Investigation on characteristics of leachate and concentrated leachate in three landfill leachate treatment plants

• NO3-N was the major nitrogenous compound in concentrated leachate.
• Toluene and PAEs were abundant in landfill leachate and concentrated leachate.
• Conjugated nitrogen existed in the form of FA and HyI in the concentrated leachate.
• Higher microbial diversity in the concentrated leachate.

Concentrated leachate from membrane treatment processes is a potential pollution source for the surroundings. In this study, with comparison of the landfill leachate, chemical and microbial characteristics of concentrated leachate including biodegradability, amount of nitrogenous compounds and heavy metals, dissolved organic matter composition, and microbial community were investigated in three landfill leachate treatment plants. The results showed that hydrophilic (HyI) fraction was the major dissolved organic carbon in the landfill leachates, accounting for 54.6–60.7%, while humic substances including humic acid (HA) and fulvic acid (FA) were relatively higher in the concentrated leachates, ranging from 61.7% to 69.2%. Conjugated nitrogen existed mainly in FA and HyI in the concentrated leachates. The analysis of excitation emission matrix fluorescence spectroscopy, specific ultraviolet absorbance at 254 nm (SUVA254) and GC/MS showed that aromatic compounds, long-chain hydrocarbons and halohydrocarbons were abundant in the concentrated leachates. During landfill leachate treatment processes, Cl−, SO42- and heavy metals were commonly accumulated in the concentrated leachates. NO3-N and/or NH4+N were the major nitrogenous compounds in the concentrated leachates. All the leachates from three landfill sites contained toluene in the range of 44.5–728.4 μg L−1. Ethylbenzene, chlorobenzene, and the phthalic acid esters including dibutyl phthalate, dimethyl phthalate and di-n-octyl phthalate were also detected in the concentrated leachates. Higher microbial diversity was observed in the concentrated leachate in comparison with landfill leachate.