List of top Environmental Engineering Questions on Quality and Characteristics of Sewage

One-third of the solid matter in a sludge containing 90 % water is composed of fixed mineral solids with specific gravity 2.5, and two-third is composed of volatile solids with specific gravity 1.0.
Specific gravity of all solids lies between

The 2.4 ml of raw sewage is diluted to 240 ml. The Dissolved Oxygen (DO) of the diluted sample at the beginning of Biochemical Oxygen Demand (BOD) test was 8 mg/l and it was 6 mg/l after 5-day incubation at 20°C.
The BOD₅ (in mg/l) of the raw sewage is

The average sewage from a city is 90 million litres per day and the average 5-day Biochemical Oxygen Demand (BOD₅) is 300 mg/l. Average standard BOD₅ of the domestic sewage is 0.08 kg/day/person. The population equivalent of the city is

The theoretical aerobic oxidation of biomass (C₅H₇O₂N) is
\[ \mathrm{C_5H_7O_2N + 5\,O_2 \rightarrow 5\,CO_2 + NH_3 + 2\,H_2O} \]

Given a first-order biochemical oxidation with $k=0.23\, \text{d}^{-1}$ at $20^{\circ}$C (base $e$) and neglecting the second-stage oxygen demand, find the ratio BOD₅ at $20^{\circ}$C to TOC (round to two decimals).

Atomic weights: C=12, H=1, O=16, N=14 g/mol

The theoretical aerobic oxidation of biomass (C₅H₇O₂N) is
\[ \mathrm{C_5H_7O_2N + 5\,O_2 \rightarrow 5\,CO_2 + NH_3 + 2\,H_2O} \]

Given a first-order biochemical oxidation with $k=0.23\ \text{d}^{-1}$ at $20^{\circ}$C (base $e$) and neglecting the second-stage oxygen demand, find the ratio BOD₅ at $20^{\circ}$C to TOC (round to two decimals).

Atomic weights: C=12, H=1, O=16, N=14 g/mol