4. Oxygen and microorganisms are placed in a closed bottle. In this bottle, enough nutrient was added for microorganisms to consume oxygen. The bottle may be treated as a batch reactor, and the decay of oxygen may be treated as a first-order reaction. The initial oxygen concentration was 8.0mg/L, and the first-order rate constant was 0.5d1. Write the general mass balance equation for the bottle. Calculate the concentration of oxygen from day 1 to 10 (Day 1,2,3,4,5,6,7,8,9&10; show table day vs concentration). Show the also graph using a spreadsheet program, such as excel. (10 pts) 5. Liquid waste is blended in a CSTR having a volume of 0.2m3 (wastewater). The initial concentration of the liquid waste was 8mg/L. The flow rate of the wastewater is constant at 4.0L/s. After a certain time, the liquid waste concentration was increased to 10mg/L, and kept this concentration. The liquid was conservative. How long will it take the effluent from the CSTR to reach the liquid waste concentration of 9mg/L ? (10 pts) 6. A sewage lagoon with a surface area of 100,000m2 and a depth of 1m receives 8,640m3/ day of sewage containing 100mg/L of biodegradable contaminant. At a steady state, the measured effluent from the lagoon was 20mg/L of biodegradable contaminant. Assuming the lagoon is well mixed and that there are no losses or gains of water in the lagoon other than the sewage input, Estimate the first-order biodegradation reaction rate coefficient (k,d1).(10pts) 7. The total length of a 5,000m wastewater discharge pipe (area: 20m2 ) is connected to the Pacific ocean. The wastewater velocity is 0.5m/s.5.0mg/L of nitrate was detected at the inlet of the pipe. In this pipe, nitrate degradation occurred with 0.3 hour-1(first-order reaction). Calculate the effluent nitrate concentration at the discharge point (mg/L).(10pts)