硫酸盐对污泥高级厌氧消化过程中甲基汞迁移转化的影响

为研究污泥高级厌氧消化过程中甲基汞的迁移转化特征以及硫酸盐对污泥厌氧消化过程中汞形态迁移转化的影响,本研究以高温热水解污泥的厌氧消化为研究对象,考察了不同硫酸盐投加浓度下污泥厌氧消化过程中甲基汞的迁移转化特征.结果表明,污泥厌氧消化初期(第1～3 d)发生了汞的甲基化作用,平均甲基汞/总汞比例由0.024%(比值范围为0.019%～0.033%)增加到0.038%(比值范围为0.030%～0.048%),甲基汞净增量分别增加了3.97、 6.09、 0.17、 3.71和1.66倍,随后第3～5 d却发生了明显的汞去甲基化作用,甲基汞净增量降低了71.25%(范围为67.42%～75.10%).硫酸盐对厌氧消化初期汞的甲基化有一定的抑制,而厌氧消化后期,硫酸盐对汞甲基化影响并不明显,这与带电基团HgHS~-_2、 HgS_2~(2-)降低了中性汞络合物的生物有效性及铁硫化物、硫化汞等对S~(2-)和生物可利用态汞的固定作用有关.通过冗余分析,汞的甲基化受到多种环境因素的影响,丙酸、异丁酸和异戊酸等有机质和Fe可能促进汞甲基化,而蛋白质和较高的pH值可能是污泥厌氧消化过程中汞甲基化的抑制因子.

Effect of Sulfate on the Migration and Transformation of Methylmercury in Advanced Anaerobic Digestion of Sludge

To study the migration and transformation of methylmercury during advanced anaerobic digestion of sludge and the role of sulfate, this study investigated the migration and transformation of methylmercury during different stages of sludge anaerobic digestion (AD) with thermal hydrolysis pretreatment and under different dosages of sulfate addition. The results showed that mercury methylation occurred in the initial stage of AD (Day 1-3), the ratio of methylmercury to total mercury increased from 0.024% (range of 0.019%-0.033%) to 0.038% (range of 0.030%-0.048%), and the net increment of methylmercury increased by 3.97, 6.09, 0.17, 3.71, and 1.66 times, respectively. In the following Day 3-5, the demethylation process occurred with the net yield of methylmercury decreased by 71.25% (ranging from 67.42% to 75.10%). Sulfate inhibited the methylation of mercury in the initial stage of AD, but had little effect on it in the late stage. This was related to the reduction of the bioavailability of neutral mercury complexes by charged groups of HgHS₂^2- and HgS₂^2-, as well as the immobilization of iron sulfide and mercury sulfide on S^2- and bioavailable mercury. Redundancy analysis (RDA) showed that mercury methylation was affected by several factors:organic substances such as propionic acid, isobutyric acid, isovaleric acid, and Fe may promote mercury methylation, whereas protein and higher pH may be inhibitors of mercury methylation in AD of sludge.