hotopic v-biological treatment processesywang/ce 551 spring 2016/handout/topic vi... ·...
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Topic VI: Biological Treatment Processes
Learning Objectives:
1. Discuss microbiology and relate it to wastewater treatment.
2. Describe growth kinetics of pure bacterial culture with Monod expression and MATLAB.
3. Analyze wastewater composition and calculate nutrient requirement for biological treatment.
4. Describe activated sludge processes and
their design as well as operation considerations.
5. Discuss kinetic model of activated sludge process and determine parameters using linear regression technique.
Reading Assignments:
Capter 12 (skip 12.16) and supplement
Types and Characteristics of Microorganisms
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Activated Sludge Process Microbilogy
Heterotrophic bacteria
Autotrophic bacteria
Aerobes
Anaerobes
Facultative bacteria
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Aerobic:
Anaerobic:
Metabolism, Energy, and SynthesisEnergy Conversions in Anaerobic Metabolism
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μ
μm
Ks S
Table 12.1 Approximate Composition Of An Average Domestic Wastewater
Before After BiologicalSedimentation Sedimentation Treated
Total solids 800 680 530Total volatile solids 440 340 220Suspended solids 240 120 30Volatile suspended solids 180 100 20BOD 200 130 30Ammonia nitrogen as N 15 15 24Total nitrogen as N 35 30 26Soluble phosphorus as P 7 7 7Total phosphorus as P 10 9 8
Nutrient Requirement for Biological Treatment Mixing Waste Streams
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Example 1: Nutrient RequirementsWastewater
40% coffee wastewater
60% domestic wastewater
Coffee Wastewater : 840 mg/L BOD
6 mg/L Total Nitrogen
2 mg/L Total Phosphorus
Domestic Wastewater : 200 mg/L BOD
35 mg/L Total Nitrogen
7 mg/L Total Phosphorus
If BOD/N/P = 100/6.0/1.5 is required, are the N & P adequate in the combined wastewater ? How much pure NH4NO3 and H3PO4 must be added if the nutrient content is insufficient?
Wastewater Flow and Strength Variations
Example 2: Population Equivalent
Domestic wastewater contains 0.24 lb of suspended solids and 0.20 lb of BOD per 120 gal.
a. Calculate the suspended-solids and BOD concentrations in mg/L.
b. Calculate the BOD equivalent population and the hydraulic equivalent population of an industry that discharges 0.1 mgd of wastewater with an average BOD of 450 mg/L.
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Q, B, S are average annual wastewater flow (mgd), BOD load (lb/day), and SS load (lb/day) respectively.Qm, Bm, Sm = average flow, BOD, and SS values during the peak month.
Qd, Bd, Sd = average flow, BOD, and SS values for the peak day.
Suspended-Growth Treatment Systems
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Return sludgeWaste sludge
Primary
Final Effluent
Conventional activated sludge process
Influent
Fig 12.33 Conventional Activated Sludge Process (a) Long rectangular aeration tank with submerged coarse-bubble diffusers along one side (Santee, CA)
Fig 12.33 Conventional Activated Sludge Process (b) Cross section of typical aeration tank illustrating the spiral flow pattern created by aeration along one side
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Return sludgeWaste sludge
Influent Primary
Final Effluent
Step Aeration Activated Sludge process
Aerationθ=30 ~ 90 min
Reaerationθ=3 ~ 6 hr
Sed.
Return sludgeWaste sludge
Effluent
Influent
Contact Stabilization without Primary Sedimentation
Effluent Final
Return sludge
Influent Aeration
Waste sludge
Extended aeration without Primary Sedimentation
Table 12.3 General Loading and Operational Parameters for Activated-Sludge Process
BOD LOADING AVERAGEPROCESS lb BOD/ lb BOD/ SLUDGE AERATION RETURN
1000 ft3/ day/lb of AGE PERIOD SLUDGEdaya MLSS (days) (hr) RATES (%)
Step aeration 30-50 0.2-0.5 5-15 5.0-7.0 50Conventional(tapered aeration) 30-40 0.2-0.5 5-15 6.0-7.5 30
Contact stabilization 30-50 0.2-0.5 5-15 6.0-9.0 100
Extended aeration 10-30 0.05-0.2 20+ 20-30 100
High-purityoxygen 120+ 0.6-1.5 5-10 1.0-3.0 30
a 1.0 lb/1000 ft3/day = 16 g/m3.d
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Design and Operation ParametersExample 3: Aeration Tank Design
Size a conventional activated sludge process receiving a wastewater flow of 18.2 mgd with 200 mg/L unsettled BOD.
Primary Settling
Secondary Settling
Aeration Tank MLSS
V
QQ, SSe
QR, SSe
Qw, SSw
Sludge Age (Mean Cell Residence Time)
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Example 4: Loading and operational parameters
Giving the data below, calculate the loading and operational parameters:
settled wastewater flow = 3.67 mgd
aeration tank volume = 120,000 ft3 = 0.898 mil gal
return sludge flow = 1.27 mgd
waste sludge flow = 18,900 gpd = 0.0189 mgd
MLSS in aeration tank = 2350 mg/L
SS in waste sludge = 11,000 mg/L
influent wastewater BOD (settled) = 128 mg/L
effluent wastewater BOD = 22 mg/L
effluent SS = 26 mg/L
Kinetic Model of Activated Sludge Process
Example 5: Kinetic Constant Determination
A municipal wastewater was tested to determine the kinetic constants using a bench-scale unit. Determine the values for Y, kd, k, and Ks from the following laboratory data.
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Loading and Operational Parameters
1. Quantity of air supply to the aeration basin.
2. Rate of activated sludge recirculation.
3. Amount of excess sludge withdrawn to control MLSS in the aeration tank, F/M, and sludge age.
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Endogenous phase
Declining growth phase
Exponential growth phase
Poor settling characteristics
Poor BOD removal efficiency
High BOD removal efficiency
Good settling characteri-stics
Range of operation for most activated-sludge-treatment systems
Food/microorganism
Rat
e of
met
abol
ism
Fig. 12.15 Rate of metabolism versus increasing food/microorganism ratio
Sequencing Batch Reactor (SBR)
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Stabilization Ponds, Lagoons, Oxidation PondsFlat-bottomed pond enclosed by an earth dike.
Liquid depth: 2 ~ 5 ft
Treat raw or partially treated wastewater.
Low BOD loading: 0.1 ~ 0.3 lb/1000 ft3/day or 25 ~ 35 lb BOD/acre/day (Northen States), 40 ~ 50 lb BOD/acre/day (Southern States).
Long liquid retention times: 50 ~ 150 days
Process microbiology: symbiotic relationship between bacteria and algae.
O2 CO2, NH3, PO43-
Completely Mixed Aerated Lagoons
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Example 6: Aerated Lagoon
Size an aerated lagoon to treat a wastewater flow of 0.3 mgd with an average BOD of 600 mg/L. The temperature extremes for the lagoon contents range from 10° C in winter to 35° C in summer. Minimum BOD reduction through the lagoon should be 75%.
Fixed–Film Biological Process
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InfluentPrimary Filter
EffluentFinal
Recirculation and sludge return
InfluentPrimary Filter Final
Direct recirculation
Sludge return with or without recirculation
(a)
(b)
Effluent
Influent Primary Filter FinalFilterEffluent
Direct recirculation
Sludge return
Primary Filter FinalFilter
Recirculation
Sludge return
Inter
Recirculation
Influent Effluent
Fig. 12.29 Typical flow diagrams for two stage trickling filters
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Efficiency Equation for Stone–Media Trickling Filters
Example 7: Trickling Filter
Calculate the BOD loading, hydraulic loading, BOD removal efficiency, and effluent BOD concentration of a single-stage trickling filter based on the following data:
average raw wastewater flow = 280 gpm
recirculation ratio = 0.5
settled wastewater BOD = 130 mg/L
diameter of filter = 18.0 m
depth of media = 2.1 m
wastewater temperature = 18° C
Efficiency Equation For Plastic-Media Tricking Filters