Question

A pickle factory discharges brine with a salt concentration of 7 g/L at a flow of 4.5 m3/s to a river with a flow of 150 m3/s and a salt concentration of 150 mg/L upstream of the pickle factory. The salt concentration in the river cannot exceed 400 mg/L.

(a) Is the factory in compliance with this standard? Support your answer with calculations. (pay attention to units!)

(b) Describe (in complete sentences) at least one potential environmental impact of the brine. It is not sufficient to copy and paste words from the lecture slide, you need to explain the issue.

Answer 1

(a)  Concentration of brine from factory = 7g/L = 7mg/m3   (1g = 1000mg; 1L = 10-3m3 )

Flow rate of brine from factory = 4.5 m3/s

Quantity of salt flowing into the river = 4.5*7 = 31.5 mg/s ---------(1)

Similarly,

Concentration of brine in upstream = 150mg/L = 0.15 mg/m3   ( 1L = 10-3m3 )

Flow rate of river = 150 m3/s

Quantity of salt present in the river (upstream) = 150*0.15 = 22.5 mg/s---------(2)

Total salt flowing in downstream river = (1) + (2) = 54mg / s

Concentration of salt in downstream river = total quantity of salt / total flowrate = 54 / (150+4.5) = 0.349 mg /  m3  = 349mg /L

As we can see, the downstream concentration of the river (349mg/L) is less than the given standard value (400mg/L). Therefore, the factory is in compliance with the norms.

(b) One major environmental impact of brine is seen in soils:

The sodium content present in the brine will disperse the soil - which damages the soil structure. This soil now, cannot hold the water and hence is futile for agriculture. This results in dwarfed plant growth and also stops the seeds from germinating. The sodium and chloride ions also impede the absorption of nutrients from the soil to the plant.