No abstract

Systematic investigations of the acidic dissolution of P, Al, Fe and Ca from Al-containing tertiary sludge were carried out in this work. The results were then compared with the dissolution behaviour of Al-containing anaerobically digested sludge to evaluate the P–recovery potential in the form of struvite from tertiary sludge versus anaerobically digested sludge. Additional investigations of synthetically produced Al–sludge served as a comparison for the dissolution behaviour of P and Al without the influence of other contaminants (metals, biomass). In addition, the acid consumption was analyzed as a function of the target pH during the dissolution. The dissolution efficiency of PO4-P in tertiary and anaerobically digested sludge after acid treatment at pH 2 was ∼90%. The dissolution efficiency of Al and Ca in tertiary sludge was also ∼90% at pH 2, while the release efficiency of Al and Ca in anaerobically digested sludge was lower, ∼70% at pH 2. In tertiary sludge, about 75% of Fe was found dissolved at pH 2, whereas in anaerobically digested sludge this value was higher, ∼90%. Based on the experimental data, it can be concluded that significant dissolution of phosphorus from Al–containing tertiary sludge can take place at pH < 3. The highest sulphuric acid consumption for P–dissolution was observed in the case of tertiary sludge at pH 2.