1 CTC 450 Review Preliminary & Primary Treatment Preliminary & Primary Treatment Measure flow Measure flow Screen Screen Grit chamber Grit chamber Primary Settling Primary Settling

2 Objectives Understand basic processes of biological treatment Understand basic processes of biological treatment

3 Stone Media Trickling Filter /2TricklingFilter.jpg

4 Stone-Media Trickling Filters Major components Major components Rotary distributor Rotary distributor Underdrain system Underdrain system Filter media (5-7’ depth) Filter media (5-7’ depth) Most common media is crushed rock, slag or field stone (3-5” in dia.) Most common media is crushed rock, slag or field stone (3-5” in dia.) Media must be durable, insoluble and resistant to spalling Media must be durable, insoluble and resistant to spalling

5 Stone-Media Trickling Filters Some ww is recycled to the filter Some ww is recycled to the filter Two-stage consists of 2 filters in series (with or w/o an intermediate clarifier) Two-stage consists of 2 filters in series (with or w/o an intermediate clarifier) Second filter is less efficient since food concentration is less Second filter is less efficient since food concentration is less BOD removal is influenced by temp. BOD removal is influenced by temp.

Recirculation 6

Recirculation Ratio (R) R = Qr divided by Q R = Qr divided by Q Where: Where: Qr=recirculation flow Q=incoming wastewater flow R can be less than 1 or greater than 1 R can be less than 1 or greater than 1 7

8 Biological Towers Plastic media is used Plastic media is used High percentage of voids High percentage of voids High surface area per unit of volume High surface area per unit of volume Uniform media (random or modular) Uniform media (random or modular) Light weight Light weight Chemical resistance Chemical resistance Can treat high-strength wastewaters Can treat high-strength wastewaters

9 Biological Tower Plastic media - Trickling filter at Madras Refineries Ltd, Chennai -

10 Biological Tower Media / filtermat/e_riesel.htm

11 Biological Tower Theoretical removal rates get complex and are based on soluble BOD Theoretical removal rates get complex and are based on soluble BOD Packing configuration impacts residence time, which is related to hydraulic loading and filter depth Packing configuration impacts residence time, which is related to hydraulic loading and filter depth Another complication is that effluent from the tower is recirculated (see Figure ; page 311) Another complication is that effluent from the tower is recirculated (see Figure ; page 311)

12 Biological Tower Recirculation Sp is soluble BOD of primary effluent Sp is soluble BOD of primary effluent So is soluble BOD of tower influent So is soluble BOD of tower influent Se is soluble BOD of tower effluent Se is soluble BOD of tower effluent Equation can be used to calculate the efficiency of a biological tower (w/ random packing) Equation can be used to calculate the efficiency of a biological tower (w/ random packing)

13 Example 11-3 Biological Tower Flow is 1.6 mgd Flow is 1.6 mgd Primary Clarifier/Biological Tower/Secondary Clarifier Primary Clarifier/Biological Tower/Secondary Clarifier Single Stage Biological Tower: Single Stage Biological Tower: Diameter = 70’ Diameter = 70’ Media Depth = 7’ Media Depth = 7’ Primary Effluent has a soluble BOD of 100 mg/l Primary Effluent has a soluble BOD of 100 mg/l Water temp is 15C (59F) Water temp is 15C (59F) Constants for random plastic media are: Constants for random plastic media are: n=0.44 n=0.44 k 20 = k 20 = A s =35 square ft per cubic foot A s =35 square ft per cubic foot Calculate the effluent soluble BOD assuming indirect recirculation to the wet well of 560 gpm Calculate the effluent soluble BOD assuming indirect recirculation to the wet well of 560 gpm

14 Example 11-3 Biological Tower Rework and understand example on page Rework and understand example on page

15 Combine filters/activated sludge Biological tower can be used before activated sludge Biological tower can be used before activated sludge Analyzing the process is difficult Analyzing the process is difficult Read discussion on page Read discussion on page

16 Filter/Tower Problems Odor Odor Effluent quality Effluent quality Cold weather Cold weather Flies Flies Snails Snails

17 Covers Odor Control Odor Control Limits heat loss Limits heat loss

18 Activated Sludge Liquid suspension of microorganisms (mixed liquor) Liquid suspension of microorganisms (mixed liquor) MLSS-mixed liquor suspended solids MLSS-mixed liquor suspended solids Aerobic process Aerobic process

19 Activated Sludge Settleability Depends on food-to-microorganism ratio and sludge age Depends on food-to-microorganism ratio and sludge age High MLSS concentrations and extended times encourage endogenous growth High MLSS concentrations and extended times encourage endogenous growth Endogenous growth-microorganisms are starved and rapidly utilize the food source Endogenous growth-microorganisms are starved and rapidly utilize the food source

20 Activated Sludge Example 11-5 Rework example to understand calculations Rework example to understand calculations

21 RBC 40% submerged 40% submerged Four stages often used (each with separate tanks) Four stages often used (each with separate tanks) Plug flow Plug flow _DATA/WATER/WATER_1 /html/Doc_204.html

22 Stabilization Ponds (lagoons) Used in rural areas (7% of population) Used in rural areas (7% of population) Used as polishing ponds (tertiary treatment) Used as polishing ponds (tertiary treatment) Can be facultative, aerated or anaerobic Can be facultative, aerated or anaerobic

23 Disinfection Chlorine added by rapid initial mixing in a contacting basin Chlorine added by rapid initial mixing in a contacting basin UV (hypochlorite used as standby) UV (hypochlorite used as standby)

Outfall-Railroad Interceptor Outfall-Railroad Interceptor 24

Outfall-Grace Creek Outfall-Grace Creek 25

26 Private Systems 25% of homes not connected to a municipal system 25% of homes not connected to a municipal system Septic tank and drainfield (absorption field) Septic tank and drainfield (absorption field)

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