River Mile: 364.5 RDB

Serving over 4800 customers, Keokuk Municipal Water Works is responsible for providing its residential, commercial and industrial customers with high quality and reliable water supply. The Water Works service area, 105 miles of pipe within a 20 sq. mile area, includes the entire incorporated area of the city of Keokuk, Iowa. Additionally the water system serves two small private water systems outside the Keokuk corporate limits.

Several large centrifugal pumps move Mississippi river water (raw water) to the plant and into the head tank from the river. Prior to the head tank the first chemical that is introduced at the intake tower is potassium permanganate. This chemical oxidizes soluble manganese so that it can be taken out in the clarification process. Manganese is dead vegetation and dead alga that cause taste and odors in the raw water. Next, two chemicals are added directly into the raw water line, a liquid alum, a coagulate aid and cationic polymer are fed directly into the raw water before the head tank. This is the start of the coagulation process. Carbon is then fed at the head tank to also help control any odors that may occur in the clarifiers. After the raw water is mixed with the chemicals, it goes to four claricone Clarifier units where an anionic polymer can be fed directly into the sludge blanket in the Clarifiers. Lime is also introduced at the bottom of the cones in a slurry form to remove the minerals that cause calcium hardness from the raw water. The entrance velocity of the raw water promotes mixing within the vessel’s lower cylinder. The slower rotation in the middle section provides good particle contact and flocculation. There is little turbulence in the top section of the claricone, which makes for good settling of the particles and produces clarified water. The claricones operate on what is called a sludge blanket principal; the water passes upward through a blanket of flocculated material called a sludge blanket, which entraps slowly settling particles that would otherwise pass through into the filters. This blanket is suspended below the water level at about 8 feet. Since the sludge is always accumulating from the dirt and turbidity of the water, the sludge blow down system is designed so that it opens a valve to the claricones. Sludge is drawn off the top of the blanket through the sludge concentrator, this is the cone shaped device in the center of the claricone that is 8 feet below the water level, this device can be raised and lower to determine the right height for the sludge blanket. The clarified water off the top of the claricones goes to the re-carbination tank. The water has a high pH and a high concentration of calcium carbonate. Carbon dioxide gas is added to the tank to form soluble calcium bicarbonate and to reduce the pH to 9.0 or to a level at which the water is stabilized to prevent scale formation or corrosion of water mains or piping. From the re-carbination tank the water goes into a water pipe where it is chlorinated again and hydrofluosilic acid is applied, more commonly known as fluoride. The water is then gravity fed into the filters. There are four sand filters used to remove what little particulate was not removed in the claricones. Chlorine is then added. After the water goes through the filters it enters the clearwell or storage well. Here liquid ammonia is added to combine with the free available chlorine to form a weaker form of disinfectant. The treated water is then pumped into the distribution system and to two elevated storage towers through one of four high service pumps. All the plant control is achieved through the use of Allen-Bradley PLCs using the ICONICS Genesis32 Software for the HMI user interface and alarm notification.

Ultrafiltration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane. This separation process is used in industry and research for purifying and concentrating macromolecular (10^3 - 10^6 Da) solutions, especially protein solutions. Ultrafiltration is not fundamentally different from reverse osmosis, microfiltration or nanofiltration, except in terms of the size of the molecules it retains.

Ultrafiltration is a lower pressure membrane separation technology used to remove suspended solids, oils and other impurities from wastewater. Membrane filtration can be used in pollution prevention to recover/recycle process water and valuable process chemicals. This technology can also be used as a polishing step without the addition of treatment chemicals.

How it Works:

Membrane separation technology is based upon molecular size. The semi permeable membrane in an ultrafiltration system has pore sizes in the range of 0.0025 to 0.01 microns. Pressure is applied to one side of the membrane so that water and low molecular weight compounds in the waste stream flow through the pores as permeate, while the larger molecules and suspended solids flow across the membrane and become part of the concentrate.

In an ultrafiltration system, wastewater flows parallel to the membrane surface, as compared to the perpendicular flow of ordinary filtration. The cross flow motion of the water within an ultrafiltration system allows high filtration rates to be maintained continuously, whereas the constant build up of solids along the filter surface can cause blockage in an ordinary perpendicular filtration system.

How the System Is Set Up:

There are three primary configurations of ultrafiltration membranes: tubular, hollow fiber, and spiral wound. The tubular membrane is generally used in small flow, high solids loading applications. The construction of this membrane allows easy cleaning, therefore it is the membrane of choice when severe fouling is expected. The hollow fiber design consists of a membrane would into a hollow cylinder. Cylinder diameters vary; the expected solids loading governs the size of cylinder necessary for a specific application. The third configuration of ultrafiltration membranes is the spiral-wound, and it is usually used for high volume applications. The spiral membrane is constructed by rolling a flat membrane that is netted together with specially-designed spacer material. This type of membrane cannot be mechanically cleaned, and is usually reserved for applications where TSS loading is low or has been reduced by pre-filtration.