Wastewater Treatment Systems
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What is a Class 4 Sewage System?
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Septic Tank
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What are the classes of effluent?
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Level 2: 30-25, Level 3: 15-15, Level 4: 10-10
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A treatment unit with a leaching bed must not exceed what class of concentrations?
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Level 4
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Is it true that all units must be fitted with alarms?
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Yes
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For a leaching bed as a shallow buried trench, the total length of distribution pipe must not be less than:
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30 meters
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This formula is used to calculate length for any other leaching bed:
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L=QT/300
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What are the daily flow limits for filter beds?
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5000L w/ septic tank OR 10,000L where unit is a level 2, 3, or 4
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When used in conjunction with a filter bed, loading on surface should not exceed:
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100L/m2/day
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Treatment unit with dispersal bed should not exceed level _____ unit
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4
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Type A dispersel bed must be backfilled with _____ to avoid ______
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leaching bed fill, depressions
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In a type A dispersal bed, the combined thickness of sand and stone layer must not be less than:
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500mm
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Sand in a type A diserpsal bed must have a percolation time of:
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not less than 6 but not more than 10
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Sand in type A dispersal bed must not have more than ____ fines passing through a ____ sieve
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5%, No. 200
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Sand in type A dispersal bed must have an area not less than:
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A=QT/850
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The stone layer in a Type A dispersal bed must not be less than ____ thick
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200mm
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The bottom layer of stone in a Type A dispersal bed must be at least ____ above the groundwater table
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600mm
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The minimum area of the stone layer in a Type A dispersal bed must not be less than this formula:
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A=Q/B
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The slope of a Type B dispersal bed must not exceed this many units:
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1 unit horizontally to 7 units vertically
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Type B dispersal bed must not be more than ____in depth with a percolation time of:
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1000mm, P>15 minutes
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Type B dispersal bed must be backfilled with:
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leaching bed
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Type B dispersal bed must be this high above water table:
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600mm
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(Type B Bed) Self-draining distribution pipes must be at least ____ in diameter
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3mm
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(Type B Bed) Stone layer must not be ____ below or ___ above the pipe
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250mm, 50mm
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(Type B Bed) pipes must not be more than _____ apart or _____ from the edge of the bed
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1.2mm, >600mm
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Area of a Type B bed determined by:
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A=QT/400
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(Type B Bed) Linear loading rates must not be greater than:
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40L/m if P > 24 min 50L/m if P < 24 min
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width of Type B bed must not exceed:
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4 meters
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A Class 5 Sewage system is:
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a holding tank designed to accept sewage until the tank capacity is reached, it is then pumped away to an offsite
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Class 5 system usually has _____ chambers
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1
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(Class 5) Working capacity must be no less than:
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9,000L
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(class 5) All tanks in residual dwellings must have a minimum of ____ day carrying capacity
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7
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Scenarios in which a Class 5 sytem is used:
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-temporary, 12 months or less -remedy to an unsafe system -an upgrade, if class 4 is not possible -municipal systems not yet available
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Do class 5 systems require an alarm?
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Yes, for capacity
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Vents on a class 5 system must be no less than:
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3 inch trade size
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A class 5 system must terminate _____ above finished grade, or _____ if the area is flood prone
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300mm, 600mm
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(class 5 system) must terminate at least _____ away from any air inlet
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3.5 meters
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Class 5 System Clearances
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1.5m from structures 15m from all wells 15m from springs 3m from the property line
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(CP) plans and specifications should include:
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-cross sectional drawing -site plan -list of materials
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(CP) Treatment and holding tanks must conform to:
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CSA-CAN3-B66
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(CP) distribution piping must not be less than ____ for gravity flow and ____ for pressurized sytems
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3 inches, 1 inch
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(CP) fill stone for trenches must be covered with:
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untreated building paper or permeable geo-textile
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(CP) Unacceptable fill material includes:
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-material where PT>20min/cm -too much silt or clay
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(CP) important installation factors include:
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-depth of installation -debris removal -leveling and backfilling -uplift prevention -backfill compaction
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(CP) a pump is required when:
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-effluent must be delivered to higher elevation, if lenth of pipe is more than 150m a Type B diserpsal system is used
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(CP) pumps must have capacity large enough to deliver dosage of effluent within:
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15 minutes
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(Trenching) trenches must be at least ____ and not more than _____ wide, centres no closer than ____apart
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500mm, 1000mm, 1.6m
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(trenching) not less than _____ and not more than ____ in depth, providing a minimum of ____ of stone beneath.
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600mm, 900mm, 15cm
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The bottoms and sidewalls of a trench must be:
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Scarified
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(trenching) stone fill at least ____ thick placed at bottom layer
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15cm
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(Trenching) layer of washed stone at least ____ deep on top of pipes
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50mm
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(trenching) after pipe and stone installation, what installed to block fine soil particles?
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filter interface of building paper or geo-textile fabric
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(trenching) backfill must be composed of:
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porous soil
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(trenching) topsoil layer of at least _____ to allow for grass
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15cm
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What is the purpose of a raised leaching bed?
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-to fix poor soil conditions -to fix inadequate soil depth or bedrock -to deal with a high groundwater table
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(trenching) an area must be graded ____ below natural grading
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25cm
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(trenching) what are the 2 purposes of the fill material?
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leaching bed and mantle
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leaching bed fill layer must be ____ from the water table:
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900mm
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The mantle fill layer must extend ____ beyond the distribution pipes in any horizontal direction
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15m
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Raised bed and mantle cannot have slope sides exceeding:
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1 unit horizontally to 4 units vertically
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What are four main signs of a malfunctioning system?
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-foul odour -sewage backup -breakout to surface -water contamination
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How can a sump pit be involved in malfunction?
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efflunt is picked up by weeping tile and being drained into building's sump pit, indicating break in pipe from building to treatment unit
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What is usually the cause of a breakout to surface?
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hydraulic capacity of soil/fill beneath leaching bed being exceeded
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What is an important measure of groundwater contamination?
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presence of faecal coliform
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What is one of the main causes of groundwater contamination?
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installation less than 900mm above the groundwater table
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What building factors can reduce the performance of a sewage system?
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-added bedrooms -exceeds 15% of finished area of dwelling unit -installation of new plumbing fixtures
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What are the main infrastructural factors of Durham's sewage system?
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-12 wastewater treatment systems -42 pumping stations -2055kms of sewer pipe
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What is the simplest sewage treatment method in Durham?
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waste stabilization pond
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What was the average flow for Durham in 2010?
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41,392m3/day
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What are the two main factors of primary treatment in Durham?
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-screening to remove solids -primary clarifier, which consists of two settling tanks
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What happens during secondary treatment in Durham?
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2 bioreactor tanks use anoxic and aerobic zones, air is bubbled through the tank. micro-organisms break down components to NO2, CO2, and H2O
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What are five bugs found in the basin in Durham?
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-bacteria -protozoa -metazoa -filamentous bacteria -algae and fungi
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What are some facts about the secondary clarifier in Durham?
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-a sedimentation process that takes 4-6 hours -Return Activated Sludge is returned to head of aeration tank for further use -Waste Activated Sludge is removed from system
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Explain the disenfection process in Durham:
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-achieved using a sodium hypochloride solution -200 organisms/m3/s -before discharge to lake, effluent is dechlorinated
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Sampling and analysis is performed at Durham how often?
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Daily
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Once sewage is stabilized, it is sent to one of these two places:
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Dufferin Creek WPCP or Corbett Creek WPCP
