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. 2019 May 13;14(5):e0216040.
doi: 10.1371/journal.pone.0216040. eCollection 2019.

Efficiency of chlorine and UV in the inactivation of Cryptosporidium and Giardia in wastewater

Folasade Esther Adeyemo  1   2 , Gulshan Singh  1 , Poovendhree Reddy  2 , Faizal Bux  1 , Thor Axel Stenström  1
Affiliations

Efficiency of chlorine and UV in the inactivation of Cryptosporidium and Giardia in wastewater

Folasade Esther Adeyemo et al. PLoS One. .

Abstract

Wastewater from different sources is contaminated by protozoan parasites including Cryptosporidium and Giardia. Many protozoan parasites are becoming resistant to chemical treatment. The challenge of finding alternatives is presented to researchers by exploring other methods of eliminating protozoan parasites from wastewater. The aim of this study was to assess the speciation and the viability of Cryptosporidium and Giardia in environmental samples with the specific objective of evaluating if effluent chlorination and UV affect the viability. Different doses of chlorine with different exposure times were experimented with both distilled water and waste water spiked with (oo)cysts derived from environmental samples. UV irradiation at different doses was also experimented using the same spiked samples. Two methods of quantification and detection, namely, microscopy and flow cytometry, were used in the experiment. Two vital dyes, Syto-9+PI and DAPI+PI, were the used for staining the collected wastewater samples. It was found that the (oo)cysts responded to chlorination and UV treatments with Giardia responding better than Cryptosporidium. Giardia responded very well to UV irradiations with almost 0 percent remaining viable after a low dose of UV. Cryptosporidium was found to be resistant to chlorination even at high doses but responded well to high UV doses. DAPI+PI dye gave a lower mean percentage viability values than Syto-9+PI. Flow cytometry gave higher mean percentage than microscopy from the results. It is concluded that UV is a promising alternative to Chlorine in removing Cryptosporidium and Giardia from waste water. Appropriate treatment method for wastewater is necessary to minimize water resources pollution when wastewater is released into water systems.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Mean percentage viability of Cryptosporidium and Giardia related to UV doses in treatment with spiked samples in distilled water and wastewater samples.
Fig 2
Fig 2. Mean percentage viability of Cryptosporidium and Giardia at different UV doses using Syto-9+PI and DAPI+PI dyes.
Fig 3
Fig 3. Mean percentage viability of Cryptosporidium and Giardia after prolonged exposure to 0.5 ppm, 2 ppm and 5 ppm of chlorine treatments for distilled water and wastewater.
Fig 4
Fig 4. Mean percentage viability of Cryptosporidium and Giardia at different chlorine exposures using Syto-9+PI and DAPI+PI dyes for distilled water and wastewater (microscopy method).
Fig 5
Fig 5. Flow cytometry histogram and dot plots showing viability of Cryptosporidium and Giardia at 40 seconds after exposure to UV irradiation.
Note: Samples of Region P1 and P2 represent gates for non-viable and viable (oo)cysts with P1 as side-scatter (SSC) against forward side-scatter (FSC).
Fig 6
Fig 6. Flow cytometry histogram and dot plots showing viability of Cryptosporidium and Giardia at 15 seconds after exposure to 5 ppm of chlorine.
Note: Samples of Region P1 and P2 represent gates for non-viable and viable (oo)cysts with P1 as side-scatter (SSC) against forward side-scatter (FSC).
See this image and copyright information in PMC

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