D-Rainclean® Pollution Control.
The Problem
On heavily trafficked roads and adjacent parking areas, between 5 and 15 metres from the carriageway, contaminants reach critical concentrations and regularly exceed the threshold values.
Composition of Contaminants
Exhaust gas, abrasion dust, losses due to drips and corrosion are the most important sources of emissions in road traffic. In the combustion chamber of engines a large number (up to 150) of polycyclic aromatic hydrocarbons (PAK) are formed. Apart from “PAK”, monocyclic aromatics such as benzene, toluene, xylene and phenol are given off. Petrol engines emit around 3mg/km of benzene, petrol engines with a catalyst around 0.5mg/km. Over and above the exhaust gases, chromium, zinc, copper and nickel are given out, in total around 0.1-1 mg/km plus around 0.05 mg/km of cadmium.
Tyre abrasion alone is taken as 120 g per kilometre of road per 100 vehicles, per year. Along with difficult to break down organic compounds, zinc, cadmium, lead, copper, chromium and nickel are emitted. Due to abrasion of brake linings the heavy metals nickel, chromium, lead, zinc and particularly copper occur.
With road wear on asphalt roads, it is predominantly mononuclear and poly-nuclear aromatic hydrocarbons that have to be reckoned with, particularly “PAK”. Corrosion on bodywork releases heavy metals dependant on the paint mix and steel alloy used. Hydrocarbons, lead, zinc, chromium and copper have been found in coolant along with mineral oil.
The Solution
The above contaminants are cleansed by D-Rainclean® before reaching the ground water, by filtration, absorption and depositing, ion exchange, precipitation and biological breakdown. Soil contamination and pollution of water courses and groundwater is prevented.
Heavy metal sorption/desorption and precipitation
Heavy metals are tied up in different ways in D-Rainclean®. Nickel is chiefly held by sorption, whilst lead, cadmium, copper and zinc are captured in D-Rainclean® by sorption and precipitation. Cadmium together with zinc and nickel belongs to the mobile, relatively easily displaced, heavy metals. With cadmium, a particularly and constantly high pH value in DRainclean® is therefore very important. In soil, lead behaves in a very limpid way. Similarly to copper, lead is tied up by specific absorption processes. Mercury is similarly attached to the organic substances in D-Rainclean®.
At higher pH values, chromium is mainly tied up in a complex way with iron ions into very difficult to dissolve Cr(OH) and CrO.
Water Retention Capability
In the warm seasons of the year particularly, the microbiology of the soil provides important break down capacity. A prerequisite for this is adequate moisture in the filter media. This is achieved by:
• a large void volume
• a high proportion of organic substances and clay minerals
• a high proportion of special water absorbers
The D-Rainclean® filtration channel also provides a water reservoir of approx. 3.0 litres per linear meter of filtration channel in the bottom.
Sorption of Contaminants
With the set kf value of 1 – 5 x 10–4 m/s (permeability to water) the dwell time of water flowing through the D-Rainclean® filtration channel is 25–30 minutes. After the water has passed through the filter media, the test limits for assessing the effective path from solid to groundwater in accordance with § 8 Clause 1, Paragraph 2, No. 1 of the Federal Soil Protection law are not breached (see table below).
| Arsenic | As | 10 | μg/ |
| Lead | Pb | 25 | μg/ |
| Cadmium | Cd | 5 | μg/ |
| Chromium | Cr | 50 | μg/ |
| Copper | Cu | 50 | μg/ |
| Nickel | Ni | 50 | μg/ |
| Mercury | Hg | 1 | μg/ |
| Zinc | Zn | 500 | μg/ |
Test limits for Soil-Groundwater accordance with Federal Soil Protection Law.
The sorption isotherms for the relevant heavy-metals lead and zinc have been recorded for soil and D-Rainclean®.
Laboratory Investigations
The D-Rainclean® filter media has distinctly better absorption results than a “good soil”. For zinc, the outlet figures show that, as a mean, around 90% of the zinc is absorbed. With lead, the absorption is considerably higher at 99%. When the concentration limits of the test figures for assessing the effective path from soil to groundwater are reached, the absorption capability of D-Rainclean® filter media can be regarded as fully utilised. Depending upon the density of traffic this event will occur after some 15–20 years. After that, the D-Rainclean® filter media should be replaced.
Working life of D-Rainclean® related to zinc at a “medium contamination loading” (Category 6- 8 ATV A138).
Water Permeability Coefficient
The D-Rainclean® filter media has a water permeability coefficient of 1 – 5 x 10–4 and thus an adequate soakaway rating. In addition to this D-Rainclean® guarantees an appropriate dwell time for the water being cleaned. The balance between a filter media free of silting and at the same time having a high pH value has been achieved with the D-Rainclean® material. In the development process, adequate long term water permeability has been proven – even after 20 years.
Complete with filter media
In accordance with ATV Regulation A138 for contaminated surface water.
Organic Contaminants
D-Rainclean® filter media has an organic matrix that promotes the capture and dispersal of organic contaminants. Mineral hydrocarbons and halogenated volatile hydrocarbons in the concentrations and the state (residual distribution) in which they occur on compacted driving surfaces are well brokendown. They are thus removed from the system. Since the micro-organisms in the D-Rainclean® filtration channel settle on wet surfaces, the total surface of D-Rainclean® is an important performance feature in the breakdown of organic materials. This is why D-Rainclean® has an extremely large surface area.
Void Volume
If oil drips, for example get in to the D-Rainclean®, the oil will find a large void space in the area saturated by water flow. Due to this, the oil will lose its flow capacity and will lie as a thin coating on the surrounding granules. In this “pendular” distribution the oil is best able to be attacked by the micro organisms. A prerequisite for this is large void space in the filter material. D-Rainclean® filter media has a void space of at least 60%.
Suitability as a Planting Site
It is not necessary to plant D-Rainclean® filtration channel. In the event that planting of the D-Rainclean® filtration channel is required, the D-Rainclean® filter media was developed to be very low in nutrients. The selected soil cover will nevertheless provide an adequate supply of nutrients.
pH Value
The carbonate buffer area of the D-Rainclean® filter media is above pH 7.0.
Cation Exchange Capacity
The cation exchange capacity (KAKpot) defines the maximum absorbable quantities of cations. Heavy metals are cations. The exchange capacity of the D-Rainclean® thus also represents places for capturing heavy metals. The exchange processes are characterised by the type of ion. A KAKpot of at least 20 cmolckg is aimed for. The value is achieved to a considerable extent by the addition of clay preparations in pelletised form and zeolites.
| KAKpot Acetate | minimum 40 cmolckg |
| KAKpot | minimum 20 cmolckg |
The ability of the D-Rainclean® filter media to function as an ion exchanger guarantees the capture of heavy metal ions.
Washing out of the heavy metals is prevented, which results in active groundwater protection.
Major properties of the D-Rainclean® Substrate
| Water permeability coefficient | 1-5 x 10-4 m/s (kf value) |
| Water storage capacity | minimum 58% |
| Cation exchange capacity | minimum 20 cmolc/kg |
| KAKpot Acetate | minimum 40 cmolc/kg |
| Absorption capacity | > Pb2 + >Cu2 + >Zn2 + |
| pH value | >7.2 |
| N (NO3) | <100mg/l |
| P2O2 available | <100mg/l |
| K2O available | <100mg/l |
Working Life
Light contamination – working life minimum 20 years
Roof surface water, yard surfaces, cycle and foot paths, parking areas, roads with a maximum 300 traffic movements per day, residential areas and comparable commercial areas (Category 1 – 5 ATV A 138).
Medium contamination – working life minimum 18 years
Roof surface water in commercial and industrial areas with significant air pollution, roads with 300 to 5000 traffic movements per day (Category 6 – 8 ATV A 138).
Severe contamination – working life of minimum 15 years
Surfaces in industrial areas, car-parks with frequent interchange of vehicles, roads with 5000 to 15000 traffic movements per day (Category 9 – 11 ATV A 138).
The construction of the D-Rainclean® filtration channel in special plastic with a high load bearing capacity enables:
• fulfilment of the requirements of the ATV regulation A138
• space saving, easy and secure installation
• freedom of design for the surrounding areas
• ability to be traversed by cars
• protection from compaction of the filter media
• ease filling or replacing
Suggestion for Planting
If the D-Rainclean® filtration channel is used as an open channel (i.e. without cover) it can be planted e.g. to each
compartment 2 pachysandra or 2 mahnia and vinc minor or 1 cotoneaster in varieties.
Filtration Channel Components
Application Examples
 |
 |
| D-Rainclean® filtration channel, open top. | D-Rainclean® filtration channel, open top with overflow into natural filtration channel. |
 |
 |
| D-Rainclean® filtration channel, enclosed with paved surface on both sides. |
D-Rainclean® filtration channel, open version with D-Raintank®. |
 |
|
| Car-park installation options enclosed or open top (also planted) with overflow into D-Raintank®. | |