Managing Hazardous Municipal Wastewater: A Membrane-Integrated Hybrid Approach for Fast and Effective Treatment in Low Temperature Environment

Protection of natural water resources like lakes from the onslaught of hazardous municipal wastewater is often a challenge particularly in the cold regions. For treatment of enormous quantity of municipal wastewater, biological treatment is normally adopted but high COD (Chemical Oxygen demand) of such wastewater turns biological treatment slow and difficult. At low temperature environment, effective treatment of such municipal wastewater becomes extremely difficult due to weakened microbial activities. The present study was carried out with a hybrid approach comprising chemical treatment and membrane separation under psychrophilic conditions. Well–known Fenton’s treatment was adopted under response surface optimized conditions that helped recovery of nitrogen and phosphorus nutrients as value–added struvite fertilizer or magnesium ammonium phosphate (NH4MgPO4∙6H2O). The optimal COD removal was found to be 96% at a low temperature of 15oC and pH of 6.3 using Fe2+/H2O2 ratio of 0.10 and of H2O2 1.9 g/l with reaction time of 2 h. Down–stream purification of the struvite-free water by microfiltration and nanofiltration largely fouling–free flat sheet cross flow membrane modules ultimately turned the treated water reusable through reduction of dissolved solids, conductivity and salinity

Effect of alcohols on water solubilization in surfactant-free diesel microemulsions

Microemulsions are preferred over other methods of mixing two immiscible liquids as they are thermodynamically stable, but require a high percentage of surfactant. Surfactant-free microemulsions, on the other hand, use an amphisolvent instead of surfactants, making them an economical alternative. The current experimental investigation focuses on formulation of surfactant-free water-in-diesel microemulsions with the help of straight-chain aliphatic alcohols as diesel replacement for IC engines. Dynamic light scattering measurements revealed these microemulsions had average water droplets of less than 10 nm. The microemulsions were formulated using single-alcohol, two-alcohols, and three-alcohols. It becomes crucial to study the water solubilization of microemulsions as the addition of water in diesel improves combustion efficiency. The water solubilization in surfactant-free microemulsions was found to be dependent on the hydrophilic–lipophilic balance (HLB) of the alcohols, as it determined the solubilizing property of alcohol. The microemulsions could only be formulated in the HLB range of 6.27 to 7.76 and were found to have maximum water solubilization in the HLB range of 6.67 to 7.63. Butanol had the highest water solubilization in a single alcohol system, butanol–ethanol in the ratio of 3:1 for the two-alcohol system, and propanol–butanol–octanol in the ratio of 3:1:1 for three-alcohol systems. Alcohols with higher HLB were more hydrophilic, causing migration of alcohol from the interface to bulk water. In comparison, alcohol with a lower HLB caused the migration of alcohol from the interface to bulk diesel, which resulted in reduced water solubilizations. Hence, the microemulsions could not be formulated beyond specific HLB range. The formulated microemulsions could be a prospective substitute for diesel fuel as alcohols can be derived from renewable routes