Adsorption and antibacterial studies of a novel hydrogel adsorbent based on ternary eco-polymers doped with sulfonated graphene oxide developed from upcycled plastic waste.

A novel ternary blended polymer composed of cost-effective and readily available polymers was synthesized using poly (vinyl alcohol) (PVA), iota carrageenan (IC), and poly (vinyl pyrrolidone) (PVP). Sulfonated graphene oxide (SGO), prepared from recycled drinking water bottles, was utilized as a doping agent. Varying amounts (1-3 wt%) were combined into the polymer matrix. The produced hydrogel film was examined as a potential adsorbent hydrogel film for the removal of methylene blue (MB) and Gentamicin sulfate (GMS) antibiotic from an aqueous solution. The experimental results demonstrate that the presence of SGO significantly increased the adsorption efficiency of PVA/IC/PVP hydrogel film. The antimicrobial tests revealed that the PVA/IC/PVP-3% SGO hydrogel film exhibited the most potent activity against all the tested pathogenic bacteria. However, the adsorption results for MB and GMS showed that the addition of 3 wt% SGO resulted in a removal percentage that was a two fold increase in the removal percentage compared with the undoped PVA/IC/PVP hydrogel film. Furthermore, the response surface methodology (RSM) model was utilized to examine and optimize several operating parameters, including time, pH of the solution, and initial pollutant concentration. The adsorption kinetics were better characterized by the pseudo-second-order kinetics model. The composite film containing 3 wt% SGO had a maximum adsorption capacity of 606 mg g-1 for MB and 654 mg g-1 for GMS, respectively. The generated nanocomposite hydrogel film demonstrated promising potential for application in water purification systems.

Biogenic sulfur recovery from sulfate-laden antibiotic production wastewater using a single-chamber up-flow bioelectrochemical reactor.

The high-concentration sulfate (SO42-) in the antibiotic production wastewater hinders the anerobic methanogenic process and also proposes possible environmental risk. In this study, a novel single-chamber up-flow anaerobic bioelectrochemical reactor (UBER) was designed to realize simultaneous SO42- removal and elemental sulfur (S0) recovery. With the carbon felt, the cathode was installed underneath and the anode above to meet the different biological niches for sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria (SOB). The bio-anode UBER (B-UBER) demonstrated a much higher average SO42- removal rate (SRR) of 113.2 ± 5.7 mg SO42--S L-1 d-1 coupled with a S0 production rate (SPR) of 54.4 ± 5.8 mg S0-S L-1 d-1 at the optimal voltage of 0.8 V than that in the abio-anode UBER (control reactor) (SRR = 86.6 ± 13.4 mg SO42--S L-1 d-1; SPR = 25.5 ± 9.7 mg S0-S L-1 d-1) under long-term operation. A large amount of biogenic S0 (about 72.2 mg g-1 VSS) was recovered in the B-UBER. The bio-anode, dominated by Thiovirga (SOB genus) and Acinetobacter (electrochemically active bacteria genus), exhibited a higher current density, lower overpotential, and lower internal resistance. C-type cytochromes mainly served as the crucial electron transfer mediator for both direct and indirect electron transfer, so that significantly increasing electron transfer capacity and biogenic S0 recovery. The reaction pathways of the sulfur transformation in the B-UBER were hypothesized that SRB utilized acetate as the main electron donor for SO42- reduction in the cathode zone and SOB transferred electrons to the anode or oxygen to produce biogenic S0 in the anode zone. This study proved a new pathway for biogenic S0 recovery and sulfate removal from sulfate-laden antibiotic production wastewater using a well-designed single-chamber bioelectrochemical reactor.

Novel composites of activated carbon and layered double oxide for the removal of sulfate from synthetic and brackish groundwater.

Sulfate (SO42-) is a major water and environmental concern that causes severe diarrhea, death of invertebrates and plant species, and clogging of industrial pipes. In the current work, treatment of SO42- from synthetic and real groundwater having 3901 mg(SO42-)/L was investigated for the first time using Zn-Al and Mg-Al layered double oxides doped granular activated carbon (GAC/Mg-Al LDO and GAC/Zn-Al LDO). The co-precipitation method was followed to synthesize the GAC/LDO composites using an Mg or Zn to Al molar ratio of 3:1. The GAC/Mg-Al LDO possessed a higher specific surface area (323.9 m2/g) compared to GAC/Zn-Al LDO (195.1 m2/g). The GAC/Mg-Al LDO demonstrated more than 99% removal of SO42- from synthetic water, while it was 50.9% for GAC/Zn-Al LDO and less than 1% for raw GAC at an initial concentration of 50 mg/L. The GAC/Mg-Al LDO was selected for further batch experiments and modeling investigation. The equilibrium data followed the Redlich-Peterson and Langmuir models with determination coefficients of 0.943 and 0.935, respectively. The maximum Langmuir adsorption capacity was 143.5 mg/g. In the real groundwater adsorption study, the screening experiment revealed high selectivity towards SO42- with 62% removal efficiency. The optimum dosage was found to be 50 g/L with an uptake capacity of 61.5 mg/g. The kinetic data of SO42- removal from synthetic and brackish water were in excellent agreement with the pseudo-second order model, and the equilibrium was attained in 5 h. Accordingly, it can be concluded that the GAC/Mg-Al LDO is an efficient material for treating SO42- from real groundwater and can be utilized as a pretreatment unit for high sulfate water resources.

Effect of organic loading rate and effluent recirculation on biogas production of desulfated skim latex serum using up-flow anaerobic sludge blanket reactor.

High sulfate contents in skim latex serum (SLS) can be reduced by rubber wood ash (RWA). Subsequently, the desulfated skim latex serum (DSLS) can be further anaerobically treated more effectively with the accompanying generated biomethane. In this study, DSLS was treated using an up-flow anaerobic sludge blanket (UASB) reactor operated at 10-day HRT and under mesophilic (37 °C) conditions. The effect of organic loading rates (OLR) at 0.89, 1.79 and 3.57 g-COD/L-reactor∙d on DSLS biodegradability was investigated in Phase I-IV using NaHCO3 as an external buffering agent. Maximum methane production yield of 226.35 mL-CH4/g-CODadded corresponding to 403.25 mL-CH4/L reactor·d was achieved at the suitable OLR of 1.79 g-COD/L-reactor∙d. UASB effluent recirculation which was then applied to replace the NaHCO3. It was found that with 53% effluent recirculation similar to an OLR of 2.01 g-COD/L-reactor∙d, an average of 185.70 mL-CH4/g-CODadded corresponding to 371.40 mL/L reactor·d of methane production was reached. The dominant bacteria in UASB reactor were members of Proteobacteria, Bacteroidota, Firmicutes, and Desulfobacterota phyla. Meanwhile, the archaeal community was majorly dominated by the genera Methanosaeta sp. and Methanomethylovorans sp. The study clearly indicates the capabilities of UASB reactor with effluent recirculation to treat DSLS anaerobically.

Bioregeneration of sulfate-laden anion exchange resin.

Ion exchange technology removes ionic compounds from waters effectively but treatment of the spent regenerant is expensive. The bioregeneration of sulfate-laden strong base anion exchange resin was successfully tested using both pure and mixed sulfate-reducing bacterial cultures. The resin was first used for removal of sulfate from neutral (pH 6.7 ± 0.5) synthetic sodium sulfate solutions, after which the spent resin was regenerated by incubating with a viable sulfate-reducing bacterial culture in batch and column modes. In the batch bioregeneration tests, the achieved bioregeneration was 36-95% of the original capacity of the fresh resin (112 mg SO42-/g) and it increased with regeneration time (1-14 days). The capacity achieved in the column tests during 24 hours of bioregeneration was 107 mg SO42-/g after the first regeneration cycle. During the bioregeneration, sulfate was mainly reduced by the sulfate-reducing bacteria (approx. 60%), but part of it was only detached from the resins (approx. 30%). The resin-attached sulfate was most likely replaced with ions present in the liquid sulfate-reducing bacterial culture (e.g., HCO3-, HS-, and Cl-). During the subsequent exhaustion cycles with the bioregenerated resin, the pH of the treated sodium sulfate solution increased from the original 6.7 ± 0.5 to around 9. The study showed that biological sulfate reduction could be used for sulfate removal in combination with ion exchange, and that the exhausted ion exchange resins could be regenerated using a liquid sulfate-reducing bacterial culture without producing any brine.

Fabrication and characterization of a novel Ba2+-loaded sawdust biochar doped with iron oxide for the super-adsorption of SO42- from wastewater.

Biochar is a low-cost adsorbent used in the treatment of contaminated wastewater. We investigated the potential of an Fe-impregnated, Ba2+-loaded biochar (Fe-(Ba-BC)) for the removal of SO42- from aqueous solutions. The Ba2+-loaded biochar was synthesized from sawdust impregnated with iron oxide via pyrolysis at 600 °C. The porous structure of the Fe-(Ba-BC) was identified by scanning electron microscopy before sulfate was adsorbed onto the adsorbent. Functional groups were determined by energy-dispersive spectrophotometry and Raman spectrometry.. The Fe-(Ba-BC) Raman peaks before the experiment were higher than after, suggesting the precipitation of BaSO4. The presence of BaCl2 on the surface of the biochar was confirmed by X-ray diffraction. Batch sorption results showed that Fe-(Ba-BC) strongly adsorbed aqueous SO42- with a removal efficacy of 96.7% under the optimum conditions of 0.25 M BaCl2, a contact time of 480 min, a pH of 9 and an adsorbent dose of 2 g. The optimum condition for removal and reaction rate kinetics analysis indicated that adsorption curve fitted well with PSO, k2 0.00015 confirmed the removal of SO42- via chemisorption. Thus, Fe-(Ba-BC) was found to be a favorable adsorbent for removing SO42-.

Enhanced sulfur recovery and sulfate reduction using single-chamber bioelectrochemical system.

The aim of this study was to investigate the feasibility of sulfate removal and elemental sulfur (S0) recovery in the single-chamber bioelectrochemical system (S-BES). The performance of S-BES was compared with that of dual-chamber bioelectrochemical system (D-BES). The S-BES was constructed with graphite felt as the anode and graphite brush as the cathode. The D-BES was constructed with proton exchange membrane as the separator between anode and cathode chambers. With an applied voltage of 1.0 V and 1 g/L acetate as the substrate, the S-BES and D-BES were tested by feeding with 480 mg/L SO42- in the phosphate buffer. Results showed that the maximum current density of 37.6 ± 4.5 mA/m3 was reached in the S-BES, which was higher than that in the D-BES (i.e., 22.2 ± 2.6 mA/m3). The SO42- removal was much higher in the S-BES than in the D-BES (99.5% vs. 57.2%). In the effluent and the electrodes of S-BES, S0 was identified with Raman and X- Ray diffraction analyses. The S0 recovery on the anode was 13.7 times of that on the cathode of S-BES, indicating that S0 was mainly produced on the anode. The measured total S0 recovery reached 67.5% in the S-BES. High relative abundance of Desulfurella (47.1%) and Geobacter (26.1%) dominated the community in the anode biofilm of S-BES. The excellent performance of S-BES may be attributed to the neutral pH in the solution and the synergistic reaction between the anode and cathode. Results from this study should be useful to enhance the S-BES applications in treating wastewater containing sulfate.

Basic oxygen furnace sludge to treat industrial arsenic- and sulfate-rich acid mine drainage.

In this study, four systems (S1, S2, S3, and S4) were evaluated to determine whether basic oxygen furnace sludge (BOFS), mainly composed of Fe (84%, mostly as elemental Fe and FeO), Ca (3%, as CaCO3), and Si (1%), is capable of removing As-spiked, Mn, Mg, and sulfate from an industrial acid mine drainage (AMDi) collected in a gold mine in Minas Gerais, Brazil. In the S1 system (BOFS/deionized water pH 2.5), the stability of the residue was evaluated for 408 h under agitation. The results showed that only Ca and Mg were solubilized, and the pH increased from 2.5 up to 11.4 within the initial 24 h and kept still until the end of the experiment (408 h). The S2 system (BOFS/AMDi) achieved 100% removal of As and Mn, and 70% removal of sulfate after 648 h. In the first 30 min, the pH increased from 2.5 to 10, which was maintained until the end of the experiment. The removal of As, Mn, and sulfate in the presence of hydrogen peroxide (S3 and S4 systems - BOFS/AMDi/H2O2) was similar to that in the S2 system, which contained only BOFS. The formation of iron oxides was not accelerated by H2O2. As regards the removal of arsenic and sulfate species, the formation of incipient calcium arsenate and calcium sulfate dehydrated was indicated by X-ray diffraction analysis and PHREEQC modeling. Dissolved manganese and magnesium precipitated as oxides, according to the geochemical modeling. After contact with AMDi, the raw BOFS, initially classified as hazardous waste, became a non-inert waste, which implies simplified, less costly disposal. Except for sulfate, the concentrations of all the other elements were below the maximum permitted levels.

The potential of electrotrophic denitrification coupled with sulfur recycle in MFC and its responses to COD/SO42- ratios.

Electrotrophic denitrification is a promising novel nitrogen removal technique. In this study, the performance and the mechanism of electrotrophic denitrification coupled with sulfate-sulfide cycle were investigated under different anodic influent COD/SO42- ratios. The results showed that electrotrophic denitrification contributed to more than 22% total nitrogen removal in cathode chamber. Higher COD/SO42- ratios would deteriorate the sulfate reduction but enhance methane production. Further mass balance indicated that the electron flow utilized by methanogenic archaea (MA) increased while that utilized by sulfate-reducing bacteria (SRB) decreased as the COD/SO42- ratio increased from 0.44 to 1.11. However, higher COD/SO42- ratios would produce more electrons to strengthen electrotrophic denitrification. Microbial community analysis showed that the biocathode was predominantly covered by Thiobacillus that encoded with narG gene. These findings collectively suggest that electrotrophic denitrification could be a sustainable approach to simultaneously remove COD and nitrogen under suitable COD/SO42- ratio based on sulfur cycle in wastewater.

Acid mine drainage treatment using zero-valent iron nanoparticles in biochemical passive reactors.

Acid mine drainage (AMD) is the major effluent generated from metal and coal mines, causing serious ecological risks and degradation of aquatic habitats and surrounding soil quality. Biochemical passive reactors (BPRs) are an option for improving AMD affected water. This study investigates the effect of the size and concentration of zerovalent iron nanoparticles (nZVI) on the efficiency of batch BPRs during AMD remediation. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were also used as complementary techniques for the investigation of the changes in microbial cells and nZVI properties after the AMD remediation. The results from the batch experiment showed that the concentration of nZVI increases the pH and decreases ORP during AMD treatment, thus favouring the removal of metals. The results also suggest that metal sulfide precipitation occurred in all the batch with reactive mixture but was greater in reactors amended with nZVI of larger size. This study revealed that the presence of nZVI in the BPR leads to metal removal as well as the inhibition of sulfate-reducing bacteria (SRB) activity. Microscopy study indicated that the addition of nZVI creates a morphological change on certain microorganisms in which the cellular membrane was fully covered with nZVI, inducing cell lysis process. These results show that nZVI is a promising reactive material for the treatment of AMD in BPR systems.

Sulfate removal from lignite coal mine drainage in Thailand using ettringite precipitation.

This research was studied the optimum conditions for sulfate removal from lignite coal mine drainage in Thailand by ettringite precipitation using Central Composite Design. The effects of Ca/S and Al/S ratio (mole basis), reaction time and temperature on the sulfate removal efficiency were investigated. The statistical analysis showed that the Al/S ratio and reaction time had a significant effect on sulfate removal efficiency. The sulfate removal efficiency increases when Al/S ratio and reaction time are increased. The Ca/S ratio in the range of 1-7 was found to have no significant effect on sulfate removal efficiency. The optimal reaction time obtained from the predicted equation was 6.14 h, while the Ca/S and Al/S ratios were fixed at 4 and 4.5, respectively, at ambient temperature. Under the optimum conditions, sulfate removal of 99.6 and 99.0% was achieved in both Lamphun and Lampang mine drainage, respectively, which is very close to the predicted value (100%). This study showed that the sulfate removal efficiencies of Lamphun and Lampang mine drainage sharply increased from 33.3 to 89.9% and 42.3 to 81.8%, respectively, when the temperature was increased from 25 to 80 ○C during a 3 h reaction time. XRD results match well with a majority of ettringite and a minority of calcium carbonate when the precipitation was done at ambient temperature. However, monosulfate was found to be the majority when the precipitation was done at 80 ○C due to the decomposition of ettringite to monosulfate at the high temperature.

Competitive adsorption of pollutants from anodizing wastewaters to promote water reuse.

Anodizing wastewater contains principally phosphate (PO43-) anions according to previous studies, but with the purpose to promote water reuse in this type of industry, a complete characterization of wastewater was made to remove other anions and cations also present in significant concentration. Particularly, the adsorption of sodium (Na+), potassium (K+), fluoride (F-), sulfate (SO42-) and phosphate (PO43-) was studied using different sorbents such as: coconut shell activated carbon, bone char, bituminous coal activated carbon, natural zeolite, silica, anionic and cationic exchange resins, a coated manganese-calcium zeolite, coconut shell activated carbon containing iron and iron hydroxide. All sorbents were characterized using FT-IR spectroscopy, potentiometric titration, nitrogen adsorption isotherms at 77 K, X-ray diffraction and SEM/EDX analysis to study the adsorption mechanism. The adsorption studies were performed in batch systems under constant agitation using both standard solutions of each ion and real anodizing wastewater. Results showed that, in general, the adsorption of all anions and cations is higher when mono-component standard solutions were used, since in the anodizing wastewater all species are competing for the active sites of the adsorbent. Na+ present in anodizing wastewater was efficiently adsorbed on coated manganese-calcium zeolite (20.55 mg/g) and natural zeolite (18.55 mg/g); while K+ was poorly adsorbed on all sorbents (less than 0.20 mg/g). Anions such as F-, SO42- and PO43-, were better adsorbed on the anionic resin (0.17, 45.38 and 2.92 mg/g, respectively), the iron hydroxide (0.14, 7.96 and 2.87 mg/g, respectively) and the bone char (0.34, 8.71 and 0.27 mg/g, respectively). All these results suggest that adsorption is a promising tertiary treatment method to achieve water reuse in the anodizing industry.

Implementation of a Sulfide-Air Fuel Cell Coupled to a Sulfate-Reducing Biocathode for Elemental Sulfur Recovery.

Bio-electrochemical systems (BES) are a flexible biotechnological platform that can be employed to treat several types of wastewaters and recover valuable products concomitantly. Sulfate-rich wastewaters usually lack an electron donor; for this reason, implementing BES to treat the sulfate and the possibility of recovering the elemental sulfur (S0) offers a solution to this kind of wastewater. This study proposes a novel BES configuration that combines bio-electrochemical sulfate reduction in a biocathode with a sulfide-air fuel cell (FC) to recover S0. The proposed system achieved high elemental sulfur production rates (up to 386 mg S0-S L-1 d-1) with 65% of the sulfate removed recovered as S0 and a 12% lower energy consumption per kg of S0 produced (16.50 ± 0.19 kWh kg-1 S0-S) than a conventional electrochemical S0 recovery system.

SP3 Protocol for Proteomic Plant Sample Preparation Prior LC-MS/MS.

Quantitative protein extraction from biological samples, as well as contaminants removal before LC-MS/MS, is fundamental for the successful bottom-up proteomic analysis. Four sample preparation methods, including the filter-aided sample preparation (FASP), two single-pot solid-phase-enhanced sample preparations (SP3) on carboxylated or HILIC paramagnetic beads, and protein suspension trapping method (S-Trap) were evaluated for SDS removal and protein digestion from Arabidopsis thaliana (AT) lysate. Finally, the optimized carboxylated SP3 workflow was benchmarked closely against the routine FASP. Ultimately, LC-MS/MS analyses revealed that regarding the number of identifications, number of missed cleavages, proteome coverage, repeatability, reduction of handling time, and cost per assay, the SP3 on carboxylated magnetic particles proved to be the best alternative for SDS and other contaminants removal from plant sample lysate. A robust and efficient 2-h SP3 protocol for a wide range of protein input is presented, benefiting from no need to adjust the amount of beads, binding and rinsing conditions, or digestion parameters.

Using hypothesis testing on the mass-transfer effect with sulfate removal as an application.

Sulfate and chemical oxygen demand removal by an anaerobic batch reactor treating of acid mine drainage is modelled. Available models are abundant but excessively complex, with large numbers of free parameters. Here, maximum likelihood and chi-squared hypothesis tests are applied to three simple models, with Malthus-Monod and Fick description, in increasing order of complexity: (i) planktonic single population (of sulfate-reducing bacteria); (ii) planktonic double-competing populations (adding fermentative bacteria); (iii) granule bound double-competing populations. The data set consists of 6 time profiles, sampled from 120 days of operation after stabilization of the reactor in pH 4. Single population is refuted by all profiles, in which the sulfate reduction is 72% larger than fermentatives. The planktonic double-competing population description is refuted at 119 days, with inner granule diffusion rate as low as 10% of the previous period. The results showed that, after an operation time, the influence of mass transfer became more evident and the incorporation of Fick's law in the model was fundamental to the description of this trend. All tests and inferences are performed at the 90% confidence interval due to large systematic uncertainties in the data.

Efficiencies of available organic mixtures for the biological treatment of highly acidic-sulphate rich drainage of the San Jose mine, Bolivia.

The environmental contamination due to mining activities in the Andean region of Bolivia is a serious concern, as it leads to highly acidic (pH 2.4) acid mine drainage (AMD), severely polluted by sulfate (>12,000 mg L-1). Passive bioreactors entailing biological sulfate reduction and removal of metals through sulfide precipitation have been recognized as a promising biotechnology. The reactivity of mixtures containing locally available substrates: sheep manure, compost and straw, was assessed through batch experiments conducted with a synthetic solution simulating the composition of AMD from San José mine (Oruro). The removal of sulfate and metals was successful in all reactors, at the end of the experiment (56 days) sulfate concentrations dropped to 1378-2081 mg L-1, corresponding to a removal efficiency between 84% and 89%, while average removal for Fe, Zn, Pb, and Cd were 99.8%, 98.5%, 94.7%, 98.6%, respectively. The sulfate and metal removal showed three phases. In the first phase, the removal was independent of the organic composition and attributable to pH-controlled mechanisms i.e. adsorption, precipitation of oxy(hydroxides) and co-precipitation. During the second phase, sulfate and metals concentrations remained rather constant; while in the third phase, the removal was affected by the organic matter composition. Sulfate removal rate attained the highest values (227-243 mg L-1 d-1) in the third phase, and it was attributable to biological reduction with not sulfate limitation. The depletion of nutrients rather than the sulfate availability may have limited the sulfate removal at the end of the experiment.

Sulfate removal using colloid-enhanced ultrafiltration: performance evaluation and adsorption studies.

Colloid-enhanced ultrafiltration (CEUF), i.e., micellar-enhanced ultrafiltration (MEUF) and polymer-enhanced ultrafiltration (PEUF), was investigated to remove sulfate ions from aqueous solution in batch experiments, using cetyltrimethylammonium (CTAB) and poly(diallydimethylammonium chloride) (PDADMAC) as colloids, respectively. Ultrafiltration performance was evaluated under different initial concentrations of sulfate (0-20 mM) and CTAB/PDADMAC (0-100 mM). The highest retention rate (> 99%) was found in dilute sulfate solutions. At high sulfate concentrations (e.g., 10 mM), a dosage of 50 mM CTAB or PDADMAC can retain approximately 90% of sulfate ions. Though concentration polarization behavior was observed, membrane characterization indicated that the fouling was reversible and membranes can be reused. Furthermore, adsorption equilibrium and kinetics studies show that Freundlich isotherm and pseudo-second-order kinetics can describe the sulfate-colloid interaction, indicating that the surface of absorbents are heterogeneous and the rate-controlling step is chemisorption. Both MEUF and PEUF show potential as effective separation techniques in removing sulfate from aqueous solutions. Under the same conditions examined, PEUF shows advantages over MEUF in its higher retention at lower polymer-to-sulfate ratios, cleaner effluent, and higher adsorption capacity, but compromises on severer flux decline and a tendency of membrane fouling. To overcome this disadvantage, membranes with higher molecular weight cut-off can be used.

Biostimulation of sulfate-reducing bacteria and metallic ions removal from coal mine-impacted water (MIW) using shrimp shell as treatment agent.

This paper comprises several assays aiming to identify the basis for the bioremediation of mine-impacted water (MIW). To do so, the conditions for build anoxic microcosms for treating this effluent were varied, containing MIW, and a source of chitin, to biostimulate sulfate-reducing bacteria (SRB). The chitin sources were: commercial chitin (CHIT) and shrimp shell (SS), which in addition to chitin, contains CaCO3, and proteins in its composition. The CHIT assays were not successful in sulfate-reduction, even when the pH was increased with CaCO3. However, in all SS assays the SRB development was successful (85% sulfate removal for assay 3), including the metal-free (MF-SS) assay (75% for assay 5). High-throughput sequencing analysis revealed the structure of bacterial community in the SS assay: the most abundant genera were Clostridium and Klebsiella, both fermentative and chitinase producers; a few SRB from the genera Desulfovibrio and Desulfosporosinus were also detected. In the MF-SS assay, Desulfovibrio genuswas detected but Comamonas was dominant. It could be deduced that SS is a suitable substrate for SRB development, but CHIT is not. The sulfate-reduction process was provided by the cooperation between fermentative/chitinase-producer bacteria together with SRB, which leads to efficient MIW treatment, removing sulfate and metallic ions.

Sulfate removal from mine-impacted water by electrocoagulation: statistical study, factorial design, and kinetics.

This work aimed to remove sulfate and acidity from mine-impacted water (MIW) via electrocoagulation (EC), a technique which stands as an advanced alternative to chemical coagulation in pollutant removal from wastewaters. The multiple electrochemical reactions occurring in the aluminum anode and the stainless steel cathode surfaces can form unstable flakes of metal hydroxysulfate complexes, causing coagulation, flocculation, and floatation; or, adsorption of sulfate on sorbents originated from the electrochemical process can occur, depending on pH value. Batch experiments in the continuous mode of exposition using different current densities (35, 50, and 65 A m-2) were tested, and a statistical difference between their sulfate removals was detected. Furthermore, the intermittent mode of exposure was also tested by performing a 22-factorial design to verify the combination with different current densities, concluding that better efficiencies of sulfate removal were obtained in the continuous mode of exposition, even with lower current densities. After 5 h of electrocoagulation, sulfate could be removed from MIW with a mean efficiency of 70.95% (in continuous mode of exposition and 65 A m-2 current density), and this sulfate removal follows probable third-order decay kinetics in accordance with the quick drop in sulfate concentration until 3 h of exposure time, remaining virtually constant at longer times. Graphical abstract.

Low temperature advanced nitrogen and sulfate removal from landfill leachate by nitrite-anammox and sulfate-anammox.

Under anaerobic conditions, ammonium (NH4+) can react with nitrite (NO2-) and sulfate (SO42-), termed nitrite-anammox (NirAnammox) and sulfate-anammox (Sulfammox), respectively. However, how to remove NH4+ and SO42- together from leachate is unclear. In this study, NirAnammox and Sulfammox cooperatively achieved nitrogen and sulfate removal from leachate using a biological process at low temperature (14-15 °C). NH4+, total nitrogen (TN), and SO42- concentrations in the influent were 610-700, 670-900, 1870-1920 mg/L, respectively, and 10 ± 1, 35 ± 3, and 897.7 ± 10 mg/L, respectively, in the effluent. Sulfammox, and NirAnammox (including partial nitrification) removed 44.2% and 35.46% of the NH4+, respectively. Therefore, because leachate contains high concentrations of NH4+ and SO42-, NirAnammox and Sulfammox can easily occur together, with nitrogen removal by Sulfammox being more than NirAnammox. The relative abundance of dominant bacteria of the Sulfammox were 10-20 times that of Candidatus Kuenenia (NirAnammox) in each reactor. Organic matter negatively affected NirAnammox, but not Sulfammox. Dissolved oxygen negatively affected both.