The Application Of Marine Cadmium-resistant And Self-flocculating Bacteria In Saline Wastewater Treatment

In recent ten years,the components of wastewater have become more and more complex due to the rapid development of industry and the continuous improvement of the people’s living standards,and the treatment has become increasingly difficult.Due to the toxic effects of heavy metals on microorganisms and the inhibitory effects of salinity on microbial activity,the biological treatment of heavy metal wastewater and saline wastewater becomes very difficult.However,the metal smelting wastewater and seafood farming wastewater usaully contain both salinity and heavy metals,which further increases the treatment difficulty of this kind of wastewater.At present,the functional microorganism is ofen selected as the biological treatment of saline wastewater and heavy metal wastewater.Deep-sea microbes which are living under extreme conditions such as high pressure,high salinity,low/high temperature,darkness and oligotrophy,form a very special biological structure and metabolic mechanism system which make them have the huge potential of degrading or converting various toxic and harmful pollutants.So deep-sea is an excellent place for screening of functional microorganism.Therefore,the functional strains with cadmium resistance and the self-flocculating strains with salt-tolerance were screened from the deep-sea sediments to treat cadmium-containing wastewater and saline wastewater,respectively.And this also provides a viable method for saline-cadmiun-containing wastewater treatment.This study can achieve efficient and low-cost removal of toxic and harmful pollutants,thereby reducing environmental pollution and ecological damage.It has important environmental,ecological and economic benefits.In this study,we studied the contribution of EPS,proteins and polysaccharides to self-flocculation through extraction of EPS from self-flocculating bacteria.Then the self-flocculating mechanism was revealed by the measurement and analysis of Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),Zeta potential,surface hydrophobicity,particle size and specific gravity etc.Then the shake flask batch experiments were used to verify the feasibility of self-flocculating functional bacteria in treating saline wastewater.Finally,the cadmium-resistance functional bacteria was inoculated into dynamic membrane bioreactor(DMBR)to treat cadmium-containing wastewater and self-flocculating functional bacteria was inoculated into sequencing batch reactor(SBR)to treat saline wastewater by continuous operation at laboratory scale.Moreover,the treatment efficiency and biological community structure of the reactors were also tested and analyzed.The main research results obtained in this paper are as follows:(1)The cadmium-resistance functional bacterium Pseudoaltreromonas sp.SCSE709-6(Ps.sp.SCSE709-6)was inoculated into a DMBR to treat cadmium-containing wastewater through bioaugmentation techniques.The experimental results are as follows:(ⅰ)During the whole operation,the cadmium-resistance functional bacteria Ps.sp.SCSE709-6 enhanced dynamic membrane bioreactor(RB)demenstrated a stable removal efficiency of Cd(Ⅱ),COD,TN and TP(99.1%,94.0%,61.8%and 60.1%respectively,170 d average)which significantly better than the un-bioaugmented dynamic membrane bioreactor(RA)removal efficiency of Cd(Ⅱ),COD,TN and TP(94.9%,89.4%,56.0%and 52.1%,respectively)as the influent Cd(Ⅱ)concentration continuously increases.Moreover,the removal efficiency of RA fluctuated widely,and the effluent Cd(Ⅱ)can not meet the discharge standards;(ⅱ)The rapid formation of the dynamic membrane is an important indicator to ensure the stability of the effluent turbidity and membrane flux.Moreover,no obvious membrane fouling was observed during the experiment;(ⅲ)Fluorescence in situ hybridization(FISH)confirmed the presence of cadmium-resistance functional strain Ps.sp.SCSE709-6 in DMBR;(ⅳ)The community composition and structure of DMBRs were revealed by High-throughput sequencing technology.On the one hand,the Proteobacteria(accounting for 89.82%)in activated sludge became the most important phylum under the stress of cadmium.The addition of cadmium reduced the biological diversity in DMBR which maked the entire community structure become relatively simple.In addition,it is worth noting that the nitrifying bacteria in the activated sludge basically disappeared which made the removal efficiency of ammonia nitrogen become worse,thereby affecting the denitrification efficiency of the entire system.It also indicated that nitrifying bacteria was most sensitive to cadmium.On the other hand,the bioaugmentation of Ps.sp.SCSE709-6 significantly improved the compositions of activated sludge.The proportion of Proteobacteria decreased from 89.82%to 66.83%,while the proportion of Bacteroidetes increased from 6.32%to 28.13%.This changes showed that bioaugmentation increased the abundance and diversity of the community,which improved the treatment effeciency in turn.Moreover,this change also indicated that the cadmium resistance of the Bacteroidetes was higher than that of Proteobacteria.In general,the bioaugmentation of Ps.sp.SCSE709-6 improved the community structure of the dynamic membrane bioreactor,which in turn improved the overall treatment efficiency of the system.(2)A strain with high salt tolerance and high self-flocculation efficiency was screened out of 426 strains in the South China Sea.16S rDNA gene sequencing identified the strain as Psychrobacter aquimaris X3-1403(Ps.A.X3-1403).This strain was deposited at the China Type Culture Collection,Address:Wushan,Wuchang,Wuhan,China.Deposit number:CCTCC M 2016155.(3)The EPS of the self-flocculating bacteria Ps.A.X3-1403 was extracted by CER.And the the EPS yield,chemical structure and the contents of proteins and polysaccharides were analyzed,respectively.Then the flocculation experiment was used to determine the contribution of EPS,protein and polysaccharide to flocculation.At last,the mechanism of self-flocculation was further illustrated by combining the analysis results of Zeta potential,surface hydrophobicity CSH,particle size and specific gravity.The results showed that:(i)EPS yield was 130.2 mg/g-cell dry weight.The protein and polysaccharide yields were 97.9 and 31.8 mg/g-cell dry weight which accounting for 75.2%and 24.4%(w/w)of EPS respectively;(ii)The flocculating efficiency of strain Ps.A.X3-1403 before EPS extraction was as high as 90.3%,whereas the flocculating efficiency after extracting EPS was only 67.9%.The contribution rates of protein and polysaccharide to self-flocculation of Ps.A.X3-1403 were 64.0%and 26.9%,respectively.This indicated that protein played an important role in the self-flocculation process;(iii)The chemical structure of EPS was analyzed by FTIR and XPS.The hydrophobic functional group C-(C/H)accounted for 55.8%,while the sum of hydrophilic functional groups C-OH(23.3%),C=O(19.5)and O-C=O(1.4%)only accounted for 44.2%.This showed that the hydrophobic functional group played a key role in the self-flocculation process of the strain Ps.A X3-1403;(iv)The cell surface hydrophobic CSH,particle size and specific gravity of the bacterium increased with the growth of the bacterium and reach a maximum value at the stationary phase.The bacterial particles then form large and dense bacterial particles by collision and recombination between the internal bacteria.However,the bacterial particles could not become larger,but maintained their structure under the hydraulic shear force.(4)Three identical SBRs were used to continuously treat the seawater flushing wastewater.The reactor A(RA)was only inoculated with the self-flocculating seed sludge,the reactor B(RB)was inoculated with self-flocculation seed sludge and activated sludge with mixing ratio of 1:1(w/w),while reactor C(Rc)was only inoculated with activated sludge.The intial concentrations of the three SBRs after inoculation were all around 5000 mg/L.One cycle of SBR was 8 h,including 5 min influent,450 min aeration,15 min settlement and 10 min water discharge.The volumetric exchange rate of SBR was 62.5%,so the HRT of SBR was 12.8 h,the sludge residence time(SRT)was 21 d,and the dissolved oxygen concentration was controlled between 2-3 mg/L.The treatment efficiency and community structure of SBRs were recorded and analyzed.The results showed that:(i)During the 120 days continuous operation,RA showed a very low sludge index and a high proportion of sludge due to the excellent salt tolerance and biomass retention,which ensured the effective settlement of the self-flocculating bacteria sludge.This enabled the retention of self-flocculating bacteria in SBR to ensure the stability of the reactor operation and the high efficiency of the treatment.However,in RB and RC,the activated sludge started to bulk and disintegrate under long-term salinity stress which resulted to the decrease of sedimentation performance.Then a large amount of sludge run away the reactor with effluent to cause the collapse of entire system after 90 days operation.The removal rates of SBR to COD,NH4+-N,TN and TP were 98.0%,93.1%,74.0%,and 56.7%,respectively.During 0-50 days,the removal rates of RB and RC to COD,NH4+-N,TN and TP were 97.3%and 97.2%,91.0%and 92.0%,68.0%and 70.0%,36.7%and 33.3%,respectively.While during the 50-80 days,the removal rates decreased to 63.2%and 57.9%,39.0%and 24.0%,16.7%and 9.6%,19.9%and 10.1%,respectively;(ii)High-throughput sequencing technology was used to analyze community structure of SBRs.While a large proportion of genera were not identified and classified in the sequencing results.So no ideal results were obtained at twice High-throughput sequencing.Therefore,effort should be given to find the reasons and solutions.Through the above studies,we can find that it is feasible for the application of cadmium-resistance functional strain Ps.sp.SCSE709-6 to treat cadmium-containing wastewater and salt-tolerant self-flocculating bacteria Ps.A.X3-1403 to treat seawater flushing wastewater.The study provides a new method for the treatment of heavy metal-containing wastewater and saline wastewater.It also provides strong data support for the treatment of salt-heavymetal-containing wastewater.This study has important theoretical and practical values.In addition,the development and application of this new technology has important strategic significance for alleviating the pressure of tight supply and demand of freshwater resources in coastal areas.