In an effort to reduce reliance on dwindling surface and groundwater supplies in Texas, the Colorado River Municipal Water District (CRMWD) constructed a new Raw Water Production Facility (RWPF) in Big Spring.
Big Spring is a 27,000-member community located in West Texas approximately 300 miles west of Dallas. This RWPF treats secondary wastewater to a standard that allows it to be re-introduced directly into the raw water supply for the water treatment plants of Big Spring, Odessa, and other communities in the region.
A Multi-Barrier Approach
Treatment at the RWPF utilizes a multi-barrier approach consisting of micro-filtration and reverse osmosis (RO), followed by UV-oxidation for the further removal of organic contaminants and final disinfection. The result is advanced-treated, “synthesized” raw water capable of being combined with the “natural” surface raw water from the E.V. Spence Reservoir or other system supplies.
The combined raw water supply from the production facility and reservoirs is then delivered to the drinking water treatment plant of Big Spring as well as those of the neighboring communities of Stanton, Midland and Odessa for further treatment and distribution.
Choosing to Remake and Resupply Raw Water for Reuse as Purified Drinking Water
CRMWD, in a 2004 study, recognized that meeting future water needs and ensuring reliable supply in times of significant water shortage required consideration of additional sources of drinking water. Reusing treated wastewater for potable drinking water was considered to be an important new source because it was a cost-effective and sustainable way to augment and preserve the existing water supply.
However, several alternatives were also considered, including:
- Obtaining Additional Drinking Water from Groundwater Wells and Existing Reservoirs
The aquifer has little recharge potential, and therefore does not offer the long-term sustainability that reuse offers. Additional reservoirs are distant, and the water is subject to high purchase costs in addition to the transportation cost. The wide geographic extent of drought conditions has also resulted in other lakes in the region suffering decreasing levels.
- Reusing Treated Wastewater for Non-potable uses such as Irrigation and Recreational Use
Previous studies concluded that non-potable water reuse would effectively offset the use of drinking water for these tasks. However, the small size and widely-distributed nature of the non-potable demands located in Big Spring and the surrounding municipalities meant that proceeding with this option would require the creation of extensive distribution networks to deliver treated water. Further, demand for non-potable reuse water for irrigation and recreation fluctuated seasonally and did not provide a dependable “year-round” solution. As a result, this option was not considered to be economically feasible and was also eliminated.
- New Raw Water Production Facility
Treatment of secondary-treated wastewater to standards that allow it to be re-introduced into the raw water supply involves three independent treatment technologies: microfiltration, RO and UV-oxidation. The final treatment step, UV-oxidation, provides a highly cost-effective additional barrier to contaminants that, due to low molecular weight, can pass through microfiltration and RO membranes. An example is N-nitrosodimethylamine (NDMA), a probable carcinogen which is effectively destroyed through direct exposure to UV light.
The final treatment provided by UV-oxidation enhances the reliability of the potable reuse treatment process. This three-step treatment train is identical to that used by other successful potable water reuse facilities, including the Orange County Water District (OCWD) in California, to treat wastewater for re-supply into local groundwater aquifers. With the demonstrated success of OCWD, numerous other facilities including Big Spring, have adopted the proven treatment processes to confidently provide new potable water.
Full Scale System Design Parameters
|Design Flow Capacity||1.8 MGD|
|Design Log Reduction of NDMA||1.2 Log|
|Design Log Reduction of 1, 4-Dioxane||0.5 Log|
|Disinfection Method||UV Light|
Direct Use of Treated Effluent
An important design difference between the referenced OCWD site and the RWPF is that the synthesized raw water from the RWPF is pumped directly into the drinking water intake systems of the local drinking water treatment plants. There is no ‘environmental buffer’ in the RWPF facility design. The direct use of the highly treated wastewater is testament to the Water District’s confidence in the treatment process, reliability and operation.
The TrojanUV Solution
Trojan delivered UV-oxidation equipment for CRMWD’s Raw Water Production Facility at Big Spring. Two TrojanUVPhox™ systems, along with hydrogen peroxide (H2O2) dosing equipment, treat contaminants such as NDMA, pharmaceuticals and endocrine-disrupting disrupting compounds that are not removed through upstream membrane treatment.
At the same time this system provides disinfection of microorganisms including E.coli, Cryptosporidium and Giardia.