[1] Class 2b
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
[1]
Class 2b
[2]
Three main constituents:• Domestic inputs (inc schools etc)• Commercial / Industrial inputs• Infiltration / Inflow
Constituents will vary depending on:• Geographical location• Population• Industry types• System characteristics• System condition
Nature of Waste Water
[3]
• Water use levels can vary considerably from person to person – average 140 - 200 l/h/d.
• Average consumption levels can be used to estimate inputs to the system.
• In the UK, 95% of water supplied reaches the sewer.
• In warmer climates this can be much less –75-85% in the Middle east.
• Lifestyle factors should also be considered –only 60% of water is returned in the USA.
Waste Water – Domestic Quantification
[4]
Waste Water – Domestic QuantificationWater use also changes with time:
Long term – Water demand is rising.
Annually – We use more water in the summer (more baths and gardening – but we do flush the WC less).
Weekly – We use more water at the weekends as we tend to wash more.
Daily – Peak water usage is in the morning, with smaller peaks in the early & late evening.
Waste Water – Domestic Variability
[5]
Waste Water – Domestic Variability
[6]
COD Load
Waste Water – Domestic Variability
[7]
Waste Water – Domestic Variability
[8]
Waste Water – Domestic Variability
[9]
Estimating Foul Flows
Based on water consumption in similarcatchments [be careful to exclude supply network leakage – in some parts of the
UK this may be high].
[10]
Estimating Foul Flows
EN 752-4:1997 gives values for typical per capita EU average domestic dry weather flows [DWF] flows and peak design flows. UK flows are noted as being in the range 200 to 400 l/h/d and the peak is 6×DWF.
[11]
Estimating Foul Flows
BS EN 12056-2:2000 “Gravity drainage systems inside buildings - Sanitary pipework, layout and calculation” gives an overview of how probability theory may be used to combine flows from different fixture units to give an estimate of peak flows.
This method does not allow for the attenuationof inflow waves, so may result in longer pipe run s being oversized.
[12]
Commercial – Demand from drinking, food preparation washing and sanitary facilities.
Industrial - The demand from industrial processes should also be considered.
Waste Water – Com. & Ind. Quantification
[13]
Infiltration / Inflow must be quantified and (if possible) reduced as it leads to:
• A reduction in sewer capacity.• Overloads mechanical infrastructure
(pumps, WWTW etc).• Can cause premature CSO operation.
Typically, infiltration will range from 0.01 – 1.0 m3/day/mm of pipe diam/km. This can equal 50% of DWF.
Infiltration / Inflow – Quantification
[14]
With Infiltration
Without Infiltration
Infiltration
[15]
System condition
[16]
Campaign for the Renewal of Sewerage Systems (CROSS) make this claim about some UK systems:
“Some 9% of the UK catchments have been shown to have infiltration rates greater than 50%, and 28% of catchments have infiltration rates of more than 25%.
That is, more than 50% and 25% of the sewer flow respectively are derived from infiltrating groundwater.”
CROSS
[17]
Estimation methods for infiltration tend to utilise flow data recorded during dry weather by subtracting the base flow (often derived from population/water usage data) from the site-measured flow.
However, this fails to take into account peaks in rainfall-induced infiltration occurring during sustained wet periods.
Where infiltration is less diffuse, it may be identified using CCTV inspections.
Infiltration estimation methods
[18]
Infiltration
[19]
Infiltration – Annual Variability
0
10
20
30
40
50
60
00:00 06:00 12:00 18:00
time
Dry
weath
er
flow
[l/s
]
March
April
May
June
July
[20]
Q1 Compare and contrast the mechanisms and implications of exfiltration, infiltration and inflow.
Q2 Combined sewerage systems, separate drainage systems and sustainable drainage systems are all commonly in use in the UK. Explain why they were introduced and the merits and problems associated with them in draining urban runoff. Particular attention should be paid to the underlying design philosophy rather than simply listing differences between the systems.
SAQ
Related Documents
