Understanding the fundamentals of bio-struvite biomineralization in wastewater.

Biomineralization can be exploited to recover phosphorus from liquid streams and wastewater through struvite (i.e. bio-struvite) production. However, there is a lack of knowledge regarding the attributes of the microorganisms involved, the mechanisms of bio-struvite production and possible benefits, compared with traditional struvite recovery. Five microorganisms (Bacillus pumilus, Brevibacterium antiquum, Halobacterium salinarum, Myxococcus xanthus and Idiomarina loihiensis) were investigated in this PhD thesis. Investigation of the biochemical properties and growth conditions indicated that all the microorganisms were able to use proteins as carbon source and produced urease (except I. loihiensis). Although B. pumilus, M. xanthus and I. loihiensis were identified as facultative anaerobes, bio-struvite biomineralization only occurred under aerobic conditions. In synthetic solution, all the microorganisms grew to increase the pH and release ammonia to create supersaturated conditions for struvite crystallization. Bio-struvite crystals occurred when supersaturation index of struvite achieved 0.6 to 0.8. The bio-struvite produced in B. antiquum and I. loihiensis cultures presented high homogeneity (both morphology and size) and intracellular vesicle-like structures, packed with electron-dense granules/materials, were observed, indicating a biological controlled mineralization process. On the other side, bio-struvite formation by B. pumilus, H. salinarum and M. xanthus was identified as a biological induced mineralization process. The same biomineralization mechanisms were identified in municipal wastewater. However the wastewater limited microbial growth and changed the dominant crystal morphology from coffin-lid to trapezoidal-platy shape. Compared with abiotic struvite precipitation, bio-struvite could be produced at low initial phosphorus concentrations in wastewater (≥19.7 mg/L), expanding the type and quality of waste streams that could be applied for nutrient recovery. Furthermore, the recovered bio-struvite presented high purity and met heavy metal limits set for inorganic fertilizers regulation. Overall, bio-struvite production presented important advantages, in comparison with abiotic struvite, and the process should be further developed for implementation at pilot and full scale.PhD in Wate