Chemistry in Wastewater Treatment
Sonali Sengupta, Chandan Pal
Abstract
The treatment processes involved in each type of wastewater are different by their aim and procedure according to the quality and end use of the treated water. These various treatment processes involve the application of chemistry, chemical reactions, and reagents at almost each step. Coagulation and flocculation is the process which is applied to remove suspended solids present in wastewater. This process removes a variety of pollutants such as fluorides, phosphorous, metals, and heavy metals by using chemical reagents called coagulants. Chemical precipitation is the process that precipitates water-borne pollutants and contaminants, using a suitable precipitating agent. Precipitation depends on the pH of the medium. Hydroxide, sulfate, carbonate, etc. are common precipitating agents. Heavy metals are one of the major contaminants that are removed by this process. Chemical oxidation of polluted water treatment involves an oxidative chemical process to chemically convert the contaminant via oxidation to lower the concentration in the polluted water using suitable oxidizing agents. Advanced chemical oxidation processes (AOP) use several combinations—oxidants (e.g., H2O2/O3/Fenton's), radiative measures (e.g., UV/ultrasound with oxidants), and catalysts involving metal ions or photocatalysts—to generate the hydroxyl radical electrophile. Some exemplary AOPs are mentioned with their qualifications. The combinations H2O2/Fe2+, TiO2/UV/O2, H2O2, and TiO2/UV/H2O2 are discussed.