Materials and methods
2.1. Experimental set-up and MBR
operation In this study, we installed pilot-scale two-stage MBR at a solid waste disposal site in Thailand. The system consisted of two reac-tors connected in series (Fig. 1). The first anoxic reactor had a total volume of 1.25 m3—volume of 1 m3 was used for operation andthe other volume of 0.25 m3 was used for sludge storage zone.The reactor was equipped with inclined tube module—size 0.15 mchannel width, 0.45 m depth—for sludge separation and followedby another aerobic reactor with 1 m3working volume which had two hollow fiber membrane modules (Sterapore SURTM, PE, 0.4 mpore size, 9 m2 surface area per module) immersed inside the tankfor solid-liquid separation. Intermittent suction (10:10 min on andoff) was performed to withdraw permeate from the membrane module and maintain permeate flow at 2 m3/d. Therefore totalhydraulic retention time (HRT) in the two-stage MBR was main-tained at 1 day which found appropriate for high strength leachatein our previous study [15]. Aeration was continuously supplied tothe MBR reactor for maintain the dissolved oxygen (DO) level at4–5 mg/l. The sludge was cultivated and maintained within the sys-tem for 500 days. They were re-circulated at a rate of 100% of feedflow rate from aerobic tank back to anoxic tank to maintain mixedliquor suspended solids (MLSS) concentration in the aerobic reactorat about 7–9 g/l. Due to this re-circulation, DO level in anoxic reac-tor was maintained at 0.5 mg/l. There was no sludge drainage fromsystem except a minimal amount for analytical purp