Evaluating the efficacy of slow-releasing carbon source tablets for in situ biological heterotrophic denitrification of groundwater.

Slow-releasing precipitating tablets (SRPTs) and slow-releasing floating tablets (SRFTs) were formulated to release fumarate as a carbon source (CS) and/or electron donor (ED) in an in situ biological heterotrophic denitrification system. These tablets were prepared using pharmaceutical manufacturing. Soil column tests were conducted to evaluate nitrate denitrification efficacy, microbial population changes, and mass balance of fumarate and potential electron acceptors. Significant and simultaneous consumption of both fumarate and nitrate, and the production and consumption of nitrite were observed in both SRPT-treated and SRFT-treated soil columns. These results suggest that SRPT and SRFT releasing fumarate, induce heterotrophic biological denitrification. In the SRPT- and SRFT-treated columns, 65% and 73% of fumarate were associated with heterotrophic denitrification, respectively. Particularly, surplus citric acid, originally designed to serve as a floating agent, was utilized for 36% and 28% for SRFT flotation and denitrification, respectively. The results of 16s RNA analyses revealed that a bacterium that shared 99% 16s rRNA sequence similarity with those of Azoarcus sp. AN9, and Pseudogulbenkiania sp. NH8B, a facultative heterotrophic denitrifier, was detected in the column effluent. This study confirms that SRPT and SRFT can effectively operate long-term in situ biological denitrification processes, because it is possible to supply detailed CS and/or ED uniformly by applying both SRPT and SRFT in the well.

The difference of morphological characteristics and population structure in PAO and DPAOgranular sludges.

We examined how long-term operation of anaerobic-oxic and anaerobic-anoxic sequencing batch reactors (SBRs) affects the enhanced biological phosphorus removal (EBPR) performance and sludge characteristics. The microbial characteristics of phosphorus accumulating organism (PAO) and denitrifying PAO (DPAO) sludge were also analyzed through a quantitative analysis of microbial community structure. Compared with the initial stage of operation characterized by unstable EBPR, both PAO and DPAO SBR produced a stable EBPR performance after about 100-day operation. From day 200 days (DPAO SBR) and 250 days (PAO SBR) onward, sludge granulation was observed, and the average granule size of DPAO SBR was approximately 5 times larger than that of PAO SBR. The DPAO granular sludge contained mainly rod-type microbes, whereas the PAO granular sludge contained coccus-type microbes. Fluorescence in situ hybridization analysis revealed that a high ratio of Accumulibacter clade I was found only in DPAO SBR, revealing the important role of this organism in the denitrifying EBPR system. A pyrosequencing analysis showed that Accumulibacter phosphatis was present in PAO sludge at a high proportion of 6%, whereas it rarely observed in DPAO sludge. Dechloromonas was observed in both PAO sludge (3.3%) and DPAO sludge (3.2%), confirming that this organism can use both O2 and NO3- as electron acceptors. Further, Thauera spp. was identified to have a new possibility as denitrifier capable of phosphorous uptake under anoxic condition.