Elsevier

Bioresource Technology

Volume 102, Issue 2, January 2011, Pages 753-757
Bioresource Technology

Performance of a pilot-scale sewage treatment: An up-flow anaerobic sludge blanket (UASB) and a down-flow hanging sponge (DHS) reactors combined system by sulfur-redox reaction process under low-temperature conditions

https://doi.org/10.1016/j.biortech.2010.08.081Get rights and content

Abstract

Performance of a wastewater treatment system utilizing a sulfur-redox reaction of microbes was investigated using a pilot-scale reactor that was fed with actual sewage. The system consisted of an up-flow anaerobic sludge blanket (UASB) reactor and a down-flow hanging sponge (DHS) reactor with a recirculation line. Consequently, the total CODCr (465 ± 147 mg L−1; total BOD of 207 ± 68 mg L−1) at the influent was reduced (70 ± 14 mg L−1; total BOD of 9 ± 2 mg L−1) at the DHS effluent under the conditions of an overall hydraulic retention time of 12 h, a recirculation ratio of 2, and a low-sewage temperature of 7.0 ± 2.8 °C. A microbial analysis revealed that sulfate-reducing bacteria contributed to the degradation of organic matter in the UASB reactor even in low temperatures. The utilized sulfur-redox reaction is applicable for low-strength wastewater treatment under low-temperature conditions.

Introduction

An up-flow anaerobic sludge blanket (UASB) method has been represented as the core technology for an anaerobic wastewater treatment method, widely used for the treatment of medium and high organic strength wastewater. Recently, it has been applied to low-strength wastewater because of advantages such as energy saving and low excess sludge (Yoochatchaval et al., 2008, Syutsubo et al., 2008). Sato et al. (2007) revealed that UASB could be the most suitable option in terms of expenses and treatment efficiency for sewage treatment in the warm regions of India. However, for sewage treatment under low-temperature, the performance of the anaerobic methanogenic process for the anaerobic treatment method tends to degrade because methanogenic activity is suspended (Uemura and Harada, 2000, Yamaguchi et al., 2006). Therefore, it is necessary to improve the quality of water and polish up the anaerobically treated effluent using a post-treatment system. Lettinga and others reported that the anaerobic filter and the anaerobic hybrid system achieved 70% of COD removal efficiency in the hydraulic retention time (HRT) of 12 h at 13 °C (Elmitwalli et al., 2001, Elmitwalli et al., 2002, Elmitwalli et al., 2003). Álvarez et al. (2008) reported that the two-stage anaerobic system achieved 49–65% of COD removal efficiency in the hydraulic retention time (HRT) of 9.3–16.9 h at 21–14 °C. Mahmoud et al., 2004, Mahmoud et al., 2008 proposed sludge control by the combination of a UASB and a digester unit, which enhanced sludge stabilization and the generation of active methanogenic sludge that was to be recirculated to the UASB reactor.

We proposed low-strength wastewater treatment process that can be used under low-temperature conditions. The process consisted of a UASB reactor as an anaerobic pre-treatment unit and a down-flow hanging sponge (DHS) reactor as an aerobic post-treatment unit with a recirculation line. In the sulfur-redox process, organic matter was degraded by sulfate-reducing bacteria (SRB) which produced sulfide. The sulfide, one of the COD compound, is oxidized to sulfate by sulfur-oxidizing bacteria (SOB). The DHS reactor is a novel technology that was developed by the Harada Research Group, Japan. The DHS reactor (cube-type DHS) achieved high COD removal efficiency of 90% in the HRT of 10.7 h at 15 °C (Tawfik et al., 2006). Bungo et al. (2004) and Yamaguchi et al. (2006) reported that 90% of the fed artificial wastewater was degraded in the sulfur-redox UASB/DHS system at 8 °C in the HRT of 12 h. In addition, it appeared that using sulfur-redox reaction, the UASB and the aerated fixed bed system could be applied to actual sewage treatment under low-temperature conditions as well (Sumino et al., 2007). This study examined the performance of the UASB/DHS system for treating actual sewage in ambient low-temperature conditions and a microbial community and focused on the contribution of the sulfur-redox reaction.

Section snippets

Experimental setup

Fig. 1 shows the schematic diagram of the experimental setup of a pilot-scale sewage treatment system, which was installed at the Higashi-Hiroshima city wastewater treatment center, Japan. The system consisted of a denitrification (DN) reactor (1.40 m3), a UASB reactor (8.40 m3), a DHS reactor (13.87 m3), and sand filtration (1.00 m3) with a recirculation line. The treatment flow was as follows: sewage was passed through a 5-mm-mesh screen device and pretreated by a DN reactor and a UASB reactor.

Reactor performance

Fig. 2 shows the time course of the sewage temperature, SS, and total CODCr over 900 days. The system was operated under ambient temperature conditions, and the daily average influent sewage temperature ranged between 2.6–30.2 °C. For SS, 280 ± 177 mg L−1 of sewage SS was removed to 36 ± 14 mg L−1 of UASB effluent and 48 ± 28 mg L−1 of DHS effluent. The sand filtration decreased to less than 10 mg L−1. The captured SS of the sand filtration flowed into the recirculation line to the denitrification reactor.

Conclusions

A pilot-scale sewage treatment system using UASB/DHS, operating at HRT of 12 h and recirculation ratio of 2 for over 900 days, performed organic matter removal with high efficiencies of 79% of SS, 84% of CODCr, and 95% of BOD, and nitrogen removal at 38% of the theoretical level under low temperatures such as 7.0 ± 2.8 °C. The SRA/MPA ratio increased at low temperatures. A sulfur-redox reaction collaborating with SRB and SOB, particularly for Thiobacillus species in the system, was found to effect

Acknowledgements

This study was conducted as a project at the Hiroshima Prefectural Institute of Industrial Science and Technology. We received cooperation from Higashi-Hiroshima city, especially in the establishment of the UASB/DHS system.

References (21)

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