Abstract:
This study focused on the investigation of the impact of household cleaning and
personal care products on the quality of grey water and the assessment and optimisation
of grey water treatment by a novel constructed wetland design. The prototype wetland
design which comprised three-stage cascading beds (0.27 m
2
by 0.20 m deep) with sand
media, (d10: 1.0 mm and d90: 4.0 mm) was tested for treatment performance to meet
non-potable reuse standards in three versions, unplanted open beds, unplanted covered
beds, and planted beds (comprising mixtures of Iris pseudacorus, Iris chrysographes,
Carex elata Aurea and Mentha aquatica). The prototypes were benchmarked against a
standard single-pass wetland (6 m
2
by 0.7 m) planted with Phragmites australis.
Performance was measured in terms of removal of conventional water quality
determinant parameters, as well as Total coliforms and E coli, and surfactants.
Microbial dynamics were also monitored during the study by looking at variations in
microbial compositions with time for the different wetlands. All the wetland versions
effectively removed more than 98 % turbidity and organics meeting the most stringent
reuse wastewater reuse standards of < 2.0 NTU and < 10 mg BOD5/L respectively. The
influent grey water had low BOD:COD ratio ranging from 0.27 – 0.45, which is
indicative of low biodegradability. The comparison of the cascade wetland
performances showed the following: open beds > planted = covered, with the open beds
version meeting reuse standards virtually throughout the monitoring period, despite
recurrence of schmutsdecke in the top bed. All wetland technologies supported viable
populations of microorganisms. Only phospholipid fatty acids (PLFAs) of lower carbon
chain length (< C20) had concentrations greater than 1 mol %, in all the wetlands beds,
confirming that the majority of the PLFAs in the media were from contribution of
microbial organisms and not plant organic matter. Characterisation of microbial
organisms was carried out to understand the constructed wetlands functioning and thus
the treatment processes. The household products showed nutrient deficiency signifying
low treatability. Product branding did not show correlation with any water quality
parameters. In terms of toxicity, laundry and cleaning products were more inhibiting to
soil microorganisms than were personal care products.
