Performance, comparison and utilization of reduced sulfur (-2) compounds (S2-, FeS and SCN-) in autotrophic denitrification process by thiosulfate-driven autotrophic denitrifier.

The coexistence of reduced sulfur (-2) compounds (S2-, FeS and SCN-) are found in some industrial wastewaters due to pre-treatment of Fe(II) salts. These compounds as electron donors have attracted increasing interest in autotrophic denitrification process. However, the difference of their functions still remain unknown, which limit efficient utilization in autotrophic denitrification process. The study aimed to investigate and compare utilization behavior of these reduced sulfur (-2) compounds in autotrophic denitrification process activated by thiosulfate-driven autotrophic denitrifiers (TAD). Results showed that the best denitrification performance was observed in SCN-; while the reduction of nitrate was significantly inhibited in S2- system and the efficient accumulation of nitrite was observed in FeS system with cycle experiments continuing. Additionally, intermediates containing sulfur were produced rarely in SCN- system. However, the utilization of SCN- was limited obviously in comparison with S2- in coexistence systems. Moreover, the presence of S2- increased the accumulation peak of nitrite in coexistence systems. The biological results indicated that the TAD utilized rapidly these sulfur (-2) compounds, in which genus of Thiobacillus, Magnetospirillum and Azoarcus might play main roles. Moreover, Cupriavidus might also participate in sulfur oxidation in SCN- system. In conclusion, these might be attributed to the characteristics of sulfur (-2) compounds including the toxicity, solubility and reaction process. These findings provide theoretical basis for regulation and utilization of these reduced sulfur (-2) compounds in autotrophic denitrification process.

The efficient utilization of thiocyanate on simultaneous removal of ammonium and nitrate through thiosulfate-driven autotrophic denitrifiers and anammox.

The efficient utilization of thiocyanate remain be an important bottleneck in the low-cost nitrogen removal for wastewaters containing thiocyanate. The study aimed to investigate the feasibility of thiocyanate in removal of nitrate and ammonium through anammox (AN) and thiosulfate-driven autotrophic denitrifiers (TSAD). The results showed that removal of nitrate and ammonium were achieved rapidly utilizing thiocyanate, which was attributed to degradation of thiocyanate by TSAD and cooperation with AN. The utilization efficiency of thiocyanate in nitrogen removal was increased by 250% due to the microbial cooperation. Excess thiocyanate and ammonium did not influence the nitrogen removal amount. However, the nitrogen removal were affected obviously by the biomass ratio (XAN/XTSAD) between AN and TSAD Moreover, the dynamics related to removal of pollutants was described successfully by a modified Monod model with time constraints. These findings offer an insight for efficient utilization of thiocyanate in nitrogen removal via microbial cooperation.

Bisulfite activated permanganate for oxidative water decontamination.

Recently, bisulfite-activated permanganate (MnO4-; Mn(VII)) process has attracted considerable attention as a novel class of advanced oxidation technology for destruction of organic contaminants in water. However, disputes over the underlying activation mechanism as well as reactive species generated in the Mn(VII)/bisulfite system remain for a long period due to the fairly complex chemistry involved in this system. This article aims to present a critical review on scientific development of the Mn(VII)/bisulfite system, with particular focus on the generation and contribution of various reactive intermediates. Both reactive manganese species (RMnS) (i.e., soluble Mn(III), Mn(V), and Mn(VI)) and radical species (primarily SO4•-) are identified as the oxidizing components responsible for enhanced degradation of organic contaminants by the Mn(VII)/bisulfite system. Bisulfite plays a dual role of being an activating agent for reactive intermediates generation and acting as a complexing agent to stabilize RMnS. Solution chemistry (e.g., the [Mn(VII)]/[bisulfite] molar ratio, solution pH, the type of contaminants, ligands, and water matrix components) greatly impacts the generation and consumption of RMnS and radicals, thus influencing the degradation kinetics and pathways of organics. Particularly, dissolved oxygen (DO) is a vital factor for driving the oxidation of organics since the absence of DO can block the generation of SO4•- and meantime causes the consumption of RMnS by excess SO3•- as a strong reductant. Interestingly, ferrate (FeO42-, Fe(VI)) and hexavalent chromium (CrO42-/HCrO4-, Cr(VI)) that are high-valent metal oxyanions analogous to Mn(VII) can be activated by bisulfite via a similar pathway (i.e. both high-valent metal-oxo intermediates and reactive radicals are involved). Furthermore, key knowledge gaps are identified and future research needs are proposed to address the potential challenges encountered in practical application of the Mn(VII)/bisulfite oxidation technology.

A feasibility study of metal sulfide (FeS and MnS) on simultaneous denitrification and chromate reduction.

Metal sulfide-based biological process is considered as a promising biotechnology for next-generation wastewater treatment. However, it is not clear if simultaneous bio-reduction of nitrate and chromate was achievable in this process. This study aimed to evaluate the feasibility of metal sulfides (FeS and MnS) on simultaneous denitrification and chromate reduction in autotrophic denitrifying column bioreactors. Results showed that simultaneous reduction of nitrate and chromate was achieved using metal sulfides (FeS and MnS) as electron donors, in which sulfate was the sole soluble end-product. Apart from the sulfur element in the metal sulfides, Fe(II) and Mn(II) were also involved in nitrate and chromate reduction as indicative by the formation of their oxidative states compounds. In microbial communities, SHD-231 and Thiobacillus were the most predominant bacteria, which might have played important roles in simultaneous denitrification and chromate reduction. Compared to FeS, MnS showed a higher performance on nitrate and chromate removal, which could also reduce the toxic inhibition of chromate on nitrate reduction. According to results of XRD and XPS, as well as a lower sulfate production in the FeS system, FeS might have been covered easily to hydroxides due to its bio-oxidation, which limited mass transfer efficiency and bio-availability of FeS. The findings in this study offered insights in the development of promising approaches for the treatment of toxic and hazardous compounds using metal sulfide.

Are free radicals actually responsible for enhanced oxidation of contaminants by Cr(VI) in the presence of bisulfite?

Recently, the technology for the remediation of Cr(VI) pollutant via bisulfite has been found to be effective for fast elimination of co-contaminants especially in acidic solution, where free radicals (i.e., sulfate and/or hydroxyl radicals) are proposed to act as dominant oxidants. Here, it was demonstrated that high-valent Cr intermediate played a primary role in the Cr(VI)/bisulfite system through applying methyl phenyl sulfoxide (PMSO) as a probe. PMSO was effectively transformed in the Cr(VI)/bisulfite system with appreciable generation of methyl phenyl sulfone (PMSO2) product, while PMSO was oxidized by free radicals to hydroxylated and/or polymeric products rather than PMSO2. The involvement of high-valent Cr species was further supported by the formation of 18O-labeled PMSO2 in 18O labeling experiments, where the incorporation of 18O from solvent water H218O into PMSO2 was likely resulted from competitive oxygen exchange of Cr-oxo species with water. The relative contribution of high valent Cr species versus free radicals was evaluated based on the yield of PMSO2, which was dependent on the solution chemistry such as [Cr(VI)]:[bisulfite] ratio and dissolved oxygen. This work advances the understanding of chromium chemistry involved in the Cr(VI)/bisulfite system. These findings have important implications on the application of this "waste control by waste" technology for environmental decontamination.

Response of environmental variables and microbial community to sodium percarbonate addition to contaminated sediment.

Sodium percarbonate (SPC) is a common reagent used for in situ remediation of contaminated soil. Current studies focus on the effects of SPC on pollutant removal; however, a knowledge gap exists for the biochemical process following SPC addition. In this study, a microcosm batch experiment was conducted to investigate the residual effect caused by different doses of SPC addition on native microbial communities, as well as on the environmental variables of contaminated sediments. The obtained results showed that the more SPC was added, the more dissolved matters were generated and the oxidation-reduction potential was lowered. Furthermore, the metabolic activities of the microbial community were enhanced and the microbial community structure responded differently to different SPC doses: the microbes that increased at high SPC dose mainly belonged to the phylum Firmicutes, the class Clostridia, and the genera Petrimonas and Proteiniclasticum. The microbes that increased at medium SPC dose mainly belonged to the class Alphaproteobacteria and the genus Brevundimonas. In contrast, vulnerable microbes mainly belonged to the phylum Acidobacteria, the class Caldisericia, Holophagae, and the genus Sulfuricurvum. Microbes capable of fermentation, ureolysis, and chemohetrotrophy increased. These results indicate that SPC addition could indirectly provide both electron acceptors and donors, thus improving the metabolic activities of the microorganisms in the contaminated sediment. Furthermore, the utilized SPC dose should be considered to achieve the optimal benefit for in situ remediation. This study forms a valuable reference for the application of SPC in ecological engineering.

Competitive removal of Cu-EDTA and Ni-EDTA via microwave-enhanced Fenton oxidation with hydroxide precipitation.

Ethylenediaminetetraacetic acid (EDTA) can form very stable complexes with heavy metal ions, greatly inhibiting conventional metal-removal technologies used in water treatment. Both the oxidation of EDTA and the reduction of metal ions in metal-EDTA systems via the microwave-enhanced Fenton reaction followed by hydroxide precipitation were investigated. The Cu(II)-Ni(II)-EDTA, Cu(II)-EDTA and Ni(II)-EDTA exhibited widely different decomplexation efficiencies under equivalent conditions. When the reaction reached equilibrium, the chemical oxygen demand was reduced by a microwave-enhanced Fenton reaction in different systems and the reduction order from high to low was Cu(II)-Ni(II)-EDTA ≈ Cu(II)-EDTA > Ni(II)-EDTA. The removal efficiencies of both Cu(2+) and Ni(2+) in Cu-Ni-EDTA wastewaters were much higher than those in a single heavy metal system. The degradation efficiency of EDTA in Cu-Ni-EDTA was lower than that in a single metal system. In the Cu-Ni-EDTA system, the microwave thermal degradation and the Fenton-like reaction created by Cu catalyzed H2O2 altered the EDTA degradation pathway and increased the pH of the wastewater system, conversely inhibiting residual EDTA degradation.

Flocculation mechanism by a novel combined aluminum-ferrous-starch flocculant (CAFS).

A combined flocculant (CAFS) was prepared with Al(2)(SO(4))(3)·18H(2)O, FeSO(4)·7H(2)O and starch. The flocculation mechanism of reactive brilliant red X-3B was studied. The results showed that CAFS was a cationic polymeric flocculant with high charge density, and its mesh starch chains grafted polyaluminum and polyferrous. At the preliminary stage, the main flocculation mechanism was adsorption and charge neutralization. At a later stage, the high molecular weight and flexible linear chains of CAFS initiated bridge-aggregation and sweep-flocculation. Moreover, the zeta potential and dynamic changes of flocs were closely related to flocculant dosages and the pH. The optimum dosage of CAFS and pH value were 0.990 mg/L and 5.0. Taken together, these results suggested CAFS as a novel flocculant in water treatment, with good results for the studied conditions.

Synthesis, flocculation and adsorption performance of amphoteric starch.

A novel amphoteric copolymer flocculant was synthesized by incorporating a cationic moiety 2,3-epoxypropyl trimethyl ammonium chloride (GTA) and an anion moiety phosphate onto the backbone of starch with microwave radiation. The synthesized starch copolymer was characterized and examined by FTIR, (1)H NMR spectroscopy, scanning electron microscopy (SEM), molecular mass and polydispersity, swelling power and solubility index. Flocculation performance was evaluated in 50mg/L methyl violet solution. It has been found that these flocculation characteristics mainly depended on the charge neutralization, followed by the interchain bridging of the amphoteric copolymer. Also, adsorption to Pb (II) solution was investigated by jar test. The results showed that the adsorption capacity of amphoteric copolymer correlated with pH value, adsorption time and initial Pb (II) concentration.