Abstract
With the development of economy and the improvement of people’s living standard, landfill leachate has been increasing year by year with the increase in municipal solid waste output. How to treat landfill leachate with high efficiency and low consumption has become a major problem, because of its high ammonia nitrogen and organic matter content, low carbon to nitrogen ratio and difficult degradation. In order to provide reference for future engineering application of landfill leachate treatment, this paper mainly reviews the biological treatment methods of landfill leachate, which focuses on the comparison of nitrogen removal processes combined with microorganisms, the biological nitrogen removal methods combined with ecology and the technology of direct application of microorganisms. In addition, the mechanism of biological nitrogen removal of landfill leachate and the factors affecting the microbial activity during the nitrogen removal process are also described. It is concluded that the treatment processes combined with microorganisms have higher nitrogen removal efficiency compared with the direct application of microorganisms. For example, the nitrogen removal efficiency of the combined process based on anaerobic ammonium oxidation (ANAMMOX) technology can reach more than 99%. Therefore, the treatment processes combined with microorganisms in the future engineering application of nitrogen removal in landfill leachate should be paid more attention to, and the efficiency of nitrogen removal should be improved from the aspects of microorganisms by considering factors affecting its activity.
Highlights
In recent decades, the output of municipal solid waste has been increasing year by year with the acceleration of urbanization, the changes of lifestyle and the growth of population [1,2,3]
Bacillus salmalaya strain 139SI, which removed 78% of ammonia nitrogen when the concentrations of NH4 + -N in leachate, are about 2000 mg/L [106]. He et al nitrified the landfill leachate under the conditions of pH 7.5–8.5 and dissolved oxygen (DO) 0.5–2.0 mg/L in a continuous stirred tank reactor (CSTR) by inoculating the ammonia-oxidizing bacteria (AOB) AHAA-4, and the ammonia removal was over 95% [107]
The ammonia nitrogen removal efficiency was positively correlated with DO concentration, and total nitrogen (TN) removal efficiency reached over 90% at the optimal DO
Summary
The output of municipal solid waste has been increasing year by year with the acceleration of urbanization, the changes of lifestyle and the growth of population [1,2,3]. According to the statistics of China Statistical Yearbook (2009–2018), the annual output of municipal solid waste reached 22.818 billion tons. Solid waste treatment has become an important part of urban management. Landfill and incineration are the main treatment technology for municipal solid waste in China [7]. It is reported that there are a total of 1091 municipal solid waste treatment sites in China, including 994 waste incinerators and landfills [8]. Landfill leachate is a kind of high-concentration organic wastewater [12], which contains a variety of organic and inorganic pollutants [13,14], such as humus, heavy metals, inorganic salts, ammonia nitrogen and so on [8]. High ammonia nitrogen content is a typical feature of mature
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