Physical–chemical characterization of sludge and granular materials from a vertical flow constructed wetland for municipal wastewater treatment

Abstract

The use of vertical flow constructed wetlands (VFCWs) is well developed in France and other countries for the treatment of wastewaters from small communities. The patented Azoé® process has been developed by a French company, SCIRPE, in order to improve denitrification and phosphorus removal as compared to classical VFCWs. It includes a biological trickling filter pretreatment followed by two stages of partially flooded VFCW. The performances of partially flooded VFCW are well demonstrated for the removal of organic matter and nitrogen. The system is now being considered for phosphorus removal as well. In this article, sludge and granular materials sampled from the filters of a municipal plant where the Azoé® system has been operated for 8 years were analyzed in order to provide data that may contribute to a better understanding of the dynamics of phosphorus retention. Elemental analyses showed that phosphorus was predominantly captured in the sludge layer accumulated at the surface of the first stage. The progressive mineralization of the sludge over time was also clearly highlighted. The phosphate phases were mainly associated with iron and calcium. The transport of phosphorus via the migration of fine particles through the porous medium in the first stage was also observed.

Influence of the water saturation level on phosphorus retention and treatment performances of vertical flow constructed wetland combined with trickling filter and FeCl3 injection

“…In addition, a layer of 10 cm of surface deposit sludge (sampled from the real scale plant) was disposed at the top surface of the VFCW. The characteristics of the sludge deposit were described in a previous study (Kim et al, 2013). Finally, 8 young common reeds (Phragmites australis) per square meter were planted in the surface deposit layer.…”

“…Dissolved reactive P is firstly precipitated by FeCl 3 injection at the outflow of the trickling filter. The particulate forms of P are subsequently retained by filtration though the first stage of VFCW (Kim et al, 2013). The deposits, which progressively accumulate at the surface of VFCW, are usually removed every 10-15 years.…”

Influence du pH sur la libération du phosphore accumulé dans les boues de surface d'un filtre planté de roseaux recevant des eaux usées traitées avec du FeCl3

“…La rétention du phosphore dans le système Azoé ® est réali-sée en utilisant le chlorure ferrique (FeCl 3 ) comme coagulant puis par filtration des flocs formés via les FPR. Les travaux de Kim et al (2013) ont montré que le phosphore se retrouve principalement dans les boues issues de la coagulation qui s'accumulent en surface des FPR pendant plusieurs années en fonction de la périodicité de curage des filtres (en général 10 à 15 ans). Si l'efficacité de coagulation du phosphore par ajout du FeC l3 est bien démontrée (Szabó et al, 2008;Caravelli et al, 2010 ;De Gregorio et al, 2011), l'évolution dans le temps des boues produites et retenues par les filtres plantés reste très peu étudiée.…”

“…Phosphorus thus precipitated is thereby accumulated in the form of a sludge layer mostly at the surface of the 1st filter. Over time, the sludge layer progressively grows and may eventually release part of the accumulated phosphorus depending on the biophysicochemical conditions (Kim et al, 2013). The objective of this study was to determine the influence of pH on the solubilization of phosphorus from sludge material sampled from a plant in operation.…”

“…Les résultats obtenus indiquent respectivement un taux de matière sèche de 20,0 % (humidité de 80,0 %) de la masse brute et un taux de matière organique de 59 % de la masse sèche. Les boues ont fait l'objet d'une caractérisation physico-chimique présentée en détails par Kim et al (2013). Le tableau 1 présente les résultats des analyses élémentaires effectuées.…”