When you’re developing a treatment strategy for your industrial wastewater, one of the first choices you’ll make is whether to use chemical or biological treatment. These two processes use quite different techniques to treat wastewater streams filled with varying types of contaminants. The guide below will discuss chemical vs. biological wastewater treatment methods in more detail to help you make an informed decision.
The Importance of Proper Wastewater Treatment
Why is proper wastewater treatment essential? Worldwide, especially in developing countries, about 80% of wastewater goes back into the environment without treatment — sometimes causing environmental damage and sickening local populations. In contrast, proper wastewater treatment provides several valuable benefits, including:
- Removing harmful pollutants: Industrial wastewater comes in various forms because it is a byproduct of so many different industries. One thing all wastewater streams have in common is a high concentration of contaminants. Wastewater treatment removes these otherwise harmful contaminants so the water is safe for discharge.
- Protecting the environment: Many of the contaminants in industrial wastewater are toxic to the environment. If facilities discharge toxins in their wastewater, the surrounding ecosystem will suffer. Wastewater treatment ensures that discharge is fresh so the soil and water will remain clean and plants and wildlife can thrive.
- Keeping people healthy: If people ingest improperly treated wastewater, they often become seriously ill. Gastrointestinal illnesses are common consequences of untreated wastewater discharge, as are conditions like heavy metal poisoning. Proper wastewater treatment kills or sterilizes harmful microorganisms like viruses and bacteria so they won’t make people sick.
- Complying with regulations: Industrial facilities must abide by the local or federal regulations that govern wastewater discharge. These regulations exist to help preserve a clean environment and protect human health. Failure to comply with health and safety regulations can result in penalties, so facilities should understand the statutes well and implement policies to ensure compliance.
Chemical and biological treatments both remove harmful pollutants in wastewater, but each process is ideal for different contaminants. A facility will need to choose the optimal treatment for the contaminants it deals with.
Chemical Wastewater Treatment
Chemical treatment of wastewater uses chemical reactants to break down pollutants. It is ideal for wastewaters with high chemical toxin contents, such as the wastewaters from chemical or pharmaceutical manufacturing, pump and paper mills, laboratories, and textile manufacturers. It is also optimal for removing the heavy metals found in mining wastewater. The chemical effluent treatment plants (ETPs) that treat these wastes use chemical treatment methods.
Which Types of Pollutants Do Chemical Wastewater Treatments Remove?
Wastewaters that contain toxic substances, especially toxic soluble metals, generally require chemical treatments. Any industry that uses raw materials from the earth — including industries like mining, steel manufacturing, and oil and gas extraction and refining — will produce wastewater with toxic soluble metals. These industries are more likely to use chemical treatment.
Below are a few of the common contaminants chemical waste management treatments can remove:
- Antifreeze: Antifreeze is common in wastewater from automotive manufacturing or repair shops and industries that use heavy machinery requiring antifreeze.
- Dyes: Wastewaters from pulp and paper mills and textile manufacturing contain the dyes used to color the paper or fabrics. Up to 200,000 tons of these dyes end up in wastewater every year. They have historically been challenging to remove because their design optimizes them for resisting intense lights, temperatures, and detergents.
- Paints and solvents: Paints often come from manufacturing industries that use paints and varnishes to finish their projects. Solvents in wastewater may come from the processes used to clean and polish the products for consumer use or the cleaning procedures used on equipment after production is complete. They may also come from the solvents used to break down harder materials like wood into pulp.
- Metal residues: Metal residues found in wastewater often include aluminum, cobalt, copper, iron, lead, mercury, nickel, and zinc. Heavy metals in particular can be toxic because they bind to proteins and enzymes in the body to alter their function. They can also generate free radicals — atoms with unpaired electrons that make them less stable — that damage the body. Chemical treatment breaks the metals’ chemical structures apart and renders them harmless to the environment and human tissues.
What Is the Process of Chemical Wastewater Treatment Like?
Chemical treatment may be a straightforward or complicated process depending on the contaminants in the water and the chemical reactions that take place. Most wastewater chemical treatment involves the following steps:
- Precipitation: During precipitation, chemical wastewater treatment facilities cause metals to precipitate out of the wastewater. Chemical treatment often adds charged ions to the water that the existing metallic ions can react with to form new, harmless substances.
- Coagulation and flocculation: Coagulation in chemical wastewater treatment means adding chemical substances that combine with the smaller waste particles to form larger, heavier particles. The chemical coagulants are often aluminum-based substances such as alum and polyaluminum chloride. Flocculation occurs when the smaller, suspended particles come out of suspension to form large, solid clumps the plant can easily remove.
- Ion exchange: During ion exchange, treatment plants use ion-containing resins to cause harmless ions to trade places with the toxic ions in the wastewater. In chemical water treatment, ion exchange is a common step for processes intended to produce pristine water, such as drinking water or water for industrial processes.
- Disinfection: Disinfection, which kills or sterilizes harmful microorganisms like viruses and bacteria, is sometimes the final stage for wastewater that requires a stringent level of treatment before reuse. Chlorine is a common and economical disinfectant. Other options include ozone treatment and ultraviolet (UV) light sterilization.
Depending on the contaminants, the wastewater may undergo intermediate steps, such as pH adjustments to enhance coagulation or temperature adjustments to optimize chemical reactions.
Biological Wastewater Treatment
The main alternative to chemical wastewater treatment is biological wastewater treatment. Instead of using chemicals to break down waste, this process uses beneficial microorganisms to biodegrade waste material.
What Types of Pollutants Do Biological Wastewater Treatments Remove?
Biological wastewater treatment is best at removing contaminants that biodegrade easily. Compounds with simple molecular structures – monomers and dimers, rather than complex polymers – are easiest for microorganisms to digest. Below is a list of contaminants biological wastewater treatments commonly remove:
- Aromatic compounds: Aromatic hydrocarbons are highly stable compounds that contain only carbon and hydrogen. Many small aromatic compounds such as benzene, toluene, and xylene have simple structures that are easy to break down. These compounds often show up in municipal and industrial wastewaters because they are common in substances like paint thinners, varnishes, paints, adhesives, rubbers, and gasoline.
- Carbohydrates: The carbohydrates in wastewater include starches, sugars, and long-chain sugars known as polysaccharides. Dairy wastewater, for instance, contains a high concentration of sugars, and the wastewater from food and beverage production contains sugars and starches.
- Edible fats: Edible fats often come from food and beverage production. They may also come from other industries that use plant-based oils as lubricants or surfactants.
- Hydrocarbons: Hydrocarbons like ethane, hexane, and oxane are easy for bacteria to digest. Wastewaters from industries like petroleum refining often contain substantial amounts of hydrocarbons.
- Proteins: Proteins are common in dairy wastewater and other wastewater from food and beverage processing. Their organic composition makes them easy for microorganisms to break down.
What Is the Process of Biological Wastewater Treatment Like?
Like chemical treatment, biological wastewater treatment often includes several steps. Below are a few standard biological treatment methods:
- Pre-treatment: Pre-treatment often consists of settling chambers where the wastewater sits long enough for larger particles to settle out for removal.
- Anaerobic treatment: Secondary wastewater treatment usually consists of aerobic or anaerobic treatment. The anaerobic treatment uses anaerobic microbes, which are microorganisms that do not require oxygen for their metabolic processes. It takes place in tightly sealed containers that keep out oxygen and is ideal for wastewaters with extreme organic matter loads.
- Aerobic treatment: Aerobic treatment takes place in the presence of oxygen because the microbes it uses require oxygen to break down and digest waste. This treatment typically uses aerators or diffusers to add air to the water column and facilitate oxygen transfer. Flocculation, coagulation, activated sludge return, and biofilm processes like the use of a membrane-aerated biofilm reactor (MABR) or moving bed biofilm reactor (MBBR) are forms of aerobic treatment.
- Disinfection: The last, optional step in biological wastewater treatment is disinfection, also known as tertiary treatment. Chlorine treatment is cost-effective and easy, and plants may also use ozone treatment or UV sterilization.
What Is the Cost of Chemical and Biological Wastewater Treatments?
The costs of chemical and biological wastewater treatments depend on a wide range of factors. A treatment that is efficient and economical in one facility may not work well in another. Below are some of the factors that go into determining wastewater treatment costs:
1. Reactants
Unlike biological wastewater treatments, chemical treatments use chemical reactants. Much of the cost associated with chemical wastewater treatment is the cost of purchasing the reactants. The volume of wastewater, the pollutants’ complexity, and the amount of reactant necessary will help determine the total expense.
2. Installation
Biological treatment generally uses large tanks or lagoons, often with moving mechanical parts like aerators, diffusers, or thousands of media pieces to facilitate bacterial growth and waste digestion. Much of the cost of running a biological wastewater treatment plant comes from installing the tanks and equipment.
3. Energy Use
Because wastewater treatment plants tend to be large and complex, they require a tremendous amount of energy to run. All that energy adds up to substantial utility bills. Across the United States, municipal wastewater treatment plants typically consume about $2 billion in electric costs, and energy costs tend to make up anywhere from 25% to 40% of a plant’s total operating budget. On average, wastewater treatment represents 1% to 3% of the energy use of most countries. Figures may differ somewhat for industrial operations, but energy still constitutes a significant expense.
4. Technicians
A wastewater treatment plant needs to be trained, experienced people, to run it. Paying technicians and plant managers their salaries and benefits is another part of the cost of operating a wastewater treatment plant. In 2018, plant operators in the United States earned median annual pay of $46,780.
5. Maintenance
A wastewater treatment plant requires regular maintenance to ensure high performance and functionality. Membranes may become fouled and need cleaning, or parts may break down and require replacements. Ongoing maintenance costs contribute to the expense of running a wastewater treatment plant.
Choosing the Right Wastewater Treatment Method for Your Facility
How should you determine the right treatment method for your wastewater streams? Below are a few steps to get you started:
1. Consider Your Wastewater Profile
The type of contaminants in your wastewater is one of the most critical factors to consider. Chemical treatment and biological treatment each remove certain types of contaminants, so you’ll need to select the treatment method best suited to your wastewater. If your wastewater contains high concentrations of toxic materials like heavy metals, you’ll likely need chemical treatment. If your wastewater contains high concentrations of biodegradable material like biosolid waste, you’ll want biological treatment instead.
Because chemical treatment tends to work better on more complex molecules, some facilities also deploy a combination of chemical and biological processes. They use chemical processes first to break down the complicated molecular structures and switch to biological processes when the molecules become smaller and easier to biodegrade.
2. Assess Contaminant Levels
Additionally, you’ll need to evaluate the concentrations of contaminants in your wastewater. Denser contaminant levels will require more chemicals or more strenuous biological treatment levels.
3. Adapt to Existing Land and Utility Resources
Your choice of wastewater treatment may depend on the space and utilities available. If building a sprawling, multi-tank complex on a small amount of land is not possible, consider more compact treatment operations instead. And if electricity is at a premium because of high demand, you’ll want to invest in more energy-efficient methods.
4. Learn Regulatory Requirements
Federal and local regulations may govern how low contaminant levels must be when you discharge treated wastewater back into the environment. You may need a specific type of wastewater treatment or a service that can reliably remove the correct volume of pollutants.
5. Consult With a Professional Waste Disposal Company
Even with all the information you have about treatment options, your company may be uncertain about how to choose the right industrial wastewater treatment method. Consulting with a waste disposal company is an excellent solution. Professionals in the field know the details and advantages of different processes and are intimately familiar with the regulations that govern your area and industry. They can help turn a complicated decision into a straightforward one.
Explore the Wastewater Treatment Options at Environmental Recovery Corporation’s Treatment Facility
To provide chemical or biological treatment for your facility’s wastewater, contact the experienced professionals at ERC. We are a full-service environmental company with the ability to handle all residual waste streams, and our wastewater treatment facility offers reliable, responsible, and environmentally friendly treatment solutions for industrial wastewater.
When you work with us, you’ll gain peace of mind knowing you’re engaging in sustainable practices, remaining compliant with regulations, and procuring efficient, effective wastewater treatment services. We can even take a sample from your waste stream and have it analyzed for free in the Pennsylvania Department of Environmental Protection state-certified laboratory to give you the most accurate picture of your wastewater composition and treatment needs.
To know more, please check ERC.