research project details
Project Title: Application of bioreactor system to low concentration perchlorate-contaminated water (Phase II)
Investigator(s): Bruce Logan
Sponsor: American Water Works Association Research Foundation
Summary:
The purpose of the Phase I project was to evaluate three different fixed-film biological treatment
processes at the bench scale in order to determine their feasibility for being scaled up to treat large
quantities of perchlorate-contaminated water to drinking water levels (<18 ug/L).
These treatment systems were:
- A packed bed (slow sand or GAC filter) amended with soluble substrates (acetate, lactate, methanol, and ethanol);
- A hydrogen gas fed four-phase (hydrogen gas, water, biofilm, and support media), unsaturated trickle-type packed column; and
- A membrane-bound biofilm reactor.
Based on bench tests, we were to estimate the costs of treating waters using in full scale systems and to recommend one of these treatment systems for pilot-scale testing at the Crafton-Redlands site in Redlands, CA.
All three systems successfully removed perchlorate at rates sufficient to achieve an acceptable level of perchlorate removal for subsequent treatment for potable use. Our economic and engineering analysis indicated that the least-expensive, most reliable system was an acetate-fed packed bed reactor. The packed-bed sand reactor achieved the highest perchlorate removal rates of the three systems. In addition, there was a precedent for using an acetate-fed biological reactor for drinking water treatment in the U.S., making it likely that a reactor of this type would gain public acceptance. Nitrate has been treated using an acetate-fed packed bed reactor for drinking water pretreatment at a site in Coyle, Oklahoma. In addition, biological denitrifying systems have been successfully used in Europe for several years. The wider acceptance of biologically activated filters in the U.S. also points to new trends in the acceptance by water utilities to incorporate biological treatment into drinking water treatment trains. These factors, coupled with a national trend towards "green engineering" and sustainable technologies, suggests that an acetate fed bioreactor is a feasible perchlorate treatment technology.
The primary purpose of Phase 2 will be to conduct pilot-scale testing at the Crafton-Redlands site in Redlands, CA, of an acetate-fed, packed-bed bioreactor, referred to here as the Penn State University Perchlorate Treatment (PSU-O4) System. To fully evaluate scale up and operating considerations, we will field test two acetate fed reactors, one packed with sand and the other with plastic media.
The Crafton-Redlands groundwater source contains necessary trace minerals for biological growth of perchlorate-reducing bacteria. However, in addition to perchlorate, it contains as competing electron acceptors, dissolved oxygen and nitrate-nitrogen. Dissolved oxygen is the preferred electron acceptor and the system is designed to biologically remove this first in the treatment system. As flow progresses through the reactor, nitrate and perchlorate will be simultaneous removed by the perchlorate-acclimated culture. All three electron acceptors will be removed in the fixed bed reactor by adding an electron donor (acetate) at sufficiently high concentrations to ensure their complete removal. A small amount of ammonia phosphate and ammonia-nitrogen may be needed to satisfy bacterial nutritional requirements. Residual electron donor in the effluent will be removed in a post treatment system (biological aerobic filter).
The major questions, or outstanding issues, that will be addressed during this phase of the project are:
- What are the major design criteria for facilities to reliably remove perchlorate with the tested processes?
- How much will the facility cost to construct and operate? Costs of the various processes tested can then be compared with each other to determine what is the best approach to treat perchlorate-laden waters.
- How much time is needed to stabilize the process?
- How difficult will it be to operate? For example, is it more difficult to operate and maintain process stability than a POTW wastewater treatment facility?
- What are the auxiliary needs for this process? Do we need to treat the waste product before discharging to a sewer or stream?
- What treatment processes are needed downstream of the bioreactor to produce water that meets drinking water standards?
- What will the primacy regulatory agencies require to approve this process?