Expanding for Quality

A Florida water plant operations team steps up with extensive training to master a new advanced nanofiltration and reverse osmosis process
Expanding for Quality

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The upgraded Norwood-Oeffler Water Treatment Plant in North Miami Beach, Fla., is unique in many ways. It is the first in the county to tap the brackish Floridan Aquifer and desalinate the water for drinking.

It is also one of the few plants in the country to use the latest nanofiltration (NF), reverse osmosis (RO) and traditional lime softening technologies. The plant blends and tests five different streams before distribution.

The plant started planning for the upgrade in 1997 with a feasibility study. This was followed by a small pilot system and a rigorous training program for operators during and after construction. Started up in December 2007, the new process created challenges for the plant’s 14 operators, who are continuously learning about the equipment and making adjustments.

Despite the system’s complexity and the operators’ learning curve, the plant won the 2010 Class A Outstanding Water Treatment Plant award from the Florida section of the American Water Works Association.

 

More independence

The second largest in Miami-Dade County, the Norwood-Oeffler plant serves 32,800 metered connections in North Miami Beach, Golden Beach, Sunny Isles, Miami Gardens, Aventura, and a portion of Northwest Miami-Dade, with a total population around 180,000. The plant also provides water to Sun Life Stadium, home of the Miami Dolphins, Florida Marlins, the University of Miami Hurricanes, and the Orange Bowl.

The original 16 mgd traditional lime softening plant was built in 1949, purchased by the City of North Miami Beach in 1957, and expanded in 1957 and 1970. To meet demand, 12 to 14 mgd of finished water was purchased from the Miami-Dade Water and Sewer Department. Raw water was sourced from 12 Biscayne Aquifer wells with a total capacity of 27 mgd.

“In the late 1990s, we decided to be more independent and stop buying water from Miami-Dade,” says Dr. Jeff An, assistant director of public services for North Miami Beach. “To serve all our customers with our own water and provide superior quality, we began an expansion program to increase capacity from 16 to 32 mgd.”

 

Advanced technology

The city operated an NF pilot system at the plant before deciding to add membrane technology to the existing lime softening process. To supplement Biscayne Aquifer water, the city added the brackish Floridan Aquifer to supply the additional 40 percent of raw water required to meet demand.

“After the engineering firm conducted feasibility studies on enhanced lime softening or membrane treatment, we chose membrane treatment to comply with the more stringent regulations we knew were coming,” says An.

The initial capacity of the membrane treatment system is 15 mgd. That includes 9 mgd of NF and 6 mgd of RO treated water. The membrane system can be expanded to 20 mgd with an additional 3 mgd NF train and an additional 2 mgd of RO membrane.

The plant switched from gas chlorine to liquid chlorine disinfection, constructed a lime sludge gravity thickener (WesTech) to replace the wet pond and dry pond system for lime sludge treatment and disposal, and replaced two 1-million-gallon storage tanks with one 5-million-gallon tank. Air-stripping units were added to the lime softening process to treat volatile organic compounds (VOCs).

Biscayne Aquifer water is pumped to sand separators (LAKOS) and adjusted for pH. An antiscalant is added, and the water passes through microfilters (Parker Hannifin). Then it is pumped via high-pressure pumps (Afton) to a two-stage NF system (Hydranautics membranes). The concentrate goes to a 3,400-foot deep injection well.

Raw water from the Floridan Aquifer undergoes the same treatment, but without the sand separators step, and with RO (Hydranautics membranes) instead of NF. An energy recovery device installed in the second-stage RO system boosts the second-stage pressure without pumps. The RO concentrate is also sent to the deep injection well.

The permeate flows from the NF and RO membrane processes are combined for post-treatment and stabilization and blended with finished water from the existing lime softening process and the filtered raw water blend. Blended finished water is transferred to a new 5-million-gallon tank and existing 2-million-gallon ground storage tank before delivery to the distribution system.

To save energy, the high-pressure pumps are equipped with variable-frequency drives, and the plant uses new energy-saving lighting.

 

Learning curve

Learning about membrane technology and a more sophisticated SCADA system created major challenges for the operators. “There was a big learning curve and a lot of training involved,” says water production manager Pat Mitchell. “For example, the SCADA system we had before was very limited and was basically only able to turn the wells on and off. Most of the operations were manual.”

Before the pilot system was installed, the city hired an engineering company to train operators on membrane treatment theory and operation. Once the pilot system was online, the operators were able to see the equipment. During construction, they received hands-on training from the contractor as the pieces of equipment were installed.

Although the city started recruiting operators with experience in the new processes, most of the operators were trained on the job. Says Mitchell, “Some people learn quicker than others, and those that did trained their co-workers.”

An recalls, “There was an operator shortage in Florida at the time, so we had open positions for a while. With the old plant, we had 10 operators. The new plant operates 24/7, and since there is now a lot more equipment to operate, we need at least two operators on site, including the evening and weekend shifts.” The plant ended up hiring four new operators and started a training program to help them pass their Class C certification test — a basic requirement.

“Change is hard,” says Mitchell. “We recently added a new batch slaker (RDP Technologies) and slurry pumping system to the lime treatment system. Initial training and startup went well, but as we adjusted to the new routine and fine-tuned the new system, we found we needed to do refresher training on hydraulics and flow. Applied math is one of the hardest things to learn; we reduced the math to filling out a form and added it to the routine.”

Operators are active in the Florida Water and Pollution Control Operators Association (FWPCOA), the AWWA Florida Section, and the South East Desalting Association (SEDA). They attend meetings for continuing education credits and to network with their peers.

 

Complex permit

Among other permits, two critical ones are required for the new plant: a water use permit from the South Florida Water Management District (SFWMD) and a Class I injection well permit for membrane concentrate disposal from the Florida Department of Environmental Protection (FDEP).

The water use permit allows 26.31 mgd to be taken from the Biscayne Aquifer and 12.07 mgd from the Floridan Aquifer. The plant must produce the first 4 mgd of water from the Floridan Aquifer and monitor saltwater intrusion with 16 monitor wells installed throughout the water system, mostly east of the well field. Operators monitor the water table level and chloride levels monthly and report data to the SFWMD quarterly.

To meet the injection well permit, the plant must continuously monitor the well pressure and injection flow rate. Operators test the water to be injected monthly for TDS, chloride, specific conductance, TSS, ammonia nitrogen, TKN, pH, sulfate, and field temperature. They also test annually for primary and secondary drinking water standards. To monitor radionuclides, the gross alpha (pCi/L) is tested quarterly.

“We have to follow the same requirements for the concentrate disposal as wastewater plants do,” says An. “We negotiated with the county to use the sewer system as a backup when the deep injection well needs maintenance or repairs. This has saved us a lot of money, since otherwise we would have had to build another deep injection well at a cost of $5 million just for construction.”

 

Future considerations

Meeting permit requirements will always be a challenge. “We have to produce an average of 4 mgd from the RO system, and in a few years we will need to increase the NF recovery from 80 to 85 percent,” says An. “In the future, we may have to reuse the concentrate.”

The city is thinking about its next upgrade, this time to the lime softening system, which is old and inefficient. As for another capacity expansion, the city doesn’t see that happening unless the area experiences substantial economic growth.

Mitchell advises other plants considering upgrades to embrace change and plan ahead for what’s coming. “Surprises are not good,” he says. And, for those who have just gone through an upgrade, An stresses systematically running through a process and tweaking it until it’s right: “It’s all about working smarter, not harder.”



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