Analytical data from recent experimental work shows that initial bacteria $($contaminants$)$ count

for a $1000$ liter stirred tank bioreactor $($working volume $80\%)$ was found to be approximately

${10}^6$ cells $/mL.$ If reaction rate constant, $k$ is $0\mathrm{.}613mi{n}^{-1},$ estimate sterilization time $($in minutes$)$

needed to minimize bacteria count down to one in thousand.