Regeneration methods of the ultrafiltration membranes applied in coke oven wastewater treatment

The work aimed to determine the possibility of using an ultrafiltration membrane to pretreat the coke oven wastewater for the preparation of feed for the high-pressure process. The membrane selectivity is only one important parameter. The second is a possibility to carry out the process continuously that necessitates mechanical cleaning of the membrane during the process. Four different membranes with different pores size, material and producer were tested. The most effective rejection was observed for turbidity and iron compounds. For these compounds, the retention coefficient R for all tested membranes was in range 0.9-1.0. The minor rejection was observed for organic compounds (R was in the range 0.2-0.4), while the highest values were obtained for a PVDF membrane of Berghof with the biggest size of pores (0.03 mu m). It suggests that pore size was not a dominating parameter during this separation. All tested membranes were prone to contamination. After about 30 min, the permeate flux was close to zero. Mechanical regeneration was necessary, and it was realized by backflushing, hydraulic flushing and sponge balls. Hydraulic flushing was the cheapest method, and an increase of linear velocity to 8 m s(-1) for 30 s was enough for proper surface regeneration. Satisfactory results were obtained for CUT and Katmaj membranes. For Berghof membrane, backflushing allowed two times better renewal of its surface than hydraulic flushing. Sponge balls test with PCI membrane revealed to be the most effective (in 87%) method of regeneration. If a membrane diameter allows fitting sponge balls into it, this method is recommended at the coke oven wastewater treatment.