Nanofiltration in Combination with Limestone Filtration for Treating a Soft Spring Water Containing High Amounts of Humic Substances

The paper presented here describes experiments with a nanofiltration pilot plant treating spring water which contains high amounts of humic substances. With this process, water components such as humic substances, iron, manganese, and aluminum may be very well removed. However, the low pH value of the NF filtrate does not conform with the German standards. This is why the pH value will be increased in a second treatment step by limestone filtration. Prior to limestone filtration, CO₂ dosage is required in order to make sure that the pH value stays below the upper limit of the German standards of 9.5. With this treatment, a drinking water results which meets the German standards and has good chemical properties with respect to corrosion. The operation of the nanofiltration pilot plant for the treatment of the very soft spring water did not require the continuous addition of chemicals in order to prevent scaling. Although the spring water entered the NF without chemical pretreatment, there was no decrease in filtrate capacity observed over a period of six months. This is in contrast to other investigations involving colour reduction from very hard surface waters. When treating very hard waters by nanofiltration, the addition of complexing agents or acid is required in order to prevent scaling of the membranes. Such intricate pretreatment procedures cause doubt of the application of nanofiltration for the treatment of hard waters in large plants. However, in the case presented here, the application of NF in combination with the hardening step is quite simple, so that the full-scale plant may be operated mainly automatically and will require only little maintenance.     

Maßnahmen zur Sanierung und Restaurierung des Elsterstausees bei Leipzig

Redevelopment and Restoration Measures for Lake Elsterstausee (Leipzig) Lake Elsterstausee is an artificial lake in the south of the town Leipzig. It was built in 1933, has an actual area of 50 ha, and an average depth of 2 m. Between 1970 and 1991, the lake was used for intensive fishery. Because of fish feeding and supplying the lake with highly nutrient loaded water from river Elster the waterbody was in a polytrophic state during this time. Secchi depth seldom exceeded 0.4 m, but pHvalues often exceeded 9. Therefore and because of ammonia concentrations between 1.5 and 4.0 mg/L fish kills often occured. Lake Elsterstausee had no usability as bath waterbody although it was orginally built for this purpose. In 1991, a complete programme for redevelopment and res-toration of the lake started. The main measures were the total exchange of trophic loaded water and the only supply with treated groundwater, the drastic decrease of fish populations – in 1991 140 tons of fish (90% carps) were removed from the lake, – the development of healthy wild fish populations and of a eutrophication diminishing food chain, and the development of a reed zone almost around the lake. The groundwater treatment was steadily improved between 1992 and 1996. Actually, the following optimized system works: Drained groundwater from the surface lignite mine Zwenkau (pH = 6.95) and percolating water from the heaps (pH = 3.01) are mixed in the proportion 1:1 after intensive aeration. The water flows through a ditch that is 1 600 m long and has a performance up to 300 m³/h. In the well-diversified ditch, up to 90% of the iron is removed by precipitation and filtration effect of submerged macrophytes and filamentous algae. In the same time, deacidification occurs primarily by sulfate reduction in the sediment. Meanwhile, the water has a pH of 4.64 immediately after mixing, this value enhances up to the end of the flowing distance to 7.3. Internal restoration of the lake started in November 1991 with the total removal of loaded water and of almost all carps and white fishes. In 1993, 4 000 carnivore fishes (zanders, pikes, welses) were given into the lake to keep white fish popu-lations on a low level. Additionally, every year between 5 and 7 kg of water fleas (Daphnia sp.) were added. By means of this initial biomanipulation, food chain in lake Elsterstausee was stabilized. As results of the above mentioned measures, nutrient content in the waterbody decreased and secchi depth increased steadily. Between 1991 and 1997, trophy degree according to Klapper developed from 5 (hypertrophic) to 3 (eutrophic).