Study On The PH Change Factors And Adjustment Measures Of Carbon Ponds In O₃-BAC Process In Pearl River Delta Region

With the rapid economic development, the living standard has rised greatly, and the qualityrequirement of drinking water also has gradually improved. At present, drinking water sourcespollution in the Pearl River Delta region are increasingly heavier. It has becoming loweralkalinity and lower hardness water, and water is neutral or slightly acidic. When taking thewater purification technology with the ozone biological carbon process, effluent water pH hadbeen declined which contrast to the raw water after a long operation. In order to improve thewater quality and ease the water supply network corrosion, the existing waterworks mostlytake the measurese to improve water pH with dosing caustic soda solution between carbonponds and clear water ponds. But there were certain water quality risk problems. Through thisproject studing, it could solve the risk problems, and perfect related operation process andtechnical parameters in the ozone-biological activated carbon water treatment technique, andalso improve the level of the water purification in the pearl river which had an importantsignificance in theory and practice.Relying on someone waterworks in Guangzhou, in view of the raw water characteristicsin the Pearl River Delta region, key factors and adjustment technology about pH droppedphenomenon in the Ozone biological carbon process （O3-BAC） were studied. Experimentalresearch shows that:（1）When the raw water pH for7.20⁷.25, the ozone dosing quantity from0to2mg/l,water pH value changed slightly and remained in the range of7.10to7.15; The alkalinity ofraw and effluent water were basic for about50mg/lCaCO3, which was a little impact in waterbasicity. Macromolecular organic matters by ozone oxidation produced organic acid,whichhad no effect on the water pH in carbon ponds.（2）Without ozone addition, CO₂content was0.0343%; and with the increase of ozonedosing quantity, the amount of CO₂was micro increased, but the carbon ponds pH changerange was only0⁰.05, which could be almost negligible.It show that the CO₂increase of thecarbonate buffer system did not affect the carbon effluent water pH value.（3）With alkali addition, when pH increased to9.0, effluent water pH value was still7.0;with acid addition, when pH lower to6.0, effluent water pH value was still around7.0.Carbonponds inflow water quality had no effect on the carbon ponds pH. But with the increase ofcarbon layer height, the effluent pH were down （and alkali） or up （plus acid）. Carbon pondshad strong acid-base buffering function there, and could neutralize OH-or H+.（4） Activated carbon （AC） was the key factor on carbon ponds pH change. Activated carbon surface existed acid-base functional group, which had the buffer role, and couldmaintain the same pH between carbon ponds and carbon itself. When AC was modified bycaustic soda, surface chemical properties of AC was changed, and the alkaline functionalgroup was increased, avoiding activated carbon to buffer the effluent water to lower pH.（5） Pilot tested four different combination pH regulating modes. The water qualityindexes could meet the requirements of "sanitary standard for life drinking water"（GB5749-2006）.Through the analysis on outlet water saturation index IL, stability index IR,erosion index of AI, the results showed that the combination in sand ponds to add lime withthe modified AC was more economic and more effectively to improve the quality of the outletchemical stability. Productive experiment was further verified that the combination in sandponds to add caustic soda with the modified AC to regulate outlet pH was feasible.