INVESTIGATIONS OF ALUMINUM HYDROXYPHOSPHATES AND ACTIVATED-SLUDGE BY AL-27 AND P-31 MAS NMR

High-resolution solid-state Al-27 and P-31 MAS NMR has been used to in vestigate the nature of aluminum- and phosphorus-containing solids for med during wastewater treatment. Although difficult to characterize by conventional techniques, these amorphous solids can be characterized by MAS NMR, providing information about their short-range ordering. In the present study, most of the solids were precipitated under conditi ons of high alkalinity, similar to those encountered during wastewater treatment. The ageing time of the aluminum hydroxide prior to the add ition of phosphate (t(1)), the ageing time of the aluminum hydroxyphos phates after the addition of phosphate (t(2)), and the phosphorus to a luminum molar ratio were controlled while the effects of changing the parameters were examined. It was found that the aluminum MAS NMR chemi cal shift was related to the amount of phosphate present in the solid, which in turn was related to t(1), t(2), and the P:Al molar ratio. Th e results also lend support to the hypothesis that phosphate removal o ccurs through an adsorption process onto amorphous aluminum hydroxide, rather than through direct precipitation of aluminum phosphate. The i ncreased understanding of aluminum and phosphate chemistry and the spe cies formed during wastewater treatment will be useful in optimizing w astewater treatment processes.