Pilot testing of a fluidized bed reactor used to recover phosphate, in the form of struvite, from anaerobic digester supernatant was conducted at the Advanced Wastewater Treatment Plant, City of Penticton, British Columbia. The main objective of this study was to demonstrate the ability of the reactor to remove at least 70% of the phosphate in the supernatant from a digester fed with a combination of primary and secondary sludge. It was found that the operation of the reactor could be controlled to achieve any desired level of phosphorus removal up to 90%. Analysis of the recovered struvite crystals showed essentially pure struvite (>99% by weight) with small amounts of calcium (<0.5% by weight) and traces of potassium and iron. The recovered crystals had mean diameters increasing from 0.5 to 1.8 mm over the course of the study. The increasing diameters are believed to be the result of changes in the crystal structures that caused them to become stronger over the course of the study.Résumé : Des essais pilotes d'un réacteur à lit fluidisé utilisé pour la récupération du phosphate, sous forme de struvite, à partir d'un surnageant d'un digesteur anaérobie, ont été effectués sur place, dans l'usine « Advanced Wastewater Treatment Plant », située dans la ville de Penticton, en Colombie-Britannique. L'objectif principal de l'étude était de démontrer la capacité du réacteur à éliminer au moins 70 % du phosphate contenu dans le surnageant d'un digesteur alimenté d'une combinaison de boues primaires et secondaires. Nous avons trouvé que l'opération du réacteur pourrait être contrôlée afin d'atteindre un niveau de récupération du phosphate pouvant atteindre 90 %. L'analyse des cristaux de struvite récupérés a montré que la struvite était essentiellement pure (>99 % poids) avec de petites quantités de calcium (<0,5 % poids) et des traces de potassium et de fer. Les cristaux récupérés avaient des diamètres moyens augmentant de 0,5 à 1,8 mm durant l'étude. Cette augmentation de diamètre est probablement causée par des changements dans la structure cristalline, solidifiant les cristaux au fur et à mesure de la progression de l'étude.

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The recovery of nutrients from wastewater during treatment has gained attention both as a way of removing the nutrients as required by the plant's discharge permit and to make the recovered resource available for beneficial use. The Waste Activated Sludge Stripping To Remove Internal Phosphorus process (WASSTRIP patent pending) has been proposed to facilitate the nutrient recovery as well as to minimize the formation of struvite within the solids processing system. Benchtop testing was conducted at the Durham Advanced Wastewater Treatment Facility (AWWTF) to determine the rate of phosphorus and magnesium release within the waste activated sludge (WAS) tank as part of the WASSTRIP process. Testing included both endogenous release and release with the addition of volatile fatty acids (VFA) in the form of overflow from the plant's fermenter thickener.Results of the study reveal release rates were 5 times higher with VFA addition than those of endogenous release. However, the VFA concentration had little impact in the release rates when applied at ratios higher than 0.015 mg VFA / mg VSS (volatile suspended solids). The release of magnesium versus phosphorus occurred 0.20 -0.25 milligrams of magnesium per milligram of total phosphorus which agrees with the results previous testing.Process modeling was used to describe the results of testing. The modeling results suggested lower anaerobic hydrolysis and a lower sequestration rate of phosphorus accumulating organisms (PAO). The lower sequestration rate indicates that the rate of phosphorus and magnesium release was limited by another factor.The results of theist testing were used to assess the use of the existing tankage at the Durham AWWTF for conversion to the WASSTRIP process. The evaluation shows that this configuration is expected to be successful but will be contingent on consistent operation of the EBPR process and the fermenter during the winter.

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