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                                REED-BED TECHNOLOGY TO TREAT WASTE WATER                    

 
The reed bed system is a self contained, artificially engineered, wetland ecosystem for treatment and recycling of sullage, sewage and industrial effluent.  It is designed to optimize the microbiological, chemical and physical processes naturally occurring in the reed bed.  Wetland plants, such as reeds, transfer atmospheric oxygen down through their roots in order to survive in waterlogged conditions.  This creates both aerobic and anaerobic soil conditions, allowing a rich microbial diversity comprising of bacteria and fungi use organic pollutants as a food source, breaking down a wide range of organic chemical products.  So, chemical are not simply stored in the reed bed and are actually degraded into harmless smaller components.  Other contaminants comprising of heavier metals are transformed from a toxic, mobile state into fixed state by complex chemical reactions in the soil.  Also adsorption capacity of soil acts as a buffer for peak or shock effluent loads.

The complexity of microbial life and powerful reactions within the root zone of the soil based reed bed system results in extraordinary water cleaning or treatment capacity.
  

Components of reed bed system
 Resembling a beautiful garden of flowering wetland plants, the reed bed system comprises of the following components;

                          A sedimentation tank
                     A reed bed consisting of
                       -    Filling media
                       -    Acclimated, aerobic, anaerobic and facultative bacteria & fungi
                       -    Selected indigenous wetland plants (phragmite species)

            Combing mechanical filtering, chemical precipitation and biological degradation in one step, the system effectively removes suspended solids and organic matter in the form of BOD and COD

  

Working of Reed bed system  

After primary settling in the sedimentation tank, the breakdown of contaminants is achieved by the controlled seepage of wastewater through the root zone of the selected wetland plants.  Organic pollutants are broken down as a food source by microorganisms and the plants, while the other contaminants, such as metals are fixed in the humic acid (via cation exchange bonds) in the soil or mineral substrates in which the plants are rooted.  During this process suspended solids, BOD and COD are reduced to an acceptable level. 

  This method requires a detention period of at least six hours but provision of eight hours detention time is preferable.  Hence, an effective and efficient treatment of wastewater is produced within the Reed bed in a sustainable and natural manner.  There is no ongoing electricity cost to run pumps and air blowers, the power source is the sun which powers the plants through the natural process of photosynthesis.
The system will not clog up over time as the design ensures that the rate of breakdown exceeds the rate of loading in the Reed bed, so the performance of a reed usually increases not decreases, over time. Biomass is removed and not permitted to clog the voids of the gravel bed.  This treatment involves a careful and continuous thinning of the growth so that biological activity does not get reduced.  The reed so removed can be utilized and they have considerable commercial value.

 

The Role of Plants

The specially selected plant species( Phragmite species e.g. Phragmite karka and Typha angustus) with in the Reed bed have the following three main functions:
 

    They provide the means for secondary restructuring of the soil system.  The very extensive root and rhizome system creates channels for the water to pass through and also keeps the soil open through the constant growth.

    The roots of the aquatic plant introduce atmospheric oxygen down into the body of soil, facilitating the diversity of microorganisms to flourish around the plant roots.  It is essential for the effective breakdown of various organic and inorganic compounds.

    The plants are capable of taking up a certain amount of nutrients from the wastewater itself.
   

 

Features of the Reed Bed System

1.   Operation and maintenance free: The reed bed system has no mechanical/moving parts.  There is also no wastage of energy since mechanical aeration is not needed.

2.   Clean and efficient: Since all chemical, physical and biological changes occur underground, there are no strong odours or sludge formation.

3.   Self-sustaining and long lasting: Once installed and become operational, the reed bed system can sustain itself for more than 40 years.

4.   Adaptability: The reed bed systems are suitable for concentrations from a few mg/l 20,000 mg/l of COD and 400 mg/l of nitrogen.  Their capacity varies from about 1m3/day to more than 10,000 m3/day.

5.   Can handle difficult effluents: As the reed bed system has diversity of microbes and the wetland and the plants, it can adapt itself to diverse types and varying shock loads of effluents, including difficult waste waters containing.

        Organic compounds like Chlorinated hydrocarbons, dyes and sulphur
    containing aromatics.

        Nitrogen compounds such as ammonia and nitrates.

        Sulphur compounds like sulphides and sulphates

        Heavy metals and pathogens

Applications 

The reed bed system is effective in treating effluent from
                 -    Rural areas
                 -    Food processing industry
                 -   Breweries
                 -   Animal husbandry
                 -   Sullage and sewage from residential, institutional and industrial
                     complexes. 
                 -   Chemical industry

 

 

Benefits

              It offers a low cost, low maintenance and sustainable solution to effluent
               problems.

    A single reed bed system is able to treat effluents from a number of sources.

    This method requires smaller space as compared to conventional modes of wastewater treatment including trickling filters.

    The operational cost of this mode is also less, as no trained staff is required for its operation.

    The treated effluent can be safely used for irrigation and the crops grown have higher yield and do not create any health problem.

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