A METHOD AND A SYSTEM FOR ADJUSTING S/NA -BALANCE OF A PULP MILL

The invention relates to a method and a system for adjusting S/Na-balance of a pulp mill， wherein an aqueous pulp mill liquor containing sulphides is diverted into a bioreactor and oxidized by means of sulphur-oxidizing microbes， thereby producing an aqueous suspension from which elemental sulphur can be separated as a precipitate and the residual solution may be directed to causticizing. Optionally， prior to oxidation in the bioreactor， the aqueous pulp mill liquor may be first stripped to obtain a gas stream containing H2S which is then scrubbed with a scrubbing solution to obtain an aqueous spent scrubbing solution containing sulphides， in which case the residual solution can be used to replenish the scrubbing solution.