Letter Report on: The Blue Grass Chemical Agent Destruction Pilot Plant's Water Recovery System (2012)
Chapter: Letter Report
THE NATIONAL ACADEMIES
Advisers to the Nation on Science, Engineering, and Medicine
Board on Army Science and Technology
Mailing Address:
500 Fifth Street, NW
Washington, DC 20001
www.nationalacademies.org
February 28, 2012
Mr. Conrad Whyne
Program Executive Officer
U.S. Army Element, Assembled Chemical Weapons Alternatives
5183 Blackhawk Road
Building E4585, Room 1
Aberdeen Proving Ground, MD 21010-5424
Re: The Blue Grass Chemical Agent Destruction Pilot Plant’s Water Recovery System
Dear Mr. Whyne:
At your request, the National Research Council of the National Academies established the Committee to Review the Water Recovery System for the Blue Grass Chemical Agent Destruction Pilot Plant (BGCAPP). Specifically, the committee’s purpose was to review the design and materials of construction of the water recovery system (WRS) that will be used to recycle combined effluents from the supercritical water oxidation (SCWO) system and from the cooling tower and steam blowdown for reuse in the facility. The statement of task with its introductory context is provided in Attachment A, and the study tasks are presented below. Personally, I am very impressed with the expertise of the members who were recruited for this committee by the National Research Council. Their names are listed in Attachment C and a short biography of each member is given in Attachment D.
The committee’s statement of task is as follows:
- Obtain information from the equipment vendor on water recovery system (WRS) installations that treat comparatively similar effluents to those at BGCAPP.
- Contact a representative industrial installation to review its reverse osmosis (RO) system operational and maintenance history, and determine the degree to which operability has been acceptable.
- Ascertain the likelihood that the quality of the recycled water will meet requirements for its re-use as quench water in the plant.
- Review materials of construction to determine whether adequate performance can be expected over the anticipated operational life of BGCAPP, specifically addressing potential concerns for corrosion, fouling, and stress cracking.
- Produce a letter report on determinations resulting from the above examinations.
Data gathering began at the committee’s first meeting, in July 2011 in Richmond, Kentucky. The committee received technical information on the BGCAPP WRS and engaged in extensive discussions with BGCAPP staff. A follow-up teleconference was held with BGCAPP staff members during the committee’s second meeting, in September 2011. Additionally, BGCAPP staff and their vendor answered several sets of written questions from the committee.
During discussions with you and your staff, it was agreed that visiting other vendors of reverse osmosis water treatment systems was not necessary because the committee membership had adequate experience with water treatment and recovery systems to complete its work without conducting such visits. Furthermore, the sponsor and committee agreed that, since no other treatment facilities process effluent streams with a composition similar to the effluent streams that the BGCAPP WRS will treat, no useful comparison could be drawn from existing industrial operations. The committee did not review the SCWO design. It accepted the data on SCWO effluents provided by the sponsor and evaluated the planned WRS on the basis of those data, although it did note differences between the parameters used for the calculations made using the ROSA RO process modeling software and the data from the tests conducted with actual blended SCWO effluents. The committee also took the following limitations into account during its work:
- The footprint for the RO system in the building is limited by the present design;
- The BGCAPP design is complete and construction is underway, making significant changes to the design challenging;
- This RO system will only be operational for 3 to 5 years, until all the munitions are destroyed and the resulting hydrolysate has been treated; and
- Any modifications to the design will necessitate amendments to the present Resource Conservation and Recovery Act permits, which govern plant operations, and will require negotiations with the Kentucky Department for Environmental Protection.
The study’s scope is defined to encompass operations that begin with the arrival of SCWO effluent and blowdown waters at the WRS for treatment and end with the RO system effluents leaving the WRS to be stored in tanks. The study is organized to describe and review the system at a high level as the effluent streams proceed from the water-softening step through the pretreatment steps and finally to the RO system. The materials of construction are reviewed in the “Materials of Construction” section of the report.
The committee commends the decision to reuse process water, reducing the overall demand for water made by the plant. The committee believes that, as long as the WRS functions properly and meets its treatment goals, the recovered water will be suitable for reuse as quench water in the SCWO process. However, on the basis of the information provided to it, the committee has significant reservations about the WRS functioning as planned. These reservations fall into three main areas:
- Materials of construction. The committee noted a lack of testing of potential materials of construction for use in the anticipated service environment. The committee believes that more testing of candidate materials of construction would
be ideal. Another strategy is to select materials using conservative criteria. The committee discussed some testing that can be performed that, while not representative of the expected service environment, might give some insight into the suitability of the selected materials of construction for service in the BGCAPP WRS. The committee recognizes that the opportunity for representative testing is limited or non-existent prior to the start of operations, and so it also discusses the possible use of a duplex alloy, such as 2205, in the WRS to be conservative.
- Pretreatment. The committee’s attention and concerns were focused to a large extent on the operation of the pretreatment system and the RO system. There is no way of predicting the level of solids that will arrive at the pretreatment system from the SCWO system, making it difficult to design an adequate pretreatment system. The hydrolysate and SCWO effluent storage tanks will provide some opportunity for suspended solids to settle out. The committee discusses the design of these tanks vis-à-vis providing the maximum opportunity for settling to occur, and suggests a possible way of compensating for the deletion of the originally planned clarifier by using the SCWO effluent storage tanks.
Given the uncertainty about the composition of the effluents that will enter the pretreatment system, and given the results of SCWO tests using blended actual agent and energetics hydrolysates, the committee is concerned about the planned media filtration system’s being rapidly overloaded with incoming solids. Any overload and shutdown of the pretreatment system would have a catastrophic effect on the reverse osmosis membranes. The committee is concerned about the choice of coagulant and whether it will perform adequately. In this vein, the committee discusses risk mitigation for the media filtration system, as well as the option of using membrane filtration instead of media filtration. Membrane filtration would present some advantages over media filtration, given the uncertainty over the actual quality of the water entering the pretreatment system, and it could also have a smaller footprint in the plant.
If the pretreatment steps are effective in removing suspended solids from the effluents to be passed through the RO membranes, the committee does not anticipate that membrane fouling will be a significant problem. Also, if the pretreatment step operates adequately, the committee believes that recovery may exceed the target of 70 percent. - RO membranes. The committee’s main concern with the RO system is the length of time that it will be stored with the membranes in place—3 years. The committee addresses the option of taking late delivery of the membranes to alleviate this concern; late delivery would have the additional benefit of allowing dry system storage, alleviating any concern about microbially influenced corrosion. The committee also discusses membrane cleaning, as some fouling over time is inevitable.
The complete details of the committee’s assessment are incorporated in the findings and recommendations with supporting text in the report that follows.
Sincerely,
Robert A. Beaudet, Chair
Committee to Review the Water
Recovery System for the Blue Grass
Chemical Agent Destruction Pilot Plant
Attachments
