In this research, efficient operation technologies for the successful performance of upflow anaerobic sludge blanket(UASB) reactors fed on concentrated complex soluble substrates was studied. Digesters seeded with digested sewage sludge were operated for six months in mesophilic condition. In an attempt to enhance the reactor performance, granular sludge or powdered activated carbon(PAC) were added to the seed sludge. Superficial upflow liquid velocity was increased by effluent recirculation and its effect was studied. The efficiency of the modified gas-solid separator(GSS) device was also investigated. The biological characteristics and morphological structures in inner and surface parts of granular sludge consortia were examined with electron microscopes.
By the stepwise increase of organic loading rate, granular sludge of 0.5-2.0mm in diameter was developed. The granular surface was mainly of filamentous bacteria of Methanothrix spp.. Diverse bacteria appeared to be surround by extracellular biopoymer in the core part of granular sludge, but the biopolymer was not observed in long filaments of Methanothrix spp.. Granulation process seemed to be controlled by physical stress on the reactor content during the start up.
Inoculation of granular sludge to seed sludge enhanced COD removal efficiency, granulation, sludge activity, and sludge retention in the reactor, but PAC enhanced the reactor stability rather than the granulation process. The modified GSS device prevented sludge washout significantly from the reactor at high volumetric loading rate as well as at the vulnerable start-up period to improve the reactor performance.
The severe sludge washout during the start-up period could be decreased by the intermittent effluent withdrawals and the effluent recycle, resulting in the enhanced start-up and improved performance of the UASB reactor. Increased upflow liquid velocity promoted COD removal as well as the release of biogas entrapped in the sludge and increased methane content by 10%. However, the increase of mixing intensity in the reactor during the initial phase hindered the granulation process.
