Temporal Variation of Microbial Population in Acclimation and Start-Up Period of a Thermophilic Desulfurization Biofilter
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International Biodeterioration & Biodegradation 109 (2016) 157e164 Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod Temporal variation of microbial population in acclimation and start- up period of a thermophilic desulfurization biofilter * Jingying Zhang, Lin Li, Junxin Liu , Yunping Han Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China article info abstract Article history: Microorganisms in a biofilter play important roles in the gas contaminants treatment process. In this Received 22 April 2015 study, thermophilic desulfurization bacteria were inoculated in a thermophilic biofilter for SO2 treatment Received in revised form after acclimation and enrichment. Molecular biology techniques were applied to detect temporal vari- 27 January 2016 ation of microbial population during acclimation and biofilter start-up period. The acclimation tem- Accepted 28 January 2016 peratures were 50, 55, and 60 C. Desulfurization bacteria dominated the enrichments. During Available online 6 February 2016 acclimation, desulfurization bacteria and thermophilic bacteria increased from 36.84% to 78.95%e52.94% and 88.24%, respectively. In addition, the microbial diversity indices of these enrichments decreased with Keywords: fl Thermophilic biofilter time. Substrate species and acclimation temperature in uenced the microbial structure of the enrich- ments. The thermophilic biofilter inoculated with enrichments could achieve a rapid start-up, and over SO2 Desulfurization bacteria 80% of removal efficiency could be obtained within two weeks. The maximum elimination capacity was À3 À1 À3 Acclimatization 38.71 g m h at 152 mg m inlet concentration. The total sulfur bacteria proportion increased Start-up period obviously during the start-up period. Moreover, desulfurization bacteria that originally existed in inocula, DGGE analysis e.g., Pseudomonas putida, Bacillus thioparans, Microbacterium sp., and Thermoanaerobacteriaceae, were abundant in the thermophilic biofilter for SO2 removal. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction months. Microbial analysis indicated that SO2 was degraded by Paenibacillus sp. in the IZ, and by Paenibacillus sp. and Ralstonia sp. Off-gas generated from most industrial and agricultural pro- in the SZ (Lin et al., 2015). Reactor stability and efficacy are main- cesses threatens human and ecological health and causes envi- tained by functionally, compositionally, and spatiotemporally dy- ronmental pollution, such as odor nuisance, health effects, crop namic and diverse communities (Xue et al., 2013). Various factors damage, smog formation, and global warming (Devinny et al., 1999; affect the growth kinetics of participating microorganisms, van Groenestijn and Hesselink, 1993). including substrate concentration, moisture content, temperature, Compared with physical (adsorption, absorption, and conden- electron acceptor, pH, toxic intermediates, and availability of min- sation) and chemical (catalytic combustion, scrubbing, and oxida- eral nutrients. Any or a combination of these factors can limit tion) methods, biotechnology provides a more economical and biomass growth rate and substrate biodegradation (Beuger and sustainable approach owing to its low operational costs, high Gostomski, 2009; Ottengraf, 1986; Sakuma et al., 2008). removal efficiency, and lack of secondary pollutant generation (Li Three important time-dependent conditions generally exist for and Liu, 2006; Ralebitso-Senior et al., 2012). For most applica- biofilters: start-up response, response to varying loads, and long- tions, biological air treatment systems have traditionally relied on term performance. “Start-up” time is the acclimation time microorganisms, generally bacteria, found under ambient envi- required to establish an optimal biological removal. Depending on ronmental conditions (Devinny et al., 1999). An integrated biore- ambient and site conditions, this start-up procedure may last for actor with two sections, a suspended aerobic zone (SZ) and weeks or months (Devinny et al., 1999). The start-up period de- immobilized aerobic zone (IZ), was applied to treat SO2 for six pends on the amount of initial microbial population that can degrade the pollutants; thus, inoculation from an adapted popu- lation is desirable (Shareefdeen and Singh, 2005). As an inoculum * Corresponding author. source, sewage/activated sludge can be trickled over or inoculated E-mail addresses: [email protected] (J. Zhang), [email protected] (L. Li), directly into a support medium. Alternatively, inocula can be [email protected] (J. Liu), [email protected] (Y. Han). http://dx.doi.org/10.1016/j.ibiod.2016.01.021 0964-8305/© 2016 Elsevier Ltd. All rights reserved. 158 J. Zhang et al. / International Biodeterioration & Biodegradation 109 (2016) 157e164 2À cultured in feed reactors to specific biomass concentrations before MgCl4,6H2O; 0.50 NH4Cl; and 5.00 beef extract. Given that S was introducing waste gas. A six times-faster biofiltration start-up of converted into H2S and was lost as gas from aerobic enrichment, volatile organic solvents can be achieved through inoculation with Na2S2O3 was used instead of Na2S as the sulfur substance. The adapted microorganisms (Saake and Hübner, 1989). Wright et al. initial pH of the media was adjusted to 6.5e7.0. Agar (2%) was found that acclimation in compost biofilters is faster in treating added as a solidifying agent. The inocula were replaced monthly gasoline vapors when the biofilters are inoculated with culture with fresh media at a ratio of 10:1 and were sampled regularly to grown on gasoline (Wright et al., 1997). Leson and Smith reached a analyze the microbiological indicator. similar conclusion, suggesting that inoculation hastens acclimation but does not affect the ultimate removal efficiency (Leson and 2.2. Bioreactor setup Smith, 1997). However, few studies have focused on the characteristics of After the inocula were enriched at 50, 55, and 60 C for 12 microbial population during acclimatization and bioreactor start- months, the inocula were mixed at a ratio of 1:1:1 to inoculate into up period. SO2, generated from the thermal conversion process- a thermophilic biofiltration (Fig. 1). The biofiltration was a stainless ing of fuels in power plants, refineries, coal- and oil-fired boilers, column with a height of 30 cm and a diameter of 10 cm. The packing and paper pulp production, is harmful to the environment and the material was polyurethane foam cube with an average size of 3 human health (Philip and Deshusses, 2003). Therefore, SO2 was 1.0 cm . A high-pressure cylinder continuously supplied SO2 to the used as a target compound in the present study. Desulfurization biofiltration from the air inlet at the bottom of the column. A bacteria were acclimated and enriched to inoculate a thermophilic calibrated mass flow meter was used to control the gas flow rate, fi bio lter to treat SO2. The temporal variations of microbial popu- and a temperature-controlled oven was supplied to heat the SO2 À lation during acclimatization and biofilter start-up period were inlet. The total flow rate was 0.6 m3 h 1, and the column was analyzed via polymerase chain reaction-denaturing gradient gel maintained at 60 C through a thermostat-controlled heating belt. fl electrophoresis (PCR-DGGE), and uorescence in situ hybridization After inoculation, the SO2 concentrations of the inlet and outlet (FISH) was applied to describe the microbial population distribu- were monitored online using a flue gas analyzer (rbr, Ecom-J2KN, tion. Biofilter performance was also investigated after desulfuriza- Germany) to determine the removal efficiency. The performance tion bacteria inoculation. The aim of this present study is to provide of the bioreactor was evaluated by series parameters, which were data for rapid start-up and steady operation of the bioreactor, defined as follows (formulas 1 and 2): especially for the thermophilic biofilter. ¼ð À Þ = R Cin Cout 100 Cin (1) 2. Materials and methods ¼  ð À Þ= EC Q Cin Cout V (2) 2.1. Acclimation method where R is the removal efficiency (%), Cin is the inlet concentration À3 À3 of SO2 (mg m ), Cout is the outlet concentration of SO2 (mg m ), Inoculum samples were collected from a bioreactor that con- À À EC is the elimination capacity (g m 3 h 1), Q is the flow rate tained SO2 with three packing layers for off-gas treatment. From the 3 À1 fi 3 bottom to the top layer, the operation temperatures were 60, 55, (m h ), and V is the volume of bio lter (m ). and 50 C. The packing samples were obtained from each layer. The detail information of samples was described in Table 1. After 2.3. Microbiological analysis transporting to the laboratory, the packing mediums were soaked in LuriaeBertani (LB) medium (BR, Aoboxing Biotech, Co., China). Bacteria were incubated in agar-containing LB medium (BR, The mediums were then shaken for 1 h using ultrasonic oscillators Aoboxing Biotech, Co., China) at 60 C for 24 h. Sulfur bacteria were (KQ-250B, Kunshan, China). The liquids with suspended cells were cultivated in SCM medium at 60 C for 3 d. The culture plates were cultured in the same nutrient solution in incubator shakers (HZ- placed in a biochemical incubator (SPX-70BIII, AISITE, Tianjin, 9211K, Taicang, China) at 50, 55, and 60 C, and at 120 rpm to enrich China) for thermostatic incubation, and the amount of cells was the microorganisms. counted and reported as colony-forming units (CFUs/ml).