Impact of different recirculation schemes on nitrogen removal and overall performance of a laboratory scale MBR.

For membrane bioreactors (MBR) with enhanced nutrients removal, rather complex recirculation schemes based on the biological requirements are commonly recommended. The aim of this work was to evaluate other recirculation options. For a laboratory scale MBR, four different recirculation schemes were tested. The MBR was operated with COD degradation, nitrification, post-denitrification without carbon dosing and biological phosphorus removal. For all configurations, efficient COD, nitrogen and phosphorus removal could be achieved. There were no big differences in elimination efficiency between the configurations (COD elimination: 96.6-97.9%, nitrogen removal: 89.7-92.1% and phosphorus removal: 97.4-99.4%). Changes in the degradation, release and uptake rates were levelled out by the changes in contact time and biomass distribution. With relatively constant outflow concentrations, different configurations are still interesting with regard to oxygen consumption, simplicity of plant operation or support of certain degradation pathways such as biological phosphorus removal or denitrification.

Enhanced post-denitrification without addition of an external carbon source in membrane bioreactors.

This study investigates a post-denitrification process without the addition of an external carbon source combined with an enhanced biological phosphorus removal (EBPR) in a membrane bioreactor (MBR). Three trial plants, with two different process configurations, were operated on two different sites, and a variety of accompanying batch tests were conducted. It was shown that even without dosing of an external carbon source, denitrification rates (DNR) much above endogenous rates could be obtained in post-denitrification systems. Furthermore, the anaerobic reactor located ahead of the process had a positive impact on the DNR. Given these surprising results, the project team decided to identify the carbon source used by the microorganisms in the post-denitrification process. Batch tests could demonstrate that lysis products do not play a major role as a C-source for post-denitrification. The following hypothesis was proposed to explain the observations: the glycogen, internally stored by the substrate accumulating bacteria, if anaerobic conditions are followed by aerobic conditions could act as carbon source for denitrification in post-denitrification system. First exploratory batch tests, where the glycogen evolution was monitored, corroborate this assumption.

Nutrients removal in MBRs for municipal wastewater treatment.

Owing to increasingly stringent effluent quality requirements, intensifications of the conventional activated sludge process (ASP) are required. Due to high biomass concentrations employed, higher metabolic rates and better nutrient removal are possible in membrane bioreactors (MBRs). Decoupling of hydraulic and solids residence times offers additional possibilities for process design and optimisation. Recently, unconventional concepts like post-denitrification and enhanced biological phosphorus removal in MBRs have emerged. The objective of this paper is to present current knowledge on nutrients removal in MBRs and trends in process optimisation in comparison with conventional ASP.

[X-ray findings in primary bilateral pulmonary hypoplasia-- correlation with pathologico-anatomical findings]. / Röntgenbefunde bei primärer bilateraler Lungenhypoplasie--Korrelation mit pathologisch-anatomischen Befunden.

Comparative radiologic/pathologic study of 45 newborns with primary and secondary pulmonary hypoplasia. 43 cases were proven at autopsy. From 9 cases with primary pulmonary hypoplasia, 7 could be identified by 3 independent observers. The roentgen criteria of primary pulmonary hypoplasia are evaluated and should serve in the future to clinically diagnose this condition.

[HIV infection in children of seropositive mothers]. / HIV-Infektion bei Kindern seropositiver Mütter.

Both resolved and still open questions are discussed. The natural course of HIV infection from the time at which a child becomes symptomatic is known. The incidence rate of HI-virus transmission to the child remains uncertain. Likewise the time of transmission and its cofactors as well as data about the incubation and latency periods remain open questions. The greatest problem thus, is the early and reliable definition of HIV infection. Initial results from prospective HIV-perinatal studies are presented, showing that a transmission rate between 20% and 40% is to be reckoned with.