Water Quality Concepts II Dr. S.K. OngGeneral Characteristics of Groundwater and Surface WaterClassification of Degree of Hardness of WatersExample ProblemCE 326 Principles of Environmental EngineeringWater Quality Concepts II Dr. S.K. OngGeneral Characteristics of Groundwater and Surface WaterGroundwater Surface WaterTypical Water Quality (common cations and anions)Major (________ mg/L) Secondary (____________ mg/L)Cations CationsSodium, Na+Iron, Fe2+ and Fe3+Calcium, Ca2+Potassium, K+Magnesium, Mg2+Manganese, Mn2+Anions AnionsBicarbonate, HCO3-Carbonate, CO32-Sulfate, SO42-Nitrate, NO3-Chloride, Cl-Silica, SiO2 or Si4+Fluoride, F-pH- is a measure of the hydrogen ion activity/concentration for dilute solution and is given by:where [ ] is in terms of moles/literWater ionizes to form H+ and OH- and is given by the balanced equationThe product of the activity or concentration of H+ and OH- is a constant at a given temperature, i.e., [H+][OH-] = Kw = __________ Kw is called the ion product of waterCarbonate systemBicarbonates (HCO3-), carbonates (CO32-) and carbon dioxide in water (H2CO3) are the most dominant ______________acids/bases system in natural waters.Weak acid or bases are defined as acids or bases that do _________ dissociate completely.In contrast, strong acids such as sulfuric acid, hydrochloric acid and nitric acid dissociates completely when added to water, ex.Let us examine the carbonates in water: 1Sources:- carbon dioxide in the atmosphere dissolve in water to form carbonic acid - carbonate minerals such as limestone will contribute HCO3- and CO32-to natural watersThe different carbonate species are formed in natural water depending on the pH and can be expressed as follows:Ka1 = 10-6.3Ka2 = 10-10.3______________ – measure of the capacity of a water to neutralize strong acids (attributed to bases such asHCO3-, CO32-, OH-)______________ – measure of the capacity of a water to neutralize strong base (attributed to acids such as HCO3-, H2CO3, H+)Total alkalinity (moles/L) = _________________________________________________Total alkalinity (mg/L as CaCO3) = _________________________________________(units in mg/L as CaCO3)Alkalinity is measured by titrating a known volume of water sample (usually 50 ml) with a standard solution of a strong acid to about pH 4.5. Alkalinity = Normality of Acid x Volume of acid added x 50,000in mg/L as CaCO3 Volume of water sample__________________(TH) – is the sum of all polyvalent cations (expressed as mg/L as CaCO3)Example - Ca2+, Mg2+, Fe2+, Fe3+, Mn2+But in most waters, Ca2+ and Mg2+ are dominant cationsTotal Hardness (TH) commonly taken as equal to the sum of _________________ expressed as mg/L as CaCO3Carbonate Hardness (CH)- temporary hardness, heating removes it- equal to the total hardness or alkalinity whichever is less2Noncarbonate hardness (NCH)- permanent hardness, cannot be removed by heating- equal to total hardness in excess of alkalinity- if alkalinity is equal to or greater than total hardness – no noncarbonate hardness is presentClassification of Degree of Hardness of WatersSoft ______________ mg/L as CaCO3Moderate Hard ______________Hard ______________Very Hard ______________Example ProblemYour friend dug a well recently and sent the water sample for analysis. The water analysis is as follows: Ca2+ = 83 mg/L = _________________ HCO3-= 220 mg/L = _______________________Mg2+ = 27 mg/L = __________________ CO32-= 15 mg/L = _______________________CO2= 48 mg/LpH = 9.43Questions(i) Express the concentrations above in terms of mg/L as CaCO3(ii) What is the [H+] concentration in the water? _____________________________________(iii) What is the [OH-] concentration in water? _____________________________________(iv) What is the alkalinity of the water as mg/L as CaCO3?(v) What is the total hardness in mg/L as CaCO3? Is the water hard or soft?(vi) What is the carbonate hardness?(vii) What is the noncarbonate