The major goal of water reclamation is to remove solids and biological pollutants before returning the water, called effluent, back into the environment.
Nature has an amazing ability to cope with small amounts of water wastes and pollution, but it would become overwhelmed if the billions of gallons of wastewater and sewage produced every day were not treated. Most of the water used in homes, industries, and businesses must be treated at a water reclamation facility before being released back into the environment. Water reclamation facilities reduce pollutants in wastewater to a level nature can handle.
The Reclamation Process
BCWS has two large regional plants and four smaller satellite plants that treat more than 6 billion gallons of wastewater per year. We treat wastewater because we care about our environment and our health.
Here's a step-by-step guide describing what happens at each stage of the reclamation process and how pollutants are removed to help keep our waterways clean.
The wastewater system generally relies on the force of gravity to move sewage from your home to the treatment plant. Therefore, wastewater-treatment plants are located on low ground, often near a river where the treated water can be released. When gravity alone will not transfer flow from homes to the plant because of elevation problems, lifts stations are used. Lift stations do exactly as their name describes, they lift (pump) the wastewater up from a lower elevation to a higher elevation so that the water can flow by gravity again. Once the sewage reaches the plant, it’s pumped from the influent well up to the preliminary treatment building. From here on, gravity takes over to move the wastewater through the treatment process.
2. Influent Screening
Wastewater entering the treatment plant (influent) includes items such as wood, rocks and even dead animals. If they are not removed, these items can cause problems later in the treatment process such as restricting flow, clogging pipes or damaging pumps. The materials are collected in a dumpster and shipped to a landfill.
3. Fine Screening
Unlike influent screening, fine screens are designed to remove smaller items like plastics, rags, and small toys. Once these are removed from the sewage, they are put under pressure to remove as much water as possible. The material is then placed in a dumpster. This serves to both minimize our cost of hauling the dumpsters to a landfill and keeps the organic material (food) in the wastewater.
4. Grit Removal
After fine screening, we now must try to remove the heavier material in the wastewater that is called grit. Grit is composed of materials like eggshells, gravel and sand. Since these materials are heavier than water, they settle to the bottom of the tanks, taking up capacity over time. They are also very abrasive and can damage equipment and cause valves not to work properly.
The natural weight of the grits is used to help us remove them from our system. The wastewater flows through a tank that has paddles running under the water level that forces the heavier material (grit) to the outside of the tank and then down the sloped floor for storage. Once collected, the grit is then pumped up to a grit classifier that further separates the grit from any remaining water and then places it in the same dumpster as the fine screenings that we removed earlier.
5. Metering and Sampling
Influent flow is sampled for two purposes: regulatory and process control. The waste stream is checked for things like pH, temperature, solids in the stream, metals, nutrients and amount of flow. These measurements help operators make decisions on how to run the plant.
Influent flow is combined with sludge from the clarifiers. (See step 7) The “bugs” or microorganisms have a healthy appetite and the organics in the influent flow are what they like to eat. In the aeration tanks, operators maintain the environment for the bugs. Operators keep oxygen levels, food, nutrients, temperature and the absence of toxic materials in check.
7. Final Settling
Wastewater then enters the clarifiers or final settling tanks. Here, the sludge (mainly consisting of “bugs” or microorganisms) settles out of the wastewater and is pumped back to aeration tanks. Some of the bugs are removed from the system. The clean water flows from the clarifiers to be disinfected, aerated and returned to the environment.
8. Filtration and Disinfection
After solids are removed, the liquid sewage is filtered through a substance, usually sand, by the action of gravity. This method gets rid of almost all bacteria, reduces turbidity and color, removes odors, reduces the amount of iron, and removes most other solid particles that remained in the water. Water is sometimes filtered through carbon particles, which removes organic particles. The clean water is then passed over intense ultra violet light. The UV light disinfects the water making it safe to return to creeks, rivers and lakes.
Just before the treated water (called effluent) is discharged to a local body of water, it passes over a series of concrete steps. The rolling action adds oxygen to the water. The steps look like a series of small waterfalls.
Another part of treating wastewater is dealing with the solid-waste material. The solids removed from the final settling tanks are further processed. These solids are kept for 20 to 30 days in large, aerated tanks called 'digesters.' Here, the “bugs” break down (digest) the material, reducing its volume, odors, and getting rid of organisms that can cause disease. A centrifuge is used to further reduce the volume by forcing out more of the water. The remaining biosolids are then sent to either an incinerator or to a landfill.