REVERSE OSMOSIS TECHNOLOGY

In the small Central Illinois City of Wenona, water quality has always been a headache for residents as well as elected officials. But in November of 1987, this headache became a full-blown migraine. In that month, the City received an enforcement notice letter from the Illinois Environmental Protection Agency (IEPA). The IEPA and the Federal Safe Drinking Water Act Amendments set acceptable levels of radium well below the levels present in the City's water supply. The radium level in Wenona's water supply was four times the State and Federal standards.

The City was instructed by the IEPA to secure the assistance of a registered professional engineer and to submit an interim compliance report that described what compliance options the City was investigating. Farnsworth & Wylie, P.C. of Bloomington was the consultant chosen and they set out to compile the necessary data to respond to the list of requests made by the IEPA and to report to the City how they might best comply with the regulations in the most cost effective manner. After an in-depth examination of the City's water systems and components, water usage projections, water supply adequacy, raw water quality, and water treatment needs, a compliance report was submitted to the IEPA in March of 1989.

Farnsworth & Wylie's study revealed a number of interesting points. The raw water pumped from the St. Peter sandstone aquifer is very high in total dissolved solids (TDS). The largest fractions of TDS are made up of sodium and chlorides. High sodium levels are of concern to people with hypertension and heart diseases. The water hardness was also high and the iron content was enough to cause stains on clothing and fixtures. The TDS was high enough to give the water a "salty mineral" taste and occasionally cause discoloration or "red water problems." The water also contained hydrogen sulfide gas which was obvious because of the "rotten egg" odor.

At the time, the only regulatory concern the City had was to reduce the level of radium by 78% to meet IEPA limits. However, the City also decided to look into the feasibility of reducing the amount of sodium and dissolved solids that would provide a higher quality of water for the citizens. The three alternatives of treatment technology the City had to choose from were sodium zeolite ion exchange softening, lime softening, or reverse osmosis. The two softening technologies would have effectively reduced radium levels to within IEPA limits but would not significantly reduce sodium and total dissolved solids. This would have left the City with the same discolored, poor quality water as before but with reduced levels of radium.

After an in-depth look into the treatment options, a search for another source of water, and a comparison of the alternatives Wenona faced, the engineers narrowed the choice of treatment to either zeolite softening or a reverse osmosis treatment system. The advantages and disadvantages of the options were weighed against one another and a final engineer's recommendation was made for a reverse osmosis system. It was left up to the City Council to compare the costs and benefits and make their decision.

Sodium zeolite ion exchange softening is highly efficient in both removing radium and softening water, it requires little operator attention, and has the lowest cost of construction and operation. But zeolite ion exchange will increase the levels of sodium in the water and will not remove dissolved solids or improve the taste of the water. Realizing that one of the main objectives the City had set for the project was to improve the quality of water as well as remove radium, the Council decided to proceed with the reverse osmosis system. The Coun-

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cil also wanted to look to the future for any other regulations that might be on the horizon.

Reverse osmosis was seen by the City Council as the technology that would best achieve the desired results and provide the highest quality of water at a reasonable cost. The reverse osmosis process involves forcing water through semi-permeable membranes under high pressure. Water passes through the membrane but dissolved solids can't and are washed away by water that does not pass through the membrane. About 95% to 98% of the TDS are removed in the process. The treated water is then mixed with 20% untreated water to make up the finished product that complies with all regulations and has about one quarter of the total dissolved solids of the raw water.

The reverse osmosis technology can also be used for other water treatment and removal requirements. Elements in water systems such as nitrates, chloroform, herbicides, pesticides, insecticides, trihalomethanes and other organic materials can be removed and result in a safe supply system. The cost of the Wenona facility was approximately $600,000 with half of that cost being funded by the Illinois Department of Commerce and Community Affairs. The flow from the system was 150 GPM for a maximum daily usage of 180,000 gallons per day.

The City is proud of the fact that we are one of the first communities in Illinois to adopt this new type of water system. We feel that we are in the forefront of a technology that will lead us into the twenty-first century. From the first day that the new water plant went on line there has been an extreme increase in the quality of the water. The difference in taste, color, and smell is beyond the expectations that the City had set when we first started the project. If your community is experiencing the same type of problems as the City of Wenona, a look into reverse osmosis technology will be well worth your effort. •

July 1992 / Illinois Municipal Review / Page 27