All About Wastewater Flow Measurement

What is wastewater?

Simply put, wastewater is clean water that has become dirty, contaminated, or polluted through an event or a process. It is generally acknowledged that there are three main source categories of wastewater: domestic/residential/commercial, industrial, and stormwater.

There are some schools of thought that would separate stormwater into its own category, independent from an overarching “wastewater” designation. For the purposes of this discussion, and because wastewater and stormwater must be collected and handled different in different systems, we will treat stormwater as its own independent entity. To learn more about stormwater and how to accurately measure it, visit our Stormwater Article.

What are some examples of wastewater?

While there are certain types of wastewater that are easy to give a name to and view as a unique entity, like sewage, hospital wastewater, or fracking water generated by oil and gas production, there are countless varieties of wastewater. Nuclear power generation also produces its own challenging version of wastewater that is typically treated on site.

Many industrial processes use water and can result in a contaminated by-product. These types of wastewater can have any number of chemicals, additives, or contaminants. Wastewater produced by residential/domestic sources are generally created by the same few water-usage activities. These are the common everyday things we do in our homes and non-industrial businesses that consume water like: showers, bathroom activities, cooking, washing hands, washing dishes, doing laundry, and brushing our teeth.

What is the difference between wastewater and sewage?

The difference between wastewater and sewage is that one is a subset of the other. All sewage is wastewater but not all wastewater is sewage.

Why should we care about wastewater?

There are two main reasons. One, after we create it, we don’t want it hanging around. We want it removed. After it is removed, it must go somewhere and be turned into something safe that will not hurt people or the environment.

Two, water is becoming a more limited and expensive resource, especially in highly populated areas that are prone to drought. There just isn’t enough to meet the demands. Reclaiming and reusing water is gaining more and more focus as a critical environmental and sustainability issue.

Increasing Demand for a Decreasing Finite Resource

Water is a limited resource and as it continues to be more so, especially in certain geographical areas, reusing reclaimed wastewater can be an option for certain tasks like irrigation or lawn care, where the plants are not harmed by anything still present in the water and where the plants and ground themselves then naturally continue the filtration process before the water returns to the freshwater table.

Where does wastewater go?

That depends on a lot of factors. Some industrial wastewater is removed and placed deep underground or in evaporative ponds. This is usually wastewater created by an industry of some sort like oil and gas or nuclear power generation. Wastewater from hospitals also has its own special challenges due to biohazard concerns. It is often pretreated on-site before being sent to another processing facility.

The majority of wastewater produced by residential/domestic/non-industrial processes ends up going to one of two places, depending on where the wastewater originated. In areas where there is a higher population density, wastewater is taken from the home or business in pipes that then deposit it into a serious of pipes that are part of a larger connected sewer system. They are moved within the pipes to a municipal wastewater treatment plant to be processed. In rural areas, there is usually not enough population density to justify the expenses of such a system. Because the waste-per-acre of ground is so much lower than populated areas, simpler and more natural options are available like individual septic systems and leach fields.

What happens to wastewater?

For environmental reasons, wastewater and sewage must be treated to remove as many contaminants as possible before it is released into natural water sources like rivers, lakes, and oceans. Sometimes treated wastewater can also be reused, before reintroduction to the overall watershed system, in applications like irrigation and sprinkling where the ground can continue to process it before it officially makes a return to the freshwater table underground.

In most areas it is required that the system that collects, processes, and returns stormwater is separate from sewage/wastewater systems. This is to protect the environment and eliminate/reduce the potential for a single collection system to be overrun by stormwater events, leading to the release of untreated water into fresh water sources. It also allows for more precision control over the treatment process. In the past, both wastewater and stormwater were channeled into one system, but as the population grew this was no longer feasible or safe. More people create more wastewater/sewage, and more concrete creates more stormwater runoff to manage.

Rural Wastewater Treatment by Septic Systems and Leach Fields

Roughly one fifth of private homes in 2021 utilized a single onsite treatment system. The manner of treatment and filtration is much simpler in nature than municipal wastewater treatment plants. Wastewater from the home is brought to a septic tank where the sludge settles out and fermentation begins via the presence of naturally occurring bacteria that begin to decompose the organic matter. The only monitoring instrumentation in rural septic systems is generally a float type level that actuates the pump when the septic tank level reaches a predetermined height, like our line of Float Level Switches.

The sludge at the bottom of the septic tank does decompose somewhat, but it never decomposes entirely. This sludge must be periodically removed by a vacuum pump from the tank every few years.

The remaining wastewater is then pumped into a leach field. No, that is not a field full of leeches. It is an underground area that contains permeable soil, sand, or dirt that can move liquid through it via gravity at an acceptable rate. In areas where the natural soil is not suitable, because the ground is either rock bed or has a high clay content, then a hill or mound of suitable permeable soil is constructed on top of the existing ground level.

You may have heard the term “perc test” in reference to someone looking at piece of property to build a home on. This refers to the natural percolation properties of the soil and whether it is permeable enough to serve as a leach field. If it is not, then the higher cost of a sand mound system has to part of the decision-making process.

In both natural leach fields and constructed sand mounds, the water is pulled through the ground by gravity, and it is filtered by the soils and biological elements naturally present. Most contaminates are removed simply by ground and gravity before they are allowed to return to the freshwater table underneath.

How is wastewater treated?

Wastewater treatment plants vary from plant to plant, but most employ similar core tactics. Treating wastewater and sewage usually happens in a minimum of three steps and involves screening, separation, physical and biological processes, mechanical agitation, and the use of sunlight, bacteria, and algae.

Primary Treatment

Because incoming wastewater can have very large particulate matter, it is sometimes screened before entering the first phase. Pumps, flow meters, and other sensitive equipment can be damaged, and accuracy can be compromised if large particulate matter is present in the liquid moving through the system. The filtered wastewater is brought into the first treatment process where it is placed in a tank for a period of time. Here, large particulate matter sinks to the bottom and lighter contaminants to float to the surface, like oils and grease. The matter that collects on the bottom of the tank is referred to as raw sludge and is removed from the bottom of the tank by scraping mechanisms. The surface is also skimmed and the elements on the top are removed.

Secondary Treatment

This phase continues to remove suspended particulates that remained after phase one if they were not light enough to float or heavy enough to sink. It also removes soluble elements like food particles. The methods of this phase can vary but most rely on natural biological processes where microorganisms and bacteria consume and remove the organic particulates. Bacteria can be helpful in a lot of ways we don’t think about. Different mechanical agitation processes are used to facilitate this process and create an optimal environment for the microbes to flourish and do their jobs.

Part of this process in phase two usually includes the partially treated wastewater being moved to an outdoor pond. Most of us are familiar with seeing the round open-air tanks in our local municipal treatment facility. Those of us who are unfortunate enough to be living near them on a day where the wind is blowing from us to them can also attest to familiarity of smelling them as well.

Here, out in the open, sunlight plays a prominent role, along with more bacteria and algae. This stage increases oxygen levels in the water, which is essential to aquatic plant and animal life, through the good old process of photosynthesis. Sometimes mechanical aerators assist in this process as well.

More settling also occurs during this phase and the sludge is periodically removed by dredging. Before the wastewater moves to the next phase, the algae are removed via filtration or chemical treatment.

Phase Three of Treatment

Treatment in the third phase is determined by where the processed wastewater will be released. Some of these processes are biological in nature and some are mechanical. Elements removed here are usually even more suspended solids, phosphates, ammonia (which is deadly to aquatic life), and nitrates.

In some applications it can also include a period of ground filtering where contaminants are filtered out by permeable ground and plants. This can be accomplished by sprinklers or recharge basins where the water is either returned to groundwater or collected from a sloped area by a ditch at the bottom. Treated water from municipal plants is typically released into a nearby body of water.

What is peak flow in wastewater?

The creation of sewage and the resultant rate of flow can vary widely throughout the day. Peak flow, or the maximum amount passing through the system, generally occurs in the morning and evening hours when people are at home and not at work. It makes sense because we generally shower, go to the bathroom, cook, wash, and do laundry in the morning and evening.

What is influent and effluent water?

Influent water is the raw, dirty, contaminated, polluted and untreated water that is brought to the wastewater treatment facility through a sewage system. Effluent water is the treated water that is released by the treatment facility.

What is wastewater flow?

Wastewater flow is simply the rate at which wastewater is traveling through the system of sewage piping on its way to the wastewater treatment plant. It can also refer to the rate of flow of the effluent water as it is released.

Why is wastewater measured?

Effluent water is regulated by governing authorities and determines the acceptable level of elements still in the water before it can be released. These standards are set in place to protect the ecosystems and habitats where the water will be returned to the watershed. Governing authorities also require that the minimum, maximum, and average rate of influent water entering the water treatment facility be recorded and reported.

How is wastewater flow measured?

Wastewater flow is measured by a variety of techniques, depending on which part of the wastewater process the water is in, whether it is the influent or effluent wastewater. The common tool for both is a flow meter. Influent water is far more challenging to measure as it contains large, suspended elements that can damage certain types of flow meter technology.

What are the best flow meters for wastewater processing?

There are two main flow meter types that standout for wastewater treatment, magnetic and ultrasonic flow meters. Both employ measurement methods that do not contain any parts that protrude into the stream of flow. They also do not contain any gears that could be damaged by particulate matter passing through.

The accuracy of a wastewater flow meter is of paramount importance when reporting influent and effluent wastewater rates to the governing authorities and it is important to select a flow meter that will deliver high accuracy and ensure the water is properly treated.

The first wastewater flow meter type is ultrasonic wastewater flow meters. These flow meters deliver significant advantages over any other technology for wastewater measuring and monitoring. They are available in a clamp-on version, like our DUC Clamp-on Ultrasonic Flow Meter that is an ideal portable or stationary wastewater flow meter. The DUC consists of a pair of transducers that are affixed to the outside of the pipe with permanent or temporary straps or chains. However, the pipe material must be suitable for ultrasonic impulses to pass through. Because they are affixed to the outside of the pipe, they provide a significant cost savings for processes with large lines sizes.

They do not require any intrusion into or disruption of the system to install or move. They also do not touch the media at all. This is ideal for wastewater measurement because large elements present in influent water could cause damage to an inline flow meter. Also, inline flow meters for large pipe sizes are generally very cost prohibitive for very large flow bodies. Clamp-on flow meters are only available in ultrasonic technology and are not available in magnetic technology. Ultrasonic flow meters also deliver excellent turndown ratio which means that they can accommodate a wide variety of flow rates that can be found in wastewater treatment.

Magnetic flow meters are also a popular choice for effluent or wastewater measurement. Inline magnetic flow meters, like our cost-effective MIS Magnetic Flow Meter, can also be used for influent wastewater measurement when the incoming pipe sizes do not make it cost prohibitive. The MIS can accommodate lines sizes up to 8” and is an ideal flow meter for effluent water. Insertion magnetic flow meters are also an option for effluent water that contains no remaining particulate matter to damage the insertion probe. Insertion magnetic flow meters would not be suitable for influent water as the probe would be subject to damage. Magnetic flow meters employ no moving parts to wear and require minimal maintenance and deliver a long service life. They are also viewed as a favored tried and true flow meter technology.

Magnetic wastewater flow meters, like our chemically resistant MIK Magnetic Flow Meter, are ideal for the chemical injection phase of wastewater treatment. Because our meters are available in different wetted materials, these meters can handle media that other flow meters cannot. They also deliver accurate precision dosing through a batching function integral to the flow meter, ensuring there are no dangerous mistakes in the misapplication of chemical amounts. Our MIK flow meter is a well-known solution for wastewater chemical injection.

What are the advantages to using ultrasonic flow meters for wastewater?

Easy to Install (ensure there are no gaps between transducer and pipe and ensure pipe is acoustically conductive)
Clamp-on versions deliver cost savings over inline meters for large diameter pipes
There is no pressure or flow energy loss
They offer a wide turndown ratio to accurately accommodate a wide range of flow rates

What are the advantages of magnetic flow meters for wastewater?

Minimum pressure loss with no intrusions into the flow stream
Low maintenance, no mechanically moving parts to wear and deteriorate
Deliver great accuracy if installed correctly
Do require a full pipe to operate correctly

How much do wastewater flow meters cost?

The price of a wastewater flow meter will vary greatly depending on the technology you choose and the features provided by the exact model of flow meter. The size of your line is also a pricing variable. The larger the inline flow meter, the higher the price. Quality also comes into play. A cheaply manufactured meter may look attractive initially but cost more in the end due to a short service life and inadequate product support.

We provide excellent customer support throughout the life of your flow meter and have some of the deepest knowledge in the industry because we make, sell, and support our products. If you are tired of trying to figure out what wastewater flow meter is best for your exact application needs and your budget, please feel free to utilize our free expert advice from our engineering staff.

Sewage Flow Meter Manufacturers

KOBOLD is proud to provide reliable products for use in the various phases of sewage treatment. While we recognize that there are many companies providing flow meters for wastewater and sewage treatment, we believe that we deliver a superior value and a superior experience and are positioned to know exactly which flow meter will be the ideal solution for your application. Contact us today and we would be happy to help you in your sewage flow meter selection.