Present Facilities and Operation
 

North Water Treatment Plant Basins and River
 

The Henderson Water Treatment Plant now treats water in a series of steps which are modifications of the basic “conventional” methods.  The first step utilizes chemicals known as coagulants to react with suspended particles in the water to promote their removal in two (2) large rectangular clarification basins.  In the second step, a gravity clarification basin is used for further clarification of the water prior to filtration.  Filters are then used as a final step in the process to remove a very high degree of any remaining solid particles not removed in the clarification processes.

The following is a brief and simplified description of the various treatment processes utilized within the Henderson Water Treatment Plant.

RIVER WATER IS PUMPED TO THE PLANT

Untreated water is supplied to the water treatment plant raw water pumping station “wetwell” from an intake structure located on the Ohio River and operated by the Municipal Power and Light.  From this station the water is pumped at demand related controlled rates into the water treatment plant.

FLASH MIXING

The raw water enters a high-energy mixing chamber where it is treated with several chemicals for a variety of purposes.  Either chlorine or chlorine dioxide is added for primary disinfection.  These chemicals are used to destroy or inactivate potentially harmful bacteria and other microorganisms which may be present in the water.

Hydrated Lime is added to control the pH (acidity – alkalinity), and to produce a palatable, non-corrosive water.

Potassium Permanganate is added as an oxidant to reduce taste and odor from several naturally occurring organic formations such as algae growth found in the Ohio River water during the summer months.

COAGULATION AND FLOCCULATION

Also in the flash mixing chamber, a chemical coagulant is added to the water to aid in the removal of fine suspended solids.  Since these solids, by themselves, are too small to be removed from the water by gravitational settling within a practical period of time, the coagulant is added to increase particle size and weight, thus improving solids removal during the clarification and filtration processes.  The chemical used for this purpose in Henderson’s Water Treatment Plant is Liquid Aluminum Sulfate, commonly called Alum.

The alum reacts with the natural alkalinity of the water to form a gelatinous precipitate called Aluminum Hydroxide.  As the water passes through the distribution laterals into the clarification basins, a mixing action takes place and this gelatinous precipitate entraps the fine suspended solids and forms larger and denser masses called “floc”.

A cationic polymer is also added in this step to neutralize the natural negative electrical charges of the solids in the water.  The charge neutralization further reduces the tendency for the solids to stay in suspension.

CLARIFICATION BASINS

After coagulation, the water is distributed uniformly over the bottom of two large parallel clarification basins.  The steady flow rate is changed to a pulsating flow to increase solids movement and solids contact.  A six foot (6’) deep conditioned solids blanket is maintained in these basins through which the floc in the incoming water is removed by a solids contact filtering action.  This step clarifies the water 95 to 98%.  This clarified water then passes up through parallel plate distributors and into submerged parallel collection pipe laterals and into an effluent trough and out of the clarification basins.

The excess accumulation of solids deposited in the clarification basins, overflows into concentration hoppers located in the center of the basins.  This accumulation of solids is now called “sludge”.  The sludge is concentrated, and then siphoned from the sludge hoppers and into a pumping station, where it is discharged to Henderson’s sanitary sewer system.

AERATION

The water then flows through aeration basins where air is pumped through fine bubble diffusers and bubbled up through the water.  This introduces oxygen into the water to aid in the oxidation and removal of certain types of volatile organic compounds which primarily affect taste and odor during summer months.  This is a unique feature only provided at a small number of water treatment plants in the United States.

SECONDARY CHEMICAL TREATMENT

From aeration, the water flows into a secondary chemical addition and mixing zone where several other chemicals may be introduced into the treatment process to provide for further treatment and subsequent clarification.

Alum of Ferric Salts may be added to provide for secondary coagulation.

Hydrated Lime is added to further control pH and adjust the corrosivity of the water.

Powdered activated carbon may be used as an absorbent for taste and odor control or to remove a wide variety of chemicals that may accidentally contaminate the river water supply.  Carbon in this form absorbs volatile chemicals in the same way as charcoal absorbs charcoal lighter fluid used in a backyard grill.  The carbon then settles to the bottom of the sedimentation basin where it is removed with the sludge and discharged into the sanitary sewer system.

Chlorine is introduced for further disinfection purposes and also to provide residual disinfection in the distribution system.

SECONDARY SEDIMENTATION

The water then flows into a secondary mixing and sedimentation basin which provides extended time for chemical reaction as well as secondary clarification by gravity settling.

The water is first gently mixed by horizontal paddles, which move up and down in the water.  This mixing moves the water around the secondary floc particles and brings more suspended solids into contact with the floc, enhancing floc growth.  As the floc grows, the particles become large enough in size to settle to the bottom of the sedimentation basin.  This basin is covered with honeycomb-type inclined tube settlers which provide high efficiency sedimentation.

FILTRATION

After the treatment processes of coagulation and clarification, the clarified water flows through dual media filter beds to remove a very high degree of any remaining solids.  Prior to filtration, over 98% of the impurities have been removed by the preceding treatment steps.

Six (6) filters provide a total of 2,160 square feet of filter area with a filtration capacity of 15 million gallons per day (gdp).  This allows the plant to operate at full capacity even with one (1) filter out of service.

The filter beds are constructed of layers of anthracite coal, filter sand and supported gravel.  Twenty inches (20”) of anthracite having an approximate diameter of 1.0 mm rest over ten inches (10”) of fine sand with an average diameter of 0.5 mm.

As the water passes down and through the filters, the remaining suspended solids become entrapped in the interstices of the filter media.  At routine intervals, the filters are cleaned of the entrapped solids by forcing clear, fully treated water in the reverse direction at high velocities.  This reverse flow is called backwashing and is required to remove the build-up of captured solids within the upper levels of the filter media.  This water and the solids it carries is then discharged into the sanitary sewer system

FINISHED WATER STORAGE AND PUMPING

Following filtration, the water is treated with a final control dosage of chlorine to adjust the residual disinfection concentration.  Sodium Hydroxide is added as needed as a final pH adjustment and a polyphosphate is added for corrosion control.

Fluoride is added to reduce the insistence of tooth decay in children who drink Henderson’s water.

The treated water is stored in an underground reservoir called a “clearwell”.  The clearwell has a capacity of 1.2 million gallons.

From the clearwell, water is then pumped directly into the distribution system with three (3) high service pumps having a total of 950 horsepower.

FINISHED WATER DISTRIBUTION

By both weight and volume, the delivery of water is, by far, the largest transportation operation in the United States.  A complex network of pipes, booster pumping stations, tanks and reservoirs is necessary to move the water form the treatment facilities to the customer.  Henderson’s distribution system contained about 175 miles of pipe ranging in size from 1-1/2 to 24 inches.

In each of the pressure areas, there is at least one (1) tank or reservoir.  The height of the water in the tank or reservoir determines the pressure in the area.  These facilities ensure a relatively uniform pressure in the supply system with sufficient reserve storage for high demand periods, and an adequate supply of water for emergencies such as fighting fires.  Alight variations in pressure cannot be avoided.  For example, in the early evening hours as people return from work, the demand of water may increase.  As a result, the water level in storage tanks is lowered and the pressure drops slightly.  During the night, when industrial activity is reduced and people are sleeping, pumps continue to work, and the tanks and reservoirs are refilled to provide maximum storage for the next day.

The tanks in Henderson’s system have a combined capacity of 7.58 million gallons.  The names and capacity of the tanks are as follows: 

While fire hydrants are largely taken for granted, their presence is mute testimony that the Water Department and Fire Department are ready to respond in mitigating or preventing the potential destruction caused by an unexpected fire.

WATER QUALITY MONITORING

Henderson’s finished treated water has a quality much better than the national average and far superior to that required by the Safe Drinking Water Act of 1974, as amended.  This is primarily a result of strict monitoring, testing, and control of the treatment process.

A common measure of water quality is the degree of clarity of the water measured as the turbidity (a measure of the cloudiness).  The purity of the water, to a certain extent, is directly related to the clarity.  The measure of water turbidity is an important parameter which is used to control the treatment process by continuous monitoring at several locations throughout the treatment plant.

Other physical, chemical and bacteriological laboratory analyses are also performed at various stages of the water treatment process.  All of the testing is necessary to ensure cost effective operation of the plant and to produce a uniform product of highest possible quality for this process.

In addition to the wide array of analyses performed at the treatment facility, samples are also collected throughout the distribution system and analyzed for possible bacteriological contamination.  These tests are carried out to ensure that water quality is maintained and that all regulations and health standards are constantly met.

Remember, when you call upon water for your many needs, you may rest assured that the Employees of the Henderson Water Treatment Plant and Distribution System are behind your faucet 24 hours-a-day to ensure that a safe, abundant supply is delivered.