In Situ Testing

Measurement of pH, DO, Conductivity, Salinity and Temperature were done by Polarographic method in situ. The probe we used at the site was a combined pH, DO, Conductivity, Salinity and Temperature probe.

The probe is immersed into a sample and the value of the respective parameters will be shown on the screen after the meter stabilises. The values are recorded down.

DO vs BOD

The higher the BOD, the lower the DO present in the sample. This is caused by the organisms thriving in water, especially bacteria in polluted water such as the Grease Trap. And since the organisms in the waters require high amount of Oxygen for their activities, it results in the decrease of DO.

Given that the values of BOD are 4.75mg/L in average, it falls into the standard values of BOD of Raw Water source which is 3 to 15 mg/L.

DO vs TEMPERATURE

The higher the temperature of the sites, the lower the Dissolved Oxygen (DO). This is due to several reasons:

1. The solubility of oxygen varies with temperature. The concentration of Oxygen in the water is inversely proportionate to the temperature.
2. Due to high temperature (28 degrees Celcius), organisms such as tadpoles, planktons, plants and bacteria in the water require higher amount of DO to respire and carry out their activities as per normal.

Our results, however, shows a weak relation between these two parameters. This was probably due to experimental errors in measuring the temperature and DO values on site. Instead of dipping the DO cum Temperature probe into the water bodies, we collected samples from the sites into bottles before measuring them. The samples were left in the bottles for a length of time before they were measured for their temperature and DO values.

Hence, we can assume that some of the DO had escaped into the atmosphere and that the temperature had changed slightly when we tested them, causing varied or inaccurate values.

Dissolved Oxygen

Dissolved oxygen is a measure of the degree of pollution in water. Tap water has the highest level of DO while grease trap has the lowest level. Tap water has the highest level because there is a low amount of micro-organisms in the water, hence not much of oxygen is taken up. Grease trap has low level of DO because there is more organic waste in the water and that the bacteria needs to consume oxygen to survive, thus level of dissolved oxygen in grease trap is low.