For these processes typically found in the wastewater treatment plant: a. What r
ID: 503900 • Letter: F
Question
For these processes typically found in the wastewater treatment plant: a. What removals of BOD and SS can be expected from the Primary Settling process? b. What % removals of BOD and SS can be expected from the influent to the Secondary Treatment process - which includes the settling? c. How much sludge is typically produced in a treatment plant based on BOD treated? What is a typical solids concentration in the aeration basin? d. In the Activated Sludge process, with clarifier and sludge return, is the hydraulic detention time the same as the sludge detention time (also called sludge age)? Longer or shorter? e. What are some of the key features of Suspended and Attached Growth secondary treatment systems? f. When are Aerated Lagoons and Oxidation Ponds useful/necessary?Explanation / Answer
a. Primary settling process is the first step in wastewater treatment. This process allows heavy organic solids to settle down as sludge, achieved by reducing the flow of wastewater. In the primary settling process, approximately, 60 % of suspended solids (SS) and 35 % of Biochemical oxygen demand (BOD) are removed from the wastewater.
b. The secondary treatment process is done after primary setlling. The secondary treatment process involves a settling step and a biological process to remove dissolved and suspended organic impurities from wastewater. It removes 85 % of BOD and SS (including the primary settling process). If we consider the influent of the secondary process, about 25 % SS and 50 % BOD are removed in the secondary process. (subtract 60% SS and 35 % BOD removed in primary process from 85 %)
c. A BOD treatment plant produces about 25-45 g sludge per population equivalent of the microorganism used. Typical solids concentration in an aeration basin varies between 20-35 %
d. Hydraulic retention time generally goes upto 8 hours while sludge detention time is longer (more than 20 days). If the sludge detention time or sludge age is short, it results in membrane fouling
e. In suspended growth treatment, waste flows through freely suspended microorganisms and gather as flocs. The sludge contains active microorganisms as in activated sludge process and can be resued for treatment. Whereas, in attached growth treatment like trickling filters, the microorganisms are attached to fixed supports, through which waste water flows and forms a biofilm. During the treatment, the biofilm grows thicker and thicker and finally falls off.
f. Aerated lagoons and oxidation ponds convert wastes in water using the combined action of oxygen and microorganisms. They are epecially useful and cost-effective when large land facility is available for water treatment. They are also effective in removing pathogens from waste water.