A study of upward flow pilot plant filters

Abstract

In,general, it has been observed from past experience that there are numerous limitations and operational problems associated with the conventional downflow filters. Intensive research in many parts of the world, particularly in Europe, America, and Russia lead to the introduction of many improvements on the operation and design of filters. An upward flow filter is one such innovation which was found to offer many advantages over the conventional downflow filters; in terms of compactness of plant, turbidity removal, higher filtration rates and the generally low operational and maintenance costs. It has been identified that one of the major causes of slow sand filter failures, in Kenya is high raw water turbidity. There is therefore a need for research to alleviate this problem. TWo pl10t plants were set up. One was at the Environmental Health Engineering Laboratory. 'I'h i s pilot plant utilised?artificially prepared turbid raw water. The parameters of t.urbidity, colour I headloss development and pH variations were monitored. Nine test runs were carried out in all using vari ab Le f LLt.r at Lcn rat.es of C.? m/hr to 1 m/hr. The influent turbjdity varied from 10 FTU to 170 FTU. No pretreatment of the raw water was provided. The second pilot plant was set up at Kabete water works with naturally turbid water. No pretreatment was also provided. The parameters of turbidity colour and pH were monitored. An attempt on microscopic investigation into the presence or absence of Plankt~life in the filter was eventually aband6ned when the slides inserted into the filter became constantly covered with sand. Four test runs were made using this filter. Experiments with fille sand media of effective size 0.22 rom and coefficient of uniformity of 2.46 gave unsatisfactory results. The sarid media was too fine and lower depth of the filter media tended to clog rapidly with high values of raw water turcidity. Recomendations on areas of future research have been made.