Biological Treatment 1 Jae K. (Jim) Park, Professor Dept. of Civil and Environmental Engineering University of Wisconsin-Madison

Treatment Objectives 1980 to 2000 Removal of toxic compounds and nutrients (N & P) 2 Early 1970s to 1980 Based on aesthetic and environmental concerns Began to address nutrient removal Improved treatment efficiency and widespread treatment of wastewater 1900 to early 1970s Removal of suspended and floatable material Treatment of biodegradable organics Elimination of pathogenic organisms 21 st Century Endocrine disrupting chemicals (EDCs) and other synthetic compounds, emerging pathogens, etc.

Minimum National Standards for Secondary Treatment 3 ParametersUnits30-day ave. conc.7-day ave. conc. BOD 5 mg/L30/45 a 45/65 Suspended solidsmg/L30/45 a 45/65 Hydrogen-ion conc.pH units6~9 b 6~9 b Carbonaceous BOD 5 c mg/L2540 a Average removal  85% b Only enforced if caused by industrial wastewater or by in-plant chemical addition c May be substituted for BOD 5 at the option of the National Pollution Discharge Elimination System (NPDES) permitting authorityNational Pollution Discharge Elimination System

Kinetics of Biological Growth Lag phase log (# of cells) Log (exponential) growth phase Stationary (declining) phase Death (endogenous decay) phase t 4

Dispersed growth Cause: Microorganisms do not form but are dispersed, forming only small clumps or single cells. Effect: Turbid effluent. No zone settling of sludge. Slime (jelly) viscous bulking; or non-filamentous bulking Cause: Microorganisms are present in large amounts of exocellular slime. In severe cases, slime imparts a jelly-like consistency to the activated sludge. Effect: Reduced settling and compaction rates. Virtually no solids separation in severe cases resulting in overflow of sludge blanket from secondary clarifier. In less severe cases a viscous foam often is present. Bulking Cause: Filamentous organisms extend from flocs into the bulk solution and interfere with compaction and settling of activated sludge. Effect: High SVI - very clear supernatant. Low RAS and WAS solids concentration. In severe cases, overflow of sludge blanket occurs. Solids handling processes become hydraulically overloaded. 5 Activated Sludge Separation Problems (1)

Settling Problem in Activated Sludge Processes 6

Activated Sludge Separation Problems (2) Pin floc or pinpoint floc Cause: Small, compact, weak, roughly spherical flocs are formed, the larger of which settle rapidly. Smaller aggregates settle slowly. Effect: Low SVI - a cloudy, turbid effluent Blanket rising Cause: Denitrification in secondary clarifier releases poorly soluble N 2 gas which attaches to activated sludge flocs and floats them to the secondary clarifier surface. Effect: A scum of activated sludge forms on surface of secondary clarifier. Foaming/scum formation Cause: Caused by non-degradable surfactants and by the presence of Nocardia spp. and sometimes by presence of Microthrix parvicellar. Effect: Foams float large amounts of activated sludge solids to surface of treatment units. Nocardia and Microthrix foams are persistent and difficult to break mechanically. Foams accumulate and can putrefy. Solids can overflow into secondary effluent or overflow tank free-board on to walkways. 7

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Floc Formers 9

Foaming Nocardia spp. 10

Life 1. Matter: H, O, C, N, P, S and minor elements 2. Energy Solar radiation: Photo-synthetic autotrophs Organics: Heterotrophs Inorganics: Chemoautotrophs 11 More plant-like (producer) More animal-like (consumer) Gets carbon from atmosphere Gets carbon from organic materials AutotrophHeterotroph

Classification of Microorganisms Animals Rotifers Crustaceans Plants Mosses Ferns 12 Eucaryotes: multi-cellular Algae Procaryotes: “before nucleus”, unicellular Blue green algae FungiProtozoa Bacteria Microorganisms

Redox Reaction Organic molecule (C+H+O+N+S+P) (wastewater, hazardous chemicals, etc.) CO 2, H +, and e - A molecule Oxidized Reduced Electron donor Electron acceptor 13

Aerobic Condition Aerobic respiration O 2 present Electron acceptor: O 2 (→ H 2 O) Good for large volumes of dilute wastewater (< 500 mg BOD 5 /L) High growth rates, thus high sludge production (0.3~1 lb VSS/lb BOD 5 ) Produce a more stable end product O 14

Anoxic Condition Anaerobic respiration (denitrification) No dissolved oxygen NO 3 - and NO 2 - present Electron acceptor: NO 2 - and NO 3 - (→ N 2 + H 2 O) Relatively high sludge production Should be avoided in the clarifier AX 15

Fermentation No O 2, NO 3 -, NO 2 -, or SO 4 2- present Electron acceptor: endogenously generated by the microorganism Good for concentrated wastes (> 1000 mg BOD 5 /L) Low sludge production Complex organic compounds Low molecular weight fatty acids CH 4, CO 2, and H 2 O Anaerobic Condition AN 16

Biological Treatment: Conditions Required to Remove Target Compounds Organics (carbonaceous energy)  Aerobic, heterotrophs (aerobic oxidation) Ammonia (nitrogenous energy)  Aerobic, chemoautotrophs (nitrification) Nitrite/nitrate (nitrogenous energy)  Anoxic, heterotrophs (denitrification) Phosphorus (nutrient)  Anaerobic, heterotrophs (luxury uptake) 17

SVI Measurement One-liter graduated cylinder 30 minute settling period SVI = (mL/L)/(g/L) = mL/g, i.e., volume occupied by one gram of settled solids 1-L mL 18

SVI Example Calculation 19 Settled sludge vol.: 260 mL/L Mixed liquor Suspended Solids (MLSS): 2,000 mg TSS/L = 2 g/L < 75Excellent 75 < SVI < 120Good 120 < SVI < 250Poor > 250Bad, bulking t = 0 10 min 20 min30 min 260 mL Bulkin g sludge Well settled sludge Aeration basin