The northern suburbs of Philadelphia, Pa., include two counties – Montgomery and Bucks – which are not only among the state’s most populous but also among the fastest growing. In 2005, Bucks County-based Forest Park Water, owned and operated by the North Penn and North Wales Water authorities, began work to expand the Forest Park Water Treatment Plant in Chalfont, Pa., to accommodate the needs of its 52,000 customers in the two counties.
The Forest Park plant releases water from Lake Galena approximately three miles north of Chalfont into the North Branch Neshaminy Creek tributary, from which the water is pumped to the Forest Park Plant for treatment. This surface water supply is supplemented with water that is pumped from the Delaware River about six months per year.
Faced with increasing water consumption demands from its growing customer
base, Forest Park Water needed to double the capacity of its existing facility.
The new plant would incorporate membrane filtration along with pre-existing
processes, including pre-ozone coagulation, sedimentation, post-ozone biological
filtration, pH corrosion control and chlorination. For its chlorination needs,
Forest Park chose an on-site
sodium hypochlorite generating system, which has delivered record, never-before-validated efficiency levels.
Choosing the chlorination system
According to Wayne Letourneau, Forest Park Water’s facilities director, “We considered gaseous chlorine, bulk sodium hypochlorite and on-site sodium hypochlorite generation. Ultimately, we selected on-site sodium hypochlorite generation. It eliminates concerns surrounding the storage of chlorine gas and regulations related to transportation and storage of bulk chlorine gas. The generation of chlorate by-product that results with the storage of bulk sodium hypochlorite was an important consideration, too. And the 12-15 percent concentration solution strength of potable grade bulk sodium hypochlorite would have required the development of a Risk Management Plan and HAZMAT training. The 0.8 percent on-site sodium hypochlorite solution is non-hazardous. The only by-product is hydrogen gas, which can be safely vented to the atmosphere. The 0.8 percent solution is stable, too, and it doesn’t degrade like bulk sodium hypochlorite with exposure to ultraviolet light.”
Forest Park’s engineering firm, Gannett Fleming of Harrisburg, designed the on-site sodium hypochlorite generation and the water authorities awarded the general contract, which included two 1,200 lb/day ClorTec® generating units, to Severn Trent Services.
Three common consumables are used in the sodium hypochlorite generating process: salt, water and electricity. The system operates by feeding softened water into a brine dissolver. The salt dissolves to form a brine solution, which is further diluted to the desired salt solution. The salt solution is then passed through electrolytic cells, which apply a low-voltage DC current to the brine to produce the sodium hypochlorite. The solution is then safely stored in three 12,000-gallon day tanks. When it reaches the low-level set point, the system automatically restarts to replenish its supply.
The 0.8 percent solution generated from the ClorTec system can also be directly used and fed to the membrane elements to act as a disinfectant during routine maintenance and cleaning procedures for the membrane filtration system.
The ClorTec unit’s clear cylindrical cell allows full visibility and easy access to the electrode array. Cells can be removed as a single unit, eliminating the time and labor spent disassembling cell structures and handling electrodes individually.
Performance Guarantee
In order to maximize ratepayer dollars, Forest Park Water and Gannett Fleming used a “guaranteed whole life” approach to the procurement process, allowing each supplier to submit a bid with guaranteed efficiencies backed by a performance bond. Typically, an on-site sodium hypochlorite generating system consumes 2.5 kWh/lb of chlorine and 3.5 lbs of salt/lb of chlorine. Severn Trent has significantly advanced on-site hypochlorite generation technology through an enhanced proprietary electrode coating, which significantly reduces the consumption of salt and electricity, providing greater operational efficiency. To meet its operational efficiency guarantee at the Forest Park facility, Severn Trent provided a coating with enhancements that:
- reduced salt consumption from 3.5 to 2.34 lbs/lb of chlorine, representing a cost reduction of more than 25 percent in salt consumption
- reduced energy consumption from 2.5 kWh to 1.94 kWh/lb of chlorine – a cost reduction of more than 20 percent in power
The new Forest Park Water Treatment Plant began operation in November 2006 and operates at an average flow rate of 15 MGD, with seasonal fluctuations ranging to more than 23 MGD. The on-site hypochlorite generation system has produced more than 400,000 lbs of chlorine since it was commissioned.
With more than two years of operational data, the enhanced efficiency at the Forest Park installation represents the first time such performance has been validated, according to Ali Giti, national sales director for Severn Trent Services. “Such operating cost reductions over the life of the equipment can, in some applications, amount to hundreds of thousands of dollars,” he says. “Since the Forest Park installation, we have validated the performance of many other ClorTec installations using our proprietary enhanced electrode coating, and this technology is now available to all customers using the guaranteed whole life approach.”
Not only has the ClorTec system surpassed the performance requirements of the contract, Letourneau expresses satisfaction with the system’s design and operation.
“The ClorTec computer program makes our job easier by identifying and pinpointing the source of any operational problems. That minimizes the time we have to spend trouble shooting system problems. The ClorTec computer program makes our job easier by identifying and pinpointing the source of any operational problems. That minimizes the time we have to spend trouble shooting system problems. The lack of ongoing maintenance issues with the system has been a pleasant surprise, too. We were told we’d need to acid wash the system every six months to a year, but after two-and-a-half years, we haven’t had to perform this maintenance yet. The use of high quality salt and soft water feed into the systems has enabled us to go this far without the need to acid wash. And the installation of the ClorTec system, the training and the service made the change from gas to liquid seamless.”
For more information, e-mail info@severntrentservices.com.