Problem 50 - Chemistry The Central Science In Si Units

Question

Sewage causes removal of oxygen from the fresh water into which the sewage is discharged. For a town with a population of 100,000 people, this effluent causes a daily oxygen depletion of \(50.0 \mathrm{~g}\) per person. How many liters of water at \(8 \mathrm{ppm} \mathrm{O}_{2}\) are \(50 \%\) depleted of oxygen in a day by the population of this town?

Step-by-Step Solution

Answer

1,250,000,000 liters of water are 50% depleted of oxygen in a day.

Step 1: Calculate the Total Oxygen Depletion

First, calculate the total daily oxygen depletion by the entire population. Given that each person contributes to a depletion of 50.0 g of oxygen, the total depletion is the population size multiplied by the depletion per person.\[\text{Total Oxygen Depletion} = 100,000 \text{ people} \times 50.0 \text{ g/person} = 5,000,000 \text{ g}\]

Step 2: Determine the Oxygen Content in Water

Next, convert the oxygen concentration from ppm to grams per liter of water. Since \(1 \text{ ppm} = 1 \text{ mg/L}\), and given \(8 \text{ ppm} \text{ O}_2\), the concentration is:\[8 \text{ ppm} = 8 \text{ mg/L} = 0.008 \text{ g/L}\]

Step 3: Calculate the Volume of Water Affected

Since we want to find the volume of water that is 50% depleted, first calculate the oxygen depletion factor for this: \(50\%\) depletion means using up half of the available oxygen per liter. Each liter starts with \(0.008 \text{ g/L}\), so after 50% depletion, \(0.004 \text{ g/L}\) is used.\[\text{Volume of water} = \frac{\text{Total Oxygen Depletion}}{\text{Depletion per Liter}} = \frac{5,000,000 \text{ g}}{0.004 \text{ g/L}}\]

Step 4: Calculate and Conclude

Perform the final calculation to determine the volume of water affected by the daily depletion.\[\text{Volume of water} = \frac{5,000,000 \text{ g}}{0.004 \text{ g/L}} = 1,250,000,000 \text{ L}\] Thus, 1,250,000,000 liters of water are 50% depleted of oxygen in a day.

Key Concepts

Sewage Impact on Water

Sewage is often seen as an environmental issue primarily because of its impact on water bodies. When sewage is discharged into fresh water, it introduces a variety of organic materials. These materials serve as food for microorganisms present in the water. As these microorganisms break down the organic waste, they consume oxygen in the process, leading to a significant reduction in the oxygen levels of the water.
This process is known as "oxygen depletion", and it can cause severe imbalances in aquatic ecosystems. Fish and other marine life require a certain level of dissolved oxygen to survive; without it, they risk suffocation. Moreover, the presence of sewage leads to an increase in nutrient levels, which can promote the growth of algae, further exacerbating the problem of oxygen depletion.

• Sewage introduces organic waste into water bodies.
• Microorganisms consume oxygen to break down this waste.
• Oxygen depletion can threaten aquatic life.

Oxygen Concentration in Water

Oxygen concentration in water refers to the amount of dissolved oxygen available to aquatic life. This is typically measured in parts per million (ppm). For the thriving health of most aquatic organisms, a sufficient concentration of oxygen, usually around 5-8 ppm, is crucial.
When sewage enters water systems, it can severely impact these water bodies by depleting the oxygen. The example problem shows that for every liter of water with an initial concentration of 8 ppm, half of that oxygen can be consumed due to sewage, resulting in only 4 ppm remaining. This decrease makes the environment less hospitable for many aquatic species.

• Dissolved oxygen is vital for fish and other marine life.
• 8 ppm is a healthy initial concentration in water.
• Sewage can drastically reduce this concentration.

Environmental Chemistry

Environmental chemistry is a branch of chemistry focused on chemical processes occurring in the environment, often as a result of human activity. This field is critical for understanding oxygen depletion due to pollutants like sewage. By examining how chemical reactions occur in natural waters, scientists can develop strategies to mitigate adverse effects.
Sewage emission is a prime example where environmental chemistry is applied; understanding the reactions involved in organic matter decomposition helps predict oxygen demand. This predictive capability is essential for managing water quality and ensuring sustainable aquatic habitats.

• Studies chemical reactions and processes in nature.
• Helps in understanding the impact of pollutants like sewage on oxygen levels.
• Enables development of strategies for environmental protection.

Water Pollution

Water pollution occurs when harmful substances are introduced into water bodies, degrading their quality. Sewage is a major source of water pollution, bringing organic waste and pathogens into aquatic ecosystems. This pollution not only affects the water quality but also the organisms relying on that water.
In particular, sewage can lead to eutrophication, a process where nutrient overload causes excessive algae growth. When the algae die, their decomposition further depletes the oxygen in the water, compounding the problem of oxygen scarcity.

• Degrades water quality and affects aquatic life.
• Sewage contributes to algae blooms through nutrient overload.
• Can cause widespread ecological harm if unmanaged.