Search

Sulfide produced from dissimilatory sulfate reduction can combine with hydrogen to form hydrogen sulfide, causing odor issues and environmental pollution. To address this problem, ferrihydrite-humic acid coprecipitate was added to improve assimilatory sulfate reduction (ASR), resulting in a decrease in sulfide production (190.2 ± 14.6 mg/L in the Fh-HA group vs. 246.3 ± 8.1 mg/L in the Fh group) with high sulfate removal. Humic acid, adsorbed on the surface of ferrihydrite, delayed secondary mineralization of ferrihydrite under sulfate reduction condition. Therefore, more iron-reducing species (e.g. Trichococcus, Geobacter) were enriched with ferrihydrite-humic acid coprecipitate to transfer more electrons to other species, which led to more COD reduction, an increase in electron transfer capacity, and a decrease in the NADH/NAD + ratio. Metagenomic analysis also indicated that functional genes related to ASR was enhanced with ferrihydrite-humic acid coprecipitate. Thus, the addition of ferrihydrite-humic acid coprecipitate can be considered as a promising candidate for anaerobic sulfate wastewater treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The activated sludge (AS) process is widely applied in dyestuff wastewater treatment plants (WWTPs); however, the nitrogen removal efficiency is relatively low and the effluent does not meet the indirect discharge standards before being discharged into the industrial park's WWTP. Hence it is necessary to upgrade the WWTP with more advanced technologies. Moving bed biofilm processes with suspended carriers in an aerobic tank are promising methods due to enhanced nitrification and denitrification. Herein, a pilot-scale integrated free-floating biofilm and activated sludge (IFFAS) process was employed to investigate the feasibility of enhancing nitrogen removal efficiency at different hydraulic retention times (HRTs). The results showed that the effluent chemical oxygen demand (COD), ammonium nitrate (NH 4 + -N) and total nitrogen (TN) concentrations of the IFFAS process were significantly lower than those of the AS process, and could meet the indirect discharge standards. PCR-DGGE and FISH results indicated that more nitrifiers and denitrifiers co-existed in the IFFAS system, promoting simultaneous nitrification and denitrification. Based on the pilot results, the IFFAS process was used to upgrade the full-scale AS process, and the effluent COD, NH 4 + -N and TN of the IFFAS process were 91-291 mg/L, 10.6-28.7 mg/L and 18.9-48.6 mg/L, stably meeting the indirect discharge standards and demonstrating the advantages of IFFAS in dyestuff wastewater treatment.

Coking wastewater contains many types of toxic and hazardous pollutants that have serious toxic effects on human beings as well as aquatic organisms. However, few studies have evaluated the detoxification efficiencies of the treatment processes that are extensively performed in operational coking wastewater treatment plants (WWTPs). This study investigates the detoxification efficiencies of a combined anaerobic-anoxic-oxic (A 2 O)-ozonation and A 2 O-Fenton oxidation process in two coking WWTPs using an acute immobilization test for Daphnia magna, acute toxicity test for adult zebrafish, embryo toxicity test for zebrafish and the comet assay. The raw coking wastewaters displayed high acute daphnia and fish toxicity, zebrafish embryo toxicity and genotoxicity. The A 2 O processing unit effectively removed acute and embryo toxicity, but not genotoxicity. In addition, the A 2 O effluent quality did not meet the integrated wastewater discharge standard in China (GB18918-2002). The ozonation and Fenton oxidation units used as post-treatments in these two plants not only treated the coking wastewater to the discharge standard but also reduced the genotoxicity. However, the final effluents still showed potential genotoxicity after high dilution. The results suggest that the discharge of treated coking wastewater probably poses potential risks to human health and the environment even if it met regulatory standards., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Anaerobic digestion (AD) is an important energy strategy for converting organic waste to CH4. A major factor limiting the practical applicability of AD is the relatively long hydraulic retention time (HRT) which declines the treatment efficiency of digesters. A coupling process of anaerobic digestion and 'electromethanogenesis' was proposed to enhance anaerobic digestion at a short HRT in this study. Microorganisms analysis indicated that the electric-biological reactor enriched hydrogenotrophic methanogens in both cathodic biofilm and suspended sludge, helping achieve the high organic removal (71.0% vs 42.3% [control reactor]) and CH4 production (248.5mL/h vs 51.3mL/h), while the additional electric input was only accounted for 25.6% of the energy income from the increased CH4 production. This study demonstrated that a bioelectrochemical enhanced anaerobic reactor could improve the CH4 production and organic removal at a short HRT, providing an economically feasible scheme to treat wastewater., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

An integrated fixed-film activated sludge (IFAS) process (G1) and an activated sludge anoxic-oxic process (G2) were operated at nitrate liquor recirculation ratio (R) of 100, 200 and 300% to investigate the feasibility of enhancing nitrogen removal efficiency (RTN) and reducing R by improving simultaneous nitrification and denitrification (SND) in the IFAS process. The results showed that the effluent NH4(+)-N and total nitrogen (TN) of G1 at R of 200% were less than 1.5 and 14.5 mg/L, satisfying the Chinese discharge standard (NH4(+)-N < 5 mg/L; TN < 15 mg/L). However, the effluent NH4(+)-N and TN of G2 at R of 300% were higher than 8.5 and 15.3 mg/L. It indicated that better RTN could be achieved at a lower R in the IFAS process. The polymerase chain reaction-denaturing gradient gel electrophoresis results implied that nitrifiers and denitrifiers co-existed in one microbial community, facilitating the occurrence of SND in the aerobic reactor of G1, and the contribution of SND to TN removal efficiency ranged 15-19%, which was the main reason that the RTN was improved in the IFAS process. Therefore, the IFAS process was an effective method for improving RTN and reducing R. In practical application, this advantage of the IFAS process can decrease the electricity consumption for nitrate liquor recirculation flow, thereby saving operational costs.

Anaerobic reactors with ferric iron addition have been experimentally demonstrated to be able to simultaneously improve sulfate reduction and organic matter degradation during sulfate-containing wastewater treatment. In this work, a mathematical model is developed to evaluate the impact of ferric iron addition on sulfate reduction and organic carbon removal as well as the volatile fatty acids (VFA) composition in anaerobic reactor. The model is successfully calibrated and validated using independent long-term experimental data sets from the anaerobic reactor with Fe (III) addition under different operational conditions. The model satisfactorily describes the sulfate reduction, organic carbon removal and VFA production. Results show Fe (III) addition induces the microbial reduction of Fe (III) by iron reducing bacteria (IRB), which significantly enhances sulfate reduction by sulfate reducing bacteria (SRB) and subsequently changes the VFA composition to acetate-dominating effluent. Simultaneously, the produced Fe (II) from IRB can alleviate the inhibition of undissociated H2S on microorganisms through iron sulfide precipitation, resulting in further improvement of the performance. In addition, the enhancement on reactor performance by Fe (III) is found to be more significantly favored at relatively low organic carbon/SO4(2-) ratio (e.g., 1.0) than at high organic carbon/SO4(2-) ratio (e.g., 4.5). The Fe (III)-based process of this work can be easily integrated with a commonly used strategy for phosphorus recovery, with the produced sulfide being recovered and then deposited into conventional chemical phosphorus removal sludge (FePO4) to achieve FeS precipitation for phosphorus recovery while the required Fe (III) being acquired from the waste ferric sludge of drinking water treatment process, to enable maximum resource recovery/reuse while achieving high-rate sulfate removal.

Direct utilization of solar energy for photocatalytic removal of ammonia from water is a topic of strong interest. However, most of the photocatalysts with effective performance are solely metal-based semiconductors. Here, we report for the first time that a new type of atomic single layer graphitic-C(3)N(4) (SL g-C(3)N(4)), a metal-free photocatalyst, has an excellent photocatalytic activity for total ammonia nitrogen (TAN) removal from water. The results demonstrated that over 80% of TAN (initial concentration 1.50 mg · L(-1)) could be removed in 6 h under Xe lamp irradiation (195 mW · cm(-2)). Furthermore, the SL g-C(3)N(4) exhibited a higher photocatalytic activity in alkaline solution than that in neutral or acidic solutions. The investigation suggested that both photogenerated holes and hydroxyl radicals were involved the TAN photocatalytic oxidation process and that the major oxidation product was NO3(-)-N. In addition, SL g-C(3)N(4) exhibited good photocatalytic stability in aqueous solution. This work highlights the appealing application of an inexpensive metal-free photocatalyst in aqueous ammonia treatment.

Anaerobic digestion of waste activated sludge usually requires pretreatment procedure to improve the bioavailability of sludge, which involves considerable energy and high expenditures. This study proposes a cost-effective method for enhanced anaerobic digestion of sludge without a pretreatment by directly adding iron into the digester. The results showed that addition of Fe(0) powder could enhance 14.46% methane yield, and Fe scrap (clean scrap) could further enhance methane yield (improving rate 21.28%) because the scrap has better mass transfer efficiency with sludge and liquid than Fe(0) powder. The scrap of Fe with rust (rusty scrap) could induce microbial Fe(III) reduction, which resulted in achieving the highest methane yield (improving rate 29.51%), and the reduction rate of volatile suspended solids (VSS) was also highest (48.27%) among Fe powder, clean scrap and rusty scrap. PCR-DGGE proved that the addition of rusty scrap could enhance diversity of acetobacteria and enrich iron-reducing bacteria to enhance degradation of complex substrates., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In this study, a novel approach was developed for sulfate - containing wastewater treatment via dosing Fe₂O₃ in a two - stage anaerobic reactor (A1, S1). The addition of Fe₂O₃ in its second stage i.e. acidogenic sulfate-reducing reactor (S1) resulted in microbial reduction of Fe (III), which significantly enhanced the biological sulfate reduction. In reactor S1, increasing influent sulfate concentration to 1400 mg/L resulted in a higher COD removal (27.3%) and sulfate reduction (57.9%). In the reference reactor without using Fe₂O₃ (S2), the COD and sulfate removal were 15.6% and 29%, respectively. The combined performance of the two-stage anaerobic reactor (A1, S1) also showed a higher COD removal of 74.2%. Denaturing gradient gel electrophoresis (DGGE) and phylogenetic analysis showed that the dominant bacteria with high similarity to IRB species as well as sulfate reducer Desulfovibrio and acidogenic bacteria (AB) were enriched in S1. Quantitative Polymerase Chain Reaction (qPCR) analysis presented a higher proportion of sulfate reducer Desulfovibrio marrakechensis and Fe (III) reducer Iron-reducing bacteria HN54 in S1., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Azo dye wastewater treatment was enhanced in an acidogenic reactor (A1) by Fe(0) dosing. Both COD (50%) and color (60%) removal in A1 were stable when the dye concentrations were increased from 200 to 800 mg/L. However, the performances of a Fe(0)-free control reactor (A2) showed low COD (34%) and color (32%) removals. The reason was attributed that Fe(0) dosing enhanced the activity of fermentative bacteria, which played an important role in acidogenesis and decolorization. The methanogenic reactor fed with the effluent of A1 exhibited higher removal efficiency and treatment stability. These results suggested that Fe(0) powder dosing was helpful to improve acidogenesis and decolorization to create a favorable feeding condition for the subsequent methanogenic treatment., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Zero valent iron (ZVI) is expected to help create an enhanced anaerobic environment that might improve the performance of anaerobic treatment. Based on this idea, a novel ZVI packed upflow anaerobic sludge blanket (ZVI-UASB) reactor was developed to treat azo dye wastewater with variable influent quality. The results showed that the reactor was less influenced by increases of Reactive Brilliant Red X-3B concentration from 50 to 1000 mg/L and chemical oxygen demand (COD) from 1000 to 7000 mg/L in the feed than a reference UASB reactor without the ZVI. The ZVI decreased oxidation-reduction potential in the reactor by about 80 mV. Iron ion dissolution from the ZVI could buffer acidity in the reactor, the amount of which was related to the COD concentration. Fluorescence in situ hybridization test showed the abundance of methanogens in the sludge of the ZVI-UASB reactor was significantly greater than that of the reference one. Denaturing gradient gel electrophoresis showed that the ZVI increased the diversity of microbial strains responsible for high efficiency.

A zero valent iron (ZVI) bed with a pair of electrodes was packed in an anaerobic reactor aiming at enhancing treatment of azo dye wastewater. The experiments were carried out in three reactors operated in parallel: an electric field enhanced ZVI-anaerobic reactor (R1), a ZVI-anaerobic reactor (R2) and a common anaerobic reactor (R3). R1 presented the highest performance in removal of COD and color. Raising voltage in R1 further improved its performance. Scanning electron microscopy images displayed that the structure of granular sludge from R1 was intact after being fed with the high dye concentration, while that of R3 was broken. Fluorescence in situ hybridization analysis indicated that the abundance of methanogens in R1 was significantly greater than that in the other two reactors. Denaturing gradient gel electrophoresis showed that the coupling of electric field and ZVI increased the diversity of microbial community and especially enhanced bacterial strains responsible for decolorization., (Crown Copyright © 2010. Published by Elsevier Ltd. All rights reserved.)

Membrane filtration has been increasingly used for water treatment and wastewater reclamation in recent years. To further improve the effectiveness of membrane process and reduce membrane fouling, a highly reactive photocatalytic membrane, Ag-TiO(2)/hydroxiapiate (HAP, Ca(10)(PO(4))(6)(OH)(2))/Al(2)O(3), was employed to realize microfiltration (MF) coupling photocatalysis for surface water treatment. The effectiveness on the potential of membrane was investigated by removing humic acid (HA) test under different feed total organic carbon (TOC), light intensity and transmembrane pressure (TMP). The HA removal and anti-fouling property of as-prepared membrane was improved under UV irradiation, likely due to photocatalytic degradation of foulants along with filtration simultaneously. Under given feed water composition, increasing the light intensity resulted in increased removal of HA from aqueous solution. However, a limiting TMP seems to exist beyond which the increased HA removal cannot be sustained. Fouling behavior analysis indicated that the transition in fouling mode from initial pore blocking to cake filtration occurred much slower as UV irradiated. Furthermore, a superior efficiency on removal of trace organic contaminants, as well as milder flux reduction, was presented from surface water treatment, which demonstrated that the integrated system with enhanced performance is foreseen as an emerging technique for water treatment., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Catalytic wet air oxidation (CWAO) is a promising method for the treatment of heavily contaminated wastewater. However, its application is restricted due to severe operation conditions (high pressure and high temperature). A microwave (MW) assisted oxidation method was investigated aiming to treat heavily contaminated wastewater under milder conditions. H-acid (1-amino-8-naphthol-3, 6-disulfonic acid) was selected as target compound to evaluate the performance of this novel process. The removal of H-acid and TOC (total organic carbon) for H-acid solution of 3000 mg/L reached as high as 92.6% in 20 min and 84.2% in 60 min, respectively under optimal conditions. The existence of activated carbon and oxygen proved to be critical for effective treatment. The activated carbon acted not only as a catalyst for H-acid decomposition, but also as a special material for the absorption of MW energy. Air was supplied to the reactor as an oxygen source at constant flows. The amino group in H-acid was converted ultimately into nitrate, and sulfonic group into sulfate. This observation gave an evidence of H-acid mineralization although other organic intermediates were unable to be determined. The value of BOD(5)/COD (ratio of 5d biochemical oxygen demand to chemical oxygen demand) increased from 0.008 to 0.467 indicating a significant improvement of biodegradability for the solution, which is beneficial for the further biological treatment of the wastewater.

Abstract: Membrane filtration has been increasingly used for water treatment and wastewater reclamation in recent years. To further improve the effectiveness of membrane process and reduce membrane fouling, a highly reactive photocatalytic membrane, Ag-TiO2/hydroxiapiate (HAP, Ca10(PO4)6(OH)2)/Al2O3, was employed to realize microfiltration (MF) coupling photocatalysis for surface water treatment. The effectiveness on the potential of membrane was investigated by removing humic acid (HA) test under different feed total organic carbon (TOC), light intensity and transmembrane pressure (TMP). The HA removal and anti-fouling property of as-prepared membrane was improved under UV irradiation, likely due to photocatalytic degradation of foulants along with filtration simultaneously. Under given feed water composition, increasing the light intensity resulted in increased removal of HA from aqueous solution. However, a limiting TMP seems to exist beyond which the increased HA removal cannot be sustained. Fouling behavior analysis indicated that the transition in fouling mode from initial pore blocking to cake filtration occurred much slower as UV irradiated. Furthermore, a superior efficiency on removal of trace organic contaminants, as well as milder flux reduction, was presented from surface water treatment, which demonstrated that the integrated system with enhanced performance is foreseen as an emerging technique for water treatment. [ABSTRACT FROM AUTHOR]

Phytic acid (PA) induced graphene macrostructures were synthesized and investigated for the sorption characteristics and mechanisms of mercury. The as-synthesized graphene foam possessed large specific surface area and amphiphilicity. FTIR and XPS analysis revealed that the as-prepared graphene macrostructure retained oxygen-containing functional groups after hydrothermal reduction and also captured new phosphorus-containing groups because of the introduction of PA. Different experimental parameters, such as pH, PA fractions and contact time were applied to probe into the Hg(II) adsorption performance of as-synthesized macrostructure. Pseudo-second-order kinetic model and Langmuir isotherm model fitted well to the obtained sorption kinetic and isothermal data. The maximum adsorption capacity at pH = 7.2 for mercury was 361.01 mg/g. The dominant mechanisms for mercury removal were mainly ion exchange and surface complexation. Real application in river water and seawater exhibited very promising results, indicating its broad prospect in water purification. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we proposed a facile method for preparation of hierarchical porous ceramic membrane with energetic catalytic ozonation capability aiming at enhancing the performance of water treatment by using the combined ozone-membrane system. The strategy involved preparation of TiO2 macroporous membrane as a backbone and subsequently coating it with mesoporous Ti–Mn catalyst layer. Scanning electron microscope, transmission electron microscope and nitrogen sorption isotherms characterization demonstrated that the TiO2 membrane was composed of TiO2 nanorods with 200–400nm diameter, 5μm length, and mesoporous Ti–Mn layer was coated on the membrane surface uniformly with the thickness of about 100nm and pore size of 10nm. Energy dispersive X-ray spectroscopy, X-rays photoelectron spectroscopy and X-ray diffractometer showed that Ti–Mn mixed oxide was spread into the inner voids of the membrane to form a hierarchical porous structure. Treating simulated wastewater (aqueous solution of dye Red-3BS and Aniline) it was found that hierarchical porous catalytic membrane exhibited high catalytic ozonation capability which resulted in an enhancement of membrane antifouling, separation and degradation of organic pollutants when the membrane was used as a key device in the combined membrane and ozone system. [Copyright &y& Elsevier]