Anaerobic cyanides oxidation with bimetallic modulation of biological toxicity and activity for nitrite reduction.

Cyanide is a typical toxic reducing agent prevailing in wastewater with a well-defined chemical mechanism, whereas its exploitation as an electron donor by microorganisms is currently understudied. Given that conventional denitrification requires additional electron donors, the cyanide and nitrogen can be eliminated simultaneously if the reducing HCN/CN- and its complexes are used as inorganic electron donors. Hence, this paper proposes anaerobic cyanides oxidation for nitrite reduction, whereby the biological toxicity and activity of cyanides are modulated by bimetallics. Performance tests illustrated that low toxicity equivalents of iron-copper composite cyanides provided higher denitrification loads with the release of cyanide ions and electrons from the complex structure by the bimetal. Both isotopic labeling and Density Functional Theory (DFT) demonstrated that CN--N supplied electrons for nitrite reduction. The superposition of chemical processes reduces the biotoxicity and enhances the biological activity of cyanides in the CN-/Fe3+/Cu2+/NO2- coexistence system, including complex detoxification of CN- by Fe3+, CN- release by Cu2+ from [Fe(CN)6]3-, and NO release by nitrite substitution of -CN groups. Cyanide is the smallest structural unit of C/N-containing compounds and serves as a probe to extend the electron-donating principle of anaerobic cyanides oxidation to more electron-donor microbial utilization.

Evolution of biochemical processes in coking wastewater treatment: A combined evaluation of material and energy efficiencies and secondary pollution.

The application of advanced biological treatment technology results in improved coking wastewater (CW) effluent quality at lower material and energy input practiced by wastewater treatment plants. In wastewater treatment, the diversity of biological processes combinations affects the variety of microorganisms and biochemical reactions resulting in effluent quality. Four full-scale CW processes, anaerobic-anoxic-oxic (A/A/O), anoxic-oxic-hydrolytic-oxic (A/O/H/O), anoxic-oxic-oxic (A/O/O), and oxic-hydrolytic-oxic (O/H/O) were compared for their consumption of chemicals and energy, emissions of greenhouse gases, and excess sludge production. A new performance indicator combining the above mentioned parameters was proposed to comprehensively evaluate processes in capacity to CW. The O/H/O process showed stable and reliable operation with minimum chemicals cost and the average energy consumption, whereas A/A/O at its good performance in TN removal required a large amount of alkaline chemicals to maintain stability. Besides, a substantial addition of chemicals in A/A/O results in larger average amounts of inorganic sludge. Also, the A/A/O process with a single aerobic unit appeared to be incapable of energy saving when dealing with CW rich in nitrogen and poor in phosphorus. The process with dual aerobic units can achieve more complete carbon and nitrogen removal, which is related to the sequence of biochemical reactions. Diverse sequence combinations can create variation in HRT and DO, whereby contaminants proceed through distinct channels of degradation. In the comparative analysis of CWPIs, it could be seen that O/H/O is the biological treatment process with the least equivalent energy consumption input at present thus exhibiting promising application in CW treatment. The A/O/O and A/O/H/O combinations are good attempts of development; however, more energy-efficient operation modes have to be further investigated.

In-situ growth of Co/Ni bimetallic organic frameworks on carbon spheres with catalytic ozonation performance for removal of bio-treated coking wastewater.

The Co/Ni-MOFs@CS composite derived from Co/Ni bimetallic organic framework was synthesized and characterized. Compared with a single O3 system, the synergy between carbon sphere (CS) and metal organic frameworks (MOFs) improved the electron transfer efficiency and the formation rate of •OH. The coexistence of Co and Ni in various valence states might accelerate the cyclic process of Co(II)/Co(III) and Ni(II)/Ni(III), thereby improving the catalytic activity. Taking levofloxacin as a model pollutant, the mechanism of catalytic process was discussed, and the catalytic reaction was successfully applied to the removal of residual organics in bio-treated coking wastewater (BTCW). The removal rates of chemical oxygen demand (COD) and total organic carbon (TOC) in 60 min were 50.85%-53.71% and 39.98%-43.48%. From the perspective of UV absorption and 3D EEM, catalytic ozonation was more conducive to breaking the electronic protection of inert organic molecules such as heterocyclic compounds, and achieving higher efficiency of mineralization. It provides a new idea for catalytic ozonation technology of wastewater treatment in the future from theory, technology and application.

A spectrophotometric method for measuring permanganate index (CODMn) by N,N-diethyl-p-phenylenediamine (DPD).

A new spectrophotometric method for measuring permanganate index (chemical oxygen demand using potassium permanganate (KMnO4) as oxidant, CODMn) in water was established. The method was based on the rapid oxidation of N,N-diethyl-p-phenylenediamine (DPD) by residual KMnO4 in digestion solution under neutral pH condition to form the stable pink radical (DPD●+). Only 20 s were enough to form the pink DPD●+. The generated DPD●+ could be quantitatively measured by a visible spectrophotometer at 551 nm. Stoichiometric coefficient of the reaction between KMnO4 and DPD was close to 1:5 (1:5.07). There was a well linear relationship (R2 = 0.999) between the change of the absorbance of DPD●+ at 551 nm and the concentration of CODMn in the range of 0-4.46 mg L-1. Limit of detection of the DPD method was as low as 0.02 mg L-1 CODMn. The DPD method was highly accurate for measuring CODMn in standard solutions with well recovery rates of 99.17%-102.22%, and was well tolerant to the interference of coexistent Cl- and Fe3+. The DPD method was successfully applied for measuring CODMn in real water samples, including surface water, underground water and drinking water. In comparison to the traditional titration method, the proposed DPD method was more convenient to operate, required less samples and digestion reagents (i.e., KMnO4 and H2SO4) and could be employed for online monitor.

Spectrophotometric determination of trace permanganate in water with N,N-diethyl-p-phenylenediamine (DPD).

A sensitive spectrophotometric method (the N,N-diethyl-p-phenylenediamine (DPD) method) was established for the determination of trace permanganate concentration (0-10 µM) in water. The DPD method was based on the oxidative coloration reaction where permanganate could oxidize DPD to form the red colored DPD radical (DPD•+) with a second-order rate constant of 2.96 × 104 M-1 s-1 at pH 6 (50 mM phosphate buffer). The generated DPD•+ could be quantitatively measured at 551 nm using an UV-Vis spectrophotometer. There was a good linear relationship (R2 = 0.999) between the absorbance of DPD•+ and permanganate concentration. The DPD method was highly sensitive, and the absorbance of generated DPD•+ at 551 nm was as high as 5.70 × 104 cm-1 per M (mol L-1) of permanganate. The reaction of permanganate with DPD in the pH range of 4.0-8.0 had a stoichiometric coefficient of 1:2.71. The residual absorbance of DPD•+ in ultrapure water and natural waters was fairly stable for 30 min. Limits of detection of the proposed DPD method in ultrapure water and natural waters were calculated to be as low as 0.010 µM and 0.017 µM, respectively. Moreover, trace permanganate concentrations of 0.04 and 0.10 µM were found in natural waters and wastewater by the proposed DPD method. Additionally, the DPD method could be applied to measure the second-order rate constants of the reaction of permanganate with phenol at pH 7.0 (28.2 M-1 s-1).