Study On The Adsorption Behaviors Of PPCPs Onto Sediment In The Weihe River

PPCPs are a new type of micropollutant, having characteristics such as variety, hugeproduction and consumption, as well as large extent of existence in the environment, whichbecome a hot topic in the research of dangerous pollutants. Nowadays, different kinds ofPPCPs exist in the environment of different locations, antibiotics as well as analgesic andantipyretic drugs are most frequently detected among them. The pollution of PPCPs has beenan environmental problem all over the world. When the surface water infiltrates to thesubsurface system, river sediment is the important medium which influences the watermovement and solute transport to the groundwater system. The adsorption characteristics ofpollutants onto river sediment directly influence their mobility from the sediment-waterinterface to sediment beneath the channel surface. The Weihe River is the biggest tributary ofthe Yellow River, and a large population resides in the Weihe River basin. Many cities andlivestock industries lie along it. A large quantity of PPCPs (for both human beings andlivestock industries) enters the Weihe River through sewage system of municipal works.Although there exist wastewater treatment plants in the Weihe River basin, they are currentlynot designed for the elimination of micropollutants such as PPCPs. Therefore, research onadsorption behaviors of PPCPs onto sediment in the Weihe River is important tounderstanding the transport and fate of PPCPs in the Weihe River basin. Such research alsoprovides the theoretical basis for the effective prevention of PPCPs pollution to thegroundwater system in the Weihe River basin.This study choosed the mid-Weihe River as a typical research region, and selectedoxytetracycline (antibiotics) and acetaminophen (analgesic and antipyretic drugs) as the targetpollutants. Took the considerations of mineral composition （feldspar, quartz and mica）andpartical diameter（divided into solid particle and colloid）, conducted experiments by batchequilibrium method. Systematically studied the kinetic and thermodynamic characteristics ofthe target pollutants for their adsorption onto the sediment, discussed the adsorption modelsand analyzed the adsorption mechanisms of the target pollutants onto the sediment. Theresults are given as follows:1. The adsorption of the target pollutants onto sediment got equilibrium in about24 hours. The adsorption kinetics of the target pollutants were found to follow thepseudo-first-order model. The equilibrium adsorption data fitted well with Langmuir andFreundlich isotherm models. However, the Langmuir isotherm was more suitable to describethe adsorption behaviors of the target pollutants because it gave a comparatively lower errorfunction compared with the Freundlich model.2. The adsorption of the target pollutants were feasible, spontaneous, entropy increasingand endothermic in nature, and the adsorption capacities increased with increasingtemperature. The mechanisms controlling the target pollutants adsorption onto sediment wereneither pure chemisorption nor pure physisorption, but they were complex processes whichwere mainly physisorption.3. The pH had certain influences of the adsorption of the target pollutants. The ionicstrength had significant negative effects on the target pollutants adsorption onto sediment.4. Feldspar, quartz, mica and dark-colored mineral were the major mineral compositionof sediment. For the sediment of partical diameter exceeded0.5mm, the content of feldsparand quartz took over more than90%. The adsorption of the target pollutants onto typicalminerals (feldspar, quartz and mica) in sediment were found little, almost had no adsorption.5. The adsorption of the target pollutants onto solid particle and colloid in sediment gotequilibrium in different times. For solid particle, the adsorption got equilibrium in about48hours. While for colloid, the adsorption got equilibrium in about12hours. The adsorptioncapacity for the same target pollutant onto solid particle and colloid had a big variety, whilefor the same media the adsorption capacity of different target pollutants had variety either.The equilibrium adsorption data for solid particle and colloid both fitted well with Langmuirisotherm model.6. The adsorption of the target pollutants onto solid particle and colloid in sediment werefeasible, spontaneous, entropy increasing and endothermic in nature, and the adsorptioncapacities increased with increasing temperature. The mechanisms controlling the targetpollutants adsorption onto solid particle and colloid were mainly physisorption. Comparedwith adsorption onto colloid, physisorption took more proportion in adsorption onto solidparticle.