Development of Advance Oxidation Plasma Micro- Reactor for Wastewater Treatment

Abstract

Availability of clean drinking water is decreasing while the increase in the world population and economic development during last century has resulted in an exponential in demand of water. The situation is even worse in developing countries due to lack of wastewater treatment. Wastewater discharge into environment without “adequate” treatment cause of waterborne diseases. To date, around 52% people of Pakistan do not have supply to clean drinking water. Water from local aquatic bodies such as surface aquafiers are used for drinking purposes causing number of life threatening diseases. According to an estimate, around fifty percent of hospital beds in Pakistan are occupied with the water-borne diseases. In rural areas, mostly drinking water is not sterilized. Usually, water is boiled which sometime is not enough to remove all pathogens. In urban areas usually chlorination is carried out for sterilization of drinking water. Chlorine, although good at its job, produce tens of oxychloro compounds making water carcinogenic. The production of carcinogens is known for last fifty years. However, sadly, the process is still in practice in Pakistan. A comparative analysis of the sterilization technologies demonstrates, the use of ozone not only removes the pathogens but also ensure no by product is harmful by-product is formed. Commercially, ozone is produced from air or oxygen using Corona or Dielectric Barrier discharge (DBD)-types of non-local thermal equilibrium (Non-LTE) plasmas in large scale ozone generators and dosed to water through gas diffusers. Ozone generation is an energy intensive process and utilizes large amount electricity. Ozone is also very reactive and converts to oxygen molecules by colliding with itself and with the walls of the container. More importantly, detailed kinetic study show, a number of oxidizing species (OH* and O*) with higher oxidation potential exist in oxygen and air plasmas. The species have a very short lifetime (~ns) and converts into more stable products like O3 and/or NOx. The study is based on developing an advance plasma microreactor capable of generation dosing of ozone into water simultaneously. This will have twofold advantage-(1) increasing the energy efficiency of the process by generating and dosing in situ and (2) oxidizing species, due to their higher oxidation potential, will increase the sterilization efficiency. A sustainable argon plasma has been generated. Ozone was produced from air plasma. As a case study, comparison with the existing plasma technologies and optimizing the process parameters, Methylene blue solution was used as a target substrate. Maximum efficiency of methylene blue removal is obtained at 70 kV and f3 for all value of concentrations (80, 60, 40, 20 ppm). Several plasma micro-reactor configurations have been tested to see is oxidising species along with ozone could be produced and dosed in water. Sintered borosilicate diffuser glass reactor with inner ground electrode is design to diffuse plasma directly into wastewater.