Attenuation of Wastewater-Derived Contaminants in an Effluent-Dominated River

TextTo assess attenuation rates under conditions encountered in such systems, samples from the Trinity River were analyzed for a suite of wastewater-derived contaminants during a period when wastewater effluent accounted for nearly the entire flow of the river over a travel time of approximately 2 weeks. Results of this study indicate that natural attenuation can result in significant decreases in concentrations of wastewater-derived contaminants in large rivers.Univ. of California Dept. of Civil and Env. Engr.Center for Research in Water Resource

Dissolution of mesoporous silica supports in aqueous solutions: Implications for mesoporous silica-based water treatment processes

Under pH 7-10 conditions, the mesoporous silica supports proposed for use in water treatment are relatively unstable. In batch experiments conducted in pH 7 solutions, the commonly used support SBA-15 dissolved quickly, releasing approximately 30mg/L of dissolved silica after 2h. In column experiments, more than 45% of an initial mass of 0.25g SBA-15 dissolved within 2 days when a pH 8.5 solution flowed through the column. In a mixed iron oxide/SBA-15 system, the dissolution of SBA-15 changed the iron oxide reactivity toward H 2O 2 decomposition, because dissolved silica deposited on iron oxide surface and changed its catalytic active sites. As with SBA-15, other mesoporous silica materials including HMS, MCM-41, four types of functionalized SBA-15, and two types of metal oxide-containing SBA-15 also dissolved under circumneutral pH solutions. The dissolution of mesoporous silica materials raises questions about their use under neutral and alkaline pH in aqueous solutions, because silica dissolution might compromise the behavior of the material

Local perspectives on water

No abstract available

Production of oxidizing intermediates during corrosion of iron; implications for remediation of contaminants from mineral and metal processing

Elemental iron has a long history of use for reductive recovery of dissolved metals from waters associated with ore bodies, mining and mineral processing activities. It has recently been recognized that Fenton's reagent, which generates powerful oxidants, may be generated when iron corrodes in the presence of oxygen. If the iron is nanoparticulate, enough oxidant may be generated for practical applications. However, there is ample indication in the literature that oxidation reactions on iron at near-neutral pH are strongly sensitive to the source of the iron, which affects the surface. This was investigated here for electrolytic iron powder, and two types of nanoparticulate iron, using a modified packed powder electrode. The behavior of bulk iron was investigated using a rotating disk electrode. The results revealed significant differences in the corrosion behavior of the different iron samples, indicating that these would yield significantly different results if employed for oxidation reactions

Kinetics and efficiency of H 2O 2 activation by iron-containing minerals and aquifer materials

To gain insight into factors that control H 2O 2 persistence and OH yield in H 2O 2-based in situ chemical oxidation systems, the decomposition of H 2O 2 and transformation of phenol were investigated in the presence of iron-containing minerals and aquifer materials. Under conditions expected during remediation of soil and groundwater, the stoichiometric efficiency, defined as the amount of phenol transformed per mole of H 2O 2 decomposed, varied from 0.005 to 0.28%. Among the iron-containing minerals, iron oxides were 2-10 times less efficient in transforming phenol than iron-containing clays and synthetic iron-containing catalysts. In both iron-containing mineral and aquifer materials systems, the stoichiometric efficiency was inversely correlated with the rate of H 2O 2 decomposition. In aquifer materials systems, the stoichiometric efficiency was also inversely correlated with the Mn content, consistent with the fact that the decomposition of H 2O 2 on manganese oxides does not produce OH. Removal of iron and manganese oxide coatings from the surface of aquifer materials by extraction with citrate-bicarbonate-dithionite slowed the rate of H 2O 2 decomposition on aquifer materials and increased the stoichiometric efficiency. In addition, the presence of 2 mM of dissolved SiO 2 slowed the rate of H 2O 2 decomposition on aquifer materials by over 80% without affecting the stoichiometric efficiency

Police posing as juveniles online to catch sex offenders: Is it working?

Abstract This paper explores the extent and effectiveness of proactive investigations in which investigators pose as minors on the Internet to catch potential sex offenders. It utilizes a subsample of cases from the National Juvenile Online Victimization Survey, which concerned persons arrested for Internet sex crimes against minors in the year beginning July 1, 2000. Results suggest proactive investigations represented a significant proportion (25%) of all arrests for Internet sex crimes against minors. Such investigations were being conducted at all levels of law enforcement. The online personas assumed by investigators paralleled the ages and genders of real youth victimized in sex crimes that started as online encounters. These proactive investigations accessed an offender group that appeared somewhat less deviant in terms of adult sexual behavior and arrest history but equally deviant as other online offenders in terms of possession of child pornography. Prosecution of these cases produced high rates of guilty pleas and low rates of dismissed or dropped cases. The entrapment, fantasy or role-playing, and factual impossibility defenses were used but not successfully. Findings suggest that the Internet sometimes allows law enforcement to interdict before a youth is victimized, gather solid evidence of offenses, and find and track some offenders