The presence of acidity and dissolved aluminium in the alum plant waste liquor has been used in the treatment of wastewaters of alkaline nature. The wastewaters from soap plant, textile milt copper ore-concentrate and milk processing plant were made to interact with the alum plant liquor in such volume ratios as to produce equilibrium pH of 7. Parallel runs to produce equilibrium pH 6 of the resulting mixtures were also carried out. The percentages of removal of TDS and COD of the interaction fluids at the pH 7 were found to be 95.0 and 97.5, respectively, for interaction with the soap plant wastewaters, 82.3 and 93.2 with the textile wastewaters 75.5 and 92.3 with copper ore wastewaters, and 60.9 and 94.4 with milk processing wastewaters. There was also significant lowering in the values of ionic species. Compared to the interaction at the equilibrium pH of 6, that at the equilibrium pH of 7 was found to give a higher degree of removal of the pollutional characteristics of the wastewaters.