ABSTRACT
3The global situation for nitrogen is getting out of hand. There is a serious imbalance between the influx and efflux of N in the biosphere. The direct cause is the rapidly increasing production of chemical fertilisers. The annual production of fertiliser N has increased 9 fold over the past 40 years and amounts currently to some 37% of the world-wide biological N-fixation. Such a massive introduction of reactive forms of nitrogen into the environment over a relatively short period of time has numerous deleterious consequences, causing environmental and public health problems, both locally and at a global scale. The response to increasing pollution problems necessitated the promulgation of effluent standards for nutrients. In this framework environmental legislation in most countries includes stringent limitations for nitrogen to be discharged. However, the implementation of effluent standards at a global scale is limited due to the phenomenal costs of the high-rate wastewater treatment technology. It remains a challenge to come up with nitrogen pollution control strategies, which are effective and low cost. Other sources of nitrogen pollution than domestic should be considered. Industrial wastewater not only represents twice the volume of domestic wastewater, but also is usually more concentrated. Having a cost-effective N-removal technology in industry is still a target and needs more attention. Biological nitrification- denitrification is the most common processes for nitrogen removal from wastewater; nitrification is the rate-limiting step in biological nitrogen removal. Nitrification in industrial wastewater presents a number of difficulties, including a wide range of different and varying temperatures, pH, presence of toxic compounds and salinity.
Studies on the effect of salt on nitrification show a decline in activity for ammonia and nitrite oxidisers. However, no information is available on the maximum acceptable salt level and which nitrifying group is most sensitive to salt stress. The need for understanding the precise effects of salt on nitrification was addressed, as the main aim of this study.
