Wilmington WWTP

The Wilmington Wastewater Treatment Plant was originally built in 1964, major upgrades to the facility and collection systems were completed in 1988-89 and a refurbishment project was recently completed in June 2016.

The treatment process contains the following processes:
1.    Collection System
2.    Primary Treatment using EcoMat Rotating Belt Filter which also dewaters the solids
3.    Rotating Biological contactors
4.    Aerated Lagoons
5.    Chlorination / Dechlorination
6.    Composting

1.    Collection System:

The collection system includes 7 lift (or pumping) stations and approx. 7 miles of sewer lines.  There are approx. 275 connections to the collection system.  The yearly sewer rent of a single family dwelling is approx. $353.  Special grinders, called “Muffin Monsters”, are located at the treatment plant and Pump Station #1.  These grinders grind the incoming material into small pieces which reduces pump clogging and also reduces the observation of plastic materials in the clarifier.

2.    Primary Treatment:

“Blue Water’s Eco MAT™ RBF removes solids through the use of a continuous-loop fine mesh belt screen. As the screen moves it acts like a conveyor and carries solids out of the incoming wastewater. A patent-pending cleaning system discharges the solids from the belt screen and deposits them into the screenings hopper, virtually eliminating any solids carry-over. Periodic hot-water flushes further clean the belt screen by removing oil and grease that may accumulate over time. An optional screw press dewaters the collected screenings between 20-40% dry solids while screened wastewater continuously passes through the unit.

Blue Water’s Eco MAT™ RBF removes between 30-80% TSS and 20-40% BOD from wastewater and the unique design allows for removal of organic and inorganic solids as fine as 15-30 micron. The Eco MAT RBF units are compact, completely enclosed low-maintenance solutions for wastewater. The integral odor containment of the design allows for indoor installation in a clean environment, and the Eco MAT RBF filter was designed for food-grade compatible maintenance in an FDA regulated environment. Blue Water offers additional equipment for conveyance, de-watering, and bio-solids reuse as applications require.”


3.    Rotating Biological Contactors:

A rotating biological contactor is a “fixed film” biological treatment system using rotating plastic media.  The media provides a surface on which micro organisms attach themselves and grow, thus creating a “fixed film”.  These micro organisms creates a “slime” on the plastic media.  The slime is rotated into the settled wastewater and then goes into the atmosphere to provide oxygen for the organisms.  As the drum rotates, the media pick up a thin layer of wastewater which flows over the biological slimes on the discs.  Organisms living in the slimes use organic matter from the wastewater for food and dissolved oxygen from the air, thus removing wastes from the water being treated.  As this slime passes through the wastewater, some falls off the media and is carried to the lagoons in the wastewater.

4.    Aerated Lagoons:

We have two lagoons, 52’ X 150’, normal operating water level is 11.58’.  The two lagoons together hold approx. 1.35 million gallons of wastewater.  The lagoons run in series to each other.  Air is added to the lagoons to stimulate the aerobic bacteria and other living organisms in the wastewater.  The aerobic bacteria thrives on the abundant oxygen and continues to digest the organic solids in the wastewater.  In the lower level of the lagoons, the solids or sludge that has accumulated is without oxygen (anaerobic), but continues to be digested by anaerobic bacteria.

5.    Chlorination / Dechlorination:

Liquid chlorine (hypochlorite), is injected into the wastewater which kills the pathogens (disease causing bacteria).  A contact time of approx. 1 hour is allowed to insure that all of the wastewater is mixed with hypochlorite.  After this contact time, liquid sodium bisulfite is added.  Sodium bisulfite neutralized the hypochlorite so that none is discharged into the river which could result in the death of aquatic life in the river.

6.    Composting:

We use equipment purchased from Green Mountain Technologies  in 1996, and have been using this in-vessel composting system since 1994.  We have a Comptainer that is used for composting the sludge.

After the sludge is dewatered, we mix it with woodchips at about a 2 or 3 to 1 ratio of woodchips to sludge depending on the moisture content of the sludge and woodchips.  After mixing the material is conveyed into the Comptainer.  Aeration tubes are connected and a built in computer is restarted to start the composting process.  The computer reads data from temperature probes that are inserted into the sludge/woodchip mixture and regulates the temperature inside the Comptainer to insure that a uniform temperature is maintained throughout the Comptainer.  To meet EPA regulations, the mixture must reach a temperature of 55 degrees Celsius (131 F), for three consecutive days.  This is known as the “procedure to further reduce pathogens” (PFRP).  The mixture must also maintain a temperature of 45 c or 113 f or 14 consecutive days to obtain proper (VAR) or “vector attraction reduction”.  The mixture stays in the Comptainer for approx. 21 to 30 days, then is dumped using a roll-off truck and allowed to cure and the necessary laboratory analysis are completed.  After curing and analysis are complete, the final product is delivered free to Wilmington residents in 5 yards loads.  The product is used mostly as a mulch for flower gardens or as a soil conditioner.  It is a class A compost, but is not certified to be  used in vegetable garden.