Problem Suppose the sewers shown in Figure below have Qs = 80 L/min and QA and Q

Question

Problem Suppose the sewers shown in Figure below have Qs = 80 L/min and QA and Qc are unknowns. By sampling the flow at the first manhole, it is found that the concentration, CA, of dissolved solids in the flow coming into Manhole 1 is 65 mg/L. The flow, QB = 80 L/min contains 25% dissolved solids. The flow through Manhole 2 is sampled and found to contain 800 mg/L dissolved solids. 1. Is this a conservative or non-conservative system? 2. State all assumptions. 3. What is the flow rate of wastewater in the sewer (QA), in m^3/min?

Explanation / Answer

1. As ( QA + QB ) is not equal to QC   The system is showing non-conservative.

2. a) Rate of incoming flow is equals to rate of outgoing flow at a point during a flow of fluid for conservative system.

b) The flow should be through along the axis for laminar or steady flow.

3. In Manhole A the flow rate = 25/100 * 80L/min = 20 L/min

where as the dissolved solids concentration at manhole B = 800mg/L

Dissolved solids concentration at manwhole A is 65mg/L

So waste water flow rate at A is 75 % of 80L/min = 60L/min

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