Wastewater Treatment Process
The Kalamazoo Water Reclamation Plant (KWRP) processes 25 million gallons of wastewater per day at its location on North Harrison Street in northeast Kalamazoo, adjacent to the Kalamazoo River. We all create dirty water, whether it's from the dishwasher, bathtub, drinking fountain, drain or, of course, the toilet. Industry produces a lot of wastewater through a variety of cleaning, cooling and manufacturing processes. Whenever water goes down a drain into a sewer in the greater metropolitan area, it finds its way to KWRP.
When wastewater first leaves its point of origin, it flows downhill at about two feet per second through over 890 miles of sewer line until it reaches one of more than 60 lift stations located throughout the area. You would seldom notice such a station, as it generally consists of a manhole and a small control unit. The pump in the lift station raises the water so it again can use the force of gravity to flow closer and closer to the plant. Also, as the flows get closer to the plant, the sewer lines get larger and larger in order to accommodate greater flows, finally reaching a diameter of 72".
Many years ago, when the City of Kalamazoo was first constructing its sewer lines, it kept the sewer flows separate from the storm water flows. Such excellent forethought on the part of the City Fathers has prevented hydraulic overload on the KWRP during rainstorms and spring thaws, thus protecting the Kalamazoo River from receiving raw sewage. Other cities with combined systems are not so fortunate.
When the wastewater arrives at the KWRP, it contains much less than one-tenth of one percent solids. Solids consist of dissolved detergents, food, dirt, oil, industrial and human wastes. The goal of the plant is to remove as much of the solids as possible. The KWRP receives almost 18,000 gallons of wastewater per minute. Those 18,000 gallons contain less than one quarter pound of solids. Withdrawing those solids and disposing of them properly keeps our environment - especially our streams and rivers - safe for plants, animals, ourselves and future generations.
Raw wastewater, also called "influent", is generally gray in color. It has a musty but not unpleasant odor.
The first step in cleaning the water is to remove the large solids - such as rags, toys, sticks, the occasional tire, snake or shoe - by allowing the water to flow through a screen. Then the water is pumped above ground through an aerated grit channel. Air is injected into the channel, creating a mixture of air and water that has a lower specific gravity than grit. The air also produces a rolling action that keeps lighter solids in suspension and allows smaller, heavier particles such as egg shells, sand, metal shavings and the like to settle to the bottom of the channel. These small particles are then removed. Had they not been removed, they could cause damage to the pumps located downstream in the KWRP.
After the grit channel, the water flows into as many as six primary settling tanks. These large tanks slow the water to the point where it appears almost motionless. Heavy solids settle along the bottom of the tanks, and floating solids - such as plastic or grease - collect on the surface. A collector pushes settled solids toward a pumping area where this "sludge" is pumped away for further treatment. The same collector skims the floating solids, called "scum", out of the tank to a disposal container. The remainder of the water - called primary effluent - contains dissolved and suspended solids. From this point the effluent flows to the mixing chamber. In the mixing chamber, primary effluent mixes with carbon and internal flows from the plant and becomes the secondary influent flow. From here, the wastewater flows to the secondary aeration tanks.
The KWRP uses Biological Nutrient Removal (BNR) with powered activated carbon (PAC), a complex biological process, to treat wastewater. Microscopic organisms commonly referred to as "bugs", use dissolved solids in the waste stream as food. In as many as nine aeration tanks, the water is continuously agitated by air bubbles. Settled sludge or biosolids from the secondary clarifiers is returned to the head of the aeration tanks to mix with the secondary influent. This mixture, called "mixed liquor," creates the ideal environment for the bugs to survive, eating the dissolved solids and being eaten by increasingly larger organisms (though still microscopic.) After several hours, the mixed liquor flows into as many as seven final clarifiers. Here the bugs, having eaten all the dissolved solids and full of "food," settle to the bottom of the clarifier along with the carbon. The result: clear effluent or "supernatant."
The final - tertiary - stage of treatment consists of filtering the effluent through sand and then dosing it with chlorine to kill any pathogenic bacteria, and then neutralizing the chlorine with bisulfite. The treated water, called plant effluent, is released to the Kalamazoo River, clean, clear and safe for fish and other riparian wildlife.
Remember the one quarter pound per minute of solids that entered the plant? Dealing with those solids after they've been separated from the water constitutes a large amount of the KWRP physical and financial resources.
Settled sludge or biosolids from the Primary settling tanks is pumped to Primary Thickeners. A portion of the Secondary mixed liquor is pumped to Secondary thickeners. In these thickeners the biosolids are allowed to settle and become thicker. The settled sludge from the thickeners is pumped to a belt filter press, which mechanically squeezes as much water as possible from the sludge. This can be done separately or the two types of sludge can be mixed together, called co-mingled sludge. The result, whether separate or co-mingled, is a fairly dry cake sent to a landfill.
Successful wastewater treatment involves removal of most solids, disinfection, and treatment of removed solids - all without negatively affecting the environment. The City of Kalamazoo can proudly state it does this job well.
You can tour the Kalamazoo Water Reclamation Plant. For more information visit the Plant Tour page or contact the Administrative office at (269) 337-8701.