Abstract:
Water recycling is now widely accepted as a sustainable option to respond to the
general increase of the fresh water demand, water shortages and for environment
protection. Because greywater represents up to 70% of domestic wastewater volume
but contains only 30% of the organic fraction and from 9 to 20% of the nutrients
(Kujawa-Roeleveld and Zeeman, 2006), it is seen as one of the most appropriate
sources to be treated and reuse. A broad range of technologies has been used for
greywater recycling including soil filters (Itayama et al., 2004), membranes (Ahn et
al., 1998) and biological aerated filters (Surendran and Wheatley, 1998). However, at
small scale, such as individual household, the variability in strength and flow of the
greywater and potential shock loading affect the efficacy of biological technologies.
Moreover, simple physical processes, efficient to reduce the physical pollution within
the greywater, are often limited to degrade the organic fraction (Jefferson et al, 2000).
There is then a need for alternative technologies that would not be affected by such
problems and that could provide the treatment required for reuse.
This project investigated the potential of alternative technologies for greywater
recycling. Four chemical systems, coagulation, MIEX®, adsorption and membrane
chemical reactor based on an advanced oxidation process (TiO2/UV), were assessed at
bench scale. Coagulation and MIEX® were found to achieve a limited treatment of the
greywater and consequently to be not suitable in case of strict reuse standards.
Whereas, adsorption with activated carbon and membrane chemical reactor provided
a very good treatment of the greywater with an advantage to the advanced oxidation
process as it could meet the strictest standard for reuse for BOD, turbidity and
suspended solids as well as for the total and faecal coliforms.
Following this results the membrane chemical reactor was tested at pilot scale and
compared to a benchmark system, a membrane bioreactor. Both systems achieved a
very good treatment of the greywater; however, the MBR was found to be a more
robust technology with all the samples tested for BOD and turbidity below the most
stringent standards. The main difference between the two systems was observed in
terms of the hydraulic conditions. Indeed, important membrane fouling was occurring
in the MCR.
A more detailed study of membrane fouling in the MCR was carried out for a better
understanding of the phenoma occurring. It was found that little fouling occurred
when TiO2 was dispersed in clean water. Alternatively, a significant fouling could be
observed when TiO2 was coated with specific products suggesting that a reaction
occurs when TiO2 is in solution with particular chemicals changing its fouling
propensity.
Overall, the MBR was found to be the best technology in terms of performance and
robustness. However, it was also found that spiking of domestic products can alter its
performance due to their toxicity. Chemical systems, which are not affected by
toxicity, seem to be a good alternative to biological systems. However, none of the
systems tested here could match the effluent quality achieved by the MBR.
Alternatively, the MCR achieved good treatment performance and limitation of the
membrane fouling would make it a very good alternative.