Water treatment

total solids (ts)

the residue remaining after a water sample has been dried at a specified temperature (103-105 degrees); ts = tss + tds

total suspended solids - tss

portion of the total solids retained on a filter with a specified pore size, measured after being dried ata specified temperature - 105 degrees

total dissolved solids - tds

portion of the ts in the filtrate (the liquid that went through the filter) after filtered using a filter with a specified pore size, measured after being dried at a specified temperature - 105 degrees

volatile suspended solids - vss 

solids that can be volatilized (evaporated) and burned off when the tss are ignited - 500 +- 50 degrees

solid content determination process

• crucible with filter at top

• put sample volume ( x ml) of liquid into the filter and dry at approx 103 degrees

• using total weight of crucible, total solids can be calculated

• dry filter at 103 degrees as well

• using weight gain of filter, tss can be calculated

• after drying, place filter in furnace and ignite at 550 degrees

• using weight loss of filter, vss can be calculated

• place filtrate in crucible and dry at 103

• using weight fain of crucible, tds can be calculated

filtrate

product of filtration - a liquid or solid that has been passed through a filter

total solids formula

weight gain of crucible / x ml = ts

total suspended solids formula

weight gain of filter / x ml = tss

volatile suspended solids formula

weight loss of filter/ x ml = vss

total dissolved solids formula

wieght gain of crucible / x ml = tds

turbidity

measure of the light transmitting properties of water - how transparent water is

what is turbidity based on

based on comparison of the intensity of light scattered by a sample to the light scattered by a reference suspension under the same condition

turbidity units

nephelometric turbidity units - ntu

treated water turbidity relationship

• TSS [mg/L] = TSSf * T

• tss - total suspended solids in mg/l

• tssf - converting factors

• turbidity in ntu

electrical conductivity

a measure of the ability of a solution to conduct an electrical current - ec proportions to ion concentrations

electrical conductivity units

millisiemens per meter - mS/m

water and minerals

when minerals dissolve in water, cations and anions are dissociated

ec and tds

electrical conductivity is a surrogate measure of total dissolved solids

ec and tds formula

TDS = EC * f

• tds in mg/l

• ec in dS/m

• f value between 0.55 - 0.70 (depends on type of tds)

electroneutrality process

in water dissolved substances dissociate into charged ions

cations and anions - neutrality

the sume of positive ions (cations) must equal the sume of the negative ions (anions) in the solution

cations

positiviely charged speices in solution expressed in terms of equivalent per liter, eq/l or milliequivalent per liter, meq/l

anions

negatively charged species in solution, eq/l, or meq/l

electroneutrality

the number of equivalents related to how many electrons a species donates or accepts

equivalent weight

grams per equivalent - the molecular weight of the species divided by the number of equivalents in the species (g/mol divided by eqv/mol = g/eqv)

converting mol/l to eq/l

eq/l = mol/l * equivalent

concentration units

either in mol/l or eq/l or mg/l

converting mg/l to eq/l

eq/l = (mg/l) / equivalent weight

water hardness - total

total hardness is the summary content of calcium and magnesium

carbonate hardness

aka temporary water hardness is caused by the presence of carbonates and hydrocarbonates of calcium and magnesium

carbonate

carbonate is a salt of carbonic acid, characterized by the presence of a carbonate ion

noncarbonate hardness

caused by the presence of Ca2+ and Mg2+ and anions like Cl- SO4 2- and NO3 -, which do not decompose and do not precipirate during boiling water 

washing with hard water

hard water requires more sopat and detergents for home laundry/washing & contributes to scaling - because compounds in soap react with calcium in hard water and precipitate out as scum - only once all the calcium and magnesium ions have been precipitated out as scum, can the soap then lather up and remove grease

concentration in miliequivalent/liter formula

meq/l = (concentration in mg/l) / (equivalent weight in g/eqv)

hardness calculation

hardness is the total sum of concentrations of  ca2+ and mg2+ as miliequivalent/liter - (can also be expressed in mg/l as CaCO3 - calculate in meq/l and then multiply by 50g of caco3/eqv)

pH

hydrogen ion concentration - pH = -log[H+] 

pH and dissassociation

ph is connected closely with the extent to which water molecultes dissasociate - H2O ←> H+ + OH-

pH equilibrium constant

Kw = [H+][OH-]

organic compounds

carbon, hydrogen, oxygen, with nitrogen in some cases

wasterwater organic compounds

protein 40-60%, carbohydrate 25-50%, oils and fats

total organic carbon

measure of the total amount of carbon in organic compounds present in water

do

dissolved oxygen - the amount of oxygen dissolved in water, essential for life in aquatic environments

theoretical do demand

for e.g. carbon dioxide, tells us how much oxygen would be required to fully oxide all organic carbon into co2 - do demand for co2 = 32/12 * toc

real do demand

Lower than theoretical because:

• Biological use of DO < 100% efficient

• Other elements (e.g., nitrogen) also consume DO

• Some TOC is inert and not biologically available

cod - chemical oxygen demand

indirect measure of the amount of oxygen consumed by chemical reactions / oxidation of organic matter in a sample/water

cod process

uses strong oxidizing chemical to oxidize organic matter

cod vs theoretical do

cod is generally greater than the theoretical oxygen demand, bcs it accounts for all chemically available sources - even those not biodegradable

bod - biological oxygen demand

the amount of dissolved oxygen required by aerobic biological organisms to break down organic material in water

bod measurement conditions

typically measured at 20 degrees over 5 days, written as BOD5

BOD units

expressed in mg O2 per liter of sample

bod measurement method

take two samples

• test one immediately for dissolved oxygen

• incubate the other at 20 deg in the dark for 5 days, then test for do

• the difference = BOD (in mg/L)

bod vs cod

BOD < COD, since some organic matter is inert and not biologically degradable

relationship between theoretical do demand, bod and cod

toc→ theoretical do demand < BOD < COD

nitrogen in water

nitrogen from organic matter, and nitrogen from nitrogen compounds such as NH4 + and NO3 -

nitrogen

an essential nutrient for growth - many organic compounds contain nitrogen (all contribute to overall N in environment, water, wherever)

forms of nitrogen

• Organic nitrogen (proteins, urea, etc.)

• Inorganic: NH₄⁺, NO₂⁻, NO₃⁻

• All contribute to nitrogen load in water

Conversion Factors (mg/L compound → mg/L N)

• NH₃: × (14/17)

• NH₄⁺: × (14/18)

• NO₂⁻: × (14/46)

• NO₃⁻: × (14/62)

nitrogen cycle

• Plants absorb nitrate from soil → build proteins

• Animals eat plants → nitrogen in biomass, nitrogen is passed to animals

• Waste & decay → ammonia (ammonification) - nitrogen from protein is returned to the environment as ammonia

• Bacteria convert ammonia → nitrite (NO₂⁻) → nitrate (NO₃⁻) (nitrification)

• Under anoxic conditions: nitrate → N₂ gas (denitrification) . denitrifying bacteria convert nitrates to molecular nitrogen

• Atmospheric nitrogen goes through biological nitrogen fication and ends up in soil, etc. - nitrogen can exist in solid form

Kjeldahl Nitrogen (TKN)

• Sum of organic nitrogen + ammonia (NH₄⁺-N).

• Does not include oxidized forms (NO₂⁻, NO₃⁻).

too much nitrogen

can be toxic - leads to euphication

euphication

• Over-enrichment of water with nutrients (N, P).

• Causes algal blooms, oxygen depletion, fish kills.

phosphorus

also an essential nutrient for growth

• Orthophosphate: PO₄³⁻, HPO₄²⁻, H₂PO₄⁻, H₃PO₄ (bioavailable)

• Polyphosphate (chains of phosphate)

• Organic phosphate (bound in organic matter)

phosphorus in water

• too much phosphorus stimulates a lot of plant growth

• if TP is too high, there is high risk of algea bloom (eutrophication)

• > 0.03 mg TP/l in river - eutrophication

phosphorus cycle

• Geological sources (mining, erosion)

• Uptake by plants and microbes

• Returned via decomposition

• Fluxes: e.g. ~22 million tons/year mined

phosphorus as a solid

phosphorus is only possible as a praticle, as a solid - it does not exist in the atmosphere as a gas

phosphorus levels in environment

• phosphorus more scarce than nitrogen

• bioavailable P is limited

• so in healthy water body, concentration should be low

phosphate mining

• phosphate rock can release phospherus during mining

• mined to give it to plants, used in fertilizer

Orthophosphate (PO₄³⁻-P)

• Bioavailable form of phosphorus (directly usable by organisms).

• Includes PO₄³⁻, HPO₄²⁻, H₂PO₄⁻, H₃PO₄.

Total Phosphorus (TP)

• Orthophosphate + polyphosphate + organic phosphorus.

• Important indicator of eutrophication potential.

C:N:P Ratio

Typical nutrient balance for microbial growth = 100 : 7.2 : 1.

• phospherus is generally the limiting nutrient preventing exponential growth as there is not enough of it bioavailable

carbon cycle

Carbon moves between atmosphere (CO₂), biosphere (plants/animals), hydrosphere (dissolved carbon), and geosphere (rocks/fossil fuels).

• Photosynthesis: CO₂ → organic matter

• Respiration & Decomposition: organic matter → CO₂/CH₄

• Combustion: fuels/biomass → CO₂

• Sedimentation/Fossilization: long-term storage in rocks & fuels

• Human impact: burning & deforestation add extra CO₂ → climate change

phosphurus cycle 2

Phosphorus cycles through rocks, soil, water, and organisms (no gas phase).

• Weathering of rocks → phosphate (PO₄³⁻) released

• Assimilation: plants/animals use phosphate for ATP, DNA, membranes

• Decomposition: organic P → inorganic phosphate

• Sedimentation: phosphate locked in rocks/sediments long-term

• Human impact: mining phosphate rock for fertilizer → excess P in water → eutrophication

nitrogen cycle 2

Nitrogen cycles between atmosphere (N₂), soil, water, plants, and animals.

• Fixation: N₂ → NH₄⁺ (by bacteria/industry)

• Nitrification: NH₄⁺ → NO₂⁻ → NO₃⁻

• Assimilation: plants/animals use nitrogen for proteins/DNA

• Ammonification: organic N → NH₄⁺

• Denitrification: NO₃⁻ → N₂ (back to atmosphere)

• Human impact: fertilizer use, wastewater → eutrophication

lack of oxygen in water

if too many algae grow, they use up all the oxygen in the water body and the fish die and suffocate

dissolved oxygen in water - sources

• Diffusion from atmosphere

• Photosynthesis in water

DO sinks

• Respiration by organisms

• Oxidation of organic matter

• Oxidation of reduced compounds (NH₄⁺, Fe²⁺, S²⁻, etc.)

control of DO

DO in water is controlled by both consumption (sinks) and aeration (sources)

ideal gas law

PV = nRT

gases common in water

• O₂, N₂, CO₂ (natural)

• NH₃, CH₄, Cl₂, H₂S (pollution/byproducts)

things that determine amount of gas in water

• solubility of the gas defined by henry’s law

• the partial pressure of the gas in the atmosphere

• the temperature

• the concentration of the impurities in water (e.g. sailinity, suspended solids)

partial pressure

• Pressure exerted by one gas in a mixture.

• Example: air = 21% O₂ → PO₂ = 0.21 atm.

partial pressure formula

partial pressure (p_i) = mole or volume fraction (ppm_v) * total pressure (p_total)

henry’s law

The amount of gas dissolved in water is proportional to its partial pressure above the water.

• Higher pressure → more gas dissolves

• Higher temperature → less gas dissolves

• Solubility also affected by salinity and impurities

henry’s law formula

[Gas]=KH​×Pgas​

• [Gas] = dissolved concentration (mol/L)

• Kₕ = Henry’s Law constant (mol/L·atm)

• Pgas = partial pressure of the gas (atm)

heavy metals in water

toxic even at low concentrations, many are priority pollutants - pose risk because they are persistent, bioaccumulate, toxic to humans and ecosystems

• cadmium

• chromium

• lead

• mercury

• other: copper, iron, manganese, nickel, zinc

cadmium

carcinogen, accumulates in liver/kidneys

chromium

carcinogenic and corrosive

lead

toxic, brain and kidney damage, birth defects

mercury

toxic to central nervous system, birth defects

living organisms in water

• bacterial

• fungi

• algae

• protozoa

• viruses

organic pollutants in water

• disinfection byproducts - DBPs

• agircultural chemicals

• emerging contaminants

disinfection byproducts

• Formed when chlorine reacts with organic matter

• Examples: Trihalomethanes (THMs), Haloacetic acids (HAAs)

agricultural chemicals

Pesticides, herbicides, fertilizers

emerging contaminants

• Pharmaceuticals (antibiotics, prescription & non-prescription drugs)

• Hormones (endocrine disruptors)

water treatment

to remove undesired or add desired water constituents to meet the required water quality for:

• drinking water

• domestic wastewater

• industrial wastewater

different or same technologies and processes could be applied to remove different constitutentswater

water treatment process

• intake

• chemical addition - chlorine, lime, alum (these chemicals facilitate coagulative process)

• mixing

• coagulation and flocculation

• sedimentation

• filtration

• disinfection

• storage

• distribution

size of substances in water & filtering

water molecule is approx 0.27 nanometers - most particles bigger than that, so one possibility is to use a nano sized filter - then mostthings can be removed but water can still pass through (tho is quite costly) 

colloids

need to be removed using coagulation