Startup of anaerobic UNITANK reactors with primary and secundary sludge from municipal WWTPS: results of bench-scale experiments
1997
Smedt, M. de | Gerards, R. | Vriens, L. (Seghersengineering Water, Wespelaar (Belgium))
The startup of anaerobic UNITANK reactors in countries where anaerobic seed sludge is not available (Middle East, Eastern Europe) creates the need for techniques to make sludge with good settling characteristics and high methanogenic activity on site. In many cases, the most suitable raw material available is primary and/or secondary sludge from a nearby municipal wastewater treatment plant (MWWTP). We have performed experiments in bench-scale UASB-reactors to determine the optimal conditions for the development of anaerobic sludge starting with MWWTP waste sludge. The reactors were seeded with a raw mixture of primary and secondary MWWTP sludge and operated under identical conditions for several months. The feed of both reactors consisted of a mixture of acetate and sucrose with addition of nitrogen and phosphorus; while one of the reactors was also fed with a commercial additive, stimulating the development of granular sludge. The results showed that gas production of all reactors started after one month. The upflow in the reactors was than increased up to a relative high rate; sludge washout gradually decreased down to a minimum at day 60. A dense sludge bed of less than 7 per cent of the active volume was observed at day 60. Microscopic analysis also revealed a bigger and denser floc compared to the control reactor. After re-seeding the reactors with the same raw material, the gas production of the reactors reached its maximal value after 3 days. At day 90, the reactor which recieved the growth-stimulating additive, contained 15 per cent more biomass than the control reactor. Sludge granules are observed in both reactors after several months. The research has resulted in a procedure for the startup of full-scale anaerobic UASB-reactors with MWWTP waste sludges.
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