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The mechanism and design of sequencing batch reactor systems for nutrient removal--the state of the art.

The Sequencing Batch Reactor (SBR) process for carbon and nutrient removal is subject to extensive research, and it is finding a wider application in full-scale installations. Despite the growing popularity, however, a widely accepted approach to process analysis and modeling, a unified design basis, and even a common terminology are still lacking; this situation is now regarded as the major obstacle hindering broader practical application of the SBR. In this paper a rational dimensioning approach is proposed for nutrient removal SBRs based on scientific information on process stoichiometry and modelling, also emphasizing practical constraints in design and operation.

Biodegradation, Environmental↗

Life testing of the vapor compression distillation urine processor assembly (VCD/UPA) at the Marshall Space Flight Center.

Wastewater and urine generated on the International Space Station (ISS) will be processed to recover pure water using vapor compression distillation (VCD). To verify the long-term reliability and performance of the VCD Urine Processor Assembly (UPA), life testing was performed at the Marshall Space Flight Center (MSFC) from January 1993 to April 1996. Two UPAs, the VCD-5 and VCD-5A, were tested for 204 days and 665 days, respectively. The compressor gears and the distillation centrifuge drive belt were found to have operating lives of approximately 4800 h, equivalent to 3.9 years of operation on ISS for a crew of three at an average processing rate of 1.76 kg/h (3.87 lb/h). Precise alignment of the flex-splines of the fluids and purge pump motor drives is essential to avoid premature failure after about 400 h of operation. Results indicate that, with some design and procedural modifications and suitable quality control, the required performance and operational life can be met with the VCD/UPA.

Ecological Systems, Closed↗

[Ecologo-hygienic evaluation of the use of petroleum-refining waste for road construction in the lower Volga region].

A scheme has been developed for sanitary assessment of the safety of road building materials containing oil slurry waste. It includes 2 units: 1) sanitary and chemical studies and 2) ecological and toxicological ones. The sanitary and chemical unit consists of a preliminary stage, wherein priority waste-specific substances are selected, and two experimental studies air- and water migration ones that evaluate the environmental effects of the substances selected. The ecological and toxicological unit includes microbiological, phytotoxic, hydrobiological, and toxicological studies. This scheme of ecological and sanitary studies of road building composite materials containing oil slurry waste allows their ecological and toxicological safety to be comprehensively evaluated.

Environmental Pollutants↗

Malaria control: achievements, problems and strategies.

Even if history has not always been the Magistra vitae, Cicero expected it to be, it should provide, as Baas said, a mirror in which to observe and compare the past and present in order to draw therefrom well-grounded conclusions for the future. Based on this belief, this paper aims to provide an overview of the foundations and development of malaria control policies during the XX century. It presents an analysis of the conflicting tendencies which shaped the development of these policies and which appear to have oscillated between calls for frontal attack in an all-out campaign and calls for sustainable gains, even if slow. It discusses the various approaches to the control of malaria, their achievements and their limitations, not only to serve as a background to understand better the foundations of current policies, but also to prevent that simplistic generalisations may again lead to exaggerated expectations and disillusion. The first part of the paper is devoted to the development of malaria control during the first half of the century, characterised by the ups and downs in the reliance on mosquito control as the control measure applicable everywhere. The proliferation of "man-made-malaria", which accompanied the push for economic development in most of the endemic countries, spurred the need for control interventions and, while great successes were obtained in many specific projects, the general campaigns proposed by the enthusiasts of vector control faced increasing difficulties in their practical implementation in the field. Important events, which may be considered representative of this period are, on the campaign approach, the success of Gorgas in the Panama Canal, but also the failure of the Mian Mir project in India; while on the developmental approach, the Italian and Dutch schools of malariology, the Tennessee Valley and the development of malaria sanitation, included the so called species sanitation. The projection of these developments to a global scale was steered by the Malaria Commission of the League of Nations and greatly supported by the Rockefeller Foundation. Perhaps the most important contribution of this period was the development of malaria epidemiology, including the study of the genesis of epidemics and their possible forecasting and prevention. Although the great effectiveness of DDT was perhaps the main determinant for proposing the global eradication of the disease in the 1950s, it was the confidence in the epidemiological knowledge and the prestige of malariology, which gave credibility to the proposal at the political level. The second part deals with the global malaria eradication campaign of the 1950s and 1960s. It recognises the enormous impact of the eradication effort in the consolidation of the control successes of the first half of the century, as well as its influence in the development of planning of health programmes. Nevertheless, it also stresses the negative influence that the failure to achieve its utopian expectations had on the general disappointment and slow progress of malaria control, which characterised the last third of the century. The paper then analyses the evolution of malaria control funding, which often appears out of tune with political statements. The fourth part is devoted to the search for realistic approaches to malaria control, leading to the adoption of the global malaria control strategy in Amsterdam in 1992, and the challenge, at the end of the century, to rally forces commensurate with the magnitude of the problem, while aiming at realistic objectives. After discussing the conflicting views on the relations between malaria and socio-economic development and the desirable integration of malaria control into sustainable development, the paper ends with some considerations on the perspectives of malaria control, as seen by the author in early 1998, just before the launching of the current Roll Back Malaria initiative by WHO.

Animals↗

Drinking water supply and management practices in British Columbia, 1997-98.

BACKGROUND: Questions regarding control over a water fluoridation system in a British Columbia (BC) community led to a drinking water management survey in 1997-98. METHOD: A questionnaire was constructed based on published drinking water control and management criteria and was sent to 91 communities. RESULTS: 73/91 surveys were returned (80% response rate); 31 reported a protected water supply system, 40 reported logging and/or cattle grazing in watershed areas, 25 reported a lack of primary disinfection. Water fluoridation was reported in 12 locations, 3 of which did not monitor fluoride levels. Testing for protozoans was done routinely in 19 locations, 15 using approved laboratories. 15 water contamination events were reported, 9 of biological origin. Statistically significant associations were found between contamination events and: wooden delivery systems, lack of primary chlorination, increased number of protozoan tests, and increased number of personnel. INTERPRETATION: At the time of the survey in British Columbia, a number of communities were vulnerable to preventable drinking water contamination.

British Columbia↗