Two shallow lagoons connected in series, each having a surface area of 5 km^2 and depth of 1m, are receiving 8640 m^3/day of sewage containing 100mg/L of biodegradable contaminant. At a steady state, the concetnration of the contaminant in the effluent from the second lagoon must not exceed 20 mg/L. Assuming the lagoons are well mixed and that there are no losses or gains of water in the lagoon other than the sewage input, what biodegradation reaction rate coefficient (in day^-1) must be achieved for a first order reaction that governs the degradation of the contaminant