Plant allows Alliance to treat two water sources
When Alliance, Ohio, decided build a new water treatment plant to replace an outdated facility, it looked for an affordable design that provided a flexible treatment process. Flexibility is critical because the city relies on two surface water sources, the Deer Creek Reservoir and the Mahoning River. Having two water sources is a major advantage, but the challenges of developing a treatment strategy for both can be difficult.
Finkbeiner, Pettis & Strout, Akron, Ohio, designed the new 10-mgd plant using proven technology and conventional equipment in an unconventional manner. Water can flow through the plant’s reactor basins and circular flocculation clarifiers in a parallel fashion or can snake through in series form. Two treatment basins, each 100 feet in diameter, house the flocculation clarifiers. Since the basins are covered by aluminum domes, operators do not have to contend with icing.
The dual media filters at the plant are arranged in a cluster arrangement that costs less to construct than do the long piping galleries common in most plants. The simultaneous use of both air and water to backwash the filters results in a “cleaner” bed.
A wall inside the plant’s clearwell divides it in half through the use of baffles in each section that force incoming water to travel along the wall, thereby minimizing short-circuiting and allowing optimum disinfection. The disinfection concentration/contact time requirements can be met year round, even with half of the clearwell out of service.
Different locations for the feeding of chemicals like potassium permanganate, chlorine and chlorine dioxide give operators more flexibility in treating seasonal tastes and odor or short-term iron and manganese spikes. Combined with multiple series and parallel flow paths, the Alliance plant permits differing treatment techniques depending on the dual source raw water quality.
“As I see it, the foremost advantage of the design is the flexibility of the plant,” says James Butler, supervisor of the plant.
“Provisions for additional treatment processes that we are anticipating to be future requirements, such as ozonation and enhanced coagulation, have been incorporated into the hydraulic design of this plant,” he says.
Since 1993, when the plant opened, Butler and his staff have been experimenting with different chemical combinations and flow schemes. The chemicals tested have varied from conventional coagulants such as aluminum sulfate to low-pH acidulated coagulants.
Historical records of all plant processes, alarms and associated events are automatically recorded by the plant’s computerized distributed control system. The system monitors and controls the entire plant and four remote locations, logs daily plant operations and maintains extensive documentation on the performance of the plant.
Staff operators maintain additional records of the results of their experiments. Using these files as a reference point, Butler and his staff keep track of different treatment scenarios, along with the results these treatments produced.
Although not every chemical and process combination is successful with the same water quality conditions, having an historical point of reference has helped the staff explore and document the many different treatment options available.
After a period of time, plant managers plan on compiling a report with suggested treatment options for different circumstances, providing a long-term treatment strategy for varying raw water conditions.
“Regulators understandably look more closely at the quality of treated surface water in comparison to groundwater because of the volatility,” Butler says. “The regulations that we are required to meet today are a lot tougher than the requirements we had to meet just six years ago, [and] we expect regulations in the future, particularly with regard to total organic carbons and disinfection byproducts, to be much more stringent.”
Several cost-saving measures were incorporated into the design of the $12.6 million plant. For instance, although the new plant is located on a different city-owned site than the original plant, engineers made use of an existing 10,700-foot raw water transmission main. Also, the clearwell from the original water treatment plant was reused as a raw-water pump suction well.
The plant received the 1995 Ohio Outstanding, Civil Engineering Achievement Award from the Ohio Council of Local Sections of the American Society of Civil Engineers. Alliance is now using the plant as a marketing tool to attract new industries to the city.