Removal of total organic carbon and color from astana municipal landfill leachate by uv-fenton, UV-H₂O₂ and fenton reaction

In the present work, UV-Fenton, UV-H₂O₂ and Fenton processes were employed to treat a leachate from the municipal solid waste landfill of Astana (Kazakhstan). Each experiment lasted 120 minutes, and the treatment efficiency was assessed through total organic carbon (TOC), total nitrogen (TN) and color removal. The total volume of the treated solution was 250 mL and an annular UV (254 nm) photoreactor operated in batch recycle mode was used in the case of photochemical treatment. The landfill leachate, which currently is left untreated, had initial carbon concentration equal to 5868 mg L^-1 and pH 8.16. The total carbon was by 40-45% inorganic, and nitrogen was 90% inorganic in the ammonium form. Preliminary experiments showed that inorganic carbon acting as hydroxyl radicals scavenger inhibited significantly the UV-Fenton treatment. Consequently, pretreatment process in two steps was applied: continuous air stripping for 24 hours at pH = 12 to remove ammonia and then pH adjustment to 5 to remove inorganic carbon. The pretreated leachate was further diluted with tap water in a ratio of 1/2.4 and sent for chemical/photochemical treatment. The leachate used as feed to next processes had initial carbon concentration in the range of 1100-1300 mg L^-1 (all carbon was organic) and pH 5.1-5.3. The experiments were conducted using 400 ppm of Fe(II) and 6660 mg L^-1 of H₂O₂. In the case of the UV-Fenton treatment, the results obtained showed that the presence of inorganic carbon had significant effect on total carbon (TC) removal; without the pretreatment steps only 7.7% TC removal was observed, while 29% TC (equal to TOC) removal was achieved when the inorganic carbon was removed at the pretreatment steps. The initial pH value was ranged in 2.4-5.4 and had also a considerable effect on total organic carbon and color removal. Specifically, the highest TOC removal (44.3%) was achieved when initial pH was adjusted at 3.0. Temperature dependence in the range of 25-40^oC was of minor importance compared to rest operating parameters. UV-H₂O₂ treatment did not result in any TOC removal, which is in contrast with the results obtained for simple solutions. Using classical Fenton process instead of photo-Fenton process led to TC removal around only 20%. Finally, the use of Fe(III) instead of Fe(II) was beneficial in terms of TOC and color removal achieved.