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.

A combined process model for wastewater treatment based on hydraulic retention time and toxicity inhibition.

Hydraulic retention time (HRT), as an important parameter in the wastewater treatment process, has a great impact on water quality and energy consumption. With the rapid advances in computer technology and deepened understanding of in microbial metabolism, a series of activated sludge models (ASMs) have been developed and applied in wastewater treatment. However, ASMs simulation based on the nexus of HRT, water treatment process, water quality and energy consumption has yet to be verified. In this study, HRT was creatively linked to water treatment process variation. And a novel combined process model (CPM) was developed based on the operational data and treatment performance data from 4 full-scale coking wastewater treatment processes. In the CPM, an array of biological treatment processes were represented by setting the HRT in respective treatment units of the anaerobic-oxic-hydrolytic & denitrification-oxic (A/O/H/O) process. The relationships between HRT, effluent quality and energy consumption were systematically analyzed. Results showed that: (i) for A/O/H/O process, the HRT of first oxic (O1) reactor has a key effect on the effluent water quality and energy consumption, while the impact of the anaerobic (A) reactor HRT was limited; (ii) the O/H/O process has a clear advantage in treating coking wastewater due to the carbon removal and detoxification function of O1 reactor; (iii) the lowest energy consumption (with the total system HRT below 210 h) to meet the biological effluent quality requirements (COD = 200 mg/L, TN = 50 mg/L) is 4.429 kWh/m3. Since the CPM could effectively work out the optimal process configuration and break the boundaries between HRT and process variation, it has enormous potential to be extended to the design of other wastewater treatment processes.

Fate and distribution of phosphorus in coking wastewater treatment: From sludge to its derived biochar.

Due to the phosphorus (P) deficiency in coking wastewater, sufficient P needs to be provided in the treatment process to maintain biotic activity. However, most of the dosed P sources are transferred to the sludge phase out of the chemical equilibrium. After an in-depth investigation of P morphology changes in coking wastewater treatment, it is found that above 71.6 % P applied to the full-scale O/H/H/O (oxic-hydrolytic & denitrification-hydrolytic & denitrification-oxic) process for coking wastewater treatment is ended up in the sludge phase of the aerobic reactors in the forms of non-apatite inorganic phosphorus (NAIP). Theoretical simulations suggest that the P forms precipitates such as FePO4·2H2O, AlPO4·2H2O, MnHPO4 at pH < 7, and Ca5(PO4)3OH at pH > 7. Microbial utilization of P in coking wastewater treatment is swayed by precipitation, pH and sludge retention time (SRT). By pyrolysis treatment of the waste sludge at 700 °C, phosphoric substances in coking sludge are enriched and converted into Ca5(PO4)3OH, Ca5(PO4)3Cl, Ca3(PO4)2, etc. with apatite phosphorus (AP) accounting for 65.7 % of total phosphorus. Moreover, the heavy metals in biochar were below the national standard limits for discharge. This study shows that hazardous waste (coking sludge) can be transformed into bioavailable products (P-rich biochar) through comprehensive management of the fate of P. Combined with the O/H/H/O process, the mechanisms of phosphorus consumption in coking wastewater treatment are revealed for the first time, which will facilitate a reduced consumption of phosphorus and provide a demonstration for other phosphorus-deficient industrial wastewater treatment.

Simultaneous removal of Cr(VI) and phenol contaminants using Z-scheme bismuth oxyiodide/reduced graphene oxide/bismuth sulfide system under visible-light irradiation.

An all-solid-state Z-scheme system containing Bi-based semiconductors bismuth oxyiodide (BiOI) and bismuth sulfide (Bi2S3) was constructed on reduced graphene oxide (rGO) sheets through an electrostatic self-assembly method to simultaneously remove aqueous Cr(VI) and phenol. In this Z-scheme that mimicked natural photosynthesis, photoinduced electrons in the conduction band (CB) of BiOI were transferred through rGO and reacted with photoinduced holes in the valence band (VB) of Bi2S3, which significantly increased its photocatalytic activity. The reduction and oxidation reactions were performed on Bi2S3 and BiOI photocatalysts, respectively. Furthermore, complex contaminants of coexisting heavy metal Cr(VI) and organic phenol were treated using the system under visible-light irradiation. Results showed that Cr(VI) reduction and phenol oxidation were achieved efficiently with optimum reductive and oxidative efficiencies up to 73% and 95% under visible-light irradiation, respectively. This work provided a promising method of simultaneously removing heavy metals and organic pollutants by using a Z-scheme system with enhanced photocatalytic activity.

Cadmium ion adsorption by amine-modified activated carbon.

Cadmium (Cd) is one of the most toxic metals found in water and sediments. In the effort to develop an effective adsorbent for aqueous Cd removal, activated carbon (AC) was modified with an amino-terminated organosilicon (3-aminopropyltrimethoxysilane, APS). Response surface methodology was used to optimize selected operational parameters of adsorption of aqueous Cd by considering a central composite design with three input variables, temperature of the mixture solution, the contact time and feed ratio (APS/AC), on the surface modification. Results demonstrated that the strong Cd-binding amine ligands were effectively introduced onto the AC surfaces through the silanol reaction between carbon surface functional groups (-COOH, -COH) and APS molecules. The optimized preparation condition is 77 °C, 4 h and 2.1 ratio. The adsorbent presented a favorable adsorption of the aqueous Cd(II).

Morphological effect of BiVO4 catalysts on degradation of aqueous paracetamol under visible light irradiation.

Morphological effect of bismuth vanadate (BiVO4) on visible light-driven catalytic degradation of aqueous paracetamol was carefully investigated using four monoclinic BiVO4 catalysts. The catalysts with different morphologies were controllably prepared by a hydrothermal method without any additions. The prepared catalysts were fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis diffuse reflectance spectroscopy (DRS). Under the visible light irradiation, these catalysts with different morphology were investigated to degrade aqueous paracetamol contaminant. The degradation effects were evaluated based on the catalyst morphology, solution pH, initial paracetamol concentration, and catalyst dosage. Cube-like BiVO4 powders exhibited excellent photocatalytic performance. The optimal photocatalytic performance of the cube-like BiVO4 in degrading paracetamol was achieved.