Location: City Corporation, Russellville, AR

Engineers: Garver, USA

Written by:    Michael Donn, Force Flow

The Water Treatment Plant in Russellville, Arkansas, is operated and maintained by City Corporation. It rests on the edge of Lake Dardanelle, just about 100 yards from the dam that separates the lake from the beautiful Illinois Bayou. The issue arises with the public access for fishing, allowing people within 20 yards of the water treatment facility. With the heightened security awareness of the world we live in, the staff of City Corporation realized that chlorine gas could possibly be a safety concern for the personnel at the Water Treatment Plant, as well as for the general public in the surrounding area. After researching alternative disinfection methods, Sodium Hypochlorite was determined to be the best solution.

Like buying orange juice and detergents, water treatment chemicals are almost always less expensive to purchase in higher concentrations. Unfortunately, this introduces a new set of issues to deal with. Sodium Hypochlorite degrades rapidly with heat, sunlight, and time. Also, feeding high strength Hypo into process water can create problems for the water treatment operator. These problems may stem from things like extremely low feed rates, chemical off-gassing, hard process water and safety or regulatory concerns in handling high strength chemicals. An innovative engineer, along with the progressive staff of City Corporation, set out to solve these problems with a chemical dilution system that met both their budget and design criteria.

The Project
Early in 2005, City Corporation contracted Garver Engineers in Little Rock, AR to design a Sodium Hypochlorite facility for their main water treatment plant. Garver Project Engineer, Kyle Breckenridge & Senior Project Manager Ron Pierce, teamed up with key personnel from City Corporation, Craig Noble, General Manager, Larry Collins, Operations Manager, and Jonathan Shipley, Lead Operator, to create a state of the art water treatment facility, that would meet the current and future needs of City Corporation. The end product of this collaboration was a safe, reliable and cost effective Sodium Hypochlorite dilution and feed system.

Safety & maintenance concerns from using high strength Hypo (12% Sodium Hypochlorite)
Garver knew that chemical suppliers typically deliver Hypo in the range of 12-12.5% chemical strength. Although it is far more cost effective to purchase this chemical in the higher strengths, Hypo degrades rapidly when stored in high strength. The degradation rate that Hypo would experience during the hot Arkansas summers, was something that needed to be addressed. Considering the degradation issue, as well as the safety concerns Garver and City Corporation had about operating and servicing a chemical feed system with high strength Hypo, a creative solution was needed. It was therefore decided to feed low strength Hypo in the range of 6% concentration, or less.

Buy chemicals, not water
In order to feed low strength Hypo, City Corporation had three choices:

(1) purchase low strength Hypo which is mostly water

(2) manually dilute high strength Hypo when it arrives on site

(3) devise an automated chemical dilution system to reduce the Hypo strength on site.

Option (1) (buying diluted Hypo) was quickly disregarded when they realized that purchasing pre-diluted chemical would be far too costly due to the transportation costs for shipping a product that is mostly water. Option (2) (manual dilution) was disregarded because it was labor intensive, could potentially produce inconsistent results, and would further expose operators to the dangers of high strength Hypo. It was therefore decided to go with an automated dilution system.

The system
As built, the system has two 5250 gallon tanks for storing the Hypo as it comes off the truck. This Merlin Dilution System (MDS-500D) utilizes a 500 gallon dilution tank, and is capable of creating approx. 1500 gallons of dilute per hour. After the Hypo is diluted it is pumped into one of nine 5250 gallon tanks to be stored until needed. With the current storage capacity of over 47,000 gallons, they have the equivalent of over 23,000 pound of liquid chlorine available. At the present time this facility has the ability to treat over 19 MGD.

Weight based batching system
Having used weighing systems to monitor chemical tanks in the past, Garver Engineers knew that a weight based system would be extremely accurate and reliable. They therefore contacted Force Flow Inc in Concord, CA in regards to providing a weighing system and controller that would allow Hypo and water to be automatically batched into a dilution tank by weight.

The most important design criteria were:

(1) Diluting the Hypo in a short period of time, so that it would not begin degrading in the heat of the summer.

(2) The ability to dilute an entire truckload of 12% Hypo with the push of a single button.

(3) The ability to accommodate different starting and ending solution strengths,

(4) System accountability through inventory control and process alarms

(5) Accuracy and consistency of the diluted chemical strength

(6) Safety & Redundancy in the event that the dilution system should fail.

Any strength at the touch of a button
With prior experience in designing dilution systems, Force Flow was able to accommodate all of City Corporation’s needs through some minor changes to existing hardware and software. Force Flow’s Merlin Dilution System automatically calculates the necessary amounts of water and Hypo based on the chosen beginning and ending chemical strengths. The system was designed for the operator to easily accommodate different “neat” (beginning) Hypo strengths at will. If City Corporation changes chemical suppliers or if their current supplier changes the strength delivered, they can easily accommodate this at the touch of a button. Additionally, it is just as easy to change the diluted (ending) strength of the Hypo. If process conditions change or the operators need to fine tune what strength is easiest to feed to their water stream, they can do so at the touch of a button. Another benefit to this flexibility is the fact that they can keep their metering pumps operating in their “optimum” range simply by adjusting the chemical strength.

Inventory control & process alarms
Because many state and federal agencies require the tracking of chemical usage, detailed accounting was extremely important. By tracking nine different variables such as chemical usage, feed rates and remaining chemical quantities, the Merlin dilution controller is able to give City Corporation a full accounting of their chemical feed and dilution process. In addition, by tracking throughput and using timers to track the dilution process, six different process alarms give operators early warning of potential problems with their Hypo feed system.  Remote monitoring of chemical feed rates and remaining chemical supplies is accomplished through 4-20ma signals back to the operators control room.

Conclusion
City Corporation’s concerns about chemical degradation were alleviated through feeding a low strength Hypo solution. By devising an automated onsite chemical dilution system, they were able to avoid the cost of purchasing pre-diluted chemical, eliminate the operator contact with high strength chemicals, as well as the labor and safety concerns that manual dilution would demand. They also avoided potential maintenance problems due to scaling and off-gassing. They also have the added features of integrated inventory control and process alarms to make their system safe and reliable for many years to come.

Noteworthy accomplishment
Garver received the prestigious ACEC of Arkansas Engineering Excellence Award for Water and Wastewater for the Sodium Hypochlorite Facility, in Russellville, Arkansas.

Michael Donn is the Manager of Product Development for Force Flow Inc. in Concord, CA. For more information on this case study or other chemical dilution systems, he can be contacted at 800-893-6723 or michael.donn@forceflow.com.