Biological wastewater treatment is a bioremediation process that uses microorganisms, such as bacteria, fungi and algae, to break down or transform pollutants in water into less harmful substances. Treatment techniques involve either attached growth processes, where microbes grow on the surface of stone or plastic media, or suspended growth processes, where microbes float in an aerated water mixture. Each technique, along with the type of microorganisms used, has benefits and drawbacks that must be considered when choosing a biological wastewater treatment method.

This blog post outlines common biological treatment methods and offers guidance on selecting the right one for your situation.

Wastewater bioremediation

Bioremediation is a cost-effective, environmentally safe technology for reducing and removing heavy metals and other contaminants from wastewater. Many microorganisms thrive in water polluted by heavy metals and act as biologically active methylators, converting pollutants into non-toxic forms.

Bacterial bioremediation

Bacteria are widely used in industrial wastewater treatment. Species such as Bacillus subtilis, E. coli and Pseudomonas have been used to remove heavy metals from wastewater. Mechanisms of bacterial bioremediation of heavy metals include:

• Biosorption. Bacteria bind heavy metals to functional groups like amino, carboxylate, phosphate and hydroxyl groups on their cell walls.
• Bioaccumulation. Bacteria actively transport heavy metals into their cells and store them in the cytoplasm.
• Bioprecipitation. Bacteria produce substances like exopolysaccharides (EPS) that bind to heavy metals and precipitate them out of solution.
• Biotransformation. Bacteria transform heavy metals into forms that are less toxic, such as converting hexavalent chromium to trivalent chromium.
• Bioleaching. Bacteria dissolve heavy metal compounds so they're easier to extract and recover.

Fungal bioremediation

Fungi, including Penicillium, Aspergillus, Ascomycetes and yeast can remove heavy metals from wastewater. Mechanisms of fungal bioremediation include:

• Bioprecipitation. Fungi like Aspergillus niger convert soluble metal ions into insoluble forms to precipitate them out of solution.
• Enzymatic degradation. Fungi secrete various enzymes that can degrade complex organic pollutants into simpler, less harmful compounds.
• Biosorption. Like bacteria, fungi bind heavy metals to functional groups on their cell walls through ionic exchange, complexation and chelation.
• Bioaccumulation. Fungi actively transport metals into their cells and store them in vacuoles or bind them to intracellular proteins.
• Biotransformation. Fungi mediate redox reactions that transform and detoxify pollutants in wastewater.

Effects of biological wastewater treatment

The effectiveness of bioremediation depends on several factors, including the microbial species used, the type and number of contaminants and environmental circumstances. Biological remediation methods have numerous benefits when applied properly.

Benefits of biological treatment of wastewater methods

Safety. Bioremediation methods are completely natural and produce no adverse side effects to the environment.

Cost. The input and maintenance costs of bioremediation are low compared to other techniques for detoxifying wastewater.

Energy. Bioremediation techniques consume little energy in comparison to other techniques like landfilling and incineration.

Speed. Biological techniques have a rapid turnaround time to make contaminated water useful again.

Liability. Bioremediation methods are less likely to result in contaminant leaks, reducing overall liability.

In-situ. Most bioremediation applications are in-situ and do not require hazardous material transportation.

Challenges and drawbacks​

One drawback of bioremediation is its limited effectiveness for applications outside of biodegradable contaminants and heavy metals. Its usefulness for remediating pharmaceutical pollutants, for example, is still being explored. Bioremediation is a highly selective process targeting specific contaminants, which makes it difficult to apply it more broadly.

The attached growth process, which passes wastewater through a bed of media containing microorganisms, is relatively inexpensive but creates an additional challenge. Sometimes, pieces of biomass will slough off the media and contaminate wastewater, so water must pass through a secondary treatment tank to allow these pieces to settle out. The suspended growth process, which is also known as the activated sludge process, is more costly than the attached growth process because it requires higher energy use. 

Determining the biological treatment of wastewater methods

Fehr Graham has the expertise to help you determine the best bioremediation method for your wastewater. Our projects include helping the City of Coggon, Iowa, upgrade its Wastewater Treatment Plant to meet regulations regarding biochemical oxygen demand, ammonia limits and mercury. We also upgraded the Wastewater Treatment Plant for the City of South Beloit, Illinois, converting it into an Enhanced Biological Phosphorus Removal treatment process with Integrated Fixed Film Activated Sludge technology.

Partner with Fehr Graham​

At Fehr Graham, we are committed to helping communities improve water safety through biological wastewater treatment. Our team of licensed engineers design and oversee projects while helping secure funding for system upgrades. With Fehr Graham, you can trust that your water will comply with regulatory standards.

Lucas Elsbernd, a Professional Engineer and Senior Project Manager, finds innovative solutions to challenging water and wastewater projects. He manages municipal, commercial and industrial planning and design projects in the water resources environment. He fosters a positive client experience and collaborates with leaders throughout the firm on project pursuits and technical issues. Lucas is one of the firm’s water and wastewater experts. He has a strong technical knowledge of water and wastewater treatment design and construction engineering. He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..