Abstract
An integral treatment process for landfill leachate reverse osmosis concentrate (LLROC) is herein designed and assessed aiming to reduce organic matter content and conductivity, as well as to increase its biodegradability. The process consists of three steps. The first one is a coagulation/flocculation treatment, which best results were obtained using a dosage of 5 g L−1 of ferric chloride at an initial pH = 6 (removal of the 76% chemical oxygen demand (COD), 57% specific ultraviolet absorption (SUVA), and 92% color). The second step is a photo-Fenton process, which resulted in an enhanced biodegradability (i.e., the ratio between the biochemical oxygen demand (BOD5) and the COD increased from 0.06 to 0.4), and an extra 43% of the COD was removed at the best trialed reaction conditions of [H2O2]/COD = 1.06, pH = 4 and [H2O2]/[Fe]mol = 45. An ultra violet-A light emitting diode (UVA-LED) lamp was tested and compared to conventional high-pressure mercury vapor lamps, achieving a 16% power consumption reduction. Finally, an optimized 30 g L−1 lime treatment was implemented, which reduced conductivity by a 43%, and the contents of sulfate, total nitrogen, chloride, and metals by 90%. Overall, the integral treatment of LLROC achieved the removal of 99.9% color, 90% COD, 90% sulfate, 90% nitrogen, 86% Al, 77% Zn, 84% Mn, 99% Mg, and 98% Si; and significantly increased biodegradability up to BOD5/COD = 0.4.
Highlights
Landfill leachate is an extremely harmful wastewater for the environment because it contains a high amount of organic and inorganic pollutants
The pre-treatment of coagulation/flocculation with ferric chloride achieved better COD removal results than with alum (76% vs. 60%), and the remaining dissolved iron in the landfill leachate reverse osmosis concentrate (LLROC) after coagulation was efficiently used for its post-photo-Fenton treatment step, avoiding the need to add more iron to the solution to catalyze the process
The most important difference between optimal coagulant doses, with regard to a posterior photo-Fenton process, was the dissolved iron content that remained in the medium (168 and 800 mg L−1 of Fe for 5 and 10 g L−1 of FeCl3 ·6H2 O coagulation, respectively) affecting the kinetics of the reaction; so that the time of irradiation was reduced from 300 min to 180 min, respectively
Summary
Landfill leachate is an extremely harmful wastewater for the environment because it contains a high amount of organic and inorganic pollutants. Physical processes using pressure-driven membranes (microfiltration and/or ultrafiltration followed by nanofiltration or reverse osmosis) [6,7,8] are widely used because of the high quality of the permeate water that is obtained. These technologies have the drawback of producing a leachate concentrate containing the retained pollutants [9]. This reinjection increases the content of persistent organic compounds, salts, nitrogen, and phosphorous in the leachate [15], which increases membrane fouling and progressively limits the efficiency of the treatment in the medium to the long term [16]
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