دانلود رایگان مقاله انگلیسی حذف انتخابی فلزات سنگین از شیرابه زباله توسط فیلترهای گرانولار واکنشی - الزویر 2018

abstract

The pre-treatment of landfill leachate prior to its co-treatment in the municipal plants of waste water processing could represent an appropriate and cost-effective solution for its management. Pre-treatment is necessary especially to remove heavy metals, which may be transferred to the excess sludge preventing its valorisation. In the present paper, we propose a chemical-physical pre-treatment of leachate using four different granular reactive media able to selectively remove the contaminants present in the leachate. The efficiency of these materials was investigated using synthetic leachate through batch tests and a column test. In the latter case the four materials were placed in two columns connected in series and fed an under constant upward flow (0.5 mL/min). The first column was filled half (50 cm) with a granular mixture of zero valent iron (ZVI) and pumice and half (50 cm) with a granular mixture of ZVI and granular activated carbon (GAC). The second column, which was fed with the effluent of the first column, was filled half with zeolite (chabazite) and half with GAC. Heavy metals were mainly removed by the ZVI/pumice and ZVI/GAC steps with a removal efficiency that was higher than 98, 94 and 90% for copper, nickel and zinc, respectively, after 70 days of operation. Ammonium was removed by zeolite with a removal efficiency of 99% up to 23 days. The average reduction of the chemical oxygen demand (COD) was of 40% for 85 days, whereas chloride and sulphate removal was negligible.

4. Conclusions

The results obtained in this paper show how the combined use of different granular reactive media (i.e. ZVI, GAC and zeolite) allows to remove heavy metals contained in the leachate and to safely treat it in WWTPs. This methodology of leachate pre-treatment could be economically advantageous to valorise the excess sludge via composting rather than landfilling it, which, in turn, could considerably reduce the cost of sludge disposal.

The methodology proposed could be used as an on-site technology for the pre-treatment of leachate having characteristics similar to these described in this study. The investigated reactive materials could be placed into a tank, which could include up to three slots connected in series and containing the ZVI/pumice mixture, the ZVI/GAC mixture and zeolite as reactive materials since, as shown by the results derived by this study, the contribution given by the GAC section towards contaminants removal was negligible. The system could allow the replacement or isolation of each reactive medium at any time when an exhaustion of one of the three media is observed.

According to the results of this paper a filter, composed of the same reactive materials used in this study and having a surface of 2.5 m2 and a height of 1.5 m, could treat 1 m3 /day of leachate, having characteristics similar to the leachate formulated in this study, with an efficiency higher than 99% for Cu, than 94% for Ni and than 96% for Zn for three months. If only the ZVI/pumice and ZVI/GAC layers were to be used (height equal to 1 m) the efficiency would be reduced to about 93% for Cu, 73% for Ni and 71% for Zn.