Changes in water quality due to anthropogenic activities and feasible biological nitrogen removal methods for saline water– case study in new zealand

New Zealand is an agricultural intensive country, surrounded by ocean. Therefore, it is regularly faced with water quality issues under the combined pressure of nitrogen pollution and seawater intrusion. As means of nitrogen treatment, biological methods are efficient and cost-effective. However, biological treatment in saline conditions possess difficulties or complexities, due to loss of cell activity or death of microbial species due to osmosis. To negate these effects for biological treatment, this study aimed to search indigenous nitrifiers and denitrifiers that can survive in saline conditions and function efficiently to remove inorganic nitrogen contaminants. For dentification, hydrogenotrophic denitrification was particularly investigated as an alternative method. Especially as, instead of requiring organic carbon, hydrogenotrophic denitrifiers synthesize organic carbon from carbon dioxide in the atmosphere, a characteristic which could help New Zealand achieve its recently set goal of being net zero carbon by 2050. The enriched communities oxidized ammonia from 170 mg NH4-N L-1⋅d-1 down to 27 mg NH4-N L-1⋅d-1 at peak removal rates of 50±5 mg NH4-N L-1⋅d-1, with nitrate and nitrite reduction (i.e. denitrification), achieving average removal rates of 25±5 mg NO3-N L-1⋅d-1 and 30±5 mg NO2-N L-1⋅d-1, respectively. In this regard, the removal achieved the maximum allowable nitrate and nitrite concentrations of 0.2 mg NO2-N L-1 and 11 mg NO3-N L-1⋅d-1, set by the World Health Organization. Therefore, it was found that by using this method the adverse impact of intensified agriculture on water resources can be mitigated, improving water quality of saline polluted water through sustainable methods.