Sulfate Reduction Behavior in the Leachate Saturated Zone of Landfill

Science of the Total Environment 730 (2020) 138946 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Sulfate reduction behavior in the leachate saturated zone of landfill sites Zhiyuan Jin a, Manting Ci a, Wenyi Yang a, Dongsheng Shen a, Lifang Hu b, Chengran Fang c, Yuyang Long a,⁎ a Zhejiang Provincial Key Laboratory of Solid Waste Treatment and Recycling, School of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou 310012, China b College of Quality and Safety Engineering, Institution of Industrial Carbon Metrology, China Jiliang University, Hangzhou 310018, China c Key Laboratory of Recycling and Eco-treatment of Waste Biomass of Zhejiang Province, Zhejiang University of Science and Technology, Hangzhou 310023, China HIGHLIGHTS GRAPHICAL ABSTRACT • Remarkable sulfate reduction observed in leachate saturated environment. • H2S, MM, DMS emissions were most vi- olent at 50 and 60 °C. • Whole microbial structure and activity were influenced by the temperature. • dsrA and dsrB quantity decreased under higher temperatures. • Dethiobacter may contribute to higher sulfate reduction rate. article info abstract Article history: Municipal solid waste landfills are considered one of the most important parts of the sulfur cycle. However, few Received 2 April 2020 studies have focused on sulfate reduction in the leachate saturated zone, where the temperature may be variable. Received in revised form 21 April 2020 In this work, the sulfate reduction behavior was evaluated in a landfill leachate saturated zone under tempera- Accepted 22 April 2020 tures between 30 and 80 °C. The results show that microbial sulfate reduction is high in the saturated zone, es- Available online 25 April 2020 pecially when the temperature is at 50–60 °C. The microbial diversity and the abundance of functional genes fi Editor: Huu Hao Ngo results reveal that speci c sulfate-reducing bacteria such as Dethiobacter, the bacteria that offer energy to them, and genes other than dsrA and dsrB may have a close relationship with the variation in the reduction of Keywords: sulfate. This work may improve the knowledge of sulfate reduction in the landfill sites and therefore offer theo- Landfill retical support to management strategies. Leachate saturated zone © 2020 Elsevier B.V. All rights reserved. Sulfate reduction Odors Microbial community 1. Introduction Landfill remains one of the most used waste disposal methods be- ⁎ Corresponding author. cause of its relatively low construction and maintenance cost, as well E-mail address: [email protected] (Y. Long). as its high usability (Ying et al., 2019). However, landfill gas emissions https://doi.org/10.1016/j.scitotenv.2020.138946 0048-9697/© 2020 Elsevier B.V. All rights reserved. 2 Z. Jin et al. / Science of the Total Environment 730 (2020) 138946 have elicited great concern because of their strong odors. Hydrogen sul- was cut into pieces b1 cm in diameter. A sieve was not used since the fide (H2S) is a problematic landfill emission because of its low odor moisture content of the waste was extremely high. Then the cut refuse threshold (around 0.5 ppb) and high toxicity (Long et al., 2016). In ad- was gathered and intensively mixed again, then kept in an airtight plas- dition to H2S, volatile organosulfur compounds (VOSCs) such as methyl tic bag in a 0 °C refrigerator. mercaptan (MM) and dimethyl sulfide (DMS) are deemed to be the Since the in-situ leachate from the real landfill site was hard to main contributors to landfill odor (Lu et al., 2015). MM has an even collect simultaneously with the landfilled refuse, simulated leachate lower odor threshold than H2S (0.07 ppb) (Tamai et al., 2006). A low was prepared according the real leachate water quality. The main concentration of MM may cause headaches and nausea, whereas anes- characteristics of the landfilled refuse and simulated leachate are thesia occurs at higher concentrations. Sufficiently high concentrations listed in Table 1. can even cause respiratory paralysis and death (Borras et al., 2016). DMS has the highest odor threshold of the three (5.9 ppb), and may 2.2. Experimental design cause skin irritation, respiratory irritation and serious eye damage (Long et al., 2017). To achieve a leachate-saturated environment, 500-mL anaerobic Importantly, H2S, MM and DMS are generated by the sulfate reduc- bottles were used as the reactors. One hundred grams of collected refuse ing process. Therefore, the landfill odor arising from H2S, MM and and 300 mL of leachate were gathered in 18 bottles, and the headspace DMS merits particular attention. However, landfill sites are complicated volume (V) was recorded. Then the bottles were sealed with butyl rub- man-made facilities with a variety of temperature and moisture con- ber stoppers and plastic caps. Two three-way valves, connected with a tents as depth increases. The moisture content shows distinct variation long and a short needle tube, respectively, were connected to each bot- with depth in the landfill. Moisture content is a vital factor controlling tle through the caps, and the long tube was able to reach the leachate microbial metabolisms and activity. Sulfate reducing bacteria (SRB) surface. Then a Shih's fermenter was connected to the three-way are bacteria that have the function of sulfate reduction, and are also sub- valve with the short needle, to acquire the gas generation volume ject to differences in moisture factors. Our previous research found that (V1). A diagram of the reactor is shown in Fig. S1. Six of the bottles the refuse with different moisture contents inside a landfill site showed were sterilized with an autoclave and the six water bath kettles were different H2S production behaviors (Ying et al., 2019). Moreover, tem- set at 30, 40, 50, 60, 70 and 80 °C, respectively. Two unsterilized reactors perature discrepancies inevitably cause major variations in microbial and one sterilized reactor were settled into each kettle to simulate the community and activity. Studies have shown that the sulfate reduction different temperatures. rate is higher in sediment of hot springs than in the soil environment (Adams et al., 1981; Fishbain et al., 2003). Fishbain et al. (2003) also 2.3. Analytical methods of sulfur-containing components, nitrogen- found that the sulfate reduction rate could range from undetectable to containing components and organic carbon 2− −3 −1 over 10 mmol SO4 ·cm ·d in hot springs with different temperatures. However, various odor emission phenomena have been observed Samples from gaseous phase in the bottle were collected by an injec- due to the temperature discrepancy in landfill environment (Hu et al., tor through the three-way valve with short needle, and detected di- 2017; Bhattarai et al., 2018). rectly on a daily basis until no sulfur-containing odor could be In the deeper layers of the landfill site, the refuse always stays in a detected. The H2S, MM and DMS concentrations were determined saturated state because of the accumulation of leachate. Moreover, the using a gas chromatograph equipped with a flame photometric detector deeper layer always has a high temperature because it has more active (GC 7890A; Agilent Technologies, Santa Clara, CA, USA) (Zhang et al., microbial metabolism than other layers. Hao et al. (2017) reported that 2017). The H2S, MM and DMS concentrations were recalculated accord- the highest temperature of the landfill bottom layer can reach over ing to Eq. (1). 80 °C. It is reasonable to assume that intense sulfate reduction behavior can occur in the landfill leachate saturated zone, especially in terms of V C ¼ C0 Â ð1Þ the relative higher temperature. High sulfate reduction rates are fre- ðÞV þ V 1 quently observed in the sediment interface where solid and liquid are −3 in close contact, considered a special saturated zone (Jorgensen et al., where C is the revised concentration of H2S, MM or DMS, mg·m ; C0 is fi −3 2019). The land ll leachate saturated zone is a more complicated sce- the detected concentration of H2S, MM or DMS, mg·m ; V is the head- 3 3 nario than marine or lake sediments, because of the continuous input space volume in the reactor, m ;andV1 is the generated gas volume, m . 2− 2− 2− of electron donors and acceptors from the top refuse layer. Unfortu- Sulfate (SO4 ), sulfite (SO3 ), thiosulfate (S2O3 ), sulfur (S0), sul- 2− − − nately, to our best knowledge, no previous studies have considered sulfide (S ), nitrate (NO3 ), nitrite (NO2 ) and dissolved organic carbon fate reduction in the leachate saturated zone. (DOC) concentrations in the solid and liquid phase were determined be- In this research, a series of landfill leachate saturated zones were fore and after the experiment. The methods used to determine the con- simulated under various temperatures and the generation of H2S, MM centrations were in accordance with the previous work (Fang et al., and DMS was tracked. Moreover, the microbial diversity and the func- 2016; Ying et al., 2019). All analyses mentioned above were performed tional genes abundance were analyzed. This study aimed to provide ac- in triplicate. curate landfill management strategies for odor control by determining the sulfate reduction behavior discrepancy and its associated 2.4. Microbial diversity community analysis mechanisms. Five grams of sample from each unsterilized reactor were collected 2. Materials and methods after no sulfur-containing odor could be detected, and the samples at 2.1. Materials Table 1 Mineralized waste refuse was collected from a real municipal solid The main characteristics of mineralized refuse and leachate. waste landfill in Beijing, China. A drilling machine was employed to 2− 2− 0 2− + − − gather the waste from 10 points. A certain quantity of waste was gath- SO4 S2O3 S S TOC NH4 NO3 NO2 ered from 3 to 15 m beneath the cover.

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