Advanced oxidation processes, carbon adsorption, and biofilm degradation of synthetic organic chemicals in drinking water.

摘要

Widespread contamination of ground and surface water supplies by pesticides and synthetic organic chemicals poses serious hazard to human health. Many of these contaminants are recalcitrant to biodegradation and resistant to chemical oxidation, and therefore, their removal from drinking water at trace levels presents a technical and economic challenge. In this research, advanced oxidation processes (AOPs) were investigated for ultimate destruction of the pesticides alachlor and heptachlor. Activated carbon adsorption was investigated for removal of these two pesticides as well as the insecticides toxaphene and aldicarb. Carbon adsorption studies were also conducted for polychlorinated biphenyls (PCBs). Furthermore, fixed-film biodegradation was investigated for the degradation of alachlor.; Advanced oxidation processes including ozonation, ultraviolet/hydrogen peroxide, ozone/hydrogen peroxide, and UV photolysis achieved complete destruction of alachlor and heptachlor. Alachlor oxidation kinetics using {dollar}rm UV/Hsb2Osb2{dollar} was 15 times faster as compared to those using UV alone. Alachlor oxidation was mainly achieved by hydroxyl free-radical reactions, while heptachlor oxidation was facilitated by reactions with molecular ozone. A reaction pathway for heptachlor oxidation was proposed. Among the by-products identified in alachlor and heptachlor oxidation were formaldehyde, acetaldehyde, glyoxylic acid and glyoxal.; Carbon adsorption technology was found effective in removing alachlor, aldicarb, heptachlor, PCBs, and toxaphene to below the maximum contaminant levels (MCLs) allowed in drinking water. Mathematical modeling, scale-up similitude, and cost analysis were used for appraisal of adsorption technology. Presence of natural organic matters (NOM) adversely impacted the carbon performance through competition and complexation. Toxaphene and PCBs formed strong complexes with humic acid. Heptachlor hydrolysis and aldicarb transformations were also evaluated. A protocol for modeling, up-scaling and design of carbon adsorbers was developed. This protocol was used in conjunction with a new cost evaluation model. Significant increase in carbon adsorber capacity was experienced due to biofilm degradation. A mathematical model (thin-film biologically active carbon--TFBAC) was developed and successfully used to predict the behavior of bioactive adsorbers. Bacterial (Comamonas testosteroni and Comamonas acidovorans) and fungal (genera Chaetomium) strains utilizing alachor as sole carbon source were isolated.