For industrial companies producing wastewater as part of its process, some type of wastewater treatment system is usually necessary to ensure safety precautions and discharge regulations are met. The most appropriate wastewater treatment system will help the facility avoid harming the environment, human health, and a facility’s process or products (especially if the wastewater is being reused). It will also help the facility curb heavy fines and possible legal action if wastewater is being improperly discharged into a POTW (publicly owned treatment works) or to the environment (usually under a National Pollutant Discharge Elimination System, or NPDES, permit).
But what is a wastewater treatment system and how does it work?
The complex answer to this question (which largely depends on the wastewater characterization in relation to regulatory requirements for discharge from the plant) is simplified and broken down for you below:
What is a wastewater treatment system?
A wastewater treatment system is a system made up of several individual technologies that address your specific wastewater treatment needs.
Treating wastewater is rarely a static process, and a wastewater treatment system that is engineered to accommodate fluctuations in treatment needs will go a long way in avoiding costly replacements/upgrades down the line.
An efficient and well-designed wastewater treatment system should be able to handle:
- process variations in contamination and flow
- variations in water chemistry needs and required chemical volumes adjustments
- possible changes in water effluent requirements
What’s included in a basic wastewater treatment system?
As mentioned above, the exact components of a wastewater treatment system depend on the wastewater characterization in relation to regulatory requirements for discharge from the plant, but in general, a basic wastewater treatment system typically includes some type of:
- clarifier to settle suspended solids that are present as a result of treatment
- chemical feed to help facilitate the precipitation, flocculation, or coagulation of any metals and suspended solids
- filtration to remove all the leftover trace amounts of suspended solids (again, the level of filtration needed will depend on the degree of suspended solids removal required to pass local discharge regulations)
- Final pH adjustment and any post treatment
- control panel (depending on the level of automated operation needed)
Depending on the needs of your plant and process, these standard components are usually adequate, however, if your plant requires a system that provides a bit more customization, there might be some features or technologies you will need to add on. For example, for facilities that generate biological demand such as food and beverage a biological treatment system will be required to reduce the BOD (biochemical oxygen demand), etc.
What does a wastewater treatment system typically remove?
A wastewater treatment system might be made up of the technologies necessary to remove any number of the following:
Biochemical oxygen demand
Biochemical oxygen demand, or BOD, refers to the amount of dissolved oxygen needed by aerobic biological organisms to break down organic matter into smaller molecules. High levels of BOD indicate an elevated concentration of biodegradable material present in the wastewater and can be caused by the introduction of pollutants such as fecal waste, cleaning, and wash-down from food processing or fertilizer runoff.
Nitrates and phosphates
If large amounts of nitrates and/or phosphates are not removed from wastewater and these nutrients are discharged into local environments, they can lead to an increase BOD and extensive weed growth, algae, and phytoplankton. This can further lead to eutrophication, or the deoxygenation in a body of water, killing the organisms and potentially leading to hypoxia or environmental dead zones.
Pathogens are bacteria, viruses, fungi, or any other microorganisms that can be present in wastewater that can lead to all kinds of health issues, including acute sickness, severe digestive problems, or death. When domestic or industrial wastewater contains these harmful pathogens and is not treated, it can spread illnesses and diseases such as cholera, dysentery, salmonellosis, hepatitis A, botulism, and giardiasis, to name a few.
Mostly found in wastewater as a result of various industries, manufacturing processes, when left in wastewater in high concentrations, metals can cause extensive damage to the environment and human health. They are particularly damaging because they don’t break down and tend to accumulate, causing toxic environs.
Total suspended solids
Total suspended solids (TSS) in wastewater, the organic and inorganic solid material suspended in the water, can, like many of the other contaminants listed, harm aquatic life. They can also be problematic if the wastewater is being reused for a process, so depending on whether or not you need to discharge your wastewater in a publicly owned treatment works (POTW) or environment, or reuse the wastewater for process, will determine how harmful the TSS will be. TSS can decrease levels of oxygen in aquatic environments and kill of insects. They can also scale and foul piping and machinery.
Total dissolved solids
Total dissolved solids (TDS) are any anions, cations, metals, minerals, or salts found in wastewater. They can cause issues with aquatic life, irrigation and crops, and they can also seep into groundwater. TDS can be generated in wastewater from just about any industry.
When pesticides and other chemicals are used / made in the manufacturing process, they can be transmitted to humans and the environment through wastewater, causing damage to the environment and human health. Some common chemicals found in wastewater include diethylstilbestrol, dioxin, PCBs, DDT, and other pesticides. These “endocrine disruptors” can block hormones in the body and affect the functions these hormones control.
How does a wastewater treatment system work?
Specific treatment processes vary, but a typical wastewater treatment facility process will usually include the following steps:
Coagulation is a process where various chemicals are added to a reaction tank to remove the bulk suspended solids and other various contaminants. This process starts off with an assortment of mixing reactors, typically one or two reactors that add specific chemicals to take out all the finer particles in the water by combining them into heavier particles that settle out. The most widely used coagulates are aluminum-based such as alum and polyaluminum chloride.
Sometimes a slight pH adjustment will help coagulate the particles, as well.
When coagulation is complete, the water enters a flocculation chamber where the coagulated particles are slowly stirred together with long-chain polymers (charged molecules that grab all the colloidal and coagulated particles and pull them together), creating visible, settleable particles that resemble snowflakes.
The gravity settler (or sedimentation part of the wastewater treatment process) is typically a large circular device where flocculated material and water flow into the chamber and circulate from the center out. In a very slow settling process, the water rises to the top and overflows at the perimeter of the clarifier, allowing the solids to settle down to the bottom of the clarifier into a sludge blanket. The solids are then raked to the center of the clarifier into a cylindrical tube where a slow mixing takes place and the sludge is pumped out of the bottom into a sludge-handling or dewatering operation.
The dewatering process takes all the water out of the sludge with filter or belt presses, yielding a solid cake. The sludge water is put onto the press and runs between two belts that squeeze the water out, and the sludge is then put into a big hopper that goes to either a landfill or a place that reuses the sludge. The water from this process is typically reused and added to the front end of the clarifier.
The next step is generally running the water overflow into gravity sand filters. These filters are big areas where they put two to four feet of sand, which is a finely crushed silica sand with jagged edges. The sand is typically installed in the filter at a depth of two to four feet, where it packs tightly. The feed water is then passed through, trapping the particles.
On smaller industrial systems, you might go with a packed-bed pressure multimedia filter versus gravity sand filtration. Sometimes, depending on the water source and whether or not it has a lot of iron, you can also use a green sand filter instead of the sand filter, but for most part, the polishing step for conventional wastewater treatment is sand filtration.
Ultrafiltration (UF) can also be used after the clarifiers instead of the gravity sand filter, or it can replace entire clarification process altogether. Membranes have become the newest technology for treatment, pumping water directly from the wastewater source through the UF (post-chlorination) and eliminating the entire clarifier/filtration train.
After the water flows through the gravity sand filter, the next step is typically disinfection or chlorination to kill the bacteria in the water.
Sometimes this step is done upstream before filtration so the filters are disinfected and kept clean. If your system utilizes this step prior to filtration, you will need to use more disinfectant . . . this way the filters are disinfected and kept free from bacteria (as well as the filtered water). When you add the chlorine up front you’re killing the bacteria and have less fouling. If bacteria sits in the bed, you might grow slime and have to backwash the filters more often. So it all depends upon how you’re system operates . . . whether your system is set up to chlorinate upstream (prior to filtration) or downstream (after filtration).
If the wastewater is being reused in an industrial process, it’s typically pumped into a holding tank where it can be used based on the demands of the facility. If for municipal use, the treated water is usually pumped into a distribution system of water towers and various collection and distribution devices in a loop throughout the city.
Other possible steps to the wastewater treatment process
In waters where you have high hardness or sulfates, or other constituents you need to precipitate or take out, a lime and/or a lime soda process is used. It raises the pH, causing hardness and metals in the water to precipitate out. Cold, warm, or hot lime processes can be used, and each will yield a different efficiency. In general, hotter water removes more hardness.
Ion exchange softening
In some industrial and municipal applications, if there’s high hardness, there may be post treatment for the removal of the hardness. Instead of lime, a softening resin can be used; a strong acid cation exchange process, whereby resin is charged with a sodium ion, and as the hardness comes through, it has a higher affinity for calcium, magnesium, and iron so it will grab that molecule and release the sodium molecule into the water.
As we stated above, wastewater and effluent regulations differ everywhere you go. We have discussed some of the most common steps in a wastewater treatment plant. Typically there are special process steps to treat for a specific issues, such as the removal of certain metals or organics, or to reduce TDS for recycling etc. For these various problems specific to your individual needs, careful consideration must be given for the proper method of treatment.
SAMCO has over 40 years’ experience custom-designing and manufacturing wastewater treatment systems, so please feel free to reach out to us with your questions. For more information or to get in touch, contact us here. You can also visit our website to set up a call with an engineer or request a quote. We can walk you through the steps for developing the proper solution and realistic cost for your wastewater treatment system needs.