Coke ovens and by-product plants — removal of low-strength phenolic water Phenolic wastewater from coke ovens with phenol concentration less than 100 mg/L is best treated by which method?

Introduction / Context:
Phenolic water is a common effluent from coke ovens and by-product recovery units in integrated steel plants. When phenol concentrations are relatively low, choosing a cost-effective and reliable treatment process is vital to meet discharge norms while minimizing operating costs.

Given Data / Assumptions:

• Source: coke oven and by-product plant effluent.
• Phenol concentration: less than 100 mg/L (low-strength phenolic water).
• Goal: reduce phenol to environmentally acceptable limits with stable operation.

Concept / Approach:
Biological processes are well suited for low to moderate concentrations of biodegradable organics, including phenols. Oxidation ponds (stabilization ponds) provide long detention time, sunlight exposure, algal–bacterial symbiosis, and natural aeration, enabling biodegradation of phenols at low loadings. Chemical coagulation is generally used for suspended solids and some colloids; it does not reliably destroy dissolved phenolic compounds. Chlorination can oxidize some phenolics but risks forming chlorinated by-products and is inefficient as a sole treatment at these concentrations.

Step-by-Step Solution:
Classify the wastewater as low-strength phenolic (< 100 mg/L).Match to a biological process that can mineralize phenols: oxidation pond is appropriate and economical.Exclude methods focused on solids removal (coagulation) or with by-product risks (excess chlorination).Select biological oxidation pond as the primary removal step.

Verification / Alternative check:
Design manuals for steel plant effluents recommend biological treatment (oxidation ponds, trickling filters, or activated sludge) for low phenol concentrations, with polishing if required.

Why Other Options Are Wrong:

• Chlorination: may form chlorophenols and is not efficient as a single-step treatment.
• Chemical coagulation: targets particulates, not dissolved phenols.
• None of these: incorrect because an appropriate method (biological oxidation pond) exists.

Common Pitfalls:

• Overdosing oxidants and creating toxic chlorinated by-products.
• Assuming physico-chemical clarification removes dissolved phenols effectively.

Final Answer:
Treatment in a biological oxidation pond