Oxidative destruction of foaming agent, COD and TOC in wastewater using advanced oxidation technologies
In recent years, improvement in ozone based advanced oxidation process design and efficiency resulted in lower capital and operating costs. An investigation into alternatives for hard COD, TOC and foaming agent oxidative destruction which is economically attractive and do not generate sludge, lead to the evaluation of our ozone based advanced oxidation processes (AOP). The results of this pilot study indicate that ozone-based AOP can effectively remove COD and TOC without the generation of sludge and totally eliminate the foaming agent problem. The process is a viable alternative to traditional treatment technologies. It eliminates the need for additional treatment units and solid management program as is typically required with chemical/precipitation/membrane methods. This report presents the results of the AOP pilot experimental work.
Advanced Oxidation test work using Ozone / UV/ Hydrogen Peroxide
The advanced oxidation with ozone, hydrogen peroxide and ultra-violet (UV) is a proven technology for the oxidation of a wide range of chemical compounds, COD and TOC in water.
Advanced oxidation systems for water treatment are designed to inject ozone and hydrogen peroxide (preferably in the presence of UV, depending on water quality) in controlled ratios into the water, and then mix the oxidizing agents to form free hydroxyl radicals (•OH).
Ozone (O3), hydrogen peroxide (H2O2), and hydroxyl radicals are strong oxidizing agents capable of oxidizing a wide range of organics, COD and TOC. The final products resulting from the complete oxidation of organics and oxygenates are carbon dioxide and water.
AOP Pilot Testing Project
The customer is working on a project for a phosphate beneficiation plant.
There is a sulfonated fatty acid used in part of the process to produce foam.
A residual of this compound is present in the recirculation water and customer is looking for a solution to inactivate the agent, and reduce COD and TOC.
The customer tried anti-foam solution but this option had a high operational cost and it doesn’t always work and does not solve the COD problem.
The received waste water sample was slightly colored and had some sort of sludge like particles/precipitate.
All experiments were conducted using settled waste water samples.
To solve the problem, ESCO International designed an AOP skid pilot system to evaluate the alternatives to treat the waste water. ESCO International conducted pilot tests to evaluate the performance of an ozone-based advanced oxidation system to oxidize the foaming agent and reduce COD and TOC.
The test work was conducted with a pilot system which consisted of a skid mounted advanced oxidation system with a capacity of 15L. The AOP skid system included an oxygen-fed ozone generator, UV oxidation reactor, hydrogen dosing and injectors. A cooling system was used to control the water temperature.
The purpose of the pilot test was to demonstrate the effectiveness of the AOP technology to the client, obtain operation data, and estimate costs for a full scale water treatment system.
Materials and Methods
The AOP Pilot system includes (figure 1):
- Oxygen fed Ozone generator
- UV/Ozone/H2O2 oxidation reactor
- Feed /Recirculation Pump
- Applied Ozone Dosage: measured at reactor inlet and outlet by ozone gas monitor
- H2O2 dosing: dosage varied according to ozone dosage
- pH and temperature control
- ozone off gas destructor
- COD, BOD, TOC analysis
The ozone-AOP pilot system consisted of an O3/H2O2/UV oxidation chamber.
Injector supplied ozone generated from a PSA oxygen source at specific gas flow rate and O3 concentration (6% – 13% by weight), depending on the electrical current setting of the ozone generator.
Ozone was monitored in the influent gas and the off-gas before being completely destroyed by the ozone destruct unit and vented to atmosphere.
Influent and effluent ozone dosages were monitored using an ozone gas analyser.
Ozone concentrations in the feed-gas and hydrogen peroxide were adjusted to provide the desired oxidants concentrations. Before and after each set of tests, the pilot plant was flushed with clean water.
Ozone-AOP oxidation treatment efficiency was monitored by COD, TOC and BOD analysis, measured according to UK Standard Methods by an approved UK Analytical Laboratory.
The AOP skid systems allowed the treatment of settled wastewater using only three different AOP configurations:
- UV/H2O2
- UV/O3
- O3/H2O2/UV
The O3/H2O2 test could not be conducted due to insufficient wastewater volume.
AOP Test Results and Data Analysis
Tables below show COD, BOD and TOC results for three AOP configurations and conditions.
COD, TOC and BOD analysis were conducted in order to gather information about the effectiveness of the AOP system.
Treated samples were taken at specific treatment conditions and times.
All AOP test results are presented in tables below.
Test results
Test 1: UV/H2O2
| C 1776440 ESCO International: | ||||||
| Laboratory Number | 18633623 | 18633624 | 18633625 | 18633626 | ||
| Customer Sample Ref. | *A0 | A10 | A15 | A20 | ||
| Sample Matrix | Not Specified | Not Specified | Not Specified | Not Specified | ||
| BOD + ATU (5 day) | WAS001 | mg/l | 7 | <1 | ||
| COD (Total) | WAS040 | mg/l | 110 | 64.0 | ||
| TOC as C | WAS005 | mg/l | 24.3 | 21.3 | ||
Note: *A0: COD, TOC and BOD of untreated waste water, settled.
Remarks:
Slight formation of foam during first minute of test. Foaming stopped after 1 min test.
Treated sample shows color improvement and reduced odor.
The analytical lab did not have a method to neutralize excess H2O2 before analysis, hence higher test results.
From previous experience, we know that the presence of H2O2 leads to overestimation of measured COD values since it consumes the oxidation agent. The extent of H2O2 interference in COD analysis is proportional to the remaining H2O2 concentration at the moment of sampling, and the ratio depends on the wastewater quality and the persistence of organic materials in the wastewater.
UV/H2O2 process is not, in this case, a suitable treatment solution for COD and TOC reduction due to low UV transmission of the waste water and analytical problems due to H2O2 excess used in UV/H2O2 processes.
Test 2: UV/O3
| 18633623 | 18633632 | 18633633 | 18633634 | ||
| *A0 | D10 | D20 | D30 | ||
| Not Specified | Not Specified | Not Specified | Not Specified | ||
| BOD | 7 | 3 | 1 | <1 | |
| COD | 110 | 41 | 18 | 19 | |
| TOC | 24.3 | 7.1 | 4 | 3.1 | |
Note: *A0: COD, TOC and BOD of untreated waste water, settled.
Remarks:
Very little foaming during start, then stopped. Treated sample shows significant color and odor reduction.
COD reduced to 18/19 ppm
TOC reduced to 4/3.1 ppm
Test 3: UV/O3/H2O2
| 18633623 | 18633627 | 18633628 | 18633629 | ||
| *A0 | B10 | B15 | B20 | ||
| Not Specified | Not Specified | Not Specified | Not Specified | ||
| BOD | 7 | <1 | <1 | <1 | |
| COD | 110 | 305 | 174 | 25 | |
| TOC | 24.3 | 18.4 | 10.2 | 2.8 | |
Remarks:
Very little foaming during start, then stopped. Treated sample shows significant color and odor reduction.
COD reduced to 25 ppm
TOC reduced to 2.8 ppm
The COD and TOC removal performances for O3/UV treatment, were +83 %, + 83 %, respectively.
The COD and TOC removal performances for O3/H2O2/UV treatment, were +77 %, +88%, respectively.
Although specific to this wastewater and treatment conditions in this study, O3/UV was more efficient in removing COD than O3/H2O2/UV while application of O3/H2O2/UV was superior to O3/UV for TOC reduction.
Higher COD and TOC reduction rates can be achieved through optimization of the ozone based-AOP processes.
Flotation tests
The Flotation tests have been conducted to check if foaming has been totally eliminated after AOP treatment.
The tests consist of blowing air/oxygen using an air diffuser into the AOP treated water.
The flotation tests were performed with tap water (used as blank test), untreated wastewater and with AOP treated samples.
Test results clearly show that foaming has been completed eliminated due to oxidation destruction of the foaming compound.
Concluding remarks
The laboratory tests results indicate that , under our testing conditions & analytical procedures, the waste water can be successfully treated for COD to meet and exceed customer requirement.
TOC results is another indication that the Ozone-based advanced oxidation process is very effective in achieving total oxidative destruction of the foaming agent and refractory organic compounds present in the wastewater.
The COD and TOC removal performances for O3/UV treatment, were +83 %, + 83 %, respectively.
The COD and TOC removal performances for O3/H2O2/UV treatment, were +77 %, +88%, respectively.
Although specific to this wastewater and treatment conditions, O3/UV was more efficient in removing COD than O3/H2O2/UV while use of O3/H2O2/UV was superior to O3/UV for TOC reduction.
Higher COD and TOC reduction rates can be achieved by optimization of the ozone based-AOP processes.
An analysis of the AOP pilot test results indicate that Ozone-AOP oxidation technology can achieve the required COD and TOC reduction levels and ensure total oxidation and elimination of the foaming agent.
ESCO International can provide optimized design for a full scale O3-based AOP system to meet end-user treatment requirements for COD, TOC and foaming agent oxidative reduction.