Abstract: The present invention relates to a process for the controlling the sodium and sulfur levels in a pulp mill, comprising the steps of: a) providing a pulp mill stream comprising sulfide and having a total alkali concentration of at least 2 Molar; b) supplying a portion of the pulp mill stream to a reactor comprising sulfide oxidizing bacteria and removing sulfide from the pulp mill stream by subjecting said stream to sulfide oxidizing bacteria in the presence of oxygen, and at a pH in the range 8 to 11, to oxidize the sulfide to elemental sulfur, c) withdrawing from the reactor a treated pulp mill stream comprising sulfur, wherein the portion of the pulp mill stream is mixed with a portion of the sulfide oxidizing bacteria present in the reactor prior to supplying the pulp mill stream to the reactor in step b).

Abstract: The present invention relates to a process for the treatment of industrial alkaline streams comprising sulfide and carbonate, comprising the steps of: a) providing an industrial alkaline stream comprising sulfide and carbonate; b) supplying the industrial alkaline stream to a bioreactor comprising sulfide oxidizing bacteria and removing sulfide from the industrial alkaline stream by subjecting said stream to sulfide oxidizing bacteria in the presence of oxygen, and supplying a pH adjustment agent to the bioreactor to maintain a pH in the range in the range 8 to 11, to oxidize the sulfide to elemental sulfur, c) withdrawing from the bioreactor a treated industrial alkaline stream comprising elemental sulfur, wherein a portion of the sulfide oxidizing bacteria is removed from the bioreactor and mixed with the industrial alkaline stream prior to supplying the industrial alkaline stream to the bioreactor in step b).