A chat with Larry Wilt of American Water/ Tolt Water Treatment Plant in Seattle, WA
Drinking water treatment plants are constantly challenged to manage coagulation chemicals as they strive for the precise dosage to enable a stable floc to form. The chemicals are critical to the filtration process, whether it is a convention floc/sed system or direct filtration, including membrane filtration.
Chemicals are expensive and account for a considerable amount of a plant’s operating budget, so their oversight can significantly impact the efficiency, operational bottom line, and overall performance of the plant in response to its local demand.
After installing Zetasizer WT, we reduced the cost of producing water by $4.65 per one million gallons. When you produce more than 16,900 million gallons annually, that is quite a savings. Our savings were enough to pay for the Zetasizer within the first year of operation
Larry Wilt | American Water/ Tolt Water Treatment Plant in Seattle, WA
While traditional methods of coagulant dosage management are falling short of providing operators what they need to control the process and minimize expenses, Industry 4.0 is enabling real-time data at the control center to make better decisions and reduce overall costs.
We spoke with Larry Wilt of American Water, who manages the Tolt Water Treatment Plant in Seattle, WA, about using Malvern Panalytical’s Zeta Potential (Zp) analyzer. Mr. Wilt started his water treatment career with American Water in 1992 in New Mexico where he worked as a meter reader before being promoted to operations. After obtaining his water treatment certification, he moved to Washington in 2003 and worked as plant operator at the 120 MGD Tolt Water Treatment plant where American Water has a contract with the city of Seattle. In 2011, he was promoted to manager.
Malvern Panalytical has long been promoting the use of Zeta Potential (Zp) to better understand the effect of the coagulant dose used in pre-treatment processes to enable a floc to form and allow filtration to work efficiently.
As a technology, zeta potential (Zp) is a first principle measurement technique of the particle charge, reported in mV. Raw water particles are typically in a Zetasizer range of -15mV to -25mV. A good floc can form in the zeta potential range of -8mV to +3mV. Adding coagulants (which are positively charged) neutralizes the repulsive (negative) charge of the particles in the raw water and enable a strong floc to form.
We have a big swing in water temperature between summer and winter. During the summer months, the plant would produce high-quality water, but during the winter months when the water can drop down to 4⁰ C, we were having a hard time keeping the turbidities down and the chemical taste was apparent. Without zeta potential, it was guesswork and experience.
Testing was done on a daily basis; the seasons play a big part of chemical dosing and weather also could bring in higher raw turbidities.
The only method we used in the past were streaming current meters.
The meters were hard to use for us because of the changing of flows, they were reliable only to let us know if there was a pump failure. We were not able to know if the chemical dose was correct and did not have them set up to adjust the chemical dosage.
After hearing about the Zp and going to other plants in the area, we decided to rent one to see how well to would work for us. It was like day and night; we were way over-feeding chemicals during the winter months. It was a no brainer, we had to get one.
Our raw particle count can be very low during the summer and quite high during the late fall rainy season. The lower the particle count the lower the chemical dose.
The Zp works in a much easier way, once we found our sweet number, we just adjust the chemical dose to keep that number in the range we know works best.
We do a monthly check on the Zp standards and clean the hoses, replace pump on a quarterly basis.
We do not have to adjust our chemical dose very often, normally it is in the late spring and late fall.
In the past over feeding did no good, just wasted product. The cost of over feeding is a big factor in the reason of the Zp.
We are unable to do jar testing at this plant. The way it is designed and the addition of ozone at the beginning, addition of lime later in the process makes it difficult to see what is to happen and when.
We have dropped our chemical dose during the winter by 1/3.
Our chemical dosing has dropped off tremendously since the Zp has been in place. Streamlining chemical doses and cost savings are the biggest value the Zp has done for us. The savings paid for the meter in the first 9 months.
There is a100 percent difference when dealing with ‘storm event’ issues. We used to fight with trying different doses and now we just adjust the chemical dose until our desired ‘Zp’ number is correct.
Big chemical savings and better chemical dosing.
We have convinced corporate that all new facilities need a Zp and it will drop chemical cost and time. We have the data to back this up in chemical cost and SCADA data to back it up.
During the rental period, we saved more than $20,000.00 on chemicals. This savings was enough to pay for Zp within the first year of operation. Last year we reduced the cost of producing water by $4.65 per one million gallons. When you produce more than 16,900 million gallons annually, that is quite a savings. Even other water companies like Veolia have asked about our success. It is the best purchase we have made in quite some time!
Zeta Potential and the On-line Zetasizer WT supports the challenge of monitoring changes to incoming raw water (storm, seasonal, source) and how to quantitatively determine the chemical dosage needed to ensure a strong floc formation. This optimization process often results is significant chemical cost savings and the ability of the plant to ensure efficiencies are met in near real-time.
Malvern Panalytical will hold a webinar about zeta potential and optimizing coagulation in the water treatment process. Key areas covered:
- Theory and role of zeta potential in optimizing water treatment clarification
- Case studies of how coagulant addition is optimized and the chemical cost savings that can be achieved.
Register now to learn how coagulant addition is optimized using zeta potential measurements with the Zetasizer.