Introduction / background info:
The Mula Mutha River in Pune, Maharashtra is located right alongside the Kharadi sewage treatment plant. The presence of aquatic life in the water body is negligible. There are various factors that might cause this including pesticide toxicity, pathogenic bacteria, oxygen stratification etc. Sewage discharge is a major component of water pollution, contributing to oxygen demand and nutrient loading of the water bodies, promoting toxic algal blooms and leading to a destabilized aquatic ecosystem. This problem is compounded in areas where wastewater treatment systems are simple and not efficient (1) In this experiment, I will focus primarily on the effects of eutrophication (algal blooms).
The phenomena of eutrophication occurs when excessive nutrients introduced to a water body cause an increase in the number of algae present, leading to an algal bloom. Via the endogenous respiration of the algae themselves, and the aerobic, bacterial decomposition of these algae when they die, oxygen in the water body is used up, leading to hypoxia, and the death of marine life in the water body.
The loss of biodiversity caused by the lack of proper treatment of sewage before release is a major environmental issue, specifically in a developing country like India where environmental legislation is not usually strictly enforced. According to the United Nations World Water Development Report 2017 : “The discharge of untreated wastewater into seas and oceans partially explains why deoxygenated dead zones are rapidly growing: an estimated 245,000 km2 of marine ecosystems are affected, and this affects fisheries, livelihoods, and food chains”.
The magnitude of this issue goes way beyond the confines of water pollution, but it leads me to question the value of life itself. We kill other species, because it’s an easy method of getting rid of garbage, which implies that we value convenience over life. This outright disregard for bio- rights is abhorring, and it’s possible that people are simply unaware of the consequences of their actions. For this purpose, I’m carrying out this experiment to prove correlation and causation, and hopefully make a difference.
To measure the level of eutrophication : samples of water (100 ml each) will be collected from two different water bodies into test tubes. I will then check for the presence of algae with a microscope, and count the number of algae in a specified quantity of water for all samples. To promote accuracy, I will also measure the dissolved oxygen levels, using a dissolved oxygen meter (indirect indicator of the presence of bacteria that facilitate aerobic decomposition), as both of these factors are influenced by eutrophication.
Research question : To what extent does the release of sewage into water bodies (in this case from the Kharadi sewage treatment plant into the Mula Mutha River) contribute to eutrophication (and hence, loss of marine biodiversity) ? Variables : A. Release of sewage waste (independent) B. Eutrophication
Aim: The investigation will aim to model a correlation between the extent of eutrophication caused by the release of inadequately treated waste-water (sewage) into a water body. Hypoxia caused due to the eutrophication leads to a loss of marine biodiversity, which is a major global environmental issue, involving bio-rights.
Hypothesis: Due to the continuous addition of sewage waste into the water body, algal blooms will have formed, which will be observed in the samples collected via lower dissolved oxygen concentration than are considered normal. According to the Washington State DO standards, a DO concentration of more than 6.5mg/l is considered “good”. Light absorbance will also be compared with the sample from another water body (a pond in the Poona club golf course where there is no correlation to sewage release). Absorbance should be greater in the samples collected from the pond due to a lower algal density, which would allow greater amounts of light to pass through.
Experimental variables :
Materials required :
- Fifty test tubes (50ml each) with plungers – (5 samples * 5 trials * 2 sources)
- Ten reagent bottles (250 ml volume each)
- Colorimeter
- Dissolved oxygen meter (electronic)
- Measuring cylinder (100 ml)
- Lab approved gloves
Procedure :
At five points that are ten metres apart, collect five samples of water – 50ml each (measured using measuring cylinder) into reagent bottles, from the two water bodies
Repeat step 1 five times, label these samples sample 1, sample 2 … and so on upto sample 50, with sample 1-25 from the Mula Mutha river and sample 26-50 from the pond in the golf club.
Transport these samples to the lab, making sure you bubble wrap them so that the glass doesn’t break during transportation. During transport, the bottles should be kept in a dark container, to prevent any photochemical reactions from occurring.
Empty the reagent bottles into test tubes
Calculate the dissolved oxygen saturation by dipping the prongs of the DO meter into the water samples in the test tubes (make sure the prongs are completely immersed in the sample), connecting the output cable to a computer and recording the plotted values displayed on the computer. The readings for samples collected from different water bodies should be distinctively recorded.
After performing the DO test, the test tubes should be kept in a rack and the colorimeter should be set up. After connecting the colorimeter to a power supply, we should first calibrate it to zero using the black knob facing us. Then, the filter should be set to red light, (represented by the number 65) and the test tubes should be placed in the holder one by one. The numerical value shown by the screen is the absorbance reading, and these should also be distinctly recorded. Absorbance readings are unitless because they are calculated from a ratio of the intensity of light transmitted through the sample (I) to the intensity of light transmitted through a blank (Io). Absorbance = log (Io/I)
Compare the different results observed amongst all the 50 samples and plot two line graphs, one for the DO amongst two water bodies and one for the level of absorbance, to analyse a correlation.
Note : Five trials will be conducted with five different sets of samples and average values used to increase accuracy. The comparison of algal quantity amongst the two sources helps to better analyse the extent of eutrophication the release of sewage causes.
The reason for using two water bodies is to ensure that the changes in DO saturation and algal quantity is solely because of the sewage disposal, as the pond in the golf club has no link with the wastewater plant.
Ethical and safety considerations :
Due to the release of sewage into the river, it may contain certain pathogenic organisms. While collecting water samples, adequate safety measures such as the use of tight rubber gloves must be in place.
It’s a safety hazard to collect water samples from a river, as slipping and falling into the river is a dangerous possibility. Care should be taken so as to not lose balance and slip while collecting samples, which could be ensured by wearing sturdy shoes.
When testing water samples, the time taken between collecting the samples and performing the experiment should be kept as low as possible in order to prevent any other reaction from taking place and hampering the results.
The Puna golf club is privately owned. Before collecting water samples from their pond, I will obtain written permission from the management to prevent unethical practices.
Bibliography :
(1) : Ogunfowokan, A.O., Okoh, E.K., Adenuga, A.A. and Asubiojo, O.I., 2005. An assessment of the impact of point source pollution from a university sewage treatment oxidation pond on a receiving stream–a preliminary study. Journal of applied sciences, 5(1), pp.36-43.