Experimental Study On Treatment Of Heavy Metals In Rainwater By Combined Filtration Percolation

Urban non-point source pollution on the surface water environment has attracted more and more attention.In particular,early rain runoff contains numerous organic pollutants and heavy metal pollutants.It has a great impact on the water quality of the river water.It has great significance of collecting,purifing,treating and using early rain runoff for prevention.Artificial rapid infiltration system（CRI）has rarely been applied to the early rain runoff treatment.This paper is based on the"twelfth Five-Year Plan"Yixing Water subject of"urban water pollution control and water environment function improvement technology research".The removal rules of zeolite and limestone for four common low concentrations co-existed ions lead,copper,zinc and cadmium was researched.Taking organic matter such as COD,TN,TP and NH₄⁺-N into account to remove,in the case of zeolite and limestone as fillers,new types of fillers such as river sand,fly ash,steel slag,and wood are added to the CRI system to explore the feasibility and effectiveness of the CRI system in handling early rain runoff.The main contents of this paper are as follows:（1）The adsorption experiments of zeolites and limestones for the removal of Pb²⁺,Cu²⁺,Zn²⁺and Cd²⁺,typical heavy metal ions in rainwater,shows that within a certain range,the greater the amount of adsorbent added,the better removal effect of heavy metals;When the adsorbent is increased to 0.5 g,the removal effect of heavy metals does not change significantly.For zeolites and limestones,the removal rate of heavy metals increases with the increase of contact time.When the time increases to 300 min,the removal rate change is no longer obvious.The effect of temperature on the removal of heavy metals for limestone and zeolites is not completely the same and the affection varies of different heavy metal ions.The initial concentration of heavy metals has different effects on the removal of heavy metals by zeolites and limestones,and different heavy metal ions are also affected by concentration changes differently.（2）Langmuir and Freundlich equations both can describe the isothermal adsorption curves of zeolite and limestone on the four heavy metal ions.The fitting effect is different for different ions.The zero-order equation,the pseudo-first-order kinetic equation and the pseudo-second-order kinetic equation have different fitting effects for different heavy metal adsorption processes.The zero-order equation has a poor fitting effect on the adsorption process.Quasi-first-order kinetics and quasi-two The kinetic equations have good fitting effects on the adsorption process of different heavy metals.（3）Under the competitive adsorption system of zeolites to four heavy metal elements,the competitive adsorption capacity of each ion is Pb²⁺>Zn²⁺>Cd²⁺>Cu²⁺.Under the competitive adsorption system of limestone to four heavy metal elements,the competitive adsorption capacity of each ion is Cd²⁺>Zn²⁺>Cu²⁺>Pb²⁺.The desorption experiments show that NaCl has a good desorption effect on zeolites,and desorption of four heavy metal ions is almost proportional to the concentration of sodium ions.（4）Optimize the filling of the artificial rapid infiltration system to treat heavy metal and organic matter in the early rain runoff.The experimental analysis shows that the CRI system shows good results for the adsorption and regeneration of heavy metals.The average removal rates of Pb²⁺,Cu²⁺,Zn²⁺,and Cd²⁺were 83.05%,79.02%,68.69%,and 95.74%,respectively,when the system was stable.The CRI system used in this paper also has good removal performance for organic matter.The average removal rates of COD,TN,TP,and ammonia nitrogen were 86.60%,84.38%,71.95%,and 75.00%,respectively,when the system was stable.Especially,the addition of wood hoe to the lower filler makes the system have a better removal effect on TN.