Constructed wetlands - The natural way of treating waste water

Wastewater consists of water with organic suspended soils such as soap, depending on the origin of the pollution. As soon as the dirty water is flowing through the substrate of the facility, a "biological lawn" forms on the surface of the granulate material which is the medium for rapidly colonizing micro-organisms.

Carbon and nitrogen in the slop serve the microbes as nutrients. They are eliminated in aerobic and anaerobic processes, while phosphates are removed by sorption. The water coming off the constructed wetland can not be drunk. It is almost clean, but not pure enough for consumption. But it can be reused for domestic (toilet flushing) and industrial use as well as for watering the garden or for irrigation.

: Constructed wetland in Germany. Running since 1993 without any maintenance!

Structure and function

In a first process step solids are extracted from the wastewater in septic tanks. The wastewater running now off is piped by pumps or with a mechanical construction into the wetland field. Depending on installation type the wastewater flows through the constructed wetland in horizontal or vertical direction.

The field consists of sands and gravel in various granulations, endemic plants like helophytes grow on its surface (and, by the way, offer a beautiful sight). The roots penetrate the gravel-sand-bedding, ventilate it and keeps it hydraulically permeable.

Visual: 1. Branch; 2. Rain spillway basin; 3. Technical station; 4. Septic tank; 5. Constructed wetland; 6. Downspout

Ability of constructed wetlands to clean waste water

Despite fluctuating contamination (red line) properly planned, installed and maintained constructed wetlands can continuously match the different benchmarks like BSB, CSB und NH4-N (blue line below).

Fields of application

Constructed wetlands require 1,5 up to 3 m² of area for every inhabitant connected.

But not only where the area necessary is available at low cost the wetland can be operated economically. For communities or companies it mostly is the better choice to purify domestic wastewater from households, camping sites and hotel plants; likewise the wastewater from cities and municipalities; and sewage of commercial origin (e.g. slaughterhouses, dairies, tannery, etc.) can be cleaned reliably.

Medium discharge value

COD 20 - 50 mg/l

BOD 5 - 20 mg/l

N total 5 - 18 mg/l

P tot 1 - 2 mg/l

Decentralised waste water treatment in China, Shanghai, HuaXin

The city of HuaXin lies in the larger area of Shanghai. The wastewater situation required an ecological and economical solution. The demand of the local government was to reach this result, the local benchmarks must be met.

May 2003: HuaXin / Shanghai / China One year later: The vertical flow constructed wetland was settled into the channel. The first construction period was designed for a daily load of 80 m³. An extension for 600m³/d is planned.

The benchmarks for Shanghai to be matched have been: (DB31/199-1997):

CSB 100 mg/l, TOC 15 mg/l, BSB5 30 mg/l, NH4-N 15 mg/l,

Achieved results: CSB < 50 mg/l, TOC < 10 mg/l, BSB5 < 10 mg/l, NH4-N < 10 mg/l,

: Decentralised and sustainable waste water treatment in Shanghai, inside the living area of the population. Ideal combination of German planning and local production.

Benefits of constructed wetlands

The construction materials are available everywhere and do not have to be imported.
The technology itself is easy to maintain.
As the system is nature-oriented longevity is proven.
Expenses for investment and maintenance amount about half compared with conventional purification systems.
First attempts to clean water with constructed wetlands in Germany took place in the early 70's. Meanwhile more than 50,000 plants provide reliable performance.
Successful track record available in EUROPE (Germany, Austria, Switzerland, Albania, Hungary, Spain, France, Bulgaria, Greece), AMERICA (Mexico, Argentina, Chile, Paraguay, Bolivia) ASIA (China, Thailand)

Examples

: A large number of running systems that proof their proper functioning in Germany and abroad. Whether for private purposes, waste water treatment for whole communities or industries.