The location of ozone use in WWT will determine the goal of treatment. A simple way to explain a classical WWT will be break up the process into:
Decolourisation & Deodorization
Due to new government restrictions for the discharge of colored water and the increasing discharge costs of waste water Ozone oxidation for decoloration is becoming more and more popular. The effected industries are companies producing textiles, dyes, paper or chemicals. Additional to the very successful results in decoloration, Ozone brings further benefits like desinfection, improved BOD/COD-ratio, reduced AOX and reduction of odour. Waste water or recycling water can be treated in an environmentally-friendly way without any residuals or concentrates by using Ozone.
Some of the more common toxic substances that are found in waste water (Industrial and Municipal too) are:
We are quite aware of toxic substances such as pesticides, phenolic compounds that has been addressed by pollution control authorities in India. However the world as woken up to a new set of compounds know as EDC.
EDCs are micro pollutants
Effluents of biological treatment plants for municipal sewage still contain substances that prevent a reuse: Reasons for waste water disinfection can be removal of :
These can be responsible for causing several water borne diseases.
Some of the international regulations for waste water disinfections are:
The table below gives some idea of the choice of different technologies available for waste water treatment. Mostly the choice of a particular technology is governed by two criteria:
|INCINERATION AND EVAPORATION||15000 – 100000||1M3 /hr to 10M3/hr|
|ANEROBIC BIOLOGICAL TREATMENT||15000 – 100000||10M3/hr to 100M3.hr|
|WET AIR OXIDATION||8000-50000||5M3/hr to 100M3/hr|
|AOP ( UV /H2O2/FENTON )||1000-6000||0.5M3/HR TO 10M3/HR|
|AEROBIC BIOLOGICAL TREATMENTINCLUDING ACTIVATED SLUDGE/MBR/BIO FILTER||15 - 10000||10M3/HR-10000 M3/HR|
|OZONE||10 - 1200||1M3/HR TO 10000M3/HR|
|ELECTROLYTIC OZONE INCLUDING LBT UV SYSTEMS||0.1 - 0.7||0.5M3/HR TO 100M3/HR|
From the above it can be seen that Ozone technology is not restricted due to the flow of the effluent . However the choice of this technology will entirely depend on the COD content. The choice of Ozone will depend on the goal of the treatment.
Sludge handling costs have now become one of the main operating costs ( even up to 40-50% of the total costs of the waste water treatment ) for waste water treatment plant operators. Especially in the textile industry, major sludge formation is due to the use of flocculants for the removal of color during primary and secondary treatment. In spite of this large usage of flocculants, color removal of certain types of dyes has not been very satisfactory. The COD reduction has also not been very consistent with classical treatment. Ozone has been tried with the main goal of sludge reduction. Large amounts of Ozone are required for sludge reduction if used during primary or secondary treatment process but results have been obtained. However it is up to user to evaluate the costs associated with the use of Ozone compared to the costs incurred in handling the sludge generated by conventional treatment.
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