Hydrology (Flow diagram)

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