Water and Wastewater Treatment L1

Question 1

Sources of water pollutants

Answer 1

Sewage, manure - nitrogen, phosphorus, pathogenic organisms, biodegradable chemicals (consume O2)
Fertilisers- nitrogen, phosphorus
Pesticides, oil
Toxic chemicals
Sediments

Question 2

Conventional Water Pollutants

Answer 2

Pathogenic organisms, organic matters, Nutrients (e.g. N, P), salts, suspended solids, toxic and hazardous substances

Question 3

Emerging Water Pollutants

Answer 3

Colloids: nanomaterials
Pharmaceuticals: antibiotics, anti-inflammatory drugs…
Endocrine disrupting chemicals: hormones, steroids…

Question 4

Define Oxygen demanding material

Answer 4

Anything that can be oxidised by water dissolved oxygen, usually including organic matter and ammonia

Question 5

Define oxygen demand and what it can be used for

Answer 5

Amount of oxygen required to oxidise a waste (aka any organic matter present in the water), gives an indirect measurement of the amount of organic/carbon containing impurities/contaminants in water

Question 6

Define BOD, COD and ThOD

Answer 6

Biochemical oxygen demand (amount of oxygen required to oxidise any organic matter present in the water biochemically),
Chemical oxygen demand (equivalent amount of oxygen required to oxidise any organic matter in a water sample by means of a strong chemical oxidising agent),
Theoretical oxygen demand (amount of oxygen required for microbes to degrade by oxidation a known compound completely to CO2 and H2O. Most useful to assess strength of an organic pollutant)

Question 7

Define waste stabilisation

Answer 7

Process of microorganisms oxidising waste to CO2 and H2O

Question 8

Define Carbonaceous biochemical oxygen demand (CBOD)

Answer 8

Oxygen demand only from carbon containing compounds and not from inorganics such as ammonia of ferrous iron. Often used to term measurement using waste stabilisation

Question 9

Define Nitrogenous biochemical oxygen demand (NBOD)

Answer 9

2 step oxidation of ammonia (by bacteria):
NH4+ + 3/2 O2 —-nitrosomonas—> NO-2 + H2O + 2H+
NO2- + 1/2 O2 —nitrobacter—> NO3-
———————————————————
NH4+ + 2O2 —————> NO3- + H2O + 2H+

Question 10

List BOD5 analysis standard conditions

Answer 10

Temp 20C
Darkness (prevent algae from producing O2)
Excess of nutrients for microorganisms (no limit in growth or stabilisation)
Depending on BOD concentration and water characteristics: Dilution, essential nutrients (N,P,K,Fe, etc.) and bacterial seed
Duration of analysis : BOD5 5 days (BODu ultimate test of 20 to 30 days)

Question 11

Describe a process causing eutrophication

Answer 11

Human activity release excess N and P (rare in nature which controls microbial population) into environment (exceeding ecosystem loading limit) promotes excessive growth of algae and cyanobacteria which block light. They also become oxygen demanding material when they die. Their decay depletes oxygen in the water suffocating fish and shellfish and rotten the water.

Question 12

List some toxic and hazardous substances

Answer 12

Heavy metals
Other inorganic elements
Acids/Bases
Oxidants/reductants
chlorination by-products
combustion by-products
volatile organic compounds (VOCs)
Hydrophobic organic compounds
Surfactants
Petroleum Additives
Pesticides

Question 13

Steps in developing the DO sag curve

Answer 13

1. Determine initial conditions
2. Determine the deoxygenation rate from BOD test and stream geometry
3. Determine the reaeration rate from stream geometry
4. Calculate the DO deficit as a function of time
5. Calculate the time and deficit at the critical point