The radioactive liquid waste treatment facility (RLWTF) at Los Alamos National Laboratory (LANL) located in Los Alamos, New Mexico treats radioactive wastewaters originating in laboratories and from equipment in radiological facilities, chiefly cooling tower and chiller system blow downs, sump pump downs, and seal water systems. One of the main treatment processes at the RLWTF is a tubular ultrafilter (TUF). There is no redundancy to this particular process at the RLWTF. If the TUF were to become nonoperational both the quantity of water treated and the quality of the RLWTF effluent would be dramatically reduced. In the effort to provide backup capability for this critical unit operation, funds were allocated to obtain and "pilot" test other microfiltration and ultrafiltration technologies in competition with the TUF on actual radioactive liquid waste. If a particular technology proved to be superior to the TUF in permeate quality and/or in operational considerations then a full-scale unit employing that technology would be purchased. This paper documents these efforts, which took place at LANL's RLWTF during May and June 2002, to determine the optimal membrane filtration technology to give the RLWTF redundant filtration capability for the TUF. Four "pilot" membrane filtration technologies were tested: tubular microfiltration; hollow-fiber microfiltration; vacuum driven hollow-fiber ultrafiltration; and, pressure driven hollow-fiber ultrafiltration; As a result of this "pilot" testing effort, RLWTF management decided to attain the redundancy of a second filtration unit not by installing a second unit but rather by having on-hand all critical spare parts for the TUF. A complete rebuild of the TUF can be accomplished in three working days. Less major repairs can be accomplished in one working day. This decision was made on the basis that no "pilot" filtration technology was capable of producing permeate of as high a quality as the TUF. It is true, however, that other filtration technologies were operationally and mechanically less complex than the TUF. This advantage of some of the "pilot" technologies was counter balanced by the RLWTF's two and a half years of operational experience with the TUF which includes numerous treatment optimizing design modifications. Includes table, figures.