Magmeters resolve wastewater overflow

Problem

During high-water events, the main wastewater treatment plant of the Greater Pottsville (Pa.) Area Sewer Authority flooded, causing combined sewer overflows to the Schuylkill River and fines from the state Department of Environmental Protection. To find a solution, the city hired the Buchart-Horn engineering and architectural firm in York. Senior engineer Bruce Hulshizer brought in Krohne Inc. to decide how to divide the sanitary and stormwater flows.

 

Solution

Krohne recommended 21 Tidalflux electromagnetic flowmeters. By partially filling them, the authority could measure normal flows, which would not fill the magmeters. Once the plant personnel knew the normal flows, they knew how much stormwater to divert during heavy rains.

The capacitive flow-level measuring system, built into the wall of the measuring tube, provides accurate flow measurements in the partially filled pipes, with levels between 10 and 100 percent of the pipe cross-section. The units were wet-calibrated by direct comparison of volumes for an accuracy of plus or minus 0.2 percent of actual value. “The flowmeters give a steady display of measured values regardless of rough product surfaces and distorted flow profiles,” says Hulshizer.

 

Result

The load on the plant was substantially reduced in high-water events, allowing it to meet the DEP consent order and protect the environment. 800/356-9464; www.krohne.com.

 

Air/gas mass flowmeter improves treatment efficiency

Problem

Plant engineers for a wastewater treatment facility near Phoenix, Ariz., needed to place airflow meters underground in a rugged area requiring remote access. The site was further challenged with straight pipe run limitations, the presence of hazardous gases, and a wet and dirty environment.

The meters had to be installed in a 24-inch line for blower airflow to the aeration basins. Accurate airflow measurement was necessary for the control system to maintain correct levels of dissolved oxygen in aeration basins and proper wastewater treatment. The meters needed to be accurate over a wide wastewater flow range based on flow rates projected to increase from 0.5 to 3.0 mgd.

 

Solution

The engineers selected the ST98 flowmeter from Fluid Components International (FCI) because of its accurate performance over a wide flow range, ease of installation, reliable performance, and low maintenance. The meter’s thermal dispersion mass flow sensing element promised the necessary performance in the harsh environment. To compensate for flow disturbances from the limited straight pipe runs, the Vortab Insertion Panel Flow Conditioner (Model VIP) was installed to ensure accuracy.

 

Result

Optimizing the aeration process by measuring and controlling the aeration system’s airflow with an accurate, reliable flowmeter significantly improved plant efficiency. The control of airflow to the aeration tanks enabled useful bacteria growth to increase together with the removal capacity for suspended organic materials.

The treatment process is now better controlled to meet peak demand processing requirements such as wet weather. The remaining water can leave the aeration secondary treatment process at least 85 percent cleaner than when it arrived. 760/744-6950; www.fluidcomponents.com.

 

Reinforcing risk management

Problem

The Trenton (Mich.) Wastewater Treatment Plant processes 4 mgd with a design flow of 6.5 mgd. Even with the extra capacity, heavy rains occasionally cause overflows into the Detroit River. In 2002, Trenton upgraded its plant and lift stations with process protection and redundancies hardware and software from Rockwell Automation. Five years later, with the city facing budget shortfalls, Rockwell offered a way to minimize maintenance costs while adding a services and support contract.

 

Solution

The main process control system upgrade featured components from Allen-Bradley. Besides ControlLogix programmable automation controllers, the FactoryTalk AssetCentre change management software ensured compliance with state disaster recovery requirements.

The plant’s power distribution system used IntelliCENTER motor control center software with Powermonitor meters. Operators monitor the SCADAsystem by redundant servers running FactoryTalk View SE human-machine interface software. It uses wireless EtherNet/IP to monitor four remote pumping stations running on PowerFlex drives. The standardized system enables Pat Raftery, plant superintendent, to run the facility with 11 operators and one electrical technician.

The services contract includes monthly visits from a Rockwell technician, staff training, access to specific area specialists, software upgrades, a fixed rate for emergency service, and unlimited, real-time Automation TechConnect support.

 

Result

When the facility’s main server failed, operators faced the risk of an overflow or process failure. A Rockwell technician quickly transferred plant operation to the redundant system, bringing remote monitoring and control functions back online within five hours. “The meltdown made us immediately aware of how dependant we’d become on our monitoring, diagnostic, and control capabilities,” says Raftery. “With the service contract, we don’t have to worry about operation failures from technical issues.” 519/244-3681; www.rockwellautomation.com.