ESCO International UK – October 2015
Introduction
An investigation into alternatives for refractory COD removal in industrial waste waters which is economically attractive and do not produce sludge lead to an evaluation of ozone based advanced oxidation processes.
The results of this ozone based AOP pilot study indicate that refractory COD from pre-treated refinery wastewater effluent can effectively be destroyed and is a viable alternative to traditional chemical precipitation removal technologies for COD removal.
The pilot study results show that the primary control parameters for COD and BOD removal using ozone based-AOP are oxidant 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%.
The test results for COD and BOD5 of the two ozone treated waster water samples are summarised in Table 1.
Table 1: laboratory analysis of untreated and treated samples.
Results analysis:
The graphs below (fig 1 and fig 2) show the COD reduction trends for samples A and B, based on pilot test results.
The simulated pilot test results indicate that by simply increasing the ozone & H2O2 dose rates (Cx T), we can easily achieve less than 10 ppm in COD in both cases, if needed.
Fig 1. COD reduction vs C.T ( concs. x time) for sample A.
Fig 2. COD reduction vs C.T ( concs. x time) for sample B.
Conclusions
An analysis of the AOP Ozone pilot tests for oxidative destruction of COD and BOD in industrial wastewater effluent was conducted. The results of this study indicated that ozone AOP oxidation process can efficiently remove COD to below 10 ppm without the generation of sludge. This eliminates the need for an additional treatment system and solid management program as is typically required with precipitation methods.
Kinetics have been developed for full scale AOP design which show that our high intensity mixed ozone based AOP reactor system design can provide highly improved kinetics and would result in lower ozonation dosage, hence, lower capital and running costs and smaller system footprint.
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