Effects of environmental factors on anaerobic granular sludge in upflow anaerobic sludge blanket reactors.

摘要

Effects of environmental factors (micronutrients and toxicants) on high rate anaerobic digestion and anaerobic granular sludge were studied in laboratory-scale (20 litres) and bench-scale (1.2 litres) upflow anaerobic sludge blanket (UASB) reactors.;The anaerobic bacteria, when grown in feed lacking iron and cobalt, could become iron and/or cobalt deficient and had low specific activity. Supplements of iron and cobalt in the feed provided sufficient amount of these elements for the bacterial metabolism, and excellent COD digestion rates could be maintained in the reactors. Yeast extract showed a strong positive effect on the bacterial growth rate, but had no significant contribution to the specific activity of bacteria.;The bacterial growth rate was enhanced by high COD loading rates, and by supplements of yeast extract and vitamins. High concentrations of sulfite in the feed also favoured bacterial growth rate. High bacterial growth rates in the reactors increased organic matter inside the granules and negatively affected the granule settling properties. By contrast, inorganic cations in the feed, especially calcium, tended to form inorganic precipitates in the granules and therefore promoted the granule settling rate. The extractable extracellular polymeric substance (EPS), excreted by the anaerobic bacteria, was affected by the environmental factors. The carbohydrate concentration in the extracted EPS was significantly related to the supplements of iron and yeast extract in the feed.;Minimal sulfite toxicity was observed under gradual and shock load conditions at sulfite concentrations of up to 1000 mg S/l if proper process acclimation was allowed to occur. No inhibition was caused by the generated sulfide in the effluent when its concentration was 310 mg/l. The COD digestion rate was inhibited at a cadmium dosage of 2.0 g/l under both acclimation and shock load conditions. Most added cadmium was removed in the inorganic precipitate or absorbed by granular sludge. The bacteria could not be reactivated after being poisoned by cadmium.;A heterogenous microbial population, including Methanothrix-like, Methanobrevibacter-like, Methanococcales-like, Pelobacter-like and Spirochaete, was present on the granule surfaces. Methanothrix-like bacteria dominated in the inner-layer of all granules. Supplements of trace metals, yeast extract and sulfite did not significantly change the bacterial population.