* not completed

. Which one(s) of these compounds is/are used for municipal drinking water disinfection? (Please select all that apply)

O₃ correct incorrect

H₂O₂ correct incorrect

ClO₂ correct incorrect

Cl₂ correct incorrect

F₂ correct incorrect

* not completed

. Regarding measurements of toxicity, which statement(s) is/are true? (Please select all that apply)

The toxicity effect may depend on both the species and its stage of development correct incorrect

Chronic responses are readily measured correct incorrect

Guidelines for drinking water typically set limits of toxicant concentrations at twice the LC₀ correct incorrect

Other environmental factors are not accounted for in most dose-response studies correct incorrect

The terms LD₅₀ and LC₅₀ are synonymous correct incorrect

* not completed

. Which is/are correct statements about drinking water supplies? Please select all that apply.

Diffuse sources of contamination of water sources are more dilute and therefore less serious correct incorrect

Guidelines for drinking water such as provided by the WHO use the LD₅₀ as the recommended upper limit correct incorrect

Standards for drinking water usually take into account the appearance of the water correct incorrect

Guidelines for potential contaminants in water are expressed as total amount not to be exceeded correct incorrect

Some experiments to measure LD₅₀ use microorganisms as the test population correct incorrect

* not completed

. Which of the following statements correctly apply to drinking water treatment? (Please select all that apply)

Chlorine bubbled into water has a small acidifying effect correct incorrect

Activated carbon is used in the filter medium to remove small hydrophobic organic molecules correct incorrect

Chlorine dioxide produces fewer disinfection by-products than chlorine correct incorrect

When chlorine is used for water purification, Cl₂ is not the active disinfecting agent correct incorrect

UV and ozone treatment do not leave a residual disinfecting agent in water correct incorrect

* not completed

. Which of the following statements correctly apply to wastewater?  (Please select all that apply)

The biological oxygen demand value of municipal wastewater is usually smaller than the chemical oxygen demand value correct incorrect

The activated sludge process is carried out under aerobic conditions correct incorrect

Very little phosphorous is removed during activated sludge treatment correct incorrect

All of the sludge produced in the aerator is sent to waste correct incorrect

Addition of alum enhances coagulation and also assists in chemical removal of phosphorous correct incorrect

* not completed

. Which of the following statements about aluminium-based coagulants is/are true? (Please select all that apply)

Trivalent metal hydrated ions are readily deprotonated in aqueous solutions correct incorrect

Al³⁺ added to water has increased solubility under both low and high pH conditions correct incorrect

When salts containing Al³⁺ are added to a typical wastewater, carbon dioxide is released correct incorrect

FeCl₃ can be used as an alternative coagulant to alum in some cases correct incorrect

Physical entrapment of clay particles by insoluble aluminium hydroxide occurs to some degree correct incorrect

* not completed

. Which of the following statements about phosphate removal in wastewater is/are true? (Please select all that apply)

Phosphate is removed by chemical reaction with coagulants like alum correct incorrect

Phosphate is removed by being incorporated within the microbiological 'sludge' correct incorrect

Iron(III) chloride solutions used in phosphate removal are highly corrosive correct incorrect

The sludge produced in wastewater treatment can be a source of phosphorus when used as a fertilizer correct incorrect

In constructed wetlands, removal of phosphorus without addition of coagulant is inefficient correct incorrect

* not completed

. Which of the following statements about nitrogen in wastewater is/are true? (Please select all that apply)

Nitrogen compounds are removed to a substantial extent by coagulants like alum correct incorrect

Nitrate remaining in discharged wastewater contributes to the BOD correct incorrect

Ammonium can be removed by converting it to gaseous forms correct incorrect

Ammonium ion is removed during the chlorine-based disinfection step of water treatment correct incorrect

Both ammonium and nitrate ions can contribute to eutrophication of water bodies correct incorrect

* not completed

. The time (in minutes) it takes for a 0.05 mm spherical particle (particle density of 2.27x10³ kg m^-3) to settle in a 3 m tank is (assume P° and 20°C):

0.29 correct incorrect

39 correct incorrect

2.9 correct incorrect

29 correct incorrect

3.9 correct incorrect

* not completed

. Which of the following statements about microbiological nitrogen removal is/are true? (Please select all that apply)

Nitrogen can be removed from wastewater using a two-step microbiological process correct incorrect

The first of two steps involves denitrification, converting ammonium ion to nitrate correct incorrect

The second of two steps requires anaerobic conditions and the presence of specific types of bacteria correct incorrect

Methanol is often added to aid in denitrification correct incorrect

Biomass in the wastewater acts as an electron acceptor as soluble nitrate is converted into nitrogen gas correct incorrect