Sulfate Reduction Efficiency Research Articles

Treatment of textile wastewater using sequential sulfate-reducing anaerobic and sulfide-oxidizing aerobic membrane bioreactors

This study aims at evaluating the performance of sequential sulfate-reducing anaerobic and sulfide-oxidizing aerobic membrane bioreactors (MBRs) for the treatment of synthetic textile wastewater. The process performance was evaluated under varying concentrations of COD (1000–2000mg/L), NaCl (500–1000mg/L), and sulfate (500–1500mg/L), but keeping dye (Remazol Brilliant Violet 5R) concentration constant at 200mg/L. In sulfate reducing anaerobic MBR (AnMBR), COD removal efficiency remained between 80% and 85%. The sulfate reduction efficiency was directly related with COD/sulfate ratio. Almost complete decolorization was attained in the AnMBR, whereas slight recolorization was observed in the AeMBR due to autooxidation of aromatic amines. EDS analyses illustrated that cake layer in AnMBR contained much higher amounts of S, Fe and Cu due to formation of metal–sulfide precipitates, whereas Ca and P were the major inorganic elements in AeMBR. In the cake layers of both MBRs, high molecular weight soluble organics were observed by gel permeation chromatographic analyses together with the identification of proteins and polysaccharides by the FT-IR analyses. Capillary suction time, specific resistance to filtration and supernatant filterability tests illustrated that AnMBR sludge had less filterability and stable operation was possible with a flux of around 5LMH.

Effect of sulfate addition on methane production and sulfate reduction in a mesophilic acetate-fed anaerobic reactor.

A mesophilic anaerobic moving bed biofilm reactor (MBBR) was operated to evaluate the effect of sulfate addition on methane production and sulfate reduction using acetate as the sole carbon source. The results show that at the organic loading rate of 4.0 g TOC/L/day, the TOC removal efficiencies and the biogas production rates achieved over 95 % and 7000 mL/L/day without sulfate, respectively, and slightly decreased with sulfate addition (500-800 mg/L). Methane production capacities were not influenced significantly with the addition of sulfate, while sulfate reduction efficiencies were not stable with 23-87 % in the acetate-fed reactor. Fluorescent in situ hybridization (FISH) was used to analyze the functional microbial compositions of acetate-degrading methane-producing bacteria (MPB) and sulfate-reducing bacteria (SRB) in the reactor. The results found that as the increase of sulfate concentration, the proportion of Methanomicrobiales increased up to 58 ± 2 %, while Methanosaeta and Methanosarcina decreased. The dominant methanogens shifted into hydrogenotrophic methanogens from even distribution of acetoclastic and hydrogenotrophic methanogens. When hydrogenotrophic methanogens were dominant, sulfate reduction efficiency was high, while sulfate reduction efficiency was low as acetoclastic methanogens were dominant.

High sulfate reduction efficiency in a UASB using an alternative source of sulfidogenic sludge derived from hydrothermal vent sediments.

Sulfidogenesis in reactors is mostly achieved through adaptation of predominantly methanogenic granular sludge to sulfidogenesis. In this work, an upflow anaerobic sludge blanket (UASB) reactor operated under sulfate-reducing conditions was inoculated with hydrothermal vent sediments to carry out sulfate reduction using volatile fatty acids (VFAs) as substrate and chemical oxygen demand (COD)/SO4 (-2) ratios between 0.49 and 0.64. After a short period of adaptation, a robust non-granular sludge was capable of achieving high sulfate reduction efficiencies while avoiding competence with methanogens and toxicity to the microorganisms due to high sulfide concentration. The highest sulfide concentration (2,552 mg/L) was obtained with acetate/butyrate, and sulfate reduction efficiencies were up to 98 %. A mixture of acetate/butyrate, which produced a higher yielding of HS(-), was preferred over acetate/propionate/butyrate since the consumption of COD was minimized during the process. Sludge was analyzed, and some of the microorganisms identified in the sludge belong to the genera Desulfobacterium, Marinobacter, and Clostridium. The tolerance of the sludge to sulfide may be attributed to the syntrophy among these microorganisms, some of which have been reported to tolerate high concentrations of sulfide. To the best of our knowledge, this is the first report on the analysis of the direct utilization of hydrothermal vent sediments as an alternate source of sludge for sulfate reduction under high sulfide concentrations.

Use of Marine Waste Extract as a Nitrogen Source for Biological Sulfate Reduction: Development of a Suitable Alternative

Marine wastes extract (MWE), prepared from marine organic wastes, was used to develop an alternative nitrogen source for sulfate-reducing bacteria (SRB) in environments like acid mine drainage that are acidic in nature and contain high levels of sulfate and dissolved metals. The MWE contains 13.95 g L−1 of nitrogen, and other micronutrients like K, Na, P, S, Ca, Fe, Mg, Mn, Zn, Co, Cu and Ni, and has a C/N ratio of 0.107. A modified SRB medium (MSRB) was developed by replacing the commercial nitrogen source of standard SRB growth medium with MWE. MSRB was compared with modified Postgate B, Postgate B, and Widdel and Pfennig media, which contained bactopeptone and NH4Cl, as nitrogen sources. Results showed that the growth media could support a total microbial population of 2.8 × 1012–6.2 × 1012 cells mL−1 with 96, 80, 92.5, and 65 % SRB in MSRB, Postgate B, modified Postgate B, and Widdel and Pfennig media, respectively. The sulfate reduction efficiency was 97, 87, 72, and 68 % at reduction rates of 12.41, 11.10, 4.35, and 8.8 mg L−1 h−1, respectively, for the same media. We conclude that MWE could be a cost-effective substitute for commercially available nitrogen sources for SRB for large-scale treatment of sulfate-rich wastewater.

Bioremediation of copper-containing wastewater by sulfate reducing bacteria coupled with iron

In order to treat copper-containing wastewater effectively using sulfate reducing bacteria (SRB), iron (Fe0) was added to enhance the activity of SRB. The SRB system and the SRB + Fe0 system were operated under continuous operation. The sulfate reduction efficiency of the SRB + Fe0 system was twice as much as that of the SRB system with the sulfate loading rate at 125 mg L−1 h−1. The effect of COD/SO42− on sulfate reduction indicates an enhanced activity of SRB by adding Fe0. 99% of total sulfate was deducted in both systems at pH 4.0–7.0, and temperature slightly influenced the removal of sulfate in the SRB + Fe0 system. In the copper-containing wastewater treatment, the SRB + Fe0 system shows a better performance since sulfate removal in this system was higher than the SRB system, and the removal ratio of Cu2+ was held above 95% in SRB + Fe0 system at all influent Cu2+ concentrations.

Biological inverse fluidized-bed reactors for the treatment of low pH- and sulphate-containing wastewaters under different COD conditions

The feasibility of removing sulphate using low-density polypropylene pellets as carrier material in two lactate-fed sulphidogenic inverse fluidized-bed reactors was investigated. Two different COD/sulphate ratios and two different feed–sulphate concentrations were used for the operation of the reactors. During the 242 days of operation, the robustness of the system was studied by suddenly decreasing the feed pH to 3.00. A 10% fluidization degree was used since the carrier material adopted showed not to be adequate to attain a satisfactory immobilization of the biomass with higher fluidization degrees. This resulted in a failure of the process when the feed pH was intentionally decreased to 3.00 in reactor 2, operated with a COD/sulphate ratio of 4.00. On the contrary, when a slightly acidic feed solution was fed to reactor 2, a 97% sulphate reduction efficiency was obtained. In reactor 1, operated with a COD/sulphate ratio of 0.67 throughout the experiment, COD removal and sulphate reduction efficiencies reached the highest values of 75% and 35%, respectively. Higher efficiencies were not achieved also due to the accumulation of acetate and the most likely presence of microbial competition between sulphate reducers and other microorganisms.

Implications of volatile fatty acid profile on the metabolic pathway during continuous sulfate reduction

Volatile fatty acid (VFA) profile is an important parameter in anaerobic reactors because it enables the assessment of metabolic pathways. Volatile fatty acids were monitored during sulfate reduction in a UASB (upflow anaerobic sludge blanket) reactor treating 2g/L sulfate concentration and with the organic loading increasing from 3.5 kg COD/m(3)d to 5.9 kg COD/m(3)d, for a 1-day residence time. In the absence of recirculation, the best outcome (65% reduction) was noticed with the lowest organic loading (3.55 kg/m(3)d). When recirculation was applied, sulfate reduction yields increased to 89%, corresponding to a sulfate removal rate of 1.94 kg SO(4)(2-)/m(3)d. The reactor performance was discussed in relation to microbial diversity and metabolic pathways. At high organic loading, two metabolic pathways account for lactate degradation: (i) lactate is oxidized to acetate and carbon dioxide by the incomplete-oxidizer SRB (sulfate-reducing bacteria) Desulfomonas, Desulfovibrio, Desulfolobus, Desulfobulbus and Desulfotomaculum spp.; (ii) lactate is converted to acetate by fermenting bacteria such as Clostridium sp. High propionate concentrations imply that there are low sulfate reduction efficiencies.

Sulfidogenic biotreatment of synthetic acid mine drainage and sulfide oxidation in anaerobic baffled reactor

The treatment of synthetic acid mine drainage (AMD) water (pH 3.0–6.5) containing sulfate (3.0–3.5 g L −1) and various metals (Co, Cu, Fe, Mn, Ni, and Zn) was studied in an ethanol-fed sulfate-reducing 4-compartment anaerobic baffled reactor (ABR) at 32 °C. The reactor was operated for 160 days at different chemical oxygen demand (COD)/sulfate ratios, hydraulic retention times (HRT), pH, and metal concentrations to study the robustness of the process. The last compartment of the reactor was aerated at different rates to study the bio-oxidation of sulfide to elemental sulfur. The highest sulfate reduction efficiency (88%) was obtained with a feed sulfate concentration of 3.5 g L −1, COD/sulfate mass ratio of 0.737, feed pH of 3.0 and HRT of 2 days without aeration in the 4th compartment. The corresponding COD removal efficiency was about 92%. The alkalinity produced in the sulfidogenic ethanol oxidation neutralized the acidic mine water from pH 3.0–4.5 to pH 7.0–8.0. Effluent soluble and total heavy metal concentrations were substantially reduced with removal efficiencies generally higher than 99%, except for Mn (25–77%). Limited aeration in the 4th compartment of ABR promoted incomplete oxidation of sulfide to elemental sulfur rather than complete oxidation to sulfate. Depending on the aeration rate and HRT, 32–74% of produced sulfide was oxidized to elemental sulfur. This study demonstrates that by optimizing operating conditions, sulfate reduction, metal removal, alkalinity generation, and excess sulfide oxidation can be achieved in a single ABR treating AMD.

Comparison of sulfidogenic up-flow and down-flow fluidized-bed reactors for the biotreatment of acidic metal-containing wastewater

Biotreatment of Cu- and Zn-containing synthetic wastewater was studied in sulfate-reducing up-flow (UFBR) and down-flow fluidized-bed reactors (DFBR) at 35 degrees C. The robustness of the systems was studied by stepwise increasing feed metal concentrations (total metal concentrations 25-300 mg/L) and decreasing feed pH (down to 2.0). Lactate was used as a carbon and energy source for sulfate reducing bacteria. After start-up, sulfate reduction and COD oxidation efficiencies were 60-86% and 87-95% in UFBR and, 40-88 and 55-95% in DFBR, respectively. Optimum COD/sulfate ratio for sulfate reduction was 0.85 and 1.25 for UFBR and DFBR, respectively. Approximately 70% and 55% of the electrons produced from lactate oxidation were used for sulfate reduction in UFBR and DFBR, respectively. Sulfide production and metal precipitation capacity of UFBR were higher than those of DFBR, although down-flow regime gave the possibility of metal recovery. Metals were precipitated more than 99% in both reactors. XRF analyses showed that metals were precipitated as metal-sulfides.

Biotreatment of acidic zinc- and copper-containing wastewater using ethanol-fed sulfidogenic anaerobic baffled reactor

The treatment of acidic (pH 6.5-3), sulfate- (2-3 g/L), Zn- and Cu- (total metal 0-500 mg/L) containing wastewater was studied in a four-stage anaerobic baffled reactor (ABR) at 35 °C for 250 days. Ethanol was supplemented (COD/SO4(2-) = 0.67) as carbon and electron source for sulfate reducing bacteria. Sulfate reduction, COD oxidation and metal precipitation efficiencies were 70-92, 80-94 and >99%, respectively. The alkalinity produced from sulfidogenic ethanol oxidation increased the wastewater pH from 3.0 to 7.0-8.0. The electron flow from organic oxidation to sulfate averaged 87%. Decreasing feed pH to 3 and increasing total metal concentrations to 500 mg/L did not adversely affect the performance of ABR and sufficient alkalinity was produced to increase the effluent pH to neutral values. More than 99% of metals were precipitated in the form of metal-sulfides. Accumulation of precipitated metals in the first compartment allowed metal recovery without disturbing reactor performance seriously.

Sulfate reduction during the acidification of sucrose at pH 5 under thermophilic (55 °C) conditions. II: Effect of sulfide and COD/[formula omitted] ratio

This work studied the effect of the sulfide concentration and COD/SO42- ratios (4 and 1) on sulfate reduction and acidification in a thermophilic (55°C) UASB reactor fed with sucrose (4gCOD(lreactord)−1) operated at a reactor mixed liquor pH controlled at 5 for a period of 301days. When implementing N2 stripping, sulfate reduction efficiencies up to 95%, corresponding to volumetric sulfate reduction rates of 0.87 and 4.2g (lreactord)−1 at the COD/SO42- ratios of 4 and 1, respectively, were achieved. Sulfide was toxic to sulfate reduction at a total dissolved sulfide concentration of 100mgl−1. Acidification was always complete and acetate was the only form of substrate in the effluent at a COD/SO42- ratio of 1. The sludge was well retained in the reactor and kept its granular shape throughout the reactor run.

Microbial Consortia from Taptapani Hot Water Springs for Mining Effluent Treatment

Problem statement: Soluble sulfate load in effluent is a crucial problem from mining industries. The study involved isolation of efficient Sulfate Reducing Bacterial (SRB) consortium from hot water spring for bioremediatrion of sulfate contaminated waste water. Approach: The enriched bacterial consortium was isolated in medium DSMZ 16695. The sulfate reduction efficiency was measured by turbidometric method. The Km and Rmax value of the consortium was determined. It was immobilized in 10L bioreactor and the sulfate reduction was measured in presence of media and mine effluent. Results: The consortium was found to reduce 2000ppm of sulfate in 36h under optimum condition. The Km of 1.1530 ppm and Rmax value of 0.030h−1 was obtained under optimum conditions of pH-7.5 at 40°C with 2% inoculum. Consortium immobilized under ambient condition in a 10L packed bed reactor yielded about 21-41% reduction of soluble sulfate in synthetic medium prepared using effluent water and tap water respectively. Conclusion: This study reports for the first time the use of efficient SRB consortia from hot water spring for bioremediation of mine effluent.

ISOLASI DAN IDENTIFIKASI BAKTERI PEREDUKSI SULFAT PADA AREA PERTAMBANGAN BATU BARA MUARA ENIM, SUMATERA SELATAN

Sulfate reducing bacteria utilize sulfate as their terminal electron acceptor and reduce it to sulphide. Acid mine drainage, by-products of mining activities, is an acidic sulfate-rich wastewater suitable habitat for sulfate reducing bacteria. Isolation and identification of sulfate reducing bacteria collected from Muara Enim coal mining, South Sumatra was carried out at Laboratory of Environmental Biotechnology, Indonesian Center for Biodiversity and Biotechnology (ICBB), Bogor, and Laboratory of Microbiology, Faculty of Veterinary, Bogor Agricultural University. Postgate B liquid media was used for isolation and purification via serial dilution. Physiological and biochemical characterization was done based on Bergeys Manual of Determinative Bacteriology. Fifteen pure isolates have been isolated with diverse characteristics. Eight isolates can sustain at pH 3, while the rest sustain at pH 4 or above. Sulfate reduction efficiency of each isolates were different, but increased as the pH increased. The bacteria are classified as Desulfovibrio sp., which is characterized straight rods, motile, non spore-forming and able to grow in simple organic carbon.

Extent of Precipitation and Sorption During Copper Removal from Synthetic Wastewater in the Presence of Sulfate-Reducing Bacteria

A sulfate-reducing bacterial culture was successfully enriched from the seed sludge of anaerobic sludge digester. Sulfate-reducing bacteria (SRB) in the enriched culture (around 42%) were characterized by fluorescence in situ hybridization (FISH) with group and genus specific 16S rRNA-targeted oligonucleotide probes. Desulfosarcina, Desulfococcus, Desulfofaba, and Desulfofrigus spp. were identified as the dominant species of the enriched SRB. Subsequently, batch experiments were conducted at initial copper and sulfate concentrations of 10 and 300 mg/L, respectively, to quantify the ability of the enriched SRB in simultaneous sulfate reduction and copper removal. Sulfate reduction efficiencies of the culture in the absence (biotic system without copper, BS-1) and the presence (biotic system with copper, BS-2) of copper were 96.8 and 98.8%, respectively, after 6 days. In BS-2, 99.2% copper removal was observed after 1 day. However, 67% of copper was removed by chemical precipitation and bioaccumulation. No significant inhibition of bacterial growth was observed at the copper concentration studied, that is, 10 mg/L. Chemical precipitation as hydroxide/carbonate caused a copper removal of 44% in AS-1 (abiotic system without lactate) and 36% in AS-2 (abiotic system with lactate), after 6 days. However, the majority of copper was removed as copper sulfide well before the occurrence of copper hydroxide precipitation. Energy dispersive X-ray spectroscopy (EDS) analysis of the precipitates obtained from biotic and abiotic systems confirmed the origin of copper sulfide as the result of SRB. As a whole, the results of this study could be useful to understand the mechanisms of copper removal, i.e. chemical precipitation, bioprecipitation and biosorption/bioaccumulation during sulfate reduction by SRB.

Performance of sulfidogenic anaerobic baffled reactor (ABR) treating acidic and zinc-containing wastewater

The applicability of anaerobic baffled reactor (ABR) was investigated for the treatment of acidic (pH 4.5–7.0) wastewater containing sulfate (1000–2000 mg/L) and Zn (65–200 mg/L) at 35 °C. The ABR consisted of four equal stages and lactate was supplemented (COD/SO 4 2− = 0.67) as carbon and energy source for sulfate reducing bacteria (SRB). The robustness of the system was studied by decreasing pH and increasing Zn, COD, and sulfate loadings. Sulfate-reduction efficiency quickly increased during the startup period and reached 80% within 45 days. Decreasing feed pH, increasing feed sulfate and Zn concentrations did not adversely affect system performance as sulfate reduction and COD removal efficiencies were within 62–90% and 80–95%, respectively. Although feed pH was steadily decreased from 7.0 to 4.5, effluent pH was always within 6.8–7.5. Over 99% Zn removal was attained throughout the study due to formation of Zn-sulfide precipitate.

Dynamics of sulfidogenesis associated to methanogenesis in horizontal-flow anaerobic immobilized biomass reactor

Two bench-scale horizontal anaerobic fixed bed reactors were tested to remove both sulfate and organic matter from wastewater. First, the reactors (R1 and R2) were supplied with synthetic wastewater containing sulfate and a solution of ethanol and volatile fatty acids. Subsequently, R1 and R2 were fed with only ethanol or acetate, respectively. The substitution to ethanol in R1 increased the sulfate reduction efficiency from 83% to nearly 100% for a chemical oxygen demand to sulfate (COD/sulfate) ratio of 3.0. In contrast, in R2, the switch in carbon source to acetate strongly decreased sulfidogenesis and the maximum sulfate reduction achieved was 47%. Process stability in long-term experiments and high removal efficiencies of both organic matter and sulfate were achieved with ethanol as the sole carbon source. The results allow concluding that syntrophism instead of competition between the sulfate reducing bacteria and acetoclastic methanogenic archaeal populations prevailed in the reactor.

Comparisons of Initial Experiments and Reactor Model Predictions in High Temperature Black Liquor Gasification

Pressurized high temperature black liquor gasification might significantly improve the efficiency of the energy and chemical recovery cycle in kraft pulping. The process, which is based on the entrained-flow principle, is under development, and a scale-up from an existing pilot gasifier is planned. We developed a self-consistent com-putational fluid dynamic (CFD) model, in conjunction with pilot gasifier experiments, as a tool for scale-up. This report compares model predictions against experimental pilot gasifier data. The agreement between model and experiments is encouraging in certain areas, but significant discrepancies resulted for other areas. Model predic-tions of global performance parameters, such as sulfate reduction efficiency and carbon conversion, are in reason-able agreement with the experiments, but the predicted gas composition differed significantly from results of the experiments. Direct measurements of quantities to validate the current model validation are difficult to obtain because of severe conditions in the gasifier, and many of the model comparisons are based on indirect values. Hence, it is difficult to judge whether the errors come from the experiment or the simulation. Before we can draw a definite conclusion about the model’s validity, improved in-situ measurements inside the gasifier are necessary and are currently under development.

Anaerobic degradation of landfill leachate using an upflow anaerobic fixed-bed reactor with microbial sulfate reduction

This study evaluated the anaerobic degradation of landfill leachate and sulfate reduction as a function of COD/(SO 4 2−) ratio in an upflow anaerobic fixed-bed reactor. The reactor, which was inoculated with a mixed consortium, was operated under a constant hydraulic retention time (HRT) of 5 days. We investigated the effect of COD/(SO 4 2−) ratio variation on the sulfate reduction efficiency, hydrogen sulfide production, chemical oxygen demand (COD) removal, conductivity, and pH variation. The best reactor performance, with significant sulfate reduction efficiency and COD removal efficiency of 91% and 87%, respectively, was reached under a COD/(SO 4 2−) ratio of 1.17. Under these conditions, microscopic analysis showed the abundance of vibrios and rod-shaped bacterial cells. Two anaerobic bacteria were isolated from the reactor sludge. Phylogenetic studies performed on these strains identified strain A1 as affiliated to Clostridium genus and strain H1 as a new species of sulfate-reducing bacteria affiliated to the Desulfovibrio genus. The closest phylogenetic relative of strain H1 was Desulfovibrio desulfuricans, at 96% similarity for partial 16S RNA gene sequence data. Physiological and metabolic characterization was performed for this strain.

Sulfate reduction at pH 4 during the thermophilic (55°C) acidification of sucrose in UASB reactors

Continuous sulfate reduction at pH 4.0 was demonstrated in a pH controlled thermophilic (55 degrees C) upflow anaerobic sludge bed reactor fed with sucrose at a COD/SO(4)(2-) ratio of 0.9 and an organic loading rate of 0.8 and 1.9 gCOD (l(reactor) d)(-1) for a period of 78 days. A nearly complete sulfate reduction efficiency was achieved throughout the reactor run, corresponding to sulfate removal rates of 0.91 and 1.92 g (l(reactor) d)(-1) at sulfate loading rates of 0.94 and 2 g (l(reactor) d)(-1), respectively, by keeping the sulfide concentration below 20 mg l(-1) due to stripping with nitrogen gas. Acidification was always complete and acetate was the only degradation intermediate left in the effluent, which did not exceed 180 mgCOD l(-1) in pseudo-stationary states. The sludge was well retained in the reactor and kept its granular form. Zn, Cu, Se, and Mo accumulated in the sludge, whereas Co, Ni, Fe, and Mn leached from the sludge, despite their continuous supply to the reactor via the influent. The bacterial diversity in the reactor sludge at the end of the reactor run was low and the culture was dominated by one acidifying species, resembling Thermoanaerobacterium sp., and one sulfate reducing species, resembling Desulfotomaculum sp.

Comparison of CSTR and UASB reactor configuration for the treatment of sulfate rich wastewaters under acidifying conditions

The effects of lowering the operational pH from 6 to 5 on mesophilic (30 °C) sulfate reduction during the acidification of sucrose at an organic loading rate of 5 gCOD (l reactor d) −1 and at a COD/SO 4 2− ratio of 4 were evaluated in a CSTR and in a UASB reactor. The HRT was 24 h and 10 h, respectively. Acidification was complete in both reactors at pH 6 and the lowering of the operational pH to 5 did not affect the acidification efficiency in the CSTR but decreased the acidification efficiency of the UASB to 72%. The decrease to pH 5 caused an increase in the effluent butyrate and ethanol concentrations in both reactors. Lowering the pH from 6 to 5 caused a decrease in sulfate reduction efficiencies in both reactors, from 43% to 25% in the CSTR and from 95% to 34% in the UASB reactor. The acidification and sulfate reduction efficiencies at pH 5 could be increased to 94% and 67%, respectively, by increasing the HRT of the UASB reactor to 24 h.