Abstract: Acid ground waters contaminated with radioactive elements (U, Ra, Th), toxic heavy metals (Cu, Zn, Cd, Mn, Fe), arsenic and sulphates were treated by means of a permeable barrier. The barrier was filled with a mixture of biodegradable solid organic substrates (spent mushroom compost, sawdust and cow manure) and was inhabited by a mixed microbial community consisting of sulphate-reducing bacteria and other metabolically interdependent microorganisms. An efficient removal of the pollutants was achieved by this barrier during the different climatic seasons, even at ambient temperatures close to degrees C. The microbial dissimilatory sulphate reduction and the sorption of pollutants by the organic matter in the barrier were the main processes involved in this removal.

Abstract: Surface-flow wetlands are generally considered sinks for Fe and Mn but they may also export and affect the partitioning of these metals. This study was undertaken to evaluate the effect of a young constructed wetland on the retention and transformation of both dissolved and particulate Fe and Mn. Duplicate water samples were collected every three days at the inlet and outlet structures of the Monahan Wetland, Kanata, Ontario, from spring of 1997 to 1999. While on a yearly basis the wetland showed significant retention of che dissolved phase, the retention of total Fe and Mn was poor. There were strong seasonal differences in retention and, during the winter, the wetland was a source. The wetland transformed dissolved into particulate Fe and Mn from spring to fall whereas during the winter, dissolved Fe and Mn were released. Changes in pH, alkalinity and temperature could explain 11% and 40% of the outlet variation in the ratio of dissolved to total Fe and Mn respectively. Furthermore, from spring to late summer, planktonic algal biomass was negatively related to the ratio of dissolved to total Fe and Mn implying a role in Fe and Mn transformations in young wetlands where emergent and submerged vegetation have yet to dominate the system. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: In temperate areas of abundant freshwater there is seldom an urgency to recycle. The statutory protection of inland waters for beneficial uses such as drinking, food processing and game fishing is requiring industries to choose recycling. A European success in this trend is a base metal mining/milling industry which, since 1977, is implementing hydraulic, hydrological, treatment and ecological studies with wastewaters and mine tailings. A model activity, located 50 km from Dublin is considered. Zinc and lead concentrates produced and exported to smelters ultimately yield approximately 194,000 t and 54,000 t of these respective metals (32 and 21 percent of European production). Water use as originally planned would have been approximately 6m(3)/t of ore milled. While ore milling increased by 25 percent to 8,500t/d in 1993, water use declined by 33 percent to 4m(3)/t. The components making up this reduction range from milling technology efficiency to greater recycling from the 165 ha tailings pond. Environmental standards, based on framework regulations originating in EU Directives, have been instrumental in achieving wastewater savings. A conclusion is the value of integrating water quantity, quality, recycling, storage, production and other factors early in project planning. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.