Influence of initial pH on bioleaching of river sediments to achieve deep dehydration

Acidification is one of the important methods of bioleaching and a rate-limiting steps in the reaction, with initial sediment pH having an important influence on bioleaching efficiency. Therefore, in this study, bioleaching treatments were assessed on river sediments with initial pH ranging from 3.0 to 11.0. Shake-flask tests were performed, using inoculated microorganisms and fresh river sediments in 500 mL Erlenmeyer bottles at a ratio of 1:9, with the addition of 5 g/L FeS₂ and 2 g/L S⁰ as energy sources. Erlenmeyer flasks were shaken for 72 h at 180 rpm and 28 °C, in a homeothermic oscillating water-bath. Results show that the bioleached sediment CST decreased from 39.10 s to between 10.3 s and 13.0 s. Sediment dewaterability reached a maximum level when the initial pH was 5 and the bioleaching duration was 36 h, with CST decreasing from 39.10 s to 10.30 s, a decrease in the CST rate by 82.25%, and moisture content was reduced to 57.5%. Illumina high-throughput sequencing results showed that the relative abundance of dominant microorganisms under different initial pH conditions had no significant difference at the phylum level. However, significant differences were apparent at the genus level. When the initial pH value increased from 3 to 5 in sediments, the relative abundances of the autotrophic bacteria Alicyclobacillus and Ferritrophicum and the heterotrophic bacteria Acidocella, which oxidize S⁰ and Fe²⁺, increase and dominate the microbial community, reaching abundances of 8.88%, 5.11%, and 4.87%, respectively. The heterotrophic bacteria Acidocella can biodegrade CLs products and eliminate their inhibitory effect on autotrophic bacteria Alicyclobacillus and Ferritrophicum with this synergistic effect improving the sediment dewatering performance. When the initial pH increased further to 9, the relative abundances of dominant bacteria decreased to varying degrees. In addition, variation in the initial pH conditions had no effect on the elimination efficiencies of pathogenic microorganism which were constantly > 98%. Graphical abstract .