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Aerated Stabilization Basins

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Biological Growth Curve in Aerated Stabilization Basins

Bacteria are present throughout an aerated stabilization basin (ASB), though their form and concentration may differ in the different areas of the ASB. At the front end of the ASB, where the influent enters and there is the highest concentration of biochemical oxygen demand (BOD), bacterial concentrations are higher and bacteria are dispersed as they are busy consuming the BOD. At the back end of the system, where BOD is sparse, bacteria form floc and settle out. The bacterial growth curve, as seen in Figure 1, characterizes the different growth stages of bacteria in relation to the amount of food (BOD) available.

Bacterial growth curvebbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbFigure 1: The Bacterial Growth Curve

The growth rate of the bacteria in the ASB is directly proportional to the amount of BOD available. Figure 1 shows the growth rate of the bacteria over time. The blue curve represents the amount of BOD available for consumption. The red curve represents the amount of bacterial mass in the bulk water. There are four distinct phases of bacterial growth: lag phase, log phase, declining growth phase and endogenous respiration phase.

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Activated Sludge Systems, biochemical oxygen demand, aeration, filamentous bacteria, biochemical oxygen demand bod, asb, growth pressures, Aerated Stabilization Basins, activated sludge, industrial wastewater treatment, chemical oxygen demand, aeration basin, effluent, filaments

Aerobic vs. Anaerobic Treatment in Wastewater Systems: Part 1

A Focus on Aerobic Treatment in Aerated Stabilization Basins (ASBs)

There are 2 major types of systems used for wastewater treatment: aerobic and anaerobic systems....

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Activated Sludge Systems, biochemical oxygen demand, aeration, filamentous bacteria, biochemical oxygen demand bod, asb, growth pressures, Aerated Stabilization Basins, activated sludge, industrial wastewater treatment, chemical oxygen demand, aeration basin, effluent, filaments

Aerobic vs. Anaerobic Treatment in Wastewater Systems: Part 2

A Focus on Anaerobic Treatment

There are 2 major types of systems used for wastewater treatment: aerobic and anaerobic systems. Each has different uses along with pros and cons. This particular article focuses on anaerobic treatment. Aerobic treatment is the focus of a companion article written by EBS.

Anaerobic Treatment

Anaerobic treatment is a process where wastewater or material is broken down by microorganisms without the aid of dissolved oxygen. However, anaerobic bacteria can and will use oxygen that is found in the oxides introduced into the system or they can obtain it from organic material within the wastewater. Anaerobic systems are used in many industrial systems including food production and municipal sewage treatment systems.

Anaerobic digestion is commonly used to treat sludges in the first areas of a wastewater treatment plant. This process is popular because it is able to stabilize the water with little biomass production. Anaerobic treatment occurs in many different stages. The key microorganisms are methane formers and acid formers. The acid formers are microorganisms that create various acids from the sludge. Methane formers convert the acids into methane.

The two main anaerobic systems are batch systems and continuous systems. In a batch system, the biomass is added into a reactor that is sealed for the rest of the digestion process. This is the simplest form of anaerobic treatment but can have odor issues associated with it. As the most simple, it is also one of the least expensive ways to achieve treatment.

A continuous system has organic matter constantly added to the treatment system. Since it is continuously being fed, there is a need for the byproduct to continuously be removed. The byproduct can result in a constant source of biogas, which can be used as an alternative source for energy. This system is usually more expensive to operate because of the need for constant monitoring and manpower.

Biogas is produced as the bacteria feed off the biodegradable material in the anaerobic process. The majority of the biogas produced is methane and carbon dioxide. These gases can be stored and used for energy production. The methane in the biogas can be burned to produce heat and electricity. The heat and electricity can be used to aid the process of the anaerobic system by providing power and heat for digestion to occur.

Biogas can also be used as an alternative source for fuel. This has received a lot of attention due to the ever-rising cost of burning fossil fuels. To produce fuel, the biogas must be treated to reduce or eliminate hydrogen sulfide. The treatment may become expensive but is necessary because the EPA has strict limits on the amount of hydrogen sulfide released into the atmosphere.

Whether it is aerobic or anaerobic treatment, each treatment system has its place in the world today. They are very different in the process but both are used to achieve maximum degradation while meeting the strict regulations set by the environmental agencies that regulate what is released into the air, ground, or water.

This article is multi-part

Aerobic vs. Anaerobic Treatment in Wastewater Systems: Part 1

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Aerated Stabilization Basins

Methods for Assessing Wastewater Lagoon Performance

EBS, recently presented at the 2019 AL/MS Water Jam on “Methods for Assessing Wastewater Lagoon Performance.” The presentation addressed ways to identify and troubleshoot issues that may arise in your wastewater treatment system.

Aerated Stabilization Basin (ASB) performance issues can be associated with several root causes, both chronic and intermittent. Events such as temporary upsets frequently occur due to spills, increased production, or high effluent flow rates. It is critical to be able to assess the wastewater treatment system performance during these times. In doing so, you gain a better understanding of your lagoon performance, which will assist you later when troubleshooting issues.

Performance can be evaluated while running tests to comply with permit limits or taking a more proactive approach through process control testing. It’s important to be educated on ways to monitor the health of the system to begin identifying arising issues to try and avoid potential violations and loss of system performance.

Process control testing typically consists of COD, BOD, TSS/VSS, DOUR, nutrients, DO, pH, and a variety of others. Knowing the right parameters to run for each process control, the correct methods and procedures, frequency of testing, proper sample locations, and lastly, a general understanding of the 8 Growth Pressures are all key to maintaining healthy process control.

A growth pressure is any critical factor affecting the microbial community. Whether it’s one or several growth pressures that are limiting, each of them can have a profound effect on the overall health and efficiency of the system. Through consistent monitoring and an understanding of the role of each growth pressure, operators and environmental personnel can diagnose the areas of poor performance that need to be addressed.

Because of a lagoon’s long retention times, ongoing volume loss, and gradual performance loss, it is easy to ignore an ASB in the name of cost reduction. However, failure to routinely monitor and assess the performance and capacity of the system can lead to compliance issues and may put you in a difficult situation to defend. Listed below are several ways to monitor each of the Growth Pressures both on a frequent (daily or weekly) basis and infrequent or as-needed basis:

Regular testing of the 8 Growth Pressures for process control

  • Temperature: Continuous in-line monitoring at the aeration basin influent and effluent
  • pH: Continuous in-line monitoring at the aeration basin influent and effluent
  • DO: In basin if possible, although often difficult due to size
  • Loading: BOD and surrogates such as COD or TOC
  • Nutrients: Residual testing at key sample locations within the basin
  • Retention Time: Flow and basin level measurements
  • Toxicity and Inhibition: Micro exam and DOUR testing
  • Biomass: Micro exam, nutrient residuals, DOUR, TSS/VSS

Infrequent testing of the 8 Growth Pressures for good process control

  • Seasonal performance profile studies with samples being collected across the basin for temperature,
    pH, DO, loading, and nutrients.
  • Loading: Confirming BOD and surrogates are correlated up to date
  • Retention Time: Depth and tracer studies
  • Toxicity and Inhibition: Advanced chemical analysis
  • Biomass: Micro exam, nutrient residuals, DOUR, TSS/VSS, viability of biomass

Process control is critical for identifying and troubleshooting issues with lagoon performance. Routine testing and monitoring of the system’s health provide professionals with a greater understanding of the lagoon’s performance. Proper process control makes identifying performance issues easier and quicker. It also makes troubleshooting more proficient by knowing what a healthy system looks like when operating at peak performance.  Don’t wait to begin testing after an issue arises start routine testing by establishing a good process control.

 

 

 

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floc, aeration, filamentous bacteria, abundance, heterotrophic organisms, Aerated Stabilization Basins, filament, activated sludge, aerator, filamentous organisms, aeration basin, effluent, carbon compounds, filaments

Filamentous Bacteria in Aerated Stabilization Basins Part 2

Concern or Curiosity?

Part 2 – Thiothrix and Type 021N

Mike Foster, Principal Consultant – Environmental Business Specialists, LLC
Paul Klopping, Principal Consultant – Callan & Brooks

ThiothrixIn part one of this series, we discussed the differences between activated sludge and aerated stabilization basins (ASBs) with regard to filamentous bacteria and filamentous bulking. We also talked about one of the most common filaments found in ASBs, Haliscomenobacter hydrossis. In this article, we will discuss three other filament species found in aerated stabilization basins – Type 021N, Thiothrix, Beggiatoa.

These three filaments all share a common metabolic trait – mixotrophy. These organisms can grow on a number of organic compounds heterotrophically, but also may gain energy for growth from the simultaneous oxidation of inorganic, reduced sulfur compounds (e. g. H2S). Thus the presence of reduced sulfur compounds in wastes being treated may give these filamentous organisms a growth advantage over other strictly heterotrophic organisms (i.e. floc formers). It should be noted that actual energy capture from sulfur oxidation has not been vigorously proven, as yet, and that true autotrophy does not occur, as organic carbon compounds are always required for growth.

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Activated Sludge Systems, continuous operation, lagoon system, Biological Treatment, industrial wastewater, Aerated Stabilization Basins, activated sludge system, cold weather, carbon source, aeration equipment, clari, inorganic matter

Pros and Cons of Aerated Stabilization Basins and Activated Sludge Systems

In North America, there are predominantly two systems used to biologically treat industrial wastewater: the aerated stabilization basin (ASB or aerated lagoon) and the activated sludge system. These two systems have far more similarities than differences. Both pro ­cesses are based on the utilization of dissolved oxygen by microorganisms in converting organic and inorganic matter into a settleable form. The following provides information on the pros and cons of each system.

Aerated Stabilization Basin – Figure 1

The ASB, also known as a lagoon system, is a large body of water used for biological treatment. The placement and continuous operation aeration equipment is both the most important part of the system and the most expensive. Untreated effluent comes into the primary clari­fier and then into the ASB. As the effluent passes through the system, the BOD or “food” present is used as energy and a carbon source for bacteria. Once the treated water has gone through the ASB it typically enters a polishing pond for tertiary treatment where the remaining TSS (total suspended solids) settles out before being discharged as the final effluent.  These systems are particularly widely used in the pulp and paper industry in the southeastern United States, where mills are usually remote and have access to large tracts of land.

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