Neco Model Questions Vol1 2019 Chemistry Question 6

A river has a flow of \(200\,000\) L day\(^{-1}\) and already carries a BOD load of \(0.10\) kg day\(^{-1}\). Two factories discharge into the river. Factory B releases \(10\,000\) L day\(^{-1}\) with a BOD concentration of \(80\) mg L\(^{-1}\). Factory A will discharge \(20\,000\) L day\(^{-1}\) of wastewater whose untreated BOD concentration is \(300\) mg L\(^{-1}\). The permissible BOD concentration in the river after mixing is \(5\) mg L\(^{-1}\).\n\n(a) What is the maximum BOD concentration (in mg L\(^{-1}\)) that Factory A may have in its effluent after treatment so that the river limit is not exceeded?\n\n(b) What percentage reduction in BOD must Factory A achieve relative to its untreated concentration of \(300\) mg L\(^{-1}\)?