Journal of Water and Environment Technology, Vol.13, No.2, 2015 Development of UASB-DHS System for Treating Industrial Wastewater Containing Ethylene Glycol Takahiro WATARI 1), Daisuke TANIKAWA2), Kyohei KURODA1), Akinobu NAKAMURA1), Nanako FUJII3), Fuminori YONEYAMA3), Osamu WAKISAKA3), Masashi HATAMOTO1), Takashi YAMAGUCHI 1) 1) Department of Environmental Systems Engineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan 2) Department of Civil and Environmental Engineering, National Institute of Technology, Kure College, 2-1-11 Agaminami, Kure, Hiroshima 737-8506, Japan 3) Fundamental Material Laboratory Office, Material Technology Research and Development Laboratory, Research and Development Headquarters, Sumitomo Riko Company Limited, 3-1 Higashi, Komaki, Aichi 485-8550, Japan ABSTRACT This study evaluated the performance of a novel treatment system consisting of an upflow anaerobic sludge blanket (UASB) and a downflow hanging sponge (DHS) for the treatment of industrial wastewater containing 8% ethylene glycol and 2% propylene glycol discharged from a rubber production unit. The system achieved high COD removal (91 ± 4.3%) and methane recovery (82 ± 20%) at an organic loading rate of 8.5 kg-COD/(m3·day). The UASB allowed an organic loading rate of 14 kg-COD/(m3·day) with a constant hydraulic retention time of 24 h. The COD of DHS effluent was 370 ± 250 mg-COD/L during the entire experimental period. Thus, the proposed system could be applicable for treating industrial wastewater containing ethylene glycol. Massively parallel 16S rRNA gene sequencing elucidated the microbial community structure of the UASB. The dominant family Pelobacteriaceae could mainly degrade the organic compounds of ethylene glycol and decomposed products of ethanol. In Archaea, the hydrogenotrophic methanogen family Methanobacteriaceae was predominant in UASB granular sludge. Keywords: downflow hanging sponge, ethylene glycol, upflow anaerobic sludge blanket INTRODUCTION Ethylene glycol is produced by the conversion of ethylene to the intermediate ethylene oxide and then to ethylene glycol. It is used in many industries as a raw material for polyester fibers and for polyethylene terephthalate resins used in bottling and anti-/de-icing fluids. Several industries, such as the manufacture of rubber products, discharge high-strength industrial wastewater containing ethylene glycol. This is usually treated by conventional aerobic processes such as an activated sludge system (Bieszkiewicz et al., 1978; Kilroy and Gray, 1992). However, this system has disadvantages like high operation costs, large space requirements, and the discharge of excess sludge. Therefore, applying an anaerobic treatment system is economically viable for the treatment of industrial wastewater containing ethylene glycol. Previous researches reported that ethylene glycol has high biodegradability under anaerobic condition (Means and Anderson, 1981; Dwyer and Tiedje, 1983). However, to the best of our knowledge, there is no report for applying an anaerobic treatment system for treating industrial wastewater containing ethylene glycol. Address correspondence to Takashi Yamaguchi, Department of Environmental Systems Engineering, Nagaoka University of Technology, Email: [email protected] Received June 3, 2014, Accepted October 3, 2014. - 131 - Journal of Water and Environment Technology, Vol.13, No.2, 2015 Anaerobic treatment has been widely applied for treating different types of industrial wastewater. Previous studies have demonstrated the performance of anaerobic treatment for treating many types of medium- and high-strength industrial wastewater (Chan et al., 2009). Of anaerobic treatment systems, the upflow anaerobic sludge blanket (UASB) system is one of the most promising systems. The highlights of UASB include high organic loading rates (OLRs), low operational costs, and energy recovery in the form of methane. UASB reactors are especially preferred for treating highly polluted industrial wastewaters because of their high chemical oxygen demand (COD) removal capacity (Lettinga and Hulshoff Pol, 1991; Rajeshwari et al., 2000). However, the effluent from the UASB treatment of such high-strength industrial wastewater still contains high concentrations of organic compounds. Thus, aerobic systems are usually applied as post-treatment to remove residual organic matter and achieve permissible effluent standards (Chan et al., 2009). Our research group has been developing a combined anaerobic-aerobic system consisting of a UASB and a downflow hanging sponge (DHS) as an energy-saving wastewater treatment system (Tandukar et al., 2007). DHS is an aerobic trickling filter system that uses sponge as the supporting medium (Takahashi et al., 2004), and it has been used for treating various industrial wastewaters (El-Kamah et al., 2011; Onodera et al., 2013). First, UASB removes most of the organic compounds and converts them to methane. Then, DHS removes residual organic compounds in the effluent to achieve the permissible standard for discharge. In this study, a combination of UASB and DHS reactors was used for the treatment of high-strength industrial wastewater containing ethylene glycol. We also observed the 16S rRNA genes in UASB granular sludge to understand the microbial communities treating industrial wastewater containing ethylene glycol. MATERIALS AND METHODS Raw wastewater In this study, industrial wastewater containing ethylene glycol and propylene glycol was used. It was continuously discharged during the manufacturing process of glycol entrapping some rubber products. The wastewater was stored at normal temperature and the characteristics of the raw wastewater are shown in Table 1. Table 1 - Characteristics of raw wastewater. Parameter Units Concentration pH 7.5 SS mg/L 88 Total-COD mg-COD/L 203,000 Soluble-COD mg-COD/L 183,000 Total nitrogen (TN) mg-N/L 130 Total phosphorus mg-P/L 4.24 (TP) - 132 - Journal of Water and Environment Technology, Vol.13, No.2, 2015 Reactor system description and operational conditions Figure 1 shows a schematic diagram of the proposed treatment system, which consisted of UASB and DHS reactors. The UASB reactor (height: 0.90 m) was equipped with a gas-solid separator and three sampling ports. It had a working volume of 10 L. It was seeded with mesophilic granular sludge obtained from another UASB reactor treating wastewater from the food industry (mixed liquor suspended solids (MLSS) = 32.8 g-MLSS/L, mixed liquor volatile suspended solids (MLVSS) = 22.2 g-MLVSS/L). The DHS reactor had a height of 0.80 m. The distributor was connected at the top of DHS reactor to ensure the equal distribution of UASB effluent to the DHS sponge media. Square sponge cubes (dimensions: 30 mm × 30 mm × 30 mm) covered by a plastic net ring were used as media. The sponge media was placed on 2 stages of the DHS reactor to increase an air supply and improvement of maintenance and sampling. The reactor volume and sponge volume of the DHS reactor were 11 L and 5.7 L, respectively. The reactors were placed in a temperature-controlled (35°C) room. The influent of the reactor was raw wastewater that was diluted to the appropriate COD concentration using tap water. DHS effluent was recirculated to the UASB influent to reduce the amount of tap water used for dilution (circulation ratio: 5) and its alkalinity was adjusted using 1.0 g-NaHCO3/g-COD of sodium bicarbonate. The COD:N:P ratio was adjusted to 100:10:1 using ammonium chloride and dipotassium hydrogen phosphate. A summary of the initial wastewater composition for the three operating phases is shown in Table 2. The wastewater was stored at 7°C. Fig. 1 - Schematic diagram of the UASB and DHS combined system, (1) substrate reservoir; (2) pump; (3) – (5) sampling port (6) gas-solid separator; (7) mixer; (8) water seal; (9) desulfurizer; (10) gas meter; (11) distributor; (12) recirculation pump. Table 2 - Initial wastewater compositions for the three operating phases. Operation phase 1 2 3 Day 190-222 223-300 301-355 Total COD (mg-COD/L) 6,000 8,000 13,000 NH4Cl (mg/L) 22 28 18 K2HPO4 (mg/L) 2.8 3.92 6.72 NaHCO3 (mg/L) 600 940 1,440 - 133 - Journal of Water and Environment Technology, Vol.13, No.2, 2015 Analytical methods Samples of the influent, UASB effluent, and DHS effluent were collected for routine analysis. pH was measured using a portable pH meter (AS-212, Horiba, Japan). COD, total nitrogen (TN), and total phosphorus (TP) were determined using a HACH water quality analyzer (DR-2800, HACH, USA). Volatile fatty acid (VFA) concentrations were determined using a gas chromatograph equipped with a flame ionization detector (GC-1700, Shimadzu, Japan). Biogas production was measured using a wet gas meter (WS-1A, Shinagawa, Japan) after desulfurization. Biogas composition was analyzed using a gas chromatograph equipped with a thermal conductivity detector (GC-8A, Shimadzu). Massively parallel 16S rRNA gene sequencing Sludge samples were collected from the sampling ports (at heights of 20 cm, 35 cm, and 50 cm) of the UASB reactor on day 317 (OLR: 14 kg-COD/(m3·day)). These samples were washed with phosphate-buffered saline (PBS: 137 mM NaCl, 2.7 mM KCl, 10 mM Na2HPO4·12H2O, and 1.8 mM KH2PO4) and homogenized using an ultrasonic homogenizer (UH-50, MMT, Japan). DNA was extracted using a Fast DNA SPIN Kit for Soil (MP Biomedicals, USA), and the DNA concentration was measured using a Nanodrop spectrophotometer (ND-2000, Thermo Fisher Scientific, USA). PCR amplification was performed using universal primer 515F (5′-GTG CCA GCM GCC GCG GTA A-3′) and reverse primer 806R (5’-GGA CTA CHV GGG TWT CTA AT-3’) with annealing temperature of 50°C (Turner et al., 1999; Walters et al., 2011). PCR products were purified using a MinElute PCR Purification Kit (QIAGEN, USA). Massively parallel 16S rRNA gene sequencing and data analysis were performed on the basis of the methods of Caporaso et al. (2012). Sequencing data analysis was conducted using quantitative insights into microbial ecology (QIIME) software package ver.1.7.0. (Caporaso et al., 2010). Taxonomic classification was determined using the Greengenes database ver.