Electrochemical dewatering for the removal of hazardous species from sludge

A novel conditioning approach for amelioration of sludge dewaterability using activated carbon strengthening electrochemical oxidation and realized mechanism

Sludge dewatering is an essential process for reduction of sludge volume to decrease cost of ultimate disposal. In this study, a novel method using activated carbon (AC) strengthening electrochemical (EC) treatment (EC/AC) was adopted to improve greatly sludge dewaterability. It was shown that capillary suction time (CST) and water content of dewatered sludge cake (Wc) were reduced to 55.9 ± 1.24 s and 64.3 ± 1.23%, respectively, under the optimal conditions of EC voltage 20 V, EC time 30 min and 0.2 g/g dry solid (DS) AC. AC with rich functional groups as "the third electrode" intensified electrooxidation by forming multiple microelectrodes and electron transfer capacity and conductivity of sludge were strengthened by AC in EC system, which were illustrated by electrochemical analysis. It could be found that zeta potential and particle size were increased and surface roughness was reduced after EC/AC treatment intensifying sludge hydrophobicity. Form the results of rheological behaviors of sludge, flowability was strengthened and viscosity was weakened under the conditioning of EC/AC. Besides, colloidal force and gel-like network strength were lessened, which was also verified by organic matters and percentage of inviable cells. At the same time, intracellular matters were released and degraded and bound water was released converting into free water. In addition, sludge compressibility and structural strength were increased and porous structure was formed facilitating water outflow via addition of mesoporous AC as skeleton builder, which eventually led to an improved separation efficiency of solid-water and sludge dewaterability. The results of heavy metals suggested that sludge cake after EC/AC treatment was favorable for land application.

Halocarbon Emissions from Hazardous Waste Landfills: Analysis of Sources and Risks

Landfills are sources of fugitive volatile organic carbon (VOC) emissions, including halocarbons. The objective of this study was to evaluate the contribution of halogenated VOCs to the health risks associated with the exposure of workers operating in landfills, gathering information on the role of endogenous/exogenous sources present in anthropized areas. A hazardous waste landfill located in Turin, Italy was used as a case study. Ambient concentrations of 10 pollutants (BTEX, styrene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, 1,2-dichloroethane, and 1,2-dichloropropane), measured in 10 points of the landfill area, were considered and analyzed. The data had a monthly frequency and covered two years. A cumulative health risk analysis was conducted by applying a Monte-Carlo method. The results showed that the contribution of 1,2-dichloroethane and 1,2-dichloropropane was 17.9% and 19.4% for the total risk and hazard index respectively. Benzene and ethylbenzene gave the highest contribution to the total risk (56.8% and 24.8%, respectively). In the second phase of the study, waste typologies that are possibly responsible for halocarbon emissions were investigated. Halocarbon concentration trends and waste disposal records were compared. Although further investigation is needed, some waste typologies were not excluded to contribute to halocarbon emissions, in particular sludge coming from wastewater treatment plants.

Electrochemically assisted dewatering for the removal of oxyfluorfen from a coagulation/flocculation sludge

This work focuses on the evaluation of the electrochemical dewatering of sludge obtained in the coagulation of wastes polluted with oxyfluorfen. To do this, sludge samples were treated, aiming not only to reduce the sludge volume, but also to facilitate the degradation of oxyfluorfen contained in the cake via electrolysis with a boron-doped diamond anode. Results show that water can be effectively recovered through three sequential stages. First, a gravity-driven stage, that can recover around 60% of initial volume and where no oxyfluorfen is dragged. Then, a second stage that involves the application of pressure and which accounts for the recuperation of an additional 25% of the total volume of the water removed and in which oxyfluorfen also remained in the cake. Finally, an electrochemical stage, which involves the application of electricity with increasing electric fields (1.0, 2.0, 4.0, and 16.0 V cm^-1), accounting for the recovery of the rest of water released and where an electrolytic degradation of oxyfluorfen is obtained, whose extension depends on the electrode configuration used in the electro-dewatering cell. This electrode configuration also influences the retention or loss of oxyfluorfen from the cake, being the optimum choice the placement of the cathode downstream, next to the outlet of the dewatering cell.