Effects of Upflow Liquid Velocity on Performance of Expanded Granular Sludge Bed (EGSB) System
Seni Karnchanawong and Wachara Phajee
Abstract
The effects of upflow liquid velocity (ULV) on performance of expanded granular sludge bed (EGSB) system were investigated. The EGSB reactor, made from galvanized steel pipe 0.10 m diameter and 5 m height, had been used to treat piggery wastewater, after passing through acidification tank. It consisted of 39.3 l working volume in reaction zone and 122 l working volume in sedimentation zone, at the upper part. The reactor was seeded with anaerobically digested sludge and operated at the ULVs of 4, 8, 12 and 16 m/h, consecutively, corresponding to organic loading rates of 9.6 – 13.0 kg COD/ (m3·d). The average COD concentrations in the influent were 9,601 – 13,050 mg/l. The COD removal was not significantly different, i.e. 93.0% - 94.0%, except at ULV 12 m/h where SS in the influent was exceptionally high so that VSS washout had occurred, leading to low COD remo
val. The FCOD and VFA concentrations in the effluent of all experiments were not much different, indicating the same range of treatment performance. The biogas production decreased at higher ULV and ULV of 4 m/h is suggested as design criterion for EGSB system.
Keywords—Expanded granular sludge bed system, piggery wastewater, upflow liquid velocity
I. INTRODUCTIONreactor 翻译
Anaerobic digestion (AD) of wastewater can concurrently remove organic matter as well as produce biogas which is the renewable energy. The application of AD as pretreatment step for high chemical oxygen demand (COD) wastewater, preferably higher than 2,000 mg/l, is economically suitable while higher COD also results in higher biogas production [1]. In Thailand, piggery wastewater is increasingly treated by AD technology such as upflow anaerobic sludge blanket (UASB) system, anaerobic pond, channel (plug flow) digester and anaerobic covered lagoon. The biogas is generally used for on-farm electricity generati
on via induction motor. UASB system is the high-rate wastewater treatment process where wastewater is fed at the bottom and flows upward, passing through layers of anaerobic bacteria with upflow liquid velocity (ULV) 0.5 – 1.5 m/h. The bottom layer, referred to as sludge bed, consists of granules with high suspended solids (SS) concentration (~1-5 %) while the upper layer, referred to as sludge blanket, consists of flocculent sludge (SS ~ 0.3-0.5 %). The granule has very high settling velocity as well as treatment efficiency since it consists of layers of bacteria, responsible for various anaerobic digestion steps [2]. The biogas produced is separated by gas-solids separator (GSS) installed at the upper part of reactor while sedimentation zone, above GSS, help SS removal as well as  return it back to reactor. The reactions occur under enclosed part and smell is minimal.To improve the efficiency of UASB system, high ULVs (5 -15 m/h) were applied by effluent recycling and resulted in sludge bed expansion throughout the reactor’s height. The high total biomass allowed the improved system, called expanded granular sludge bed (EGSB) system, to accommodate higher organic loading rate (OLR) than UASB system [3]. Since EGSB system is recommended for low SS wastewater, the application on piggery wastewater whi
ch has high SS should be firstly verified by laboratory experiment. Moreover, high ULV results in high pumping cost which should be minimized. The objective of this study was to determine the effects of ULV on performance of EGSB system as well as to determinethe suitable ULV for piggery wastewater treatment.
II. MATERIAL AND METHODS
The laboratory scale EGSB reactor, made from galvanized steel pipe 0.10 m diameter and 5 m height with digestion volume of 39.3l, was used. The upper part of reactor was sedimentation zone, made from steel plate 0.5 m diameter, 0.6 m height with 0.10 m freeboard and working volume of 122l (Fig. 1).  The biogas was measured by gas meter, i.e. revolving boxes with counter. There were 17 sampling ports along reactor’s height at 0.3 m spacing. The major sampling ports were at 0.4,1.9, 3.4 and 4.6 m – height. The piggery wastewater was biweekly collected from 2 pig farms, firstly Kittiwat Farm and secondly Chomthong Farm. The wastewater was stored in 0 – 4 C storage room prior to using. It was daily prepared in 70-l plastic tank equipped with mechanical mixer (EYELA m
odel MDC-MS). The wastewater was pumped by a peristaltic pump (Watson Marlow model 505s) to the complete-mix acidification tank, operated at 8-h hydraulic retention time (HRT). The acidification tank was made from plastic water tank, 0.25 m diameter, 0.30 m height and working volume of 12.8l. The complete -mix condition was maintained by a circulating pump, submersible type (8.5 watts). There was no seeding in acidification reactor. The acidification tank effluent was pumped to EGSB reactor at the rate of 1.6 l/h with expected OLR of 10 kg COD/ (m3·d). The EGSB effluent was stored in a 70-l plastic tank and was recycled by a peristaltic pump (Watson Marlow model 505s) to control ULV at 4, 8, 12 and 16 m/h, consecutively. The EGSB reactor was seeded with anaerobi cally digested sludge from Chiang Mai University wastewater treatment plant at 25,000 mg VSS/l. During start up period, OLR and ULV were stepwise increased to the target values. The water samples were taken 2 times/week and analyzed according to Standard Methods [4]. The experiments had been conducted under ambient temperature, tropical climate at the Department of Environmental Engineering, CMU, Thailand, during May 2003 to May 2004.
III. RESULTS AND DISCUSSION
The piggery wastewater was firstly collected from Kittiwat Farm. During the last period of run 1, this farm which was medium- sized sometimes did not have uniform wastewater flow rate so a bigger farm, Chomthong Farm, was chosen throughout the study. The wastewater characteristics had high fluctuations of COD and SS and the acidification tank helped stabilizing the wastewater concentrations. The performance of acidification tank was rather poor, i.e. COD removal 0 – 5%, VSS removal 2.2 – 27.6%. There was no pH adjustment in acidification tank. The influent pH was in neutral range, 6.8 -8.0, while the effluent pH was slightly decreased, 6.8 -7.8. The effluent VFA from acidification were not significantly increased and sometimes slightly decreased, indicating methanogenesis in reactor. It is expected that bacterial enrichment from pig feces plays an important role inVFA degradation. The

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