Reverse Osmosis Unit Removes Nitrates for Farm Workers
by Randy Theilmeir
Circuit Rider #2, CRWA
Late last year, Michael Wenstrom, EPA Environmental Justice Division, requested CRWA to help with a project to evaluate how best to supply migrant farm workers with safe drinkhg water. Tbe project would be paid for through the supplemental environmental projects funds. The initial project would be located at Gilcrest Migrant Camp. This camp is composed of an eight-plex, with separate buildings for bathrooms and lsundry.
The well water was known to be approximately 2 times the MCL in nitrates. One hundred and eleven chemicals were analyzes, all in the VOC/SOC categories. Of these, 98 were no-detects, with the remaining 13 detected, but well below the MCL's. Bacteria testing will be conducted throughout the operational evaluation period.
CRWA decided that a small Reverse Osmosis unit would work well as an evaulation tool. After getting the OK to proceed, CRWA purchased the RO Unit, capable of producing 360 gallons of RO water per day, a 40 gallon stainless steel storage tank, float switch and an electrically operated water valve, and an enclosure for this equipment. We assembled the unit, took it to Gilcrest Migrant Camp, and installed it. VOC/SOC, Nitrate/Nitrite, and Bact-T sampling was done by Mr. Niok Melliadis, CDPH&E, and Mr. Wenstrom, EPA. TDS, temp, and recovery rate calculations by Mr. Randy Theilmeir, CRWA circuit rider.
Operation of the unit is relatively simple. Cold water from the pressurized system is sent to the unit, which has a pre-filter, two activated carbon filters, then through a four-stage RO unit, and then a final carbon polishing filter. This water is then forced into a stainless steel storage unit for use. When the tank is full, the float switch inside the tank turns off the solenoid valve, which shuts off the inlet line to the tank. Waste from the unit is routed to the sink drain in the building.
The camp was vacated on October 10, and we winterized the unit. Next spring the unit will be placed on line and used for a complete growing season. Replacement costs for the filters and RO cartridges will be $380.00 for approximately every 12 months of operation. Exact periods of filter and cartridge replacement won't be known until the units TDS removal rates decrease to about 75%. Results were as expected. The nitrate dropped from 19.0 mglL to 4.1 mgll, and TDS removal was between 95% on August 10, to 93% on September 2 1. Well water TDS is in the range of 750 mglL while the RO water TDS is averaging 52 mg/L. Average use is 37 gallons per week for the unit. Population was approximately 32 people during the season. Using a figure of $0.50 per liter for purchased bottled water, this unit is supplying $70.00 per week of quality water to the camp.
Conclusions:
Use of a much smaller unit would save on initial costs and cartridge replacement. A smaller storage tank could be used in place of the 40 gallon tank assuming weekly usage is consistent. A small RO unit like this can remove nitrate to levels that are safe for drinking and cooking. These small RO units can provide safe drinking water to homes on individual wells that have high nitrates and a host of other contaminants, with a minimum of inconvenience.
