The Henderson Water Utility, under the jurisdiction of the Henderson Municipal
Water & Sewer Commission and regulated by the Kentucky Department of Natural
Resources and Environmental Protection Agency, operates the Wastewater Treatment
Plant and 54 Pumping Stations. The Wastewater Collection System covers
approximately 25 square miles and consists of some 190 miles of sanitary and
combined storm-sanitary sewers ranging in size from six-inch (6”) to 48-inch.
There are approximately 11,000 service connections flowing to the pump stations.
The Wastewater Treatment Plant proudly serves the approximately 36,000 residents
and industries of the City of Henderson, Henderson County & the city of Corydon.
The Wastewater Treatment Plant was constructed as a primary treatment
facility in 1954 and upgraded to secondary treatment in 1975. The plant was
renovated and expanded in 1991 & 1998 (additional aeration basins, secondary
clarifier and RAS pumping station). The primary settling clarifiers were taken
off line in 2001.
The current plant is operated 24 hours-per-day, 365 days-per-year and
provides full primary and secondary treatment. The plant has the capacity to
provide treatment to remove over 98% of the contaminants from the water at an
average flow of 7.5 million gallons per day (MGD) with a design flow of 15.0 MGD.
This process is a dynamic process which must be properly monitored and
controlled to assure maximum effectiveness with changing flow rates and organic
Wastewater is the potable water supply of a community after it has been used
in homes, businesses, and industries and has been contaminated by various uses.
Wastewater Treatment utilizes a combination of processes which alter and reduce
the contaminants and removes them from the water. The purpose of a wastewater
treatment plant is to accelerate the natural processes by which water is
As wastewater enters the plant, it passes through a row of two closely spaced
coarse, vertical bar screens. Large objects which are trapped by these screens
are removed by automatic mechanical rakes. The wastewater then flows to a
centrifugal-type grit removal tank in which sand, cinders, and gravel are
removed from the wastewater. The flow then passes through two fine bar screen
removal units. After the initial screening and grit removal, the wastewater
still contains high concentrations of dissolved, small suspended solids and
organic materials. This process is known as preliminary treatment.
After the wastewater leaves preliminary treatment it enters a secondary
treatment system. The secondary process uses an extended aeration variation of
the activated sludge process. The water is first pumped to a very large aeration
tank where it is mixed with air and activated sludge. The detention time in this
basin is 18 – 60 hours depending upon influent flow. During this time the
aerobic bacteria and microorganisms present in the activated sludge consume by
“eating” most of the organic matter. These bacteria and microorganisms, referred
to in the industry as “bugs”, depend on oxygen for their respiratory systems the
same as humans. For this reason large quantities of air are pumped into the
aeration basin where air bubbles rise continually up through the liquid to
provide sufficient oxygen for the bugs to breathe.
Four (4) groups of bugs do most of the “eating” in the activated sludge
process. The first group is bacteria which eat the dissolved organic compounds.
The second and third groups of bugs are microorganisms known as free-swimming
and stalked ciliates. These larger bugs eat the bacteria and are heavy enough to
settle by gravity. The fourth group are microorganisms known as Suctoria &
Rotifers which feed on the larger bugs and assist with settling.
An interesting item about the bacteria that eat the dissolved organics is
that they have no mouth. The bacteria have a fascinating characteristic in that
their “fat reserve” is stored on the outside of their body. This fat layer is
sticky and is what the organics adhere to.
Once the bacteria have “contacted” their food, they start the digestion
process. A chemical enzyme is sent out through the cell wall to break up the
organic compounds. This enzyme, known as hydrolytic enzyme, breaks the organic
molecules into small units which are able to pass through the cell wall of the
In wastewater treatment, this process of using bacteria-eating-bugs in the
presence of oxygen to reduce the organics in water is called activated sludge.
The first step in the process, the contact of the bacteria with the organic
compounds, takes about 20 minutes. The second step is the breaking up, ingestion
and digestion processes, which takes four (4) to 24 hours.
The fat storage characteristic of the bacteria is also an asset in settling.
As the bugs “bump” into each other, the fat on each of them sticks together and
causes flocculation of the non-organic solids and biomass.
From the aeration tank, the wastewater, now called mixed liquor, flows to
secondary clarification basins to allow the flocculated biomass of solids to
settle out of the water. The solids biomass, which is the activated sludge and
contains trillions of bacteria and other microorganisms, is used again by
returning it to the influent of the aeration basin splitter box for mixing with
the raw sewage and ample amounts of air.
Henderson’s Wastewater Treatment Plant is unique in that a third or tertiary
clarification section consisting of two (2) tertiary clarifiers are used to
remove a higher degree of suspended solids prior to discharge to the Ohio River.
These two tertiary clarifiers also act as the chlorine contact basins.
The final phase of treatment consists of the addition of chlorine to the
effluent water from the secondary clarification basin. Chlorination accomplishes
disinfection by killing more than 99% of the remaining bacteria. The disinfected
water is then de-chlorinated, using Sodium Hydrogen Sulfite (aka Bisulfite) to
remove the toxicity effect of chlorine on certain forms of aquatic life. The
water is finally discharged through a submerged outfall pipe into the Ohio
As a result of the biochemical decomposition, the volume of the sludge is
reduced and the organic solids, such as sugar, carbohydrates and fats, are
broken down into smaller inert organic and inorganic solids. Carbon dioxide,
methane and water are the by-products of organic reduction process.
When digestion has been completed, the sludge is withdrawn from the digesters
to dewatering devices known as belt filter presses. The digested sludge consists
of approximately 97 - 98% water, therefore it is necessary to remove enough of
the water to produce a material which is dry enough to be hauled in trucks.
Water is removed from the sludge by use of porous fabric belts which pass around
a series of rolls at increasingly higher pressure. For more effective separation
of the water and solids, the sludge is first treated with a liquid cationic
polymer which chemically causes the water and solids to separate. The polymer
treated sludge is introduced as slurry between the fabric belts. As the belts
wrap around the rolls, a large quantity of water is squeezed out of the sludge
and escapes through the porous belts. The process of removing the water is
somewhat similar to that used by wringer clothes washing of years past. The
dewatered sludge cake at 14 - 18% solids is scraped from the belts on the
discharge end of the presses where it drops onto a belt conveyor and is
deposited in a storage building. The sludge cake is pushed into a hopper at
floor level onto a belt conveyor and loaded into trucks. The sludge cake is
taken to a local farm for land application and/or composting.
Supporting all the various phases of the wastewater treatment and sludge
disposal process is the laboratory where numerous tests and analyses are
performed on a daily basis to assure that the process variables and life support
conditions for the bacteria and microorganisms are within optimum ranges. The
laboratory also helps meet our required reporting for State & Federal reports.
Although not an integral part of the actual treatment process, but critical
to the success of the process, is the Industrial Pretreatment Program. This
program is an EPA permit requirement established by the Clean Water Act of 1977,
the purpose of which is to guard the quality of the wastewater entering the
plant. The program consists of monitoring, surveillance and regulation of the
wastewater discharge from major industrial contributors to the municipal
wastewater collection (sewers) system. Discharge of certain types of chemicals
and metal compounds can have a severe toxic effect on the wastewater treatment
process and therefore must be regulated to prevent such discharges. The
characteristics of the discharges from some industries are such to require that
the industry construct and operate a contaminant loads prior to discharge to the
municipal wastewater collection system.
The operation of the Henderson Wastewater Treatment System contributes to
improvement of water quality in the Ohio River, and as a result, helps to
provide recreation and health benefits for the entire community. The Ohio River
is, in certain respects, one of the community’s most valuable assets and the
protection of this asset is a primary goal in the operation of the Wastewater
Treatment System. The higher water quality also helps, proportionally, to
provide a cleaner water source for many cities downstream of Henderson all the
way to the Gulf of Mexico.