Bacterially mediated removal of phosphorus and cycling of nitrate and sulfate in the waste stream of a "zero-discharge" recirculating mariculture system

M. D. Krom, A. Ben David, E. D. Ingall, L. G. Benning, S. Clerici, S. Bottrell, C. Davies, N. J. Potts, R. J.G. Mortimer, J. Van Rijn*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Simultaneous removal of nitrogen and phosphorus by microbial biofilters has been used in a variety of water treatment systems including treatment systems in aquaculture. In this study, phosphorus, nitrate and sulfate cycling in the anaerobic loop of a zero-discharge, recirculating mariculture system was investigated using detailed geochemical measurements in the sludge layer of the digestion basin. High concentrations of nitrate and sulfate, circulating in the overlying water (~15mM), were removed by microbial respiration in the sludge resulting in a sulfide accumulation of up to 3mM. Modelling of the observed S and O isotopic ratios in the surface sludge suggested that, with time, major respiration processes shifted from heterotrophic nitrate and sulfate reduction to autotrophic nitrate reduction. The much higher inorganic P content of the sludge relative to the fish feces is attributed to conversion of organic P to authigenic apatite. This conclusion is supported by: (a) X-ray diffraction analyses, which pointed to an accumulation of a calcium phosphate mineral phase that was different from P phases found in the feces, (b) the calculation that the pore waters of the sludge were highly oversaturated with respect to hydroxyapatite (saturation index=4.87) and (c) there was a decrease in phosphate (and in the Ca/Na molar ratio) in the pore waters simultaneous with an increase in ammonia showing there had to be an additional P removal process at the same time as the heterotrophic breakdown of organic matter.

Original languageAmerican English
Pages (from-to)109-121
Number of pages13
JournalWater Research
StatePublished - 1 Jun 2014

Bibliographical note

Funding Information:
We would like to thank David Ashley for his help and advice with many aspects of the chemical analyses carried out in this project and in particular for the inspirationa l way in which he carried out sampling and analysis late into the night during the major sampling trip in Israel. We also thank Amir Neori for his useful comments on the text. This work was funded by a UK–Israel BIRAX grant ( BY2/BIO/01 ) to JvR and MDK and by a USA–Israel Binational Science Foundation grant ( 2008216 ) to JvR and EI. LGB would also like to acknowledge part support for her work during this project through a UK Natural Environment Research Council award (NE/C004566/1).


  • Anaerobic sludge
  • Apatite formation
  • Aquaculture
  • Denitrification
  • Phosphorus removal
  • Sulfur cycling


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