Sewage was purified in 6 nonwoven membrane bioreactors (filtration surface 189 cm(2), vol. 1.5 L) operated either in quasi-continuous mode or periodically (portions added every 12 h). After start of growing beds and biofilm in the filters, BOD5 and COD were detd. before and after purifn. The quasi-continuously fed bioreactors were slightly more efficient than the periodical ones.