DE19750811C2 - Filter mat for the filtration and sorptive purification of leachate in rainwater infiltration - Google Patents

Description

The invention specified in PATENT Claim 1 is based on the problem that precipitation is derived in separation systems in many metropolitan areas and then the rainwater is seeped away in the soil. Through atmospheric deposition and the redissolution of substances The rainwater is contaminated with pollutants via the drainage path (Precipitation-related entry of dirt into the sewage system, Karlsruhe Be richte zur Siedlungswasserwirtschaft, 1993, issue 73, 537 pages), which leads to a Contamination of the soil and groundwater. To the To design pollutant inputs in an environmentally friendly manner, the soil depending on the infiltration technology (surface or selective infiltration), only rainwater for a certain period of time. This time space is made up of the composition of the rainwater and the soil body-dependent (High-rate land treatment I, Infiltration and hydraulic aspects of the flushing meadows project, Journal water pollution control federation, 1974, vol. 46, No. 5, page 834).

The pollutants in the rainwater can be suspended in solids, in persistent organic compounds, in heavy metal and inorganic Ver bonds are divided. The pollutant effect of the suspended solids is that they are carriers for heavy metal and halogenated hydrocarbons are compounds. These connections can occur during leakage redissolved in the leachate and entered into the soil. Furthermore, the solids can seep into a colmatation of the top layers of soil (High-rate land treatment II, Water quality and economic aspects of the flushing meadows project, Journal water pollution control Federation, 1974, Vol. 46, No. 5, page 844), so that disposal or Rege generation of these layers must be carried out in order to further infiltration enable.

Persistent organic compounds such as e.g. B. PCBs, dioxins, furans, amino organic and metal-organic compounds from motor vehicle traffic or ver combustion processes, undergo almost no biological conversion in the soil and the binding forces on soil particles are low. These two boundary conditions  cause these substances to leak during the leakage process are transported through the soil and into the ground water conductors (report on the results of the research project 02WA9035- 9039, investigations for the detection and evaluation of leaky channels with regard on the danger to the underground, BMFT joint project, 1994, part 2, 46 Pages). The third group of pollutants consists of heavy metal compounds, which in ionic form. These connections can mainly only be in the upper soil are temporarily bound to the soil particles by sorption. The Binding forces on the soil particles and the dissolution of these connections in the leachate depend to a large extent on the value of the metal ions, the redox potential and the pH value in the soil.

Among the inorganic compounds (fourth pollutant group) are the Nitrates, nitrites, chlorides and sulfates pose a hazard to the soil and represents the groundwater. The chlorides and sulfates lead to a salting in the Soil and groundwater caused by the spreading of salt in winter months. The nitrates are only to a small extent in the Rainwater dissolved, their main source of origin are nitrifics processes in the soil. The resulting nitrate can pass through the soil microorganisms, however, due to a lack or insufficient Carbon source in the deeper soil layers cannot be denitrified and ge reaches through the soil body into the aquifer.

To prevent or to prevent the soil filter from colmatating during seepage delay, one or two-layer nonwovens made of geotextiles have been used (Special print from 1st congress "Plastics in Geotechnics", K-GEO 88 in Hamburg, infiltration systems with geotextile filters, German Society for Erd- und Grundbau e. V., 1988, 8 pages). By using these nonwovens only the suspended solids retained. Because the nonwoven materials none special functions for the retention of the other three pollutant groups indicate, these pollutants dissolved in the leachate are almost undiminished in the soil body and subsequently entered in the aquifer.

DE 35 05 076 A1 describes a filter mat for the filtration and sorptive Treatment of leachate known for rainwater seepage, with a first layer in the form of a Fleece is provided for the retention of suspended solids. A yourself subsequent second layer contains an organic adsorbent in the form of  Activated carbon to adsorb biologically persistent organic compounds.

A retention function for inorganic compounds dissolved in the leachate and for heavy metals, the known filter mat does not have. It is therefore required to embed them in layers of clay.

The object of the invention is therefore to develop a filter mat with the broadest possible range of pollutants are removed from leachate can.

This task is ge by the features listed in PATENT Claim 1 solves.

The new filter mat (PATENT CLAIM 1) makes these organic and inorganic compounds as well as heavy metals. The first layer of the filter mat is used for conventional fleece or felt the filtration of the rainwater. The filtration effect of the Filter mat is based on the physical effects of blocking fibers and the Gravity sedimentation in the pores of the tissue.  This allows a large portion of the suspended solids to accumulate as well adhering pollutants on the surface or in the uppermost pore layers of the first filter layer are retained.

The second layer of the filter mat is covered with an organic adsorbent (activated carbon, Activated coke, etc.). The organic pollutant compounds have one high affinity for this adsorbent. The binding of organic pollutants at the active centers (lattice vacancies) of the adsorbent takes place within the be standing temperature levels (≈ 253-303 K air temperature) by electrostatic tables and VAN DER WAALS forces (physisorption).

In the third and fourth layer of the filter mat is a mineral or orga African cation or anion exchange material introduced. As a natural Polyelectrolytes are mainly zeolites based on aluminum silicates or apatite for the cation or anion exchange. The functional Ionic compounds are formed by alkali and / or alkaline earth metal (clinoptilolite, Laumontite) or by fluorine, chlorine or hydroxyl ions (apatite) (apatite, American Geological Institute, Mineralogical Journal, 1989, Vol. 11, No. 3, 104 pages). The pollutants are bound by exchanging the free ions within the exchange matrix against the heavy metal or inorganic Ions. The selectivity of the ion-ion bonds and the bond strength are proportional to the size and value of the exchangeable ions, to the ions concentration, the reaction time and the physico-chemical properties properties of the exchange matrix.

Because of these selectivity properties, the heavy metals, such as, for. B. mercury, lead, copper, chromium and zinc, and ammonium ions to an increased extent against the "natural" metal ions of the alkali (Na ⁺ , K ⁺ ) and alkaline earth metals (Mg ²⁺ , Ca ²⁺ ) ( An evaluation of the use of natural clinoptilite to remediate metals contaminated water, Geologi cal Society of America, 1995, Vol. 27, No. 4, 50 pages).

The anion exchange in the fourth layer mainly takes place through fluorine, chlorine and hydroxyl ions. Because of the fact that especially the chlorides in this Layer to be bound sorptively can only be used as exchange materials Zeolites with free fluorine or hydroxyl ions, such as. B. apatite can be used.

However, the advantages achieved with the invention are based not only on the sorptive  Removal of the pollutant molecules from the leachate, but through the on The selectivity is related to the order of the different layers of the filter mat improved on the connections to be removed as well as the soil revitalization.

Through the use of an organic adsorbent, a certain selectivity of the pollutant molecules reached on the adsorption heat or the polarity of these substances is due. The less polar the Pollutant molecules are, the higher their heat of adsorption (effect of the Hydro phobia) and the better their binding to the adsorbent surface (activated carbon and its industrial application, Enke-Verlag, 1980, 213 pages). In general decreases the biological persistence of the pollutant molecules with decreasing pola rity (e.g. polarity of aromatic hydrocarbon compounds increases with increasing degree of halogenation and the biological persistence). because through the organic sub punching predominantly retained in the second layer of the filter mat and biodegradable organic substances attracted to the soil leads. These organic compounds serve as microorganisms in the soil Substrate and thereby lead to an increase in microbial activities in the Soil (wastewater irrigation Hiltpoltstein, report on project section 1, teaching Chair for water quality and waste management, Technical University of Munich, 1996, 127 pages), which in turn brings about a soil improvement.

Biodegradation of inorganic compounds such as ammonium and Nitrate is favored within the sorption layers of the mat because of the pollutant retention of the effect is similar to that of the natural soil. Due to the sorptive removal of the persistent organic compounds in the In the second sorption layer, the dissolved oxygen concentration in the leachate remains high, so that in the third filter layer in addition to a physical removal of the A biological conversion can also take place in ammonium. In addition, due to the large specific surface area of the adsorption layer and the cation exchange material the settlement of slowly growing nitrificants günstigt.

The structure of the filter mat leads to partial or full in the fourth layer permanent anaerobic areas and organic compounds as electrons donors for biological implementation are available. These boundary conditions are necessary prerequisites, in addition to a sorptive binding of the chloride, Sulfate, nitrate and nitrite ions denitrify the sorptively bound and im To enable leachate of dissolved nitrate or nitrite.  

Another advantageous embodiment of the invention is set out in PATENT Claim 2 give. By coating the fabric fibers with the adsorbents, the Mass transfer area for the leachate constituents increased and the individual Layers can be made more compact. The use of powder active Coal in the second layer of the filter mat leads to an improved loading ability of the organic adsorbent, because of the shorter diffusion paths in the activated carbon particle has a higher amount of adsorpt (per persistent organic compounds) can be bound. Clinoptilolite and Apatite are widely used natural exchange materials that can be used with little Modify effort specifically for the present invention, so before increases the heavy metals and inorganic constituents of the leachate tie. By homoionization, e.g. B. with sodium ions, the adsorb Capacity of clinoptilolite and selectivity to heavy Improve metal ions. Apatite is predominantly in three natural forms (Fluorine, chlorine and hydroxyl ions in the exchange matrix), of which the Hydroxyl-apatite is ideally suited for the invention, since the Exchange of hydroxyl ions also the chloride and sulfate ions in the leachate get tied up.

PATENT CLAIM 3 specifies the adaptation of the filter mat to different leachate compositions and the regeneration of the be loaded filter mat and the variable adaptation of the filter mat to the be required infiltration area is an improvement. By separating the four Layers through a support grid can change the filtration layer in its thickness and the pores volume as well as each functional layer due to its individual content Sorbents are adapted to the composition of the leachate. So z. B. in the cold season with increased chloride levels in the seepage water the fourth layer through a higher amount of apatite to the changed seepage water situation to be adjusted. When the filter is fully loaded the individual layers can be specifically regenerated depending on the adsorpt (e.g. thermal regeneration for the organic sorbent layer, acid / basic extraction for the exchanger layers). The holding frame for the filter mat is designed so that individual frames overlap each other can be added. This allows the filter mat to accumulate Volume flows of rainwater and the desired seepage rate Adjust the properties of the underbody.  

PATENT CLAIM 4 characterizes a compact embodiment of the filter mat for the use or retrofitting of decentralized infiltration techniques such as B. pipe, shaft and drainage infiltration. Through the fixed Connections of the individual layers reduce the mat thickness and the loose Mats can be sewn into cylindrical or bag-like filter inlays. In the case of trenches, the cylindrical filter inlays can be between wall and filling to be built in. In the case of pipe infiltration, the pipes can be connected to the cylinder shaped filter inlays or with existing pipe infiltration systems can be retrofitted. The bag-like filter inlays are suitable in be special way for shaft infiltration.

An embodiment of the holding frame with support grid and separate layers of the filter mat is described in Fig. 1. The sorption layers 1 , 2 , 3 , 4 , separated by the support grid 5 , are inserted under tension into the grooves of the holding frame 6 . The closed holding frame has a vertical, upright Z-shaped profile on its back. This profile is arranged between the left and right edge and between the top and bottom edge reversed, so that one frame 7 can be inserted in the next overlapping. Due to the weight of the holding frame and the interlocking effect of the individual frames, additional fastening of the frames (screwing, welding or the like) is not necessary.

The use of the filter mat for the surface seepage (infiltration trough) in a support frame system shown in FIG. 2. About the inlet of paved surfaces 8 or a surface-area inlet 13 of the infiltration trough is supplied with the rain water. The maximum water level 9 above the filter mat / holding frame system 10 depends on the amount of precipitation, the infiltration area and the filter mat / underground system. The filter mat / support frame system lies directly on the top floor 11 . This can minimize the cost of installing the system. During the leaching process, the pollutants in the leachate are first bound in the filter mats and then the leachate infiltrates the top soil. The remaining easily degradable organic compounds can be converted microbially in the topsoil and any other leachate constituents that may be present can be bound. After the upper soil has seeped through, the seepage-capable layer 12 is infiltrated by the cleaned seepage water, which subsequently accumulates in the aquifer.

A further application example for the filter mat specified in PATENT Claim 4 is shown in FIG. 3 for the pipe infiltration. The rainwater is supplied to the shaft 16 via the surface inlet 21 in the top floor 14 or the underground inlet 18 . The perforated drain pipe 20 is lined with the cylindrical filter mat 19 . The leachate collected in the shaft is fed to the leachable layer 17 via the filter mat and the drain pipe below the poorly permeable bottom layer 15 . This layer infiltrates the soil with the leachate and drains it into the aquifer.

Claims (4)

1. Filter mat for the filtration and sorptive purification of leachate at Rainwater seepage, whereby in four special layers both the suspended solids and the ge dissolved persistent organic and inorganic compounds as well Heavy metals are largely removed from the leachate. The four Layers are made of fabric, fleece or felt and bonded together (e.g. sewn, matted or needled) or carried out in separate layers and have a layer structure based on natural (e.g. cotton or Wool) or artificial fibers (geotextiles such as polypropylene, polyester, Polyamide). Due to the first layer of the filter mat in the seepage direction of the Rainwater first becomes the suspended solids through Filtra restrained effect. In the second layer is an organic adsorb agent (e.g. activated carbon or activated coke) mixed in, or the fibers coated with the adsorbent to make the biologically persistent orga African compounds in rainwater, such as. B. dioxins and furans from automotive engines or PCBs and halogenated hydrocarbons from combustion processes to bind adsorptively. The third and fourth layer is with one Mixing or sheathing the fibers with a natural or provided synthetic cation or anion exchange material for sorp tive removal of ammonium and heavy metal ions or nitrate, nitrite, Chloride and sulfate ions. 2. filter mat according to claim 1, characterized, that the fibers of the second, third and fourth layers pass through the sorbents are covered, powder activated carbon in the second layer, in the third layer Clinoptilolite and in the fourth layer hydroxyl apatite is used. 3. filter mat according to claim 1 or 2, characterized, that the four layers of the filter mat are separated by support grids and in one Holding frames are joined together.   4. filter mat according to claim 1 or 2, characterized, that the four layers of the filter mat are brought together in a carrier mat.