Treatment of organic pollutants in high salinity wastewater : new catalysis systems

Sammanfattning: High salinity wastewater (HSW, NaCl mass fraction ≥ 1%) from industries and aquacultures contains massive organic matters with a wide variety. These organic matters have been considered as significant threaten to both human and environment. The removal and degradation of them before discharge emerge as necessity. However, the traditional treatment methods show significant drawbacks for this purpose. Therefore, new efficient treatment methods need to be developed. Electrochemical catalysis (EC) and photo-electro catalysis (PEC) have shown their potential for organic matter degradation in HSW due to their high efficiency, environmental compatibility, saving of energy/material and automation, etc. In EC and PEC methods, the working electrodes (anode or cathode) utilize the rich components in HSW to produce strong degradation agents, leading to high efficiency with no need of extra chemical agents. However, the issues of expensive electrode price, waste of electric energy and limited degradation performance still retain as bottlenecks for future application.Therefore, in my thesis work, new EC and PEC systems were developed to address these issues. Low-cost and high-efficiency electrode materials were employed as anodes and cathodes. These systems were developed basing on the new concept of using duo working electrodes (EC-D and PEC-D), rather than the single working anode or cathode in traditional systems (EC-S and PEC-S). This allowed the synergistic degradation between anode and cathode, leading to the performance enhancement. The key results are as follows:New EC-D system performed well and showed higher degradation and removal efficiency, with lower energy cost, compared to EC-S. This was due to the synergistic work between anode and cathode, where active chlorine and H2O2 produced on anode and cathode contributed to degradation work together. Several indicating factors such as pH value, pollutant content, current density and NaCl concentration yielded significant effect to the performance. Simple EC method showed shortage when dealing with complex and refractory organic matter, such as Norfloxacin (NOR). This should be attributed to the limited reaction activity of EC produced degradation agents (active chlorine and H2O2). PEC system significantly enhanced the performance of EC system. This was associated with the synergistic work between photo and electric power, by which the EC produced degradation agents transferred to stronger free radicals. PEC systems also avoid harmful residual chlorine result in EC systems by transferring them into free radicals.In PEC system, anode and cathode both contributed significantly to degradation work, with anode as prior. Both direct adsorption-degradation and indirect degradation by agents contributed significantly, where indirect route performed more importantly. PEC-D showed high performance in real HSW treatment with low initial organic matter concentration, the biological harmless outflow can be achieved. It is suitable for the treatment of left refractory organic matters after the main degradation process. In conclusion, both new EC and PEC showed bright prospects in organic matter removal and degradation in HSW. However, before large scale application, their performance of degradation and adaptability in various conditions should be further developed. The practical design of large-scale plant should be focused. In addition, not only organic matters, but also the treatment of other critical pollutions in HSW by EC and PEC should draw attention.