| A sequential chemical/biological oxidation process was studied for simazine mineralization. Simazine first was oxidized by ozonation, UV irradiation, and combined O{dollar}sb3{dollar}/UV, and then treated in a biological process. Studies were conducted to assess the rate and extent of simazine chemical oxidation and also to identify the oxidation products. Biodegradation tests then were conducted on these products to assess the feasibility of the sequenced oxidation process.; The rates of simazine destruction by ozonation were found to follow second order kinetics with respect to both simazine concentration and solution phase ozone concentration. The major ozonation by-products were 2-chloro-4,6-diamino-s-triazine (CAAT), ammeline (OAAT), and ammelide (OOAT), with CAAT being the predominant species at higher pH.; Photodecomposition of simazine was found to proceed mainly through dechlorination, with hydroxysimazine and 2-ethylamino-4-amino-6-hydroxy-s-triazine being the major products. Simazine photodecomposition rates followed second order kinetics with respect to both the applied UV light intensity and simazine concentration.; The major oxidation products from the combined ozone/UV oxidation were OAAT, OOAT, and cyanuric acid (OOOT). OOOT was determined to be the final product for combined ozone/UV oxidation.; The relative biodegradability of the observed products were assessed in batch shaker flasks, with simazine and its products serving as the limiting nitrogen source in the feed media. Inoculum for the biodegradation tests was returned activated sludge, from a municipal wastewater treatment plant, which was enriched for s-triazine biodegradation for more than 10 months in a batch enrichment process using the aforementioned s-triazine as sole nitrogen sources. When utilized as single nitrogen sources, simazine and its chemical oxidation products were all amenable to biodegradation. Simazine oxidation products biodegradation rate was found to be related to substituent groups on the s-triazine ring in the following order: -OH {dollar}>{dollar} -NH{dollar}sb2{dollar} {dollar}>{dollar} -NHC{dollar}sb2{dollar} H{dollar}sb5{dollar} {dollar}>{dollar} -Cl.; In general, greater chemical oxidation resulted in products having higher biodegradation rates. Of the three chemical oxidation methods studied, combined ozone/UV oxidation appeared to be the most effective method in enhancing biodegradation. Because simazine is biodegraded slowly, the added cost of chemical oxidation must be weighed against the benefits obtained through enhanced biodegradation from the sequential process. |
