Forward Osmosis Treatment System Assessment
In many arid regions wastewater represents an underutilized source of recycled water. However, wastewater contains feces, urine, surfactants, food wastes, pathogenic microorganisms, blood, and salts, which make it inappropriate for direct reuse for irrigation. Conventional tertiary treatment, which treats wastewater to levels considered appropriate for irrigation, is typically too costly for small-scale applications and does not remove salts. A low cost, low power system capable of treating wastewater generated in small communities to standards appropriate for reuse as irrigation water could find wide application in many arid regions. Such a system must be inexpensive, economical to install and operate, and should result in no impairment of land and water resources due to prolonged exposure of treated wastewater. The system described in this proposal should accomplish these goals and is ideally suited to application in small communities, such as the Navajo Nation, who want to utilize wastewater as an irrigation resource. The system is referred to as the forward osmosis wastewater to fertilizer (FO-WTF) process.
The FO-WTF is the result of technology transfer from The NASA, where the technology has been developed for the recycle of spacecraft wastewater FO-WTF treats wastewater using a hydrophobic membrane similar to that of a reverse osmosis system but one that does not require a pressure gradient to function. This membrane removes solids, surfactants, salts, large molecular weight and polar organics, bacteria, and viruses. The technology is based on the process of forward osmosis (FO).
Reclamation and NASA have been collaborating at the Desert Research and Technology Studies (D-RATS) Habitat Demonstration Unit (HUD) to transfer the proposed technology to address the needs of local Navajo communities in Northern Arizona. The FO-WTF configuration described is an evolution of the D-RATS system designed to meet the needs of these Native American communitie
Need and Benefit
Many rural communities in arid regions suffer from water restrictions, poor wastewater treatment, and poor disposal practices. These conditions can limit the economic development of communities, especially that dependent upon agriculture. The development of new water resources can enable cultivation of fallow land and contribute to the economic development of the local community. In addition, the proper and efficient treatment of wastewater can improve the health and welfare of the community, as well as contribute to the effective stewardship of local environmental resources.
The combination of developing new water resources from wastewater treatment also has the added benefit of providing an economic model where the benefits of new water resources produced can offset the costs of wastewater treatment. This is a model that can generate resources to provide system maintenance and upkeep. This is particularly important in rural and under privileged communities.
The use of low-pressure FO membranes enables the development of simple inexpensive systems that can be operated autonomously and require minimal maintenance. Membrane modules are low cost due to low-pressure operation and can be fabricated out of PVC pipe. Modules can be designed to be modular and easily replaceable, limiting the need for highly skilled operators and minimizing operator exposure to contaminated equipment.
The system is simple and potentially very economical. Power consumption will be low; it is expected to be about 5 Whr/gal. Produced water costs will be a function of the membrane life, which is not known at this time, and will require the completion of long term pilot testing to ultimately be determined. However, it is estimated that costs should be in the range of $0.01/gal to $0.05/gal.
The development of the FO-WTF system will provide the dual objectives of creating new water resources and a simple method of treating wastewater in rural and under privileged communities. The system should have a low capital and operating cost. It will be simple enough for local labor to maintain and is designed to operate unattended. It is ideal for applications such as Navajo communities in the Southwest but will also apply to communities worldwide that are likewise impacted by arid climates and economic limitations.
A scoping document will be submitted for public viewing.