| The outbreak of cyanobacteria blooms around the world has brought a series of environmental pollution problems that have posed a serious threat to the drinking water safety and human health.As an environmentally friendly,cost-effective artificial ecosystem,constructed wetlands(CWs)have been widely used for treating various domestic sewage and industrial wastewater.CWs also showed great potential for the remediation of cyanobacteria contaminated water bodies.Substrates,plants and microorganisms in CWs have an important impact on the removal of pollutants,of which microorganisms play a major role.In this study,the comparation of the algal growth inhibition capacity among four Pseudomonas aeruginosa strains was carried out to select the functional bacterial agent.And optimal initial density of target functional bacteria was also explored.The abundance of functional bacteria,residual concentration of microcystin-LR,and algal biomass were detected by qPCR,ELISA,and flow cytometry,respectively.Moreover,physical chemical indicators of water quality,including DO,temperature,ORP,etc.,were also investigated.The suitable matrix for Microcysits bloom removal and bacterial agent growth were selected from 9 kinds of wetland substrates as well as the suitable wetland plant selection from 8 kinds of wetland plants.Finally,the selected substrates and plants were combined to establish optimized CWs,and then bioaugmented CWs were also set up to evaluate the feasibility of Microcysits bloom treatment.The main results were as follows:(1)By comparing the algae removal potential of four different Pseudomonas strains,bacteria Pseudomonas aeruginosa UCBPP 14(PA14)was found to perform better on algae lysing and MC-LR removal.The density gradient test showed that the optimum initial density of PA14 was 5×10~7 cells/m L,Microcystis cells and MC-LR could have the most efficiency.Therefore,PA14 was finally selected as the functional agent for Microcystis removal in this study.(2)Through the matrix screening experiments,the substrate could affect algal density by affecting the pH of algal solution,for example,sawdust(the lowest pH)and blast furnace slag(the highest pH)maintain high and stable microcystis removal rate.The results showed that removal efficiencies of Microcystis and MC-LR in treatment group of sawdust,biomass and blast furnace slag were relatively high and stable:after5 days of treatment,the removal rate of MC-LR could reach more than 72%,after 10days,the removal rates of microcystis and MC-LR were up to 80%and 95%respectively.When treated for 5 days,the abundance of functional bacteria in the presence of zeolite was 5.07×10~8 which was the highest,indicating that zeolite had effective enrichment of functional bacteria in a short period.Although the abundance of PA14 in all treatments decreased to 5.77×10~7 copies after 10 days incubation,they were all at the effect density level.These results showed that blast furnace slag,biochar,and sawdust could be considered as optimum matrix materials in the application of CWs for Microcystis bloom remediation.(3)The results of wetland plants screening tests showed that,the pH of the wetland plant treatment groups was generally lower than that of the pure algal solution control group,and the plants could promote the removal of microcystis and MC-LR in the system when incubated with different plants.On the whole,the removal effect of microcystis in each plant group gradually increased and reached the best after 3 days of treatment.But the removal effect of MC-LR first increased and then decreased,the best removal effects were achieved after 2 days of treatment tine.The results of microcystis removal showed that the removal rate of microcystis in Thalia dealbata,Typha latifolia,and Alisma orientale treatment group were relatively good,reaching more than 98%in the end.With the addition of PA14,it simultaneously improved the removal capacity of Microcystis and MC-LR in the Alisma orientale treatments.The experiment also found that the abundance of functional bacteria in the Phragmites australis treatments were significantly higher than that in the others,2.33×10~9 copies,but the removal capacity of MC-LR was not passively correlated with the bacterial abundance,by way of example,Alisma orientale with low abundance of functional bacteria(just at 10~7 copies level)had better removal rate than Phragmites australis.And combined with the removal efficiency,it could be inferred that the abundance of functional bacteria in the rhizosphere was not the decisive factor for the removal potential of the system.The accumulation of algicidal substances secreted by functional bacteria might be the key to affect the Microcystis and MC-LR removal potential.After comprehensive consideration,Alisma orientale was selected as the wetland plant in this study.(4)According to the previous results and previous studies,zeolite was finally selected as the main matrix material,and sawdust and biochar as auxiliary materials to prepare the mixed wetland matrix.Alisma orientale and Iris pseudacorus were selected as wetland plants to optimize the establishment of artificial wetlands to simulate the treatment of natural cyanobacterial pollution at the same time.The experiment showed that during the experiment,the removal rate of Microcystis fluctuated from-118.7%to77.7%.The removal effect of microcystis was decreased along with the increasing number of treatment batches.The average removal rates of Microcystis in Alisma orientale CWs were about 43.1%;that in Iris pseudacorus CWs increased from the lowest value of-9.6%to 39.8%,and the lowest value was significantly different from others(P<0.05).The above experimental results showed that the effect of Alisma orientale CWs on removing microcystis were better than that of the Iris pseudacorus CWs;After adding bacteria,it improved the effect and stability of removing microcystis in the Iris pseudacorus CWs.The removal effect of each CWs on MC-LR gradually increased with the increasing influx of treatment batches,and the average removal rate was in the range of 96.2%～99.3%.Those showed that the optimized CWs had good MC-LR removal effects.Combined with the changes in the abundance of matrix functional bacteria,it was seen that the abundance of functional bacteria in the Alisma orientale group increased with the PA14 continuously added,and eventually increased to 1.86×10~5 copies/g;however,the abundance of substrate functional bacteria in the Iris pseudacorus CWs remained at 10~4 copies/g.This indicated the Alisma orientale CWs may had a greater potential for enrichment of functional bacteria than the Iris pseudacorus CWs.In this study,by the way of conclusion,CWs optimized by planting Alisma orientale and Iris pseudacorus separately plus using the exogenous microorganism(PA14)with the functions of efficient algae reduction and MC-LR degradation as a bioaugmentation method,it significantly improved the ability and stability of microcystis reduction in Iris pseudacorus CWs;the optimized CWs’removal effects on MC-LR gradually were increased steadily with the increasing number of influent batches;Alisma orientale CWs might have relative greater potential for enriching functional bacteria than Iris pseudacorus CWs.The results of this study provided practical experience and scientific research materials for the further research to the establishment of highly effective and stable CWs enhanced cyanobacteria contaminated water reduction. |
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