Increased demand for storm water treatment has created development in filtration technologies for storm water. Manufacturers are using different filtration facilities and different filter materials. Therefore there is a need - from manufacturers, universities and government organisations - to put together current knowledge and to clarify important aspects concerning constructed filter systems. The first part of this paper reviews filtration facilities for storm water, filter substrates that have been tested for heavy metal reduction, and processes for contaminant transport through filter substrates. The second part of the paper presents an investigation of pine bark, used as a substrate in gully-pot filters for metal reduction in storm water.
Storm water generated from road runoff contains pollutants such as metals that are either dissolved in storm water or bound to particulates. Using detention ponds for the treatment of storm water from road runoff, where particles can settle, can reduce the level of particulate-bound metals in the water, while small particles and dissolved matter pass through the detention pond. Some of these metals can be removed by filtrating water through specially constructed filter systems. This investigation is a laboratory study where different filter substrates were tested in order to evaluate their efficiency in reducing heavy metals from water. Metal solutions were filtered through columns filled with various substrates consisting of combinations of calcium silicate rock (opoka), zeolite and peat. The metal-removal efficiency was correlated to hydraulic load, and for the metal species the reduction efficiency decreased with increased hydraulic load. Mixtures of opoka and zeolite were found to be superior to the other filter-substrate combinations tested with regard to both hydraulic aspects and removal efficiency. Peat mixed with the calcium silicate rock was not successful due to clogging which stopped the experiment. A manufactured product made from the calcium silicate rock (burned opoka) was found to be less useful because of its calcium oxide (CaO) content. Among the tested filter substrates, mixtures of opoka and zeolite seemed to be the most useful compositions with respect to reduction-efficiency and clogging aspects. The removal capacity of metals varied from 0.6 to 1.8 kg m(-3) depending on the metal and the filter substrate.
In order to immobilise pollutants in storm water—such as heavy metals that are either dissolved or bound to small particles—filter systems featuring various different filter substrates can be constructed to filtrate storm water. Two important parameters for the design and functioning of such a filter system include the load capacity and removal efficiency of the material used in the filter bed. These are essential considerations in the design of the filter itself. A sound knowledge of the operational and maintenance activities of these systems is also necessary for achieving reliable treatment systems. This paper describes an experiment where storm water from a section of highway and surrounding roads has been filtrated through experimental columns filled with specially selected natural filter materials—calcium silicate rock (opoka), zeolite and pine bark. Filtration was performed in a downward direction under unsaturated conditions. The efficiency of copper and zinc removal of a number of combinations of these filter substrates has been analysed. The average reduction of these metals in filtrated storm water was around 63–81%, depending on the combination of metal and filter substrate.
Metals that are dissolved in storm water can be removed by filtrating water through specially constructed filter systems. Pine bark is an interesting material for this purpose, but it needs further investigations regarding its removal efficiency of metals. This paper presents a laboratory study where pine bark was tested to evaluate its efficiency in reducing heavy metals in water. Metal solutions were prepared and used in batch tests with pine bark. The metal removal efficiency was correlated to different metal concentrations in the solution and different contact times between the pine bark and the metal solution. The results showed that a high metal removal was achieved after a short contact time. The metal removal was low for low metal concentrations (0.1 mg/L) and higher for metal concentrations from 1 to 10 mg/L. The removal capacity was found to be 2.6 g Cu, 1.3 g Zn and 3.8 g Pb per kg pine bark. An investigation of the influence of chloride in the metal solution showed that the metal removal decreased by 15-23 %, depending on the metal, in the presence of chloride. Sorption isotherms of Zn, Cu and Pb on pine are also presented in the paper.
Accumulation of sediments and water quality were investigated in a wet storm-water detention pond in central Sweden. The drainage area surrounding the pond was covered by a section of highway and secondary roads. Sediment samples were collected from the pond and heavy-metal concentrations analysed subsequently in the laboratory. The depth of accumulated sediments was measured at several points around the pond. The investigation showed that during the 18 months that had passed since the pond was constructed, a 5-8 cm layer of sediments had accumulated near the inlet, and a 1.5 cm layer near the outlet of the pond. Storm water passing through the detention pond showed an average reduction rate of 26-84% for total metal content, 67% for total N, 78% for total P and 92% for COD.