Nov 12, 2015
A Canadian city with a population of about 95,000 operates an 80 million liter/day capacity wastewater treatment plant which discharges clean and UV sterilized water to the local river.
Product: Valmet TS Total Solids Measurement
Customer: Canadian city
Measurement Application: Feed to gravity belt thickener (GBT)
A gravity belt thickener (GBT) dewaters excess waste activated sludge from secondary clarifiers before pumping the thickened sludge to anaerobic digesters. Before the Valmet meter was installed the dewatering of the GBT was managed by operator feel and manual polymer control based on occasional lab sampling. The operators overdosed polymer to overcome process upsets. Since the process required frequent operator intervention and maintenance the costs of chemicals and labor were high, and a cost reduction was called for.
Once the Valmet TS meter was installed and calibrated on the GBT feed, the new continuous solids measurement was used to troubleshoot problems and dewatering process weaknesses. The customer reconfigured controls for the waste activated sludge (TWAS) level control tank and polymer pumping and mixing. The problems were solved with the aid of Valmet’s representative. With the process problems solved, the Valmet TS meter reading now controls a variable speed pump on the polymer dosing system. This automatic control avoids the previous overdosing with manual operation.
The plant operation staff reports that polymer savings are at least 25% and maybe more - at least $25,000 CDN per year. Additional costs savings include a stable process and almost no additional maintenance on polymer mixing and dosing equipment and tank level pumps. The ROI is less than 6 months, and will generate around $40,000 CDN per year in maintenance and chemical savings.
The customer reports, “Our project was to automate injection of the polymer dosing in our gravity belt thickener system. A key part of that was to read a solids measurement of the TWAS output using a Valmet TS meter. The first critical step was to learn how to properly configure and apply the meter to our application. Once that was accomplished we were able to begin continuously monitoring and trending a reading of the solids ratio in our TWAS. Over time it became apparent how badly out-of-tune our polymer batch mixing and injecting equipment really was. It took months of trial and error to finally correct the multiple problems in our batching and injecting equipment.
|Polymer dosing is now controlled by Valmet TS
Throughout that process, the Valmet representative stood behind their product and provided fantastic customer support with advice, analysis and experience from previous installations.”
He adds, “We now have a system that is running with far greater performance and stability. We have reduced our polymer usage now that we are properly controlling the mixing, dilution and injection of the polymer; things that were simply not possible before the installation of the Valmet TS meter.”