Ammonia - Water Treatment Challenges

Ammonia can be present in groundwater due to natural conditions or as a result of agriculture and/or industry in the area. Ammonia does not present any direct risks to health when present in water. However, it does cause taste and odour issues and depending on conditions can have indirect health effects. There are two primary effects of concern; the first being oxidation of ammonia to nitrite, which is dangerous to health even in small quantities, and the second is ammonia reacting with chlorine, reducing the effectiveness of chlorine disinfection, which can lead to bacterial outbreaks. These problems lead to ammonia removal being desirable in water treatment. Ammonia is difficult to remove due to its high solubility and limited reactiveness.

This paper discusses treatment options for water high in ammonia with specific reference to controlling issues associated with taste and odour, nitrification and disinfection by-product formation. Options discussed include breakpoint chlorination, chloramine disinfection, chlorine dioxide disinfection, ion exchange and reverse osmosis. The relative advantages and disadvantages of these methods will be discussed including additional treatment considerations of these processes. Additionally, a new treatment technology biological ammonia removal will be discussed. This technology incorporates biologically active filters seeded with ammonia oxidising (AOB) and nitrogen oxidising bacteria (NOB) and has been successfully trialled in pilot and full-scale plants in the US, Europe and Asia. The potential implementation in the New Zealand setting and risks of this process will be discussed in detail.

The paper includes New Zealand examples from South Taranaki’s Patea and Waverley WTPs. These plants have challenging groundwater sources, high in ammonia, manganese and iron. The process solution selected for these two plants varied based on raw water conditions including ammonia levels and operational challenges caused by these conditions. The technologies considered and the decision making behind the final process selection are discussed. This includes the decision to employ chlorine dioxide disinfection at the Patea WTP, which is the first know municipal water supply to employ such a treatment technology.