GATE Civil Engineering (CE) 2020 Shift 1 Solved Paper

A stream with a flow rate of $5{\mathit{m}}^3/\mathit{s}$ is having an ultimate $\mathit{B}\mathit{O}\mathit{D}$ of $30\mathit{m}\mathit{g}∕$ litre. A wastewater discharge of $0.20\mathit{m}3/\mathit{s}$ having ${\mathit{B}\mathit{O}\mathit{D}}_5$ of $500\mathit{m}\mathit{g}/$ litre joins the stream at a location and instantaneously gets mixed up completely. The cross-sectional area of the stream is $40{\mathit{m}}^2$ which remains constant. BOD exertion rate constant is $0.3$ per day (logarithm base to e). The BOD (in $\mathit{m}\mathit{g}/$ litre, round off to two decimal places) remaining at $3\mathit{k}\mathit{m}$ downstream from the mixing location, is