U.S. Army field-feeding generates hundreds of gallons of greywater each day, mostly the by-product of washing cookware after the meal. Current dishwashing operations use a three-sink Food Sanitation Center (FSC) that requires approximately 250 gallons of fresh water per day and generates an equivalent amount of greywater. The current disposal approach is to store the greywater in large sump tanks or bladders and then backhaul it for proper disposal. This becomes a logistical and environmental burden because local storage fills quickly and contracted waste removal services are expensive and can be hard to coordinate with erratic greywater generation. This can result in disposal of untreated greywater to the ground. While there is currently no specific Environmental Protection Agency (EPA) or Army regulation that prevents this, the practice poses health problems and harms the environment by adding high concentrations of biological oxygen demand (BOD), promoting bacteria blooms.
A portable greywater treatment system is needed to remediate and recycle dirty sink water from field feeding and sanitation operations. Under this project, three commercial off-the-shelf (COTS) technologies were demonstrated at Fort Lee, Virginia, in August 2004 as part of the Log Warrior Training Exercise. The field test lasted 2 weeks and each of the three systems was operated out-of-doors treating water created by actual field feeding operations. Water samples were taken before and after treatment. Systems were evaluated for water quality, percent reduction of contaminants, permeate flow rate, weight, and size.
The objective of this demonstration was to measure the performance of three portable greywater systems as used with Army FSCs and determine the feasibility of each of the technologies used. Because there are no firm EPA regulations regarding the quality of recycled greywater for use in ware washing, for the purposes of this study, the water was considered to be recyclable if it met the EPA Secondary Treated Water Quality outlined in the Code of Federal Regulations, 40 CFR 133.102. This is defined by the following: BOD of 30 mg/L or less, total suspended solids (TSS) of 30 mg/L or less, pH between 6 and 9. In addition, recyclable water should have a turbidity of 5 nephelometric turbidity units (NTU) or less. The rational for specifying Secondary Treated water is twofold; if the treated greywater is accidentally discharged to surface water such as a lake or stream, the water would be considered clean enough to do so. Secondly, most states with greywater reuse regulations base their water quality standards on the Secondary Treatment standard. In addition, each system's process rate was required to be fast enough to process the entire bulk of greywater before the next meal.
The Ovation Products' vapor compression distillation (VCD) system produced the best quality permeate at an average flow rate of 23 gallons per hour (gph). The permeate had an average BOD of 17.3 mg/L, TSS of 1.3 mg/L, oil and grease (O&G) of 5.6 mg/L, and turbidity of 2.1 NTU. It reduced the volume of greywater by 88%, the BOD by 99%, the TSS by 99%, the O&G by 96%, and the turbidity by 99%. It was, however, the heaviest system, weighing over 300 lbs, and not considered "field worthy" in its current configuration.
The permeate from Infinitex’s Splitter XD ultrafilter had a BOD higher than the requirement, but it performed well in every other category. It reduced the volume of greywater by 91% and operated at an average flow rate of 18 gph. It reduced the BOD by 78%, TSS by 98%, O&G by 90%, and turbidity by 91%. The permeate had an average BOD of 291.2 mg/L, TSS of 4.6 mg/L, O&G of 7.9 mg/L, and turbidity of 4.7 NTU.
Bristol International's tubular ultrafilter did not produce an acceptable permeate (BOD of 447.3 mg/L, TSS of 28.4 mg/L, pH of 5.8, and turbidity of 12.9 NTU). As a result, the cost analysis for this system was not performed.
Overall, the VCD system displayed exceptional water quality but had a physical configuration that was too heavy and complicated while the ultrafilter’s physical configuration was rugged and lightweight but displayed a sub-par water quality. The cost savings realized by either system will be significant, as they will drastically reduce the cost of potable water and greywater disposal. Based on average water and disposal costs, the estimated savings for the ultrafiltration system is $32.5 million per year for 25 years. The VCD system will save slightly more—an estimated $33 million per year for 25 years—because of lower capital costs.
Several benefits will be realized with the addition of a portable field feeding greywater remediation and recycling system. The first is a reduced logistical footprint. At current annual usage nationwide, the amount of water used and greywater backhauled as a result of sanitation operations is estimated to be 19.7 million gallons per year. Generating and moving water in the field costs money and the portable recycling system is expected to reduce field kitchen demand for fresh water by 55% and wastewater hauling expenses by 80%. Other benefits include a reduction in overall system weight and transportability as well as the elimination of health hazards associated with the current method where greywater is disposed of in ditches near the base camp. While some improvements must be made to the COTS systems tested, this project demonstrated the ability of these small systems to process the amount and type of greywater generated in a field environment.