The inhibition effects of salt on Anammox process: A review

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【Abstract】Anaerobic ammonium oxidation was a novel biological nitrogen elimination process and attached more and more attention owing to its effectivity and economic saving. But， many kinds of factor especially salinity could affect the activity of Anammox bacteria which had some disadvantages to the application of Anammox process. In this article， a short review about the effects of salinity on Anammox bacteria was summarized and some advices were proposed to the research and the application of Anammox process in the future.

【Key words】Anammox； Salinity； inhibition

0 Introduction

Anaerobic ammonium oxidation（Anammox） was a biological nitrogen removal process which Anammox bacteria combines ammonium and nitrite under anoxic conditions to generate nitrogen gas according to the following equation：[1]

NH4+-N + 1.32NO2--N + 0.066HCO3- + 0.13H+1.02N2+ 0.256NO3- +0.066CH2O0.15+2.03H2O （1）

Anammox， as a biological nitrogen removal process， could be effect by many kinds of factor， such as organic， salinity， temperature， pH， heavy metals and so on. Salinity was an important inhibition factor for Anammox bacteria. Salinity could inhibit microorganism growth because cell-wall and enzymes of bacteria are destroyed[2]. There were no definitive conclusions about the effect of salinity on Anammox process although there were many researchers spent lots time on this topic. But there was one conclusion that the Anammox bacteria could be domesticated from freshwater to adapt to the high salt environment was clearly[3]. This review presented a detailed previous and current researches on the inhibition of the Anammox process by salinity， aiming to provide helps on wastewater treatment with salinity by Anammox process.

1 Previous and current researches

Previous and current researches showed that Salinity could inhibit microorganism growth because cell-wall and enzymes of bacteria are destroyed[2]. It was reported that Anammox bacteria could adapt to a large range of salinity concentration. Kartal et al.[4]reported that Anammox bacteria still have activity at 75 g NaCl L-1， but the activity of Anammox bacteria was totally inhibited when the salinity concentration was 90g・L-1. This might be the highest salinity concentration that Anammox bacteria still have activity according to the reports. High salinity concentration have a serious inhibition effects on the activity of Anammox bacteria while the lower salinity concentration could promoted the activity of Anammox bacteria. Batch assays were carried out with non-adapted and adapted Anammox biomass at different salt concentrations by Depena-Mora et al.[5]， the results indicated a stimulatory effect on the specific anammox activity（SAA） at concentrations up to 6 and 15g NaCl L-1， while higher salt concentrations caused a decrease in the activity. Same conclusions were obtained by many Ma et al[6]. Salinity not only had adverse effects but also could have some positive effects on granules. Depena-Mora et al.[5]found that the addition of salt enhanced the aggregation of Anammox biomass in granules with a consequent decrease in the Sludge Volumetric Index from 80 to 25mL g VSS-1.

There were two main theories to explain why Anammox bacteria could be adapted to salinity gradually through acclimation. （1） Anammox bacteria which could be endure high salinity could gradually become the dominant bacteria in the reactor. Kartal et al.[3]reported that ‘’Candidatus Kuenenia Stuttgartiensis’’ became the dominant bacteria after salinity acclimation.（2）Anammox bacteria could adjust itself to adapt the high salinity. On the one hand， Anammox bacteria absorb some ions such as K+ to raise osmotic pressure and to balance highly osmotic pressure outside. On the other hands， Anammox bacteria could produce more extracellular polymeric substances（EPS） to oppose the highly salinity condition[7].

2 Problems and prospect

As mentioned， salinity not only had adverse effects on Anammox bacteria but also had some positive effects on Anammox bacteria. Most previous and current researches were launched using NaCl as salinity， while other kinds of salinity such as KCl using to study its effects were rarely reported. As we all known that did not every kinds of salinity have same effect on Anammox bacteria. So， more researches should be launched to study the effects of other kinds of salinity on Anammox bacteria， and only in this way can expand the application fields of Anammox process.

【References】

[1]Dapena-Mora A， Fernández I， Campos J L， et al. Evaluation of activity and inhibition effects on Anammox process by batch tests based on the nitrogen gas production[J]. Enzyme and Microbial Technology， 2007， 40（4）： 859-865.

[2]Yi Y， Yong H， Huiping D. Effect of Salt on Anammox Process[J]. Procedia Environmental Sciences， 2011， 10， Part C（0）： 2036-2041.

[3]Kartal B， Koleva M， Arsov R， et al. Adaptation of a freshwater anammox population to high salinity wastewater[J]. Journal of Biotechnology， 2006， 126（4）： 546-553.

[4]Kartal B， Koleva M， Arsov R， et al. Adaptation of a freshwater anammox population to high salinity wastewater[J]. Journal of Biotechnology， 2006， 126（4）： 546-553.

[5]Dapena-Mora A， Vázquez-Padín J R， Campos J L， et al. Monitoring the stability of an Anammox reactor under high salinity conditions[J]. Biochemical Engineering Journal， 2010， 51（3）： 167-171.

[6]Ma C， Jin R-C， Yang G-F， et al. Impacts of transient salinity shock loads on Anammox process performance[J]. Bioresource Technology， 2012， 112（0）： 124-130.

[7]Ismail S， De La Parra C， Temmink H， et al. Extracellular polymeric substances （EPS） in upflow anaerobic sludge blanket（UASB） reactors operated under high salinity conditions[J]. Water research， 2010， 44（6）： 1909-1917.