Experimental Study On Low Temperature And Low Turbidity Water Treatment Of Northwest Plateau By Coagulation-flotation Process

With the development of social economy and the rise of people living standard, theproblem of drinking water safety has gradually caused the attention, drinking water canenter into families after a lot of links and processes. From the source of water,waterworks, to water supply network, and finally assigned to each family and the waterquality security requires carefully check, it also improved the water quality standard ofdrinking water, the water purification industry faces severe challenges. Project siteselect xining, the northwest region of xining city is located in high latitude and highaltitude, the annual average temperature is low, make the region at the same time,meetdifficult purification of low temperature and low turbidity raw water and the local waterpurification methods mostly still adopts the conventional process, research onmechanism of low temperature and low turbidity water treatment, severely restricted theeconomic and social development of xining, city construction and people’s life, make itfacing double pressure of difficult purification and the rise of water quality standard.To the problem of snow melting low temperature and low turbidity water treatmentIn northwest plateau, put forward with using coagulation-dissolved air flotationprocess, effectively improve water purification quality, to ensure the safety of people’swater. Test analyse quality characteristics of the xining plateau low temperature and lowturbidity water. Investigated water type, water quality characteristics and seasonalchange rule of ice and snow melt water as drinking water sources in the typical area.Field experiment was carried out in xining, optimized coagulant and experimentalparameters, achieved a good deal with low temperature and low turbidity water innorthwest plateau region. Experiments used five kinds of coagulation to optimize,ultimately determined PAC to test the best coagulant, the best additive quantity was30mg/L. Dissolved air water refluxed ratio was20%, the dissolved air pressure was0.4Mpa, dissolved air vacuum was-0.03~-0.04Mpa, the effluent turbidity of floating poolcould reach below0.7NTU, turbidity removal rate reached80%~90%. Shock loadtests were carried out at the same time, researched the shock load capability of thecoagulation-air flotation process. This paper also studied the influence of the floc breakage and re-flocculation forflocculation-air flotation process dealing with low temperature and low turbidity water.Experimental results showed that, as the broken point backwarded and crushing strengthincreased, it was more difficult for the floc to return to that state before the break,Yielding water turbidity of air floatation was also increased. At the same time,combining with the running problems of7th xining waterwork made comprehensiveanalysis, and study the impact of the floc breakage and re-flocculation phenomenon tothe actual water purification process.Analyzed rationally air flotation process, introduced a linear probability model,further developed the original bubble-particle collision efficiency model, andcombined with bubble-particles adhesion efficiency model, and finally got the captureefficiency model. By the established model we can find that when dp>1microns,collision efficiency increased monotonically with the increase of the diameter of theparticles, and decreased with the increase of the diameter of bubble, the appropriateincreasing particle size or decreasing bubble size would in favour of collision efficiency.With the increase of bubble diameter, bubble-particle adhesion efficiency seemed to befirstly increased and then decreased, corresponding bubbles diameter of50microns,particles adhesion efficiency was maximum, and adhesion efficiency decreasedquickly after the increase of particle diameter. Then we got the capture efficiency curvewith the changes of bubbles and particles size.Made an actual engineering benefit analysis to xining seventh waterwork, it couldbe seen that the flocculation-dissolved air flotation process is favorable for waterworkactual engineering, At the same time of improving raw water treatment effect, alsoreduced the treatment cost, it was helpful for achieving social benefits.