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Ch5_1 basic concept of biotreatment

Ch5_1 basic concept of biotreatment - 1 anddissolvedforms 2...

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    Basic Concepts of Biological Treatment   1. Removal of organic pollutants in both particulate  and dissolved forms. 2. Application of an engineered biological removal  process. 3. Sludge thickening in the secondary clarifier and  sludge returning from the clarifier to the aeration  tank are of importance. 4. Large amount of excess sludge is produced. BOD (food or  substrate) Biomass  (Microbes) Biomass  (Microbes) Binary  fission Secondary Sewage Treatment
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    Basic Concepts (cont.) The main functional microbes include bacteria,  protozoa, and metazoa. Bacteria are the major group of microbes.
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    http://www.engitech.com/graphics/critter.jpg
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    Fundamentals of Biological Treatment Slime layer Bacteria Cell 2-3 x 10 12  cells/g sludge A. Slime Layer Floc In brown or dark  brown  color with  99% water DNA stained sample
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    Classification of biological  treatment systems Suspended growth system: Activated Sludge processes(AS)  Attached growth system: Trickling Filter (TF) Rotating Biological Contactor (RBC) Key issues: Microbes, food, oxygen, other nutrients,  temp, pH (6-9), and toxins
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    Activated Sludge  (AS) Key issue: production of “good flocs” to allow  good settling in the clarifier
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    Dense and strong flocs are vital in  an activated sludge process. Why? Good settleability and solid  structure of the flocs are  crucial for the operation of  an ASP plant P Sludge thickening (MLSS=10,000 mg/L) Aeration tank MLSS=1500  mg/L
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    Definition of MLSS and MLVSS MLSS  is  shortened  from    a  name  of  Mixed-Liquor  Suspended Solids  representing the mixture of water and suspended biomass in an  aeration  tank,  which  is  parameter  to  describe  the concentration of activated sludge. (Total amount of organic and mineral suspended solids)   1,000 mg/L of MLSS means that 1000 mg sludge are contained in a 1 L mixed liquor in the tank on a dry weight basis. Since usually 80-90% of the MLSS represent the amount of bacteria, the MLSS value  also  proximately  indicates  the  quantity  of  biomass  in  the tank.     To  precisely  quantify  the  biomass  concentration  in  the  tank,  a MLVSS  (Mixed-Liquor Volatile Suspended Solids ) is used. In this  parameter,  the  volatile  suspended  solids  is  referred  to  bacteria (either live or dead)  because they become volatile in a 60-minute ignition in a muffle furnace at 550 o C.        MLVSS/MLSS = 0.8 – 0.9  
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    A normal range of MLSS is 1,000 to 3,000   mg/L.
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