b. Turbidity is a parameter used to control processes in drinking water treatmen
ID: 1711922 • Letter: B
Question
b. Turbidity is a parameter used to control processes in drinking water treatment plants. What does turbidity measure? How is turbidity related to microbial water quality? What processes, which arc uscd in treating drinking water, reduce turbidity? (5 points) When raw sewage is dischargcd into a lake or river, the fecal bacteria concentration decreases by cxponential decay. If the viable bacteria concenlration is reduced by a factor of 40,000 over a decay pcriod of four days, what is the dccay constant? Show your calculations. (4 marks) c. d. ist two commercially used methods to disinfect wastewater and write an advantagc and disadvantage for each. (6 marks) Calculatc the cucrent and future (30-year design pcriod) water demand, in ML/day, for a town of 5,800 inhabitants. The town population is expected to grow exponentially, at a growth rate of 0.5 %/year, whereas thc water demand is expected to grow lincarly at 0.2 %/year from the current level of 360 L/person/day. (5 marks) e.Explanation / Answer
b. Turbidity is the extent to which light is either scattered or absorbed due to presence of suspended solids in it. However there is no quantitative relationship between the two. It measures the relative clarity in water. Basically, it indicates the haziness or cloudiness in the liquid.
Pollutants such as dissolved metals and pathogens can attach to suspended particles will enter the water. This is why an increase in turbidity can indicate higher degree of pollution, not just a decrease in water quality. Adulterants include bacteria, protozoa, nutrients (e.g. nitrates and phosphorus), pesticides, mercury, lead and other metals. Several of these pollutants, especially heavy metals, can be detrimental and often toxic to aquatic life. The addition of nutrients can lead to harmful algal blooms.
When the suspended solids concentration is due to organic materials, particularly sewage effluent and decaying organic matter, the presence of bacteria, protozoa and viruses are more. These organic suspended solids leads to decrease dissolved oxygen levels as they are decomposed.
In general, sedimentation and filteration processes are used to remove turbidity but in case of drinking water coagulation and floculation processes are used to remove the turbid substances from the water sample.
coagulant and floculants can be used according to the nature of sample and can be treated.
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