Solar disinfection for the post-treatment of greywater by means of a continuous flow reactor

Abstract

SODIS (solar disinfection) is a low-cost alternative for water decontamination. The method is based on the exposure of water, contained in PET bottles, to direct sunlight, and mainly its UV-A and infrared components. The present research studied SODIS as a low cost alternative for the inactivation of Escherichia coli (E. coli) in treated greywater, aiming at its reuse for more noble applications. Experiments were performed in (i) batch mode (2 L PET-bottles), testing the effect of turbidity on system efficiency and, (ii) in a continuous pilot-scale reactor prototype (51 L, using interconnected 2 L-PET bottles), testing hydraulic retention times (HRT) of 18 and 24 h. Samples were exposed to an average solar radiation intensity of 518 W/m2. The results obtained indicate that the SODIS system has potential for total coliforms and E. coli inactivation in the pre-treated greywater, reaching 2.1 log units E. coli inactivation in batch experiments for low turbidity samples (21 NTU), and > 2 log units inactivation of total coliforms (and E. coli, when present) for the 24 h HRT-continuous prototype. The continuous flow prototype needs more testing and structural improvements to cope with the difficulties posed by algae growth, as they complicate maintaining conditions of constant flow and make frequent maintenance inevitable.

Solar water disinfection (SODIS): A review from bench-top to roof-top

“…Despite the concerns raised about the effective inactivation achievable in recirculation and high flow rate SODIS reactors an application may still be possible in the (pre-) treatment of grey water. Pansonato et al have reported 2 log reductions in E. coli levels using a 51 L continuous pilot-scale reactor prototype using grey water [113].…”

Water Disinfection Techniques: A Review

“…Post exposure regrowth possibilities are minimised by consuming the solar disinfected water in a period less than 24 hours post exposure (McGuigan et al, 2012). Black painted solar water disinfection containers, placing the SODIS reactors on reflective surface and filtering the turbid water prior to filling into the reactor (Pansonato et al, 2011) are some advances made to enhance solar water disinfection efficiency.…”

Sustainable graywater reuse for residential landscape irrigation – a critical review

“…In general, a graywater treatment system is designed to carry out four processes, viz., sedimentation, filtration, biological treatment, and disinfection. A range of novel approaches, such as improved zeolite filters, solar disinfection, and membrane bioreactors, are gaining momentum in the field of graywater treatment (Widiastuti et al 2011;Pansonato et al 2011;Hu, et al 2011). Zeolite is a material that promotes cation exchange and is highly sensitive to contaminants in graywater such as heavy metals and ammonium ions.…”

“…Using natural zeolite filters of different origin, Widiastuti et al (2011) achieved a reduction in ammonium of up to 97%. Disinfection of graywater by using solar ultraviolet-A (long-wave) to inactivate E. coli has been found to be economical in regard to the operating costs of treatment systems (Pansonato et al 2011). In addition, membrane bioreactors can help by yielding marked reduction in the turbidity and BOD 5 of graywater (Hu, et al 2011).…”