Abstract: | PCR-single-strand conformation polymorphism (SSCP) and Southern blotting techniques were adopted to investigate microbial
community dynamics in a sulfate-reducing bioreactor caused by decreasing influent alkalinity. Experimental results indicated
that the sulfate-removal rate approached 87% in 25 d under the conditions of influent alkalinity of 4000 mg/L (as CaCO3) and sulfate-loading rate of 4.8 g/(L·d), which indicated that the bioreactor started up successfully. The analysis of microbial
community structure in this stage showed that Lactococcus sp., Anaerofilum sp. and Kluyvera sp. were dominant populations. It was found that when influent alkalinity reduced to 1000 mg/L, sulfate-removal rate decreased
rapidly to 35% in 3 d. Then influent alkalinity was increased to 3000 mg/L, the sulfate-removal rate rose to 55%. Under these
conditions, the populations of Dysgonomonas sp., Sporobacte sp., Obesumbacterium sp. and Clostridium sp. got to rich, which predominated in the community together with Lactococcus sp., Anaerofilum sp. and Kluyvera sp. However, when the alkalinity was decreased to 1500 mg/L, the sulfate-removal rate rose to and kept stable at 70% and
populations of Dysgonomonas sp., Sporobacter sp. and Obesumbacterium sp. died out, while some strains of Desulfovibrio sp. and Clostridium sp. increased in concentration. In order to determine the minimum alkalinity value that the system could tolerate, the influent
alkalinity was decreased from 1500 to 400 mg/L secondly. This resulted in the sulfate-removal rate, pH value and effluent
alkalinity dropping quickly. The amount of Petrotoga sp., Prevotella sp., Kluyvera sp. and Neisseria sp. reduced obviously. The result data from Southern blotting indicated that the amount of sulfate-reducing bacteria (SRBs)
decreased with influent alkalinity dropping. Analysis of the microbial community structure and diversity showed that the SRBs
populations were very abundant in the inoculated activated sludge and the alkalinity decrease caused the reduction of the
populations noted. Most of resident populations in the bioreactor were fermentative acidogenic bacteria (FABs), among which
the phylum Firmicute was in the majority, but SRBs were very few. This community structure demonstrates the cooperation between
SRBs and FABs, which sustains the system’s high sulfate-removal and operation stability. |