The Effects of Coagulation on Adsorption of Micropollutants in Waste Water Treatment Plants

Abstract

In this study, the potential positive or negative effects of the coagulation process during the adsorption of micropollutants were investigated in treated waste water. Single-walled carbon nanotubes (SWCNTs) were employed as adsorbents in batch adsorption processes. Alum was used as a coagulant in batch coagulation experiments carried out in the laboratory to coagulate water samples obtained from effluents at the advanced biological wastewater treatment plant in the center of Zonguldak (ZWWTP), Turkey. The ultrafiltration process (UF) was used to demonstrate the importance of the dissolved organic matter content (DOM) for the removal of micropollutants by coagulation and adsorption. Consequently, coagulation was found to be effective in the removal of hydrophobic organics, that is, DOM fractions with molecular weights of 5 kDa and 1–3 kDa, while adsorption with SWCNT was effective in the removal of hydrophilic organics (<1 kDa). SWCNT adsorption was effective for the removal of carbamazepine, diclofenac, and triclosan in combined treatment steps. Furthermore, the removal of carbamazepine, diclofenac, and triclosan was above 90% with SWCNT adsorption before coagulation. It was concluded that the significant correlation between micropollutant removal and the reduction in UV₂₅₄ is attributed to the general non-selectivity of adsorption on the SWCNTs surface. Micropollutants and UV₂₅₄ absorbing compounds adsorb simultaneously. It can be reasonably deduced that a high/low adsorptive removal of a specific micropollutant is typically accompanied by a high/low removal of UV₂₅₄-absorbing substances. Even though the majority of micropollutants also absorb UV₂₅₄, their concentrations in municipal wastewater are insignificant in comparison to the overall UV₂₅₄ measurements. Hence, correcting the actual UV₂₅₄ measurements of the combined treatment for removal by coagulation produces adsorptive UV₂₅₄ removal. In other words, if the removal of UV₂₅₄ by coagulation is already known, the actual UV₂₅₄ measurements obtained in a combined treatment step can be adjusted to produce UV₂₅₄ removal by SWCNT adsorption. Therefore, UV₂₅₄ can be used as a control parameter for carbamazepine, diclofenac, and triclosan removal and SWCNT dosing control utilizing differential U_V254 measurements can be implemented.