Abstract
Abstract Acute toxicity of raw and treated greywater towards Daphnia magna was assessed in this study. Treatment was performed with exposure of greywater to the fly-lime mixture After 48 h of exposure, 100 % mortality of D. magna was recorded when testing the following volumetric fractions of the raw greywater streams in the tested liquid medium (%; v/v): 10 % for kitchen greywater, 5 – 10 % for bathroom greywater and 1.25 – 10 % for laundry greywater. After greywater treatment with the fly-ash-lime mixture with pH adjustment to 7.0, 80 % of neonates of D. magna survived after exposure to treated laundry greywater in all dilutions at 48 h. At the same time, 100 % of neonates survived exposure to treated bathroom and kitchen greywater at all volumetric fractions. Therefore greywater had acute toxicity to D. magna, i.e. greywater treatment was required before its discharge or reuse. Values of the Pearson’s correlation coefficient between the chemical components of the raw greywater and treated greywater and the survival of D. magna indicated a lack of statistically significant correlation at 5 % level of significance (p-value > 0.05 in all cases), i.e. the survival of D. magna was independent of the concentration of chemical constituents in greywater samples tested. Further studies will have to be conducted on the chronic toxicity of the greywater effluent after treatment with the fly-lime mixture. Experiments from this study will have to be re-run for the fully scaled-up version of the fly-lime mixture-based greywater treatment systems.
Highlights
Greywater accounts for a large volume of the drinking water that is consumed daily in a household (Nondlazi et al 2017)
Nondlazi et al (2017) reported on the efficiency of a pilot-scale version of the flyash-lime-filter tower (FLFT) in greywater treatment. This system can be classified as a sanitation technology and toxicity testing with D. magna can be used to characterise the FLFT effluent before discharge (Tyagi et al 2007)
The exposure to mixed greywater was done only for the treated greywater, and a slight but significant difference (p = 0.01312) in the survival of the D. magna neonates when compared to that of the control samples. These results suggest that the raw greywater would require dilution before reuse or disposal, as this would ensure that the raw greywater is not toxic to the environment
Summary
Greywater accounts for a large volume of the drinking water that is consumed daily in a household (Nondlazi et al 2017). Further statistical analysis was done to determine the correlation between the concentration of the chemical constituents of the greywater and the survival of Daphnia magna. The correlation coefficients were calculated to indicate, whether the raw and/or treated greywater characteristics are likely important causes for the observed toxicity levels towards D. magna.
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