No abstract

No abstract

The coal-fired power industry in the United States faces growing needs to improve wastewater treatment and disposal practices, especially for wet flue gas desulfurization (FGD) systems. Zero liquid discharge (ZLD) treatment systems may be implemented, and one ZLD option is the coupling of brine concentration with solidification/stabilization (S/S). This S/S process could be achieved by co-disposing the concentrated FGD brines with coal fly ash (CFA) and Portland cement. S/S using bituminous CFA (BCFA) achieved good retainment (average 68−90%) of As V , Cd II , Hg II , and Se IV in the toxicity characteristic leaching procedure (TCLP); however, poor retainment was observed for Cr VI and Se VI . Separate experiments showed good sorption of As V , Cd II , Hg II , and Se IV (average 56−100%) but poor sorption of Cr VI and Se VI to S/S solids. Meanwhile, Cr VI and Se VI retainment could be enhanced by addition of FeSO 4 to the S/S mixture, likely due to reduction of these metals to lower oxidation states. Compared to BCFA, S/S using sub-bituminous CFA (SCFA) resulted in higher pH S/S solids and final TCLP leachate, which increased retainment of As V , Cd II , and Se VI . Apart from the pH impact on the process, As V retainment was likely improved by the high Ca content of SCFA and Se VI retainment was improved by the incorporation of SeO 4 2− in Friedel's salt (AFm-Cl) by exchange with Cl − . Friedel's salt was positively identified by X-ray diffraction in the SCFA S/S solids but not for the BCFA S/S solids. Even so, reduction of Se VI plus S/S is likely a better immobilization strategy than SeO 4 2− substitution in the AFm phase because of higher stability under long-term landfill conditions.

Large quantities of antibiotics are used annually in human therapy and in agriculture. As results of incomplete metabolism, ineffective treatment removal or improper disposal, antibiotics may be released into the aquatic environment via wastewater effluent and agricultural runoff. Results of recent studies indicate the presence of antibiotics in municipal wastewater effluent and surface water. Despite the detection of antibiotics, little is known about their distribution in the environment, their mobility and persistence in natural and engineered systems. Contamination of aquatic systems by antibiotics could perturb microbial ecology, increase the proliferation of antibiotic-resistant pathogens, and could pose threats to human health. The presence of antibiotics in the aquatic environment also presents challenges for the water industry particularly on the issues of water reuse and water resource planning.To assess the magnitude of the potential risks associated with antibiotics released into the aquatic environment, a literature review was conducted on the usage, occurrence and behavior of antibiotics. Concentrations of antibiotics in municipal wastewater and liquid animal waste were estimated and were classified according to chemical properties. The estimation of human health antibiotics was based upon the number of prescriptions administered while the estimation of animal health antibiotics was based upon the sub-therapeutic usage in feed for growth promoting. Reported data on the occurrence of antibiotics in the aquatic environment confirm the persistence of certain antibiotics. The fate of antibiotics is significantly affected by sorption and transformation processes. By combining information on environmental fate with the predicted concentrations, we identify that antibiotics of fluoroquinolones and sulfonamides are the most likely water contaminants, followed by macrolides. Among fluoroquinolone and sulfonamide antibiotics, ciprofloxacin and sulfamethoxazole are most likely to be present in wastewater effluent and sulfamethazine is most likely to be present in agricultural runoff. Azithromycin and tylosin are the most likely macrolides present in wastewater effluent and in agricultural runoff respectively. The antibiotics identified by this literature review may serve as "indicators" in analytical survey for antibiotic contamination as analyses of antibiotic contaminants in complicated water matrices can be time-consuming and costly. Furthermore, results of this literature review can also facilitate prioritizing future studies on the fate and transport of antibiotics in natural and engineered water systems.