Question: Why is elevated TOC and turbidity required throughout the full Challenge Test Water phase when testing IWPs, but only during seeding and sampling points in the Challenge Test Water phase when testing SUWPs?
Answer: During military operations IWPs are used for emergency or short term missions where water selection may be limited, requiring the use of available water regardless of quality. Requiring the full Challenge Test Water throughout provides a realistic worst case test. Missions requiring SUWPs are expected to have more latitude in source water selection, seeking out the clearest source available. Additionally, consumable parts accompany the deployed systems. In order to provide sufficient testing volume, without excessive replacement of consumables, it was decided that requiring elevated TOC and turbidity only at the seeding and sampling points, then requiring a clogging point will sufficiently challenge the systems to document capabilities.
Question: Why does an IWP have a set test capacity (135L) while the SUWP has a daily operation period (4 hours)?
Answer: IWPs by definition will supply needed water to a single individual. It has been identified that the volume needed for a single individual is 15L/day, with a mission duration of 7 days (plus 25% safety factor). SUWPs service a much less defined number of Soldiers, with system selection based on mission needs. It is considered acceptable for an SUWP to be run 4 hours per day plus maintenance time. Due to varying system sizes and flow rates, selection of 4 hours provides a test volume sufficient to evaluate system capabilities without benefitting any single sized system.
Question: Why is seeding necessary?
Answer: A system will hold a volume of water after flow has stopped. This is the void volume. This volume must be displaced before it can be assured that the microbiological challenge exposed to the system equals that of the influent, required concentration. It has been identified that 10 void volumes (vv) is appropriate. For batch systems a full batch (as long as 10 VV is achieved) will be used for ease of testing.
Questions: Should I seek full NSF Certification or NSF P248, Appendix B?
Answer: It is important to consider your market. If you are solely targeting the military, NSF P248, Appendix B will lead to being able to claim Government Reviewing Agency compliance (receive a GRA P248 Letter of Compliance). If your market is more commercial or a mix of commercial and military, NSF Certification may be needed. Full Certification would include the steps necessary to receive the GRA P248 Letter of Compliance as the military reviews ALL PSTPs. For budgeting purposes, it may be most advantageous to begin with the Appendix B piece so that the military requirements are met while the other pieces of full Certification are underway. Typically, it is material safety that is the limiting piece in completing Certification. Note that for compliance with Appendix B, the GRA requires a review of wetted contact materials. Full NSF Certification would be important information relative to material safety for the military review.
Question: I am interested in Certification to NSF P231, Microbiological Water Purifiers, and P248. How do I choose?
Answer: A discussion about your market would help with this decision. More importantly, P248 was based off the EPA Guide Standard, on which P231 uses in its entirety and unaltered. As such, the Army has agreed that those opportunities where it is possible to write a hybrid protocol without compromising the intent of P248, they will allow and will review the PSTPs.
Question: Why does the protocol require two sequential challenges for the microbiological challenging?
Answer: It has been found that some organisms are not compatible for mixing, making it difficult to quantify the organisms. The issue came up specifically due to concerns of not being able to confidently quantify MS2 and fr when co-challenged. Poliovirus and Rotavirus are also not compatible. It is important to not only consider if one organism will outcompete the other, but also if the stock of an organism contains a preservative, etc. that may inhibit the growth of a mixed organism.