Research On Aquatic Plant Litter Decomposition Characteristics And Mechanism Of Constructed Wetlands Clogging

Constructed wetland ecosystems are human-made ecosystems for sewage treatment.Currently aquatic litter is considered to be an important factor affecting constructed wetlands clogging.The litter of cattail(Typha angustifolia),canna(Canna indica)and reed(Phragmites australis)were chosen to research litter decomposition characteristics and its affected clogging of constructed wetland.The main conclusions are as follows.(1)The decomposition characteristics of different aquatic plant litter were different.The highest rate of weight loss was found for canna leaf,but cattail leaves had the lowest rate of weight loss;In addition,cattail root had highest rate of weight loss;reed root had the minimum of weight loss.Leaf litter decomposition coefficient was consistent with weight loss,and the decomposition coefficients of canna root litter were the highest.(2)Aquatic litter lignin,N,P content were the first decline,then accumulation in the process of decomposition,lignin is the main factor to influence decomposition late of litter.Lower lignin content and higher N content of litter showed faster decomposition.Such as canna leaf had lowest lignin(17.92%),and higher N content(7.3 mg/g),its weight loss was significantly higher than reed and cattail leaf.Three kinds of litter leaf residue was significantly positive correlated with N content.The higher C/N,C/P,lignin/N ratio was not benefitted to the decomposition of litter,such as leaf and root of reed had higher ratios,resulted in the slower decomposition rate in three kinds of litter.Three kinds of litter leaf residue was significantly negative correlated with ratio of lignin/N.(3)The nitrification capacity of constructed wetland followed the order of cattail treatment>canna treatment>reed treatment>CK(no litter).The lowest nitrification capacity in CK was probably related with the minimum ammonia content in substrates.Nitrification intensity of substrates was negatively correlated with litter ratio C/N,which contributed to reduction denitrifying bacteria due to the high ratio C/N.The denitrification intensity was consistent with nitrate content in constructed wetland.(4)Permeability coefficient is an important parameter to reflect the clogging of constructed wetlands,litter reduces the permeability coefficient of constructed wetlands,Permeability coefficient was influenced by residual amount of litter,such as canna had the high N,low lignin content and the lowest quantity of the residue,resulted in the highest permeability coefficient.Cattail treatment of constructed wetland has the best removal of nitrogen and ammonia because of its highest nitrification capacity,respectively,93.3%and 96.3%;canna treatment of constructed wetland permeability coefficient is higher,the CODcr removal rate is the highest and the influence of the constructed wetland clogging is the least;reed treatment of constructed wetland removal of ammonia and organics is the lowest in three kinds of litter,the influence of the constructed wetland clogging is the biggest.Constructed wetland permeability coefficient and removal of total nitrogen were significant negative correlation,removal of CODcr and permeability coefficient were significant positive correlation.