Advanced oxidative wastewater treatment using cavitational reactors

  • Rashmi Chand

Student thesis: Doctoral Thesis

Abstract

This thesis explores various novel ways of treatment of wastewater contaminated by toxic organic pollutants using single and combined advanced oxidative wastewater treatment technologies in conjunction with a variety of acoustic and hydrodynamic cavitational reactors. There have been many reports in the literature on the use of hydroxyl radicals as the core part of AOPs and hence, as the first objective, the amount of hydroxyl radical generation from different acoustic and hydrodynamic cavitational reactors was studied using the potassium iodide dosimeter. The results reveal that optimum concentrations of less toxic chloroalkanes (chloroform and dichloromethane) could be efficient alternatives to carbon tetrachloride for enhancement of hydroxyl radical generation in cavitational reactors. Increasing ultrasonic amplitudes and operating hydrodynamic cavitational pressures lead to higher rates of hydroxyl radical production. Having explored the efficiency of generation of hydroxyl radicals the capacity of the reactors to degrade the model pollutant phenol, via a modified classic Fenton reaction which uses zero valent iron catalysts (instead of iron salts) and hydrogen peroxide under acidic conditions was studied. This process, named the advanced Fenton process (AFP), is the main foundation of the phenolic wastewater treatment reported in this thesis.

Phenol degradation was assessed using different frequencies of ultrasound where a comparison between 20, 300 and 520 kHz ultrasonic reactors showed that 300 kHz was by far the most efficient US reactor resulting in 100% phenol removal and 37% total organic carbon (TOC) mineralization in 25 min.

The concept of Latent Remediation (LR) was discovered during investigations into innovative approaches towards development of cost/energy-effective methods to treat phenolic wastewater. LR consists of inputting only 15 min of either ultrasound or stirring to the reaction medium, which contains optimised amounts of hydrogen peroxide and iron catalyst, and then the silent-dark AFP phenol degradation was studied over 24 h. The excellent results revealed that >80% TOC mineralization was achieved after this time. It was also found that zero valent copper catalysts were effective for phenol degradation and offered an excellent alternative to iron in the AFP, however toxicity analysis on the 24, 48 and 72 h samples showed that zero valent iron exhibited decreased toxicity when compared to zero valent copper.

Conventional granular/powdered activated carbons were replaced with activated carbon cloth and investigations on the potential use of this material for phenol removal/decomposition was studied in detail at different operating pHs (3, 5.5 and 9), temperatures (20, 40 and 80 °C), oxidants (H2O2/O3) in various reactors (pump, shaker and US bath).

Another aspect of the AOP application, disinfection of natural waters, was studied employing hydrodynamic cavitation and ozonation in a novel Liquid Whistle Reactor system. Model markers of faecal coliforms, Escherichia coli, were chosen for the study and the combined technologies of hydrodynamic cavitation and stepwise ozonation proved be highly beneficial, resulting in ~ 6 log bacterial reduction revealing 99.9999% disinfection efficiency of the process.
Date of AwardMay 2008
LanguageEnglish
Awarding Institution
SponsorsEuropean Social Fund (ESF), European Science Foundation & Food Processing Faraday Partnership
SupervisorDavid H. Bremner (Supervisor)

Cite this

Advanced oxidative wastewater treatment using cavitational reactors
Chand, R. (Author). May 2008

Student thesis: Doctoral Thesis