The principle of biological wastewater treatment is based on bringing together the microorganisms and pollutants contained in wastewater.
Sewage pollutants constitute nutrients for microorganisms, or nourishment for development. The microorganisms are actually nourished by the pollutants and break them down. Later, this treatment separates the treated wastewater from the microorganisms (sludge). Thus the wastewater undergoes treatment. The difference between the various treatment methods is the technology applied according to the principles stated above.
Wastewater treatment using
Constructed Wetlands or a Reedbed Filter is based on the enormous
content of microorganisms present in the soil and particularly in a plant’s
root system. One gram of topsoil contains some six million bacteria! It is
these microorganisms that do the work in wastewater treatment. This method is
based on channeling the wastewater through a granular bed composed of local
soil and organic materials, which is built into a trench with suitable sloping
sides. [See proposed plan.]
Vegetation is planted in the bed and is characterized by
its ability to grow and develop in a wastewater environment, and its roots have
the ability to conduct oxygen into the root system. In this way both
aerobic and anaerobic process
are ensured. The common
reed (Phragmites),
for instance, that has
a lifespan of 150-200 years, is most suitable for these requirements.
A rich population of microorganisms develops in the root system and adapts itself to the type of pollutants present in the wastewater. As mentioned earlier, the microorganisms are nourished by the pollutants.
The organic matter in the wastewater breaks down into stable compounds and most
of it is released into the atmosphere. As the process is continuous and natural
there is no formation of surplus sludge.
Nitrogen compounds such as ammonia in wastewater break down during
nitrification and de-nitrification. In addition, phosphorous connects to the
bed particles.
The wastewater treatment process takes place with the assistance of a number of
systems:
• Physical - precipitation, filtration, absorption and evaporation.
• Chemical– absorption, hydrolysis, oxidization.
• Biological– bacterial metabolism, metabolism by vegetation.
When building a Constructed Wetland certain steps are taken to seal off and prevent pollution of outside water systems. After the system has been run in it does not require maintenance, and certainly no ongoing maintenance. There is no need to tend the vegetation, there are no energy and material costs and no fear of system failure. The quality of the treated wastewater is of the highest, and in Europe it may be channeled into streams. Treatment using
eco-technical vegetation obviates the problem of odors, as the gases released during anaerobic processes are absorbed into the particles of clay and colloids present in the bed, which are highly absorbent. There is also no problem of mosquito larva incubation as the wastewater flows underground and the topsoil is dry.Over the past decade planning Constructed Wetland has become more sophisticated and has expanded. Research and field experience have brought with them optimum usage of hydraulic conduction and control of the inflow of wastewater into the system, and removal of pollution. Today, Constructed Wetland is used for treating numerous types of wastewater such as:
• Sanitary wastewater – urban drainage.
• Industrial wastewater – food and chemical industries, coating processes
and heavy metals, the petroleum industry.
• Vehicle washing wastewater and highway residues, polluted runoff water.
• Landfill wastewater.
• Stream purification.
• Agricultural wastewater – dairy farm dung, milking parlors, pig farms.
This is a high quality treatment that can be controlled according to requirements. Scenting solid waste (dairy farm sludge) containing particularly high concentrations of pollutants can be preplanned using a system that would lower the concentration of pollutants to the level of sanitary wastewater. Thus this wastewater can be integrated into regional purification facilities without an additional fee.
Treatment of sewage with Constructed Wetland has a number of notable
advantages:
• No electricity, motors, or supplementary chemicals.
• No maintenance costs – no need to treat the vegetation, no need for a
maintenance contract.
• Environmentally-friendly solution – the purification system becomes part
of the landscape and natural surroundings.
• Reliability and flexibility – implementation of the system is not
sensitive to chance changes in wastewater flow and composition.
