Wastewater Treatment:

Water Softening(Pelunakan Air)

(Ref: Wastewater Engineering: Treatment and Reuse, Metcalf and Eddy, 4th ed., Mc. Graw Hill Book Inc., New York 2003, pp.1138-1157).

Agus Prasetya, PhD.S1 & MTPPL JTK-FT UGM

MTPB – SPs UGMS1 & MPAAL – JTSL FT UGM

MTS – FT UGM

Important Parameters:

• pH • Hardness • O2 and CO2

concentration • Silicates• Dissolved solids • Suspended solids • Organics

concentration

Consequences(possible problems):

• Scaling, Fouling

• Corrosion • Carryover of volatile minerals

• Microbial contamination.

HARDNESS OF WATER:

It is a measure of wettability of water. Hard water contains high concentration of mineral ions, e.g. Ca2+ , Mg2+ in the form of dissolved dissociated salts.

The concentration of these ions is relatively low, but affect the quality of water (in industry, particularly boiler feed water) greatly.

Total Hardness: Show the amount of ions of Ca, Mg, Fe, Al and other minerals and organic acid in the water, which reduce wettability of water.

Classification Total ion concentration, in

[mg/L] or (ppm)

Soft < 50

Moderate 50 - 150

Hard 150 – 300

Very hard > 300

DEGREE OF HARDNESS

FOULING:Occurs if solid matters in water deposited on the surface of equipment.

Solids matters enter the equipment through suspended solids in water, from various sources, e.g. sludge, colloids

SCALING:Occurs due to deposition of minerals in the water. The most common scale are: CaCO3, CaSO4 and silicate.

The scale on the surface will harden by time and become difficult to be cleaned.

The presence of scale will reduce the heat transfer capacity and decrease the energy efficiency of the system.

CORROSION:

Electro-chemical corrosion on metals occurs due to the presence of ions (because of low pH) or dissolved oxygen in the water. Other type of corrosions may occurs due to mineral deposition (under deposit corrosion), electrolysis and microorganism activity.Corrosion reduced the life-time of equipment drastically.

MICROBIAL CONTAMINATION:

Microbia, such as algae, fungi and bacteria create some operational problems, e.g. plugging, fouling (that can be followed by under deposit corrosion) and wood-component degradation.

ION EXCHANGE

ION EXCHANGE MATERIALS

• Natural (and some can be synthesized): Zeolites (a complex aluminosilicate materials and sodium/Na ions) water softening and NH4OH removal.

• Synthetic: Resin or phenolic polymer

SYNTHETIC RESIN

ION EXCHANGE REACTIONS

ION EXCHANGE REACTIONS

For SYNTHETIC RESIN

ION EXCHANGE APPLICATIONS

• NITROGEN (i.e. AMMONIUM and NITRATE) CONTROL

ION EXCHANGE APPLICATIONS

• REMOVAL of HARDNESS (MINERALS ION, HEAVY METALS and

DISSOLVED SOLID)

Disinfection– All of the previous treatment processes remove > 90% of

bacteria and viruses

– A disinfectant is used to:

• Kill microbes fast and efficiently

• Not kill humans or other animals

• Last long enough to prevent regrowth in distributions systems

– Factors that inhibit disinfection:

• Turbidity: particles shelter bacteria

• Resistant organisms

• Fe+2 and Mn+2: form particles that shield bacteria

Oxidizable compounds: become food for microbes in distribution

system

Commonly used disinfectants:

Chlorine; Chlorine Dioxide; Chloramines

Ozone; UV light