Biological wastewater treatment provides an economical and efficient approach for removing both organic and inorganic contaminants from wastewater. Although widely used to treat domestic sanitary wastewater, advanced biological treatment solutions can also be highly effective for industrial waste streams.
The wastewater treatment process
The first step in the wastewater treatment process uses primary or mechanical systems to remove large suspended and floating solids from influent wastewater In the next step—secondary biological wastewater treatment—high concentrations of naturally occurring bacteria are confined in treatment tanks and combined with protozoa and other microbes to form activated sludge. The activated sludge bacteria break down organic molecules into inert substances, producing effluent suitable for discharge to rivers, lakes, and streams.
Activated sludge can be implemented in several process configurations, each adaptable to specific effluent quality needs, including BOD, TSS, NH4, TN, and TP removal.
Biological treatment process options
Biological treatment can be implemented in several process configurations. The best fit depends on effluent limits, footprint, influent characteristics, and operational goals
- Conventional activated sludge: A flexible wastewater treatment process that uses separate aerobic, anoxic, and anaerobic zones to target specific contaminants. Aerobic zones contain oxygen which promotes the growth of microorganisms that break down carbon (organics) and ammonia. Anoxic zones rely on mixing in the absence of free oxygen to remove nitrate and lower total nitrogen. Anaerobic zones are void of both free oxygen and chemically bound oxygen and promote conditions for biological phosphorus removal.
Examples: VertiCel® systems, CASPERON™ systems, FlexZone adaptive process volume systems - Oxidation ditches: Looped reactor systems with longer solids retention times that use aeration to biologically remove organic matter and nutrients and mixing to keep the contents of the tank moving and suspended. Process controls adjust operating conditions to promote carbon removal, nitrification, denitrification, simultaneous nitrification and denitrification (SND) and phosphorus.
Examples: Bioloop® systems, Orbal® systems - Sequencing batch reactor (SBR) systems: A compact, flexible treatment system that uses a single tank for nitrification, denitrification, and biological phosphorus removal. SBRs handle flows from 0.01 to 60+ MGD and can reduce the need for primary and secondary clarifiers.
Examples: Sanitaire® ICEAS SBR systems and OMNIFLO® SBR systems with Jet Tech technology - Intensification processes: Technologies that leverage existing infrastructure to increase treatment capacity and performance. By optimizing current assets, facilities are able to treat higher flows and loads using the same tank volumes—while staying compliant with evolving effluent standards.
Examples: Taron® activated sludge filters, ballasted clarification systems - Attached growth (fixed film): A treatment system that utilizes specialized media to provide a stable surface for microorganisms to grow and form a biological film. As wastewater passes over or through the media, microorganisms consume organic matter and other pollutants, providing effective biological treatment.
Examples: Envirex® rotating biological contactors (RBC), moving bed bioreactors (MBBR)
Aeration and mixing for biological wastewater treatment
Across activated sludge, oxidation ditches, SBR, and attached-growth processes, aeration and mixing are critical to treatment performance and energy efficiency. The right equipment helps maintain consistent conditions in each step of the process.
- Aeration equipment: Used to deliver oxygen into an aerobic treatment environment with oxygen transfer efficiency varying by equipment type and process design.
Examples: Fine bubble diffusers, wide band coarse bubble diffusers, jet aeration - Mixing equipment: Ensures effective contact between solids, contaminants and substrates for optimized treatment. Suitable for anaerobic, anoxic, or suboxic, limited aerobic environments, with mechanical and compressed gas mixing options available.
Examples: BioMix™ and BioMix-DC compressed gas mixing systems, Flygt® compact and geared adaptable submersible mixers
How we can help
As effluent water quality regulations become more stringent, the demand for high-quality wastewater treatment solutions continues to grow along with methods for reducing energy consumption and expanding capacity in existing plant footprints. Xylem responds to evolving wastewater treatment standards with solutions that include biological oxygen demand (BOD) reduction, aeration, clarification, phosphorus and nitrogen removal. We also offer key innovations for simultaneous nitrification denitrification, magnetite ballasted treatment, and biological treatment for trace contaminants such as selenium and heavy metals.
In addition, when plant treatment equipment reaches the end of its useful life, Xylem can help turn what you have into what you need, to increase performance, reduce maintenance and extend lifetime to keep treatment plants up and running.
Unlock nature’s power with advanced biological treatment that turns pollutants into clean water while saving energy and improving efficiency
