Managing phosphorus in wastewater is a top priority at facilities across the U.S. due to stringent environmental regulations aimed at protecting water quality. As those treatment levels grow ever more narrow, wastewater treatment operators must respond with efficient phosphorus removal technology throughout the wastewater treatment process. 

Those regulations are coming fast, too. 

Think of the agriculture sector, where runoff from livestock and crop production can contain significant phosphorus, necessitating robust nutrient removal systems to prevent eutrophication of water bodies. Or food processing: Facilities that process meat, dairy products, and prepared foods often generate wastewater effluent with high levels of phosphorus concentration.

In those industrial settings, phosphorus-rich effluent is common and must be meticulously managed to prevent environmental damage when discharged. Systems like membrane bioreactors (MBRs) are pivotal, offering precise biological phosphate removal capabilities that meet stringent regulatory standards while supporting sustainable operational practices.

Better yet: MBR technology actually enhances the quality of treated wastewater effluent for safe reuse. This capability is vital for sustainable resource management, allowing the repurposed water to be used in agricultural irrigation, industrial processes, or even municipal non-potable applications, thereby conserving fresh water resources.

Let’s get into it.

Biological Phosphorus Removal Using MBR Technology

MBRs use enhanced biological phosphorus removal (EBPR) to leverage the capabilities of phosphate-accumulating organisms (PAOs). 

These organisms ingest excess phosphorus during anaerobic conditions, storing it as polyphosphate, and later use it during aerobic periods for growth. Those PAOs incorporate that polyphosphate into biomass, releasing phosphorus into the wastewater, which is subsequently removed during treatment.

The success of EBPR in MBRs hinges on the precise configuration of anaerobic and aerobic zones tailored to promote the specific metabolic activities of PAOs. 

The anaerobic zones foster conditions that encourage PAOs to release energy by breaking down stored polyphosphate and releasing more phosphorus into the wastewater. This process is very important, as it primes the PAOs to absorb maximal amounts of phosphorus. 

The design and operational parameters, such as the sludge retention time (SRT) and the availability of volatile fatty acids (VFAs), are key to maximizing phosphorus uptake and ensuring efficient removal. SRTs are adjusted to favor the growth of PAOs over other bacteria, typically requiring longer durations to enhance the EBPR process effectively.

Additionally, MBRs provide advanced control over the treatment environment, allowing for adjustments in response to fluctuating influent characteristics and demands. This level of control, combined with the robust biological nutrient removal processing capabilities of PAOs, makes MBR technology particularly effective for municipal wastewater treatment and industries aiming to meet stringent effluent phosphorus standards while facilitating water reuse opportunities.

Monitoring and Measuring

Now, monitoring phosphorus levels in water is technically demanding due to the requirement to detect very low concentrations, often down to 0.01 mg/L or lower. These minute amounts of dissolved phosphorous can significantly impact water quality in streams.

It is advised to employ less sensitive methods primarily for pinpointing areas with acute phosphorus pollution issues.

Detailed Process Design for EBPR

Effective EBPR requires MBR systems to have designated anaerobic, anoxic, and aerobic zones. The anaerobic zone is important for phosphorus release from PAOs, whereas the aerobic zone supports its uptake, effectively managing organic phosphorus levels.

Biological phosphorus removal operates on a cyclical process of bacterial exposure to both anaerobic and aerobic conditions, which facilitates the “luxury uptake” of phosphorus.

In anaerobic stages, PAOs absorb organic materials and expel phosphorus to generate energy, releasing it into the surrounding water. Once aerobic conditions are re-established, these bacteria utilize the stored organic substrates to create energy and biomass, simultaneously reabsorbing phosphorus to satisfy their nutritional requirements, effectively cycling phosphorus from the water back into their system.

Much like the presence of oxygen at various stages in the process, an adequate supply of VFAs to anaerobic and anoxic zones is important here, as VFAs are essential for PAOs to perform luxury phosphorus uptake effectively.

An SRT of greater than 10 days is typically optimal for promoting the growth of PAOs over other bacteria. Longer SRTs ensure that PAOs can thrive, reproduce, and effectively outcompete non-PAO bacteria, which are not capable of luxury phosphorus uptake. This extended period is crucial for establishing a stable population of PAOs that can continuously process incoming phosphorus loads effectively.

Chemical Phosphorus Precipitation as a Complementary Strategy

For scenarios where biological removal is insufficient, chemical precipitation acts as a robust supplement or alternative. This method involves introducing metal salts to the wastewater to precipitate phosphorus, which can then be physically removed through filtration.

Ferric chloride, ferric sulfate, and aluminum sulfate are added to form insoluble phosphates that precipitate out of the solution. This chemical treatment also helps in managing the particulate phosphorus in wastewater.

Managing the dosing of these salts is key for efficient phosphorus removal. It requires real-time adjustments based on fluctuating phosphorus levels to avoid the risks of under or over-treatment. Proper chemical dosing not only optimizes removal but also minimizes chemical sludge.

Integrating MBR Systems for Future Urban and Industrial Needs

Incorporating MBR technology into early infrastructure planning helps cities and industries adapt to growth while minimizing environmental impacts. The flexibility of MBR systems allows for phased integration, accommodating expansions with minimal disruptions.

Effectively treated wastewater can be repurposed in urban landscaping, agricultural irrigation, and industrial processes, reducing the demand on freshwater resources and promoting sustainability. 

For example, reclaimed water can irrigate public parks or be used in cooling towers, offering a practical solution to water scarcity issues faced by many industries and communities.

The expanded use of MBR systems for phosphorus removal meets stringent regulatory standards and supports sustainable urban and industrial growth. These systems achieve this by providing an outlet for scale that adapts to varying demands and water quality requirements, ensuring long-term environmental protection and operational efficiency.