For wastewater treatment, which statements about aerobic biological oxidation ponds (stabilization ponds) are correct regarding pathogen removal, non-biodegradable contaminants, and chlorination?

Introduction / Context:
Aerobic oxidation ponds (stabilization ponds) are low-cost, low-energy treatment units that rely on sunlight, algae, and aerobic bacteria to reduce biochemical oxygen demand (BOD) and pathogens. Understanding what they can and cannot remove informs process selection and polishing steps like disinfection.

Given Data / Assumptions:

• Aerobic pond with adequate detention time and mixing by wind action.
• Target outcomes: BOD reduction and pathogen suppression.
• Presence of some non-biodegradable organics (e.g., alkylbenzene sulfonates, ABS).

Concept / Approach:
Oxidation ponds reduce BOD via aerobic microbial metabolism supported by algal oxygen production. Sunlight (UV) and long detention times help inactivate pathogens. However, persistent non-biodegradable substances pass largely untreated. Disinfection (e.g., chlorination) after pond treatment enhances pathogen removal before discharge or reuse.

Step-by-Step Solution:
Relate process to outcomes: aerobic conditions favor BOD removal and pathogen die-off.Account for influent composition: non-biodegradables are not significantly degraded.Add a polishing step: chlorination further reduces fecal coliforms and viruses.Conclude: all three statements (pathogen removal, poor performance on non-biodegradables, enhanced removal with chlorination) are correct.

Verification / Alternative check:
Performance data from maturation ponds show high log reductions for fecal indicators with sufficient retention time and subsequent chlorination, while surfactants and other refractory organics often require advanced treatments.

Why Other Options Are Wrong:
Choosing any single statement ignores the combined reality of capabilities (pathogen reduction) and limitations (non-biodegradables), plus the benefit of chlorination.

Common Pitfalls:
Overestimating pathogen kill without adequate retention; assuming oxidation ponds can remove recalcitrant contaminants; skipping disinfection prior to reuse.

Final Answer:
all (a), (b) & (c)