CDOF Catalytic Ozonation Technology: An Efficient Pretreatment Solution for Improving Wastewater Biodegradability

Abstract

Hard-to-degrade organic wastewater, because it contains a large amount of structurally stable, strongly biologically toxic macromolecular organic matter, has poor biodegradability (B/Cratio usually < 0.2), and has long been a technical challenge in the field of industrial wastewater treatment.

Traditional biochemical treatment processes are inefficient for this type of wastewater and struggle to meet increasingly stringent discharge standards.CDOF(Catalytic Ozone Oxidation Filter(CDOF) catalytic ozonation advanced oxidation technology, as a highly efficient pretreatment technology, produces strongly oxidizing hydroxyl radicals through the synergistic action of ozone and a dedicated catalyst, which can efficiently break the chemical bonds of hard-to-degrade organic matter, converting large, toxic, and harmful substances into small molecules that are easily degraded by microorganisms, significantly improving the biodegradability of the wastewater and laying a good foundation for subsequent biochemical treatment. This article systematically expounds the CDOFtechnology's action principles, core advantages, and application scenarios in various industrial fields, providing a theoretical reference for the promotion and application of this technology.

I.Introduction

With the rapid development of modern industry, the discharge of hard-to-degrade organic wastewater from industries such as petrochemicals, coal chemicals, pharmaceuticals, and printing and dyeing has increased year by year. This type of wastewater has a complex composition, containing large amounts of long-chain alkanes, aromatic hydrocarbons, heterocyclic compounds, polycyclic aromatic hydrocarbons, and other hard-to-degrade organic substances, with the characteristics of CODhigh concentration, high toxicity, and poor biodegradability. Traditional biological treatment processes rely on the metabolic action of microorganisms to degrade organic matter, but hard-to-degrade organic matter is not only difficult for microorganisms to utilize, but also inhibits and poisons the microorganisms, leading to low sludge activity, poor treatment efficiency, and unstable effluent quality in the biochemical system.

To solve this problem, a pretreatment unit usually needs to be set up before biochemical treatment to destroy the structure of hard-to-degrade organic matter, reduce its toxicity, and improve the biodegradability of the wastewater. Advanced oxidation technology (AOPs), because of its advantages such as strong oxidation capacity, fast reaction speed, and no secondary pollution, has become the preferred technology for the pretreatment of hard-to-degrade organic wastewater. Among them, CDOFCDOF catalytic ozonation advanced oxidation technology combines the high efficiency of ozone oxidation with the selectivity of the catalyst, overcomes the shortcomings of traditional ozone oxidation such as low utilization rate and incomplete oxidation, and shows significant advantages in improving the biodegradability of wastewater, gaining wide research and application.

II.CDOFThe Principle by Which the Technology Improves Wastewater Biodegradability

 CDOFThe core of CDOF technology is the catalytic decomposition reaction of ozone on the surface of a dedicated heterogeneous catalyst, producing hydroxyl radicals with extremely strong oxidation capacity (·OH, oxidation-reduction potential 2.80V), which achieves efficient degradation and modification of hard-to-degrade organic matter through the strong oxidation of hydroxyl radicals, thereby improving the biodegradability of the wastewater.

Its mechanism mainly includes the following three aspects:

(I)Mechanism of Hydroxyl Radical Generation

CDOFIn the reaction system, ozone molecules first diffuse to the catalyst surface and are adsorbed; the active sites on the catalyst surface (such as transition-metal oxides, rare-earth metal oxides, etc.) undergo electron-transfer reactions with ozone, catalyzing ozone decomposition to produce hydroxyl radicals. Unlike ordinary ozone oxidation, which oxidizes organic matter only through direct oxidation by ozone molecules, CDOFCDOF technology enhances the oxidation capacity of ozone by several orders of magnitude through catalysis, enabling it to oxidize the vast majority of organic pollutants.

(II)Transformation Process of Hard-to-Degrade Organic Matter

Hydroxyl radicals have non-selective strong oxidation capacity and can attack various chemical bonds in the molecules of hard-to-degrade organic matter, triggering a series of complex oxidation reactions:

1. Ring-opening and bond-breaking: For organic matter with cyclic structures such as benzene rings, naphthalene rings, and heterocycles, hydroxyl radicals can destroy their stable conjugated systems, open the cyclic structure, and generate linear small-molecule organic matter; for long-chain alkane organic matter, they can break the carbon-carbon bond, breaking the large long-chain molecules into short-chain small molecules.

2. Functional-group transformation: Oxidize hard-to-degrade functional groups such as methyl, methylene, nitro, and chloro groups in organic molecules into functional groups easily utilized by microorganisms, such as hydroxyl, carboxyl, and aldehyde groups, generating intermediate products such as organic acids, alcohols, and aldehydes.

3. Detoxification and modification: Remove toxic groups from organic molecules, reduce their biological toxicity, eliminate inhibition of microorganisms, and create favorable conditions for subsequent biochemical treatment.

(III)The Essence of Biodegradability Improvement 

Through the above oxidation reactions, CDOFCDOF technology converts large, toxic organic matter in the wastewater that is difficult for microorganisms to degrade into small organic acids easily degraded by microorganisms (such as acetic acid, propionic acid, butyric acid, etc.), significantly increasing the wastewater's BOD5/CODratio (B/Cratio). Generally speaking, after CDOFCDOF pretreatment, the wastewater's B/Cratio can be increased from the original 0.1~0.2to 0.4or above, and some wastewater can even be increased to 0.5~0.6, fully meeting the requirements of subsequent biochemical treatment. At the same time, CDOFCDOF technology can also remove part of the CODand color, reducing the load on subsequent biochemical treatment.

III.CDOFThe Core Advantages of the Technology

Compared with traditional hard-to-degrade wastewater pretreatment technologies (such as Fenton oxidation, ordinary ozone oxidation, iron-carbon micro-electrolysis, etc.), CDOFCDOF technology has the following significant advantages in improving wastewater biodegradability:

(I)High oxidation efficiency, with a significant biodegradability improvement effect CDOFCDOF technology produces large amounts of hydroxyl radicals through catalysis, with strong oxidation capacity and fast reaction speed, and can complete the modification of hard-to-degrade organic matter within a short time (usually 15~30minutes), greatly improving the biodegradability of the wastewater. Compared with ordinary ozone oxidation, the ozone utilization rate is increased from less than 30%to 90%or above, and the oxidation efficiency is improved by 3~5times.

(II)No chemical dosing, almost no sludge generation CDOFCDOF technology only consumes ozone, without the need to add H₂O₂, FeSO₄, NaOHand other chemical agents, avoiding the large amount of iron-sludge hazardous waste generated by traditional Fenton oxidation from heavy chemical dosing. The entire reaction process produces almost no solid waste, greatly reducing hazardous-waste disposal costs and secondary-pollution risks.

(III)Low operating cost, good economy Because there is no need to add chemical agents and the ozone utilization rate is high, CDOFCDOF technology's operating cost is significantly lower than that of traditional advanced oxidation technologies. Under normal circumstances, the CDOFCDOF technology's operating cost is only 3~5 yuanper ton of water, while the operating cost of traditional Fenton oxidation is as high as 8~15 yuanper ton of water, with obvious economic advantages.

(IV)Modular design, small footprint CDOFThe equipment adopts a modular skid-mounted design, compact structure, with a footprint only 1/3~1/2of the traditional process, and can be flexibly combined according to the treatment water volume, suitable for both new projects and upgrading and retrofitting of existing projects. At the same time, the equipment has a short installation and commissioning cycle, simple operation and maintenance, a high degree of automation, and can achieve unattended operation.

(V)Strong resistance to shock loads, stable operation CDOFCDOF technology has strong adaptability to fluctuations in water quality and quantity, and can operate stably within a wide pHrange (pH 3~11), without the need to strictly adjust the influent pHvalue. For high-concentration, high-toxicity hard-to-degrade wastewater, it can also maintain stable treatment effects, ensuring the stable operation of the subsequent biochemical system.

IV.CDOFThe Main Application Scenarios of the Technology

CDOFWith its excellent performance, CDOF technology has been widely used in the pretreatment of various hard-to-degrade organic wastewaters to improve wastewater biodegradability. The main application scenarios include:

(I)Petrochemical Industry Wastewater

Petrochemical industry wastewater such as oilfield produced water, refining electric-desalting water, and coking wastewater contains large amounts of petroleum, aromatic hydrocarbons, phenols, sulfides, and other hard-to-degrade organic matter, with poor biodegradability. CDOFCDOF technology can efficiently break emulsions and remove oil, destroy the structure of petroleum macromolecules, convert them into easily degradable small molecules, and significantly improve the biodegradability of the wastewater. After CDOFCDOF pretreatment, the removal rate of CODin the subsequent biochemical system can be increased from 20%~30%to 70%~80%, and the effluent quality stably meets standards.

(II)Coal Chemical Industry Wastewater

Coal chemical wastewater has a complex composition, containing large amounts of phenols, polycyclic aromatic hydrocarbons, nitrogen-containing heterocyclic compounds, and other hard-to-degrade organic matter, with high toxicity and poor biodegradability. CDOFCDOF technology can effectively degrade these hard-to-degrade organic matters, reduce the toxicity of the wastewater, and improve the B/Cratio, providing good conditions for subsequent biochemical treatment (such as A/O, MBRetc.). At the same time, CDOFCDOF technology can also remove color and cyanide from the wastewater, further improving the effluent quality.

(III)Pharmaceutical Industry Wastewater

Pharmaceutical wastewater has the characteristics of high organic concentration, complex composition, high toxicity, and poor biodegradability, containing large amounts of antibiotics, drug intermediates, organic solvents, and other hard-to-degrade substances. CDOFCDOF technology can destroy the structure of drug molecules such as antibiotics, reduce their biological toxicity, convert large drug intermediates into small molecules easily degraded by microorganisms, and significantly improve the biodegradability of the wastewater. After CDOFCDOF pretreatment, the treatment efficiency of the subsequent biochemical system is greatly improved, and the effluent can meet discharge standard requirements.

(IV)Printing and Dyeing Industry Wastewater

Printing and dyeing wastewater contains large amounts of dyes, auxiliaries, sizing agents, and other organic matter, with high color and poor biodegradability. CDOFCDOF technology can destroy the chromophores of dye molecules, effectively remove the color of the wastewater, and at the same time oxidize and decompose the dye macromolecules and auxiliaries and other hard-to-degrade organic matters into small molecules, improving the biodegradability of the wastewater. Compared with traditional printing and dyeing wastewater pretreatment technologies, CDOFCDOF technology has the advantages of good decolorization effect, no sludge generation, and low operating cost.

(V)Landfill Leachate Treatment 

Landfill leachate is a highly complex high-concentration organic wastewater, containing large amounts of humus, fulvic acid, heavy metals, and other hard-to-degrade substances, with poor biodegradability and large fluctuations in water quality and quantity. CDOFCDOF technology, as a pretreatment or advanced-treatment unit for landfill leachate, can effectively degrade hard-to-degrade organic matter such as humus, improve the biodegradability of the wastewater, and at the same time remove part of the CODand ammonia nitrogen, laying the foundation for subsequent biochemical treatment or advanced treatment.

V.Conclusions and Prospects

CDOFAs a highly efficient, environmentally friendly, and economical pretreatment technology for hard-to-degrade organic wastewater, CDOF catalytic ozonation advanced oxidation technology produces strongly oxidizing hydroxyl radicals that can efficiently destroy the structure of hard-to-degrade organic matter, significantly improve the biodegradability of wastewater, and create favorable conditions for subsequent biochemical treatment. The technology has the advantages of high oxidation efficiency, no chemical dosing, almost no sludge generation, low operating cost, and small footprint, and has broad application prospects in fields such as petrochemicals, coal chemicals, pharmaceuticals, printing and dyeing, and landfill leachate treatment. In the future, CDOFCDOF technology's research and development direction will mainly focus on the following aspects:

First, develop efficient, stable, and low-cost catalysts to further improve ozone utilization and oxidation efficiency;

Second, optimize the CDOFCDOF reactor structural design, strengthening the gas-liquid-solid three-phase mass-transfer effect;

Third, study the combination technology of CDOFCDOF with other treatment processes (such as biochemical treatment, membrane separation, etc.) to form a synergistic treatment effect and further improve the treatment effect and economy; fourth, realize the CDOFCDOF system's intelligent control, improving the stability and automation level of system operation. With the continuous progress and improvement of the technology, CDOFCDOF technology will play a more important role in the field of hard-to-degrade organic wastewater treatment, providing strong technical support for the compliant discharge of industrial wastewater and the recycling of water resources.