HEDP INTERFERENCE WITH COLD LIME SOFTERING. During startup and first six months of operation, the wastewater softener was operated at pH 10.3 to 10.4 with a free carbonate residual of +15 to +25 ppm as CaCO_#. A softener effluent calcium concentration of 190 to 220 ppm as CaCO_3 was achieved rather than 50 ppm as predicted. To obtain the desired level of calcium in the softener effluent, the pH in the softener was increased to 10.8 to 11.2 and the free carbonate residual was increased to over 250 ppm in the softener. This resulted in higher usage levels of hydrated lime, soda ash and sulfuric acid.
展开▼
