New solutions for efficient application of Fenton processes to AOX removal from industrial wastewaters

• Main Author: Ribeiro, João Pedro de Sousa Peres Oliveira
• Publication Date: 2024
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10773/41267
• topic: AOX; Catalysis; Circular economy; Fenton process; Iron; Waste valorisation

In the search for more profitable and sustainable business models, industry has been investing in the replacement of traditional raw materials and production processes by innovative alternatives. However, such replacement may result in the occurrence of emerging contaminants in industrial emissions. In this framework, high-performance solutions of sustainable nature and moderate cost are continuously sought by industries to address this challenge. A viable option is Fenton process, an advanced oxidation process capable of eliminating recalcitrant pollutants. Nonetheless, the continuous consumption (and consequent wastage) of iron as process catalyst is a serious limitation to the spreading of industrial implementation of Fenton process. This work focused on finding solutions to overcome this disadvantage of Fenton process, upgrading it to a more efficient, sustainable, and attractive solution towards industrial implementation. To that end, it was tested the combination of iron with other metals; the incorporation of wastes in the treatment to maximise its efficiency; and the recovery and valorisation of the residual ferric sludge. The removal of adsorbable organic halides (AOX) from pulp and paper industrial wastewater served as case-study. In this work, the usage of waste-based materials such as residual iron dust, granulated biomass fly ash, or even the recovered Fenton sludge, offered circular alternatives to the continuous consumption of iron salts. Such waste-based materials yielded high removal of AOX, under reduced operating costs. In the case of residual iron dust, a symbiosis between pulp and metallurgic industries could be fostered, so that both parties could benefit from the valorisation of that waste. The same applies to the partial replacement of iron with other transition metals, which would be viable especially using waste materials rich in such metals. Another useful outcome of this work was the definition of a methodology to recover and valorise the residual Fenton sludge. Thermochemical treatment converted the sludge into an effective catalyst capable of maintaining its activity for at least three consecutive treatment cycles. Useful knowledge was also generated concerning the combination of Fenton process with conventional biological treatment. Microbiological activity was not greatly affected by neither the initial organic load, nor the existence of Fenton chemicals and transformation products in the wastewater composition. Through the definition of the best operating conditions to couple the two treatment processes, maximum removal of pollution was achieved under minimum resource consumption. By presenting an integrated assessment of different solutions, this work offers an innovative contribute to industrial decision-makers seeking circular, sustainable wastewater treatment practices. The work contributed also to the generation of knowledge useful for the general scientific community, to help guiding future research towards the main challenges that remain unanswered.