Thesis - faculty.ait.ac.th - Asian Institute of Technology

(b) UV-Radiation
UV-radiation is generally coupled with hydrogen peroxide or ozone to form an
oxidation complex. UV oxidize only certain organic compounds present in leachate and is
a good disinfectant. When decomposition of dioxins in a landfill by advanced oxidation
processes were studied, O3/H2O2 and UV/O3/H2O2 processes were tested to evaluate their
performances in decomposing dioxins present in a landfill leachate. The data suggested
that the UV/O3/H2O2 process had better removal efficiency of total dioxins than O3/H2O2
process in terms of toxicity (Sota, et al., 1999).
(c) Ozonation
The chemical oxidation with ozone is an innovative technology for the treatment of
effluents and leachate that are highly contaminated with organic chemicals because of its
capability to completely convert the organic contaminants to carbon dioxide.
Ozone due to its strong oxidizing ability is effective and practical as a pre-treatment
to remove refractory species and as a polishing step to treat organic or increase the
biodegradability of refractory compounds. The oxidation potential of ozone is sufficient for
the direct degradation of organic substances. The oxidation of organic compounds by
ozone is a zero order reaction, i.e. the reaction rate is constant until about 20 % of the
initial amount is left (Kylefors, 1997).
Bjorkman and Mavinic (1977) conducted an extensive study of physio-chemical
treatment of landfill leachate. The study included the use of lime, alum, ozone and their
various combinations for the treatment of municipal solid waste. In the study, after treating
the leachate with ozone, the leachate was re-circulated in an attempt to improve effluent
degradation. It was found that counter-current re-circulation minimized the foaming
problem experienced in the treatment process. However, it was concluded with ozone
concentrations above 100 mg/L was effective in marginally reducing COD present in the
leachate.
Gierlich and Kollbach (1998) reported that ozone was effective in reducing 80 %
ammonia. It was also suggested that ozone treatment was more effective and economical if
biological treatment was adopted as a pretreatment.
Sludge disintegration has been commonly used as a pretreatment for sludge digestion.
The digested sludge has the advantage of controlling and reducing sludge bulking in
conventional activated sludge processes and thus providing an internal carbon source for
biological nutrient removal. However, the feasibility of using ozone to chemically
oxygenate sludge to provide an internal carbon source for denitrification processes had not
yet been investigated. This was the research basis for a study conducted by Ahn, et al.
(2001). In the study, the ozonated sludge resulted in a sludge mass reduction and
improvement in the settleability of the sludge. The effect of sludge ozonation was
determined in terms of either mineralization or solubilization and changes in residual solid
characteristics. Both the solubilization and mineralization increases with increase in ozone
dosage.
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