A Comparative Study of the Physico- chemical Properties and Bacterial Load of Greywater in Estates in Homabay Town and Githurai Estate
Ng'ang'a, Victor G.
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In recent years concerns over dwindling reserves of ground and surface water resources coupled with an overloaded or costly sewage treatment plants has generated much interest in the reuse or recycling of greywater. Greywater is untreated household wastewater which includes water from; showers, laundry, dishwashers and washing machines. Re-use of greywater offers several advantages that include a reduction in the water bill, reduced wastewater discharge, as well as reduction in the demand on potable water supplies. Due to the insufficient supply of water, some limited reuse of greywater is practiced in rural-urban and peri-urban settlements. However, there is no information on the bacteriological quality and physico-chemical properties of the greywater produced in the selected areas. Hence the potential risk to human health arising from the reuse of greywater is unknown. Therefore this study was aimed at determining the bacriological and physico-chemical quality and safety of greywater produced by communities in a peri-urban (Githurai) and rural-urban (Homabay) settlements for reuse purposes. The bacterial load was determined using indicator organism. The method used was that of membrane filter-technique (MF) for total coliforms where bacteria count was made using colony counter. The study also investigated the presence of common pathogens in greywater. Isolation, identification and enumeration of enteric pathogens i.e. Salmonella, Shigella and Vibrio was carried out using appropriate techniques and procedures. Physico-chemical properties were determined using appropriate techniques and procedures. Results for electrical conductivity of samples from various estates, ranged from 60 to 4470 μS cm-2. However, the difference in EC among the greywater sources was not significant, but there was a significant difference in mean EC among the greywater types. Dissolved oxygen concentration of greywater ranged from 0.0 to 8.0 mg L-1 with a mean value of 3.5 mg L-1, an indication that it may be necessary to subject the greywater generated to some initial aeration. Greywater pH range of 5.0 to 10.3 was comparatively wider than that of the drinking water sources (6.7 to 7.5). The salinity of greywater samples was comparatively greater than that of drinking water with a range of 0.0-2.3 ml/L. There is a risk of increased salination of topsoil over the long term. An overall total coliform range of 1.3 -7.8 million CFUs recorded is comparatively lower than a value of 2.4 x 103 to 2.4 x 106 measured in the Dome distribution system in London but higher than the recommended value by WHO (6.0 x 103 – 1.9 x 105). Fecal coliform counts in greywater from various household operations ranged from 0.029x10 to 6.8x105 CFUs per 100 ml with a mean of 2.02 x105 CFUs per 100 ml. The presence of total coliforms and fecal coliforms shows fecal contamination, indicating the possible presence of pathogens. Attempts to identify specific pathogens in greywater samples tested revealed that Salmonella, Shigella and Vibrio species were present in various estates and greywater types. Salmonella was the most frequent and its presence was recorded in 29.4% of all the samples collected. Shigella and Vibrio cholerae were recorded in 19.6% and 8.8% respectively.The presence of pathogens indicates that untreated greywater may pose a health risk to residents. From the study, it is clear that bacteria load in greywater was generally high. It is recommended that simple greywater treatment technologies should be introduced to the residents of the study area.