Biological lamella sedimentation used for wastewater treatment

Sedimentation basins represent a low-cost system for wastewater treatment, but they need large areas and do not remove all small particles. A new sedi mentation principle known as biological lamella sedimentation, has therefor e been evaluated. The process involves establishing a biofilm on bioblocks, which are placed in the sedimentation basin, and the film should improve t he removal of suspended solids because it attaches small particles. A labor atory model of the sedimentation system was connected to the outlet of a sm all fiberglass fish tank (0.5 m(3)), which contained 123 rainbow trout with a mean weight of 206 g. The 22 days study measured inlet and outlet water values of the sedimentation basin, the feed used, fish growth and collected sludge. The results showed that it was very difficult to obtain representa tive water samples from the outlets of the fish tank and the sedimentation basin. There were wide variations between the replicates for several of the parameters analysed. However, mass budget estimates, i.e. measurements of feed used, fish growth, and collected sludge, gave reasonable values. This method was preferable to water sample analysis. The mass budget estimates s howed reasonably good removal rates for TP (43.2%) and TN (7.3%). A total o f 98.3 g (TDM) was collected per kg fish produced. The average TDM, TP and TN in the collected sludge were 2.15, 5.17 and 2.14%;, respectively. There is a potential for making technical improvements to the design of the biolo gical lamella sedimentation basin as was evaluated. (C) 2001 Elsevier Scien ce B.V. All rights reserved.