Flow Diagram

1. Flow Diagram
• A process flow diagram is a graphical
representation of how unit processes make up a
treatment train and how they interconnect.
• Another important consideration is the hydraulic
profile through the treatment train, which
establishes the amount of head (i.e. water
pressure) at each unit process. This establishes
head requirements for pumps and ensures that
the works won’t be flooded or backed up during
extreme conditions. Ideally a works should be
sited to take advantage of gravity flow through
treatment train, where possible, to reduce energy
requirements.

2. Flow Chart/Diagram

3. Impact of Wastewater Effluent on
Oxygen in Receiving Waters
• Any organic matter remaining in the treated WW
effluent (e.g. as BOD, organic nitrogen) is utilised
by bacteria that are naturally present in the
receiving water bodies, thereby consuming
dissolved oxygen (DO).
• This reduction in DO can have harmful effects on
higher forms of aquatic life (e.g. fish).
• While the WW effluent introduces an oxygen
demand, the DO is also continually replaced by
the water surface being in contact with the
atmosphere.
• There is therefore simultaneous de-oxygenation
and re-aeration, resulting in what is commonly
referred to as a DO sag curve

4. Impact of Treatment Process
• Removal of BOD by adsorption or
sedimentation in the receiving water bodies
• Addition of BOD by a tributary flow
• Addition of BOD or removal of DO by a
benthal sludge layer
• Addition of oxygen by photosynthesis (e.g.
algae)
• Removal of oxygen by plankton respiration.

5. Estimating Wastewater Quantities
Combined & Separate Sewers
• A combined sewer carries stormwater & WW
in the same pipe whereas a separate sewer
network has two pipes which carry
stormwater & WW separately. The pipe which
carries WW in a separate sewer network is
referred as a foul sewer. The WW in a
combined sewer is diluted by storm flow &
so is typically less concentrated than the WW
carried in a separate sewer network.

6. Source and Variability in Ww flow