Effects Of Modified Basalt Fiber And Its Filling Method On The Operation Of Constructed Wetland

Substrate is a basic component of constructed wetland system and plays an important role.The search for new environmental-friendly substrates with low cost,high efficiency and favorable microbial attachment is one of the hot spots in the field of constructed wetland.Basalt fiber（BF）,as a kind of green fiber material with low cost,large specific surface area and high mechanical strength,has been successfully applied in the field of water treatment with good results,and the bioaffinity of modified basalt fiber（MBF）has been enhanced,which is more favorable as a carrier material for microbial attachment.In order to investigate the feasibility of MBF as constructed wetland substrate and expand the application of BF in the field of water treatment,in this study,calcium modified basalt fiber（Ca-MBF）and polyethyleneimine modified basalt fiber（PEI-MBF）with high bioaffinity were determined through contact oxidation test,and then four groups of constructed wetlands planted with Iris.pseudacorus and filled with the MBF were built.They were named CW1（control group,no MBF filling）,CW2（Ca-MBF,vertical-bundling）,CW3（Ca-MBF,layered-tiling）and CW4（PEI-MBF,layered-tiling）,and operated continuously for 180 days.The effects of MBF filling on the decontamination performance,substrate enzyme activity,and microbial community structure of constructed wetlands were investigated to define the application advantages in constructed wetlands.The main conclusions are as follows:This study investigated the performance of four MBF（calcium modified basalt fiber named Ca-MBF,polyacrylamide modified basalt fiber named PAM-MBF,polyethyleneimine modified basalt fiber PEI-MBF,polyvinylpyrrolidone modified basalt fiber named PVP-MBF）in the contact oxidation reactor.The characterization results of SEM,EDS,and FTIR demonstrated that the modification of BF caused changes in their surface morphology and composition,and the differences caused by different methods were obvious.In the contact oxidation experiments,the removal effects of MBF on TN and TP were enhanced,among which Ca-MBF mainly enhanced the removal of NH₄⁺-N,while PEI-MBF improved the removal of TN due to its excellent removal effect on NO₃^-N.In addition,the BF modified by chemical grafting with polymer compounds was found to have the advantages of enriching denitrifying bacteria and stabilizing the system by 16S r RNA sequencing.This study investigated the wastewater treatment performance of four constructed wetlands.The results showed that the performances were enhanced in all MBF constructed wetlands.In terms of nitrogen removal,MBF constructed wetlands effectively enhanced the removal of NH₄⁺-N（p<0.05）.The CW2-4 groups were 4.82%,16.72%and 10.87%higher than the control group CW1.The filling method of layered-tiling had obvious advantages,among which Ca-MBF was superior to PEI-MBF.TN removal rule was consistent with NH₄⁺-N,NO₃^--N and NO₂^--N accumulation were not found,NH₄⁺-N became the limiting factor of TN removal.In terms of TP removal,the CW2-4 groups were increased by 4.01%,6.30%and 2.83%respectively compared with the CW1 group.Ca-MBF was obviously better than PEI-MBF,and the filling method of layered-tiling was the best.This study investigated the temporal and spatial characteristics of substrate enzyme activities in four constructed wetlands.The results showed that the filling of MBF produced alterations in wetland substrate enzyme activity.The decreasing trend of along-depth dehydrogenase activity was weakened in the MBF wetland.For urease（URE）,MBF filling could effectively protect its activity in the lower layer of the substrate,and the URE activity of CW3 and CW4 in the layered-tiling group was more evenly distributed along the process.Among the nitrification related enzymes,MBF filling was helpful to improve the activity of ammonia mono oxygenase（AMO）in the lower layer of wetland system,among which CW3was the most obvious.The average activity of along-depth AMO from high to low was CW3（3.584 nmol N/g/h）,CW4（2.901 nmol N/g/h）,CW2（2.424 nmol N/g/h）,and CW1（2.123nmol N/g/h）,which was more responsive to the nitrification ability than the inter-root activity.Ca-MBF filling was beneficial to enhance the activity of nitrite oxidase in the upper and lower layers.Among denitrification related enzymes,the average activity of along-depth nitrate reductase（NAR）from high to low was CW2（268.35 nmol N/g/h）,CW1（221.76 nmol N/g/h）,CW4（194.58 nmol N/g/h）,and CW3（154.04 nmol N/g/h）,which reflected the denitrification ability of wetland system to a certain extent.At the same time,MBF filling could alleviate the decline of NAR and nitrite reductase activities along the depth.The average activity of inter-root neutral phosphatase（NP）from high to low was CW3（283.24 ug/g/d）,CW2（264.74ug/g/d）,CW1（228.39 ug/g/d）,CW4（226.82 ug/g/d）,which was positively correlated with TP removal,and Ca-MBF filling could improve the NP activity of wetland.This study investigated the microbial community structure characteristics of four constructed wetlands.The results showed that the filling of MBF affected both the composition and distribution of microbial communities in constructed wetlands.MBF filling improved the microbial richness and diversity of the wetland,CW4>CW2>CW3>CW1.Along the depth,PEI-MBF group increased in all layers,while Ca-MBF group improved in the middle and lower layers.At the phylum level,the layered-tiling of MBF improved the overall abundance of Cloacimonetes and Chloroflex,the filling of Ca-MBF changed the distribution of Proteobacteria and Bacteroidetes,and the filling of PEI-MBF improved the relative abundance of Firmicutes.Dominant bacteria include Zoogloea,Thauera,Dechloromonas and others,and their enrichment were significantly different among groups.PCo A and biomarkers proved the differences of microbial community structure in each group.MBF increased the abundance of nitrifying bacteria（Nitrosomonas and Nitrospira）,and the layered-tiling of Ca-MBF group was the most obvious.In terms of phosphorus removal,MBF filling effectively improved the relative abundance of phosphorus accumulating bacterium Thauera.In summary,MBF has high biological affinity and can improve the richness and diversity of attached microorganisms,so it can be used as constructed wetland substrate to effectively strengthen pollutant removal.The modification methods and filling methods of MBF can significantly affect the degree of enhancement effect,and the layered-tiling of Ca-MBF had the best effect.In practical application,the MBF constructed wetland system has economic rationality and technical feasibility,which is expected to promote the further promotion and application of constructed wetland technology.