I thought this was pretty interesting. We drive on highways all the time. Many are asphalt surfaces, but there are a lot of concrete roads (many with asphalt on top of them) that provide service today. We also have a lot of utilities under these roads. Concrete is a stronger surface, but also hides leaks and breaks, making the job harder to locate and fix repairs. And it spalls in northern environments where salt is used on the roads. Utility folks don’t think about roads a lot, but they are integral to our service. 1909 was the first…
This is a very special blog – #300 on this site in the past 3+ years. Time goes by so fast!
It is also a blog on the next phase of reuse – direct potable reuse – i.e, piping the wastewater to the water plant. The concept of indirect potable reuse (IPR), the discussion the my last blog, is not as far fetched as one might think. Rivers receive treated (we hope) waste from treatment plants, and untreated runoff from agriculture all the time. The rivers partially treat this water and it becomes the input to downstream water plants. So in essence we do indirect potable reuse all the time.
But connecting the pipe from the wastewater plant to the water plant, the process of reusing treated wastewater as drinking water without an environmental buffer, is relatively rare. There are two facilities in Texas that do this. Wichita Falls Texas did it for a period of time after their reservoir dropped below 2% of capacity, but they is filled a little after rainfall in September 2015, they took the system off-line. The Colorado River Municipal Water District (CRMWD) has not.
CRMWD serves a total of 250,000 consumers in Odessa, Big Spring, Snyder, and Midland during the region’s worst drought in decades. Back in 2002, they were looking for new water supplies in our area. There was no place for surface reservoirs and most of the fresh ground water had already been developed (and as I blogged before – most of that is unsustainable groundwater withdrawals). The high evapotranspiration limited IPR options. Figure 1 shows how much that differential actually is:
Figure 1 Maps courtesy of the Water Development Board’s State Water Plan
So by May 2013 the CRMWD had completed 2 MGD, $14 million DPR plant to convert wastewater to drinking water standards. The process uses microfiltration, reverse osmosis (RO), and ultraviolet disinfection (UV), which is basically the same as the IPR project I was involved with. The DPR water is mixed with raw water from the nearby reservoir. DPR makes up 20% of the total. The raw and DPR water are then treated again using conventional drinking water treatment techniques.
Figure 2 – the process www.tceq.texas.gov
The technology is clearly available. That leaves monitoring and public perception as keys. Monitoring requires surrogates and redundancy – the multiple barrier approach. Technology will create more monitoring tools, but what we need to monitor is somewhat understood. CRMWD does this by going through a water plant after the wastewater plant – something that is likely going to be to procedure going forward as the processes are fundamentally different and remove different constituents.
Public perception is more of a challenge. Overcoming the “yuck” factor took some ongoing customer interaction for CRMWD, but in west Texas, the need for water, and the limited availability of same, overwhelmed the perception, a situation that may not exist in most areas, but which will increase with time. So the reality is that DPR is likely to received more interest, and less pushback in those dry, western areas with high population growth and limited supplies, as opposed to wet areas that appear to have more water, like Florida. But expect to see more application of IPR and DPR. Or maybe we should call both – potable reuse (PR)?
In the last blog I showed what reclaimed wastewater could do for an ecosystem. Very cool. But what about for drinking water. I actually was involved in an indirect potable reuse project several years ago. The concept was to take wastewater, filter it with sand filters, filter it with microfiltration, reverse osmosis and then hydrogen peroxide and ultraviolet light. This is what they do in Orange County California when they recharge groundwater, and have been for over 30 years. Epidemiological studies in the 1990s indicated no increased incidence of disease when that water was withdrawn from the aquifer, and then treated in a drinking water plant before distribution. So our project was similar – recharge to the Biscayne aquifer in south Florida. It worked for us. Total phosphorous was below 10 ppb, TDS was less than 3 mg/L (<1 after RO), and we were able to show 3 log removal of endocrine disruption compounds an d pharmaceuticals. It worked well. This is a concept in practice in California. And will be at some point in south Florida since only the Biscayne aquifer provides sustainable water supplies. Here is what our system looked like.
This is also the same basic concept Big Springs Texas uses for their direct potable program, demonstrating that the technology is present to treat the water. A means for continuous monitoring is lacking, but Orange County demonstrates that for indirect potable reuse projects, a well operated plant will not risk the public health. This is how we do it safely.
We have a lot of conversations about the impact of people on the ecosystem, the cost to reuse wastewater, competing water demands, water limited areas etc. All are valid issues to raise and since people control the outcomes in all of these situations, we need to be aware of consequences. So while Florida is a leader is wastewater reuse for irrigation, it is kinda cool to see what happens when we think outside the box. The Wakodahatchee wetland is a sewer treatment area created by Palm Beach County Utilities a number of years ago. This is reclaimed quality water placed into an area specifically designed to allow for nutrient removal and aquifer recharge. The County placed mosquitofish in the water to reduce mosquitos. Bluegills found there way. So did the turtles and alligators. But this is THE bird watching site in southern Palm Beach County. And it is located between the wastewater plant and a neighborhood. You can’t get parking easily. This is an example where looking at the bigger picture seems to have a positive effect on the community and the ecosystem as well. The birds don’t look unhappy.