Afactory discharges its waste into a river upstream from a lake.
the discharge release rate is 2 kg formaldehyde per day. the decay
is a first order process with a decay rate of 0.5/s. the waste
is discharge into the river 30 km upstream from the lake through an
effective diffuser. the river flow velocity is 6 km/d. the
volumetric flow rate for the river is 106 m3/d. the lake has
dimensions of 4,000 m long by 600 m wide by 8 m deep. (total volume
is 1.92 x 107 m3). there is an outlet stream from the lake with a
flow rate of 106 m3/d.
1. estimate the formaldehyde concentration in the lake using the
plug flow model for the river and the completely mixed model for
the lake.