Cindy Ren, EEI 2017 Intern
On Thursday June 15th, we visited the Bachman Water Plant facility. Unlike the previous water plant, this one produced drinking water. We were led by our guide into the phase where water was treated with ozone. Because ozone was extremely unstable, it had to be shipped to the plant in oxygen form, and be transformed into ozone on-site. Our guide explained the oxygen arrived in liquid form at extremely low temperatures, and were led through pipes indoors and heated as they were pumped in. We went in and observed as the oxygen, now in a gaseous form, was run parallel with electricity to disturb its electrons and bind to form ozone instead – however, the guide told us that this process only turned about 10% of the oxygen into ozone – the rest needed to be recycled. Despite this, the heat given off from the reaction is put to good use by heating cool water that is run parallel to it. This effective usage of all the parts of the reaction, even the energy given off, interested me. It was enlightening to see what methods they could use to make the plant as tight as possible in its energy usage and efficiency.
Figure 1. Interns had the privilege to have a guided tour through the Bachman treatment plant.
We then followed the output of ozone to large rectangular tanks, where they would treat the water. The plant made use of the effective of natural gravity by installing large panels from the top and bottom of the tanks, so that when water moved through them, it would be forced down and then up again, producing areas of pressure where the ozone would be blasted with water. The plant’s use of a simple design, rather than complex or heavy machinery (although there are many to handle chemicals) as I’d thought before, was maximizing its space and using structural advantage. As we moved further into the plant, I discovered increasing use of these more simple processes.
However, the excess ozone needed to be destroyed; we were lead into a room where several tanks again modified the ozone to become oxygen, which could be released. Because of the gas’s instability, a small bit of ozone would be diverted each time to a side pipe with a meter that read its contents, and therefore if anything happened, the staff would know and modify parts of the machine.
We proceeded outside. The water there were treated with coagulants, which combine with the sediment and dirt in there to make them clump together and sink. They swirled around slowly in giant tanks; again, surprisingly to me, there wasn’t much heavy or extremely complicated machine in motion, just mixers that made sure slow-moving water allows the dirt to clump and water to flow onto the next step. The advantage to having the water outside, I realized, was that the control room physically see the process and could more easily pinpoint a spot if something went wrong. Any rain that fell, the guide explained, wouldn’t really affect the water – their tanks were large enough to hold the extra volume. It moved towards a large pool with a conical bottom where sludge pooled and emptied – again, at this stage, there were physical controls in place that measured the sediment level in the water, as well as valves that could be manipulated to change any part of the flow. I noticed that at every part of the plant, they contained some way to assess the progress of the water, which would be extremely helpful in determining anything that went wrong by separating the process into different pieces to analyze. Having both computer-operated and manual steps set in place to regulate the plant provided an extra measure of safety – because Bachman plant processed over 160 million gallons a day to Dallas citizens, I could see the need for precaution.
Figure 2. One of the steps is the coagulation process, where organic material accumulates at the bottom and removed in a next step.
The water would then proceed to a mechanism that allowed the coagulated mud to be overflowed into a trough before being filtered through chemicals. In this area, freshwater was pumped to make the water levels rise, and the coagulants poured into a central tunnel that led away from the water, to be sent away while the water was filtered through chemicals. This area was another example of letting the flow of gravity do its job, and utilize a simpler process than I’d previously thought to get rid of the extra sediment.
In the last stage, the water would be treated with chlorine. I learned that they shipped in chlorine in liquid form as well, in giant 90-gallon tanks to destroy any pathogens inside the water; then, ammonia is combined to neutralize the effect of the chlorine and render it less toxic. Our last stop led us to the operations room, where all manual valves and chemical levels could be monitored.
The tour left me with an appreciation for the reliance of the plant on more natural and mechanical methods of cleaning water, both to conserve energy and increase efficiency, such as heating water through the ozone reaction by simply using pipes and direction, or making the most out of gravity to pressure water to flow. Like I have learned through Dallas EEI, the more chemicals that go into the water, the harder it is to predict how it interacts with other, unknown particles inside water, and the more is needed to cancel it out – as was the case with chlorine and ammonia. I dropped my preconceptions of heavy chemical use in treatment plants; additionally, the effects of water conservation that Dallas EEI is spreading through educational programs to children were visible to me in the plant. The water that we use goes through each and every part of the process in Bachman to be cleaned and reused again, and even though the plant is equipped with energy-efficient areas, it still takes a lot of energy for a specific volume of water to go through the process. This energy, including the work and innovation needed to make sure things operated ideally and effectively, could be reduced by limiting unnecessary use of water flowing into the plant – which is exactly the goal of the conservation lessons and procedures that EEI instills. That water usage comes from us.
The precise measurements in every aspect to make sure the water produced was safe to drink and maximize results – and the calculations they still do each day – impress me, and this sort of analysis can be applied to education of saving water as well, tweaking lessons and target audiences to make sure the importance of water conservation is spread far and wide.
Figure 3. The Bachman treatment plant cleans over 160 million gallons a day to Dallas citizens.