[Reduction of bacteria and viruses in purification plant discharges using microfiltration in a model plant]. / Reduzierung von Bakterien und Viren in Klärwerksabläufen durch Mikrofiltration in einer Modellanlage.

Microfiltration through a membrane matrix of a nominal pore size of 0.2 microns has been applied for advanced treatment of mechanically and biologically treated wastewater. Elimination of bacteria and coliphages as well as the decrease in some chemical constituents were studied at a flow rate of 80 l/h. Microfiltration resulted in a reduction of E. coli, coliform bacteria, fecal streptococci and of coliphages by more than 4 logs in the filtrate. Thus, the quality requirements of EC Directives for bathing water (EC, 76/160) could be maintained. As a result of microfiltration, a 43 +/- 13% removing of the total phosphorous compounds (Pt) in the pre-filtered secondary effluent from 11 +/- 2 mmol/m3 (0.34 +/- 0.06 mg/l) to 6 +/- 2 mmol/m3 (0.19 +/- 0.06 mg/l) was measured. The dosage of FeCl3 (between 30 and 150 mmol/m3) as coagulant before microfiltration improved the reduction of Pt to result in an average value of 75 +/- 16%. After adding FeCl3, orthophosphates (PO4-P) could be efficiently reduced by microfiltration. Thus, PO4-P concentrations in effluent samples were, in most cases, below the detection limit (0.01 mmol/m3).

Prophylactic reoperation for strut fractures of the Björk-Shiley convexo-concave heart valve.

Outlet strut fracture of the Björk-Shiley Convexo-Concave (C/C) heart valve is the current paradigm of structural failure of mechanical heart valve prostheses. The estimated risk of fracture for C/C valves varies from 0.02% to 2.5% per patient-year, depending on valve size, opening angle, date of manufacture and position as a mitral or aortic replacement. This report examines our experience with 396 implants, comprising 346 C/C 60 degrees valves and 50 C/C 70 degrees valves. The 30-day mortality was 1.8%. Through April 1993, mean follow up was 8.9 years, incorporating 2971 patient-years and knowledge of the current status of 91.5% (356/389) of operative survivors. Late mortality was 3.7% per patient-year, including one 60 degrees and one 70 degrees outlet strut fracture. To evaluate the risk of semi-elective valve re-replacement at our institution, we reviewed the results of isolated re-replacements of failing or incipiently failing bioprostheses in 65 patients who had no serious co-morbidity and who were NYHA Class III or lower immediately before the procedure. The 30-day mortality was 4.6% and the overall serious morbidity rate was 10.8%, necessitating six repeat reoperations. When these factors were balanced against the life expectancy and general status of five patients with large-size, higher-fracture-risk 70 degrees C/C valves, it was concluded that only two patients remained possible reoperation candidates. Consideration for re-replacement of a normally functioning C/C heart valve should take into account institution-specific experience because structural failure remains a low risk compared to valve-related complications engendered by reoperation.