What Are the Stages of Wastewater Treatment

When wastewater leaves a business or home, it enters the sewer pipes or heads to a septic tank and leach field. What happens from there? What are the stages of wastewater treatment and what can you do to have an efficient, effective wastewater treatment plant as you consider each of these stages?

Stage 1: Screening

Before anything else happens, wastewater and hauled septage have to go through screening. This is where the things that shouldn’t ever be flushed or allowed into sewer lines are filtered and removed. This includes items like a child’s toy, a plastic tampon application, rags, plastic wrappers, grease clumps, and pieces of wood. They are raked from the filters, rinsed to remove any waste products, and pressed to get out as much water as possible.

Items removed in the screening process go to landfills. The remaining wastewater moves to the second stage of wastewater treatment.

Stage 2: Grit Removal

Grit removal is a process where fine, gritty particles are removed from the wastewater. It includes particles like coffee grounds, sand, and gravel. They are removed by a pump after the grit settles on the floor of a grit chamber. From there, it gets hauled to a landfill. The remaining wastewater goes to clarifiers.

Stage 3: Primary Settling/Clarifying

At this point, the wastewater is rid of grit and trash. It sits in a circular tank to settle. Sludge sinks to the bottom of the tank, and fats float and collect on the surface. The wastewater between the two layers leaves the tank.

The fat layer is skimmed periodically from the surface, while the sludge is pumped out. Chemicals are introduced to start breaking down the phosphorus. 

Stage 4: Aeration

Aeration is the key step in processing wastewater. Pumps add air to the wastewater to help aerate it while microorganisms begin to digest the remaining sludge and pollutants and create a mixture of water, nitrogen, and cell tissue. 

Stage 4B: Activated Sludge

The remaining sludge goes through treatments of its own. To start, it is skimmed from the aeration tanks. Water is removed from the solids and returned to the start of the wastewater treatment process.

The thickened sludge mixes with primary sludge and is pumped to a primary digester. There, it’s heated and allowed to compost for over a month using anaerobic bacteria to help break it down. Pollutants from the sludge are digested by the bacteria and converted to carbon dioxide and methane gas, and water. 

After the bacteria has done its job, the remaining sludge is moved to a gravity belt where it’s mixed with a polymer that helps absorb all of the water. Water drains into a basin where it has to be slowly mixed back to the beginning of the wastewater treatment process because of its high ammonia content. Too much all at once creates problems.

The sludge goes to storage tanks where it sits for upwards of a year before going into tanker trucks to be spread at approved sites, such as fields and forest lands, to provide nutrients the soil needs for optimal plant health.

Stage 5: Secondary Settling/Clarifying

Wastewater is pumped to secondary clarifiers. At this point, the wastewater is 90% of the way to the finished product. Activated sludge is continually pumped out as it settles and goes back through Stage 4B.

Stage 6: Filtration

Now that the wastewater is cleaned. It’s filtered through some type of media. Different wastewater treatment plants rely on different types of filters. Some may use activated carbon filtration, some might rely on coconut fibers, and some use polyester. If any particles are on the filter, they’re washed and returned to Stage 1.

Stage 7: Disinfection

The filtered wastewater is now mixed with chemicals to kill any remaining bacteria or exposed to UV disinfection. Water is tested throughout the process to make sure it meets the required levels before it’s released to the area river, lake, pond, or water treatment plant for reuse.

Stage 8: Aeration

Some wastewater districts add one more step to aerate the cleaned wastewater to make sure it has the correct oxygen levels. Every wastewater treatment plan has requirements listed in its permit. Failure to complete the steps needed to bring the water quality to those levels can lead to hefty fines.

Consider Your Options for Hauled Septage

When a wastewater district also accepts septage from residences and businesses that are not on a sewer line, a septage acceptance plant is necessary. This is the station where trucks will pull up and pump out their tanks with the septage they’ve pumped out of septic tanks. 

Hauled septage is raked to remove any trash or grease clumps. The remaining wastewater and sludge get pumped to the screening stage of wastewater treatment. As septage haulers collect money from businesses and consumers and pay the wastewater district from those proceeds, you’ll want to have a computer system set up to track who is bringing in the septage, how much they dropped off, and bill them accordingly. 

Tips For Improving Effectiveness and Efficiency

You have to have a wastewater treatment plant that effectively cleans water in the most efficient manner possible. How do you ensure you’re cleaning the water effectively, avoiding raw sewage releases, and keeping costs down for the members of your wastewater district?

  1. Automation Eases Guesswork

Do you struggle to keep up with the flow rates at your facility? Do you have some days where your employees struggle with higher flow rates than estimated, so they have to constantly speed up or slow down pumps and motors? Or, do they run the motors at high speeds as a preventative measure, even when it’s unnecessary? It’s not an ideal way to operate your wastewater treatment plan.

If there’s heavy rain and your wastewater treatment plant and stormwater runoff are linked, it’s easy to flood and require raw sewage to be released. It’s not ideal for the environment. It’s also easily addressed by adding automation to your plant.

  1. Upgrade Older Equipment

Some of the easiest changes to your plant that will result in cost-saving measures are to look at the aeration system you use. Older pumps and motors can be upgraded to more energy-efficient models that do the job better while requiring less electricity.

  1. Consider Solar and Wind Power

It’s estimated that all of the municipal wastewater treatment plants in the U.S. use about $2 billion in electricity each year. Upwards of 40% of a plant’s operating costs come from the plant’s electricity consumption.

While it does cost money to establish solar or wind power systems at your plant, the savings over time are worthwhile. After a 10-acre solar panel farm was placed near the Moccasin Bend wastewater treatment plant in Tennessee and upgrades were made to some of the plant’s equipment, the plant’s power consumption dropped by $1.4 million per year. 

  1. Heat With Methane

A wastewater treatment plant ends up with methane being produced as part of the process. Why not use that methane gas to heat the plant? You’ll eliminate bills for propane, oil, natural gas, or electric heat during the winter months. 

Lakeside Equipment has decades of experience in wastewater treatment designs and equipment that boost your plant’s efficiency and keep up with changes in the flow rates during unexpected storms. We’ve been around since 1928 and provide you with an experienced engineer to design a system that meets your municipality’s needs and budget. 

From final design to installation and operation, our field engineers ensure your system is optimized to do everything you expect. Talk to our wastewater experts about the SharpBNR control system that reduces electricity costs and boosts your plant’s reliability. You can pair it with a SCADA system for optimal performance throughout your wastewater treatment plant.