Raw wastewater (sewage) is transmitted from the Village collection system to the Treatment Plant via an interceptor that was completely relined or replaced as part of the 1988 upgrade, expansion, and construction of the facilities. Raw flow (including Camp Dearborn) enters the headworks where grit (sand and other inorganics) is removed utilizing an aerated chamber, pump, and hydroscreen. The removed grit is dried on a sludge-drying bed and then hauled to an approved landfill. Flow continues on through mechanical shredding (or bar screen); flow measurement (parshall flume) enters the pump station and then is pumped up to the oxidation ditch for treatment. All in-plant flows also enter the pump station wet well.
Treatment is obtained utilizing the orbal modification (triple pass) of the oxidation ditch process by Envirex. The treatment plant is designed for an average flow of 1.042 million gallons per day, (MGD) and 2.604 MGD peak. This process is designed for biological nutrient (phosphorus and nitrogen) reduction to be maintained within our National Pollution Discharge Elimination System (NPDES) limit of 900 pounds per year of phosphorus. Raw flow, along with return sludge from the clarifiers, enters the outer pass of the ditch and progresses to the inner pass and then to the clarifiers. From the outer pass to the inner pass, the wastewater moves through step zones of variable levels of oxygen realizing the biological reduction. 5-day BOD, suspended solids, ammonia nitrogen, and dissolved oxygen limits are also met in this process. Wastewater then exits the oxidation ditch and enters the clarifiers for separation of solids and water. The settled solids are either returned to the inlet of the oxidation ditch as a constant source of bio-mass, or wasted out to the aerobic digesters for further treatment.
Treatment - Tertiary
The wastewater then continues on to the microscreens for filtration of any remaining solids not removed by the clarifiers. Filtration is by a 6 micron polyester fabric. The treated wastewater continues on to the ultraviolet light disinfection units. As the wastewater passes through these units, the bacteria and other harmful microorganisms are exposed to ultraviolet light and destroyed. This process is backed up by a standby chlorine contact chamber so that in the event of a failure of the ultraviolet units, disinfection is insured.
Flow Measurement
The treated wastewater then passes through magnetic flow meters. Flow volume values obtained from this location are used for reporting purposes as well as being used in calculation of all plant process control purposes.
The treated wastewater is then discharged into the Huron River.
Biosolids (Sludge) Handling
Waste-activated sludge is put into aerobic digesters where it will receive further treatment and stabilization. Air is applied for the continued oxidation and reduction of solids and pathogenic organisms. The biosolids are then pumped through a sieve drum concentrator where water is removed, thereby thickening the biosolids concentration and reducing total volume. This thickened biosolids are stored in a underground tank prior to ultimate final disposal by injection on agricultural farm property. This process is approved by MDEQ per our Program for Effective Residuals Management (PERM).
Applied Chemicals
Iron: (Fe) Iron salts insure the reliability to continuously achieve the 900 pounds per year limit on phosphorus. The oxidation ditch is equipped with a feed pump and chemical lines where liquid iron salts (ferrous chloride) can be fed into any one of the three passes, or to the center of each clarifier.
Polymer: As a coagulant aid, polymer can be fed into the center of each clarifier. Polymer is also used as a coagulant prior to the biosolids entry into the sieve drum concentrator.
Chlorine: After a period of time and use, the microscreens will have a buildup of growth which will reduce their efficiency. This growth can be destroyed and removed with a concentrated solution of chlorine. After the cleaning operation, the chlorine solution is disposed of by draining it back to the headworks rather than discharge with the treated wastewater into the Huron River.
Laboratory Analysis
Our NPDES permit requires that we perform daily (7 day) laboratory analysis on the treated wastewater being discharged to the Huron River. The parameters analyzed are: 5 day Biological Oxygen Demand Suspended Solids: Phosphorous Ammonia Nitrogen Fecal Coliform Dissolved Oxygen pH Chlorine Flow (MGD) For the purpose of in-plant process control, a number of other analyses are performed, which include: Solids concentration in ditch, solids concentration in RAS (return activated sludge), dissolved oxygen levels in ditch; 5 day BOD in raw, suspended solids in raw.