General description

Field of Invention

The invention - WEREC treatment system for storm water- is developed to remove oil compounds, heavy metals and phosphorus from storm water. Oil compounds and some heavy metals are removed in a first filter step with biological filter material. Phosphorus and more heavy metals are removed in a second filter step with

Calcium-based filter material. The patent application concerns the technical solution but not the filter materials.

Background of the Invention

Different types of filter material have been used operatively for several years to remove pollutants from storm water. Bark and peat materials in various forms are used to separate oil and heavy metals, often in so-called storm drain filters, which consist of a small unit that is lowered into the storm drain. Another operationally used treatment system is based on cleaning steps built into concrete chambers. The systems used today usually require filter material to be replaced/added frequently, resulting in high operating costs. Calcium-based materials have only recently begun to be used for the removal of phosphorus in storm water, in requests to the applicant. The chemical process for the removal of oil compounds and heavy metals in biological materials, and phosphorus and heavy metals in calcium-based materials is not described here. It has been described in prior patent applications and it is not the function of the material that is the focus of this application, but the technical solution. The applicant, WEREC Water Ecosystem Recovery AB (hereinafter WEREC), have conducted extensive field studies in collaboration with IVL Swedish Environmental Research Institute, showing that three different commercially available calcium-based filter materials have the ability to remove phosphorus transported with water in ditches and agricultural streams. With the low concentrations in agricultural streams, compared to domestic wastewater, and with the very dynamic flow regimes, with alternating low and high water flows and strongly varying phosphorus concentrations, however, special requirements are imposed on the technical solution. As a result of our research and development results investment funding for calcium-based filter beds can now be acquired from the Rural development programme of the Swedish l Board of Agriculture. Following the phase in which WEREC and IVL showed that filter materials based on burnt calcium work well for phosphorous removal in agricultural streams, WEREC proceeded with operational, installations of full-scale filter beds, and has now installed over twenty operational calcium filter beds for phosphorus separation. During the three years, during which full-scale, operational calcium filter beds have been installed by WEREC, we have internally developed a cost effective and robust filter bed technique, resulting in the development of the invention for which a patent application was submitted in January 2016 (patent application

1630004-8). That filter bed solution can also be used for storm water treatment, but it is based on the bed being placed at a location where the filter material can be excavated with excavator when it needs to be replaced. The present invention consists of a technical solution which means that the filter material does not need to be excavated but can be removed by suction and replaced by new material blown into the filter cassette. This is a major advantage in urban areas where recurring material replacement using excavation cannot be carried out. The invention also means that in the first filter step, for removal of oil compounds, replacement of filter material needs to be carried out only every 10-15 years instead of providing constant material supply or with replacement 1-4 times a year as in the systems used operatively today.

The technical solution has not been published, demonstrated or tested in a way that makes it publicly known.

The treatment system is capable of receiving storm water from urban areas of different sizes. The size of the facility can be varied to suit the size of the catchment area and the water flow during flow peaks. After a coarse material separation step not included in the invention, the water reaches the first step of the treatment system; a plastic and/or glass fiber cassette with size 2-10 m ³ containing a filter material based on bark shavings or peat absorbing oil compounds and some heavy metals. From this first step, the water is led to the calcium-based filter, which is built into pipe/tube modules with dimensions of 1000-3000 mm diameter. The size of the calcium-based filter is typically 3 m ³ to 300 m ³ but may be larger depending on the size of the catchment area and how much of the catchment area that consists of impervious surface. The water path through the calcium-based filter is based on the same principle as in the Calcium-based filter beds for which the patent application was submitted by WEREC in January 2016 (patent application 1630004-8), with distribution pipes in a bottom layer from which the water rises upward through the calcium-based material into a collecting layer. The technical solution for the present treatment system is completely different since the calcium-based filter is incorporated into pipe/tube modules with the associated necessary technical adjustments, and since it is part of a treatment system that also removes oil compounds and heavy metals. Sizing and dimensions of the present system are also different because flow variations are much larger in areas where impervious surface areas make up a larger portion of the land use than in agricultural areas. The filter must therefore have the capacity to receive considerably larger flows without substantial reductions in the removal capacity. The amount of filter material required per hectare catchment area is many times greater in urban areas.

Special description

Storm water treatment system including a biological filter step and a calcium- based filter in pipe/tube cassettes.

The intake (1 in drawing 1 ) of the treatment system shall take in water up to a maximum amount (liters per second) over which the water overflows and runs past the treatment plant in a parallel pipe. The water intake is therefore placed

immediately upstream of an overflow edge in the storm water pipe system, the top of the intake pipe being at the level of the overflow edge. The intake hole is protected so that twigs, leaves, and debris do not come into the intake.

Water flows to the treatment system through an intake hole (1 in drawing 2) in a pipe, usually of PVC. The pipe has a dimension in the range of 1 10-400 mm. The intake hole size is adjusted to the maximum intake flow, which may be 5-300 l/s. Around the pipe is a cylinder (2 in drawing 2), which is made of stainless steel or aluminum and perforated with tightly placed 5-10 mm holes, or optionally with grid/steel mesh with 5-10 mm holes. This cylinder is a protection against debris, leaves and living organisms, and forms part of the invention in patent application 1630004-8 submitted by us in January 2016. Therefore, permission to use the cylinder in this system is required. It is noted that WEREC AB owns both that invention and the present.

From the intake, water runs in a pipe with a diameter of 110-400 mm to the first filter step in the system, a cassette typically of plastic and / or glass fiber of size 2-10 m ³ (2 in drawing 1). If the catchment area is large, several parallel cassettes can be included in the system. The water is led to a distribution pipe system consisting of parallel, perforated pipes with diameter 50-160 mm (3 in drawing 1 , 3 in drawing 2) attached to the cassette roof. From the distribution pipe system, the water is sprayed over the filter material, which is based on bark, for example bark shavings, or on peat. The biological filter material removes oil compounds and to some extent heavy metals from the water. The water flows down through the filter material layer 30-100 cm thick, after which it reaches the collecting layer consisting of a collection pipe system (4 in drawing 1 , 4 in drawing 2). The collection pipe system consists of parallel, perforated pipes 50-160 mm in diameter, connected to the outlet pipe having a diameter of 110-400 mm.

From the cassette/cassettes outlet pipe, the water flows to the second step of the treatment system; a calcium-based filter in one or more parallel coupled pipe cassettes (5 in drawing 1 , 5 in drawing 2) that removes phosphorus and heavy metals.

Each pipe cassette typically has a length in the range of 3-50 meters, and a diameter in the range of 800-3000 mm. The number of pipe cassettes is typically 1-5 but may be larger. The number and size of the pipe cassettes are adapted to the maximum flow the treatment system is designed to be able to receive, which in turn depends on the size of the catchment area and the percentage of impervious surface in the catchment area.

Internal development at WEREC, at the operational, full scale calcium-based filter beds we have installed, has led to knowledge about the percentage of phosphorus in the water that is removed with different residence times. Our flow volume evaluations have also led to knowledge of the fall height (difference between the water level at the point of entry and at the outlet point) required for water to be flowing through the filter with the intended velocity and residence time given the specific resistance (pressure drop) of the calcium-based material. The technical solution has been designed to be used without the use of electricity. The water is led through the filter using gravity.

The water flows into the calcium-based filter step from the first step of the treatment system in pipes of diameter 1 10-400 mm.

The water is led to the bottom of the pipe cassette where the water is distributed to parallel, perforated distribution pipes (6 in drawing 1 , 6 in drawing 2) which are lying in a 20-30 cm layer of macadam and have a diameter of 50-160 mm, typically 1 10 mm. From the distribution pipes, the water is distributed evenly into the bottom of the bed. Above the macadam layer is the layer with the calcium-based material (7 in drawing 2), usually Filtralite-P but the calcium-based material may also consist of Hyttsand, Polonite or any other similar calcium-based filter material. As mentioned, the invention does not include the filter material itself, but only the technical solution. The water is pressed through the filter material layer which is typically but not always 60-120 cm deep. The calcium filter material used has a grain size in the range of 0-8 mm. The pressure drop that occurs when water is led through the material is the basis for the distance between the parallel distribution pipes in the bottom layer, which in the present solution for storm water is with 40-100 cm distance between the pipes.

On the upper surface of the filter material lies the collection pipe system consisting of perforated pipes of diameter 50-160 mm, typically 110 mm (7 in drawing 1 , 8 in drawing 2) leading to an outlet pipe (8 in drawing 1 , 9 in drawing 2). The water rises through the collecting layer, seeps into the perforated pipes and flows to the outlet pipe and further to the main pipe in the storm water system (9 in drawing 1).

The pipe cassettes are sealed with welded ends at both ends, with holes for the intake and outlet pipes (diameter 110-400 mm). Each pipe cassette has depending on its length 1-8 manholes (10 in drawing 1 , 10 in drawing 2). Through the manholes, exhausted filter material is removed by suction and new filter material is blown into the cassette every 10-15 years.