Wastewater Treatment Plant Startup and Restart

Wastewater treatment plants can experience biological upsets for many reasons. Some are predictable, while others occur with little warning.

One of the greatest challenges for wastewater operators is determining how to restart biological treatment after a biomass loss or how to establish healthy biology during the startup of a new treatment facility.

Biological treatment can be disrupted by:

Toxic industrial discharges
Petroleum or diesel entering the collection system
Chemicals associated with illicit manufacturing
Septage or grease-hauler discharges
Cleaning and root-control chemicals
Sudden changes in wastewater composition
Hydraulic washouts
Low organic loading
Other toxic or inhibitory compounds

When a toxic event significantly reduces the microbial population, operators may need to rebuild the biomass before normal treatment performance can resume.

Starting a New Wastewater Treatment Plant

A similar challenge occurs when a municipality completes construction of a new wastewater treatment plant or treatment-process expansion.

After investing significant resources into the facility, operators need to establish an active microbial population capable of meeting treatment objectives and discharge requirements.

Startup and restart strategies can be used for many types of wastewater treatment processes, including:

Activated sludge plants
Biological nutrient removal (BNR) systems
Anaerobic digesters
Aerated lagoons
Facultative lagoons
Other biological wastewater treatment systems

Several methods are available for establishing or rebuilding wastewater biomass.

Method 1: Allow the Biomass to Develop Naturally

One option is to allow microorganisms already entering the wastewater treatment system to establish the biological population naturally.

This approach requires little additional treatment material, but developing a mature and stable microbial community can take considerable time.

Depending on wastewater characteristics, temperature, loading, plant design, and operating conditions, startup may require weeks or even months before treatment reaches stable performance.

Natural biomass development may be appropriate when:

Time is not critical
Permit requirements can be maintained
Wastewater loading is stable
Operating conditions favor microbial growth

For facilities that need to establish treatment quickly, another startup method may be more appropriate.

Method 2: Seed the Plant with Activated Sludge

Another common method is to introduce activated sludge from an operating wastewater treatment plant.

Imported sludge can provide an established population of microorganisms and may accelerate biomass development compared with relying entirely on natural colonization.

However, operators should consider several factors before using imported activated sludge.

1. Transportation and Handling

Activated sludge must be transported from another wastewater treatment facility.

Depending on distance, volume, community concerns, and hauling requirements, this process can create additional logistical and operating costs.

2. Microbial Populations May Be Different

Every wastewater treatment plant receives a different influent.

Microbial populations that perform well at one facility may not contain the organisms needed to address the specific wastewater characteristics of another plant.

This can be particularly important when the receiving facility has Significant Industrial Users (SIUs) or unusual industrial wastewater sources.

3. Unwanted Microorganisms May Be Introduced

Imported activated sludge may also contain microorganisms that are undesirable under conditions at the receiving plant.

For example, excessive filamentous bacteria can contribute to:

Poor sludge settling
Sludge bulking
Foaming
Elevated effluent TSS

Understanding the condition of the seed sludge before introducing it into a new treatment system is important.

4. Trash and Other Material May Be Present

Transported sludge can also contain wipes, debris, grit, or other materials that the receiving facility may not want introduced into its process.

Method 3: Use Bioaugmentation for Startup or Restart

Bioaugmentation is another strategy for establishing or restoring microbial populations in wastewater treatment systems.

Bioaugmentation involves introducing commercially prepared microbial cultures into the treatment process.

This approach can be used for:

New wastewater plant startup
Plant restart after a toxic event
Biomass recovery
Nitrification recovery
Biological nutrient removal support
Lagoon startup or recovery
Activated sludge treatment

Depending on the system and operating conditions, concentrated microbial cultures may help establish treatment biology more quickly than waiting for microbial populations to develop naturally.

Actual startup time will vary according to wastewater temperature, organic loading, dissolved oxygen, pH, retention time, microbial population, and plant design.

What to Look for in a Bioaugmentation Product

Not all microbial products are formulated the same way.

When evaluating a wastewater bioaugmentation product, operators should understand what organisms are present and how the product is intended to perform.

Important considerations may include:

Viable microbial populations
Colony-forming unit (CFU) concentrations
Microbial diversity
Treatment objectives
Product stability
Storage requirements
Application method
Manufacturer quality control

Colony-Forming Units Matter

A colony-forming unit (CFU) measurement provides an indication of the number of viable microorganisms capable of growing under the test conditions.

Operators should pay close attention to how CFUs are reported.

For example, a product listing microorganisms per milliliter cannot be directly compared with another product listing microorganisms per gallon without converting the units.

Comparing concentrations on an equivalent-volume basis provides a more meaningful evaluation.

Microbial Diversity Matters

Wastewater contains a complex mixture of organic material and nutrients.

Different microorganisms perform different biological functions, including:

BOD degradation
FOG degradation
Nitrification
Denitrification
Organic solids decomposition
Hydrocarbon degradation
Other biological transformations

For this reason, microbial diversity can be an important consideration when selecting a bioaugmentation product.

Liquid and Dry Microbial Products

Commercial wastewater microbial products may be available in liquid, dry, or other formulations.

Each formulation has its own storage, handling, and activation requirements.

For liquid cultures, operators should pay particular attention to recommended storage temperatures and avoid conditions that may reduce microbial viability.

Regardless of formulation, the most important considerations are whether the organisms remain viable and whether the product is appropriate for the treatment objective.

Bioaugmentation vs. Biostimulation

Bioaugmentation and biostimulation are different biological treatment strategies.

Bioaugmentation

Bioaugmentation involves adding microorganisms to increase or diversify the biological population within the wastewater treatment system.

Biostimulation

Biostimulation supports microorganisms already present in the system by improving their environment or providing materials they need for growth.

These materials may include:

Supplemental organic carbon
Nutrients
Trace elements
Oxygen
Other microbial food sources

A biostimulant does not necessarily introduce new microorganisms into the treatment process.

Depending on the condition of the plant, operators may use bioaugmentation, biostimulation, or a combination of both.

Choosing the Right Wastewater Startup or Restart Method

There is no single startup strategy that is appropriate for every wastewater treatment plant.

The best method depends on:

How quickly treatment must recover
Permit requirements
Available budget
Access to suitable seed sludge
Wastewater characteristics
Plant design
Temperature
Existing microbial populations
Cause of the biological upset

Natural biomass development may be appropriate when sufficient time is available.

Imported activated sludge may be useful when compatible seed sludge is readily accessible.

Bioaugmentation may provide another option when operators need a concentrated microbial source without transporting large quantities of activated sludge.

In some wastewater treatment systems, the most effective approach may involve combining multiple startup or recovery strategies.

Preparing for Wastewater Plant Recovery

Biological upsets are not always predictable.

Keeping a plant recovery strategy in place can help operators respond more quickly to toxicity, hydraulic washouts, biomass loss, or other unexpected conditions.

A recovery plan may include:

Monitoring wastewater toxicity
Maintaining appropriate dissolved oxygen
Tracking biomass and settling characteristics
Monitoring ammonia, nitrate, BOD, and TSS
Identifying potential industrial dischargers
Maintaining access to bioaugmentation products
Planning for supplemental carbon or nutrients when appropriate

The goal is to restore a healthy, stable microbial community capable of meeting the biological treatment requirements of the wastewater facility.

For More Information

For questions about wastewater plant startup, plant restart, bioaugmentation, or biological treatment, contact:

Rick Allen
303-888-2008
rick@biolynceus.net

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For more information regarding plant startups click here.

Wastewater System Restart or Initial Start Up?