Synthesis process and hydrodynamic behavior of a new filtration material for passive wastewater dephosphatation

Abstract

International audienceThe preparation optimization of a filter material intended to be used as a phosphate sorbent in flow-through conditions is investigated. The mixing of ferrihydrite (Fh) and pozzolana (Pz) using a “dry contact method” is found to be the most efficient and leads to the formation of a micrometric thick Fh coating deposited into the honeycombed structure of Pz. The maximal Fh content of ~ 8.5 wt.% is significantly higher than the quantity deposited on other classical substrates such as sand. The phosphate sorption kinetics and isotherms, under dynamic conditions in batch experiments, are best described by pseudo-second-order and Freundlich models respectively. Moreover, under static conditions, sorption kinetics reveals intra-aggregate diffusion process. Phosphate ion retention in packed columns, and especially the breakthrough point, can be adequately predicted when coupling the classical convection dispersion equation and the surface complexation model. Breakthrough curves of phosphate ions are strongly dependent on flow rate; which is important for future industrial applications. Finally, and unexpectedly, a high value of phosphate adsorption capacity (80 mg PO4 g− 1) is observed when phosphate-containing wastewater is used as feed solution. This is mostly explained by soluble calcium ions, which favors the phosphate fixation onto the filter material surfac

Using Ca Fe layered double hydroxide transformation to optimise phosphate removal from waste waters

“…The interaction between Ca-Fe layered double hydroxide and phosphate species was studied both in homogeneous dispersion and in a flow through column experiment. In phosphate free water, the LDH was fully transformed into a mixture of a ferrihydrite- (Ruby et al, 2015). However, the high solubility of the Ca-Fe LDH led also to a strong increase of the pH (> 11) preventing any direct application of such a material for wastewater treatment.…”

“…The experiment performed in the column demonstrated that pozzolana (Pz) coated with Ca-Fe LDH was particularly efficient for removing phosphate. Indeed, the experiment may be compared to another set of column experiments performed recently using ferrihydrite (Fh) coated Pz (Ruby et al, 2015;Ruby et al, 2016) where the experimental conditions were quite similar, i.e. identical dimensions of the columns, [PO4]= 100 mg L -1 in the inflow, but with a contact time of  8 h instead of  5.5 h in this study.…”

“…The behavior observed at lower PO4 concentration (<  100 mg L -1 ) will be particularly relevant for application in waste water treatment where the concentration of PO4 is often between  10 and  60 mg L -1 (Ruby et al, 2016). Moreover, we recently developed a new method of synthesis allowing the deposition of a high amount of ferrihydrite onto a pozzolana support (Ruby et al, 2015). Such a method of synthesis was adapted here to synthesize pozzolana coated with Ca-Fe LDH (Ca-Fe LDH-Pz).…”