Abstract:
The biomineralisation mechanisms of five known bio-struvite producing microbes have been
established and their ability to recover said biomineral from synthetic solutions and sludge
dewatering liquors has been trialled. There is a lack of evidence and knowledge how these
microbes perform in open culture conditions and the impact encapsulating media has on their
ability to remove and recover orthophosphate as bio-struvite. In this PhD thesis, these
microorganisms (Brevibacterium antiquum, Bacillus pumilus, Halobacterium salinarum,
Idiomarina loihiensis, Myxococus xanthus) were investigated initially, this was streamlined
into investigating encapsulated cultures of B. antiquum and B. pumilus in wastewaters under
open culture conditions. The inoculation of all five microbes in source-separated urine in open
culture conditions showed growth rates as high as 0.18 1/h and high nucleic acid proportions
>80% within 24 hours of incubation. An orthophosphate removal of up to 70% was achieved
by B. antiquum inoculations and was increased to 100% when magnesium was increased to a
1:1, P:Mg. Encapsulated cultures of B. pumilus were incubated B4.1 growth media, the removal
of orthophosphate and chemical oxygen demand was equal to suspended cell inoculations of
B. pumilus. In pure culture and open culture sludge dewatering liquors, encapsulated cultures
of B. pumilus and B. antiquum, removed 55% and 70% of the initial orthophosphate over 24
hours respectively. The minimal difference in orthophosphate removal between pure and open
culture conditions indicates that encapsulation provided an environmental advantage to the
selected microbes to out compete the native species within the open culture sludge dewatering
liquors. Suspended cell inoculations into open culture sludge dewatering liquors did not remove
any more orthophosphate than non-inoculated controls. In continuous reactors fed by open
culture sludge dewatering liquors orthophosphate removal for both encapsulated microbes
averaged between 20% and 30%, at phosphorus loading rates of 0.4 kg P/m³ .d and 0.6 kg
P/m³ .d. Supplementing a carbon source to the equivalent of 150 mg sCOD/L and increasing
the ratio of P:Mg to 1:1.5, achieved an orthophosphate removal of 96% on average by
encapsulated B. antiquum. Bio-struvite recovered from all open culture wastewaters was
euhedral, prismatic and tabular and was typically coated in a secondary abiotic calcium
phosphate. Micropollutant analysis showed the recovered minerals were below international
heavy metal limits and were absent from faecal coliforms, pharmaceuticals and other
micropollutants for fertilisers. Potential end users and consumers from the public and industry
showed a strong willingness to use and eat produce grown from recycling derived fertilisers.
There remains to be optimisation of the biomineralisation technique to improve the efficiency
of recovery and streamline the operational set up, however the data collected in this PhD
strongly supports the development of this technique into industry and will satisfy a growing
need for circular economies and closing the nutrient loop.