Characteristics of greywater from different sources within households in a community in Durban , South Africa

The reuse of greywater is steadily gaining importance in South Africa. Greywater contains pollutants that could have adverse effects on the environment and public health if the water is not treated before reuse. Successful implementation of any greywater treatment process depends largely on its characteristics in terms of the pollutant strength. This study investigated the physico-chemical characteristics of greywater from different sources within 75 households in a community in Durban, South Africa. The study was undertaken to create an understanding of greywater quality from different sources within and between households. Greywater samples were collected from the kitchen, laundry and bathing facilities within each of the households. The samples were analysed for: pH, conductivity, turbidity, total solids, chemical oxygen demand (COD) and biological oxygen demand (BOD). There was a significant difference in the parameters analysed between the greywater from the kitchen compared with the greywater from the bathtub/shower and laundry. It was also observed that the characteristics of greywater from the different households varied considerably. The characteristics of the greywater obtained in this study suggest that the greywater generated cannot be easily treatable using biological treatment processes and/or technologies due to the very low mean BOD : COD ratio (<0.5). This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/wrd.2016.092 om https://iwaponline.com/jwrd/article-pdf/7/4/520/376228/jwrd0070520.pdf 19 B. F. Bakare (corresponding author) S. Mtsweni Faculty of Engineering, Department of Chemical Engineering, Mangosuthu University of Technology, P.O. Box 12363 Jacobs, Durban 4026, South Africa E-mail: bfemi@mut.ac.za S. Mtsweni S. Rathilal Faculty of Engineering and Built Environment, Department of Chemical Engineering, Durban University of Technology, P.O. Box 1334, Durban 4000, South Africa


INTRODUCTION
The shortage of potable water is one of the major challenges that many countries are facing today; the situation is becoming very serious and is worsening as many of these countries are experiencing drought (WHO ). Today, an inadequate supply of freshwater is one of the principal causes of public health problems facing many developing countries (WHO ; Katukiza et al. ). South Africa is a semi-arid country with spatial and temporal variability in the amount of rainfall received, coupled with high rates of evapotranspiration (Bakare et al. ). In South Africa, and around the world, there has been an increase in demand for freshwater, placing pressure on the ability of natural systems to provide an adequate quantity and quality because of population growth, urbanization and/or industrialization (Carden et al. ). This has led to large-scale interest in the application of water reclamation and reuse of domestic, mining and industrial wastewater as alternative water supply sources (Carden et al. ; Edwin et al. ).
The requirement for freshwater is becoming critical to sustaining development and economic growth in the Southern Africa region. The development of water reuse schemes in South Africa has been generally slow compared to some other developed countries. It is only recently that some water authorities in South Africa have begun to shift their focus to identify various water reuse and recycling schemes. It has been suggested that the large amount of greywater generated from South African households could be treated with simple technologies and reused for non-potable needs, such as toilet flushing and outdoor irrigation (Carden et al. ). Greywater is the water generated from household uses like bathing, laundry and washing of dishes, without input from the toilets (Edwin et al. ).
Greywater makes up to about 60-70% of domestic wastewater volume in most developed countries (Friedler ; Edwin et al. ). The generation of greywater is directly related to the consumption of water in a household and is dependent on a number of factors including the level of service provision, tolerance of residents to pollution and the communities' level of awareness of health and environmental risks (Carden et al. ). According to Carden et al. (), it could be assumed that greywater accounts for virtually all water usage in non-sewered areas except for that which is used for drinking purposes, that which is used consumptively in cooking and the water that remains on the surfaces of washed articles.
A variety of research has been conducted to characterize greywater generated from various sources in order to deter- ity of greywater depends on the source from which it is drawn as well as the use to which this water is put, but there are general characteristics that apply to greywater (Carden et al. ). Greywater can be divided into two categories based on pollutant loads: high pollutant load and low pollutant load (Friedler ). According to Li (), greywater generated from household kitchens and those from the laundry are higher in organics and physical pollutants compared to bathroom and mixed greywater. Various factors, such as the number of residents in a household, age distribution, living standard, residents' cultural habits and the quality of the water supplied to the household, may have an influence on the greywater characteristics and result in a wide variation in the quality of greywater generated from different households and from various sources within a household (Morel & Diener ).
In terms of basic water quality parameters, greywater is considered to be comparable to low-or medium-grade wastewater (Friedler ); however, there are several key differences in the quality of greywater that need to be considered in order to narrow in on the specific challenges involved in its treatment and reuse. Soaps and detergents are often alkaline, so the pH of greywater tends to be in the ) due to their ability to cause human illness. Microbial pathogens are often considered the most significant health concern associated with greywater reuse. Reviews of various characterization studies that include microbial parameters show that kitchen sink and dishwasher effluent are often the most highly contaminated due to the presence of food and grease particles and warn of high Salmonella counts in these streams (Birks & Hills ). Other sources, such as water from the bath, hand basin and clothes washing machine, are the principal contributors of organisms of faecal origin, attributable to the washing of soiled clothing or diapers, hand washing after toilet use and bathing.
Ottosson & Stenström () outline the full spectrum of hazardous microbial agents potentially present in household greywater and provide an outline for assessing the health risks they present. Pathogenic organisms identified include faecal bacteria, Campylobacter, Salmonella, Legionella, enteric viruses (especially Rotavirus), and protozoa, including Giardia and Cryptosporidium (Ottosson & Stenström ). This study was undertaken to gather information on greywater quality from different sources within and between households in order to identify the type of treatment processes that would be required for the type of reuse application. Thus, this paper reports on an investigation of the variation in the characteristics of greywater from different sources within a randomly selected number of households in a community in Durban, South Africa.

METHODOLOGY Study area
The study area used for this investigation, as in Bakare et al.

Greywater sampling
This study independently sampled and assessed the physical and chemical properties of greywater generated from the kitchen, laundry and bathing sources. Three sets of samples for each greywater source were collected from the 75 households over a period of 4 weeks mainly during the weekdays.
Grab samples were collected once a day from each source within 2 hours from production usually by/before noon in sterilized 1 L sampling bottles, and sealed and labelled before placing in a cooler box containing ice. Samples were collected directly from the shower or bathtub, and the laundry water was collected from the manual washing areas while the kitchen water was collected from the kitchen sink. Samples were immediately analysed where possible or stored at not more than 4 W C for a maximum of 24 hours.

Laboratory analysis
Physico-chemical analyses of the greywater collected were determined for the selected parameters: pH, conductivity, turbidity, total solids, COD and biological oxygen demand

RESULTS AND DISCUSSION
The results obtained from the physico-chemical characterization of greywater collected from various sources within the different households are presented as box and whisker plots in Figures 1-6. The pH results are presented in Figure 1.
The average measured pH value for the different sources (kitchen, laundry and bath) were found to be 6.25, 9.58 and 9.24 respectively. It was observed that the greywater from the kitchen had the lowest pH value. This could be attributed to the fact that greywater generated from the kitchen was mostly contaminated with fractions of food particles and oils, and degradation of the greywater will occur more rapidly in an anoxic condition compared to the greywater generated from other sources. The relatively higher pH values for greywater collected from the laundry and from bathing may be due to the alkalinity of the type of detergent and/or soap used for these activities. Statistical analyses conducted using univariate ANOVA with a post-hoc Scheffe test indicated that the difference in the measured pH values for the different greywater sources was significant (p < 0.05). The overall average pH value from the three  sources was found to be 8.35. This value falls within the range 6.5-8.4 (USEPA ) which is said to be an appropriate value that will enhance easy treatment or will not have adverse impacts on soil or plants when used for irrigation.    NTU, 170 NTU and 120 NTU respectively. Comparison using univariate ANOVA with a post-hoc Scheffe test indicated that the differences were significant (p < 0.05).
The results obtained from the measured total solid concentrations in the greywater are presented in Figure 4.
Greywater collected from the kitchen exhibited the highest total solid concentration, which was attributed to the fact that the greywater from this source was the most contaminated fraction with food particles. The average measured total solid concentration in the kitchen greywater was found to be 3,589 mg/l. The total solid concentration in the laundry greywater was lower with an average measured value of 736 mg/l while that from bathing was found to be the lowest with an average value of 504 mg/l. Comparison using univariate ANOVA with a post-hoc Scheffe test indicated that the differences was significant (p < 0.05).
COD measures the amount of oxygen required to oxidize the organic material present in a water sample. The measured value of COD is usually higher than that of measured BOD in many waste streams because many organic substances can be oxidized chemically rather than biologically. Measured COD is an indication of the polluting strength of the greywater generated from the three sources within the household investigated. Figure  The characteristics of the greywater obtained in this investigation conducted indicate the necessity of treatment prior to disposal into the environment or for reuse purposes (including non-potable reuse). However the greywater quality generated from the community in which the study was conducted cannot be easily biodegraded as revealed by the very low BOD : COD ratio.
This study therefore recommends that appropriate treatment methods should be developed to treat the greywater generated from this community. Natural treatment systems such as horizontal roughing filtration systems or constructed wetlands could be considered because of low cost and maintenance requirements.