Study of the evaporation process of saline waste from the tanning industry.

The second and third steps of wastewater treatment in the tanning industry generate sludges that are rich in salts, organic matter and suspended solids. Since these are formally catalogued as industrial wastes by environmental legislation, they cannot be disposed of directly but need a final treatment. One of the problems with these wastes is their high water content, which has to be reduced. In the particular case of the concentrated streams from the secondary and tertiary treatment steps, the sludges are first concentrated by evaporation, and the evaporated water is used in other parts of the plant. This study, which preceded evaporator design, analysed the evaporation process (laboratory scale) of a saline residue produced in the reverse osmosis step of the treatment of tanning wastewaters by the company Aquagest Levante, S.A. in Lorca (Murcia, Spain), to ascertain its behaviour in the evaporation process and the evolution of its physical properties. The study served to determine the exact mineralogy and ionic composition as well as the characteristics of the waste in question. This information was used in the last step of the design of the evaporation equipment.     

Quantitative alterations in the structure of the digestive cell of Littorina littorea on exposure to cadmium

The effects of sublethal concentrations of cadmium (Cd) on the morphology of the digestive gland of the periwinkle Littorina littorea have been investigated using a planimetric procedure. Five planimetric parameters were recorded (mean epithelial thickness: MET; mean diverticular radius: MDR; mean luminal radius: MLR; MLR/MET and MET/MDR) and tested by diverse statistical methods. The results indicate that MET is depressed after long exposures at high Cd concentrations whilst MLR increases. Variations in MDR have been attributed to different conditions in the tissues surrounding digestive tubules, and are not-significant in relation to the treatment. However, certain increases might be significant due to the presence of parasites or hemocyte proliferation. The ratios MLR/MET and MET/MDR are highly sensitive, and can be expressed as statistical functions of metal concentration and exposure time. Combination of these five planimetric parameters is reliably indicative of the structural changes occurring in the digestive gland of molluscs under conditions of environmental stress.     

Odor-annoyance estimates from roadtraffic combustion exhausts: Calibration with master scaling using pyridine as a reference

The present field study addressed the need for a procedure that provides a defined unit of measurement of perceived annoyance from environmental odors, calibrating the estimates for individual scaling behavior and context effects. In including 25 subjects, the purpose was to demonstrate the applicability of the master-scale procedure with magnitude estimation to perform such a calibration of odor-annoyance estimates for target stimuli such as road-traffic combustion exhausts (13 000 vehicles/d; averaging 47 μg/m³ over the day/night with peaks exceeding 100 μg/m³ of nitrogen dioxide; NO₂). For comparison, calibrated estimates were also obtained for a backyard expected to be considerably less polluted (comparable with 18 μg/m³ of NO₂) and for blank stimuli presented indoors. The data transformation for the calibration procedure with which annoyance is expressed in either master-scale units or pyridine equivalents requires estimates of a reference stimulus for which seven concentrations of pyridine were used. The results provide an illustration of master scaling of odor annoyance, and imply that use of a modulus (standard stimulus with a predefined annoyance magnitude), in contrast to master scaling, is not sufficient for calibration for individual scaling behavior and context effects.     

Multiple-resource modeling as a tool for conservation: Its applicability in Mexico

The current Mexican environmental law provides the legal basis for comprehensive land-use planning. Under the law, development of natural ecosystems must combine goals, policies, and practices towards the sustainable use of natural resources and the protection of biological diversity. Thus, ecosystem manipulation must be able to counter fragmentation of natural ecosystems and isolation of natural reserves, while providing for human needs. Assessment of the potential of natural ecosystems and management impacts are required. Multiple-resource simulation is an assessment and land-use planning tool that permits managers and decision makers to comply with the law, providing a flexible, user-oriented system that can meet the needs of managers, conservationists, and researchers. A multiple-resource model and an example of how it can be applied to meet planning needs is presented for discussion.     

Effects of zinc on the structure and growth dynamics of a natural freshwater phytoplankton assemblage reared in the laboratory

The response of a natural phytoplankton assemblage to different concentrations of Zn(2+) was evaluated by means of a static laboratory bioassay. Aliquots of surface water, taken in autumn from a non-polluted point of the Reconquista River (Buenos Aires, Argentia), were incubated in mineral nutrient media containing 2.5, 10 or 25 mg litre(-1) of Zn(2+) (as zinc chloride). The comparative structure and dynamics of the communities were followed through periodic physico-chemical and biological analyses of samples taken during 24 days of incubation. Under the experimental conditions of the bioassays, the existence of several Zn(2+) tolerant algal species was shown: the most important of them were Chlorella vulgaris Beij. (Chlorophyceae, Chlorococcales), Nitzschia palea (Kütz.) Smith and Gomphonema parvulum (Kütz.) Kütz. (Bacillariophyceae). It was also demonstrated that the algal responses to Zn(2+) were selectively concentration dependent: at 2.5 and 10 mg litre(-1) a stimulatory effect was observed in the diatoms; at 25 mg litre(-1), diatom toxicity occurred. In contrast, Chlorophyceae growth was stimulated at the maximal Zn level. In general, the diversity, richness and equitability of the community were adversely affected by Zn in a concentration-dependent fashion.     

瑞典四大湖泊(梅拉伦、哈马伦、韦特恩和维纳恩湖)研究工作40年:监测与治理措施对于社会可持续发展的重要意义

对瑞典的梅拉伦、哈马伦、韦特恩和维纳恩等四个大湖水质进行的监测已差不多有40年了.对湖泊的物理化学参数、浮游生物和底辆无脊椎动物进行了定期评估.对湖泊的水文和沉积条件、大型植物、鱼类、原始有机物产率、细菌和附生藻类进行了定期调查.人类活动(包括工业活动)的影响表现在湖中有机质、养分、金属和持久性有机化合物过量增加.从60年代末开始,对这些湖泊汇水区内所有市政污水处理厂都进行了更新改造,使其达到了最高技术标准(包括磷的化学沉淀处理),因而污水处理厂的磷排放减少了90%-95%.此外还对工业企业作出了规定,要求它们减少有害物质的排放.本文讨论了对湖泊采取活污措施后湖泊的变化情况以及各种指标达到的水平.这些研究有助于制定全国性湖泊监测计划.另外,通过大湖监测取得的成果有助于制定国家水质标准,包括物理、化学和生物学标准.