Comparative analysis of nitrogen removals and microbial communities in air and pure oxygen aeration systems during treatment of municipal solid waste incineration (MSWI) leachate
Graphical abstract
Introduction
Prior to the onsite incineration of municipal solid waste (MSW), it is usually settled in the waste bunker for 2–7 days to further reduce water content. During the process, a large amount of fresh leachate (MSWI leachate) is generated, which contains high contents of COD (20000–75,000 mg/L), NH4+-N (1000–3000 mg/L) and suspended solids (SS) (1000–5000 mg/L), as well as the refractory organic matters (e.g., fulvic- and humic-like substances) [1], [2], [3]. This leachate poses a threat to the environments, and needs to be safely treated before water reclaiming or directly discharging into sewage system. In a typical MSWI leachate, the ratio of biological oxygen demand (BOD5) to COD varies between 0.5 and 0.8 [4], which is suitable for and quite effective with the treatment of biological systems, such as anaerobic-aerobic-coagulation process [5], anaerobic baffled reactor (ABR)-aerobic process [6], and UASB-modified Bardenpho process [4].
In the biological treatment, aerobic process is the key step for completely degradation of pollutants, in which sufficient oxygen is supplied for boosting the proliferation of aerobic microorganisms and secretions of enzymes that engaged in degrading COD and converting ammonia to nitrate. Since oxygen only account for 21% in the air, large volume of air should be used for the treatment of high-strength leachate with the conventional air-diffusing aeration system. The excessive air aeration would cost a great deal of energy. Furthermore, severely undesired foams, volatile organic chemicals (VOCs) and other malodorous gases would derive from the high intensity air aeration [7]. As the PO partial pressure is 4.7 times higher than that of air, it can improve the oxygen transfer rate (OTR) and maintain high DO level with a lower flowrate during treatment of high concentration wastewater [8]. Previous studies reported that removal efficiencies of COD [9], total organic carbon (TOC) [10] and NH4+-N [11] were enhanced by using PO aeration in the aerobic process. To date, PO aeration has been applied for treatment of different wastewater with high-strength, including landfill leachate [12], [13], pulp and paper wastewater [14], and coal gasification wastewater [9]. Zhuang et al. reported that under the PO aeration, some species of microorganisms involved in nitrification and denitrification were enriched, which included Thauera, Comamonas, Nitrosomonas and Nitrospira [9]. However, few investigations was carried out on PO aeration for treatment of MSWI leachate, and its effects on removals and metabolism pathways of nitrogen were not fully illustrated.
To elucidate the potential effects of PO supersede air on nitrogen removals and microbial diversities, air and PO aeration were respectively applied in the aerobic processes of two full-scale anoxic-oxic systems operated in parallel for treatment of MSWI leachate. In this study, the performances of nitrogen removals were investigated, and the nitrogen metabolism mechanisms were comprehensively elucidated by metagenomics. The main objectives of this study were to (1) compare nitrogen removals with air and PO aeration; (2) identify the structures of microbial communities and their functions in nitrogen metabolism in the two systems; (3) recover the genomes of poorly-characterized microbial species, and identify their roles in nitrification and denitrification; and (4) illustrate the pathways for nitrogen removal under the air and PO aeration. To our knowledge, this work was the first time to use the metagenomic sequencing approach to compare the microbial communities and their metabolic functions in nitrogen removal under the air and PO aeration in full-scale biological treatment systems. These results would elucidate the mechanism of nitrogen removal in treatment of high strength (organic and ammonia) wastewater streams from the perspective of metagenomes.
Section snippets
Full-scale anoxic-oxic systems operated in parallel
The raw MSWI leachate was collected from an MSW incineration plant located in Changzhou (ca 31.72°N, 120.05°E), China. The original MSWI leachate treatment system was operated with a designed capacity of 400 m3/d as illustrated in Fig. S.1, which contained an equalization tank, anaerobic digestion towers, the same-sized two anoxic-oxic biological treatment systems operated in parallel (anoxic tank: 375 m3, the first oxic tanks: 877 m3; the second oxic tanks: 364 m3), and ultra-, nano- and
Performance of two full-scale anoxic-oxic systems
The removal efficiencies of COD, NH4+-N and TN, and the changes of NO2−-N and NO3−-N, in the two systems with either air or PO aeration were demonstrated in Fig. 1A–D. As shown in Fig. 1A, the influent COD was ranged from 3508 mg/L to 6163 mg/L. After treatment with the anoxic-oxic systems, CODs in the effluent of AAT and POAT were steadily around 993 mg/L and 1231 mg/L, respectively, which corresponded to 78% and 73% of the average COD removal efficiencies. In leachate, in addition to the
Conclusions
In this study, a full-scale experimental investigation of the effects of PO supersedes air on nitrogen removal and microbial communities for MSWI leachate treatment. During the experimental period, better TN removal and better COD and NH4+-N removal were obtained in POAT and AAT, respectively. Compared to air aeration, the special distribution of oxygen created by PO aeration had a remarkable influence on microbial community structures and functions, which enhanced autotrophic denitrification
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research is financially supported by the National Key Research and Development Program of China (NO. 2022YFE011372 and No. 2019YFC0408605), Research Project of Guangzhou Municipal Science and Technology Bureau (No. 201903010035) and Key-Area Research and Development Program of Guangdong Province (No. 2019B110209002). Thanks Dr. Y. Yu of Taiyuan Shengjie Science and Technology Company for the valuable advices in revision.
References (71)
- et al.
Treatment of fresh leachate with high-strength organics and calcium from municipal solid waste incineration plant using UASB reactor
Bioresour.Technol.
(2011) - et al.
Stimulation of methanogenesis in anaerobic digesters treating leachate from a municipal solid waste incineration plant with carbon cloth
Bioresour.Technol.
(2016) - et al.
Bioenergy, ammonia and humic substances recovery from municipal solid waste leachate: a review and process integration
Bioresour.Technol.
(2019) - et al.
UASB-modified Bardenpho process for enhancing bio-treatment efficiency of leachate from a municipal solid waste incineration plant
Waste Manag.
(2020) - et al.
Effective carbon and nitrogen removal with reduced sulfur oxidation in an anaerobic baffled reactor for fresh leachate treatment
J. Biosci. Bioeng.
(2017) - et al.
Effect of pure oxygen fine bubbles on the organic matter removal and bacterial community evolution treating coal gasification wastewater by membrane bioreactor
Bioresour. Technol.
(2016) - et al.
Effect of pure oxygen aeration on extracellular polymeric substances (EPS) of activated sludge treating saline wastewater
Process Saf. Environ.Prot.
(2019) - et al.
Aerobic and two-stage anaerobic-aerobic sludge digestion with pure oxygen and air aeration
Bioresour. Technol.
(2008) - et al.
Effect of oxygen concentration on biological nitrification and microbial kinetics in a cross-flow membrane bioreactor (MBR) and moving-bed biofilm reactor (MBBR) treating old landfill leachate
J. Membr.Sci.
(2006) - et al.
Performance analysis of a pilot-scale membrane aerated biofilm reactor for the treatment of landfill leachate
<sb:contribution><sb:title>Chem.</sb:title></sb:contribution><sb:host><sb:issue><sb:series><sb:title>Eng. J.</sb:title></sb:series></sb:issue></sb:host>
(2015)