Advanced Treatment Of Municipal Waste Leachate With A Circulated Ozonation- Biological Aerated Filter Process

Ozonation (O3) combined with a biological aerated filter (BAF) was used in the study for removing COD in the biologically treated effluent of municipal solid wastes incineration leachate.The installing position and dosage of the catalyst activated carbon were optimized based on batch tests, and the long-term COD removal performance was studied and compared in a single stage O3-BAF process and a circulated O3-BAF process based on long-term continuous flow tests.Intermittent ozonation tests revealed that factors such as the installing position of the catalyst activated carbon, the distribution of wastewater and ozone gas, as well as the internal hydraulic conditions in the tower, would all give great influence on the utilization rate of ozone. The installation of the catalyst activated carbon was optimized with an iodine colorimetry method, according to which the favorable installation condition was considered as follows:packs of activated carbon at least 15 cm of above the aeration plates, best in the middle of the tower, with 5 cm of gap between each pack. The removal of COD and UV254 could be divided into a fast reaction stage and a slow reaction stage. UV254 was fastly removed, almost all being removed in the fast reaction stage. By comparison, the COD removal was slow, much COD being removed in the slow reaction stage.The long-term continuous flow test’s result showed that the effluent COD was decreased to about 150 mg/L in a single stage O3-BAF process when 280 mg/L(water) of ozone was dosed and the hydraulic retention time (HRT) of the BAF was of 7 h. However, if a circulated O3-BAF was used, the effluent COD could be decreased to below 100 mg/L, stably meeting the national emission standard, at the same HRT of BAF but at a much lower ozone dosage of 128 mgO3/L(water), GC-MS analysis revealed that the dominant pollutants in the influent of O3-BAF were alkanes, aromatic compounds and heterocyclic compounds containing nitrogen. O3-BAF treatment effectively removed unsaturated compounds such as the heterocyclic compounds containing nitrogen, aromatic compounds and alkenes, but had difficulties in removing alkanes. The circulated O3-BAF developed in the study was highly efficient to remove COD, giving a promising expectation to replace the up-to-date commonly used high-cost "nano-filtration+reverse osmosis" process in landfill leachate treatment, and thereby greatly cut down both the capital cost and running cost.