AbstractMaximizing recovery and characterization of extractable proteins from secondary paper sludge is essential to explore the potential value from utilization of readily available waste products from pulp and paper mills. A multistep physicochemical recovery process was used, involving optimum alkaline solubilization of protein into an aqueous phase followed by augmented physical disruption of cell membranes. The final precipitation of solubilised protein was carried out using different acidic media. The optimization studies revealed that the best removal of intercellular contents from sludge can be achieved at pH 12; at this level, up to 88% of available protein is solubilised into the aqueous phase. Of all the precipitating agents used, sulphuric acid proved most effective by recovering 90% of disrupted protein. The combined effect of french press and sonication techniques resulted in significant improvement in the overall yield of recovered sludge protein (RSP). The characterization studies showed the presence of common and essential amino acids in RSP in significant quantities; it also showed that the recovery process can significantly reduce or eliminate heavy metals present in the sludge. The molecular weights (MW) of extractable proteins were determined by PAGE, and it was observed that RSP contains both low and high MW fractions.