What unit is used to measure oil content in effluent from an oily-water separator?

What unit is used to measure oil content in effluent from an oily-water separator?

• A. Percent by weight
• B. Parts per million (ppm)
• C. Grams per liter
• D. Milligrams per liter

Answer: (B)

Oil content in effluent from an oily-water separator is reported in parts per million because this reflects the very small amount of oil remaining in the water after treatment. In maritime regulations and on-board equipment, limits are given in ppm (for example, discharge must be at or below a set ppm value). While milligrams per liter is numerically similar to ppm for dilute water, the standard practice and the oil-content meters on ships are calibrated to ppm, making it the conventional unit for this measurement. Percent by weight or grams per liter would describe much larger fractions or different scales than the tiny concentrations involved in treated effluent, so they’re not used here.

Oil content in effluent from an oily-water separator is reported in parts per million because this reflects the very small amount of oil remaining in the water after treatment. In maritime regulations and on-board equipment, limits are given in ppm (for example, discharge must be at or below a set ppm value). While milligrams per liter is numerically similar to ppm for dilute water, the standard practice and the oil-content meters on ships are calibrated to ppm, making it the conventional unit for this measurement. Percent by weight or grams per liter would describe much larger fractions or different scales than the tiny concentrations involved in treated effluent, so they’re not used here.