Reverse osmosis water recovery project collects more than 20 million gal of water annually
It is rare that one finds a cost-effective process that also helps the environment. How people use water can be one of these rare finds. In this case study, the results of saving water will prove to not only save money, but also help the environment. While the planning stage for this particular reverse osmosis (RO) reuse system took approximately three months, the construction, testing and implementation of the system took more than two years to complete.
The reuse system begins with the collection process. During a building expansion, when the concept of the reuse system was implemented, the company added new production lines. In addition to the drains that flow back to the municipal wastewater treatment plant via the sewer system, the company installed a new drainage system alongside the city’s sanitary system. The use of gravity, like the city sanitary drains, sends water to a large underground storage tank. Because gravity collects the reuse water from numerous production lines, the collection tank had to be sunk deep enough to receive water from different parts of the building. The tank collects water from two different elevations between two buildings. When water in this tank reaches a top float, it pumps water out of the collection tank to a storage tank located on the production floor. To add a level of protection to the aboveground storage tank, a 5-µ filter was built in line to collect any residual production process debris that does not settle out in the collection tank.
Water in the collection tank is not ready for secondary use until it is proven to be of good quality. The collection and distribution systems served as a delivery and cleanup stream. Delivery pumps repressurize the RO reuse water as the water moves towards the new end use points. Water is filtered prior to collection and production use. Additional equipment was installed in the distribution line.
Challenges & Cost
The two biggest challenges to production were bacteria contamination and water overflow. Of the two, bacteria contamination was management’s most critical concern. To minimize the opportunity for bacteria growth, this system was designed to circulate continuously, even when production is not running. As a first step, a carbon filter was installed to remove any organics that may have accumulated in the collection system. A 0.2-µ filter is used immediately after the repressurization stage for the aboveground RO reuse storage tank. This helps reduce the load on the ultraviolet (UV) light, which comes next in the treatment system. The UV further minimizes the chance for bacteria colonization in the distribution piping and at the production end uses. This system also was designed so it could easily be sanitized at any time. An inductor system safely sucks in the desired chemical. Probes monitor and measure the sanitizing process. Flowmeters also were installed in every branch of the distribution system.
To further protect the system from bacteria growth, the original sanitation drain lines were plumbed separately from the RO reclaim system. As a result, some of the used process water from production flows to the sanitary drain, while water that is more cost effective to reclaim is sent to the reuse system. These precautions helped ease management’s contamination concerns.
When the system collects more water than it sends out for production, reuse is a concern, as the water could back up within the plumbing system and flood the production floor. This system needed a failsafe to ensure this does not happen. A separate line to the sanitation sewer that comes off the top of the underground storage tank was installed. To do this, a large crock was put in the ground, which established an air gap and separation. Two backwater valves were installed further upstream and downstream of the safety crock.
The final production impact that concerned management was the cost of the system versus savings on water costs. When written, the original capital had a payback of less than a year based on 20 hours of operation per day at a five-day work week with a 52-week operation. This came to fruition with a payback of only 10 months. The system now collects more than 20 million gal of water annually and provides substantial cost savings to the company per year.
Ensuring manufacturing quality started long before design and implementation stages, and a system test was devised. To prove and ensure reuse water met the quality the company required, a system of analytical probes was created. This group of monitoring probes, floats and alarms was strategically placed within both the RO reuse collection and distribution systems. Data points relayed information to software that was programmed to interpret, graph and alert to changes within the reuse water system. It was the job of the analytical probes to report exactly what was happening with the system 24 hours a day. Trending this system’s water quality took six months. During this six-month window, the reuse water was collected and sent back to the sanitary drain. Only once this test was complete and an outside lab confirmed good quality did the reuse system go online.
During the trending period, a consistent water quality value had to be established for all of the probes used in the system, including total dissolved solids, pH, turbidity, oil contamination, oxidation reduction potential and water temperature. The oil probe was installed to monitor the water only if a maintenance or equipment mishap occurred with any of the washing equipment conveyors.
The monitoring system put in place during the initial testing continues to constantly track the quality of the water. If an alert indicates a change in water quality, backup systems are automatically activated and the reuse system shut down. If a production line indicates a change in end-product quality and inquires into the quality of water, graphs could be produced to prove or disprove changes in water quality were at fault. In addition, water continuously is tested in outside labs to ensure quality.
Two backup systems were included in the initial plans for the reuse system. One is triggered in cases of contamination, the other in cases of low water. System probes were installed to detect contamination. If a contamination is found, solenoid valves are activated, which then switches the system from reuse water to virgin RO water, and line production continues without interruption.
The second is located in the RO reuse storage tank. The goal of creating the RO reuse system was to use all the water the company could collect, and it was at this point that another backup was required. When all the reuse water collected was in use, there would be no water returning to the RO reuse storage tank. With no water in the tank, the distribution pumps could run dry and fault out. To alleviate a production shutdown due to loss of water, a float was installed to measure the depth of water in the storage tank. When the float measures low water, a solenoid valve opens to add virgin RO water to the reuse storage tank.
Saving water is a nonstop effort and has become a blueprint for sustainability. As the company added more lines to the reuse system, less money was spent in the overall cost of producing the end product. When this system was being designed in 2011, the target goal was 17 gal per minute (gpm) of water saved, or 5.3 million gal annually. Seven years later, the goal is to save more than 65 gpm, or 20.2 million gal per year. When consumers and manufacturers have a desire to save money, a water reuse system can be an ecologically sound way for them to do so.