Abstract
Air stripping is commonly used to remove the ammonia in multistage treatment systems for municipal landfill leachate (LFL). This paper proposes a novel approach combining the process of stripping with biological removal of ammonia, based on simultaneous nitrification and denitrification (SND) in a single hybrid sequencing batch reactor (HSBR). To avoid the accumulation of free ammonia (N-FAN), the shallow aeration system was used for the treatment of raw LFL with N-TAN level of 1520 mg/L and pH 9.24. The mean N-FAN removal efficiency of 69% with the reaction rate of 55 mg L−1 h−1 and mean ammonium (N-NH4+) removal efficiency of 84% with the reaction rate of 44 mg L−1 h−1 were achieved within a month in such an HSBR (R1). The comparative HSBR (R2), with conventional aeration system maintaining the same concentration of dissolved oxygen (DO ≤ 1 mg/L), was removing only trace amounts of N-FAN and 48% of N-NH4+. The quantitative analysis of 16S rRNA genes indicated that the number of total bacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Beta- and Gammaproteobacteria increased during the operation of both HSBRs, but was always higher in R1. Moreover, the bacterial community shift was observed since the beginning of the experiment; the relative abundance of Firmicutes, and Beta- and Gammaproteobacteria increased by 5.01, 3.25 and 9.67% respectively, whilst the abundance of Bacteroidetes and Actinobacteria decreased by 15.59 and 0.95%. All of the surveyed bacteria groups, except Gammaproteobacteria, correlated significantly negatively (p < 0.001) with the concentrations of N-NH4+ in the outflows from R1. The results allow us to suppose that simultaneous stripping and SND in a single reactor could be a promising, cost-effective and easy-to-operate solution for LFL treatment.
Highlights
Despite the numerous solutions proposed in modern waste management models to reduce the mass of dumped municipal solid waste, landfilling is still a common method of disposal in many countries.Even those landfills which were properly designed and equipped with systems for monitoring and preventing the emissions are a potential source of environmental hazards, among which the most serious is the landfill leachate (LFL) [1,2,3]
LFL inflowing to the reactors had an initial concentration of organic compounds expressed by chemical oxygen demand exceeding 12 g/L, of which BOD5 accounted only for 4%, and humic substances even less than 2%
Since N-TAN was the only form of mineral nitrogen detected in LFL, at the level of 1.5 g/L, organics were anticipated to be effectively removed neither during the start-up of both reactors nor in their further continuous operation
Summary
Despite the numerous solutions proposed in modern waste management models to reduce the mass of dumped municipal solid waste, landfilling is still a common method of disposal in many countries Even those landfills which were properly designed and equipped with systems for monitoring and preventing the emissions are a potential source of environmental hazards, among which the most serious is the landfill leachate (LFL) [1,2,3]. Undoubtedly efficient in practice [10], all physical-chemical techniques demand a significant energy input, or a burden to the environment by consumption of chemical reagents and formation of secondary waste They are applicable where LFL contains a significant percentage of refractory organic compounds. Ammonium concentration significantly increases in LFL along with a decrease in COD concentration, when landfill’s evolution enters the anoxic phases
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