Hybrid technology for nutrients recovery as microbial biomass and ammonium sulfate from un-diluted biogas liquid digestate using a modified airlift reactor
Nutrients recovery from biogas digestate is crucial for expanding the biogas industry in intensive animal husbandry regions with limited croplands. High ammonia inhibition and high alkali addition are the principal weakness of existed biological (e.g. algae cultivation) and physicochemical (e.g. ammonia stripping) nutrients recovery methods, respectively. In this study, microbial biomass production by cultivating the indigenous microflora and ammonia striping without alkali addition were merged to maximize the nutrients recovery efficiency from un-diluted liquid digestate (LD) of chicken manure through a modified airlift reactor which was operated for three days with addition of sucrose as a carbon source. The results indicated that 59.2% of PO₄ ³⁻-P and 10.8% of TN were recovered as microbial biomass while 62.0% of TN was recovered as ammonium sulfate at the optimum aeration rate of 2 vvm (volume of air per volume of LD per minute) regarding the results of nutrients recovery efficiency, energy consumption, and microbial growth criteria. The amino acids content of the generated microbial biomass was up to 30.8% (dry matter) while the generated ammonium sulfate was pure without impurities excluding low concentrations of carbon element up to 3.6%. To avoid adding external carbon sources, this hybrid technology was suggested to interact with the biogas process where part of the volatile fatty acids could be introduced as carbon sources for the growth of cultured microflora.
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