Phosphorus Removal Of Vertical Flow Constructed Wetlands Using Different Substrates For Purifying Highly Polluted River Water

With the development of society, water eutrophication is more serious because of alot of phosphorus wastewater discharged into water. The objective of study was toreduce phosphorus concentration to improve the river water quality. The methods oflaboratory and field vertical flow constructed wetlands using different substrates werepresented.In the study adsorption isotherms, adsorption kinetics experiments of slag andgravel were examined and the effects of initial solution pH, organic materials, ions andriver water of P adsorption were investigated. In addition, the phosphorus removalperformances of the VFs separately using these two substrates were conducted. Theresults showed that:(1)Langmuir and Freundlich isotherms could well estimate the phosphorousadsorption capacities and features of slag and gravel. The slag and gravel’s theoreticalmaximum adsorption capacity of phosphorus were3.15mg·g-1and0.81mg·g-1,respectively. Besides, the phosphorus adsorption kinetics of both substrates could bevery well described by pseudo-second-order kinetic equations. The slag had muchhigher phosphorus adsorption ability than gravel(2)The initial solution pH, glucose, NH4+and CO32-had little effect on phosphorusadsorption of slag, while pH and CO32-slightly impacted on gravel.(3)The both had high capacities of phosphorus removal. The average totalphosphorus removal rates could reach76%and65%respectively, and phosphateremoval efficiencies were70.9%and48.6%. The life expectancies of slag-filled andgravel-filled VFs were estimated to be11–15a and3–4a, when the phosphorusconcentration of influent was4mg·L-1and the hydraulic loading rate was0.05m·d-1. And slag-filled system was more stable than gravel-filled, meanwhile slag created a goodphosphorus removal environment.(4)There were some similarities and differences between the adsorption test in thelaboratory and VFs test in the field. In both tests the slag had a better phosphorusremoval and anti-load capacities. However, for the slag, the performances were99%inthe laboratory,76%in the field; while, the opposite for gravel,20%in the laboratory,65%in the field.