The Analysis Of The Synedra Clogging The Sand Filters And The Mitigation Measures Of Synedra

Algae pollution has been a world wide problem in recently decades.Synedra(Synedra acus KUtzing)?a kind of diatom, is widely spread, especially insome water bodies with lower temperature, lower oxygen and better water quality.Because of the relatively lower temperature, Synedra blooms usually occur in winterand spring. In water treatment plants, Synedra can decrease the performance of thecoagulation and clog the sand filters. In some extrame cases, Synedra accumulated inthe surface of sand filters and formed a kind of biofilm leading to great decrease of flowspeed in the filters.This study focused on the removal of Synedra in a water treatment plant (fromcoagulation to sand filtration) in Shenzhen.The length of Synedra and the diameter of the sand are associated with filtersclogging. Synedra cannot get through the filters if the ratio(R0of sand diameter andSynedra length was more than3; Serious clogging occurreed when R was between3-6,however; When R was6-8, the problem was not so serious and there was no cloggingwhen R is more than8.Synedra cannot settle down in the water by itself. In conventional processes ofwater treatment, Synedra can be removed during coagulation process. The removal ratewas increased from40%to60%with the addition of4mg/L of dime. The removal ratewas increased by adding PAC when the dose of PAC was less than2mg/L. PAM,sodium alginate and HCA all attributed to coagulation, and HCA has shown betterperformance. Pre-Oxidization by using KMnO4, NaClO and ClO2optimized thecoagulation and2mg/L NaClO (Cl2) increased the removal rate of Synedra to98%.The strainers can capture Synedra but they need frequent cleaning to preventSynedra from clogging the straners. Straners with200-300meshes can capture30%-60%Synedra in6h with50%speed lose. Flotation was also taken into account in thissdudy. The results showed that the performance of flotation was not as good as thecoagulation but it saved time. Synedra removal rate in flotation was related to the waterquality, because Synedra was removed by attatching to the alumen ustum that capturedby the air bubbles and water quality affected the alumean ustum. HCA also increasedthe removal rate of flotation to about88%.To clean the clogged sand filters and prevent Synedra attaching to the sands, bothchemical?such as oxidation treatmentand?and physical methods are taken. With thesetreatments, backwashing can remove Synedra effectively.