Chemical Removal of Phosphorus from Swine Effluent: the Impact of Previous Effluent Treatment Technologies on Process Efficiency

Chemical phosphorus removal with hydrated lime was evaluated on effluents from different biological treatment processes applied to swine manure. The objective of this study was to establish the most suitable process for this kind of wastewater treatment. Effluents a UASB reactor, a nitrification reactor (NR), a modified Lutzak–Ettinger (MLE) reactor and a deammonification (DMX) reactor were evaluated. A comprehensive study was developed at laboratory scale to evaluate the effect of possible interferences, including alkalinity, total organic carbon, and ammonia, on phosphorus precipitation. The highest soluble phosphorus (Psol) removal efficiency and the lowest Ca:P molar ratio were obtained for the NR effluent (92% and 2.0, respectively). The good performance of the NR effluent could be attributed to the low level of ammoniacal nitrogen and alkalinity and to the presence of a relatively high concentration of calcium. Highly promising results were also obtained in field experiments, where a phosphorus removal unit was installed as the last step in a swine manure treatment system, and precipitation was applied to effluent from the NR. In this case, efficiencies of Psol removal higher than 90% were obtained. The produced sludge was rich in phosphorus and could be used as, for example, fertilizer. The results obtained in this work showed the importance of applying an efficient treatment system to swine manure for reduction of ammoniacal nitrogen, alkalinity, and carbon before chemical removal of phosphorus by precipitation with hydrated lime.