AOP technology a boon for drinking water treatment
Systems that use AOP technology are considered more effective than conventional oxidation processes. Phil Whittaker explains why their popularity has led to their increasing use in drinking water treatment and water reuse applications.
While ozone systems have been used successfully for disinfection and taste and odour-control applications in the past, further performance benefits can now be achieved by adopting the latest advanced oxidation process (AOP) technology.
This technology combines ozone and hydrogen peroxide (H2O2) to produce hydroxyl radical, a particularly strong oxidant, which reacts chemically with common taste and odour compounds, volatile organic compounds (VOCs) and other micro-contaminants.
Systems that use this technology are more effective than conventional oxidation processes and this has contributed to their growing appeal in drinking water treatment and water reuse applications.
An increasing focus on the sustainability agenda and tightening environmental legislation is encouraging more plant or facility managers to explore ways to reduce water consumption and minimise the impact of their activities on the environment. This has led to a steady stream of innovation in the field of water treatment technology.
In the past, effluent-producing industrial plants and municipal water treatment plants relied upon aeration systems fed by atmospheric air. In a bid to further enhance capacity and performance, pure oxygen is now widely used, as is ozone oxidation technology.
Using pure oxygen in place of atmospheric air results in a faster rate of oxygen dissolution into the treatment basin, which means more water-borne contaminants are removed more quickly.
Such systems are also more flexible as they can react according to the nature and concentration of the contaminants contained in the wastewater. In many cases, the latest oxygen aeration systems are more sustainable too as they extract oxygen from the air and there is no need to store supplies onsite.
The benefits of ozone use as a means of further boosting water treatment performance - in particular its ability to remove hard COD and micro-contaminants - have become more widely appreciated in recent years.
Ozone is a powerful oxidising agent and it is not surprising that recent technological developments have concentrated in this area.
Customers have long complained about waste and odour in drinking water. Common solutions for removing noxious taste and odour constituents include powder activated carbon (PEC), granulated activated carbon (GAC), pre-chlorination and pre-oxidation, sometimes using ozone. However, recent developments in the use of AOP technology - which uses ozone in combination with hydrogen peroxide - have led to a step change in water treatment efficiency and performance.
Switching to AOP technology for drinking water applications brings a number of benefits. In addition to being more effective at treating resistant contaminants, it can also help minimise the formation of byproducts such as bromate and, in some instances, can convert hypobromite - an intermediate that forms during bromate formation - back to bromide, so it is easier to remove. This can help water companies to meet drinking water bromate standards, which can be difficult to achieve if using ozone alone.
Another benefit is that AOP technology can also improve efficiency by minimising ozone consumption and increasing the speed of reaction.
New-generation AOP technology is suitable for a wide range of applications, including taste/odour and colour control; destruction of VOCs; disinfection for water reuse; removal of micro-contaminants such as endocrine disruptors and the removal of a host of recalcitrant compounds.
The modular design of the latest AOP systems means they can be designed to meet the requirements of the plant or facility, optimising both performance and efficiency, according to the amount of ozone needed.
If there is already an external source of oxygen at the site, this can be incorporated into the new system.
Launched in the UK earlier this year, the new HiPOxTM technology, developed by Applied Process Technology (APT) and marketed by Air Products, is extending the benefits of AOP technology to the most demanding applications by destroying contaminants to extremely low or non-detectable discharge levels.
Flexible by design, the HiPOxTM system is suitable for a wide range of water treatment applications and can be used in ozone-only mode, advanced oxidation mode or alternate between the two.
Prior to promoting the use of AOP technology, research was sourced to compare the rate of contaminant removal against conventional treatment methods. Air Products also gathered information about the required dose rate for each treatment solution in order to consider which was most efficient.
Combining ozone and hydrogen peroxide will give a much higher rate of contaminant removal when compared with conventional methods.
The benefits of ozone in the field of water treatment are now widely appreciated, and recent technological advances, which have led to the introduction of the latest AOP systems, are helping to make its use more efficient than ever before.
It is important that technological innovation continues, however, if we are to succeed in protecting the environment by treating wastewater effectively and helping to address global demand for clean drinking water supplies.
Philip Whittaker is business development lead for water systems at Air Products. www.airproducts.co.uk/environmental