Granulated Iron-Hydroxide (GEH) for the Retention of Copper from Roof Runoff

摘要

Granulated iron hydroxide (GEH) has been tested in order to investigate its ability to adsorb copper from roof runoff. The adsorption capacity was evaluated with equilibrium batch experiments using nanopure and roof runoff matrices and different copper concentration levels and pH. Adsorption has shown to be strongly pH dependent starting at pH 5 in the nanopure system and at pH 4.5 in the roof runoff system. With increasing initial copper concentrations, adsorption in the roof runoff system is enhanced, but is slightly diminished at pH above 6.2. In both cases, the adsorption capacity for technical applications revealed to be sufficient. In contrast to the nanopur system, modelling of the adsorption in real roof runoff water is possible using an adapted Langmuir model including pH effects. The equilibrium model can be implemented in a transport model for the simulation of fixed bed adsorbers. With the help of longterm column experiments, it could be shown that extrapolated adsorption capacities from model calculations can actually be reached in the top layers of an adsorber bed provided that the contact time is sufficient. In this case, almost complete copper removal was observed. As shown in the design example conditions, implementable volumes of GEH are required and varying typical flow rates in infiltration sites should not be process limiting. Full scale application of a mixed GEH/carbonate layer in the form of a trench for the removal of copper from a copper facade runoff shows excellent performance after an operation time of almost two years. Other applications such as the treatment of recuperated roof runoff water from a copper roof used for toilet flushing and the addition of an adsorption layer to a standard infiltration gallery design reveal the broad applicability of GEH for copper removal. In practice, it is good to see the increasing awareness of decision makers to use barrier systems in cases where large copper surfaces are unavoidable. But it has to be stressed that the technical solution presented with the GEH adsorber system should not be used as an argument to promote the use of copper on roofs. The ultimate goal of modern urban water management is to reach higher levels of sustainability which may be achieved by proper source control only. For new buildings, the use of less corrosive metals than copper or zinc or the use of alternative non-metal materials should be studied and evaluated with highest priority.