Wastewater treatment plants (WWTPs) have been identified as main contributors to releasing microfibres into the environment, however, WWTPs do not have microfibre-targeting technologies. In this study, photocatalysis is evaluated as a potential technology to treat microfibres in WWTPs by studying the degradation of polyamide 66 (PA66) microfibres using ultraviolet (UV) and titanium dioxide (TiO2). PA66 microfibres suspended in deionised water were exposed to different combinations of UV and TiO2. The degradation of the PA66 microfibres was monitored by changes in mass, carbonyl index and morphology using microbalance, infrared spectroscopy, and scanning electron microscopy. The formation of by-products from the degradation of the fibres was evaluated by measuring the chemical oxygen demand (COD) of the treated water. The degradation efficiency was optimised under UVC with a dose of 100 mg TiO2/L. Under these conditions, the PA66 microfibres presented a 97% mass loss within 48 h. The photocatalytic conditions applied generated a relatively low level of by-products (<10 mg/L of COD). Therefore, photocatalysis with TiO2 an UVC could potentially be a feasible technology to treat microfibres in WWTPs, although more investigation is required to establish if this treatment leads to the formation of nanofibres. Further work is needed to translate the present optimised conditions to WWTPs.

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In this study, nano-sized low cost titanium dioxide (TFS) was prepared using sludge from sewage treatment and performance was verified. To remove air pollutants, the photocatalytic degradation of methylene blue and efflorescence characteristics is assessed according to the mixing ratio of the nano-sized TFS by applying them to concrete sidewalk blocks. The photocatalytic degradation performance of concrete sidewalk blocks shows that the methylene blue removal rate of specimens containing 2.5%, 5%, and 10% of nano-sized TFS is 29%, 27%, and 38%, respectively. When the nano-sized TFS is mingled on the surface of the sidewalk block, the performance of anti-corrosion and antifouling showed excellency mainly due to the moisture blocking derived by the antifouling function of photocatalysts.

A porous photocatalyst concrete filter (deNOx PCF) is successfully manufactured to reduce NOx by mixing TiO2 photocatalyst with lightweight aerated concrete. From the results, 4% infusion rate of each foaming agent provided the smallest change of the height, and the optimal quality of the air bubbles can be produced by using foaming agent B with 4% of infusion rate. When 3% of TiO2 photocatalyst was mixed, less irregular and relatively homogeneous pores were formed on the surface with white color due to the proper amount of photocatalyst applied. For 3% of photocatalyst mixed with deNOx PCF, 1.03 μmol/hr of NO was reduced equivalent to 10.99% of NO reduction, suggesting that the TiO2 photocatalyst dispersed in the continuous and well-developed pores inside the specimen successfully performed the removal of NO flowing through deNOx PCF using synergistic effects of adsorption and photodegradation reaction. Finally, the specimen of porous deNOx PCF for reducing NOx developed in this study can be applied to various construction sites and the air quality can be solved by reducing NOx contributing to the formation of fine particles.

Two immobilization methods (i.e., ice water-soaked using a digital temperature controller vs. freeze-dried using liquid nitrogen) were applied for mass production techniques of TiO2-embedded expanded polystyrene (TiEPS) balls with nanoscale TiO2 particles embedded on EPS balls. No significant changes in crystalline structure of TiO2 nanoparticles embedded on the TiEPS balls were observed during the mass production of TiEPS balls. Greater residuals of freeze-dried TiEPS balls suggested the improved immobilization methods for mass production procedures of TiEPS balls. Although similar growth inhibition between TiEPS balls using two immobilization methods was observed within 10 hrs, both growth and reproduction of M. aeruginosa can be more significantly inhibited by applying the freeze-dried TiEPS balls after 10 hrs. These results were mainly attributed to the difference in exposed surface area of embedded TiO2 nanoparticles which generated various reactive oxygen species peroxidizing and leading to the inactivation and degradation of M. aeruginosa. Relatively greater k value (0.207 day-1) was estimated from freeze-dried TiEPS balls than that (0.089 day-1) from ice water-soaked TiEPS balls, suggesting that both growth and reproduction of M. aeruginosa were effectively inhibited with greater amounts of reactive oxygen species generated from freeze-dried TiEPS balls. Consequently, self-floating freeze-dried TiEPS balls can be readily applied to inhibit the excessive growth of harmful algae in the stagnant water body without the recovery process for long time.