What are the typical discharge limits for phosphorus? (average and max)

• A. 1 mg/L average, 2 mg/L max
• B. 2 mg/L average, 4 mg/L max
• C. 0.5 mg/L average, 1 mg/L max
• D. 3 mg/L average, 6 mg/L max

Answer: (A)

Phosphorus limits in wastewater are set to control nutrient loading and protect receiving waters from eutrophication. A common baseline limit uses 1 mg/L as the average (usually a monthly or annual average) and 2 mg/L as the maximum allowed on any given day. This pairing gives a practical target for treatment facilities: the average keeps long-term phosphorus input low, while the maximum daily limit catches spikes that could trigger blooms or degrade water quality.

Other sets of numbers would either be stricter than what many conventional permits require (for example, a lower average like 0.5 mg/L) or looser (such as 2 mg/L average or higher, with corresponding max values), which are not the typical standard seen in many municipal permits. The 1 mg/L average and 2 mg/L max represents the widely used baseline.