The BOD just downstream from a wastewater pipe is 12.9 mg/L and the DO (dissolved oxygen) is 8.6 mg/L. The saturated value of dissolved oxygen is 9.6 mg/L, the deoxygenation constant (ka) is 0.21/day, the reaeration constant (kr) is 0.42. Find the time where oxygen deficit is at a maximum and find the minimum value of DO.

An anaerobic digester (AD) is designed with the following data. Organic loading rate 1.0 kg VSS/m³.day VSS load 120 kg/day (i). (ii). Estimate the volume of the AD. If the VSS is 12 kg/m³, estimate the retention time.

Enter T next to the following true statements and F next to the false statements. Settling of suspended solids in secondary clarifiers is typical of Type II sedimentation. Thickening prior to digestion is common in many wastewater treatment plants because it reduces the size needed for the digester. Based on a temperature of 30°C, a design mean cell residenee time of about 20 days would be reasonable for a completely-mixed anaerobic digester without recycle. A volatile suspended solid is defined as an organic solid that can be oxidized to CO2 (g) at 250°C. The theoretical yield coefficient can be estimated from the observed yield coefficient if the specific growth rate constant is known. Air flotation would likely be more efficient for thickening waste activated sludge than primary sludge, while the opposite would be true for gravity thickening. The net mass of cells produced in the activated sludge process equals the total cell mass synthesized minus the cell mass wasted as waste…

In a BOD test, 5 ml of wastewater (with no dissolved oxygen) is diluted with 295 ml of water containing 8.5 mg/1 of dissolved oxygen. After 5 days incubation at 25°C, the dissolved oxygen content of the mixture is 5 mg/1. Temperature coefficient can be taken as 1.047 and BOD rate constant is 0.23 per day (base e) at 20°C. The ultimate biochemical oxygen demand of the wastewater is