The Principle of Water Treatment


THE PRINCIPLE OF WATER TREATMENT:- Part 1
By: Accot Technologies Sdn Bhd

There has been a widespread awareness for a cleaner environment. Our major sources of pollution can be from water, air, and noise. And most of us like to have a cleaner environment, but at the same time we are the major contributors or agents to our "pollutant".

Toxic chemicals, harmful bacteria, unwanted solid waste and most of these can be classified as organic & inorganic waste.

When organic waste enters into the stream, most likely it will stimulate bacterial growth that affects aquatic life forms by depleting them of oxygen level in the water. The stream becomes septic due to bacteria undergoing anaerobic metabolism, producing odors and darkening the water appearance.

The inorganic wastes such as copper, nickel, lead, when entered into the stream, are basically toxic substances that cannot be further broken-down by the bacteria and can be poisonous to human health & aquatic life forms.

These are some of the common environmental pollution-related jargons :

  1. Biodegradable organic. Those that can be broken down by micro-organism to form stable compounds such as CO2 and water.
  2. Effluent is the liquid product discharged or emerging from a process.
  3. COD (Chemical Oxygen Demand)
    It is the amount of oxygen (usually measured in mg/1 (milligram per litre) required to oxidize both organic and oxidizable inorganic compounds.
  4. BOD (Biochemical Oxygen Demand)
    It is the amount of oxygen (mg/1) required by micro-organism to consume biodegradable organic in waste-water.
  5. Total Solids is the sum of suspended solids and dissolved solids.
  6. Suspended solids are those that can be removed by filtration.
  7. Settle-able solids are those in suspension that will pass through a 2000 micron sieve and settle in one hour under gravity.
  8. pH is the hydrogen ion concentration in the medium which determines acidity and alkalinity.

The principal objective of wastewater is to remove the waste constituents that are harmful to the environment when discharged. The processes involved may include all or some of it, like the physical, chemical and biological treatments.

In our next part 2, we will look at a typical wastewater treatment plant and its concept.

THE PRINCIPLE OF WATER TREATMENT : - Part 2

In our previous part 1, we had covered the common environmental pollution jargon and the principle objective of wastewater treatment (WWT). In this issue we will look at a typical WWT. In a typical wastewater treatment process, optimum dosing of the appropriate chemicals is one of the main criteria. When there is an insufficient dosing of chemicals this may result in wastewater being untreated and at the same time, enhance pollution in the wastewater. Overdosing of chemicals on the other hand will result in more sludge volume and higher treatment cost.

Jar Test is one of the most commonly used methods employed by expert to determine the types and dosages of chemicals required for proper treatment of wastewater and also used as guideline to set the dosing rates of chemicals.

A Typical 'Waste Water Treatment Plant Flow

The raw wastewater flows into the equalization tank then into the primary process (Physical Chemical Treatment). This process will normally involved in two chemicals. A coagulant , usually an inorganic substance, is used to destabilize the electrostatic repulsive forces which tend to keep colloidal and soluble suspension particles apart and prevent them from gathering together.

The other chemical, the flocculant, usually organic in nature, must be added to combine the particles into bigger flocs, which can then be more easily floated or settled. In a well-designed system there should have proper flowrate that allows the coagulant to have sufficient time to destabilize the repulsive forces before the flocculant is added.

At the aeration (Biological Treatment) basin, organic matter acts as food supply for bacteria to metabolize the waste solids resulting in absorbing oxygen (BOD) and releasing CO2. The process removes organic matter from solution by synthesis into microbial cells. It is further transferred to a clarifier for separation of the sludge and effluent. The sludge is pollutants converted into concentrated form. This sludge has to be further treated in order to prevent further pollution of waterways. The degree of solid removal will depend on the character of the raw wastewater and the treating chemical.

The basic aim of sludge treatment is to reduce the volume and destroy or stabilize sludge solids before final disposal.

The chlorination of water and wastewater is to disinfect & destroy Pathogens and control microorganisms. Chlorine is also used for oxidation. As an oxidant it is used in iron and manganese removal, destruction of taste and odor compounds.

In general when the water appeared to be cloudy , is because there are many suspended particles floating & the electrical repulsive charge is actually holding the particles in suspension. And the processes known as coagulation will combine small particles including colloidal particles into larger bodies by destabilization.

The other process known, as FLOCCULATION will increase the growth of unstable particle aggregates into larger masses (Flocs) which can be more easily separated from liquid fraction via filtration.

In our part 3, we will look at our environmental regulation & control.

THE PRINCIPLE OF WATER TREATMENT : - Part 3

As part of our last series, we will focus at home of the attention given to the environment matters. Environmental legislation has been enacted in most countries and the standards have been made more stringent than ever including Malaysia. In our country DOE (Department of Environment) is empowered under the Environmental Quality Act 1974 ( Amendment ) 1985, to control and prevent pollution, as well as to protect and enhance the quality of the environment in Malaysia. Our government has initiated programs to control scheduled waste management to safeguard the environment and the safety of the people.

We have the Environmental quality (Scheduled Wastes) Regulations 1989, prescribed a listing of 107 categories of toxic and hazardous wastes defined as "scheduled wastes." And in 1993 the government introduced the legal control on import / export of scheduled wastes.

DOE, Ministry of Science, Technology and Environment, Kuala Lumpur reported that in 1998, the generation of hazardous wastes were metal finishing, chemical, electronics and electrical, printing and packaging. The wastes were solids, liquids and semi-solids with difference chemical compositions.

As part of the government project, in 1995, Kualiti Alam Sdn Bhd .was given the exclusive right to operate an integrated WMC (Waste Management Centre, Bukit Nanas) for 15 years. The plant is modeled after a similar plant in Denmark using Danish technologies. WMC had all the facilities required for the integrated waste management up to the final disposal stage. However, it cannot accept radioactive, explosive and pathological (from hospital) waste. The cost for the acceptance of the disposal waste varies depending on their toxicity.

An example of parameter limits of effluent and other factors A & B ( E.Q Regulations 1978 ):
THIRD SCHEDULE
ENVIRONMENTAL QUALITY ACT 1974 (ENVIRONMENTAL
QUALITY (SEWAGE AND INDUSTRIAL EFFLUENTS)
REGULATIONS 1978
[Regulation 8 (1), 8 (2), 8 (3)]
PARAMETER LIMITS OF EFFLUENT OF STANDARDS A AND B
Parameter Unit
Standard
   
A
B
       
Temperature C 40 40
pH Value   6.0 - 9.0 5.5 - 9.0
BODs at 20ºC mg/1 20 50
COD mg/1 50 100
Suspended Solids mg/1 50 100
Mercury mg/1 0.005 0.005
Cadmium mg/1 0.01 0.02
Chromium, Hexavaient mg/1 0.05 0.05
Arsenic mg/1 0.05 0.10
Cyanide mg/1 0.05 0.10
Lead mg/1 0.10 0.5
Chromium, Trivalent mg/1 0.20 1.0
Copper mg/1 0.20 1.0
Manganese mg/1 0.20 1.0
Nickel mg/1 0.20 1.0
Tin mg/1 0.20 1.0
Zinc mg/1 1.0 1.0
Borom mg/1 1.0 4.0
Iron (Fe) mg/1 1.0 5.0
Phenol mg/1 0.001 1.0
Free Chlorine mg/1 1.0 2.0
Sulphide mg/1 0.50 0.50
Oil and Grease mg/1 Not Detectable 10.0
FOURTH SCHEDULE
ENVIRONMENTAL QUALITY ACT 1974
ENVIRONMENTAL QUALITY (SEWAGE AND INDUSTRIAL EFFLUENTS)
REGULATIONS 1978 [Regulations 8 (1)]
LIST OF CATHMENT AREAS WHERE STANDARD A APPLIES
  • The catchment areas referred to in this regulation shall be areas upstream of surface or above sub-surface water intakes, for the purpose of human consumption including drinking.
  • For the purpose of this regulation, the water supply intakes shall include the public water supply intakes specified below:
Conclusion:
The consequences for not managing the waste properly will expose us to the risk of having to pay the higher price of neglect. In complying with our national legislation, we do not have to go through the above bad experiences and the costly mistakes.
Prevention is always better than cure; it makes a lot of sense, economically, environmental and socially, to prevent environmental degradation at the onset rather than rectifying after it has happened.

This is part of members commitment to help the SMI-Industry to be aware of the environment issue via knowledge sharing.
Author: The company main core team is to provide Specialty Chemical & Services for Water Treatment & Plant Processes including site consultation & support. http://accot.biz
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