1. Introduction

 

For many commercial and industrial operations, looking at ways to reduce water and wastewater monthly bill costs and ensure compliance with both current and future regulations, water reclaim is essential.

A major water treatment challenge encountered in the search for new water sources is the reduction of TOC and COD at one or more locations.

The purpose of this study is to show the importance of AOP process design and optimization and the significant implications for the technical/commercial scale design and operating costs for the oxidative destruction of organic compounds, COD and TOC in water and waster waters.

 

2. Experimental data

Experiments were carried out in two different semi-industrial scale O3/H2O2/UV AOP systems, referred to as new design AOP-NDX and old design AOP-ODX. Both AOP tanks were made of stainless steel.

Design flow rate up to 10 m3/h.

Target compound concentration:                      170 mg/l

UV power range:                                                  2kW to 14kW

Ozone concentration range:                               6%wt – 12%wt

Ozone: H2O2 ratio:                                             1:1 to 3:1

pH:                                                                         7 – 10

 

3. Results and discussion

In this section of the report, we present general results of the oxidative degradation of the model compound and the significant effect of AOP system design parameters on process performance.

Laboratory scale studies, where effects of the AOP reactor configuration and critical operation conditions are not studied, provide insufficient information and data for process technical scale up.

Large scale experiments were conducted in two different semi-industrial AOP systems.

 

O3/H2O2/UV industrial semi-pilot

 

Figure 1 illustrates the effect of AOP design configuration on the target compound reduction rate. Results show that, under similar operating conditions, target compound reduction rates of 98% and 45% were measured for AOP-NDX new design and AOP-ODX old design reactors, respectively. This indicates that AOP treatment efficiency can be significantly improved using the correct design and optimisation approach which can result in increased process performance, hence reduced capital and operating costs.

 

Fig 1. Effect of AOP reactor design on target compound reduction rate

 

 

Figure 2 shows the effect of UV power on the process performance for the optimised AOP reactor, AOP-NDX.

The efficiency of the degradation rate of the target compound is critically dependent on the intensity of the UV irradiation and the AOP reactor configuration.

A preliminary optimisation of the process indicates that excess dosage is not effective. In fact, test results show that UV power level 2, which is about 30% less than UV power level 3, is sufficient to achieve almost similar target reduction rate, resulting in significant equipment and operating costs reduction.

Therefore, for cost effective AOP processes using UV in combination with ozone or hydrogen peroxide or both, these results confirm the need to take into consideration critical design factors such as AOP chamber geometry, UV intensity power and UV spectral distribution, the positioning of the UV light sources in the AOP reactor, and the water UV transmission.

 

Fig 2. Effect of UV intensity power & reactor design on target compound reduction rate

 

The rate of chemical oxidation of contaminant, TOC, COD is limited by the rate of formation of OH radicals, and in the case of low pressure UV lamps, by the small absorption cross-section of hydrogen peroxide (i.e 19.6 1/mol. cm) at 254 nm.

Therefore, the use of standard UV systems primarily used for disinfection purposes, are not the right choice for AOP applications. Using standard disinfection UV systems in UV-based oxidation process scale up means higher capital and running costs.

For illustration purposes, it is interesting to present here the typical case of an industrial project. The application was about TOC reduction in process water for reclaim purposes. The specification called for TOC reduction from a 3 ppmC max. to below 0.25 ppm.

An internationally renowned UV manufacturer proposed a UV/H2O2 solution where 19 x 5  UV system skids were used. The company offered their standard UV disinfection systems, high intensity low pressure lamps (254 nm) at a total UV power of 660 kW. The approximate budget for such UV plant alone was about 3.5 million USD.

 

The present study suggests that the end user could have saved up to 1.0 million USD in equipment cost and no less than 30% in power consumption and spare part costs as well as labor costs associated with installation, commissioning and running of the plant.

 

Conclusions

 

A chemical compound was used as a target model for the technical development and optimisation of a cost effective advanced oxidation treatment process.

The oxidative destruction of the model compound in water was carried out as a function of AOP reactor design and geometry, residence time, UV intensity and spectral distribution of the light source.

Technical scale results show that high degradation rates can effectively be achieved by taking into consideration several critical AOP design parameters and process optimisation.

This study provides basic steps in AOP process technical development leading to significant reduction in capital and overall operating costs.

 

About ESCO International

ESCO International technologies offer sustainable solutions to some of the most critical water and waste water and gas effluent challenges using latest advances in Advanced Oxidation Processes, Ozone and UV systems and technologies.

 

ESCO International develops process technologies that enable water reclaim, reuse or recycle and address the most difficult challenges in treating process waters and wastewaters.

 

Unlike many treatment solutions, the AOP technologies have no waste streams, are environmentally friendly, and deliver significant customer value, and has the advantage of no phase transfer required, thereby eliminating secondary handling.

 

Our AOP systems offer a versatile, high-performance chemical oxidation technology based on ozone, hydrogen

peroxide and in some specific cases engineered UV oxidation systems to produce hydroxyl radicals, the most

powerful oxidant available for water treatment.

 

Process Expertise & Applications include:

 

– Water and wastewater disinfection,

– COD, TOC reduction and micro pollutants oxidation

– Water reclaim, reuse, recycle or discharge

– Tertiary Produced Water Treatment (COD, TOC, Oil reduction)

– TOC reduction and disinfection in High purity and Ultrapure water systems

– Spent caustic treatment (H2S, COD, TOC)

– Power Plant, Oil & Gas, Refineries (TOC, COD, H2S reduction)

– Mining industry wastewaters (iron, cyanides, COD..)

– Biologically treated wastewaters

– Pharmaceutical industry (COD, TOC, Antibiotics, EDCs removal)

– Condensate water treatment

– Swimming Pool disinfection & chloramines removal

– Ballast Water Treatment

– VOCs, BTEX, H2S, Mercaptans, Phenols destruction

– Gas effluent, odour and air pollution treatment

 

 

Our Products & Services:

 

– Comprehensive range of low & medium pressure UV systems

– Ozone generators, PSA Oxygen generators and ancillary equipment.

– Design & supply of Advanced oxidation systems (O3/UV, H2O2/UV, O3/H2O2, O3/H2O2/UV, CATADOX)

– Design & supply of Ozone and UV plants

– Design & Supply of skid pilot plants (Ozone, UV or AOP)

– Technical consultancy

– Pilot and laboratory services

 

 

For professional AOP solutions, please contact ESCO International at info@escouk.com or call +44 (0)1492 584140