An industry discharges 0.8 m³/s of a waste with a 5-day CBOD of 600 mg/L to a river with a flow of 4 m³/s and a 5-day CBOD of 8 mg/L. Calculate the 5-day CBOD of the river after mixing with the waste.

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### Problem Statement

An industry discharges 0.8 m³/s of a waste with a 5-day CBOD of 600 mg/L to a river with a flow of 4 m³/s and a 5-day CBOD of 8 mg/L. Calculate the 5-day CBOD of the river after mixing with the waste.

### Explanation

This problem involves calculating the 5-day Carbonaceous Biochemical Oxygen Demand (CBOD) of a river after it receives discharge from an industry. To solve this, you can use the principle of conservation of mass for CBOD concentrations:

#### Formula:
The mixed CBOD concentration (\( C_m \)) can be calculated using the formula:
\[ 
C_m = \frac{Q_w \times C_w + Q_r \times C_r}{Q_w + Q_r} 
\]

Where:
- \( Q_w \) = discharge flow rate of waste (0.8 m³/s)
- \( C_w \) = CBOD concentration of waste (600 mg/L)
- \( Q_r \) = flow rate of the river (4 m³/s)
- \( C_r \) = CBOD concentration of the river (8 mg/L)

#### Calculation Steps:
1. **Determine Total Flow:**
   \[
   Q_{\text{total}} = Q_w + Q_r = 0.8 + 4.0 = 4.8 \text{ m}^3/\text{s}
   \]

2. **Calculate Mixed CBOD:**
   \[
   C_m = \frac{(0.8 \times 600) + (4.0 \times 8)}{4.8} = \frac{480 + 32}{4.8}
   \]

3. **Simplify:**
   \[
   C_m = \frac{512}{4.8} \approx 106.67 \text{ mg/L}
   \]

#### Result

The 5-day CBOD of the river after mixing with the industrial discharge is approximately **106.67 mg/L**. 

This calculation is crucial for understanding the environmental impact of industrial waste on river ecosystems and ensuring compliance with environmental regulations.
Transcribed Image Text:### Problem Statement An industry discharges 0.8 m³/s of a waste with a 5-day CBOD of 600 mg/L to a river with a flow of 4 m³/s and a 5-day CBOD of 8 mg/L. Calculate the 5-day CBOD of the river after mixing with the waste. ### Explanation This problem involves calculating the 5-day Carbonaceous Biochemical Oxygen Demand (CBOD) of a river after it receives discharge from an industry. To solve this, you can use the principle of conservation of mass for CBOD concentrations: #### Formula: The mixed CBOD concentration (\( C_m \)) can be calculated using the formula: \[ C_m = \frac{Q_w \times C_w + Q_r \times C_r}{Q_w + Q_r} \] Where: - \( Q_w \) = discharge flow rate of waste (0.8 m³/s) - \( C_w \) = CBOD concentration of waste (600 mg/L) - \( Q_r \) = flow rate of the river (4 m³/s) - \( C_r \) = CBOD concentration of the river (8 mg/L) #### Calculation Steps: 1. **Determine Total Flow:** \[ Q_{\text{total}} = Q_w + Q_r = 0.8 + 4.0 = 4.8 \text{ m}^3/\text{s} \] 2. **Calculate Mixed CBOD:** \[ C_m = \frac{(0.8 \times 600) + (4.0 \times 8)}{4.8} = \frac{480 + 32}{4.8} \] 3. **Simplify:** \[ C_m = \frac{512}{4.8} \approx 106.67 \text{ mg/L} \] #### Result The 5-day CBOD of the river after mixing with the industrial discharge is approximately **106.67 mg/L**. This calculation is crucial for understanding the environmental impact of industrial waste on river ecosystems and ensuring compliance with environmental regulations.
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