What is the ideal nutrient ratio for carbon, nitrogen, and phosphorus in the given guidelines?

• A. Carbon 100, Nitrogen 5, Phosphorus 1
• B. Carbon 100, Nitrogen 2, Phosphorus 5
• C. Carbon 50, Nitrogen 5, Phosphorus 1
• D. Carbon 100, Nitrogen 5, Phosphorus 5

Answer: (A)

Microbes in wastewater treatment need carbon for energy and biomass, plus nitrogen for proteins and phosphorus for nucleic acids and energy transfer. The guideline sets a carbon-heavy mix of 100 parts carbon to 5 parts nitrogen and 1 part phosphorus. This balance provides enough energy while supplying essential nutrients in the right proportions to support steady microbial growth without creating excess nutrients that could cause downstream issues. If carbon is reduced or nitrogen or phosphorus are added relative to carbon, growth becomes limited by the nutrient that is in shorter supply, slowing treatment. The other options shift the N or P relative to carbon or reduce carbon, disrupting the balance and making them less effective than the 100:5:1 ratio.