ECD Alkalinity Analyser helps optimise corrosion control for Denver water treatment system

As the water utility serving a consolidated city and county government, Denver Water offers high-quality water and promotes its efficient use to residents. Its primary water sources include: the South Platte River, Blue River, Williams Fork River and Fraser River watersheds, along with South Boulder Creek, Ralston Creek and the Bear Creek watersheds (Fig 1).

Greater Denver lies near the snow-capped Rocky Mountains. Its location near to the centre of the nation has made it a hub for the storage and transportation of goods as well as services provided to the Southwestern and Mountain states, along with claiming its share of corporate headquarters and manufacturing companies that depend on Denver Water.

At an altitude of 5,280 feet, the mile-high City of Denver, along with the County of Denver’s surrounding communities, is a thriving metropolitan area that 1.5 million residents call home. They all depend on Denver Water to provide clean, safe drinking water, which includes a treatment and delivery system free of pipe corrosion issues.

The Water Challenge

Since the Flint, Michigan, drinking water crisis, Denver like many other municipal, county and state water agencies across the nation, has been concerned about the potential effects of lead piping system corrosion and moved quickly to address it. The U.S. Environmental Protection Agency (EPA) in response directed water treatment agencies to begin applying several different methods to prevent the corrosion of aging piping infrastructure, which might include lead.

One of the most popular methods of inhibiting corrosion is the use of orthophosphate treatments¹. Their use can prevent the leaching of lead and copper from water pipe systems as they age. They have been studied by the EPA and while effective can be complex to implement correctly based on multiple variables such as achieving the correct orthophosphate concentration and the corrosion scale composition levels already existing in the piping system.

Another EPA recommended method of preventing/controlling corrosion in piping is adjusting the pH/Alkalinity/DIC concentration ratios². Water engineers and technicians typically monitor and understand well their required pH and alkalinity levels needed for water disinfection and quality purposes. DIC, however, is the less familiar inorganic carbon level within water, and it is measured or inferred indirectly via an estimate based on measuring pH and alkalinity levels accurately.

Understanding the proper relationship between pH, alkalinity and DIC is important to prevent corrosion in piping, which can result in the release of lead and copper contaminants into the water system. After reviewing the EPA’s corrosion treatment guidance and the unique characteristics of its own lead piping water system, Denver Water chose the pH/alkalinity/DIC adjustment method to control corrosion.

Pilot Testing Two Alkalinity Analysers

As part of implementing its pH/alkalinity/DIC corrosion control system, Denver Water chose to conduct a pilot program to test two different alkalinity analysers. The CA900 Alkalinity Analyser from Electro-Chemical Devices (ECD) and one from another manufacturer were both tested. They were installed at a pump station and were connected to the Denver Water SCADA system.

ECD’s Model CA900 is a titration type analyser (Fig 2). ECD’s intelligent CA900 Analyser calculates alkalinity by dispensing known doses of a titrant fluid into a reaction cell while monitoring the pH level to its end point. The analyser then uses the titrant concentration and amount dispensed to calculate the level of alkalinity in the sample.

ECD CA900 Alkalinity Analyser With Titration Technology

The CA900 Titration Analyser (Fig 3) typically performs a single alkalinity measurement per analysis cycle. Its standard program sequence consists of a cleaning cycle, sample acquisition, monitoring of pH, the addition of the titrant fluid, mixing the fluid, calculation of results and data storage. The desired frequency of analysis between cycles can be easily modified to the requirements of the user’s process.

Open Cabinet Sensor View of ECD CA900 Alkalinity Analyser

Denver Water required an alkalinity measurement range of 0 to 200 pm. Most users typically select from one of four Model CA900 standard calibration ranges: 0 to 50 ppm, 50 to 200 ppm, 200 to 1000 ppm, and 0 to >1000 ppm. The Denver Water team when ordering simply requested the custom 0–200 ppm alkalinity calibration range; and the analyser came programmed by ECD to the 0–200 ppm range and it was ready to go right out of the box. The analyser’s full-featured design also comes with four 4–20 analog outputs, an Ethernet digital output and four user-configurable alarm relays.

Accessing information or customizing analysis routines are both easily accomplished with the CA900 Titration Analyser’s user-friendly menu structure and touchscreen interface. The analyser also can be web-enabled as a powerful internet of things (IoT) tool for remote monitoring and interfacing with personal handheld devices such as controllers, mobile phones, tablets, laptops and computers.

The Alkalinity Analyser Test Results

ECD’s application team was in constant contact with the team at Denver Water to provide support and the chemical reagent for the trial (Fig 4). The trial between the ECD CA900 and the other competitor was designed to last for about one year. No matter the method of corrosion prevention chosen by any water agency, accurately monitoring various water parameters is critical to the success of the system’s performance, maintenance and cost.

Denver Water Test Stand With ECD CA900 Alkalinity Analyser

At the end of the Denver Water trial, the ECD CA900 Analyser was approved because it met Denver Water’s needs with a user-friendly interface, ease of maintenance, lower cost of ownership and ECD’s customer support. A total of seven alkalinity analysers were eventually purchased for the corrosion monitoring control project and installed across Denver Water’s distribution system.

When Denver Water purchased its CA900 Analysers, the products were relatively new to the market and Denver Water experienced a few minor technical issues that were quickly resolved by the ECD applications group with software updates to the product. ECD today continues to support Denver Water as necessary with routine software upgrades, pH electrodes and other components.

^{1 White Paper, “The Role Of Alkalinity In Aerobic Wastewater Treatment Plants: Magnesium Hydroxide vs. Caustic Soda,” Martin Marrietta Magnesium Specialties, Water Online: https://www.wateronline.com/doc/the-role-of-alkalinity-in-aerobic-wastewater-0002}

^{2 U.S. EPA, “Optimal Corrosion Control Treatment Evaluation Technical Recommendations for Primacy Agencies and Public Water Systems Section: 2.3.1.”}

Top image credit: iStock.com/RoschetzkyIstockPhoto