6 Tips for Microscopic Evaluation of your Activated Sludge System
EBS believes that monitoring the microbiology (biomass) of your activated sludge system or aerated stabilization basin (ASB) is just as critical as any other test...
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Using Calcium Nitrate To Enhance BOD Removal
A common problem in aerated stabilization basins (ASBs) is oxygen deficiency. This can arise for a variety of reasons, such as a power outage, aerators being...
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.
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbFigure 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.
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....
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
Total Suspended Solids (TSS) & Volatile Suspended Solids (VSS)
TSS testing measures the total concentration of suspended (non-soluble) solids in the aeration stabilization basin (ASB) or in effluents. The total suspended solids (TSS) data is critical in determining the operational behavior of a waste treatment system. It is usually a permitted test and solids must be kept at a minimum.
In order to test the total suspended solids, a well-mixed sample should be filtered through a weighed standard glass-fiber filter. The residue left on the filter is dried to a constant weight at a temperature between 103 °C and 105 °C. The increase in the weight of the filter represents the total suspended solids of the sample. Large floating particles or submerged agglomerates of nonhomogeneous materials from the sample may be excluded in the total suspended solids measurements if it is determined that their inclusion is not representative of the entire sample. The size of sampling should also be limited to a size that yields no more than 200 mg residue.