This week, we’re continuing our discussion on how to select blower technology for industrial wastewater treatment applications. In our first installment, we defined the four stages of wastewater treatment including pretreatment, primary, secondary and tertiary treatment. Last week, we explored the six most common secondary wastewater treatment methods that utilize blowers in their processes.
Defining Air Demand
Defining air demand is the first step in selecting the proper blower for an industrial wastewater treatment application. The two most critical components for calculating air demand are pressure and air flow.
Calculating pressure. For most applications, pressure is defined as hydraulic head plus friction losses. Hydraulic head is approximated at 0.434 PSI/FT of water depth, while friction losses are determined by the size, roughness and number of elbows and tees in the piping system plus the pressure loss of the diffuser membranes or aeration nozzles.
Calculating air flow. Air flow can typically be much more difficult to calculate because of the complexity of the aeration process. Because the goal of aeration is to provide oxygen to satisfy biochemical oxygen demand (BOD), dissolved oxygen (DO) levels are monitored on a continual basis to ensure proper aeration of the tank, basin or lagoon. If the BOD is not satisfied, the bacteria responsible for breaking down organic pollutants in the wastewater may die, making the wastewater difficult to treat. In this situation, low quality effluent may be released into the environment, resulting in fines from local and/or federal regulatory bodies.
Avoiding complications. To avoid complications from air flow miscalculations, several design parameters must be taken into consideration. These parameters include standard oxygen transfer efficiency (SOTE), standard oxygen rate (SOR), water temperature, site elevation, diffuser type (bubble size) and fouling factor. Because of the large number of variables involved in calculating air flow, bringing in an engineering firm to perform the calculations and assist with equipment selection is often required.
Next Step: Evaluating Blower Technologies
Blower selection ultimately depends on the application and the air demand. Once air demand has been calculated, the evaluation of blower technologies – either positive displacement or centrifugal – can begin. Stay tuned for the next installment of our wastewater treatment series that will provide an overview of the different technologies housed within blowers, as well as discuss advantages and disadvantages of each.
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