RESUMO
The removal of natural organic matter under variable coagulation and flocculation pretreatment conditions was evaluated for three surface waters in an immersed ultrafiltration (UF) process. Coagulation with alum, flocculation and UF treatment were conducted in a bench-scale test apparatus designed to simulate pilot- and full-scale water treatment systems. Variable coagulation and flocculation operating conditions were investigated, including coagulant dose, hydraulic retention time (HRT) and mixing intensity (e.g. velocity gradient). Treatment performance was evaluated by measuring specific water quality parameters in the permeate stream, including dissolved organic carbon (DOC), UV254 and true colour. Coagulant dose was found to be the most important variable for treatment performance with regard to permeate water quality, with significantly lower alum dosages required to achieve enhanced coagulation water quality targets than conventional filtration systems. Experiments conducted to evaluate variable flocculation stage HRT and applied velocity gradient demonstrated that traditional set points for these operating variables, applied in conventional filtration systems, may not be required in UF systems. In particular, optimized UF permeate water quality was found with reduced flocculation retention times (e.g. <10 minutes) and mixing intensities (e.g. < 100 s(-1)). The impact of intermittent air scour, or air sparging, operations in the UF process tank during operation was also evaluated. The use of air scour, tested as an intermittent operation at an applied velocity gradient of 50 s(-1) was found to significantly reduce DOC concentrations and UV254 measurements in the UF permeate stream when compared with UF operations without air scour.
Assuntos
Modelos Químicos , Reologia/métodos , Ultrafiltração/métodos , Poluentes da Água/química , Poluentes da Água/isolamento & purificação , Purificação da Água/métodos , Água/química , Coloides/química , Simulação por Computador , FloculaçãoRESUMO
This report describes imaging in a patient with a unique unnamed carotid-basilar anastomosis, where the entry into the skull was via the jugular foramen. There were associated findings of absent right and hypoplastic left vertebral arteries and an aberrant right subclavian artery. We speculate that the persistent anastomosis is developmentally related to the jugular branch of the ascending pharyngeal artery. Clinical implications of the course via the jugular foramen are also discussed.