D-Rainclean^®

the soak-away channel with filter medium.

D-Rainclean^® - the way forward for rain water treatment,
in compliance with ATV Regulation Work Sheet A 138 for contaminated surface water.

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 the 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 3 mg/km of benzene, petrol engines with a catalyst around 0.5 mg/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 1000 vehicles per kilometre of road per year. Along with difficult to break down organic compounds, zinc, cadmium, lead, copper, chromium and nickel are emitted. Due to the abrasion of brake linings the heavy metals nickel, chromium, lead, zinc and particular copper occur.
With road wear on asphalt roads, it is predominantly mononuclear and poly-nuclear aromatic hydrocarbons that are encountered, particularly »PAK«.
Corrosion on bodywork releases heavy metals dependent on the paint mix and the steel alloys used. Hydrocarbons and also lead, zinc, chromium and copper have been found in the coolant along with mineral oil.

The Solution
The above contaminants are cleansed by D-Rainclean^® before reaching the ground water, by

     filtration
     adsorption 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 D-Rainclean^® in different ways :
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 is one of the mobile, relatively easily displaced, heavy metals. With cadmium particularly a constantly high pH value in D-Rainclean^® is therefore very important. In soil, lead behaves in a very immobile way.
In a similar way to copper, lead is tied up by specific adsorption processes. Mercury is mainly bonded to the organic substance in D-Rainclean^® in a very immobile form. At higher pH values, chromium is mainly tied up in a complex way with iron ions into very difficult to dissolve Cr(OH)3 and Cr2O3.

Water retention capability
In the warm seasons of the year particularly, the microbiology of the soil provides important degradation capacity. A prerequisite for this is adequate moisture in the D-Rainclean^® filter medium. 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^® soak away channel also provides a water reservoir at the bottom of the container, of approx. 3.0 litres per linear meter of channel.

Sorption of contaminants
With the set kf value of 1-5 x 10-4 m/s (permeability to water) the dwell time of the water flowing through the D-Rainclean^® soak away channel is 10-50 minutes. After the water has passed through the D-Rainclean^® filter medium, the test figures for assessing the effective path from soil to groundwater in accordance with ß 8 Clause 1, Paragraph 2, No. 1 of the Federal Soil Protection law are not reached (see table below).

Test figures Soil-Groundwater according to 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 medium 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 medium can be regarded as exhausted. Depending on the density of traffic this event will occur after some 15-20 years. After that, the D-Rainclean^® filter medium should be replaced.

Water permeability coefficient
The D-Rainclean^® filter medium has a water permeability coefficient of 1-5 x 10-4 m/s and thus an adequate soak away rating. In addition to this D-Rainclean^® guarantees an appropriate dwell time for the water being cleaned.
The balance between a filter medium free of silting and an adequate dwell time for absorption of the contaminants in the water has been achieved with the D-Rainclean^® filter material. In the development process, priority was given to adequate long term water permeability– even after 20 years.

Organic contaminants
D-Rainclean^® filter medium has an organic matrix that promotes the capture and degradation of organic contaminants. Mineral oil 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^® soak away 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 capability and will lie as a thin coating on the surrounding granules. In this ìpendularî 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 medium has a void space of at least 60%.

Suitability as a planting site
It is not necessary to plant D-Rainclean^® soak away channel. In the event that planting of the D-Rainclean^® soak away channel is required, the D-Rainclean^® filter medium was developed to be very low in nutrients. The selected ground cover plants will nevertheless find an adequate supply of nutrients.

Suggestion for planting
If the D-Rainclean^® soak away channel is used as an open channel (i.e. without cover) it can be planted e.g. to each compartment 2 pachysandra or 2 mahonia and 2 vinca minor or 1 cotoneaster in varieties.

pH value
The carbonate buffer of the D-Rainclean^® filter medium is above pH 7.0.

Cation exchange capacity
The cation exchange capacity (KAKpot) defines the maximum absorbable quantity 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 pelleted form and zeolites.

KAKpot Acetate:             minimum 40 cmolc/kg
KAKpot :                     minimum 20 cmolc/kg

The capability of the D-Rainclean^® filter medium to function as an ion exchanger guarantees the capture of heavy metal ions. Washing out of the heavy metals is prevented, which provides active groundwater protection.

Oil binding properties
The D-Rainclean^® has very good oil binding properties.
Damp D-Rainclean^® filter medium can take 10 litres of oil per metre of soak away channel, without the oil getting into the subsoil in the following 24 hours.
It is recommended that after an oil spillage, the D-Rainclean^® filter medium is removed from the soak away channel within 24 hours and disposed of properly.

Major properties of the D-Rainclean^® filter medium

Water permeability coefficient       Water storage capacity             Cation exchange capacity         KAKpot Acetate                                Absorption capacity                       pH value                                          N (NO3)                                             P2O5 available                               K2O available

1-5 x 10-4 m/s (kf-value) mind. 58 % mind. 20 cmolc/kg mind. 40 cmolc/kg >Pb2+ >Cu2+>Zn2+ >7,2 < 100 mg/l < 100 mg/l < 100 mg/l

Application Examples
D-Rainclean^® soak away channel, open version, functional principle

D-Rainclean^® soak away channel, open version with overflow into natural ditch

D-Rainclean^® soak away channel, enclosed version with paved surface on both sides

D-Rainclean^® soak away channel, open version with D-Raintanks^®