Vertical flow soil filter for the elimination of micro pollutants from storm and waste water

A technical scale activated soil filter has been used to study the elimination rates of diverse environmentally relevant micro pollutants from storm and waste water. The filter was made of layers of peat, sand and gravel. The upper (organic) layer was planted with reed (phragmites australis) to prevent clogging and was spiked with activated sludge to enhance microbial biomass and biodegradation potential. Compounds used as UV filters, antioxidants or plasticizers, namely 4-methylbenzylidene camphor (4-MBC), benzophenone-3 (BP-3), butylated hydroxytoluene (BHT), N-butylbenzenesulfonamide (NBBS), 2,6-di-tert-butyl-1,4-benzoquinone (2,6-DTB-1,4-BQ), 1,1-biphenyl-3,3-dimethyl (1,1-BP-3,3-DM) and dibenzyl (DB) have been included in this study. The chemical characteristics of these compounds ranged from the hydrophilic (pKOW 2.6) to the lipophilic (pKOW 5) properties.For the elimination studies, synthetic waste water spiked to 3000 ng L−1 with the selected compounds was used. Elimination rates with low hydraulic load (61 L m−2 d−1, water retention time: 2 d) were higher than 96%. During a storm water simulation experiment (hydraulic load: 255 L m−2, water retention time: <1 h), the elimination rates of the most analytes decreased to 79–96%. The elimination performance of the hydrophilic compound NBBS declined to 21%. Balancing studies including the soil of the filter system revealed that degradation or transformation were both relevant elimination mechanism.