Effects of coexistence of dissolved organic matter and nano zinc oxide on performance and clogging of con-structed wetlands
The presence of dissolved organic matter(DOM)affects the stability of zinc oxide nanoparticles(ZnO NPs)in water.By constructing vertical subsurface constructed wetlands,taking humic acid(HA)as a representa-tive substance of DOM,we examined the effects of coexistence of 1 mg·L-1 ZnO NPs and different concentrations of HA(1,5,10,20 and 30 mg·L-1)on the treatment performance,clogging and microbial communities of con-structed wetlands.The results showed that low HA concentration(≤1 mg·L-1)could promote the agglomeration of ZnO NPs,while the medium-high concentrations(1-25 mg·L-1)showed opposite effect.The coexistence of ZnO NPs and DOM would reduce the purification effect of constructed wetlands.At the concentration of 1 mg·L-1 HA,the removal efficiencies of COD,ammonia nitrogen and total nitrogen decreased by 18.07％,19.94％,and 26.37％,respectively.Under the condition of 1 mg·L-1 DOM and 1 mg·L-1 ZnO NPs,the constructed wetland was most seriously blocked,and the permeability coefficient decreased by 67.5％after 60 days.The coexistence of HA and ZnO NPs could affect the secretion of extracellular polymeric substance(EPS).The EPS concentration was as high as 140.30±0.29 mg·g-1 at 1 mg·L-1 ZnO NPs and 1 mg·L-1 HA,while that in the blank group was only 78.67±0.32 mg·g-1,explaining the clogging of constructed wetlands.In addition,the addition of ZnO NPs and HA reduced the richness and diversity of microbial community and promoted the growth of EPS-secreting bacteria(Thauera).The findings may provide a new explanation for the clogging mechanism of constructed wetlands.
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维普
