Apostolos Giannis

Application of sequential extraction analysis to electrokinetic remediation of cadmium, nickel and zinc from contaminated soils

An enhanced electrokinetic process for the removal of cadmium (Cd), nickel (Ni) and zinc (Zn) from contaminated soils was performed. The efficiency of the chelate agents nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA) and diaminocycloexanetetraacetic acid (DCyTA) was examined under constant potential gradient (1.23 V/cm). The results showed that chelates were effective in desorbing metals at a high pH, with metal-chelate anion complexes migrating towards the anode. At low pH, metals existing as dissolved cations migrated towards the cathode. In such conflicting directions, the metals accumulated in the middle of the cell. Speciation of the metals during the electrokinetic experiments was performed to provide an understanding of the distribution of the Cd, Ni and Zn. The results of sequential extraction analysis revealed that the forms of the metals could be altered from one fraction to another due to the variation of physico-chemical conditions throughout the cell, such as pH, redox potential and the chemistry of the electrolyte solution during the electrokinetic treatment. It was found that binding forms of metals were changed from the difficult type to easier extraction type.

Electrochemical oxidation of stabilized landfill leachate on DSA electrodes

The electrochemical oxidation of stabilized landfill leachate with 2960 mg L(-1) chemical oxygen demand (COD) over a Ti/IrO(2)-RuO(2) anode was investigated in the presence of HClO(4) as the supporting electrolyte. Emphasis was given on the effect of electrolysis time (up to 240 min) and temperature (30, 60 and 80°C), current density (8, 16 and 32 mA cm(-2)), initial effluents pH (0.25, 3, 5 and 6), HClO(4) concentration (0.25 and 1M) and the addition of NaCl (20 and 100mM) or Na(2)SO(4) (20mM) as source of extra electrogenerated oxidants on performance; the latter was evaluated regarding COD, total carbon (TC), total phenols (TPh) and color removal. Moreover, the anode was studied by scanning electron microscopy and cyclic voltammetry. The main parameters affecting the process were the effluents pH and the addition of salts. Treatment for 240 min at 32 mA cm(-2) current density, 80°C and the pH adjusted from its inherent value of 0.25 (i.e. after the addition of HClO(4)) to 3 yielded 90% COD, 65% TC and complete color and TPh removal at an electricity consumption of 35 kWh kg(-1) COD removed. Comparable performance (i.e. 75% COD reduction) could be achieved without pH adjustment but with the addition of 100mM NaCl consuming 20 kWh kg(-1) COD removed.

Comparative studies of aerobic and anaerobic treatment of MSW organic fraction in landfill bioreactors.

Four simulated landfill bioreactors operating under different experimental conditions were evaluated in this study. The reactors were filled with the organic fraction of municipal solid wastes (MSW) and operated as: anaerobic, anaerobic with pH adjustment, semi‐aerobic and intermittent aeration bioreactors. The parameters studied in the leachate included pH, redox potential, BOD5, COD, DOC, SO4 2−, NH4 +‐N, NO3 −‐N, NO2 −‐N, Cl− and electrical conductivity. Also, the MSW mass settlement was measured at certain intervals. Leachate recirculation took place in all bioreactors. The results indicated that the intermittent aerobic reactor had higher organic and ammonia removal efficiencies than the anaerobic versions. Furthermore, the necessary stabilization time was reduced under aerobic conditions and the leachate toxicity decreased more rapidly. The pH adjustment in the anaerobic bioreactor had positive results in the decomposition of the organic matter enhancing the development of microbial activity.

Reprint of: Electrochemical oxidation of stabilized landfill leachate on DSA electrodes ☆

The electrochemical oxidation of stabilized landfill leachate with 2960 mgL(-1) chemical oxygen demand (COD) over a Ti/IrO2-RuO2 anode was investigated in the presence of HClO4 as the supporting electrolyte. Emphasis was given on the effect of electrolysis time (up to 240 min) and temperature (30, 60 and 80 °C), current density (8, 16 and 32 mAcm(-2)), initial effluents pH (0.25, 3, 5 and 6), HClO4 concentration (0.25 and 1M) and the addition of NaCl (20 and 100 mM) or Na2SO4 (20 mM) as source of extra electrogenerated oxidants on performance; the latter was evaluated regarding COD, total carbon (TC), total phenols (TPh) and color removal. Moreover, the anode was studied by scanning electron microscopy and cyclic voltammetry. The main parameters affecting the process were the effluents pH and the addition of salts. Treatment for 240 min at 32 mAcm(-2) current density, 80 °C and the pH adjusted from its inherent value of 0.25 (i.e., after the addition of HClO4) to 3 yielded 90% COD, 65% TC and complete color and TPh removal at an electricity consumption of 35kWhkg(-1) COD removed. Comparable performance (i.e. 75% COD reduction) could be achieved without pH adjustment but with the addition of 100mM NaCl consuming 20 kWhkg(-1) COD removed.

Evaluation of a sequential aerobic-anaerobic treatment of municipal solid waste in a bioreactor landfill

A sequential aerobic-anaerobic bioreactor landfill was operated and monitored over a period of 184 days. The bioreactor was filled with 120 kg of organic fraction of Municipal Solid Waste. Leachate recirculation was applied. The results showed rapid degradation of organic matter with rapid settlement during the aerobic period. The initial COD and BOD5 were reduced from 46,500 and 41,500 mg/L to 9000 and 6000 mg/L, respectively, within one month. The SO42− concentration, during the anaerobic period, was decreased from 1500 mg/L to 250 mg/L. The sequential treatment had positive effects on nitrification and denitrification efficiencies.