Removal Effects And Mechanisms Of Sulfide Odorous By Oxidation And Powered Activated Carbon Adsorption

Swampy/septic odor caused by various sulfides is one of the most frequently encountered odor problems in drinking water.However,even though it is much more offensive,few studies have specifically focused on septic odor compared to the extensively studied musty/earthy problems.In this study,the oxidation and adsorption removal of sulfide odorant were evaluated comprehensively,the factors determining the removal of sulfide odorant during the oxidation and adsorption processes were identified,the adsorption competition of NOM on sulfide odorant in water was evaluated,the adsorption mechanism and influencing factors in these processes were identified,and theoretical pavement was made to guide the practical production.Dimethyl disulfide（DMDS）,diethyl disulfide（DEDS）,dipropyl sulfide（DPS）and diamtyl sulfide（DAS）were selected as typical sulfide odorants.First at all,the removals,kinetics,oxidation transformation mechanism and products of oxidation of DMDS,DEDS,DPS and DAS by KMnO₄,NaClO and ClO₂were evaluated in pure water,and the oxidation process was significant for the removal of the sulfides,and the second-order kinetic constants k of the sulfides followed the order from low to high DMDS<DEDS<DPS<DAS.The oxidation transformation mechanism and products of single S structured DPS and DAS are different with S-S structured DMDS and DEDS.DPS and DAS are easily transformed to sulfone by-products,and DMDS and DEDS contribute to the formation of disulfide by-products.Then,the oxidation removals of DMDS,DEDS,DPS and DAS by H₂O₂and O₃were evaluated in pure water.The removal effect of KMnO₄,NaClO,ClO₂,H₂O₂and O₃on the sulfides was evaluated in raw water.NOM affected the oxidation removal of the sulfides,and the removals of NaClO on the sulfides in raw water achieved 100%,which is the potential oxidation process for the removal of the sulfides.Density functional theory（DFT）calculations were conducted to identify the central sulfur atom properties as the decisive factors controlling the sulfides’s oxidation activity,oxidation transformation and mechanisms of the sulfides.The adsorption and removals,adsorption isotherms and adsorption kinetics of powdered activated carbon（PAC）for DMDS,DEDS,DPS and DAS were evaluated.The removals of the sulfides followed the order of DMDS<DEDS<DPS<DAS,and the adsorption processes were in accordance with the Freundlich isotherm model.The theoretical adsorption capacities of DMDS,DEDS,DPS and DAS were 0.05,1.56,1.73 and 4.99 mg·g^-1,respectively.Homogeneous surface diffusion model（HSDM）was applied to describe the adsorption kinetics of the sulfides,and their D_svalues were determined.The adsorption behavior of the sulfides on the PAC surface was determined by using theoretical calculations.The sulfides were adsorbed on the PAC surface in multiple layers by hydrogen bonding S...H-C hydrogen bonding,and the adsorption on the surfaces containing-OH and-COOH functional groups had the induced energy contributed by hydrogen bonding,and the adsorption on the-CHO and non-functional PAC surfaces was mainly carried out by electrostatic and dispersion forces.The influences of different characteristics of NOM on the PAC adsorption of DMDS,DEDS,DPS and DAS before and after preoxidation were evaluated.NOM before preoxidation had an inhibitory effect on the adsorption of sulfides by PAC,and NOM after preoxidation had a facilitative effect on the adsorption of sulfides by PAC.Theoretical calculations were used to clarify that NOM has a carrying effect on the sulfides,large molecule NOM inhibits the adsorption and removal of the sulfides by PAC through the carrying effect,and small molecule NOM promotes the adsorption and removal of the sulfides by PAC through the this effect.