Removing Inorganic & Solid Materials From Wastewater

Wastewater is the water and material that travels from a home, business, or factory to sewer lines or septic tanks. It includes a mixture of inorganic, organic, and solid materials. The water from showers, sinks, dishwashers, toilets, and washing machines all become wastewater. It also includes the water used in food and beverage manufacturing and processing, paper mills, and many other industries. 

Some cities and towns have stormwater drains connected to the area sewer systems, known as combined sewer overflows. Combined sewers are not ideal as any heavy rains or melting snow also become part of the wastewater a plant receives for treatment. 

Around 700 combined sewers exist in the U.S. All of these combined sewers have to have plans in place to reduce the release of raw sewage if it floods, as do all sanitary sewer overflows, which are the typical sewer lines and sewer systems found across the U.S.

Before this wastewater is released into a body of water, be it a river, lake, or pond, solid, organic, and inorganic materials must be removed. How is this done?

Understanding the Differences Between Inorganic, Organic, and Solid Materials

Solids are pretty easy to understand. It’s the fecal matter, toilet paper, and items that shouldn’t have been flushed like toys, baby wipes, and plastic wrappers. 

You also have organic and inorganic materials. Organic matter includes living things like bacteria, parasites, fungi, and algae. Inorganic matter includes the minerals, metals, chemicals, and salts that are in urine, industrial wastewater, detergents and cleaning products, and water from washing dishes and cooking.

How Solids, Organics, and Inorganic Materials Are Removed

All organic, inorganic, and solids have to be removed from wastewater, and it usually involves three main treatment steps and the different stages of each one. The steps include:

  1. Primary Treatment

In primary treatment, wastewater moves through screens where solid materials like plastic applicators and bags, sticks, and other trash catch on the screens and is raked into collection bins to be transported to the landfill. In most plants, the wastewater now goes through grit removal, where items like coffee grounds, eggshells, sand, bone chips, and seeds are removed. It’s important to remove grit before it damages equipment through abrasion and settles and clogs pipes. The grit can be transferred to compost piles or landfills.

After grit collection, the wastewater flows into tanks where it is given time to settle. During settling, the heavier waste sinks to the bottom. Lighter materials like fats, oil, and grease (FOG) float to the top. The FOG is skimmed and removed, while solids are pumped from the bottom for sludge treatment. The remaining wastewater moves to secondary treatment stages.

Sludge treatment is a separate process where it is introduced to bacteria to help it decompose. This process produces methane. Some districts have systems set up to capture the methane biogas and use it to generate power or heat the buildings in the wastewater facility. The remaining sludge may be incinerated or disinfected and used as fertilizer. 

  1. Secondary Treatment

Wastewater that isn’t part of sludge or oily scum moves to secondary treatment stages. The next stage of cleaning the wastewater involves bacteria. Any sludge that remains goes from the bottom of the tank back to the beginning of the process to start over.

Some districts use fixed film systems to encourage the growth of bacteria as wastewater flows into secondary treatment steps. Others use suspended growth systems using decomposing bacteria and aeration to help grow bacteria and speed up digestion and decomposition. This is also helpful in reducing the ammonia found in wastewater from urine.

With an aerated system, wastewater moves to aeration tanks where oxygen is added to help aerobic bacteria thrive as they consume the organic materials that remain. Bacteria will remove these particles before their lifecycle ends. At that point, the wastewater is almost clean and heads to the final steps in wastewater treatment.

  1. Tertiary Treatment

Filters may be used to help filter any remaining particulates. Biofiltration is used to filter out some of the particles remaining in the almost-cleaned wastewater. Biofiltration may use sand, charcoal, or coconut fiber filters. Each plant has its preferred biofiltration material.

Often, the levels of nitrogen and phosphorus are still too high to be safely released into area lakes and rivers. If they were released at this stage, they encourage the growth of algae blooms and invasive weeds. For that reason, the water treatment process isn’t done. 

More bacteria are needed to absorb phosphorus and nitrogen. Or, water may be moved into lagoons where plants and zooplankton absorb them over time. 

To kill any remaining pathogens, chemicals like chlorine might be introduced. If they are used, the water has to be exposed to UV lights to dissolve the chemicals to recommend levels before the treated wastewater is released or transported to a water treatment plant to go back to area homes and businesses.

The equipment used and stages followed depend on the district and what the EPA permitted levels allowed in that region. Every wastewater treatment plant has instructions from the EPA setting limits for things like chlorine, E. coli, etc. are allowed. Wastewater treatment plant stakeholders need to make sure the equipment in the plant is capable of performing the job effectively and efficiently. 

Saving money is ideal, but not if the equipment you’re saving money using is failing to do the job required of it. Upgrading equipment for better performance saves money in the long run as you won’t face fines and potential criminal charges.

Tips to Help Produce Cleaner Water

If you read the news, you probably spot articles from time to time where a wastewater district was fined for releasing raw sewage – either knowingly or accidentally. Automation is one of the best tips for getting solids and inorganics from wastewater. When you have automated wastewater treatment equipment, the computer can gauge flow rates and adjust pumps and aerators accordingly. 

This ensures the different steps are handled correctly and lowers power consumption and wear and tear by slowing down pumps when people are using less water in their homes while they’re sleeping or at work. During the busier times of day, such as morning showers or dinner-time chores and preparations, computers will increase pumps as needed.

If something is changing and needs correction, a SharpBNR and PLC instrumentation package helps prevent the release of raw sewage. Paired with SCADA systems and HMI, human error is less likely to happen as alarms are sounded before major problems occur. You have time to react, and options like Variable Frequency Drives and motor starters make adjustments so that your team isn’t rushed to get to the right area of the facility. If you don’t have this technology in place, it’s time to look into it.

Take time to talk to your district’s residents and business owners. The more they know about the problems that impede water treatment steps, the easier it is to do your job. They may not realize that a “flushable” wipe, wrapper, or applicator isn’t truly flushable. Mailers and ads help spread the word.

Lakeside Equipment has close to a century of experience in water treatment technology and equipment. We’re leaders in water quality and are happy to talk to you about your plant’s equipment and design and offer insight into the solutions available to increase efficiency and water quality, all while lowering your maintenance costs and demands. Reach out to us and let us know how we can help.