Which two advanced water treatment technologies are used to remove trace organic contaminants, and what are their basic principles?

• A. Reverse osmosis (membrane filtration removing dissolved substances) and advanced oxidation processes (AOPs using reactive radicals to oxidize organics).
• B. Distillation and coagulation.
• C. Sand filtration and chlorination.
• D. Sedimentation and flotation.

Answer: (A)

When treating water for trace organic contaminants, two advanced approaches stand out because they specifically address dissolved organics rather than just solids. One uses a semipermeable membrane to physically separate dissolved substances from water. By applying pressure, water passes through the membrane while most dissolved organics are rejected, producing clean water and a concentrated brine that needs management. The other relies on chemical oxidation with highly reactive radicals. Advanced oxidation processes generate radicals such as hydroxyl or sulfate radicals that rapidly attack and break down complex organic molecules, often mineralizing them to carbon dioxide and water or transforming them into simpler, more biodegradable forms. These radicals are effective even at very low concentrations and can handle a wide range of stubborn contaminants, including pesticides, pharmaceuticals, and industrial solvents.

The alternatives don’t target trace organics as effectively. Distillation and coagulation focus more on energy-intensive separation and particle aggregation, respectively, and aren’t optimized for removing dissolved trace organics. Sand filtration and chlorination mainly remove particulates or rely on disinfection, with chlorination capable of forming byproducts and not reliably removing low-concentration organics. Sedimentation and flotation remove mostly suspended solids, not dissolved trace contaminants.