Sludge Pre-Treatment through Ozone Application: Alternative Sludge Reuse Possibilities for Recirculating Aquaculture System Optimization

ABSTRACT

Recirculating Aquaculture Systems (RAS) reduce water consumption by efficient filtration to maintain appropriate levels of accumulating compounds and sludge. Sludge is mechanically separated by drum filters and disposed of to the detriment of overall system water budgets. Dissolved nitrogen compounds are reduced via nitrification–denitrification filters, requiring commercial external carbon sources. The reuse of sludge after ozone pre-treatment may represent the next step in RAS optimization. The present study analyzes the content of sludge from RAS and tests ozonation as a pre-treatment for recycling as carbon source. The dissociative effect of ozone and the physicochemical changes due to ozonation lead to a significant increase in soluble carbon availability. Predominantly long-chain fatty acid (FA) (saturated and unsaturated) with 16 and 18 carbon atoms independently of the treatment were found in the profiles. Saturated FA concentrations in solution increased after 20, 40, and 60 min ozonation. The solid content of the sludge was practically unaffected by ozonation in terms of FA profile: only saturated FA slightly increases after 40 min treatment. The implications of these findings for denitrifying bacteria are discussed.

Abbreviations: Recirculating Aquaculture Systems (RAS); Advanced Oxidation Processes (AOPs)

KEYWORDS:

• Ozone
• Denitrification
• Dicentrarchus labrax
• Natural organic matter
• Ozonation
• RAS
• Recycling
• Sludge
• Wastewater treatment
• Water reuse

Acknowledgments

There is no conflict of interest related to this study. The authors would kindly thank Prof Boris Koch and Prof Stefan Wittke for allowing them to use their laboratory facilities, to Jana Geuer, Claudia Burau und Dieter Jansen, for their invaluable support in DOC measurements and their expert technical assistance, to Lukas Wildförster for introducing them in the fatty acids determination. They are also grateful to Ute Marx und Timo Hirse for supplying important materials for the experiments and for measurements support.

Supplemental data

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Additional information

Funding

This study was supported by the DBU and is part of the ACOMACS project (“Activated Particulate Organic Matter as Carbon Source for Denitrification in RAS”, under Grant 31367/01-23).