The effect of biological sulfate reduction on anaerobic color removal in anaerobic–aerobic sequencing batch reactors

Hybrid constructed wetlands and filamentous fungi for treatment of mixed sewage and industrial effluents

Developing countries face multifaceted problems of water pollution and futile measures to combat water pollution. This study was conducted to explore the potential application of sustainable nature-based solutions, hybrid constructed wetlands, and the application of filamentous fungi to treat polluted river water that receives sewage and industrial wastewater. A pilot-scale hybrid constructed wetland design comprising two types of floating plants in distinct tanks along with a floating wetland and a free-water surface wetland connected in series was commissioned and tested. The system successfully removed organic pollution (BOD 94% and COD 90%), nutrients (NH4-N and NO3-N 67% and PO4-P 81%), and heavy metals (Cr 75%, Ni 56%, and Fe 79%) in 40 h and showed a high buffering capacity to cope with the varying pollutant loads. Metagenomics analysis of treated and untreated samples of river water revealed a diversified spatial bacterial community with ~ 25% sequences related to sulfur-metabolizing bacteria, genus Sulfuricurvum. The application of an immobilized strain of A. niger as a mycoremediation technique was also tested. It successfully removed pollutants in the combined sewage and industrial wastewater present in river water: COD (96%), TSS (97%), NH4-N (65%), NO3-N (67%), and PO4-P (78%). This study demonstrated that hybrid constructed wetlands and mycoremediation can be used as sustainable wastewater treatment options in the local context and also in developing countries where most of the conventional wastewater treatment plants do not operate.

Biological treatment of real textile wastewater containing sulphate, salinity, and surfactant through an anaerobic-aerobic system

Real textile wastewater containing high salinity (up to 12.6 g·kg^-1) and surfactant (up to 5.9 mg·L^-1 of linear alkylbenzene sulfonate - LAS) was submitted to biological treatment for colour (up to 652 mg Pt-Co·L^-1) and sulphate (up to 1,568.6 mg SO₄^-2·L^-1) removal. The influence of ethanol and molasses supplementation was firstly evaluated in anaerobic batch reactors for the removal of dyes and sulphate. Subsequently, aiming to remove aromatic amines (dye degradation by-products), an anaerobic-aerobic continuous system supplemented with molasses was applied. Supplementation had no influence on colour removal (maximum efficiencies around 70%), while it improved sulphate reduction (23% without supplementation against 87% with supplementation), and conferred robustness to the reactors, which recovered quickly after higher salinity impact. The aerobic reactor removed aromatic amines when the level of surfactants was lower than 1.0 mg LAS·L^-1, but the performance of the system was hindered when the concentration was increased to 5.9 mg LAS·L^-1. Findings suggest that the supplementation of an easily biodegradable organic matter might be a strategy to overcome wastewater fluctuation in composition.

Biochar Derived from Agricultural Wastes as a Means of Facilitating the Degradation of Azo Dyes by Sulfides

Dyes are common contaminants, some of which are teratogenic, carcinogenic, and causative of ecological damage, and dye wastewater often contains toxic sulfides. Biochar has been widely used for the adsorption and catalysis degradation of pollutants, including dyes and sulfides, due to its abundant surface functional groups and large specific surface area. Therefore, the simultaneous treatment of dyes and sulfides with biochar may be a feasible, effective, and novel solution. This study sought to utilize low-cost, environmentally friendly, and widely sourced biochar materials from agricultural wastes such as corn stalk, rice chaff, and bean stalk to promote the reduction of dyes by sulfides. Through the action of different biochars, sulfides can rapidly decompose and transform oxidizing dyes. The RCB800 (rice chaff biochar material prepared at 800 °C) was observed to have the best effect, with a degradation rate of 96.6% in 40 min and 100% in 50 min for methyl orange. This series of materials are highly adaptable to temperature and pH, and the concentration of sulfides has a significant effect on degradation rates. Compared with commercial carbon materials, biochars are similar in terms of their catalytic mechanism and are more economical. Scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption and desorption characterization results indicated that biochar contains more pores, including mesopores, and a sufficient specific surface area, both of which are conducive to the combination of sulfides and dyes with biochar. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that there are oxygen-containing functional groups (examples include quinones and carboxyl groups) on the surface of biochar that promote the reaction of sulfide and dye. The formation of active polysulfides also potentially plays an important role in the degradation reaction. This article outlines a new method for improving the degradation efficiency of azo dyes and sulfides via biochar materials derived from widely sourced agricultural wastes.

Functional and Transcriptomic Characterization of a Dye-decolorizing Fungus from Taxus Rhizosphere

We isolated three laccase-producing fungus strains from Taxus rhizosphere. Myrotheium verrucaria strain DJTU-sh7 had the highest laccase activity of 216.2 U/ml, which was increased to above 300 U/ml after optimization. DJTU-sh7 had the best decolorizing effect for three classes of reactive dyes. The DJTU-sh7-containing fungal consortium displayed the robust decolorizing ability. Both color removal efficiency and chemical oxygen demand were increased in the consortium mediated biotransformation. Transcriptome changes of M. verrucaria elicited by azo dye and phenolic were quantified by the high throughput transcriptome sequencing, and the activities of the selected oxidases and reductases were determined. The possible involvement of oxidases and reductases, especially laccase, aryl alcohol oxidase, and ferric reductase in the biotransformation of dye and phenolic compounds was revealed at both transcriptomic and phenotypic levels. Revealing the transcriptomic mechanisms of fungi in dealing with organic pollutants facilitates the fine-tuned manipulation of strains in developing novel bioremediation and biodegradation strategies.

We isolated three laccase-producing fungus strains from Taxus rhizosphere. Myrotheium verrucaria strain DJTU-sh7 had the highest laccase activity of 216.2 U/ml, which was increased to above 300 U/ml after optimization. DJTU-sh7 had the best decolorizing effect for three classes of reactive dyes. The DJTU-sh7-containing fungal consortium displayed the robust decolorizing ability. Both color removal efficiency and chemical oxygen demand were increased in the consortium mediated biotransformation. Transcriptome changes of M. verrucaria elicited by azo dye and phenolic were quantified by the high throughput transcriptome sequencing, and the activities of the selected oxidases and reductases were determined. The possible involvement of oxidases and reductases, especially laccase, aryl alcohol oxidase, and ferric reductase in the biotransformation of dye and phenolic compounds was revealed at both transcriptomic and phenotypic levels. Revealing the transcriptomic mechanisms of fungi in dealing with organic pollutants facilitates the fine-tuned manipulation of strains in developing novel bioremediation and biodegradation strategies.

Hydraulic retention time influence on azo dye and sulfate removal during the sequential anaerobic-aerobic treatment of real textile wastewater

In the present study, we evaluate the behavior of real textile wastewater treatment using a system composed of two sequential pilot-scale reactors (anaerobic followed by aerobic) during 622 days. The work focused on the competition between color and sulfate removal processes, when the hydraulic retention time (HRT) was increased in the anaerobic/aerobic reactors from 16/12 hours in phase I (PI) to 4/3 days in phase II (PII). The organic matter was successfully removed in both phases through the system, and the highest efficiency (75%) was achieved in PII. The increase in the HRT did not improve azo dye degradation under anaerobic conditions. Instead, it favored sulfate reduction, which removal efficiency increased from 26% in PI to 75% in PII. Aromatic amines were detected in the anaerobic reactor effluent and removed in the aerobic reactor.

Oxidation process of dissolvable sulfide by synthesized todorokite in aqueous systems

Todorokite, formed from Mn(II) in supergene environments, can affect the transformation and migration of dissolvable sulfides in soils and water. In this work, todorokite was synthesized with different degrees of crystallinity, and the redox mechanism of dissolvable sulfide and todorokite was studied in both closed and open aqueous systems. The influences of pH, temperature, crystallinity, the amount of manganese oxides, and oxygen gas on S(2-) oxidation process were investigated. It is found that S(2-) was oxidized to S(0), SO3(2-), S2O3(2-) and SO4(2-), and about 90% of S(2-) was converted into S(0) in closed systems. The participation of oxygen facilitated the further oxidation of S(0) to S2O3(2-). S(0) and S2O3(2-) were formed with the conversion rates of S(2-) about 45.3% and 38.4% after 1h of reaction, respectively, and the conversion rate for S2O3(2-) increased as reaction prolonged for a longer period. In addition, todorokite was reduced to Mn(OH)2 in the presence of nitrogen gas, and its chemical stability increased when oxygen gas was admitted into the reaction system during the process. The oxidation rate of dissolvable sulfide followed a pseudo-first-order kinetic law in the initial stage (within 10 min), and the initial oxidation rate constant of S(2-) increased with elevating temperature, increasing the quantity and decreasing crystallinity of todorokite. The initial oxidation rate of dissolvable sulfide decreased with continuous feeding of O2 into the test solution, possibly due to a decrease in active Mn(III) content in todorokite. The present work demonstrates the redox behaviors and kinetics of dissolvable sulfide and todorokite in aquatic environments.