Aerobic Polishing of Liquid Digestate for Preparation of Hydroponic Fertiliser

Lebani Oarabile Joy Mathe, Simira Ramsumer, Hendrik Gideon Brink and Willie Nicol ()
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Lebani Oarabile Joy Mathe: Department of Chemical Engineering, University of Pretoria, Pretoria 0002, South Africa
Simira Ramsumer: Department of Chemical Engineering, University of Pretoria, Pretoria 0002, South Africa
Hendrik Gideon Brink: Department of Chemical Engineering, University of Pretoria, Pretoria 0002, South Africa
Willie Nicol: Department of Chemical Engineering, University of Pretoria, Pretoria 0002, South Africa

Sustainability, 2024, vol. 16, issue 10, 1-16

Abstract: Nutrient pollution—mainly nitrogen and phosphorus—caused by organic waste continues to impact the environment. The implementation of a circular economy is integral to alleviating these effects. Liquid digestate, which is a byproduct of anaerobic digestion (a waste-valorising process), is a nutrient-dense organic fertiliser with vast applications in agriculture. Using an aerobic polishing unit, this study developed a viable method for the preparation of a hydroponic fertiliser by investigating the effect of pH on the nutrient recycling capabilities of said system. The heterotrophic bacteria present in the biofilm, identified by 16S gene sequencing, are responsible for 90% of organic carbon (as TOC) removal with minimal ammonium loss. This is ideal for promoting optimal nitrification in hydroponic systems in the absence of organic carbon to ensure plant growth is not affected. Although pH 8 was found to be ideal for batch operation, this pH condition resulted in decreased microbial longevity and, therefore, increased ammonification due to microbial decay. Therefore, continuous operation at pH 7 proved to be a better option owing to the ammonium-rich effluent (>220 mg/L) which was produced, which is on par with the nitrogen concentration of a Hoagland solution. The continuous carbon polishing of liquid digestate provides an efficient way of utilising organic fertilisers in hydroponic systems.

Keywords: nutrient recovery; carbon polishing; nitrogen retention; heterotrophs (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2024
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