FACTSPlant type: Activated sludge plant
Capacity: 10.0 Million Gallons/Day (MGD)
HOW IT WORKSWastewater contains large amounts of excess nutrients that could overwhelm the watershed if they were directly discharged into the Grand River. The Grandville Plant "cleans" the wastewater to remove those excess nutrients. Clean water meeting National EPA standards is returned to the river and the nutrients are processed and recycled in a controlled application as agricultural fertilizer.
THE WATER TREATMENT PROCESS
- Wastewater flows by gravity to the plant by a system of underground trunk sanitary sewers in the City of Grandville and Ottawa County.
- Screening structures remove inorganic materials from the water.
- The sewage is then pumped up into the treatment process and flows through the plant by gravity to be discharged about 20 hours later into the Grand River.
- Grit (inorganic sand and gravel material) is removed by either an air de-gritter or a vortex grit removal system.
- Velocity of the flow is slowed in large tanks to allow heavier organic materials to settle out of the water. These solids contain many of the excess nutrients such as a nitrogen and phosphorus. They are pumped to the solids treatment process.
- The water now is slightly cleaner, though it still has some solid nutrients and contains the nutrients that have been dissolved.
- The secondary process is the biological part of the treatment system. Large volumes of microscopic organisms are kept suspended in tanks using diffused air bubbles (like you would see in an aquarium). These microbes are normally present in nature and thrive on the dissolved nutrients. Secondary treatment is concentrating this natural process to remove more excess nutrients from the water.
- To remove phosphorus, an iron salt called Ferric Chloride (Fe) is added at the end of this process. The Fe binds with the phosphorus causing it to become heavier so it can be sent to the solids handling process.
- The flow now goes into settling tanks. Some of the microbes and most all of the nutrients settle to the bottom and are returned either to the secondary process or the solids handling process. Clean, clear water flows out of these tanks over weirs and into the last stages of treatment.
DISINFECTION AND DISCHARGE
- Because of the concentrated human use of the water it needs to be disinfected before being returned to the watershed. This is accomplished by exposing the flow to Ultraviolet Light, which removes pathogenic organisms and treats the water to meet body contact standards.
- The final step is a cascade aeration system (like a waterfall). This restores oxygen to the water before it is finally returned to the watershed.
THE SOLIDS HANDLING PROCESS
- Organic material is pumped from the primary treatment process to an anaerobic digester. Kept at a constant temperature and constantly being mixed, the material is stabilized into a nutrient rich fertilizer.
- A side benefit is this process creates methane gas. The plant uses that gas to run a generator and heat a boiler, reducing the consumption of utility power and natural gas.
- The material is then concentrated by removing excess water and stored until ready for use.
- Several times a year it is land applied to agricultural fields for crops like corn and wheat.