November 1996

Volume 15, #3

SpinTek Reduces RadWaste By 70%

To keep up with increasing regulatory requirements, the Radioactive Liquid Waste Treatment Facility (RLWTF) at the Los Alamos National Laboratories (LANL, Los Alamos, NM 87545) is replacing its 30 year old system with a new integrated hybrid technology membrane filtration system by SpinTek Systems (16421 Gothard St., Unit A, Huntington Beach, CA 92647; Tel: 714/848-3060, Fax: 714/848-3034).

The system will be designed to treat the 5 to 8 million gallons of radioactive waste per year generated by research organizations within the LANL complex. Jerry Freer and Alan Bond, each chemical engineers at LANL, have designed a solution to improve the effluent quality and reduce the volume of radioactive waste.

This is the first time a centrifugal membrane filtration system has been used in treatment of low level radioactive waste. The system consists of a tubular crossflow ultrafilter; a centrifugal microfilter and a spiral wound reverse osmosis unit. The tubular system concentrates the radioactive of the feed water to 70X, the centrifugal microfilter further concentrates this to 10,000X and the reverse osmosis system polishes the filtrate from both of these units.

Freer explained that the system was selected primarily for its centrifugal microfilter. “It reduces our secondary waste stream by a large amount, minimizing the waste volume. The centrifugal microfilter’s ability to achieve this concentration is unique for these types of separations.”

With the implementation of the new combined crossflow and centrifugal filtration technology, Freer wants to achieve waste minimization by concentrating the low level radioactive components of the waste stream. He set three system requirements-achieve a higher concentration factor over the current treatment, reduce the chemical usage, and provide high quality effluent water for discharge. SpinTek’s proprietary centrifugal microfilter is the heart of the system, enabling the engineering team to achieve these objectives.

The LANL engineering team researched other membrane systems before making their final decision to purchase a SpinTek system. As an example, a hollow fiber membrane system was tested and found to be incompatible with the Los Alamos waste stream providing only a 10X concentration of the feed stream. “We experience abrupt plugging and fouling problems with these membranes,” Freer explained. “Operating hollow fibers continually on our waste stream requires expensive pretreatment and an automated back washing system which means downtime.”

In contrast, the SpinTek tubular membrane system performed a 70X reduction on the feed stream with no fouling due to its mechanical cleaning technique. The SpinTek centrifugal filter then further concentrates the waste into a slurry of 30% solids. It is expected that the production system will achieve even higher concentrations. The higher level of solids will be achievable because there is little or no significant fouling experienced due to the high shear generated by the spinning membrane disks. The final component is a spiral wound RO unit which polishes the filtrate from both the tubular and centrifugal membrane systems-this produces a suitable effluent for discharge, having only background levels of transuranic radionuclides.

SpinTek provides a total solution to waste minimization by concentrating the radionuclides to a higher level without the need for filter aids. The LANL facility will now have a concentration factor of 10,000X or greater. This contrasts to the existing treatment facility, a chemical precipitation and clarification system followed by filtration of low level radioactive sludge, achieving a concentration factor of 320 to one.

“Since the characteristics of our waste stream, a low level radioactive water-based matrix, can change on an hourly basis, we secured a system that operates continuously,” said Freer. “The SpinTek System allows continuous operation during changes in influent waste stream characteristics, which means zero downtime for flux recovery.”

Designed for high solids and viscosity feed streams, the SpinTek system demonstrated an ability to operate reliably and consistently while producing a high solids radwaste slurry for disposal and a low level effluent for discharge into the environment.