Environmental Engineering - Water Quality

The analysis of major cations and anions in a water sample collected from a city's water supply is given below. Ions present in minor concentrations are not given. Anions Cl- SO4^2- HCO3^- CO3^2- Concentration (mM) 1.5 0...

Fecal Coliform (FC) concentration in river water was measured as 10780 cfu/100 ml. The FC concentration after the conventional water treatment, but before chlorination, was measured as 23 cfu/100 ml. The ‘Log Kill' (inac...

Free residual chlorine concentration in water was measured to be 2 mg/l (as Cl2). The pH of water is 8.5. By using the chemical equation given below, the HOCl concentration (in μmoles/l) in water is ________ (round off t...

MgCl2 and CaSO4 salts are added to 1 litre of distilled deionized water and mixed until completely dissolved. Total Dissolved Solids (TDS) concentration is 500 mg/l, and Total Hardness (TH) is 400 mg/l (as CaCO3). The am...

A compound has a general formula C_aH_bO_cN_d and molecular weight 187. A 935 mg/l solution of the compound is prepared in distilled deionized water. The Total Organic Carbon (TOC) is measured as 360 mg/l (as C). The Che...

The analyses results of a water sample are given below. The non-carbonate hardness of the water (in mg/L) as CaCO3 is _________ (in integer). Ca2+ = 150 mg/L as CaCO3 Mg2+ = 40 mg/L as CaCO3 Fe2+ = 10 mg/L as CaCO3 Na+ =...

A system of seven river segments is shown in the schematic diagram. The Rᵢ's, Qᵢ's, and Cᵢ's (i = 1 to 7) are the river segments, their corresponding flow rates, and concentrations of a conservative pollutant, respective...

The total hardness in raw water is 500 milligram per liter as CaCO3. The total hardness of this raw water, expressed in milligram equivalent per liter, is (Consider the atomic weights of Ca, C, and O as 40 g/mol, 12 g/mo...

A 100 mg of HNO3 (strong acid) is added to water, bringing the final volume to 1.0 liter. Consider the atomic weights of H, N, and O, as 1 g/mol, 14 g/mol, and 16 g/mol, respectively. The final pH of this water is (Ignor...

Henry's law constant for transferring O2 from air into water, at room temperature, is $1.3 \frac{mmol}{liter-atm}$. Given that the partial pressure of O2 in the atmosphere is 0.21 atm, the concentration of dissolved oxyg...

In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 mg/L, 36 mg/L and 122 mg/L, respectively. The atomic masses of various elements are: Ca = 40, Mg = 24, H = 1, C = 12, O = 16. The total hardness and t...

The concentration $s(x, t)$ of pollutants in a one-dimensional reservoir at position $x$ and time $t$ satisfies the diffusion equation $\frac{\partial s(x, t)}{\partial t} = D \frac{\partial^2 s(x,t)}{\partial x^2}$ on t...

A 2% sewage sample (in distilled water) was incubated for 3 days at 27 °C temperature. After incubation, a dissolved oxygen depletion of 10 mg/L was recorded. The biochemical oxygen demand (BOD) rate constant at 27 °C wa...

The hardness of a water sample is measured directly by titration with 0.01 M solution of ethylenediamine tetraacetic acid (EDTA) using eriochrome black T (EBT) as an indicator. The EBT reacts and forms complexes with div...

A 50 mL sample of industrial wastewater is taken into a silica crucible. The empty weight of the crucible is 54.352 g. The crucible with the sample is dried in a hot air oven at 104 °C till a constant weight of 55.129 g....

A water sample is analyzed for coliform organisms by the multiple-tube fermentation method. The results of confirmed test are as follows: Sample size (mL) 0.01 0.001 0.0001 Number of positive results out of 5 tubes 5 3 1...

A river has a flow of 1000 million litres per day (MLD), BOD₅ of 5 mg/litre and Dissolved Oxygen (DO) level of 8 mg/litre before receiving the wastewater discharge at a location. For the existing environmental conditions...

A water sample analysis data is given below. Ion Concentration, mg/L Atomic Weight Ca²⁺ 60 40 Mg²⁺ 30 24.31 HCO₃⁻ 400 61 The carbonate hardness (expressed as mg/L of CaCO₃, up to one decimal place) for the water sample i...