Biological Degradation Of Nitrosamines In Drinking Water Treatment

Nitrosamines are a kind of carcinogenic, teratogenic and mutagenic materials, which are widespread inwater, industrial products, and even food. In recent years, as a kind of disinfection by-products (DBPs) indrinking water treatment, nitrosamines are widely concerned. While9nitrosamines were found in drinkingwater treatment plants (DWTPs), their concentration level, formation mechanism and controllingtechnology were extensively studied. However, it is difficult to control the nitrosamines formed in thedisinfection process of drinking water treatment. Although nitrosamines can be produced in advance fromdifferent pre-oxidation processes, there are few efficient and economical technologies regarding theirremoval. In order to remove the nitrosamines formed in the pre-oxidation processes and reduce the risk ofchemical treatments in drinking water. In this study, we studied on two tpyes of biological activated carbon(BAC) and would screen effective biodegradation strains by incubation, separation and purification ofmicro-organisms based on BAC in nine nitrosamines, evaluating the biodegradation of nitrosamines. Themain contents are as follows:1. Analysis of microbial community structure in BAC: using high-throughput sequencing technologies,we analyzed the microbial community structure before and after the domestication of nitrosamines. Theresults showed that nitrosamines influenced the diversity of microbial community composition. Regardingto the level of microbial phylum, two different kinds of microorganisms in BAC were highly similar, suchas the Proteobacteria, Acidobacteria, Bacteroidetes, No Rank and Planctomycetes microorganisms,accounting for85%of the total microorganisms in all samples. Comparing two different types of BAC, wefound that the relative abundance of the Proteobacteria and Planctomycetes phylums microorganismsincreased significantly, while that of the Acidobacteria and No Rank phylums dropped, relatively. Theproportion of Proteobacteria phylum microorganisms in two kinds of BAC after nitrosaminesdomestication increased from44.8%to49.2%, from55%to63.4%, respectively. The proportion ofPlanctomycetes phylum increased by49.4%and4.5%, respectively, while that of Choroflexi phylumincreased by15.7%only in sample C and D. The increasing microbes might use nitrosamines as nitrogen orcarbon sources for survival. Acidobacteria phylum microbes reduced by58.7%and60.6%, respectively; No Rank phylum decreased by6.2%and40.6%, respectively, while the Bacteroidetes phylum onlydecreased by45.4%in sample A and B. The microbial community structure in BAC showed that microbialcommunity exposed to nitrosamines was relatively stable. Compared to the phylum, the microbialcommunity structure was also stable in class level, however, the ratios of these bacterias were changedsignificantly, such as α-proteobacteria,-proteobacteria, No Rank and Planctomycetacia classes.-proteobacteria and Planctomycetacia classes increased from5.0%and16.2%to28.7%and18.3%,respectively. The relative abundance of α-proteobacteria class in the sample A and B decreased from24.1%to13.2%, however, increased from34.8%to42%in sample C and D. In sample A and B, the relativeabundance of Acidobacteria, No Rank, δ-proteobacteria and γ-proteobacteria classes decreased, but onlyNo Rank class decreased significantly from15.6%(C) to10.3%(D) sample.2. Screening of bacterial strains and evaluating the biodegradation of nitrosamines:(1) Screening of bacterial strains: we extracted the biological membrane concentrated liquid,inoculated in the sterilized mineral medium, added nitrosamines, and then detected the residualconcentration of nitrosamines. We inoculated the microorganisms with excellent degradation effect inTryptonye Soya Broth (TSB) solid medium; saved different forms of a single colony in vitro cant;Inoculated in inorganic mineral medium with nitrosamines; and detected the residual concentration ofnitrosamines. After taking the microorganisms with excellent degradation effect for scanning electronmicroscope and gene sequencing at the same time, we got the Rhodococcus cercidiphylli A41AS-1.(2) Biodegradation of nitrosamines: we degraded nine nitrosamines using Rhodococcus cercidiphylliA41AS-1, and the biodegradable time were1,3,5,7and10days, respectively. The Results showed thatRhodococcus cercidiphylli A41AS-1could biodegradate significantly of5nitrosamines. Among5nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (Npyr) and N-nitrosodiethylamine(NDEA) decreased since the first day, and N-nitrosodi-N-propylamine (NDPA) and N-nitrosodi-N-butylamine (NDBA) declined significantly until the third day. After10days of degradation, theconcentrations of NDMA, Npyr, NDEA, NDPA and NDBA were51.3ng/L,129ng/L,130.8ng/L and65.8ng/L and138.6ng/L, respectively (The initial concentration for each nitrosamines was200ng/L). Theremoval rates of5nitrosamines were as follows: NDMA (74.4%)>NDPA (67.1%)>Npyr (35.5%)>NDEA(34.6%)>NDBA (30.7%). The correlation analysis showed that the degradation of4nitrosamines were related to the molecule weight and structure except for NDPA, and the removal efficiency decreased withthe increase of molecular weight; the degradation of nitrosamines with short chain structure was higherobviously than that of nitrosamines with long chain and ring structure. In addition, there were no significantcorrelation between the degradation effect and the Octanol-water’s partition coefficient and Henryconstants.