D-Rainclean Pollution Control System from Hoofmark (UK) Ltd - Technical Details
Heavy Metal Sorption/Desorption And Precipitation
How cleansing of pollution run off is achieved with the D-Rainclean pollution control system.
Nickel is chiefly held by sorption, whilst lead, cadmium, copper and zinc are captured in D-Rainclean by sorption and precipitation with the utilisation of petrol interceptors.
Cadmium, zinc and nickel belong to the mobile (relatively easily displaced) heavy metals group. With cadmium, a particularly and constantly high pH value, D-Rainclean is therefore very important in the cleansing of pollution run off.
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 for Microbiological Treatment of Pollution Run Off
In the warm seasons of the year particularly, the microbiological break down capacity of the soil provides an important method for treating heavy metal pollution. A prerequisite for this cleansing of pollution run off 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 metre of filtration channel in the bottom for the control of pollution run off.
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).
D-rainclean Filtration Channel Components
Test Limits For Soil-Groundwater Accordance With Federal Soil Protection Law.
| Substance | Symbol | Limit |
|---|---|---|
| Arsenic | As | 10µg/l |
| Lead | Pb | 25µg/l |
| Cadmium | Cd | 5µg/l |
| Chromium | Cr | 50µg/l |
| Copper | Cu | 50µg/l |
| Nickel | Ni | 50µg/l |
| Mercury | Hg | 1µg/l |
| Zinc | Zn | 500µg/l |
The sorption isotherms for the relevant heavy-metals lead and zinc have been recorded for soil and D-Rainclean.
Laboratory Investigations of the D-Rainclean method for treating heavy metal pollution
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.
D-Rainclean Graph
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 m/s 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.
D-Rainclean is Supplied 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 broken down. 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 the 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 cmolc/kg is aimed for. The value is achieved to a considerable extent by the addition of clay preparations in pelletised form and zeolites.
| Substance | Exchange Capacity |
|---|---|
| KAKpot Acetate | minimum 40 cmolc/kg |
| KAKpot | minimum 20 cmolc/kg |
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 |
D-Rainclean Product Image with Dimensions
Working Life of D-Rainclean Pollution Control System
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).
Frequently Asked Questions about D-Rainclean
See our FAQs page for questions about D-Rainclean.