Implementation of Solar Technologies for Water Treatment

Pilot-scale results have shown that solar photo-Fenton at acid or circumneutral pH are promising tertiary or quaternary wastewater treatment in real effluents. The implementation of solar-based technologies for water treatment led to the development of photoreactors based on compound parabolic collectors (CPCs) and more recently, the raceway pond photoreactors (RPRs). CPCs were developed for treating mainly industrial-toxic effluents needing long treatment times. RPRs were developed for municipal treatment plants (MWWTP) secondary effluents of low organic content. RPR treatment objectives are only for eliminating contaminants of emerging concern and disinfection (treatment time in the range of minutes). A solar collector for these applications must fit to the following basic characteristics: (1) adequately capture UV and visible solar radiation, (2) maintain the water at a temperature as close as possible to ambient to avoid evaporation of water and contaminants, (3) consider that the efficiency of photochemical reactions may decrease with radiation intensity, (4) take into account that diffuse radiation is an important component of the solar radiation that reaches the Earth’s surface, (5) offer little resistance to water circulation and (6) keep the wastewater to be treated in a controlled environment. The development of CPC and RPR has been discussed in detail jointly with their design, implementation and operational parameters. Photo-Fenton at circumneutral pH with stable complexes with iron has attracted the attention of researchers. It has been widely studied, but the process is governed by the short lifetime of the complexes. The short reaction time required for MWWTP effluent treatment is the key parameter for process implementation, being the most promising solar advanced oxidation process.