Depth filter microfiltration membranes produced from biodegradable poly(l-lactic acid) (PLLA) are reported in this paper. The asymmetric porous membranes reported here were formed via a process that combined nonsolvent-induced and thermally induced phase separation. The membranes served as efficient and rapid depth filters to retain bacterial cells when cell suspensions were filtered from the porous or rough side of the membrane, while serving as screen filters when the suspension was fed from the smooth skin side. After use, the depth filters were disposed of by non-enzymatic degradation - a process that was significantly accelerated in wet conditions at 60 degrees C, conditions under which composting is usually operated. The fact that the PLLA depth filters reported here can be disposed of by composting will help reduce industrial wastes in biochemical and food industries when they are used as a pre-filter. (C) 2012 Elsevier B. V. All rights reserved.