A Study On The Advanced Treatment Of Constructed Wetlands’ Filler Substrate In Tail Water From Sewage Plant

As an important part of constructed wetlands, filler substrates play a significantrole in improving the removal efficiency of pollutants inconstructed wetland sewagetreatment system. Different substrates bear different abilities of purifying pollutants,and differences in substrates’ particle size also result in a discrepancy in the removaleffects of pollutants. As a result, taking gravels and limestone as the filler substrates,this paper tries to analyze their removal efficiencies on secondary effluents inwastewater treatment plants.The removal effects of selected substrates on nitrogen and phosphorus areanalyzed firstly by adopting static test of substrates. Resorting to equation ofadsorbent kinetics, this paper then conducts the fitting of adsorbent kinetics ofnitrogen and phosphorus. A total of seven groups of dynamic experiments onconstructed wetlands are conducted to study pollutants removal efficiency of twodifferent kinds of substrates under different proportions and process conditions. Themethod of comprehensive fuzzy mathematics is used to analyze each index’s weightand determine the optimal filler of substrates. Orthogonal test is used to determinesubstrates’ optimal control conditions under such factors as different fillers, differenthydraulic loads as well as different residence time. By way of the above-mentionedmethods, results and conclusions are as follows:Substrates’ static test has a sound effect on the overall removal of TP and TN.Limestone of TP removal efficiency significantly superior to gravel; And gravel andlimestone of TN removal efficiency. The three adsorbent kinetics models have a goodremoval and fitting effect on phosphorus with significance reaching the standard level,but have a relatively poor removal and fitting effect on nitrogen with a low averagesignificance level.The overall removal efficiency of each group is calculated as follows throughfuzzy comprehensive judgment: the overall removal capacity of each experimental group ranks in the order of4#0.05~0.2cm limestone particles (A/O Process)>5#0.05~0.2cm and0.5~1cm mixed limestone particles (A/O Process)>1#0.05~0.2cm limestone particles>3#0.5~1cm gravel>2#of0.5~1cm limestoneparticles.Orthogonal test is resorted to analyzing the optimal combinations of the threesubstrate compositions under different hydraulic loading and hydraulic retention time,so as to obtain the optimal level combinations. The optimal treatment effects can beobtained when substrate fillers are limestone particles with a size of0.05~0.2cm,hydraulic load is0.29~0.33m/d and hydraulic residence time is0.8~1d.