Application of coagulation and vonventional filtration in raw water pretreatment before microfiltration membranes

摘要

Two step coagulation using iron coagulant (FeCl_3) with anionic polyelectrolyte in the first step and aluminum coagulant in the second one was made to reduce the negativ eeffect of the foulign phenomenon.The process was operated o n the ocmmercial saale.The raw water was the blowdown water from the power plant coolign system.The dead-end microfilutrationunits provided with 0.2 mum polypropylene membranes produced about 210 m~3/h of water.The results of statistical tests show a singificnat difference between the concentrations f turbidity,total hardness,sulfates(VI),total iron,aluminium,silica,nitrate nitrogen,ammonia nitrogen,oxygen sconsumption and absorbance (254nm)in the water durign the whole process.the results of previous observatios showed that he formation of the cake layer had been the main reason for the fouling phenomenon occuring on the investigated membranes.It is significant tht 75(percent)of the suspension has been removed during the pretreatment stages.The hydrobiological observations showed that the formation of the cake layer had been the main reason for the fouling phenomenon occurring on the investigated membranes.It is significant that 75(percent)of the suspension has beenremoved during the pretreatment stages.The hydrobiological observations show th epresence of Bacillriophyceae and Cyanophyta.it is possible to remove them during the coagulation and prefilutration stages.Teh ivnestigation results show that it is possible to protect the polypropylene coagulation and prefiltration stages.The investigtion results show that it is possible to protect the polypropylene membrane from fouling occuring inside the membrane pores as well as the formation of the cake layer.The use of a hybrid process combinign the traditional raw water pretreatment iwth a membrane process may be well-founded.