Inorganic characteristics of cake layer in A/O MBR for anaerobically digested leachate from municipal solid waste incineration plant with MAP pretreatment

•Inorganic insight into cake layer in MSWI leachate treatment system was studied.•Anaerobically digested leachate with MAP pretreatment caused thicker cake layer.•Residual Si and Al predominated the inorganic components in cake layer.•Si-Al obviously accumulated at the end of cake layer due to high suction pressure.

Inorganic characteristics of cake layer in an anoxic/oxic membrane bioreactor (A/O MBR) for anaerobically digested leachate from a municipal solid waste incineration plant with MAP (magnesium ammonium phosphate precipitation) pretreatment was reported. During 90 days of operation, the A/O-MBR had formed a thick cake layer, causing severe fouling. BCR (European Community Bureau of Reference) results showed that Fe, Al, Ca, Mg, Si were the dominant inorganic components (especially residual Si and Al) in the cake layer. X-ray diffraction (XRD) analysis further presented that the cake layer contained complex inorganic substances with FeSiO3, CaAl2O3, Ca5(PO4)3OH, CaCO3, CaPO3OH, Mg2(PO4)OH, etc., while Si-Al crystal was the major inorganic component in the cake layer. Additionally, SEM-EDX showed a consistent distribution of inorganics along the front cross-section of the cake layer, indicating that the stable particles and metal ions led to the steady inorganic accumulation onto the membrane surface. However, it was revealed that high suction pressure aggravated the inorganic particle accumulation, especially for the Si-Al crystals, at the end of the cake layer.

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