Control Of Disinfection Byproducts From Drinking Water By Graphene Oxide And Ultrasound

Disinfection byproducts (DBPs) control is one of the most important parts ofprotecting the safety of drinking water. DBPs precursorcontrolis considered the mosteffective method of controlling DBPs. As the most economical technology for removingDBPs precursors, coagulation is one of the essential process of almost all water treatmentplants. However, the traditional iron and aluminum salts coagulant cannot efficientlyremove DBPs precursors.Graphene has gained intense interest in scientific communitysince it was discovered in2004.As the intermediate of graphene preparation, grapheneoxide (GO) has been confirmed has the ability of adsorption and removal of muti-valentmetal ion and organic compounds due to its molecular structure possesses large quantitiesof the oxygen-containing functional group. Agglomeration and settling will be found whenapplying GO for adsorption of multi-valent ions, this phenomenon is similar with that ofcolloidal destabilization of coagulant. Common disinfectants such as O3?Cl2?ClO2cannotfurther oxide GO because it was completely oxidase by strong oxidizers such asconcentrated sulfuric acid and potassium permanganate, thus DBPs cannot be formed evenGO remained in water. The existing toxicological data have shown thatGO cannot causecytotoxicity and genotoxicity, and was considered as a green materia. In addition, itrelatively simple and economic for preparation of GO in the laboratory. Based on thereasons mentioned above, GO was used as a coagulant to control DBPs precursors fromhumic acid water, surface water, algae solution and its EOM solution.GO was prepared with pressurized oxidation method and presents transparent meshstructure and possesses obvious fold, the C/O atomic ratio of is1.63. The FTIR spectra ofGO shows it contains hydroxyl, C=O and C-O-C functional groups.Coagulation constituent formed obviously when200-400mg/L Ca2+is added into thesolution. Sedimentation rate of GO, size of the floc properties and the forming rate ofcoagulation constituent increase with pH. Floc size generated by different ionsperformance better with Ca2+than Na+, K+and Mg2+under the same ion concentration,effect can produce.Larger and more compacted GO flocs was found whtn Al3+ion wasadded. The trap effect is the main function of GO to remove organic matter, GO showsgoodhumic acid removal efficiency within the pH5-9. It is proved that pH variation hasless effect on the trap flocculation of humic acid by GO, but it has great effects on theremoval of organic matter in surface water as the best removal efficiency was found whenpH?5. The pH of surface water which initial pH is4-10will change after GO treatment andmaintain between6.3-7.7because of the rich oxygen-containing functional group on thesurface of GO. SUVA values of water samples are slightly lower after GO treatment, itshows that the GO has better removal ability on humic like matter in surface water samples.GO can effectively remove precursors of DBPs especially haloacetic acid (HAAs). At most86.5%of trichloroacetic acid (TCAA) precursors can be removed. EEM analysis showsthat GO has good removal efficiency on humic acid and fulvic acid like material, but thethe efficiency on protein like mater is not ideal.Algae control is a significant issue for guaranting the quality of drinking water for thelast decade.Traditional metal salt coagulants cannot effectivelyremoval of algaes.Chemicalpreoxidation shows good ability for controlling of algaes,but it will destroy the structure ofalgaes and resulting in releasing some organics such as algal toxin.This dissertationinvestigated the algae removal efficiency by GO. It shows that GO has good ability oftrapping algaes. Under the condition of acid and neutral, could chlorophyll a will becompletely removed under40mg/LGO, the removalefficiency of UV254and DBPsprecursors could reach at98.3%, and97.5%-100%, respectively. Under alkalcondition, theelectrostatic repulsion increases between GO and algal cells and resulting in reducingefficiency of algaecontrol.At pH10, the removalefficiency of chlorophyll a, turbidity, DOC,UV254dramatically reduced to13.8%,17.7%,42.1%,30.8%, respectively. Addingdiatomite to the system couldn't change the algaes removal efficiency, but it could reducethe sedimentation time and the amount of sludge. GO coagulation also has a good effect onremoving organic matter of EOM of algae, when pH<6, the efficiency of removing TOCcould reach61%. It showed that GO could remove the DBPs precursors of EOM,especially those of HAAs. It could remove the precursors of Monochloroaceticacid by90.1%in the absent of Br-, while remove those of trichloroaceticacid by91.0%in the present ofBr-. It showed that GO hasthe ability of removing organic mattere which containedbenzene ring structure, kind of humic acid substances and aromatic compounds, whichcontain C=C, C=O. Morever, GO has a better ability of removing hydrophilic thanhydrophobic organic maters.To the best of our knowledge, little information is available on the combined use ofultrasound (US) and quartz sand (QS) in the removal of DBPs from drinking water. Thisstudy investigates the removal efficiency for17DBPs from drinking water by20KHz sonolytic treatment, QS adsorption, and their combination. Results indicate that DBPs withlogKow?1.12could not be sonolysized; for logKow?1.97, more than20%removalefficiency was observed, but the removal efficiency was unrelated to logKow. DBPscontaining a nitro group are more sensitive to US than those that comprise nitrile, hydroxyl,and hydroxyl groups. Among the17investigated DBPs,9could be adsorbed by QSadsorption. The adsorption efficiency ranged from12%for1,1-dichloro-2-propanone to80%for trichloroacetonitrile. A synergistic effect was found between the US and QS on DBPsremoval, and12DBPs could be effectively removed by the combined use of US and QS.In the presence of US, part of the QS particles were corroded into small particles whichplay a role in increasing the number of cavitation bubbles and reducing cavitation bubblesize and then improve the removal efficiency of DBPs. On the other hand, the presence ofUS enhances the DBP mass transfer rate to cavitation bubbles and quartz sand. In addition,sonolytic treatment led to a slight decrease of pH, and TOC values decreased under all thethree treatment processes.