Question

Question 1 (a) What is water quality? Why is water quality testing important? (b) Write down the name of two organizations responsible for setting water quality standard? (c) The dilution factor D for an unseeded mixture of wastewater is 0.04. The DO of the mixture is initially 8.0 mg/L, and after 5 days it has dropped to 1.5 mg/L. The reaction rate constant K has been found to be 0.21 day!. (1) What is the 5-day BOD of the waste? (ii) What would be the ultimate carbonaceous BOD?

Answer 1

A)  Water quality refers to the chemical, physical, biological, and radiological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which compliance, generally achieved through treatment of the water, can be assessed. The most common standards used to assess water quality relate to health of ecosystems, safety of human contact, and drinking water.

The Importance of Testing Water Quality

Importance of testing water quality is define by testing parameters. these parameters include pH, turbidity, conductivity, dissolved oxygen (DO), and temperature. each parameter is explained below.

Why measure for pH?...

pH is a measure of the free hydrogen and hydroxyl ions in the water. The pH scale runs between 0 and 14 and defines how acidic or basic a body of water is along a logarithmic scale. The lower the number, the more acidic the water is; the higher the number, the more basic it is. A pH of 7 is considered neutral and ideal for drinking water. The logarithm entails that every number below 7 is 10 times more acidic than the previous number when counting down. Alternatively, when counting above 7, each number is 10 times more basic than the previous number when counting up.

Most aquatic organisms prefer a pH somewhere between 6.5 to 9.0, though some can live with pH levels outside of this range. As pH levels move away from the ideal range for an organism, hatching and survival rates can begin to be negatively affected, eventually leading to death. In addition to the detrimental biological effects of varying pH, pH levels on the extreme scale can increase the solubility of elements and compounds, meaning aquatic organisms are more likely to absorb toxic chemicals in the water.

Humans have a higher tolerance for extreme pH variances, but we can still be affected. Drinkable levels range from 4 to 11 and pH values outside of this range can cause skin and eye irritation and gastrointestinal irritation. A pH value below 2.5 can cause irreversible damage to skin and organ linings. Pipes and infrastructure may be susceptible to corrosion from pH levels outside of the ideal 6.5-9.5 range which can leach heavy metals and toxins into our water. We can measure the pH of water with a pH meter.

Why measure for turbidity?...

Turbidity indicates of the amount of suspended sediment in water, which is important for aquatic life. The suspended sediments can block sunlight from reaching aquatic plants, smother aquatic organisms, and carry dangerous contaminants such as lead, mercury, and bacteria. Turbidity makes water noticeably murky and we can measure the turbidity with a turbidimeter.

Why measure for conductivity?...

Free ions increase the water's ability to conduct electricity. Common ions in water that conduct electrical current include sodium, chloride, calcium, and magnesium. Because dissolved salts and other inorganic chemicals conduct electrical current, conductivity increases as salinity increases. Conductivity is useful as a general measure of stream water quality. Each stream tends to have a relatively constant range of conductivity that, once established, can be used as a baseline for comparison with regular conductivity measurements. Significant changes in conductivity could then be an indicator that a discharge or some other source of pollution has entered a stream.

Conductivity in streams and rivers is affected primarily by the geology of the area through which the water flows. Streams that run through areas with granite bedrock tend to have lower conductivity because granite is composed of more inert materials that do not ionize (dissolve into ionic components) when washed into the water. On the other hand, streams that run through areas with clay soils tend to have higher conductivity because of the presence of materials that ionize when washed into the water. Groundwater inflows can have the same effects depending on the bedrock they flow through. We can measure the conductivity of a waterbody with a multimeter.

Why measure for dissolved oxygen?...

Dissolved oxygen is the amount of gaseous oxygen (O2) dissolved in water. Oxygen can get into water by diffusion from the surrounding air, by aeration, and as a waste product of photosynthesis. Aquatic organisms need dissolved oxygen to respire and also for the decomposition of organic matter. We can measure the DO of a body of water with a sensor/meter duo.

Why measure for temperature?...

Temperature is an important factor to consider when assessing water quality. Temperature influences several other parameters and can alter the physical and chemical properties of water. Temperature fluctuations can also affect the behavior choices of aquatic organisms and tolerance of aquatic plants. Some aquatic organisms may choose not to inhabit a certain area of water because the temperature is unfavorable to them. High water temperatures can also increase the solubility and thus toxicity of certain compounds. The temperature is measured with a thermometer.

B) As the question to inform organizations around the world, i am mentioning the famous ones from world.

1. In Europe, European Drinking Water Directive.

2. In United States, United States Environmental Protection Agency (EPA).

C) a) BOD₅ is calculated by:

Unseeded:${\displaystyle \mathrm {BOD} _{5}={\frac {(D_{0}-D_{5})}{P}}}$ = (8-1.5)/0.04 = 162.5 mg/l

b) = 162.5 x (1-e-0.21t)-1 = 857.9mg/l.

Ultimate-CBOD = BOD5 x (1 – etter