TOC is amount of carbon bound in an organic compound (wikipedia).
Nitrate: Odourless, colourless and tasteless therefore can only be found by testing. High amount of contents will be cause of shortness of breath and blue-baby syndrome.
Lead
Biological parameters
Coliform is a group of Bacteria from various environments. Mostly, it is not harmful but presence in the water means that there is a problem with the disinfection process.
- Escherichia coliforms (E.coil.):
E. coli only comes from human and animal faecal waste.
Water treatment
In order to understand the process of potable water treatment, have a look hydrological cycle diagram is helpful. On the diagram, there are two kind of treatment, namely, fresh water treatment and wastewater treatment.
Fresh water can be defined as the water that is not polluted or water that treated by wastewater treatment. Fresh water could be water from ground water, reservoir, lake, borehole, etc.
Figure 1: hydrological cycle
Fresh water treatment is normally depends upon the characteristic or source of water. General water treatment process is as follow.
Figure 2: water treatment processes
Pre-treatment
Pre-treatment is the process that preparing the water for further treatment.
Remove the solids such as large floating materials, debris, etc in order to prevent the damage on the machinery. This process is repeated several times with the different size of screen.
For pH balancing
Aeration is simply for increasing the amount of dissolved oxygen and reducing . Amount of dissolved oxygen in the water is important as biodegradation consumes oxygen in the water (A. Azapagic, 2004). For this process, Mechanical aeration, bubble aeration, jet aeration method is used.
Primary treatment
The main purpose of primary treatment is to remove turbidity, colour and particles in the water. This can be broke down as follows.
- Coagulation and Flocculation
There are particles sizes of in the water, which cannot be removed by sedimentation process. For small particles, adding either multivalent ions or colloids in the water can aggregate it. These are added as chemical coagulants or gentle agitation (flocculation). By this process, agglomerated particle increase in size then these particles can be removed by sedimentation process and finally reduce the more physical impurities (Open university).
This process is Placing water in the settling tank and leave for ~2 hr in order to remove suspended solids and floc. In this process ~50 of suspended solids are sink to the bottom of the tank and then physical impurities are removed.
Figure3: settling tank
Secondary treatment
When organic matter is discharged into watercourse, this can lead organic pollution in the water as microorganism reduce the amount of oxygen available. In order to prevent this situation, filtration process is needed. In this process, water pass through the medium such as sand, anthracite coal, or magnetite, then particles are removed by accumulation on the medium also biodegradation take place to reduce microorganisms.
Disinfection
This is the treatment to kill pathogenic microorganisms by adding chlorine to the water or expose ozone to the water. Chlorine is easily dissolved in the water and relatively cheap but it can affect the taste of water. This process is depends on complex function of type of disinfectant, contact time and water quality characteristics.
Advanced treatment
The main purpose of advanced treatment is to reduce more suspended solid and BOD also removing toxic material or nutrients. For example, advanced treatment is needed for using water in pharmaceutical or electronic industry. However, as we are only considering potable water treatment, this stage can be ignored.
Fluoridation
Small amount of fluorine is added into water in order to prevent tooth decay. In this process, there is no removal or reducing of impurities in the water.
Schematic diagrams
- In this case, assumption is made that water is not much polluted as it is far away from population or industry. Therefore, screening and aeration process can be ignored. In the coagulation, flocculation and sedimentation process, remove physical impurities as it is assumed that water may be turbid or there are solid particles in the water. Then water goes to filtration process in order to reduce the amount of microorganisms. Finally, water goes to contact tank for disinfection process and to be distributed.
- In this case, it is assumed that water is in good condition as it is from deep ground and therefore screening, coagulation, flocculation and sedimentation process can be ignored. However, aeration is needed for providing oxygen and demineralising at the advanced treatment (softening process).
- In third case, full treatment process is needed as the water is polluted by industrial effluent, sewage, agricultural, and urban runoff. In this treatment process, in order to achieve full treatment of the water, each unit can be repeated whenever it is needed.
References
(coagulation)
A. Azapagic, S. Perdan and R. Clift, 2004, Sustainable Development in Practice.
http://www.dwqr.org.uk/public/national-water-quality/top-ten-parameters#item1
