1. The problem statement, all variables and given/known data Question 1. An industry uses a long drainage ditch to break down their wastes and in particular to remove the odour. The waste travels along the ditch at a velocity of 0.5 m/h. The odour is reduced as a first order reaction with a reaction constant of k=0.30 day-1 The company must reduce the original odour emissions of the waste by 90% to reach the environmental guideline for acceptable odour. What is the minimum ditch length (in m) to ensure the wastes reach the environmental guideline for odour? 2. Relevant equations 3. The attempt at a solution I was thinking because the velocity is 0.5m/h = 12m/day and the 90% would mean the odour would flow for 3 days, 12*3 = 36m. However I'm not sure what equation should be used or if I'm approaching this completely wrong..