The evaluation of two different PAC operations in combination with submerged ceramic MF membranes in surface water treatment

Powdered Activated Carbon (PAC) has been successfully used in conjunction with membrane microfiltration (MF) to reduce taste, odour, colour and other concerns caused by organic material present in raw drinking water sources. PAC addition also significantly reduces the extent of fouling in membranes. And the operation of continuously dosed PAC before membrane filtration is widely applied in drinking water treatment while the operation of PAC precoated on the membrane is a new approach. This research, therefore, aims at evaluating the membrane fouling on these two different PAC operations. Water from the Schie canal in Delft was coagulated with Iron (?) Chloride and enhanced with PAC, then filtered through a ceramic membrane. The trans-membrane pressure was monitored during filtration. Samples of the raw water and the permeate water were collected and analysed for DOC and UV254, while LC-OCD tests were carried out on the collected samples as well. In addition, the the backwash water and chemical cleaning solutions after soaking membrane were analysed. The PAC in the continuous dosing channel was dosed before flocculation and the membrane was frequently backwashed every 19 minutes for 1minute. However, the PAC in the precoating channel was precoated on the membrane before the experiment and operated without frequent backwashes. The results show that the membrane fouling in the continuous channel was more severe than that in the precoating channel which was mainly concluded from the recovery of TMP. That is because the different PAC addition modes lead to a different cake structure on the membrane surface. The cake layer in the continuous channel was mostly non-backwashable while it was easy to be backwashed in precoating channel. Recovery in the precoating channel was quite good with a recovery of 99.2% while the continuous channel presented a normal recovery of 85.5%. The DOC and UV254 removal for these two operations was similar. Also, the LC-OCD results of the backwash water and the chemical cleaning solution reveal that, if ignoring the cake fouling, the total fouling for the two operations were not too much different while big difference existed in compositions of NOM. Specially, about 40% of the neutrals fraction and 35% of humic substances fraction were found in sodium hydroxide solution after the membrane had been soaked 24 hours in continuous channel. Whereas, the first two important foulants in precoating channel were humic substances and bio-polymers, with approximate 33% and 19% fraction, respectively.