Abstract
This study explored the performance of TiO2 nanoparticles in combination with aged waste reactors to treat landfill leachate. The optimum conditions for synthesis of TiO2 were determined by a series of characterizations and removal rates of methyl orange. The effect of the ultraviolet irradiation time, amount of the catalyst, and pH on the removal efficiency for the chemical oxygen demand (COD) and color in the leachate was explored to determine the optimal process conditions, which were 500 min, 4 g/L and 8.88, respectively. The removal rates for COD and chroma under three optimal conditions were obtained by the single factor control method: 89% and 70%; 95.56% and 70%; and 85% and 87.5%, respectively. Under optimal process conditions, the overall average removal rates for ammonium nitrogen (NH4+–N) and COD in the leachate for the combination of TiO2 nanoparticles and an aged waste reactor were 98.8% and 32.5%, respectively, and the nitrate (NO3−–N) and nitrite nitrogen (NO2–N) concentrations were maintained at 7–9 and 0.01–0.017 mg/L, respectively. TiO2 nanoparticles before and after the photocatalytic reaction were characterized by emission scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectrometry. In addition, TiO2 nanoparticles have excellent recyclability, showing the potential of the photocatalytic/biological combined treatment of landfill leachate. This simulation of photocatalysis-landfilling could be a baseline study for the implementation of technology at the pilot scale.
Highlights
Leachates produced in landfills contain various organic and inorganic compounds, such as refractory organic material, dissolved solid particles, ammonia nitrogen (NH3–N), and heavy metals, which seriously threaten the environment and local ecosystems [1,2,3]
Over time, the reduction of the biological oxygen demand/chemical oxygen demand (BOD5/COD) ratio < 0.3 and microorganisms involved in nitrification–denitrification processes are readily hampered by high concentrations of ammonium nitrogen, making it difficult to be treated by the conventional biological and physicochemical processes [7,8,9,10]
Recirculated leachates lead to the accumulation of higher levels of NH4+–N and refractory organics compared with traditional landfills because of the increasing ammonification rate and the lack of carbon sources [13]
Summary
Leachates produced in landfills contain various organic and inorganic compounds, such as refractory organic material, dissolved solid particles, ammonia nitrogen (NH3–N), and heavy metals, which seriously threaten the environment and local ecosystems [1,2,3]. Often, combined anaerobic–aerobic biological processes can be utilized to degrade the biodegradable organic pollutants of leachates [4,5,6]. Additional carbon sources are needed to aid the nitrification–denitrification process [11]. Recirculated leachates lead to the accumulation of higher levels of NH4+–N and refractory organics compared with traditional landfills because of the increasing ammonification rate and the lack of carbon sources [13]
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