直接与间接生物淋滤法去除城市生活垃圾焚烧飞灰中重金属的研究

Comparison of heavy metals extraction from municipal solid waste incinerator fly ash in direct and indirect bioleaching using Aspergillus niger.

城市生活垃圾焚烧飞灰中的某些金属含量与低品位矿相似,可以利用。该研究分别采用黑曲霉在含有飞灰的培养基中直接淋滤和黑曲霉发酵液间接淋滤处理飞灰中的重金属,比较了2%和5%(w/v)的飞灰投加量下两种生物淋滤方法中Cd、Cr、Cu、Fe、Mn、Pb和Zn的溶出效果。结果表明,黑曲霉利用碳源产出有机酸将金属从固相溶出;随着飞灰投加量的增大,直接与间接生物淋滤的金属溶出率均降低;在高飞灰投加量(5%)下,飞灰的重金属对菌体的毒性较大,间接生物淋滤能避免菌体与飞灰直接接触,因而7种金属溶出效果均明显优于直接生物淋滤;间接生物淋滤比直接生物淋滤处理时间缩短1/3;而在低飞灰投加量(2%)下,间接生物淋滤处理12 d(包括产酸阶段与处理飞灰阶段)与直接生物淋滤处理18 d相比,飞灰中Cu和Cr的溶出率高于直接生物淋滤,其他金属溶出率均略低于直接生物淋滤。由此可知,间接生物淋滤能在较短时间内脱毒高投加量的飞灰,而直接生物淋滤较适合处理低投加量的飞灰。

The content of certain metals,which could be recycled,in municipal solid waste incinerator (MSWI) fly ash is similar to that in some low-grade ores.The metals (Cd,Cr,Cu,Fe,Mn,Pb and Zn) extraction from MSWI fly ash in direct bioleaching (Aspergillus niger grew in medium with fly ash) and indirect bioleaching (leaching fly ash using fermented suspension by A.niger) was investigated at 2% and 5% (w/v) fly ash densities using A.niger.The results indicate that the bio-produced organic acids by A.niger extracted metals in solid phase from fly ash.The metals extraction efficiency in direct and indirect bioleaching decreased with the increase of fly ash density.At the high fly ash density (5 %),the metals extraction in indirect bioleaching was markedly higher than that in direct bioleaching,due to the high heavy metals toxicities to fungi in direct bioleaching and the avoidance of fungi from the heavy metals toxicities of fly ash in indirect bioleaching.The treatment period of indirect bioleaching was 1/3 shorter than that of direct bioleaching.In contrast,at the low fly ash density (2%),the metals leaching yield of indirect bioleaching (after 12 d including organic acids production period and leaching period) was lower than that of direct bioleaching (after 18 d),except for Cu and Cr.The indirect bioleaching method detoxified fly ash at high pulp density in short time,and the direct bioleaching method was appropriate for the treatment of fly ash at lower concentration.