Treatment and Filtration

Treatment and Filtration
Fine screen protects high-rate clarifier

Floating modular cover cuts chlorine demand

Problem

Algae blooms in the Whitehall (N.Y.) potable water reservoir caused chlorine demand and residuals to fluctuate daily. Officials looked for a way to eliminate the algae, prevent waterfowl from using the basin, reduce chlorine demand, and meet chlorine residual standards.

 

Solution

The village selected the LemTec modular insulated cover from Lemna Technologies. The company custom-built the cover to fit the basin’s irregular contours, jagged rocks along the shore, and space limitations.

 

Result:

The cover created a stable system with predictable chlorine needs and a steady output that met standards. Monthly average chlorine demand dropped from 1,692 to 760 pounds, a 55 percent reduction. 612/253-2000; www.lemnatechnologies.com.

 

Underdrains modernize water plant

Problem

The Sellersville (Pa.) Water Treatment Plant had two gravity filter basins with cast iron laterals and mono-media on support gravels. Officials wanted to modernize the basins and replace the sweep arms that agitated the media during cleaning.

 

Solution

The city chose Triton PVC underdrains from Johnson Screens. The units’ 5-inch-high profile fit into the shallow basins and provided direct retention of the dual media, saving filter height for media and eliminating gravel. The system uses air agitation for backwashing. Installation was fast and trouble-free. Workers embedded the water header in a concrete floor poured within plus or minus 1/4 inch flat to eliminate leveling or grouting of the underdrains, which were anchored in place.

 

Result:

After operators developed manual backwashing procedures, the plant went online and has produced filtered water for five years. 651/636-3900; www.johnsonscreens.com.

 

Dry scrubber retrofit brings savings

Problem

The staff at the 30 mgd Jumping Brook (N.J.) Water Treatment Plant wanted to replace a 10-year-old wet scrubber with a dry scrubber to reduce maintenance and operating expenses. The liquid caustic corroded pumps and fiberglass and reacted with carbon dioxide to form sodium carbonate, which could clog nozzles and valves.

 

Solution

New Jersey American Water officials chose the Purafil Environmental Systems Division to retrofit the plant with a dry emergency gas scrubber using Chlorosorb Ultra media. The pellets remove 15 pounds of the gas for every 100 pounds of accidentally released chlorine. Purafil technicians connected the unit to the chlorine rooms by ducts and replaced the blower to achieve higher airflow. The retrofit took two weeks.

 

Result:

“In case of a leak, the wet scrubber would have discharged 1 to 4 ppm, but the dry unit will discharge less than 25 ppb,” says operations supervisor Brian Weir. “We also saw immediate savings on maintenance, disposal, and labor totaling more than $25,000.” 800/222-6367; www.purafil.com.

 

Activated carbon keeps water sweet

Problem

The United Utilities Cowm water treatment facility within the Watergrove Water Treatment Plant at Wardle, U.K., needed to add powdered activated carbon (PAC) to neutralize geosmin in the water drawn from the Cowm Reservoir. Geosmin, an organic compound produced by microbes and algae, gave the raw water a harmless but undesirable earthy taste and aroma.

 

Solution

Spiroflow Systems won the bid to install a buffer hopper incorporating high- and low-level probes feeding PAC into an ejector. The dosing system has a Type 6 bulk bag discharger with an integral hoist on a runway beam for easy loading of the PAC bags into the discharger. A flexible screw conveyor transfers PAC from the discharger to a volumetric metering feeder with a buffer hopper on top.

The conveyor transfers PAC to a second buffer hopper, maintaining a constant head of material above a Transvac venturi ejector. The ejector draws PAC under vacuum and meters it into a bypass water stream to form a slurry, which mixes with the main water flow into the water treatment plant.

 

Result:

“We had an initial problem caused by unexpected clumps of PAC that Spiroflow quickly remedied by fitting a vibrator to the collection hopper,” says Darren Glover of GCA, an alliance of contractors. “The system has worked well ever since, putting an end to our geosmin problem.” 704/291-9595; www.spiroflowsystems.com.

 

Fine screen protects high-rate clarifier

Problem

The City of Clovis, Calif., in the agriculturally rich San Joaquin Valley, is dedicated to planned growth while retaining its western atmosphere. The city’s population has more than doubled since 1975, to about 90,000, and the city encompasses 19.9 square miles. The water treatment process includes an ACTIFLO high-rate clarifier, which needed a barrier algae and particles larger than 1/4 inch, to ensure proper operation.

 

Solution

In phase II of the city’s Surface WTP project, John Meunier Inc. supplied an ESCALATOR perforated fine screen able to remove all solids above 0.236 inch.

 

Result:

The screen was installed in an 8-foot, 8-inch-wide by 8-foot-deep channel, handling a peak flow of 30 mgd. The screen continues to exhibit its flexibility in this potable water intake application. 855/564-3747; www.johnmeunier.com.



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