A. A. Ilemobade

A group decision-making tool for the application of membrane technologies in different water reuse scenarios

A global challenge of increasing concern is diminishing fresh water resources. A growing practice in many communities to supplement diminishing fresh water availability has been the reuse of water. Novel methods of treating polluted waters, such as membrane assisted technologies, have recently been developed and successfully implemented in many places. Given the diversity of membrane assisted technologies available, the current challenge is how to select a reliable alternative among numerous technologies for appropriate water reuse. In this research, a fuzzy logic based multi-criteria, group decision making tool has been developed. This tool has been employed in the selection of appropriate membrane treatment technologies for several non-potable and potable reuse scenarios. Robust criteria, covering technical, environmental, economic and socio-cultural aspects, were selected, while 10 different membrane assisted technologies were assessed in the tool. The results show this approach capable of facilitating systematic and rigorous analysis in the comparison and selection of membrane assisted technologies for advanced wastewater treatment and reuse.

Application of a constrained non-linear hydraulic gradient design tool to water reticulation network upgrade

Southern Africa has embarked on substantial expansion of its water supply network in order to ensure safe, reliable, convenient and sufficient water for everyone. To achieve this, new systems are being built and many existing systems are being upgraded. The upgrade of many existing systems is required for two reasons: some currently functional systems may run dry if subjected to additional demands as these systems were not initially designed to cater for such demand, and some systems are currently non- or sub-functional as they were ill-designed and/or ill-implemented from inception. Many of the systems that require upgrade are underdesigned due to a lack of skill, tools and/or knowledge of designers, or from other extraneous factors (e.g., illegal connections and sabotage). It is hardly surprising therefore that the failures of water projects in developing countries are recorded to be as high as 80%. Ill-designed systems increase operation and maintenance costs significantly. In especially Southern Africa, designers require simple, yet rigorously tested tools to facilitate sustainable, yet cost-effective network designs. Presented in this paper is a simple, yet robust constrained non-linear hydraulic gradient network reticulation design tool. The design tool is calibrated using the New York City water supply problem that has served as a benchmark problem for other models and then applied to the Selebi – Phikwe (SP) water reticulation network (WRN) in Botswana, which was designed based on engineering judgement. The optimization algorithm employed in the design tool is based on the concept that a hypothetical hydraulic gradient for a hydraulically balanced WRN exists that, when achieved iteratively, produces optimal pipe sizes and an optimal flow relation between each pipe. The unique problems and challenges of the SP WRN (pressure deficiencies in sections of the existing network and the proposed addition of three new residential developments) required determining the most appropriate peak and night flow operating scenarios, and optimal pipe sizes for the proposed expansion of the network. Optimization by trial and error had been previously employed in the design of the SP WRN—a common practice amongst water system designers, and the results are compared with those generated with the design tool. The design tool achieved a 62% reduction in total pipe cost from that obtained by trial and error for the SP WRN problem. At the same time, the design tool gives comparable pipe costs to those published in literature for the New York City water supply tunnels problem.

NON-POTABLE WATER USE/REUSE IN SOUTH AFRICA: REVIEW AND STRATEGIC ISSUES

In many water scarce communities across the world (e.g. Gold Coast - Australia, Hong Kong – China, Islands of the Caribbean and Pacific, and Windhoek – Namibia), non-potable water use/reuses have been employed. In essence, the non-potable water source (e.g. coastal/sea/ground saline water, mine effluent, sewage effluent, and grey water) is targeted at meeting non-potable water requirements (e.g. toilet flushing, landscape and/or crop irrigation, industrial (including mining) cooling and other processes) traditionally met using potable water. This therefore frees potable water to be used for previously unmet or increasing potable water requirements. For several reasons, the use/reuse of non-potable water for non-potable water requirements has been limited in South Africa. This is despite the fact that South Africa is a chronic water scarce country (500-1000 m 3 /person/annum) approaching absolute water scarcity (<500 m 3 /person/annum). Regulatory and guideline documents at the national, provincial and municipal level to implement such an alternative have been lacking. This paper highlights a few non-potable water reuse schemes that currently exist in South Africa and the strategic issues, which if adequately attended to, will facilitate a broader acceptance of non-potable water use/reuse.

Membrane assisted technology appraisal for water reuse applications in South Africa

Water scarcity, pertaining to many interrelated issues e.g. rapid urbanisation and increasing water pollution, has been acknowledged around the world. Water reuse has emerged as a viable water conservation measure to satisfy water demand in many communities. Among the diversity of wastewater treatment processes, membrane assisted treatment technologies have been employed for different water reuse scenarios. In this regard, one of the most critical problems is how to select an appropriate membrane technology for a water reuse scenario. This research therefore develops a decision making framework for selection of wastewater treatment technology. The framework is applied to different non-potable reuse scenarios in South African cities and suburban areas by employing a multi criteria analysis method. The results show that this approach is able to provide a systematic and rigorous analysis which can help in comparing and selecting wastewater technologies.

AN EVALUATION OF DOMESTIC AND NON-DOMESTIC WATER CONSUMPTION IN SOUTH AFRICA

South Africa is a water scarce country that constantly strives to apply its available water resources in the most efficient and equitable manner. Different users including industry, domestic, agriculture and the environment, vie for the available resources and have to be awarded an equitable and adequate share to ensure sustainability in the long term. Proper water demand management in South Africa is thus of critical importance. Researchers, municipal engineers and engineering consultants require good and reliable data and design guidelines on water demand patterns and factors influencing water demand to achieve this aim. The most commonly used South African guideline for municipal water demand was first published in 1983, and is currently included in the document titled Guidelines for human settlement planning and design. The guideline provides upper and lower limits for domestic consumer demands as a function of stand area. In this paper, the authors analyze measured water demand data of more than a million stands (domestic and non-domestic) contained in the treasury data for a cross-selection of South African towns and cities. The main objectives of the study were to evaluate the existing South African domestic demand guidelines and to evaluate the parameters that influence domestic and non-domestic water demand. The main results of the study indicate that the domestic demands of most of the users fall well within the upper and lower limit envelope curves of the South African design guideline although for larger stands the design guideline was found to be conservative. Stepwise multiple variable regressions were applied to domestic and non-domestic consumption data to determine the most significant variables influencing water demand. In a large majority of cases, either the stand area or stand value had the greatest significance. There is strong evidence that both domestic and non-domestic demand increase with increasing, stand area and stand value. In, the case of domestic demand, stand value was used as an indicator for household income level. The study found that inland domestic water demand is significantly and consistently higher than coastal demand. This trend was not observed for non-domestic demand. However, the development level (city vs. small town) was found to have a marked impact on non-domestic demand. The study also found that the frequency distributions of annual average daily demand (AADD) for specific non-domestic user categories seem to have a lognormal distribution. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).

Statistical characterisation and estimation of non-domestic water demand

Abstract Estimation of annual average water demand figures is critical for the design and evaluation of water distribution systems. This study evaluated the metered water consumption of more than 67,000 non-domestic consumers in six categories from cities and towns in South Africa. It was found that lognormal distributions provide good descriptions of the annual average daily demand (AADD) distribution in each category. The land use categories Business Commercial, Industrial, Agricultural holdings and Sports & Parks displayed similar median AADDs of between 1.5 and 1.7 kl/property/day. Educational properties used substantially more water (4.7 kl/property/day), while Government & Institutional properties used substantially less water (0.7 kl/property/day). A step-wise regression analyses showed that property size has the greatest impact on water demand for most categories. Finally, a novel statistically based method is proposed for estimating the average AADD of a given number of properties based on an acceptable risk of non-exceedance.

Software Development for the Water Sector

The water sector in the last 20 years has undergone radical paradigm shifts arising from the crisis of global proportions that have characterized the sector, prompting many international fora, including the Dublin conference in January 1992. One of the responses from academic institutions to this crisis is the development of computer-based predictive tools for better and more accurate prediction of the variables that affect water use and management. In the School of Civil and Environmental Engineering at the University of the Witwatersrand, attempts have been made to develop software to aid planning, management, and decision making in the water sector. Two of such software are Wadessy - a water distribution network design software, and a groundwater flow modelling software GEMFLOW that is based on the Green element method (GEM). Although their engines are quite robust and have been applied in field studies in Botswana and Zimbabwe, and compare favourably with published models, their elegance in terms of graphical user interface (GUI) is still rudimentary. The cost for their development has been mainly in the training of postgraduate students who have assisted in their development. Industry uptake has been very limited, which is one of the reasons why their GUIs are still rudimentary. With greater investment into the development and marketing of these and many other software, the potential exists to have “made-in-Africa” software with capabilities comparable, if not better than, those developed in more advanced countries. This paper reports on these software, compares these with similar initiatives in more advanced countries, and discusses the challenges in development, funding, and uptake by industry. The experiences described herein are most likely to be similar with other software development initiatives in sub- Saharan Africa.