In the present work, pollutant removal study of Century Pulp and Paper Mill effluent was done. A hybrid unit of upflow fixed-bed anaerobic bioreactor (UFBAB) along with slow sand filter (SSF) was compared with single unit UFBAB for pollutant removal at different hydraulic retention time (HRT). The hybrid system showed better removal efficiency which can be attributed to SSF. It was observed that SSF provides a polishing effect to the effluent treated by UFBAB. The biodegradation rate in both filters was observed to be increased in first six weeks of experiment, prior to the acclimatization of microbial communities. The relative removal efficiency of biological oxygen demand and chemical oxygen demand was found to between 0.90 and 0.99, respectively, at 24 h HRT, demonstrating very high removal efficiency of the hybrid system. The relative removal efficiency of total dissolved solids and total suspended solids was around 1 at 16 h HRT indicating 100% efficient and within the limits as prescribed by Central Pollution Control Board India (CPCB) for treated effluent discharge in surface water bodies. Best removal efficiency was observed in case of sulfate at low HRT of 8 h. Relative removal efficiency for phenols was found to be greater than 1 at 12 h HRT. SSF was found to be a suitable substrate for polishing of treated effluent of pulp and paper mill wastewater, demonstrating promising relative efficiency.

Forward osmosis (FO) is attracting worldwide attention as an emerging technology in the fields of power generation, water reuse, desalination, pharmaceuticals and food processing. Still, the critical challenge of finding a suitable draw solute for FO persists. Therefore the current research focuses on synthesizing hydrophilic magnetic nanoparticles (HMNPs) and systematically investigating their potential as draw solutes. HMNPs were synthesized using functional groups polyethylene glycol (PEG 400) and polyacrylic acid (PAA). These functional groups under different ratios with a metal precursor react by one-pot polyol and thermal decomposition methods respectively to give different diameter HMNPs. In addition the effect of different sizes of synthesized HMNPs was investigated for their recovery under an external magnetic field and reusability in FO performance. The physical properties and chemical compositions of the resultant MNPs are fully characterized. Transmission electron microscopy (TEM) analyses show the characteristics as spherical morphology with a narrow size distribution, and a mean size from 9 to 32.5 nm for PEG and 8 to 30 nm for PAA coated HMNPs depending on the ratio of the functional group and metal precursor. The PEG and PAA layer on the MNPs is confirmed by Fourier transform infrared (FTIR) analysis, and thermogravimetric analysis demonstrates a hydrophilic surface composition. The PEG and PAA coated HMNPs generate high osmotic pressures and exhibit good dispersibility in aqueous solutions. Water fluxes of >13 L m⁻² h⁻¹ are achieved across Hydration Technologies Inc. flat sheet membranes at a concentration of 0.05 M of HMNPs using deionized water as the feed solution. The HMNPs can be easily recaptured from draw solutions by applying an external magnetic field and recycling them back as draw solute in the FO process. The MNPs remain active after nine runs of recycling but with a total water flux decrease of 5% in PEG and 3% with each successive recycling due to slight aggregation, and reduced surface to volume ratio is observed. Results of the present study have demonstrated that PEG and PAA coated HMNPs can viewed as promising and potential draw solutes in the FO process.