerobic packed bed biofilm reactor (APBR) using acid-hydrolysate of rice straw as feedstock and inoculated with an anaerobic mesophilic sludge from a municipal wastewater treatment plant was investigated at three different HRTs (17, 8.2 and 2 h). Fermentable sugars solution achieved from a two-stage diluted acid hydrolysis of rice straw was used as the feedstock. First, rice straw was treated with 1% w v−1 sulfuric acid at 120 °C for 30 min with a yield of 58.5% xylose. Higher temperature of 180 °C for 10 min at 0.5% w v−1 sulfuric acid was applied in the second stage in which cellulosic crystalline structure was partially depolymerized to glucose with a yield of 19.3% glucose. Hydrogen production rate and yield were enhanced as the hydraulic retention time was decreased with a maximum production rate of 252 mL L−1 h−1 and yield of 1 mol H2 mol−1 sugar consumed at 2 h HRT. Experimental results illustrated the increase of COD conversion from 44% to 47% by shortening the HRT from 17 to 2 h. Furthermore, acetic acid and butyric acid production were reduced slower than other soluble metabolites like ethanol.

Effect of pH on lactic acid fermentation of food waste using different mixed culture inocula

AbstractBACKGROUNDIncreasing amounts of food waste (FW) have become a critical problem in the last few decades. Sustainable methods to limit the impact of FW on the environment are required. FW valorisation through lactic acid (LA) fermentation can assist by producing a valuable commodity from a cheap substrate. LA is a chemical with increasing market potential, it is used in several industrial sectors, and it is the main component of polylactic acid bioproducts.RESULTSThe role of pH on LA production from FW was tested with three anaerobic inocula and a control with solely FW. The most suitable condition for LA production was at pH < 4. The best results in terms of final LA concentration (1.8 gCOD L–1), yield (224 mgCOD/gVS), and COD conversion (50%) were found in uncontrolled pH conditions with no external inoculum addition. FW already has a good abundance of LA bacteria that are responsible for lactate production. Among the external inocula supplied, primary sludge best enabled LA accumulation at a high concentration (1.3 g COD L–1) and yield (167 mgCOD/gVS).CONCLUSIONThis study demonstrates that the reactor pH is a key factor to stimulate LA acid fermentation and its accumulation. Under acidic conditions, LA accumulated in the system instead of being converted to volatile fatty acids (VFAs); this was likely due to the inhibition of the microbial community responsible for VFAs production. Uncontrolled pH condition impacts positively the overall fermentation cost since the alkalinizing agents used to keep pH neutral are not required and simplifies the downstream processes for LA extraction and purification. © 2021 Society of Chemical Industry (SCI).

Analysing the Management of Waste and Leachate in the Final Disposal Site of Indramayu

Garbage is waste material from household, commercial, industrial or other human activities. Waste generation is the volume of waste or the weight of waste generated from types of waste sources in a certain area per unit of time. The final destination of the waste is to be processed at the Final Processing Site (TPA). In Indramayu, the waste generation is quite large and can cause environmental pollution, so there is a need for good waste management. The purpose of this study is to determine the waste management system in TPA Indramayu, to determine the amount and average of waste, to determine the generation and volume of waste and to determine the levels of BOD, COD and effectiveness in the leachate treatment unit. From the results of observations, it was found that the average receipt of waste at TPA Indramayu was 177,451 tons/day. The waste generation is known to be 2.75 l/or/day and the resulting volume of waste that goes to the TPA is 777,284 m3/hr and the volume of waste per region is 0.003 m3/or/day. The incoming leachate comes from the landfill area and is then processed in the WWTP unit with 4 holding ponds to reduce BOD and COD levels. The initial BOD level entered was 500 mg/L and the incoming COD level was 4000 mg/L, after going through the leachate treatment the results obtained were BOD levels of 33.34 mg/L and COD levels of 266.66 mg/L with efficiency BOD and COD conversion of 93.33%.

Production of n-caproate using food waste through thermophilic fermentation without addition of external electron donors

The effectiveness of producing n-caproate from food waste without external electron donors (EDs) was investigated through batch and semi-continuous fermentation. The maximum concentration of n-caproate reached 10,226.28 mg COD/L during semi-continuous fermentation. The specificity for n-caproate was the highest at 40.19 ± 3.95%, and the soluble COD conversion rate of n-caproate reached up to 22.50 ± 1.09% at the end of batch fermentation. The production of n-caproate was coupled with the generation of lactate as an ED to facilitate chain elongation reactions. When lactate was used as the only substrate, n-butyrate (64.12 ± 20.11%) markedly dominated the products, instead of n-caproate (0.63 ± 0.07%). Microbial community analysis revealed that Caproiciproducens, Rummeliibacillus, and Clostridium_sensu_stricto_12 were the key genera related to n-caproate production. In addition to n-caproate, n-butyrate dominated the products in batch and semi-continuous fermentation with a maximum specificity of 47.59 ± 3.39%. Clostridium_sensu_stricto_7 was committed to producing n-butyrate from lactate.

Effect of feed-to-inoculum ratio on anaerobic digestibility of high-fat content animal rendering wastewater

Anaerobic treatment of high-fat content wastewater could produce significant methane yields, making anaerobic treatment a promising alternative to energy-consuming aerobic treatment. However, accumulated intermediate LCFA may inhibit the conversions of both SCFA to acetate and of acetate further to methane. The effect of feed-to-inoculum ratio was evaluated in biochemical methane potential (BMP) tests for anaerobic digestibility of animal rendering wastewater (RW). Results showed that more than 90% of RW COD was converted during BMP tests with volumetric feed-to-inoculum ratio of 1. Higher feed-to-inoculum ratios led to RW COD conversion efficiencies below 64% and caused lag periods of >6 days in methane production. Degradation of acetate at different time points in relation to conversion of LCFA suggested that LCFA accumulation partially hindered acetate utilization. The methanogenic community shifted from hydrogenotrophic to acetoclastic methanogenesis in moderately-loaded BMPs. At highest feed-to-inoculum ratio of 9, acetoclastic methanogens were severely inhibited. The bacterial genus Syntrophomonas was present in increasing relative abundance with increasing feed-to-inoculum ratio. Increased relative abundance of the genus Desulfovibrio with increasing feed-to-inoculum ratio was likely a response to the high sulfate concentration in RW.

MATHEMATICAL MODELS FOR ESTIMATING METHANE PRODUCTION IN COVERED LAGOON BIODIGESTERS TREATING PIG MANURE

Covered lagoon biodigesters (CLB) have been widespread in Brazil in the treatment of pig manure. However, the quantification of biogas production in CLB using mathematical models is still limited and scarce. This study aimed to evaluate and compare six mathematical models—Chen-Hashimoto (Chen, 1983), CETESB (2006), COD Conversion (Chernicharo, 2016), IPCC (2006), Deng (Deng et al., 2014), and modified Stover-Kincannon (Yu et al., 1998)—usually used to estimate methane (CH 4 ), and propose improvements to the models, if necessary. The results were compared with the monitored production (P actual ) in a farm with CLB using the t-test (α = 5%). The Chen-Hashimoto, IPCC, Deng, and modified Stover-Kincannon models showed no statistical difference compared to P actual (405.0 m 3 CH 4 d −1 ), whereas the CETESB and COD Conversion models presented no statistical difference after the proposed improvements. All models can be considered reliable for estimating volumetric methane production after the adaptations, being relevant tools for diagnosis and decision-making regarding the energy recovery of biogas with CLB operation in pig farms.

Increasing salinity concentrations determine the long-term participation of methanogenesis and sulfidogenesis in the biodigestion of sulfate-rich wastewater

The competition between sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) depends on several factors, such as the COD/SO42− ratio, sensitivity to inhibitors and even the length of the operating period in reactors. Among the inhibitors, salinity, a characteristic common to diverse types of industrial effluents, can act as an important factor. This work aimed to evaluate the long-term participation of sulfidogenesis and methanogenesis in the sulfate-rich wastewater process (COD/SO42− = 1.6) in an anaerobic structured-bed reactor (AnSTBR) using sludge not adapted to salinity. The AnSTBR was operated for 580 d under mesophilic temperature (30 °C). Salinity levels were gradually increased from 1.7 to 50 g-NaCl L−1. Up to 35 g-NaCl L−1, MA and SRB equally participated in COD conversion, with a slight predominance of the latter (53 ± 11%). A decrease in COD removal efficiency associated with acetate accumulation was further observed when applying 50 g-NaCl L−1. The sulfidogenic pathway corresponded to 62 ± 17% in this case, indicating the inhibition of MA. Overall, sulfidogenic activity was less sensitive (25%-inhibition) to high salinity levels compared to methanogenesis (100%-inhibition considering the methane yield). The wide spectrum of SRB populations at different salinity levels, namely, the prevalence of Desulfovibrio sp. up to 35 g-NaCl L−1 and the additional participation of the genera Desulfobacca, Desulfatirhabdium, and Desulfotomaculum at 50 g-NaCl−1 explain such patterns. Conversely, the persistence of Methanosaeta genus was not sufficient to sustain methane production. Hence, exploiting SRB populations is imperative to anaerobically remediating saline wastewaters.

Evaluation of electrical current production in microbial electrolysis cells fed with animal rendering wastewater

Anode-respiring bacteria (ARB) generate electrical current from the oxidation of short chain fatty acids (SCFA), primarily acetate, in microbial electrolysis cells (MECs). Animal rendering wastewater (RW) has high fat content, which under anaerobic conditions can yield acetate, making RW a potential feed for MECs. Yet, excess intermediate long chain fatty acids (LCFA) may limit conversion of LCFA and SCFA, and impact ARB activity. Here, we evaluated electrical current production in single-chamber MECs fed with RW. In RW-fed MECs, 34.26 ± 2.69% of the COD provided was converted to electrical current in an 80-day batch cycle. LCFA accumulated in RW-fed MECs, during which conversion of acetate to electrical current was limited. Diverse sulfate-reducing microorganisms were present in the anode biofilm in RW-fed MECs, whereas the genus Geobacter dominated in inoculum-only control MECs. Detection of H2-utilizing homoacetogens suggested some internal cycling of H2 produced at the cathode. Overall, this study shows that current production is possible from RW, but to be a viable process for RW treatment, further improvement in rates of COD conversion and current production is necessary along with identifying configurations and/or conditions in which the inhibitory effect of LCFA is reduced.