Aerial view of the Watertown WWTP
5 Hz increments across a range from 5 to 60 Hz. The screenshot in Figure 2 illustrates how the system works. The pump speed, in green, is maintained at a minimum level until the orthophosphate (OP) concentration, in blue, rises above the programmed 0.7 mg P/L setpoint. Pump speed increases until the OP concentration peaks and starts to decrease. Pump speed returns to minimum speed again when the OP concentration falls below the setpoint.
Figure 2 - Phosphorus Removal System Monitoring and Control System Operation
phosphorus will take place, they can decide where to install the monitoring system. Most of our customers choose to remove phosphorus with the WAS and locate the P700 IQ analysers downstream to ensure adequate phosphorus removal.
“ In the simplest implementation of the control system the IQ Sensor Net system sends a proportional 4 to 20 mA signal to the customer’s SCADA system, or directly to the feed pump, to control chemical based on feedback from the orthoP analyser,” he adds. “A feed forward control system calculates the required chemical feed rate based on upstream orthophosphate concentration and measured wastewater flow. The IQ Sensor Net can easily be
programmed by the customer, providing the flexibility to tailor the chemical dosing to the demands of the specific plant design and wastewater characteristics.”
At the Watertown WWTP, orthophosphate measurements from a P700 IQ are taken every 15 minutes and fed into software that was custom-developed for Watertown by Starnet Technologies. Using records dating back to 2003, -when the Watertown facility was commissioned, Freber and the software team correlated historic orthophosphate, ferric chloride and final total phosphorus levels to build an algorithm to govern chemical inputs. The system reacts to readings from the P700 analyser by adjusting pump speeds in
“Once we got the program set up so the actual orthophosphate readings meant something to run the ferric chloride pumps, it was easy,” says Freber. “It just walks itself up and ramps itself down. It’s just ‘set it and forget it,’ and we’ve got the comfort of knowing we won’t be exceeding our 1 mg TP / L limit.”
Great Fit
The IQ Sensor Net P700 IQ helped the Watertown team in more ways than one. Their community of 24,000 residents prides itself on its state-of-the-art, eco-conscious wastewater treatment facility, whose dewatered biosolids “cake” is applied on farms nearby.
“The investment in automating phosphorus management paid for itself quickly,” says Freber. “This is huge, and not just for my budget. I sold the concept because we’re using so much less chemical.”
The City of Watertown Wastewater Treatment Plant Settling Tanks
Author Contact Details Steve Werblow & Xylem Analytics • Email:
analytics.asia-pacific@
xyleminc.com • Web:
www.xylem-analytics.asia
ERACHECK ECO Eco-Efficient Oil-in-Water Testing
Ecology meets economy in ERACHECK ECO by combining an advanced optical filter-based measurement technique with the ecologically safe extraction solvent cyclohexane. The use of a cost-efficient measurement technology in combination with the low-cost solvent cyclohexane gives you the most economical oil-in-water tester available today.
Adding ERACHECK ECO to Eralytics’ product line is a huge step towards a cleaner environment. But let’s take a look at the big picture and start from the beginning: In 1989 the Montreal protocol decided to forbid all CFC solvents by 2020 at the latest due to their harmful effects on the ozone layer. These types of solvents were used to measure one ecologically important parameter called oil-in-water – a closely monitored value to decide if waste water or discharge water shall be allowed to be disposed as is or if it needs to be further purified to be safe for the environment.
After 1989 the US Environmental Protection Agency (EPA) switched from the previous IR method ASTM D3921, which used a CFC solvent, to a gravimetrical method called EPA 1664B. In Europe people shifted to gas chromatography using method ISO 9377-2. Both techniques suffer from several drawbacks in comparison with the IR methods. They are less repeatable and more time consuming.
There was and still is a need for an easy-to-operate measurement technique which offers all the advantages of the IR methods but without the need for a CFC solvent such as Freon 113. ERACHECK PRO was the first oil-in-water tester released by eralytics in 2008 to offer that. It uses a high-end quantum cascade laser light source which allows measuring extracted oil in the ecologically friendly solvent cyclohexane with highest precision in the low sub-ppm range. Quantum cascade lasers are highly efficient, but on the downside, they are also a pretty costly technology. So eralytics engineers looked into finding a measurement technique that was considerably more cost-efficient, without compromising on the benefits of ERACHECK PRO.
In hindsight we can say that this was no easy task at all. But we succeeded in building an instrument based on optical high-tech filters which can measure oil-in-water down to a concentration of 0.5 mg/l. We call it ERACHECK ECO. It still uses the eco-friendly solvent cyclohexane and is the most economical highly precise analyser available on the market today.
Naturally, we continue to offer ERACHECK PRO, because it reaches an even lower limit of detection and it tops the ERACHECK ECO regarding instrument repeatability. Therefore, the PRO model remains the instrument of choice for specialised high-end applications, whereas ERACHECK ECO is designed to be the new sturdy workhorse for oil-in-water testing.
Upgrade your oil-in-water testing to the next level in terms of precision, ease of use, measurement speed and environmental friendliness with ERACHECK ECO.
43707pr@reply-direct.com
For More Info, email: email:
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www.envirotech-online.com AET October / November 2017
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