A small but important step to improve waste water treatment plant operation

Focus on a reliable on-line centrate measurement

More specifically, the plant was looking for a reliable total suspended solids measurement of centrate water from their sludge dewatering centrifuge. Reliable information on the amount of centrate water solids is the key to process operation. The only reliable method earlier was laboratory analysis from various measurement points; however, test results took too long for online process control. The customer ordered the new Valmet LS (low solids) measurement system, initially for a two-month trial period. The successful test period ended in April 2013, and based on the results, the customer finalized their purchase order for the Valmet LS system.

Valmet LS operating principle in a nutshell

The Valmet LS device can be connected online to the process and is able to measure a continuous sample flow through the system, utilizing an integrated centrifugal pump. The device has two light sources that are measure for absorption, scattering, and depolarization as they pass through the flowing media. The Valmet LS device continuously measures the suspended solids content within a range of zero to 5000 mg/l. It also measures the entrained air index, which indicates polymer overdosing. The Valmet LS measurement system deaerates, filters, and measures process solids and has self-cleaning capabilities that keep the measurement optics clean. The measurement cell has an extremely strong sapphire glass with high optical properties. The cell and sample lines are automatically cleaned at given intervals.

Process connection

At the sludge treatment system of a plant, the Valmet LS measurement application is typically connected to measure the amount of suspended solids in the centrate water flowing out from the centrifuge. The centrifuge increases the dry solids content of the sludge from about 2% up to approximately 25% before it is pumped to incineration.

Valmet LS installed to measure centrate water solids content.

Operation experience

Based on approximately one year’s operational experience, mill personnel stressed that the reliable centrate water online measurement is very important for ensuring reliable and environmentally sustainable operation. If the centrate water solids level is within the given limits, the water will be routed to further wastewater treatment phases. Otherwise, the centrate water will be circulated back to the beginning of the wastewater treatment plant. After treatment at the plant, the wastewater is sent to the local municipal wastewater plant for final purification.

In addition to being very satisfied with both the operation of the Valmet LS device and the cooperation with Valmet’s* project team, mill people stated: “The environment is the key concern for us and covers all activity areas in our mill. This ensures that only environmentally compliant products are manufactured and the most stringent environmental safeguards are maintained during production. Valmet LS has optimized our operations, targeting minimal environmental impact.”

Summary

Being one of the key players in the chemicals industry, the customer is developing their business with a vision of sustainability. In addition to environmental benefits, the mill’s visions focus on the active promotion of sustainable development to the whole supply chain, enabling both environmental and cost advantages to consumers. The company’s commitment to respecting the environment goes far beyond the legislation laid down for the industry. One of the small but important steps in achieving the company’s sustainability targets was the installation of the Valmet LS measurement system to improve the operation of the wastewater treatment process.

*) Company and product name Metso until March 31, 2015.