Question

Leachate generated from a legacy municipal solid waste dumping site has to be collected and managed carefully. Which statement is correct for treatment of such leachate?

• A. Settling chamber followed by micro-filtration units are required.
• B. Modular treatment units targeting dissolved organic matter and salts are required.
• C. Only biological treatment units like ASP with extended aeration are required.
• D. Only a combination of anaerobic–aerobic treatment units is required.

Hint:

Legacy leachate needs advanced modular systems like RO, NF, UF, and oxidation since it contains high dissolved pollutants that biological units cannot remove.

Answer 1

The Correct Option is B

Legacy landfill leachate is several years or decades old and is chemically stabilized.
It contains very high levels of refractory organics (humic and fulvic acids), ammonia, heavy metals, chlorides, sulfates, and dissolved salts.
Due to stabilization, the leachate shows:
• High COD but low BOD/COD ratio (i.e., poor biodegradability)
• Large concentration of dissolved inorganic contaminants
• High color and complex organic molecules
Because of these characteristics, biological treatment alone is insufficient.
Processes like ASP or anaerobic–aerobic reactors cannot remove salts, ammonia, or refractory organics.
Modern treatment systems therefore use modular, multi-stage physical–chemical units, such as:
• Ultrafiltration (UF)
• Nanofiltration (NF)
• Reverse Osmosis (RO)
• Ion exchange
• Advanced oxidation (ozonation, Fenton, photocatalysis)
• Ammonia stripping or air stripping
These target dissolved organic matter, color, ammonia, and salts — the primary pollutants in legacy leachate.
Option (A) only removes suspended solids — not sufficient.
Option (C) is incorrect because biological treatment is not effective for stabilized leachate.
Option (D) is also incomplete because anaerobic–aerobic steps handle BOD but not dissolved salts and refractory compounds.
Hence, the only correct and universally applicable treatment strategy is option (B).
Final Answer: Modular treatment units targeting dissolved organics and salts