Anaerobic Wastewater Treatment Research Articles

Techno-economic assessment of microbial electrohydrogenesis integration to the fruit processing industry for hydrogen production

A hypothetical facility connected to a fruit processing plant is created to investigate the techno-economic potential of H2 production from residues and wastewater via electrohydrogenesis in a microbial electrolysis cell (MEC), using mixed microbial consortium obtained from the anaerobic wastewater treatment plant. Thermal pretreatment converts cellulose in the substrate into glucose, and deactivates methanogens present in the consortium. A Rhinohide membrane separates the cathode chamber from the anode chamber of the MEC, which requires an external power supply of 0.6 V. In this study, we determine an economically optimal utilization option for H2 and the by-product CO2 by investigating 6 scenarios. Of the 6 scenarios, the option involving the combustion of H2 in a gas engine to produce electricity and CO2 sale is the most financially feasible. Several economic analyses were performed to identify the cost drivers of the H2 production in the economically optimal scenario. Depending on the electricity cost and CO2 selling price, the financial feasibility of electrohydrogenesis-based H2 production process can be further improved.

Complex inhibitions on anaerobic degradation of monosodium glutamate in wastewater under low COD/sulfate ratios

To investigate the complex inhibitions leading to the deterioration of reactor performance in anaerobic treatment of monosodium glutamate (MSG) wastewater under low COD/sulfate ratios, a comprehensive assessment of the overall reactor performance, sludge characteristics and microbial community characteristics was conducted in this study. The COD removal rate of the reactor was maintained above 90% throughout the experiment, but the gas yield decreased by 52% due to the complex competition between sulfate-reducing bacteria (SRB) and methane-producing archaea (MPA) resulting in a decreasing number of MPA. The sludge characteristics and microbial community features indicated that the complex competition between SRB and MPA included competition for hydrogen and survival space in the reactor. In addition, the competitive advantage of SRB for electrons led to the production of more sulfides in the reactor, further inhibiting the activity of MPA. Therefore, the complex inhibition within the reactor for anaerobic treatment of MSG wastewater with low COD/sulfate ratios, including sulfide toxicity inhibition, competition between SRB and MPA for substrate and space, not only led to a reduction in gas production, but also affected microbial activity and glutamate degradation.

Biocatalyst developed with recovered iron-rich minerals enhances the biotransformation of SARS-CoV-2 antiviral drugs in anaerobic bioreactors

The biotransformation of the SARS-CoV-2 antiviral drugs, ribavirin and tenofovir, was studied in methanogenic bioreactors. The role of iron-rich minerals, recovered from a metallurgic effluent, on the biotransformation process was also assessed. Enrichment of anaerobic sludge with recovered minerals promoted superior removal efficiency for both antivirals (97.4 % and 94.7 % for ribavirin and tenofovir, respectively) as compared to the control bioreactor lacking minerals, which achieved 58.5 % and 37.9 % removal for the same drugs, respectively. Further analysis conducted by liquid chromatography coupled to mass spectroscopy revealed several metabolites derived from the biotransformation of both antivirals. Interestingly, tracer analysis with 13CH4 revealed that anaerobic methane oxidation coupled to Fe(III) reduction occurred in the enriched bioreactor, which was reflected in a lower content of methane in the biogas produced from this system, as compared to the control bioreactor. This treatment proposal is suitable within the circular economy concept, in which recovered metals from an industrial wastewater are applied in bioreactors to create a biocatalyst for promoting the biotransformation of emerging pollutants. This strategy may be appropriate for the anaerobic treatment of wastewaters originated from hospitals, as well as from the pharmaceutical and chemical sectors.

Improved methane production from anaerobic wastewater treatment by conductive zero-valent iron@carbon@polyaniline

In this study, a core-shell type ZVI@C@PANI nanoparticle was prepared and used as a novel conductive medium for electron transfer between bacteria and archaea of the anaerobic system. The synthesized nanocomposite had favorable biocompatibility and a conductivity of 4.89 S/cm, which made the nanocomposite a good transfer medium to achieve efficient methane production. And the enhanced methane production by adding ZVI@C@PANI in the anaerobic sludge had been investigated. The ZVI@C@PANI enhanced methane yield peaked at doses of 2 g/L. The result showed that methane production increased by 71.36% from the anaerobic system added with the ZVI@C@PANI compared to the control system. Moreover, information on the microorganism community and enzymes in the anaerobic sludge was detected. The results showed that the Geobacter, Syntrophus, and Dechlorobacter bacteria and the Methanosaeta and Methanobacterium archaea were significantly enriched for facilitating direct interspecies electron transfer in the anaerobic system by added ZVI@C@PANI. Moreover, the ZVI@C@PANI can strengthen the production of acetic acid, which facilitated the acetoclastic methanogens to generate methane from the anaerobic system.

Anaerobic textile wastewater treatment: toxicity to methanogenic organisms

RESUMO Testes de toxicidade anaeróbia foram realizados com corantes aromáticos azo (tetra-azo Direct Black 22 — DB22 e di-azo Direct Orange 4 — DO4) e antraquinônico (Reactive Blue 19 — RB19), com o objetivo de verificar a influência dos diferentes grupos químicos desses compostos na inibição da atividade metanogênica. Para o corante DB22, foram realizados dois testes com concentrações de corante de 0,03, 0,06, 0,09, 0,12 e 0,24 mmol·L−1 (TTADB22) e 0,3, 0,6, 0,9; ,,2 e 2,4 mmol·L−1 (TTADB22Adap, com lodo adaptado). Para os corantes DO4 (TTADO4) e RB19 (TTARB19), as concentrações utilizadas foram 0,5, 1, 2, 3, e 4 mmol·L−1. Os resultados indicaram que ambos os grupamentos químicos azo e antraquinônico podem ser inibidores da metanogênese. Cada corante resultou em um potencial tóxico diferente, dependendo da natureza do corante, das concentrações utilizadas e dos subprodutos gerados. O corante antraquinônico RB19 apresentou taxa de inibição da metanogênese duas vezes maior que o azocorante DO4, sugerindo maior tolerância dos microrganismos metanogênicos ao azocorante do que ao corante antraquinônico. Entre os azocorantes, as maiores taxas de inibição foram verificadas para o DB22 (48%), que possui maior número de grupos sulfônicos em sua estrutura que o DO4. Em geral, maiores percentuais de remoção de corante foram obtidos para menores concentrações de corante aplicadas.

New Margin-Based Biochar for Removing Hydrogen Sulfide Generated during the Anaerobic Wastewater Treatment

The present research concerns the development of a new device and process intended for the purification and treatment of sulfurous elements, and more particularly, of hydrogen sulfide (H2S) from the biogas produced at the time of the anaerobic fermentation in the purification stations. The controlled dumps or any other unit are likely to produce biogas with concentrations of H2S harmful to the operation of the machines for the valorization of the produced biogas or deodorization. This device uses new biochar from a mixture of dehydrated digested sludge from sewage treatment plants and margins from traditional crushing units, followed by biological treatment in a liquid medium at a controlled temperature. The liquid medium is based on a margin (nutrient) with culture support (large granules of biochar) in suspension by the injection under the pressure of biogas coming from the biochar filter. Physico-chemical characterization of the biochar and a test practiced on the new device of raw biogas treatment were realized. The results showed that the newly synthesized biochar has a low specific surface and a highly undeveloped porosity. The spectrum corresponding to the images of the biochar reveals the presence of C, O, N, Al, Si, P, and Fe, as significant elements with the following respective percentages: 37.62%, 35.78%, 1.87%, 4.26%, 7.33%, 8.56%, and 4.58%. It is important to note that the C content of the biochar thus synthesized found by EDX is quite comparable to that estimated from ATG. Biogas treatment test results on the prototype object of the invention eliminated 97% of the H2S from the biogas produced.

Electrochemical iron production to enhance anaerobic membrane treatment of wastewater

Although iron salts such as iron(III) chloride (FeCl3) have widespread application in wastewater treatment, safety concerns limit their use, due to the corrosive nature of concentrated solutions. This study demonstrates that local, electrochemical generation of iron is a viable alternative to the use of iron salts. Three laboratory systems with anaerobic membrane processes were set up to treat real wastewater; two systems used the production of either in-situ or ex-situ electrochemical iron (as Fe2+ and Fe2+(Fe3+)2O4, respectively), while the other system served as a control. These systems were operated for over one year to assess the impact of electrochemically produced iron on system performance. The results showed that dosing of electrochemical iron significantly reduced sulfide concentration in effluent and hydrogen sulfide content in biogas, and mitigated organics-based membrane fouling, all of which are critical issues inherently related to sustainability of anaerobic wastewater treatment. The electrochemical iron strategy can generate multiple benefits for wastewater management including increased removal efficiencies for total and volatile suspended solids, chemical oxygen demand and phosphorus. The rate of methane production also increased with electrochemically produced iron. Economic analysis revealed the viability of electrochemical iron with total cost reduced by one quarter to a third compared with using FeCl3. These benefits indicate that electrochemical iron dosing can greatly enhance the overall operation and performance of anaerobic membrane processes, and this particularly facilitates wastewater management in a decentralized scenario.

Evaluation of the Physical and Chemical Treatment of Wastewater for the Dairy Industry

Dairy wastewater generally contains fats, lactose, whey proteins, and nutrients. Casein precipitation causes the effluent to decompose into a dark, strong-smelling sludge. Fluid waste contains soluble organic matter, suspended solids, and gaseous organic matter, which cause undesirable taste and smell, grant tone and turbidity, and advance eutrophication, which plays an essential role in increasing biological oxygen demand (BOD) in water. It also contains detergents and disinfecting agents from the rinses and washing processes, which increase the need for chemical oxygen (COD). One of the characteristics of dairy effluents is their relatively high temperature, high organic contents, and wide pH range, so the discharge of wastewater into water bodies without treatment leads to deterioration of water quality and ecological imbalance, and therefore treatment is required. To remove or reduce environmental damage. Dairy wastewater treatment includes mechanical, physical, chemical, and biological methods. Organic treatment techniques are reasonable for treating wastewater from the dairy business because of their high biodegradability. Notwithstanding, the long-chain unsaturated fats framed during lipid hydrolysis show an inhibitory impact during anaerobic treatment. Chain block reactors (SBR) and top stream anaerobic slop cover of sludge (UASB) frameworks are the most encouraging advancements for the organic treatment of dairy wastewater. Many papers have applied high-impact exercise and technical methods to the dairy business's anaerobic wastewater treatment of dairy wastewater. However, the two techniques actually have a few disadvantages. The most vital objective of these studies is to track down savvy and naturally manageable ways to deal with and empower the reuse and management of wastewater and waste. Consequently, elective treatments to organic treatment are physical and substance techniques, for example, coagulation, retention, layer cycles, and electrolysis. This section gives a primary survey zeroing in on physical and compound treatment strategies for dairy wastewater treatment. It is under study and checked for its viability.

BioWin® modeling of anaerobic sludge blanket treatment of domestic wastewater

Anaerobic bioreactors treating wastewater have lower operating costs and waste sludge generation and produce more energy-rich methane than traditional aerobic systems. The ability to simulate performance of anaerobic mainstream treatment allows for comparison to the existing aerobic treatment paradigm. Required modifications were determined for a computer simulation tool, BioWin, to predict wastewater treatment performance of a multi-compartment anaerobic baffled reactor system. The model was calibrated using one month of data and validated using two years of data pooled into three temperature regimes. The validation results were within 10 % of actual, measured values recorded from a multi-year study of a pilot-scale anaerobic bioreactor treating domestic wastewater. Sensitivity analysis showed the simulation was most sensitive to changes to the influent wastewater characteristics and acetogen and methanogen kinetic parameters. Thus, using BioWin, anaerobic domestic wastewater treatment can be integrated into wastewater facility design scenarios.

Insight into the Removal of Enoxacin in an Anaerobic Sulfur-Mediated Wastewater Treatment System: Performance, Kinetics and Mechanisms

The removal of enoxacin (ENO), a broad-spectrum fluoroquinolone antibiotic, was firstly examined in a sulfate-reducing up-flow sludge bed (SRUSB) bioreactor over a long-term operation (366 days). Over 94% of the ENO was removed in the SRUSB bioreactor via adsorption and biodegradation at different initial ENO concentrations (i.e., 25–1000 μg/L). Based on the results of the batch tests, the sulfate-reducing sludge exhibited a high ENO adsorption capacity within a kd of 22.7–28.9 L/g-SS. The adsorption of ENO by the sulfate-reducing sludge was a spontaneous (ΔG° < 0 KJ/mol) and exothermic (ΔH° < 0 KJ/mol) process including physisorption and chemisorption (absolute value of ΔH° = 51.882 KJ/mol). Moreover, ENO was effectively biodegraded by the sulfate-reducing sludge within specific rates of 2.5–161.3 μg/g-SS/d. The ENO biodegradation process in the sulfate-reducing sludge system was most accurately described by the first-order kinetic model. Collectively, our findings provide insight into the applicability of a sulfate-reducing sludge system for ENO-contaminated wastewater treatment.

Ball-milled Fe0/FeS2 enhanced interaction of Shewanella oneidensis MR-1 with anaerobic microbial community: Impact on 2,4-dichloronitrobenzene reduction and methane yield

The technology of integrating sulfidated zero-valent iron and functional anaerobic bacteria has been extensively explored to improve the removal efficiency of pollutants and enhance the performance of anaerobic microbial system. In this study, the simultaneous DCNB(2,4-dichloronitrobenzene) reduction and methane production by ball-milled 1:1 Fe0/FeS2 (briefly, 1:1 Fe0/FeS2), Shewanella oneidensis MR-1 and microbial consortium (MC) were firstly investigated. The result showed that the DCNB reduction was increased by 2.6 and 1.7 times in 1:1 Fe0/FeS2 + MR-1 group compared to 1:1 Fe0/FeS2 and MR-1, respectively, while it further increased by almost 2 times in 1:1 Fe0/FeS2 + MC + MR-1 group as compared to that of 1:1 Fe0/FeS2 + MR-1 group. Moreover, the methane production was drastically facilitated via the reciprocal interaction among FeS as the reaction product, MR-1 and MC. Dechlorination was not found, mainly due to the inability of 1:1 Fe0/FeS2 and the inexistence of dechlorinating bacteria in original inoculum. Meanwhile, the microbial community was also changed, with genera like Eubacterium capable of reducing nitroaromatic compound and Methanosarcina as acetoclastic methanogen enriched by 1:1 Fe0/FeS2 and MR-1. Therefore, fast DCNB reduction and methane production using 1:1 Fe0/FeS2 in anaerobic microbial system, gives useful reference for both establishment of pollutant removal and biogas production. In conclusion, Fe0/FeS2, as a kind of sulfidated ZVI, is a good candidate for enhancing both pollutant degradation and CH4 production in anaerobic wastewater treatment.

Roles of Fe-C amendment on sulfate-containing pharmaceutical wastewater anaerobic treatment: Microbial community and sulfur metabolism.

The effects of multiple two-phase anaerobic treatment involving acidification coupling Fe-C on sulfate-containing chemical synthesis-based pharmaceutical wastewater treatment were investigated. Fe-C was added as a filler with 25% vol. to acidogenic reactors for semi-continuous operation. The results suggested that Fe-C amendment promoted sulfate removal efficiency by 47.5% and shortened the reaction time by 50% in the acidogenic phase. With mitigation of sulfate inhibition, SCOD removal efficiency and methane production were further increased by 24.6% and 398% compared to direct raw wastewater anaerobic digestion, respectively, in methanogenic phase. The results of sulfate removal kinetics confirmed a 150% increase of removal rate in acidogenic phase. However, the apparent kinetic microbial sulfate removal constant without Fe-C amendment was maintained at approximately 0.06 h-1. The Fe-C amendment not only increased the relative abundance of Methanothrix and Desulfovibrio for sulfate reduction but also enriched unclassified_p__Chloroflexi and unclassified_c__Deltaproteobacteria for acidification. Metagenomic results indicated that Fe-C enhanced dissimilatory sulfate reduction and PAPS synthesis of assimilatory step. The hydrogen sulfide production through the 3-mercaptopyruvate to pyruvate pathways was also enhanced. Butyrate-oxidizing genes were increased synchronously to convert butyrate to acetate.

Anaerobic domestic wastewater treatment in a sequencing granular UASB bioreactor: Feasibility study of the temperature effect on the process performance

A laboratory-scale sequencing granular up-flow anaerobic sludge blanket (UASB) reactor was applied for the treatment of synthetic domestic wastewater at 15, 25 and 35 °C. The experiments were performed at different hydraulic retention times (gradually decreasing from a maximum of 22 h to a minimum of 9 h). Results at 25 and 35 °C showed similar COD removal efficiency and specific biogas production in the range of 84–94% and 0.14–0.27 m3/kgCODremoved, respectively. At 15 °C lower COD removal kinetics were observed, and a minimum hydraulic retention time of 14 h was necessary to obtain an effluent in accordance with current Italian legislation. At all temperatures, high quality effluent was achieved in terms of total suspended solids (TSS) concentration, while nitrogen and phosphorus exceeded the Italian law limits, as they are not removed during the anaerobic digestion process. Moreover, dissolved methane in the liquid phase was analysed: methane lost with the effluents was on average ≈ 37% at 25 °C and ≈ 24% at 35 °C of the produced amount, thus revealing higher losses at lower temperatures for the increase of gas solubility. These results show the need of research on technologies aimed at removing or recovering such energetic greenhouse gas. However, effective biogas production and potentialities for nutrients’ recovery demonstrated in this study confirm the feasibility of the anaerobic process as sustainable treatment of low-strength wastewaters.

Long-term comparison of pilot UASB and AnMBR systems treating domestic sewage at ambient temperatures

The upflow anaerobic sludge blanket (UASB) reactor and the anaerobic membrane bioreactor (AnMBR) are leading candidates for high-rate anaerobic treatment of domestic wastewater. The objective of this study was to perform a long-term comparison on the treatment of domestic sewage by the UASB and AnMBR systems at pilot scale at ambient temperature conditions and relate this to full-scale performance from a range of domestic strength UASB reactors. Analysis of overall operation indicated that the pilot reactor was more likely to be effective in removing solids (and less effective in soluble COD) than full-scale reactors, but that both had comparable performance ranges (i.e., from very effective, to very ineffective). Analyzing both UASB and AnMBR pilot plants treating the same wastewater, it can be concluded that both systems could achieve comparable performance (the UASB for very short periods), with COD removal efficiencies of more than 90%. However, the UASB could only achieve this performance for weeks at a time with good solids retention and long (>15 h) hydraulic retention time (HRT). This performance in general was not sustainable. For the UASB, the average COD removal at 15-h HRT was approximately 50%, with a significant reduction in performance as the hydraulic loading increased (which effectively reduced the HRT). Conversely, the AnMBR system produced exceptional COD removal at an HRT of 9 h. Considering this, the sustained volumetric methane production (per volume of reactor) was approximately 4 times that in the AnMBR than in the UASB system.

Effects of methanol, sodium citrate, and chlorella powder on enhanced anaerobic treatment of coal pyrolysis wastewater

To better promote environment friendly development of the coal chemical industry, this study investigated effects of methanol, sodium citrate, and chlorella powder (a type of microalgae) as co-metabolic substances on enhanced anaerobic treatment of coal pyrolysis wastewater with anaerobic sludge. The anaerobic sludge was loaded into four 2 L anaerobic reactors for co-metabolism enhanced anaerobic experiments. Anaerobic reactor 1 (R1) as control group did not add a co-metabolic substance; anaerobic reactor 2 (R2) added methanol; anaerobic reactor 3 (R3) added sodium citrate; and anaerobic reactor 4 (R4) added chlorella powder. In the blank control group, the removal ratios of total phenol (TPh), quinoline, and indole were only 12.07%, 42.15%, and 50.47%, respectively, indicating that 50 mg/L quinoline, 50 mg/L indole, and 600 mg/L TPh produced strong toxicity inhibition function on the anaerobic microorganism in reactor. When the concentration of methanol, sodium citrate, and chlorella was 400 μg/L, the reactors with co-metabolic substances had better treatment effect on TPh. Among them, the strengthening effects of sodium citrate (TPh removal ratio: 44.87%) and chlorella (47.85%) were better than that of methanol (38.72%) and the control group (10.62%). Additionally, the reactors with co-metabolic substances had higher degradation ratios on quinoline, indole, and chemical oxygen demand (COD). The data of extracellular polymeric substances showed that with the co-metabolic substances, anaerobic microorganisms produced more humic acids by degrading phenols and nitrogen-containing heterocyclic compounds (NHCs). Compared with the control group, the reactors added with sodium citrate and chlorella had larger average particle size of sludge. Thus, sodium citrate and chlorella could improve sludge sedimentation performance by increasing the sludge particle size. The bacterial community structures of reactors were explored and the results showed that Aminicenantes genera incertae sedis, Levinea, Geobacter, Smithella, Brachymonas, and Longilinea were the main functional bacteria in reactor added with chlorella.

Effects of sulfate concentration on anaerobic treatment of wastewater containing monoethanolamine using an up-flow anaerobic sludge blanket reactor

Monoethanolamine (MEA), a toxic organic chemical, is widely used in industries and is found in their wastewater. Anaerobic MEA degradation is an appropriate strategy to reduce energy and cost for treatment. Industry wastewaters also contain sulfate, but information on the effects of sulfate on MEA degradation is limited. Here, an up-flow anaerobic sludge blanket (UASB) for MEA-containing wastewater treatment was operated under psychrophilic conditions (18–20 ºC) to investigate the effects of sulfate on the microbial characteristics of the retained sludge. To acclimatize the sludge, the proportion of MEA in the influent (containing sucrose, acetate, and propionate) was increased from 15% to 100% of total COD (1500 mg L–1); sulfate was then added to the influent. The COD removal efficiency remained above 95% despite the increase in MEA and sulfate. However, granular sludge disintegration was observed when sulfate was increased from 20 to 330 mg L–1. Batch tests revealed that propionate and acetate were produced as the metabolites of MEA degradation. In response to sulfate acclimation, methane-producing activities for propionate and hydrogen declined, while sulfate-reducing activities for MEA, propionate, and hydrogen increased. Accordingly, acclimation and changes in dominant microbial groups promoted the acetogenic reaction of propionate by sulfate reduction.

A comprehensive carbon footprint analysis of different wastewater treatment plant configurations

With the growing concern of global warming, many water utilities are pioneering in mitigating greenhouse gas (GHG) emissions, with some water utilities aiming to achieve net-zero emissions operation in the next decade. However, for wastewater treatment plants (WWTPs), the carbon footprint of different treatment technologies and its contribution among various units within each treatment configuration is still unclear. This study evaluates the impacts of process design on the carbon footprint of WWTPs through the analysis of scope 1 (direct emission), scope 2 (indirect emission), and scope 3 (value chain emission) emissions. The comprehensive configuration design in this work considered three nutrient removal processes including typical aerobic and anaerobic wastewater treatment technologies. Emissions from the sludge management processes are also calculated, including aerobic and anaerobic sludge stabilization processes, short-term and long-term sludge storage, and three sludge disposal options. In total, 45 processes were analysed and the results were compared. The results showed the carbon footprints are highly dependent on the treatment configurations of WWTPs. Analysis suggested scope 2 & 3 emissions can be reduced by selecting suitable processes. In general, anaerobic wastewater and sludge stabilization technologies are more suitable than aerobic technologies to reduce scope 2 & 3 emissions, leading to a lower overall carbon footprint. In comparison, configuration design offers limited opportunities to reduce scope 1 emissions, which may be the future challenge for WWTP to achieve carbon neutrality.

An Artificial Neural Network for Simulation of an Upflow Anaerobic Filter Wastewater Treatment Process

The purpose of this work was to develop a problem-solving approach and a simulation tool that is useful for the specification of wastewater treatment process equipment design parameters. The proposition of using an artificial neural network (ANN) numerical model for supervised learning of a dataset and then for process simulation on a new dataset was investigated. The effectiveness of the approach was assessed by evaluating the capacity of the model to distinguish differences in the equipment design parameters. To demonstrate the approach, a mock dataset was derived from experimentally acquired data and physical effects reported in the literature. The mock dataset comprised the influent flow rate, the bed packing material dimension, the type of packing material and the packed bed height-to-diameter ratio as predictors of the calorific value reduction. The multilayer perceptron (MLP) ANN was compared to a polynomial model. The validation test results show that the MLP model has four hidden layers, each having 256 units (nodes), accurately predicts calorific value reduction. When the model was fed previously unseen test data, the root-mean-square error (RMSE) of the predicted responses was 0.101 and the coefficient of determination (R2) was 0.66. The results of simulation of all 125 possible combinations of the 3 mechanical parameters and identical influent wastewater flow profiles were ranked according to total calorific value reduction. A t-test of the difference between the mean calorific value reduction of the two highest ranked experiments showed that the means are significantly different (p-value = 0.011). Thus, the model has the capacity to distinguish differences in the equipment design parameters. Consequently, the values of the three mechanical feature parameters from the highest ranked simulated experiment are recommended for use in the design of the industrial scale upflow anaerobic filter (UAF) for wastewater treatment.

Performance and mechanisms exploration of nano zinc oxide (nZnO) on anaerobic decolorization by Shewanella oneidensis MR-1

Although the ecological safety of nanomaterials is of widespread concern, their current ambient concentrations are not yet sufficient to cause serious toxic effects. Thus, the nontoxic bioimpact of nanomaterials in wastewater treatment has attracted increasing attention. In this study, the effect of nano zinc oxide (nZnO), one of the most widely used nanomaterials, on the anaerobic biodegradation of methyl orange (MO) by Shewanella oneidensis MR-1 was comprehensively investigated. High-dosage nZnO (>0.5 mg/L) caused severe toxic stress on S. oneidensis MR-1, resulting in the decrease in decolorization efficiency. However, nZnO at ambient concentrations could act as nanostimulants and promote the anaerobic removal of MO by S. oneidensis MR-1, which should be attributed to the improvement of decolorization efficiency rather than cell proliferation. The dissolved Zn2+ was found to contribute to the bioeffect of nZnO on MO decolorization. Further investigation revealed that low-dosage nZnO could promote the cell viability, membrane permeability, anaerobic metabolism, as well as related gene expression, indicating that nZnO facilitated rather than inhibited the anaerobic wastewater treatment under ambient conditions. Thus, this work provides a new insight into the bioeffect of nZnO in actual environment and facilitates the practical application of nanomaterials as nanostimulants in biological process.

Influence of low operating temperature on biomass yield during anaerobic treatment of chocolate confectionery wastewater in a pilot-scale UASB reactor

It has been found that biomass yield (Yobs) increases as operating temperature decreases in batch reactors fed with synthetic substrate; nevertheless, there is a gap in literature about this phenomenon in pilot-scale reactors treating real industrial wastewaters, such as from the chocolate confectionery industry. Therefore, the effect of low operating temperature on the Yobs during the anaerobic treatment of chocolate confectionery wastewater (CCWW) was studied. In this research, the CCWW was treated in a 244-L pilot-scale upflow anaerobic sludge blanket reactor, which was operated for 275 days at short hydraulic retention time (6 h), medium total applied organic loading rates (OLRTappl) (6.7–11.6 kg-total chemical oxygen demand (CODT/m3/d)), and low operating temperature (14–20 °C). The COD removal efficiency ranged from 70 to 90 % and the methane production rate varied between 230 and 393 L-CH4/d at standard temperature and pressure (84 % of methane in biogas). The results showed that Yobs was higher at 14 °C [0.20 g-volatile suspended solids/g-removed COD (g-VSS/g-CODrem)] than at 20 °C (0.15 g-VSS/g-COD). Also, high Yobs values lead to a larger anaerobic biomass washout in the reactor effluent. The anaerobic biomass washout was also influenced by the presence of sodium in CCWW, the high OLRTappl and the low operating temperature, which made difficult the solids-liquid separation.