Nano and microplastics occurrence in wastewater treatment plants: A comprehensive understanding of microplastics fragmentation and their removal.

Nano/microplastic (NP/MP) pollution is a growing concern for the water environment. Wastewater treatment plants (WWTPs) are considered the major recipients of MP before discharging into local waterbodies. MPs enter WWTPs mainly from synthetic fibers through washing activities and personal care products. To control and prevent NP/MP pollution, it is essential to have a comprehensive understanding of their characteristics, fragmentation mechanisms, and the effectiveness of the current treatment processes used in WWTPs for NP/MP removal. Therefore, the objectives of this study are to (i) understand the detailed mapping of NP/MP in the WWTP, (ii) understand the fragmentation mechanisms of MP into NP, and (iii) investigate the removal efficiency of NP/MP by existing processes in the WWTP. This study found that fiber is the dominant shape of MP, and polyethylene, polypropylene, polyethylene terephthalate, and polystyrene are the major polymer type of MP in wastewater samples. Crack propagation and mechanical breakdown of MP due to water shear forces induced by treatment facilities (e.g., pumping, mixing, and bubbling) could be the major causes for NP generation in the WWTP. Conventional wastewater treatment processes are ineffective for the complete removal of MPs. Although these processes are capable of removing ∼95% of MPs, they tend to accumulate in sludge. Thus, a significant number of MPs may still be released into the environment from WWTPs on a daily basis. Therefore, this study suggested that using DAF process in the primary treatment unit can be an effective strategy to control MP in the initial stage before it goes to the secondary and tertiary stage.

Membrane-coupled fungi reactor--an innovative approach to bioremediation of hazardous dye wastewater.

Owing to the inherent shortcomings of conventional biological dye effluent treatment processes, researchers have proposed diverse intriguing approaches that await practical implementation. This study demonstrates the feasibility of an innovative membrane-coupled fungi reactor. Preliminary batch tests revealed the noteworthy role of biosorption along with biodegradation in decoloration, and also confirmed excellent decoloration even in the presence of hardly biodegradable polyvinyl alcohol besides recalcitrant dye in the wastewater. Conversely, the continuous reactor achieved stable 97% total organic carbon (TOC) and 99% color removal with a hydraulic retention time (HRT) of 15 h. A marked decrease in the UV absorbance of the membrane permeate, and the detection of short-chain aliphatic acids in the permeate provided evidence of the subsequent biodegradation of the aromatic group following the breakdown of the color-imparting chromophoric group of the dye.

Bioaugmented membrane bioreactor (MBR) with a GAC-packed zone for high rate textile wastewater treatment.

The long-term performance of a bioaugmented membrane bioreactor (MBR) containing a GAC-packed anaerobic zone for treatment of textile wastewater containing structurally different azo dyes was observed. A unique feeding strategy, consistent with the mode of evolution of separate waste streams in textile plants, was adopted to make the best use of the GAC-zone for dye removal. Dye was introduced through the GAC-zone while the rest of the colorless media was simultaneously fed through the aerobic zone. Preliminary experiments confirmed the importance of coupling the GAC-amended anaerobic zone to the aerobic MBR and also evidenced the efficacy of the adopted feeding strategy. Following this, the robustness of the process under gradually increasing dye-loading was tested. The respective average dye concentrations (mg/L) in the sample from GAC-zone and the membrane-permeate under dye-loadings of 0.1 and 1 g/L.d were as follows: GAC-zone (3, 105), permeate (0, 5). TOC concentration in membrane-permeate for the aforementioned loadings were 3 and 54 mg/L, respectively. Stable decoloration along with significant TOC removal during a period of over 7 months under extremely high dye-loadings demonstrated the superiority of the proposed hybrid process.