Description:
OBJECTIVE: Develop an efficient water vapor harvesting technology that can recover water vapor from centralized bathing facilities and similar infrastructure. DESCRIPTION: Supply of water for potable uses at contingency operating bases (COBs) represents a significant logistical and economic burden for the Army. To help alleviate this burden, on-site water treatment with reverse osmosis (RO) membrane technology has been applied for tactical water production. For areas with limited source water availability, on-site water generation systems that extract water vapor from air have been developed. However, current water generation systems are energy-intensive, which limits their broader application. An example of a water vapor extraction system is the use of a solid desiccant like silica for adsorbing water vapor, followed by displacement of the adsorbed water by heating back to the vapor phase, and then condensation to produce clean water. Another approach uses ionic liquid desiccants. In general, these approaches are more efficient in environments with higher relative humidity. Thus, the targeted application of these or other water vapor harvesting technologies in certain field infrastructure like centralized bathing facilities or other humid indoor environments is of potential interest. Existing ventilation systems for such facilities could be potentially modified to harvest water vapor at a reduced energy cost. To support the Army"s goal of reducing water demand at contingency operating bases (COBs) by 75%, in support of Army Science & Technology Challenge Area 4a, SBIR proposals are sought that will further onsite water generation capabilities at COBs. Specifically, the development of a supply side water generation technology that harvests water vapor from existing infrastructure is desired. Technologies that could integrate with existing field infrastructure systems such as shower stalls are of interest. Innovative systems that use alternative approaches to conventional desiccant technology but still produce the same quality of product water are also of interest. Systems should not require extensive post-treatment (beyond granular activated carbon polishing, microfiltration, and chlorination). Systems should be designed and tested against the following metrics: 1) Energy consumption of less than 40 Wh/gal (Watt-hours per gallon) product water, after discounting the energy leveraged from existing infrastructure (i.e., ventilation fans). 2) Ability to produce at least 50 gallons-per-day (gpd) of field potable water.1 3) Maintenance requirement of less than 30 min/week. PHASE I: Phase I should include a bench scale demonstration of the water vapor harvesting capability and a detailed engineering estimate of the expected energy efficiency, maintenance requirements, and physical footprint at pilot scale. Water harvesting performance testing shall be performed over a period of at least 1 month in a manner that generates reproducible and accurate data. Relative humidity ranges and temperatures tested should be representative of expected conditions in centralized bathing facilities. For pilot scale design purposes, assume the following attributes for a generic centralized bathing facility: 1) centralized shower facility; 2) interior volume of 1400 cubic feet; 3) 8 water-efficient showerheads running intermittently for 6 hrs/day each in a semi-diurnal cycle; 4) Exhaust ventilation at 1000 cfm for 10 hr/day. Bench scale testing should be scaled down from the pilot scale accordingly. During bench scale testing, product water quality should be evaluated at least once per week for total dissolved solids TDS), total coliform (TC) bacterial contamination, and total organic carbon (TOC). Engineering estimates of energy efficiency, maintenance requirements, and physical footprint shall be made for a pilot scale system that can harvest at least 50 gpd. The metrics for Phase I include: 1) Projected energy efficiency of<40 Wh/gal at pilot scale, after discounting the projected energy leveraged from existing infrastructure (i.e., ventilation fans). 2) Product water quality having TDS<500 mg/L; TC<1 cfu/100 ml; and TOC<0.5 mg/L. PHASE II: Phase II should include design, assembly, and assessment of a pilot scale system prototype in a simulated relevant environment. The first year should focus on design and assembly of the prototype and test chamber. Designs shall be drafted using professional grade drafting software, with all parts specified in terms of size, material, and source. Systems shall be assembled by the end of the first year of Phase II funding. The second year of Phase II should focus on testing the system at pilot scale in a simulated relevant environment. Systems should be tested over a 3-month period using a test protocol that clearly addresses the metrics described below. Challenge water vapor formulations and system operation schedule shall be representative of environmental conditions in a centralized bathing facility. For pilot scale design purposes, assume the following attributes for a generic centralized bathing facility: 1) centralized shower facility; 2) interior volume of 1400 cubic feet; 3) 8 water-efficient showerheads running intermittently for 6 hrs/day each in a semi-diurnal cycle; 4) Exhaust ventilation at 1000 cfm for 12 hr/day (during and after shower operations). During pilot scale testing, product water quality, energy consumption, and maintenance requirements shall be documented in detail. Product water quality measurements will be taken on a weekly basis and include: TDS, TC, TOC, and any potential materials that might leach into the product water from the vapor harvesting system itself, such as metals, specific organics, ions, etc. Phase II products shall include: 1) A pilot scale water vapor harvesting system that is ready for transition to integration with existing infrastructure. 2) A report detailing water vapor harvesting efficiency, energy consumption, product water quality, and maintenance requirements over a 3-month test period. Phase II metrics include: 1) Demonstration of maintenance intervals of at least one week and less than 30 minutes in duration (each). 2) Production of at least 50 gpd of field potable water per day, having TDS<500 mg/L; TC<1 cfu/100 ml; and TOC<0.5 mg/L, and data supporting that it will meet field potability standards.1 3) Demonstration of energy efficiency of<40 Wh/gal, after discounting the energy leveraged from existing infrastructure (i.e., ventilation fans). PHASE III: Military applications for a system that meets the metrics described herein may include water generation in contingency operating environments and at installations, and natural disaster response systems. Additional commercial markets may include: water vapor harvesting systems for residential, commercial, or industrial applications. REFERENCES: 1) U.S. Army Public Health Command (formerly USACHPPM). TB MED 577/NAVMED P-5010-10/AFMAN 48-138_IP. Sanitary Control and Surveillance of Field Water Supplies. May 2010. Available online at: http://armypubs.army.mil/med/DR_pubs/DR_a/pdf/tbmed577.pdf
