Water, Part 2 Wastewater Treatment Primary Chapter: 11 Supplemental Chapters: 8, 9 1

Activity What’s the problem with direct discharge of untreated wastewater? Write your ideas. Share with a partner. Share with the class. 2

Treatment Processes Treatment process = f(amount, type/source) Discharge limits = f(type/source, discharge location, time of year) 3

CENTRALIZED TREATMENT 4

Types of Wastewater (Section ) From where does it all come? 5

Transport of WW 6

Characteristics of WW (Section ) 7

Activity Why is it important to obtain local data on wastewater composition and flow rates rather than using typical data when designing a new or an expansion to a treatment plant? Write your ideas. Share with a partner. Share with the class. 8

Regulations (Sections and 9.3.3) What’s the primary law for WWT? 9

Activity Who must obtain an NPDES permit? A. Manufacturers B. Point source dischargers C. Farmers D. Septic tank owners E. Municipalities 10

Typical Municipal WWTP 11

Raw Sewage Bar Rack Grit Chamber Equalization Basin Pump Primary Clarifier Biological Treatment Secondary Clarifier Disinfection Receiving Body Advanced or Tertiary Treatment Preliminary Treatment Primary Treatment Secondary Treatment Solids Handling Degrees of Treatment - Example 12

BOD Solids Influent – How much is removed? 13

After Primary Treatment 14

After Secondary Treatment 15

Preliminary Treatment (Section ) Screens Comminutors (Grinders) Bar Racks Grit Chamber 16

Primary Treatment (Section ) 17

Secondary Treatment (Section 11.3) 18

OXYGEN DEMAND Section

Oxygen Demand Amount of oxygen required to oxidize a waste Methods  Theoretical oxygen demand (ThOD)  Biochemical oxygen demand (BOD)  Chemical oxygen demand (COD) 20

Theoretical Oxygen Demand Total ThOD = C-ThOD + N-ThOD C-ThOD = stoichiometric amount of O 2 required to convert an organic substance to CO 2, H 2 O, and NH 3 N-ThOD = stoichiometric amount of O 2 required to convert NH 3 and organic N to NO

Example 1 What is the total ThOD to oxidize completely 25 mg/L of ethanol (CH 3 CH 2 OH)? CH 3 CH 2 OH + a O 2  b CO 2 + c H 2 O 22

Determine Volume of O 2 or Air 23

Example 2 What is the ThOD to oxidize completely 25 mg/L of serine (CH 2 OHCHNH 2 COOH)? CH 2 OHCHNH 2 COOH + a O 2  b CO 2 + c H 2 O + d NH 3 NH 3 + a O 2  b HNO 3 + c H 2 O 24

Biochemical Oxygen Demand (BOD) 25

Lab: Unseeded BOD BOD t = BOD at t days (mg/L) DO i = initial dissolved oxygen (mg/L) DO f = final dissolved oxygen (mg/L) V s = sample volume (mL) V b = bottle volume (mL) = 300 mL DF = dilution factor = V b /V s 26

Lab: Seeded BOD B i = initial DO of blank (mg/L) B f = final DO of blank (mg/L) 27

In-Class Activity 10 mL of a wastewater sample are placed in a 300-mL BOD bottle with unseeded nutrient broth. The initial DO of the sample is 8.5 mg/L. The DO is 3 mg/L after 5 days. What is the 5-day BOD? A 17 o C sample is initially saturated with oxygen. Saturated seeded dilution water is used to obtain a 1:25 dilution. The final DO of the seeded dilution water is 8.2 mg/L while the final DO of the diluted sample is 2.8 mg/L. What is the 5-day BOD? 28

In-Class Activity Bottle NumberType 1 DO (mg/L) 10B B S S S B = blank (seeded dilution water), S = sample with seeded dilution water You received the results of a BOD test of the influent to a municipal WWTP run with 300-mL bottles. The initial DOs of the samples and seeded dilution water were at saturation (9.07 mg/L). All samples were run at a dilution factor of 40:1. The 5-day DOs are shown in the table below. The client is on the phone with your boss wanting to know why he hasn’t gotten a report yet. Justify why you threw out this data and made the lab redo the test. 29

Rate of BOD Removal Relate BOD exerted (BOD t or L t ) to total, or ultimate, BOD (BOD u or L) Assume that the BOD reduction rate (dC/dt) is proportional to the BOD remaining (C): 30

Rate of BOD Removal cont. Integration yields:  y = BOD exerted in t days = BOD t  L = ultimate BOD = BOD u  k 1 = BOD degradation rate constant = deoxygenation constant 31

Ultimate BOD 32

In-Class Activity continued 10 mL of a wastewater sample are placed in a 300-mL BOD bottle. The initial DO of the sample is 8.5 mg/L. The DO is 3 mg/L after 5 days. What is the 5-day BOD? 165 mg/L What is the 3-day BOD if the reaction rate constant is 0.23/d? 33

Chemical Oxygen Demand (COD) 34

Secondary Treatment (Section 11.3) 35

Activated Sludge: Aeration Basin (Sections ) 36

Aeration Basin Design Kinetics Mean cell residence time & hydraulic detention time 37

Kinetics: Logistic Growth  (d - 1 ) S (mg/L)  max  max / 2 KsKs 38

Aeration Basin Design Mean cell residence time & hydraulic detention time 39

MCRT from a Reactor without Recycle V, S, X Q, S o, X o Q, S, X 40

Wasting from Recycle Line Q, S o, X o V, S, X Q e = Q-Q w, S, X c VcVc Q r, S, X r Q w, S, X r 41

Example A conventional WWTP receives 2 MGD with an average BOD of 165 mg/L to the aeration basin. The aeration basin is 100,000 ft 3. The MLSS is 2,800 mg/L and the effluent SS is 25 mg/L. The WAS is 38,000 gpd from the recycle line. The SS of the recycle flow is 9,000 mg/L. What is the mean cell residence time? 42

General Equation for Mean Cell Residence Time 43

Secondary Clarifier (Section ) 44

Sludge Volume Index (SVI) 45

Other Secondary Treatment Options 46

Sequencing Batch Reactor (SBR) 47

Aerated Lagoons 48

Oxidation Ditch 49

Trickling Filters (Section ) 50

Rotating Biological Contactors (Section ) 51

DISINFECTION Section UV Generator and Lamps Chlorine Contact Basin 52

TERTIARY TREATMENT Section

Wetlands (Section ) 54

EFFLUENT DISCHARGE 55

Rapid Infiltration 56

Slow-Rate Land Application 57

Overland Flow 58

Discharge to a Stream (Section 8.2.3) Effects:  Nitrogen species  Biodiversity  DO 59

Discharge to a Stream: DO 60

Streeter-Phelps Model where D = oxygen deficit = DO sat - DO actual 61

Critical Point Obtain from dD/dt = 0: 62

Evaluation of Model Very simple to use But not like nature  Assumes steady state  Assumes a single discharge  Assumes no upstream dispersion  Assumes complete mixing  Assumes all the BOD is soluble  Doesn’t include scouring  Doesn’t include DO from algae 63

Discharge to a Lake (Section 8.2.2) Cougar Lake 64

Effect on a Lake Cougar Lake 65

SLUDGE MANAGEMENT Section

Purpose Reduce/inactivate pathogens Increase solids content Reduce odor & putrescence 67

Sludge Treatment 68

Sludge Disposal How can we get rid of the sludge??? And how do we choose which option is best? 69

OTHER DESIGN ISSUES 70

ONSITE TREATMENT 71

Conventional Septic System 72

Anaerobic Septic Tank 73

Absorption Fields Shallow Trench Drop Box 74

Septic Tank with Sand Filter Single Pass (Intermittent) Recirculating 75

Mound System Plowed Layer (Ground Surface) Topsoil and Vegetation Cover Pipe from Pump (pressure distribution line) Distribution Lateral Marsh Hay Bed of Coarse Aggregate ( ”) Sand Fill 76

Aerobic Treatment Units (ATU) 77

Lagoon/Waste Stabilization Pond 78