ESCO International

Ozone Based AOP process for refractory COD reduction in industrial waster water


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In recent years improvements  in ozone based advanced oxidation technology efficiencies have lowered capital and operating expenses, improving the viability of the use of ozone as the main oxidant.

An investigation into alternatives for refractory COD removal which is economically attractive and do not produce sludge lead to an evaluation of ozone based advanced oxidation processes

The results of this pilot study indicate that ozonation of pre-treated refinery wastewater effluent can effectively remove refractory COD and is a viable alternative to traditional chemical precipitation  removal technologies for COD and BOD removal.

The AOP  process can remove effluent COD to below 10 ppm without the generation of sludge. This eliminates the need for a treatment system solid management  program as is typically required with precipitation  methods. 

The pilot study results indicate that the primary control parameters for COD and BOD removal using ozone based-AOP are dosage, contact time and pH.

This report presents the results of the AOP pilot testing program.

Materials and Methods

The ozone-AOP pilot plant consisted of a 6 m high column, operated in a counter-current mode. 

Ceramic diffuser and injector supplied ozone generated from a PSA oxygen source at specific gas flow rate and O3 concentration ranging from 6% to 12% wt. Ozone was monitored in the influent gas and the off-gas.

Influent and effluent ozone dosages were monitored using an ozone gas analyser.

Ozone concentrations in the feed-gas and hydrogen peroxide (30%wt) were adjusted to provide the desired oxidants concentrations. 

Results and Data Analysis

The removal efficiency of the organic compounds in the two waste water samples by ozone-AOP was measured in terms of COD and BOD5. The correlation of COD removal and oxidant(s) dosage is presented in figure below.

At low oxidant(s) dosages (Conc. x Time), there does not appear to be significant COD removal.

This concurs with the observations noted in previous pilot tests that at low ozone (oxidants) concentrations there is not an adequate ozone dosage to break the long chain bond and colour. It is anticipated that there is little COD destroyed when the ozone (oxidant) attacks and does not break apart the carbon-carbon double bonds in the large, colour contributing, organic molecules. As the ozone (oxidants) dose is increased, carbon-carbon single bonds are attacked and broken, resulting in a loss of COD, BOD and TOC. At stoichiometric ozone (oxidants) dosages, COD removal rate is higher than 95%.

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