Study On Removal Characteristics Of Pharmaceutical Substances In Wastewater Treated By Coagulation, Precipitation And Sand Filtration

The pharmaceuticals are discharged into water environment from domestic wastewater, livestock and poultry breeding wastewater, hospital wastewater and pharmaceutical factory wastewater etc. Collected through urban wastewater system, the pharmaceuticals are discharged after wastewater treatment along with the effluent. Although they are in water environment with low concentration, they are discovered in aquatic animals and plants and bring bad impacts to them. Considering the accumulation of the pharmaceuticals, the potential hazards to aquatic animals and plants, human and ecology can not be ignored. Due to the unentirely removed by traditional wastewater treatment process, and there is little report about the removal characteristics of pharmaceuticals in advanced treatment like coagulation, precipitation and sand filtration.Therefore, this paper explored removal characteristics of pharmaceutical substances in wastewater treated by coagulation, precipitation and sand filtration, wishing this process can remove pharmaceuticals effectly.This paper choosed CA, CBZ, NAP and DCF as research object which are found in secondary effluent of xi’an third wastewater treatment company, and used this secondary effluent as experiment influent. A laboratory setup was established to simulate the coagulation, precipitation and sand filtration process. Through the change of dosage and dosing mode of poly aluminium chloride(PAC), polymeric ferric sulfate(PFS) and polyacrylamide(PAM) in the process of coagulation, precipitation and sand filtration, the removal characteristics of the four target substances were researched and the dosages of coagulant and flocculant were adjusted. The impact of the filtration velocity and the thickness of sand layer to the pharmaceuticals removal were inspected. Then calculating and analysing sludge-water distribution coefficient of the target pharmaceuticals to study the fate characteristics.The research has shown that with the increasing dosage of PAC, the removal efficiency of target pharmaceuticals increased gradually and then decreased, and the best dosage was 60 mg/L. At the dosage of 60 mg/L PAC, the removal efficiencies of CA,CBZ,NAP and DCF were 29.6%、40.69%、22.18% and 31.23% in turn in the coagulation- sedimentation- sand filter process, the removal efficiencies of four target pharmaceuticals reached 30.31% in total initial concentration of 2 mg/L and the sequence of removal rate was CBZ>DCF>CA>NAP. Imroving the dosage of PFS, the removal rate added but slowly. The effluent chromaticity increased and water quality was affected. The best removal rate was up to 28.96% for PFS with the dosage of 100 mg/L, and the order of removal rate was DCF>CA>CBZ>NAP. PAC had better cost performance than PFS. Removal efficiencies of pharmaceutical substances were improved obviously in the presence of PAC and PAM with dosage of 0.5 mg/L, espically to CA and NAP that have enhanced by 21.75% and 34.47%, which were due to the neutralization of negative charges of target compounds by cationic PAM. Increasing the dosage of PAM, the removal efficiencies falled. Dosing the PFS and PAM can also raise the removal rate, with the dosage of 60 mg/L PFS and 1.0 mg/L PAM, the removal efficiencies of CA,CBZ,NAP and DCF were 31.88%、43.41%、27.64% and 40.04% respectively. PAC and PAM also had better cost performance than PFS and PAM. The removal of NAP was improved while dosing PAC and PFS simultaneously, and interaction effect between PAC and PFS can attain optimization by the adjustment of their dosage and proportion. Decreasing filter speed and increasing the thickness of sand layer in sand filter can improve the removal rate of the target. Four target substances have detected in the flocs of coagulation, the sequence of their kp value was DCF>CBZ>CA >NAP. Flocs, suspended particles and biological particles in wastewater can give contribution to the removal of target pharmaceuticals.This experiment showed that the coagulation, precipitation and sand filtration processes in wastewater treatment plant can partly removed the target pharmaceuticals, but the effluent still contains pharmaceutical pollutants. In order to eliminate or reduce the water pollution and potential hazards to ecology by the trace pharmaceuticals, we should strengthen the source control, and at the same time improve the removal efficiencies in the wastewater treatment.