[Analysis of Microbial Interaction Law of Mud Membrane in IFAS Process for Treating Low Carbon Source Sewage in South China].

To assess the problem of sewage treatment under the condition of low carbon sources, we carried out a study of activated sludge and a biofilm symbiosis system (IFAS). The occurrence characteristics and interaction law of microorganisms in two phases of sludge membrane under low carbon source conditions were discussed, and their niche and influence on treatment efficiency were clarified. Through a pilot-scale experiment in actual water plants, the biofilm characteristics, sludge membrane activity, and succession law of flora were analyzed, and the microbial structure and interaction in sludge membrane in two phases under the control of different activated sludge ages were compared. The results showed that the sludge concentration in the reactor increased with the increase in SRT under variable SRT. Because the microbial concentration in SRT-H was much higher than that in SRT-L, the competition between mud films in SRT-H was more intense than that in SRT-L, and the pollutant removal efficiency in SRT-H was lower than that in SRT-L. Under the condition of low-carbon feed water, the sludge activity in the IFAS process decreased with the increase in SRT. Under the condition of low SRT(5 d), the nitrification, denitrification, phosphorus accumulation, and phosphorus absorption rate of activated sludge increased by 122%, 88%, 34%, and 44%, respectively, compared with that of high SRT (25 d). However, SRT had little effect on biofilm activity, and there was little difference in nitrification activity and denitrification activity between the two SRTs. Microbial sequencing analysis showed that the functional bacteria of the IFAS process were enriched and transferred with the change in SRT between the two phases of mud membrane. In SRT-L, the functional bacteria that were enriched and transferred between the two phases of mud film owing to the "seeding" effect were mainly unclassified_g__Enterobacteriaceae, whereas in SRT-H, Acinetobacter was mainly used. At the same time, by analyzing the distribution of dominant functional bacteria, it was found that there was some competition between denitrifying bacteria and phosphorus-accumulating bacteria in activated sludge. Under the condition of a lack of organic substrate in the influent, the relative abundance of denitrifying bacteria was obviously higher than that of phosphorus-accumulating bacteria, which indicated that denitrifying bacteria could better adapt to low-carbon source conditions. Thus, they could occupy a dominant competition position, which was mainly reflected in the increase in the relative abundance of aerobic denitrifying bacteria. In addition, the SRT change in the mud phase reacted in the membrane phase, making the residence time of biofilm change correspondingly, thus changing the flora structure, screening out different dominant bacteria genera, and further increasing the difference.

Molecular characterization of microbial populations in full-scale biofilters treating iron, manganese and ammonia containing groundwater in Harbin, China.

In iron and manganese-containing groundwater treatment for drinking water production, biological filter is an effective process to remove such pollutants. Until now the exact microbial mechanism of iron and manganese removal, especially coupled with other pollutants, such as ammonia, has not been clearly understood. To assess this issue, the performance of a full-scale biofilter located in Harbin, China was monitored over four months. Microbial populations in the biofilter were investigated using T-RFLP and clone library technique. Results suggested that Gallionella, Leptothrix, Nitrospira, Hyphomicrobium and Pseudomonas are dominant in the biofilter and play major roles in the removal of iron, manganese and ammonia. The spatial distribution of microbial populations along the depth of the biofilter demonstrated the stratification of the removal of iron, manganese and ammonia. Additionally, the absence of ammonia-oxidizing bacteria in the biofilter implicated that ammonia-oxidizing archaea might be responsible for the oxidation of ammonia to nitrite.