Solid pH adjustment

Reverse osmosis can remove dissolved metals to very low levels. It can also remove a variety of pollutants such as cyanide and residual organics from refinery wastewater. However, because it is an expensive process, it would be competitive only if removal of total dissolved solids is also required. It also requires extensive pretreatment to prevent membrane fouling and deterioration [52]. The pretreatment processes may include filtration to remove suspended solids, pH adjustment, softening, and activated carbon treatment to remove organics and chlorine. A major drawback of the RO process is the handling and disposal of the reject stream, which can amount to 20-30% of the influent flow. 

Sodium gluconate is easier to extract than the calcium salt. To obtain commercial grades of sodium gluconate tiie culture filtrate, after filtraticHi to remove mycelium and suspended solids, is simply concentrated to 45% solids, pH-adjusted to 7.5 witii sodium hydroxide and drum dried. Purer products may be obtained by active carbon treatment of the hot solution before drying or by carbon treatment and recrystallisation. 

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