Under an administrative order from the Florida Department of Environmental Protection, the City of Palm Coast Utility Department faced important decisions in developing a water treatment process compliant with its discharge permit.

From 1992-2014, the Palm Coast Water Treatment Plant No. 2 discharged concentrate from its nanofiltration process to the Royal Palms Canal through the use of an extended mixing zone under a Discharge Monitoring and Reporting permit. 

In 2008 the state Department of Environmental Protection eliminated the use of the extended mixing zone, which meant the plant could not meet certain water-quality parameters without dilution of the concentrate. The DEP gave the city 48 months to design and implement an alternate concentrate management system and stop discharging to the canal.

After carefully researching numerous technologies and options, utility leaders decided on a zero liquid discharge (ZLD) process based on membrane ultrafiltration of the concentrate stream. The result has been optimized water production and conservation.

In putting the new plant into service, the operations team experimented, explored, leaned on each other, drew on external resources, and learned by trial and error how to function more efficiently and continuously improve water quality. In 2020, the plant received the Outstanding Membrane Plant Award from the Southeast Desalting Association.

Drawing from underground

The Palm Coast Water Treatment Facility was built in 1992 as a nanofiltration plant with two filtration trains that produced 2.4 mgd. In 2004, two more trains were added and other upgrades made to achieve 6.4 mgd capacity.

With the zero liquid discharge facility, built in 2015, the plant now has 7.6 mgd capacity and produces an average of 2.8 mgd. Serving the City of Palm Coast, the distribution system includes about 600 miles of mains; three water plants are joined to the same system, allowing flexibility to take a plant offline for maintenance while continuing service to customers.

Plant No. 2 uses groundwater from the Upper Floridan Aquifer; a confined surficial well field serves plants No. 1 and No. 3. Two elevated tanks store a combined 1.15 million gallons.

To the membranes

The first treatment step is an automatic-set backwashing sand separator (HYDAC Technology) that removes particles down to 25 µm. The water then goes through Graver Technologies HVV melt blown cartridge filters to remove particles down to 5 µm. From there, pressure on the inflow is increased from 40 psi entering the plant to more than 120 psi to push it through the nanofiltration membranes (Hydranautics). Within each of the nanofiltration four trains are 189 membranes. The crossflow filtration process separates the water into permeate and concentrate streams.

The nanofiltration process removes particles down to 0.001 microns. The resulting water has a low pH (5.4) because of dissolved gasses such as carbon dioxide and hydrogen sulfide that pass through the membranes.

The first pass of pH adjustment is through two DeLoach Industries degassifiers. A dense media pack separates the water and gas molecules, and a large blower forces the gases out to the atmosphere. Degasification increases the pH to 7.0. Sodium hypochlorite and ammonium sulfate are added for disinfection. Sodium hydroxide is added to raise the pH to between 8.0 and 9.0 to make the water slightly scale-forming entering the distribution system.

Palm Coast decided to convert the concentrate (water containing substances removed from the raw water) to drinking water through a ZLD system comprised of lime softening, stabilization, ultrafiltration, disinfection and lime sludge management using a dewatering belt press. Enhanced lime softening significantly reduces total hardness, TOC and alkalinity in the concentrate.

Lime is added to increase the pH to 11.0. This enables precipitation of both calcium and magnesium to help reduce the total hardness to about 150 to 200 ppm (from 1,200 ppm). Sulfuric acid is added to lower the pH to the range of 8.5, reducing the scaling potential of the softened water. The water then goes through ultrafiltration using four skids of 96 inside-out flow Aqua-flex 55 UF modules (Pentair X-Flow). The process reduces turbidity to less than 0.15 NTU. The flow is then disinfected with chlorine. The treated concentrate is blended back with the permeate into a 2-million-gallon tank.

Setting up this complex system to run smoothly presented many challenges for the operators, none of whom had direct experience with a ZLD system. Today, the system recovers 98.5% of the source water.

“The ZLD system has been almost like adding another well to the system,” says Fred Greiner, chief plant operator. “Instead of discharging the concentrate to the canal in the past, we’re able to recover almost all the water that would normally be discharged, and it could be considered an alternative water supply.” Although the ZLD process required raising rates, its efficiency stabilized costs so that rates are unlikely to increase again in the near future.

Tenacity and testing

Greiner attributes the plant’s success to his staff members, who have come up with many ideas to improve performance and water quality. “We have a small team but they are mighty in their innovation and willingness to look for new solutions and experiment,” Greiner says.

Case in point: operator Robert Nelson found an inefficiency in the plant’s lime slaker, which was running on system pressure and would vary water flow and lime slurry concentration based on pressure differences. With a little research, he learned that changing out and adding some valves to create an automated control loop would give a consistent flow rate, eliminating the use of a booster pump. The change saved more than $100,000.

Rounding out Greiner’s team are operators Grant Newlin, Antonio Myers, Tom Williams and Anna Patrick, along with mechanical technicians, Kevin Karcher, Tristan Wilson and Eugene Warmoth. 

Taking the challenge

The ZLD process was challenging for a team familiar with the previous multimedia filters using sand and anthracite. The self-backwashing membrane filtration process uses a wider variety of valves and variations of flow rates, and its many moving parts must be constantly monitored.

“To bring this process on board, to train the staff and have them become incredibly capable of understanding and operating it so efficiently and rapidly, speaks volumes to their abilities to learn and work as a group,” Greiner says.

Nelson began to focus on trending. Although the chemical processes are automated, the probes and other items must read properly, and operators need to understand what each component is doing in relation to the rest of the system.

While Greiner was developing a daily report that encompassed everything within the entire facility, Newlin and the operations staff focused on operations and training and understanding how each process worked. Meanwhile, Karcher and the mechanical staff members focused on maintenance.

When they all felt comfortable with their level of knowledge, they would get together and share experiences to make sure everyone was on equal footing and armed with all necessary information. They continue to share ideas on how to expand their knowledge and look for process improvements.

Without the benefit of manufacturer-supplied training, the operators were largely self-taught. They were able to experiment and document findings along the way to determine which processes and maintenance methods were optimal. For example, Karcher and Newlin rerouted the belt press water into the lime sludge thickener instead of an equalization tank, reducing lime sludge maintenance cleanings from every two weeks to annually. 

“We are still learning; we’re learning every day,” says Greiner. “We read studies from different organizations, and if something looks interesting, we will try to replicate what others are doing in the lab. After that, if it makes sense, we consider incorporating it. We will always be learning and experimenting.”

Making it fun

Greiner and his team quickly saw that by working together and capitalizing on each other’s talents, regardless of certification or education level, they could make the plant run at peak efficiency and have fun doing it. They constantly optimize the plant, finding ways to improve water quality and reduce costs.

One recent experiment was a pilot project on aeration for the softening basins. The objective was to optimize THM removal. With help from CPH engineers, they had some success and hope to finalize a design and implement it soon.

Another project is looking for ways to remove ammonia from the concentrate, as it creates huge chlorine demand. Team members hope to try a conversion process they learned about in a recently published online study. If successful, it could save about $30,000 per year.

“Never look at a problem as a problem, but as an opportunity to learn and improve your process,” says Greiner. “There are no unsurmountable challenges, just chances to learn something new and different.”