Concentrations of cyclic volatile methylsiloxanes in biosolid amended soil,influent, effluent,receiving water,and sediment of wastewater treatment plants in Canada

A comprehensive surveillance program was conducted to determine the occurrence of three cyclic volatile methylsiloxanes (cVMS) octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in environmental compartments impacted by wastewater effluent discharges. Eleven wastewater treatment plants (WWTPs), representative of those found in Southern Ontario and Southern Quebec, Canada, were investigated to determine levels of cVMS in their influents and effluents. In addition, receiving water and sediment impacted by WWTP effluents, and biosolid-amended soil from agricultural fields were also analyzed for a preliminary evaluation of the environmental exposure of cVMS in media impacted by wastewater effluent and solids. A newly-developed large volume injection (septumless head adapter and cooled injection system) gas chromatography – mass spectrometry method was used to avoid contamination originating from instrumental analysis. Concentrations of D4, D5, and D6 in influents to the 11 WWTPs were in the range 0.282–6.69 μg L⁻¹, 7.75–135 μg L⁻¹, and 1.53–26.9 μg L⁻¹, respectively. In general, wastewater treatment showed cVMS removal rates of greater than 92%, regardless of treatment type. The D4, D5, and D6 concentration ranges in effluent were <0.009–0.045 μg L⁻¹, <0.027–1.56 μg L⁻¹, and <0.022–0.093 μg L⁻¹, respectively. The concentrations in receiving water influenced by effluent, were lower compared to those in effluent in most cases, with the ranges <0.009–0.023 μg L⁻¹, <0.027–1.48 μg L⁻¹, and <0.022–0.151 μg L⁻¹ for D4, D5, and D6, respectively. Sediment concentrations ranged from <0.003–0.049 μg g⁻¹ dw, 0.011–5.84 μg g⁻¹ dw, and 0.004–0.371 μg g⁻¹ dw for D4, D5, and D6, respectively. The concentrations in biosolid-amended soil, having values of <0.008–0.017 μg g⁻¹ dw, <0.007–0.221 μg g⁻¹ dw, and <0.009–0.711 μg g⁻¹ dw for D4, D5, and D6, respectively, were lower than those in sediment impacted by wastewater effluent in most cases. In comparison with the no-observed-effected concentrations (NOEC) and IC50 (concentration that causes 50% inhibition of the response) values, the potential risks to aquatic, sediment-dwelling, and terrestrial organisms from these reported concentrations are low.     

Respiratory Suspended Particulate (RSP) Concentration and its Implications to Roadside Workers: A Case Study of Hong Kong

The adsorption behaviour of Diphenylamine (DPAM), napthylamine ( NAM), napthylamine ( NAM)and aniline on pyrolusite and activated carbon has been studied.Pyrolusite shows remarkable sorption capacity for DPAM and NAM as compared to aniline; (the adsorption followed theorder:Activated Carbon: DPAM = NAM > AnilinePyrolusite: DPAM: NAM > NAM> Aniline)The maximum adsorption of NAM occurred in theconcentration range 4–20 g mL^-1 on pyrolusite (95%)and 4–50 g mL^-1 on activated carbon (100%). Theeffect of various doses of activated carbon on the adsorption of NAM confirm Langmuir and Freundlich isotherms where asFreundlich isotherm is obeyed by pyrolusite. The adsorption of NAM on both the absorbents is not affected in presence ofDPAM over a wide range of their initial concentrations (20–60g mL^-1). The desorption studies of NAM onpyrolusite was carried out by batch as well as column processes.Excellent results were obtained when a mixture of n-hexane andisopropanol (91:1) was used as eluent.     

Accelerated sunlight photocatalysis through improved electron mobility between g-C3N4 and BiPO4 nanomaterial

Herein, we report a detailed study on creating heterojunction between graphitic carbon nitride (g-C₃N₄) and bismuth phosphate (BiPO₄), enhancing the unpaired free electron mobility. This leads to an accelerated photocatalysis of 2,4-dichlorophenols (2,4-DCPs) under sunlight irradiation. The heterojunction formation was efficaciously conducted via a modest thermal deposition technique. The function of g-C₃N₄ plays a significant role in generating free electrons under sunlight irradiation. Together, the generated electrons at the g-C₃N₄ conduction band (CB) are transferred and trapped by the BiPO₄ to form active superoxide anion radicals (?O₂^?). These active radicals will be accountable for the photodegradation of 2,4-DCPs. The synthesized composite characteristics were methodically examined through several chemical and physical studies. Due to the inimitable features of both g-C₃N₄ and BiPO₄, its heterojunction formation, 2.5wt% BiPO₄/g-C₃N₄ achieved complete 2,4-DCP removal (100%) in 90 min under sunlight irradiation. This is due to the presence of g-C₃N₄ that enhanced electron mobility through the formation of heterojunctions that lengthens the electron-hole pairs’ lifetime and maximizes the entire solar spectrum absorption to generate active electrons at the g-C₃N₄ conduction band. Thus, this formation significantly draws the attention for future environmental remediation, especially in enhancing the entire solar spectrum’s harvesting.

Graphical abstract