Bulk
pH and Carbon Source Are Key Factors for Calcium
Phosphate Granulation

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Abstract

Recovery of calcium phosphate granules (CaP granules) from high-strength wastewater is an opportunity to reduce the natural phosphorus (P) scarcity, geographic imbalances of P reserves, and eutrophication. Formation of CaP granules was previously observed in an upflow anaerobic sludge bed (UASB) reactor treating source separated black water and is enhanced by Ca ²⁺ addition. However, the required operating conditions and influent composition for CaP granulation are still unknown. In this study, we have experimentally demonstrated that the carbon source and bulk pH are crucial parameters for the formation and growth of CaP granules in a UASB reactor, operating at relatively low upflow velocity (<1 cm h ^–1). Degradation of glucose yielded sufficient biomass (microbial cells and extracellular biopolymers) to cover crystal and amorphous calcium phosphate [Ca _x(PO ₄) _y], forming CaP granules. Influent only containing volatile fatty acids as the carbon source did not generate CaP granules. Moreover, bulk pH between 7.0 and 7.5 was crucial for the enrichment of Ca _x(PO ₄) _y in the granules over bulk precipitation. Bulk pH 8 reduced the Ca _x(PO ₄) _y enrichment in granules of >1.4 mm diameter from 9 to 5 wt % P. Moreover, for bulk pH 7.5, co-precipitation of CaCO ₃ with Ca _x(PO ₄) _y was reduced.

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Most cited references 30

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Extraction of extracellular polymers from activated sludge using a cation exchange resin

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Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge.

Ping Li, S. Yang (2007)

Laboratory experiments on the activated sludge (AS) process were carried out to investigate the influence of microbial extracellular polymeric substances (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), on biomass flocculation, sludge settlement and dewaterability. The heat EPS extraction method was modified to include a mild step and a harsh step for extracting the LB-EPS and TB-EPS, respectively, from the sludge suspension. Six lab-scale AS reactors were used to grow AS with different carbon sources of glucose and sodium acetate, and different sludge retention times (SRTs) of 5, 10 and 20 days. The variation in the bioreactor condition produced sludge with different abundances of EPS and different flocculation and separation characteristics. The sludge that was fed on glucose had more EPS than the sludge that was fed on acetate. For any of the feeding substrates, the sludge had a nearly consistent TB-EPS value regardless of the SRT, and an LB-EPS content that decreased with the SRT. The acetate-fed sludge performed better than the glucose-fed sludge in terms of bioflocculation, sludge sedimentation and compression, and sludge dewaterability. The sludge flocculation and separation improved considerably as the SRT lengthened. The results demonstrate that the LB-EPS had a negative effect on bioflocculation and sludge-water separation. The parameters for the performance of sludge-water separation were much more closely correlated with the amount of LB-EPS than with the amount of TB-EPS. It is argued that although EPS is essential to sludge floc formation, excessive EPS in the form of LB-EPS could weaken cell attachment and the floc structure, resulting in poor bioflocculation, greater cell erosion and retarded sludge-water separation.

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Ion-association complexes unite classical and non-classical theories for the biomimetic nucleation of calcium phosphate.

Nico A J M Sommerdijk, Isabel de Andrade, Paul H H Bomans … (2012)

Despite its importance in many industrial, geological and biological processes, the mechanism of crystallization from supersaturated solutions remains a matter of debate. Recent discoveries show that in many solution systems nanometre-sized structural units are already present before nucleation. Still little is known about the structure and role of these so-called pre-nucleation clusters. Here we present a combination of in situ investigations, which show that for the crystallization of calcium phosphate these nanometre-sized units are in fact calcium triphosphate complexes. Under conditions in which apatite forms from an amorphous calcium phosphate precursor, these complexes aggregate and take up an extra calcium ion to form amorphous calcium phosphate, which is a fractal of Ca(2)(HPO(4))(3)(2-) clusters. The calcium triphosphate complex also forms the basis of the crystal structure of octacalcium phosphate and apatite. Finally, we demonstrate how the existence of these complexes lowers the energy barrier to nucleation and unites classical and non-classical nucleation theories.

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Author and article information

Journal

Journal ID (nlm-ta): Environ Sci Technol

Journal ID (iso-abbrev): Environ. Sci. Technol

Journal ID (publisher-id): es

Journal ID (coden): esthag

Title: Environmental Science & Technology

Publisher: American Chemical Society

ISSN (Print): 0013-936X

ISSN (Electronic): 1520-5851

Publication date (Electronic): 08 January 2019

Publication date (Print): 05 February 2019

Volume: 53

Issue: 3

Pages: 1334-1343

Affiliations

[† ]Wetsus, European Centre of Excellence for Sustainable Water Technology , Post Office Box 1113, 8900 CC Leeuwarden, Netherlands

[‡ ]Sub-department of Environmental Technology, Wageningen University , Post Office Box 17, 6700 AA Wageningen, Netherlands

[§ ]Department of Chemical Engineering, Faculty of Engineering of the University of Porto (FEUP) , Rua Dr. Roberto Frias, 4200-465 Porto, Portugal

Author notes

[* ]Telephone: +31-317-483-851. E-mail: renata.vanderweijden@ 123456wur.nl .

Article

DOI: 10.1021/acs.est.8b06230

PMC ID: 6365912

PubMed ID: 30620555

SO-VID: 40f89414-a22e-44fd-a463-ce10db63a792

License:

This is an open access article published under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND) Attribution License, which permits copying and redistribution of the article, and creation of adaptations, all for non-commercial purposes.