Behavior of electro-osmotic dewatering of biological sludge with salinity

The salinity effect on electro-osmosis dewatering was investigated by measuring the solid content of sludge after dewatering. Three levels of salinity were studied, 5,000, 10,000, and 12,500 ppm. Coagulant chemicals such as alum, ferrous sulfate, and organic polyelectrolytes were used for some tests. Increasing the salinity from 5,000 to 10,000 ppm and 10,000 to 12,500 ppm was found to increase the sludge solid content about 88 and 28\%, respectively. A 2 V/cm increase in voltage intensity can also increase the solid content about 46\%. The effect of chemicals is evident at low salinity. At 5,000 and 10,000 ppm, addition of chemicals in average can enhance the sludge solid content about 44 and 16\%, respectively. Because of the electrolysis of salt solution and the release of chlorine gas, the pH of the sludge increased. Consequently the zeta potential of the sludge increased, which in turn results in an increase in dewatering rate. Therefore an S-shape solid content-time curve was observed for most of the operating conditions, contrary to the conventional shape of a linear increase followed with a decrease of rate before reaching zero rate

New halogenated disinfection byproducts in swimming pool water and their permeability across skin

Chlorine is widely used for disinfecting public swimming pool water. The disinfectant chlorine, protecting swimmers from pathogenic infection in swimming, may be responsible for some adverse effects on swimmers' skin and health. In this study, numerous new halogenated disinfection byproducts (DBPs) in chlorinated pool water were detected with a powerful precursor ion scan method using electrospray ionization triple quadrupole mass spectrometry, with or without preseparation with ultra performance liquid chromatography. These new pool DBPs were demonstrated to be mainly halo(nitro)phenols, resulting from chlorination of human body substances (such as urine) in the presence of bromide. Among these new DBPs, 2,4-dibromophenol, 2,4-dichlorophenol, 2-bromophenol, 2,6-dibromo-4-nitrophenol, 2-bromo-6-chloro-4-nitrophenol, and 2,6-dichloro-4-nitrophenol were fully identified or confirmed. For 2,4-dibromophenol, 2,4-dichlorophenol and 2-bromophenol with pure standard compounds available, their permeability values across human skin were measured to be 0.031, 0.021, and 0.023 cm/h, respectively. The effects of chlorine on human skin were also investigated. The interaction of chlorine with epidermis was found to generate many new halogenated DBPs as well as common DBPs; the corneous layer was observed to become rough and even form larger pores after chlorine interaction. It is recommended that swimmers should avoid urinating in pools, and avoid prolonged swimming to reduce chlorine contact and prevent accelerated permeation of DBPs across skin

Remediation of an electroplating contaminated soil by EDTA flushing: chromium release and soil dissolution

Purpose: Remediation of soils contaminated with Cr (as Cr(III) complexes/precipitates and/or Cr(VI) oxyanion) and cationic metals (Cu, Ni, Zn, and Pb) by ethylenediaminetetraacetate (EDTA) flushing has been challenging and rarely investigated. This study aimed to evaluate the efficiency of EDTA flushing for metal extraction of soil from an electroplating site, with a specific focus on chromium release and soil dissolution. Materials and methods: Column flushing tests were performed on a sandy soil contaminated by electroplating activities in the field. Three EDTA concentrations (5, 10, and 20 mM) and flow interruptions were employed to investigate the operation of EDTA flushing. Results and discussion: Results demonstrated that Cr, Cu, and Ni were continuously released along with dissolution of Fe, Al, Mg, and Mn throughout the entire flushing process (up to 600 pore volumes), whereas Zn and Pb removal primarily occurred in the first 50-200 pore volumes. By comparing the Cr and Fe release patterns, the observed Cr release by EDTA flushing possibly resulted from a combination of dissolution of Fe oxides, dissolution of metal-chromate precipitates, and ligand competition for the surface sites (substitution reaction). The latter two mechanisms appeared to be more influential at the early stage. It was also revealed that soil dissolution was predominant, and metal extraction became inefficient at the later stage of flushing, especially with the concentrated EDTA solution. On the other hand, when the flushing process was temporarily paused (i. e., flow interruptions), Cr, Cu, Ni, and Zn concentrations elevated, whereas Pb levels in the effluent decreased, indicating the significance of rate-limited metal exchange of newly formed metal-EDTA complexes. Conclusions: In consideration of EDTA utilization efficiency and potential ecological risks, diluted EDTA solution is recommended for field applications.Department of Civil and Environmental Engineerin