In utilities using chloramine, which parameter is used as a nitrification indicator?

• A. Nitrate
• B. Gram positive coliforms
• C. Heterotrophic plate counts
• D. Ammonia to TOC ratio

Answer: (C)

In chloraminated systems, nitrification is a microbial process that can undermine disinfection and water quality, so utilities monitor indicators that reveal microbial activity and biofilm development. Heterotrophic plate counts measure the broad range of heterotrophic bacteria present in the water. A rising HPC reflects increased microbial activity and the potential for biofilm formation in the distribution system, which can create conditions favorable for nitrifying communities to grow. Because nitrification is driven by biological activity in the system, HPC serves as a practical, overall indicator that nitrification might be occurring or is likely to occur, prompting closer examination even before direct nitrification products appear.

Nitrate is a product of nitrification, so it shows up after the process has begun rather than indicating that nitrification is starting. Gram-positive coliforms are fecal-indicator organisms rather than indicators of nitrification. The ammonia-to-TOC ratio is discussed as a potential marker of nitrification risk in some contexts, but many utilities rely on HPC as a broad, practical gauge of microbial activity related to nitrification in chloraminated systems.