High tolerance of chemolithoautotrophic sulphur oxidizing bacteria towards pulp and paper mill wastewaters and their organic constituents supporting sulphur recovery in alkaline conditions

• Effects of organics and pulp and paper mill wastewaters on S 2 O 3 biotransformation. • Up to 20 g/L acetate no effect on Thioalkalivibrio versutus . • 2.5-5 g/L yeast extract (YE) stimulated growth and S 2 O 3 biotransformation. • Inhibition at 0.25, 1, 20 and 20 g/L phenol, benzene, methanol & YE, respectively. • S 2 O 3 biotransformation in 87% ( v/v ) P&P wastewaters (PFB and WW). This study reports the tolerance of chemolithoautotrophic biotransformation of sulphurous compounds towards pulp and paper (P&P) mill wastewaters (primary filtrate of bleaching (PFB) and composite wastewater (WW)) and their constituents under haloalkaline conditions. The effects of organic compounds (methanol, acetate, D(+)-xylose, phenol and benzene) that may be present in P&P wastewaters, and yeast extract, a complex organic compound on thiosulphate biotransformation by Thioalkalivibrio versutus were investigated. All experiments were carried out in batch bioassays at pH 10 and 13-23 g Na + /L. Phenol and benzene reduced thiosulphate biotransformation by 88 and 94% at 0.25 and 1 g/L, respectively in 10 days. 20 g/L methanol, 20 g/L yeast extract and 10 g/L xylose reduced the biotransformation by 90, 88 and 56%, respectively. No inhibition of biotransformation occurred with acetate at concentrations up to 20 g/L. The growth was also enhanced by 1 to 10 g/L yeast extract likely serving as additional nutrients. At pH (∼10), the studied organic acids remain mostly unprotonated and, thus control their access through the cell membrane. Therefore, the inaccessibility of these compounds to the cytosol is a likely mechanism for having non-inhibitory effects. The 87% ( v/v ) WW did not affect thiosulphate biotransformation efficiency while 87% ( v/v ) PFB reduced it by 36% by day 10. The resistance of T. versutus to common organics present in P&P wastewaters indicates its potential use for sulphur recovery from P&P mill wastewaters at haloalkaline conditions and thus, supports the circular economy approach.