Removal Of Organics By Covalently Hybrid Coagulants For Advanced Treatment Of Municipal Sewage

Organics in wastewater have different influences on water quality and ecological environment due to their different molecular compositions and structures.Coagulation is an essential method to remove organics in advanced wastewater treatment process.Most of previous studies have focused on the changes of bulk physical and chemical characteristics of organics during coagulation,which could not guide the optimization of coagulation process to ensure the safety of reclaimed water very well.In this report,we compared the removal efficiencies of overall organics in secondary effluent(EfOM)and micropollutants in actual secondary biological effluent by several conventional coagulants and a newly reported coagulant(CBHyC).In addition,we focused on the transformations of organics in element compositions and molecular structures after coagulation by selected coagulants using Fouriertransform ion cyclotron resonance mass spectrometer(FT-ICR MS).Lastly,the mechanism of CBHyC was explored by molecular dynamics simulation.This paper compared the removal efficiencies of overall organics and micropollutants from raw water by selected coagulants.It is found that conventional coagulants can remove organics in some degree,and have a better removal efficiency for the higher MW and hydrophobic organics compared with the lower MW and hydrophilic organics.In contrast,CBHyC can effectively remove overall organics,and the removal efficiencies of most micropollutants(e.g.,POPs,PPCPs,EDCs etc.)achieved more than 90%.This present study revealed the removal characteristics of organics at molecular level by coagulation.We found that conventional coagulants can only partially remove condensed polycyclic aromatics and polyphenols with low H/C(H/C < 0.7)and highly unsaturated and phenolic compounds and aliphatic compounds with high O/C(O/C > 0.6).In contrast,CBHyC has a better removal efficiencies for all organics with different element compositions and molecular structures,especially organics that are resistant for conventional coagulants,such as highly unsaturated and phenolic compounds and aliphatic compounds located in 0.3 < O/C < 0.8 and 1.0 < H/C < 2.0 regions and sulfur-containing compounds with higher O/C.The mechanism of CBHyC was also explored in this study.It is found that CBHyC can precipitate organics from water,form flocs and remove them by electrostatic attraction,ion exchange and hydrophobic adsorption.Among them,hydrophobic adsorption is the main mechanism for the removal of DCF.