Physical Water Treatment Methods

(Small groundwater systems)

(Surface water treatment)

Types of Filters:

1. Slow Sand Filter

(Iron and manganese removal in small groundwater systems)

Slow Sand Filter

Unlike other filters, slow sand filters also remove a great deal of turbidity from water using biological action. A layer of dirt, debris, and microorganisms builds up on the top of the sand. This layer is known as schmutzdecke, which is German for "dirty skin." The schmutzdecke breaks down organic particles in the water biologically, and is also very effective in straining out even very small inorganic particles from water.

2. Rapid Sand Filter

The rapid sand filter differs from the slow sand filter in a variety of ways, the most important of which are the much greater filtration rate and the ability to clean automatically using backwashing.

Rapid Sand Filtration

It produces 125 million gallons of water per acre of filtered area per day. This requires pre-treatment with coagulants and sedimentation

4. Diatomaceous Earth Filter (Diatomite Filter)

3. Pressure Filter

F I L T R A T I O N

(beverage and food industries and swimming pools)

- is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass. The fluid that passes through is called the filtrate. When water passes through the filter, suspended particles and flocculant material come in contact with sand grains and adhere to there. This reduces the water passages resulting to straining actions. The filter is regularly backwashed to remove the entrapped material.

M E M B R A N E P R O C E S S

used in the treatment of water for potable use. It is used

to remove colloidal materials. Important membrane filtration includes:

Reverse Osmosis

Advantages

-Friendly to the environment

-Taste of the purified drinking water

-Removal of dissolved minerals, metals and other particles

Disadvantages

-Requires an enormous amount of water

-Lack of filtration specificity

REVERSE OSMOSIS

- is a pressure driven process in which a semi-permeable membrane is used to retain ions and other constituents as pressure is applied.

• Reverse Osmosis

U L T R A F I L T R A T I O N

-is a process in which pressure is used to concentrate solutions containing colloids and high molecular mass material.

Advantages

-Low operating pressure required

-Lower energy consumption than nano-filtration or reverse osmosis

-Relatively cheap

• Ultrafiltration

-Good permeate yield depending on the supply water and membrane choice

-Few manual actions required

-Disinfection through removal of bacteria. To a certain extent, UF allows viruses, phage, colloids and macro molecules to be removed.

Disadvantages

-Membrane damage at pressure > 3 bar.

-Only removes suspended matter and bacteria;

-Damage may occur when trying to prevent hard and sharp particles > 0.1 mm;

S E D I M E N T A T I O N

In the dilute suspension where the particles are free to settle without interference, the process is called free settling/discrete settling.

N A N O F I L T R A T I O N

-is an emerging technology using low pressure reverse osmosis membrane for water softening.

Disadvantages

Advantages

-Limited retention for salts and univalent ions.

-Lower discharge volumes, lower retentate concentrations than RO for low value salts

-Nano-filtration membranes are a little more expensive than reverse osmosis membranes;

-pH of water after nano-filtration is normally non-aggressive

-Softens hard water when specific softening membranes are used

-Membranes are sensitive to free chlorine (life-span of 1000 ppmh). An active carbon filter or a bisulphite treatment is recommended for high chlorine concentrations.

-Reduction in colour, tannins and turbidity

-Reduction salt content and dissolved matter content (TDS) in brackish water

-Reduction in nitrates and sulphates

-Reduction in heavy metals

-Disinfection

• Nanofiltration

As the concentration increases, the particles tend to interact and interfere with the free movement of one another is called hindred settling.

• It is a physical water displacement process using gravity to remove suspended solids, such as sand silt, loose scale, clay or organic material from the water.

8. Biological activities

1. Force of Gravity

9. Depth and shape of the basin

2. Electrical Phenomena

3. Viscosity of the Water

4. Coagulation of the settling particles

5. Operation of the basin

6. Size and specific gravity of settling particles

7. Presence of convection and other current

• It is the easiest way to remove the suspended material is to let the force of any gravity do the work.

FACTORS AFFECTING

PLAIN SEDIMENTATION

• It is a process whereby a large portion of the suspended particles in the water are removed by passing through a sedimentation basin where the larger particles will settle. This will greatly reduce the turbidity.

• Depends merely on gravity and includes no coagulation and flocculation.

• The speed at which suspended particles settle toward the bottom of the tank depends on their sizes as well on their gravity

CHEMICAL SEDIMENTATION

• Known also as sedimentation with coagulation. It is a process of mixing chemicals to water to form flocs, which will settle due to gravity.

• The nature of sedimentation process also varies with the concentration of suspended particles and their tendency to interact with one another.

• It is to reduce contaminant posing health risk and remove taste and odor.

S C R E E N I N G

Flocculation can be accomplished using a variety of means such as:

- used to remove large floating and suspended debris (logs/branches) that maybe present at the intake locations.

a. slowly rotating paddles;

b. flow through over, and under baffled chambers; and

- to prevent pump, pipe, and any other equipments from clogging/damage.

A E R A T I O N

c. with the addition of gas

- Microscreens are used to screen fine suspended materials.

- is a form of gas transfer and is used in a variety of operations including the following:

a. addition of oxygen to oxidize dissolved iron and manganese

b. removal of carbon dioxide

PRINCIPLE TYPES OF AERATION DEVICES

a. Air Diffusion Aerators

F L O C C U L A T I O N

b. Spray Nozzle Aerator

c. removal of hydrogen sulfide to eliminate odors and taste

c. Cascade Aerator

B O I L I N G

d. Coke Tray Aerator

- gentle stirring of water after the addition of coagulation chemicals which aid in the formation of settable flocs.

A E R A T I O N

d. removal of volatile oils and similar odor-and-taste producing substances released by algae and similar microorganisms

is accomplished either by:

- most economical and simplest way of treating water.

WATER AIR

OR

AIR WATER

- it destroys all forms of disease organisms (although the taste is altered/is changed)

BOILING

BUBBLES

WHILE STEAMING

MIST

WATER TREATMENT

2 Methods:

1. Physical Unit Operation

2. Chemical & Biological Unit Process

Physical Unit Operation

- methods in which changes are brought about by the application of physical forces (gravity settling)

Chemical & Biological Unit Process

- changes brought about by means of chemical

and biological reactions. (e.g. water refilling stations)

Physical Water Treatment Methods

• Boiling

• Screening

• Aeration

• Flocculation

• Sedimentation

• Filtration

• Membrane Process

Prepared By

Gantuangco, Chrisna

Pedemonte, Bernard Michael G.

Dimco, Odette Dominique F.

Eria, John Anthony