The Hutchinson (Kan.) Water Treatment Center is more than a drinking water production facility; it’s also a water reclamation facility of sorts. The center uses reverse osmosis (RO) to remove volatile organic compounds (VOCs) and chlorides from groundwater supplied by four of its water supply wells.
In the early 1980s, the U.S. Environmental Protection Agency (EPA) tested Hutchinson’s public groundwater supply wells. One well, at the intersection of Fourth Avenue and Carey Street, was found to be contaminated with VOCs.
EPA and the Kansas Department of Health and Environment (KDHE) wanted to declare the well a Superfund site. The city resisted the designation because the resulting image and economic impact would have been extremely detrimental to Hutchinson. It sought to find a way to put the water to a beneficial use.
Today, the treatment center produces “Hutchinson Blend.” The center mixes 22,700 m3/d (6 mgd) of RO-treated water with 15,100 m/3d (4 mgd) of potable groundwater to produce 37,800 m3/d (10 mgd) of higher quality drinking water.
In 1994, after a decade of negotiation, the city agreed to lead the cleanup effort. Cleaning up Hutchinson’s groundwater problem was in everyone’s best interest. Initial funding was to come from a special tax district, and the city originally had plans to dispose of the contaminated water by putting it into deep wells. Then, the city considered pumping the contaminated water from the ground, air-stripping the VOCs, and discharging the resulting remediated water to a receiving stream. However, much of the remediated water is very high in chlorides, and KDHE prohibited its disposal into waterways where it can affect downstream uses.
Finding a better way
The city sought a solution to put the natural water resource to a beneficial use as well as provide a regional solution for high-chloride waters and other industrial contamination in the area. A company already working with the city on its water distribution system, Professional Engineering Consulting (Wichita, Kan.), proposed the idea of RO treatment of the contaminated water.
RO treatment would remove both VOCs and chlorides from the water and produce a drinkable product, as well as not waste the source water. After winning city approval, the company designed and managed a pilot plant, which later evolved into a full-scale design.
The process to create Hutchinson Blend uses a series of treatment technologies.
First, the contaminated water is extracted from the ground through four remediation wells. These wells are positioned to capture the plume of VOCs and prevent its spread.
Once at the water treatment center, the water is dosed with chlorine for oxidation of iron and manganese and with potassium permanganate periodically to recharge the pressure-filter media.
Next, three horizontal vessels, each containing two pressure filters that use anthracite and greensand media, remove chemically oxidized iron and manganese. These filters, which handle 4200 L/min (1120 gal/min) in each cell, protect the downstream RO membranes and minimize membrane cleaning.
Then, six 4400-L/min (1170-gal/min) cartridge filters remove particulates, such as iron and/or sand. These cartridges serve as an extra layer of protection for the RO membranes, because some particulates can pass through the pressure filters.
Following the cartridge filters, sodium bisulfate is added to remove residual chlorine, and an antiscalant is added to inhibit RO membrane fouling.
After that, four feed pumps — one for each RO unit — pressurize the water to push it through the membranes. The 5300-L/min (1400-gal/min) pumps use variable-frequency drives so that they can maintain the desired flow rate and pressures going into the RO units. The four skid-mounted units — each of which produce 5700 m3/d (1.5 mgd) — combined contain 1008 200-mm-diameter (8-in.-diameter) membranes. The membranes remove nearly all of the dissolved and particulate materials from the water, including hardness, chlorides, and most of the VOCs. The concentrated brine is collected and pumped into two 1460-m-deep (4800-ft-deep) injection wells for disposal.
Then, the product water enters a 12-m-tall (40-ft-tall), 4-m-diameter (14-ft-diameter) degasification tower to remove carbon dioxide and the remaining VOCs. Air is passed through the water stream to achieve this. The treated water next flows to a blending facility, where it is mixed with potable water extracted from 13 uncontaminated groundwater wells. The blending, which occurs via a series of turbulent piping, stabilizes the RO water, and caustic soda is added to control the water’s pH for corrosion control purposes.
Finally, the water is disinfected with chlorine and stored for use in a series of clear wells with a combined volume of 2.9 million L (767,000 gal). Six 186-kW (250-hp) high-service pumps push the blend from the clear wells to the city’s distribution system and water towers.
The center cost about $16 million to build. The final agreement for the project’s funding reflected a shared responsibility of the cause of the contamination and the benefits it provides. Funding came from the State of Kansas and Hutchinson water ratepayers, as well as the parties originally responsible for the contamination.
Today, Hutchinson’s advanced RO treatment facility resolves supply, quality, environmental, and conservation issues. Hutchinson Blend brings several advantages, including higher overall water quality; higher available water quantity; and low-ion, high-quality water for industrial recruitment.
©2012 Water Environment Federation. All rights reserved.