University Water Plant

University Water Plant

Water Plant

Current Water Quality Status for UI campus

2016 Confidence Report Stormwater Program

The University Water Treatment Plant functions as both a water source for the University of Iowa campus, hospitals and clinics, dorms and student/staff housing and as a research facility for advanced study in Environmental Engineering.

Water Treatment Process

The basic unit operations and processes involved are chemical pretreatment, coagulation, flocculation, sedimentation, softening by chemical precipitation, recarbonation, disinfection, filtration and fluoridation. The flow diagram shown on the last page gives an overall picture of the treatment process. The following description will begin with the raw water entering the plant and ending with potable water.

Raw water is pumped from below the surface of the Iowa River. Conditions of the raw water vary with the season and weather. Influent turbidity, a measure of a liquid’s clarity and color, ranges from over 500 NTU during the spring rains to about 3 NTU during the winter months. Contributing factors to turbidity are agricultural run-off, topsoil erosion, and urban run-off and pollution. The total hardness of surface water is about 200 parts per million (ppm) in the summer and as high as 350 ppm in the winter. Calcium hardness contributes to about two-thirds the total hardness. Water hardness is defined as the magnesium and calcium ion content of water. These ions combine with fatty acid radicals in soap to form undesirable precipitates. The pH of raw water ranges from 7.7 to 8.5 depending upon temperature and season. Another raw water factor is the alkalinity or total calcium carbonate equivalent units.

Chemical Pretreatment

Influent water is strained through a rotating, one-half-inch band screen to remove any large debris: e.g., sticks, fish, junk metal, and leaves. Next the water flows through an inline power mixer where ferric sulfate is added before entering a series of basins.

Coagulation/Flocculation

Ferric sulfate is used as a base substance in the formation of floc particles. The process of causing finely divided materials (floc) suspended in water to cluster together is called coagulation. Ferric sulfate forms a positive trivalent particle with very sticky characteristics.

The water and the suspended floc next enter a series of basins. These basins have mixers, which provide gentle agitation to aid the formation and buildup of floc particles. This buildup of particles is called flocculation. Flocculation results from both the physical entrapment of impurities on the sticky ferric sulfate surface and also an ionic attraction between the negatively charged turbidity particles and the positive ferric sulfate.

Sedimentation

The settling basins provide an area for these newly formed floc particles to settle out. In the settling basin a large percentage of the influent turbidity is removed. The accumulated precipitate is mechanically collected from the bottom of the basin and pumped away. Sludge removal is an important step in effective sedimentation.

Softening by Chemical Precipitate

The University plant has three softening units, which operate in parallel. A slurry of slaked lime and ferric sulfate enters the softener riser and reaction zones, where a turbine mixes it with water from the settling basin. Slaked lime acts as a softening agent.

The chemical reactions for softening are relatively simple. The anions present with calcium and magnesium are usually bicarbonate and sulfate. Hardness is removed by introducing carbonate ions in the form of hydrated lime. Since the solubility of magnesium is low at pH above 10.8, the magnesium ion precipitates out in the softening unit.

Recarbonation

Because the pH is relatively high in the softeners, a considerable amount of hydrated lime and calcium carbonate remains in the solution. To remove these compounds, the pH must be lowered to about 9.5 by bubbling carbon dioxide gas through the water in the recarbonation zone.

Disinfection

Chlorine gas and water are mixed in a chlorinator to form a nonvolatile solution of hypochlorous acid. This dilute chlorine solution is a germicide that attacks the protoplasm of organic impurities in water.

Filtration/Fluoridation

The next step in the treatment process is filtration. Insoluble calcium carbonate particles and coagulated floc remaining in the water are removed in six rapid-bed filters. Effective filtration produces effluent water with less than 0.3 NTU turbidity. Fluoride ion is added to the filter effluent in this final step before campus distribution.

Sludge Dewatering

The University plant has a sludge dewatering facility, which is used to remove solids from the effluent that is discharged to the Iowa River. As the sludge enters a thickener, a polymer is added to promote the formation of floc particles and solids are drawn off and land applied for agricultural purposes. The supernant is discharged to the river when the total suspended solids are less than 35 mg/L, it is automatically recycled through the process until solids drop below 35 mg/L.

Quality Control

The quality of the water treatment process is maintained by certified operators monitoring results of analytic test performed every four hours and aided by on-line recording monitors. Samples of the plant’s raw and potable water are also sent to the University Hygienic labs for further analysis.

Tap vs Bottle Water Chart