3.  Overview: Wastewater Engineering  Wastewater Characteristics  Wastewater Treatment Considerations  Overview: Wastewater Treatment Plant Design  Physical, Chemical and Biological Processes

4.  Sludge Treatment ◦ Sludges are the product of biological treatment of wastewater Sludges ◦ Sludges comprise solids found in wastewater plus organisms used in the treatment process ◦ Disposal is a major issue ◦ Various disposal techniques are used but each has advantages and disadvantages

5.  Water Disposal and Re-Use ◦ Wastewater treatment generates a Cleaned Water StreamCleaned Water Stream ◦ Cleaned water is often discharged to a larger body of water for dilution ◦ Alternatively, cleaned water my be re-used for irrigation or rarely drinking water production

6. Characteristics are normally estimated by empirical methods  Wastewater Flows ◦ Flows arise from households, industry, infiltration and storm flows ◦ Flows are considered in both hydraulic and process design ◦ Levels of treatment may vary for different flowrates

7.  Wastewater Flows ◦ There is a variety of methods for estimating flowrates ◦ However there may be great variability in the factors which affect flowrates from region to region ◦ Different multiples of the Dry Weather Flow will receive each level of treatment

8.  Wastewater Composition ◦ Key design issues:  Solids: density, particle size, level of Volatile Suspended Solids  Biochemical Oxygen Demand  Temperature  Ammonia  Nutrient levels

9.  Wastewater Treatment Considerations ◦ Objective: to maintain or improve the quality of the receiving body of water ◦ Treatment stages:  Preliminary  Primary  Secondary  Tertiary

10.  Applicability and Selection of Methods ◦ Different processes are used to treat wastewater depending on the contaminants presentwastewater ◦ Similarly, different processes are used to treat sludges, depending on the objective of treatment

11.  Flowrate and Mass Loading ◦ Wastewater feed is not specified, therefore the plant must be able to treat whatever the wastewater contains Wastewater ◦ Plant design will take account of historical flows and loadings, but must also be able to deal with expansion ◦ Plant must also be able to deal with a range of flow and load conditions, plus peak upstream flow conditions (eg storms)

12.  Selection of Design Flowrates ◦ Domestic: based on a flow per head. Varies between countries ◦ Industrial: Based on records of discharge consents and of metered supplies ◦ Infiltration/Exfiltration: based on a % of the domestic flow ◦ Peaking Factors: Depends on size of community

13.  Selection of Design Flowrates ◦ Upstream Flow Equalisation  Plants are not normally designed to treat total peak arisings  Instead, hydraulic controls will direct flows above plant capabilities to storm system on larger works

14.  Selection of Design Flowrates ◦ Upstream Flow Equalisation  For larger works with storm tanks, only “Full Treatment Flow” (FTF) will receive full treatment. FTF=3PG+3E+I  Formula A-FTF will pass to storm tanks

15.  Selection of Design Mass Loadings ◦ Average mass loadings for BOD and Suspended Solids are commonly determined by Population Equivalent (PE) ◦ Design mass loadings are more complex and must take account of seasonal, diurnal and industrial load variations

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