Browsing by Author "Leng, Yirong"
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Item Open Access The mechanisms of struvite biomineralization in municipal wastewater(Elsevier, 2021-07-24) Leng, Yirong; Soares, AnaThe mechanisms of struvite production by biomineralization were investigated for five microorganisms (Bacillus pumilus, Brevibacterium antiquum, Myxococcus xanthus, Halobacterium salinarum and Idiomarina loihiensis) in municipal wastewater. The microbial exponential phase of growth occurred within the first 48 h of incubation, with growth rates varying from 0.02–0.08 1/h. These five microorganisms removed 23–27 mg/L (66–79%) of ortho-phosphate from wastewater, which was recovered as biological struvite (i.e., bio-struvite) identified by morphological, X-ray diffraction and elemental analysis. Bio-struvite crystals occurred in a low extracellular supersaturation index (0.6–0.8 units). Bio-struvite formation in B. pumilus M. xanthus, H. salinarum cultures was linked to biologically induced mineralization. Whereas B. antiquum and I. loihiensis produced bio-struvite through biologically controlled mineralization mechanism because the crystals presented homogeneity in morphology and size, and intracellular vesicle-like cell structures were observed enclosing electron-dense granules/materials. Nutrient recovery through biomineralization has potential application in wastewater streams promoting circularity within the wastewater industry.Item Open Access Microbial phosphorus removal and recovery by struvite biomineralisation in comparison to chemical struvite precipitation in municipal wastewater(Elsevier, 2023-01-10) Leng, Yirong; Soares, AnaMicrobial biomineralisation is attracting significant interest as an innovative process to recover nutrients from wastes. Nevertheless, little is understood about the requirements to form struvite using biological pathways in wastewater and how does this compare with conventional chemical processes. To address this gap, Halobacterium salinarum, Bacillus pumilus, Brevibacterium antiquum, Myxococcus xanthus and Idiomarina loihiensis were grown in wastewater to explore the relationships between cell growth, nutrients levels and properties of the recovered precipitates. The microorganisms were capable of removing ortho-phosphate (PO4-P) from municipal wastewater at concentrations ranging from 5.4 to 62.4 mg PO4-P/L. Visible crystals of biological struvite (bio-struvite) (identified by morphology XRD and elemental analysis), were observed at PO4-P ≥ 19.7 mg/L, compared to chemical struvite precipitation at 62.4 mg/L PO4-P (with pH adjustment). The initial nutrient concentrations presented a strong positive correlation with bio-struvite production yields and crystal size distribution. B. antiquum distinguished itself by relatively stable PO4-P removal (68–97%) independent of the initial nutrient concentration, with effluents containing as low as 1 mg PO4-P/L. The recovered bio-struvite presented high purity with low heavy metal contents, meeting regulations for inorganic fertiliser. The microbial processes for phosphorus (P) recovery as bio-struvite presented several key advantages: bio-struvite crystals were released to the wastewater and recoverable by filtration at PO4-P ≥ 19.7 mg/L, no need to adjust pH, bio-struvite crystals had purity equivalent to 11.8–12.3% P and low heavy metal content, which was similar or better than that of chemical struvite (12.6% P). This study validates bio-struvite’s relevance for low nutrient concentrations.Item Open Access Understanding the biochemical characteristics of struvite bio-mineralising microorganisms and their future in nutrient recovery(Elsevier, 2020-01-08) Leng, Yirong; Colston, Robert; Soares, AnaThe biochemical properties of selected microorganisms (Bacillus pumilus, Brevibacterium antiquum, Myxococcus xanthus, Halobacterium salinarum and Idiomarina loihiensis), known for their ability to produce struvite through biomineralisation, were investigated. All five microorganisms grew at mesophilic temperature ranges (22–34 °C), produced urease (except I. loihiensis) and used bovine serum albumin as a carbon source. I. loihiensis was characterised as a facultative anaerobe able to use O2 and NO3 as an electron acceptor. A growth rate of 0.15 1/h was estimated for I. loihiensis at pH 8.0 and NaCl 3.5% w/v. The growth rates for the other microorganisms tested were 0.14–0.43 1/h at pH 7–7.3 and NaCl ≤1% w/v. All the microorganisms produced struvite, as identified by morphological and X-ray Powder Diffraction (XRD) analysis, under aerobic conditions. The biological struvite yield was between 1.5 and 1.7 g/L of media, the ortho-phosphate removal and recovery were 55–76% and 46–54%, respectively, the Mg2+ removal and recovery was 92–98% and 83–95%, respectively. Large crystals (>300 μm) were observed, with coffin-lid and long-bar shapes being the dominant morphology of biological struvite crystals. The characterisation of the biochemical properties of the studied microorganisms is critical for reactor and process design, as well as operational conditions, to promote phosphorus recovery from waste streams.Item Open Access Understanding the fundamentals of bio-struvite biomineralization in wastewater.(2018-03) Leng, Yirong; Soares, AnaBiomineralization 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.Item Open Access Understanding the mechanisms of biological struvite biomineralisation(Elsevier, 2021-05-25) Leng, Yirong; Soares, AnaThe mechanisms of struvite production through biomineralisation were investigated for five microorganisms (Bacillus pumilus, Brevibacterium antiquum, Myxococcus xanthus, Halobacterium salinarum and Idiomarina loihiensis). After 72–96 h of incubation, the microbial strains tested increased the solution pH from 7.5 to 7.7 to 8.4–8.7, and removed ortho-phosphate (63–71%) and magnesium (94–99%) by biomineralisation. The minerals formed were identified as struvite (i.e. bio-struvite). Within the initial 24 h of incubation, microbial growth rates of 0.16–0.28 1/h were measured, and bio-struvite production was observed when the solution supersaturation index with respect to struvite achieved 0.6–0.8 units. The crystals produced by B. pumilus, H. salinarum and M. xanthus were thin trapezoidal-platy shaped and presented a gap size about 200 μm for intervals between cumulative volume undersize distribution at 50% and 90%. While B. antiquum and I. loihiensis produced crystals of coffin-lid/long-bar shape and a narrow size gap around 100 μm for intervals between cumulative volume percentage of 50% and 90%, indicating homogeneous crystal size distribution. Intracellular supersaturation of struvite phase was achieved within B. antiquum and I. loihiensis cells, corresponding to observation of intracellular vesicle-like structures occupied with electron-dense granules/materials. This study suggests that B. antiquum and I. loihiensis produced bio-struvite through biologically controlled mineralisation. This mechanism is the preferred for recovering nutrients from streams such as wastewater because it allows a link between manipulation of microbial growth conditions and bio-struvite production, even in highly complex streams like wastewater.