Application of biotechnology is an apparent trend in treatment of wastewaters. This primarily means the utilization of microorganisms to remove impurities from wastewater or to process sludge. However, biological processes have a limited or no use for several types of wastewaters and waste (mainly from the industrial domain) – e.g. due to toxicity or low biodegradability of the pollutants present or due to extremely low or extremely high concentrations. Such cases demand a different solution frequently consisting of physical-chemical processes (coagulation, clotting, membrane separation, oxidation processes etc.).
Modern oxidation processes
In removing the waste water pollutants that are not readily biodegradable a great potential is displayed by so called modern oxidation processes. (Advanced Oxidation Processes - AOP). Their mutual feature is their operation at common temperatures and pressure and the utilization of the outstanding reactivity of hydroxyl radicals. These radicals are the strongest oxidation agents known and are characteristic with their low selectivity, which means they are able to oxidise a wide range of compounds. There are several ways how hydroxyl radicals can be generated in waste water – for instance by adding other agents (ozone, hydrogen peroxide) or applying UV radiation, ultrasound etc. The procedures most readily applicable for this purpose are the Fenton reaction (radicals occur due to catalysed degradation of hydrogen peroxide) and ozonisation. Both the Fenton reaction and ozonisation (or their possible modifications and combinations) can be applied effectively to degrade a range of pollutants in waste waters (halogenated compounds, phenols, polycyclic aromatic hydrocarbons etc.). These methods may also be utilized in the domain of sludge management – in conditioning of sludges.
Our team successfully attempted to apply the Fenton reaction and ozonisation methods in cleaning waste waters from the production of pulp. Application of both methods significantly reduced the concentration of not readily biodegradable pollution – such as lignin and related substances originating from the delignification process or halogenated compounds occurring during whitening of the pulp.