Sulfur dioxide and o-xylene co-treatment in biofilter: Performance, bacterial populations and bioaerosols emissions

https://doi.org/10.1016/j.jes.2017.03.039Get rights and content

Abstract

Sulfur dioxide (SO2) and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO2 and o-xylene in the present study. SO2 and o-xylene could be removed simultaneously in a single biofilter. Their concentration ratio in the inlet stream influenced the removal efficiencies. It is worth noting that the removal of SO2 could be enhanced when low concentrations of o-xylene were introduced into the biofilter. Pseudomonas sp., Paenibacillus sp., and Bacillus sp. were the main functional bacteria groups in the biofilter. Sulfur-oxidizing bacteria (SOB) and o-xylene-degrading bacteria (XB) thrived in the biofilter and their counts as well as their growth rate increased with the increase in amount of SO2 and o-xylene supplied. The microbial populations differed in counts and species due to the properties and components of the compounds being treated in the biofilter. The presence of mixed substrates enhanced the diversity of the microbial population. During the treatment process, bioaerosols including potentially pathogenic bacteria, e.g., Acinetobacter lwoffii and Aeromonas sp., were emitted from the biofilter. Further investigation is needed to focus on the potential hazards caused by the bioaerosols emitted from waste gas treatment bioreactors.

Introduction

With increased treatment rates and treatment capacity of municipal sewage treatment plants, the production of sewage sludge with 80% moisture content from wastewater treatment plants reached up to 27.86 million tons in 2016. Besides moisture, organic matter, and inorganic salts, the sludge contains hazardous substances such as pathogens and heavy metals, which pose threats to human health and the environment. Sanitary landfills, composting, and incineration are three main technologies that are frequently used in sludge treatment. Among these methods, sludge incineration is the most effective and reliable technology because it minimizes the sludge volume and recovers dry sludge. The pathogens and other toxic compounds can be destroyed during the incineration process. Co-processing of sewage sludge in cement kilns is an emerging technology, characterized by feeding the sewage sludge into the cement kiln for incineration (Lv et al., 2016). The moisture content of the sludge should be reduced to below 30% before incineration in the cement kiln. Thermal drying by waste heat of the cement kiln exhaust gases is an economic way of sludge desiccation. In Europe, particularly in Germany, the sludge drying method has been frequently applied in cement kilns and coal-fired power stations (Kelessidis and Stasinakis, 2012). This environmentally friendly disposal method has attracted increasing attention in China and has been employed in Beijing, Shanghai, and Guangzhou in recent years.

In the sludge drying process, the temperature reaches up to 290°C to sterilize the sludge and destroy its gel structure. Large amounts of off-gases containing odors and volatile organic compounds (VOC) are released into the atmosphere during the process, which cause odorous air pollution that is harmful to human health and the environment. SO2, NH3, and VOC are frequently present in the emissions from the sewage sludge desiccation process. Effective treatment technologies are needed to reduce these emissions. Biofiltration is a method with low operating costs and small amounts of hazardous residual waste, and is efficient in the purification of off-gases with large flow rates and low concentrations. Biological technologies were used to remove hydrogen sulfide, mercaptans, ammonia, and amines from air. Approximately 10 years later, this technology has been extended to the removal of VOC, volatile organic sulfur, and SO2. Several studies have reported effective elimination of aromatic VOC, including BTEX by these technologies (Jeong et al., 2009, Rahul et al., 2013, Wang et al., 2013). Philip and Deshusses (2003) developed a combined bioreactor system containing a biotrickling filter followed by a biological post-treatment unit to treat SO2 from flue gases. Their results showed that nearly 100% SO2 removal efficiency was achieved by using this treatment system. Although biofilters have many advantages, there are still some problems with those methods and the performance of biofilters in the treatment of gases containing complex pollutants needs further improvements. In addition, biofilters inhabited by bacteria and fungi are sources of microbial bioaerosol emissions (Martens et al., 2001). Because of arising public concern about such emissions and possible health risks to the exposed people, further research should be conducted to understand the degree of emissions from airborne microorganisms in biofilters during the odor or VOC treatment processes.

In the present study, a laboratory-scale biofilter was established to treat the waste gas containing SO2 and o-xylene. SO2 and o-xylene were selected as representatives of sulfur-containing compounds and monoaromatic hydrocarbon compounds that are usually present in the sludge-drying tail gases. The performance of the biofilter was evaluated for over 6 months by varying the inlet load of o-xylene and SO2. The microbial population in the biofilter was analyzed using PCR-DGGE (denaturing gradient gel electrophoresis) methods to investigate the relationship between microbial characteristics and the removal of waste gas mixture with o-xylene and SO2. Bioaerosol emissions from the biofilter were also studied.

Section snippets

Experiment and procedure

The co-treatment of SO2 and o-xylene was carried out in a biofilter with a height of 2.5 m and a diameter of 0.2 m (Fig. 1). The effective volume of the biofilter was 0.056 m3. Polyurethane foam cubes with 97% of porosity were packed in the biofilter column. The volume of each cube was approximately 1 cm3. The packing density was 12–15 kg/m3. Bacteria or other microorganisms were grown on polyurethane foam cubes. SO2 and o-xylene were selected as representative compounds to be treated by the

Performance of the biofilter for SO2 and o-xylene removal

The evaluation of the biofilter performance was conducted for over 6 months by step-varying the inlet loads of SO2 and o-xylene. The entire operation period was divided into 5 stages according to the SO2 and o-xylene loads. Stages I, II, III, IV, and V lasted for 32, 34, 32, 38, and 50 days, respectively. The operation time, average concentration, and removal efficiency of SO2 and o-xylene in each operational stage are summarized in Table 1. At Stage I and Stage II, SO2 was the sole pollutant for

Conclusions

The results of this study indicated that SO2 and o-xylene could be co-treated effectively in a single biofilter. The removal of SO2 and o-xylene in the biofilter was dependent on their concentration ratio in the inlet stream. The removal of o-xylene was influenced by the amount of SO2. At same time, the presence of o-xylene at low concentrations enhanced the SO2 removal efficiency.

SOB and XB thrived and proliferated vigorously in the biofilter when SO2 and o-xylene were the main components to

Acknowledgements

The authors express their sincere acknowledgements to Editage for the English revision of the manuscript. The work was financially supported by the National Natural Science Foundation of China (Nos. 51478456 and 51308527).

References (41)

Cited by (24)

  • Characterization of sulfide oxidation and optimization of sulfate production by a thermophilic Paenibacillus naphthalenovorans LYH-3 isolated from sewage sludge composting

    2023, Journal of Environmental Sciences (China)
    Citation Excerpt :

    Previous studies of bacterium Paenibacillus naphthalenovorans with broad applications fields were mainly reported to degrade dibenzofuran and naphthalene in contaminated environments (Daane et al., 2002; Pepi et al., 2009; Thanh et al., 2019). Moreover, studies on the genus Paenibacillus have been focused on the biodegradation of dimethyl sulfide, sulfur dioxide, and organic sulfur compounds (Giri et al., 2010; Sun et al., 2018; Wang et al., 2015), yet few studies have been conducted to analyze sulfide biotransformation of P. naphthalenovorans under high-temperature conditions. Environmental conditions play pivotal roles in bacterial growth and sulfur metabolism (Tang et al., 2009).

  • Removal behavior of gaseous furfural using a biofilter packed with perlite, ripe compost, and oak woodchips

    2021, Process Safety and Environmental Protection
    Citation Excerpt :

    Although the rate of furfural adsorption on the biofilter bed has not been investigated in this study, there are several studies in the literature showing that the packing materials used in this study including compost, perlite, and wood chips could adsorb a wide range of pollutants (Amin et al., 2015; Doğan et al., 2000; Karanasios et al., 2010). The adsorption of other pollutants different from furfural has already been reported in the literature, and a similar trend was reported by Hajizadeh et al. (2018); Hassan and Sorial (2009); Sun et al. (2018), and Saravanan and Rajamohan (2009). Previous studies have shown that the pH of the packing media is an important factor which could influence the biofilter performance.

  • Performance and economic analyses of a combined bioreactor for treating odors, volatile organic compounds, and aerosols from a landfill site

    2021, Journal of Cleaner Production
    Citation Excerpt :

    In addition, these ions are precursors formed in hazy weather, which affect air pollution (Behera et al., 2015). Microorganisms in the gas may originate from the biofilter inlet or escape from the packing material (Sun et al., 2018). The concentration changes in different types of microorganisms and WSIs in the outlets of different zones during stable operation period were studied.

  • Styrene removal with an acidic biofilter with four packing materials: Performance and fungal bioaerosol emissions

    2020, Environmental Research
    Citation Excerpt :

    Generally, increasing trends were found under the higher IL (Fig. 5), which was observed in all four packing materials. The results found in our study were similar to the study of Sun et al. (2018). The counts of fungi at the time of stabilization in our study were higher than those for a conventional BF that operated at the neutral pH ( × 103–106 CFU/g dry packing material) (Cheng et al., 2016b).

  • Comparison and application of biofilter and suspended bioreactor in removing gaseous o-xylene

    2020, Environmental Research
    Citation Excerpt :

    The total removal rate was over 90%, with 24.0% in the first zone and 67.6% in the second. O-xylene and SO2 could be co-treated feasibly within one BF, and the removal of SO2 could be enhanced when low concentrations of o-xylene were introduced into the BF (Sun et al., 2018). The maximum elimination capacity of benzene, toluene, ethylbenzene, and xylene (BTEX) for a BF could be achieved with 244.2 g BTEX m−3h−1 at the inlet concentration of 12.6 mg m−3 and an empty bed residence time (EBRT) of 48s (Rene et al., 2012).

View all citing articles on Scopus
View full text