HYDRAULIC MODELING AND OPTIMIZATION OF WASTE STABILIZATION POND DESIGN FOR DEVELOPING NATIONS
CHAPTER ONE
INTRODUCTION
1.1 Background to the Study
The practice of collecting, treating and proper management of wastewater prior to disposal has become a necessity in developing and modern societies. This is because the consequences due to poor management of wastewater treatment systems have become enormous. Moreover, the need to minimize waste and make the most valuable use of nutrients present in wastewater is receiving global interest. Bixio et al. (2005) pointed out that the world’s freshwater resources are strained; therefore, reuse of wastewater, combined with other water conservation strategies can lessen anthropogenic stress arising from over-extraction and pollution of receiving waters. As reported by the World Health Organization (2000), “despite tremendous efforts in the last two decades to provide improved water and sanitation services for the poor in the developing world, 2.4 billion people world-wide still do not have any acceptable means of sanitation, while 1.1 billion people do not have an improved water supply”. This indicates that less than 1% and 15% of the wastewaters collected in sewered cities and towns in Africa and Latin America, respectively, are treated in effective sewage treatment plants. Mara (2001) also reported that out of the world population of just over 6 billion, 4 billion lack wastewater treatment and this is expected to rise to 7.8 billion by 2025. Most of these live-in developing countries where energy-intensive electro-mechanical wastewater treatment (the type favoured in industrialized countries) is too expensive and too difficult to operate and maintain.
Wastewater is the water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discarded by domestic residences, commercial properties, industry, and/or agriculture. Banda (2007) emphasized the significant composition of wastewater as the degradable organic compounds and these form an excellent diet for bacteria and are exploited in biological treatment of wastewater. In order to reduce the transmission of the excreta-related diseases and the damage to aquatic biota, Mara (2004) express the necessity to treat wastewater to meet the consent requirements of the effluent quality set by the regulatory agencies. The safe disposal of wastewater has been a great concern in developing nations, most especially in Nigeria. In 2008, estimated population of Nigeria was 151.5 million (UN, 2008) yielding an average density of 151 persons per sq km covering an area of 923,768 sq km (356,669 sq miles).
The population is projected to grow to 206 million by 2025 (Microsoft Encarta Encyclopedia, 2005). Treatment ponds serve thousands of communities around the world. In many cases, they are the only form of environmental protection that stands between raw sewage and natural waterways. Unfortunately, ignorance and lack of knowledge are responsible for poor wastewater treatment in many of these nations (Mara, 2004). Among the current, globally available processes used for wastewater treatment, waste stabilization pond (WSP) has been identified as the ideal treatment of municipal wastewaters in the tropics. This technology is well known for its simplicity of construction and operation (Mara, 2004). Shilton and Bailey (2006) noted that the only thing standing between raw sewage and the environment, into which it is ultimately discharged, is a waste stabilization pond. WSP has been emphasized to be the first-choice wastewater treatment facilities in developing countries as these operate extremely well in tropical regions at low-cost (Mara et al. 1992; Mara, 1997; Mara and Pearson, 1998). The WSP system typically consists of a series of continuous flow anaerobic, facultative, and maturation ponds. The anaerobic pond, which is the initial treatment reactor, is designed for eliminating suspended solids and some of the soluble organic matter. The residual organic matter is further removed through the activity of algae and heterotrophic bacteria in the facultative pond. The final stage of pathogens and nutrients removal takes place in the maturation pond. These three types of ponds when used in series, have demonstrated up to 95% removal of BOD and fecal coliform. (Mara, 2004; Hamzeh and Ponce, 2007).
In Nigeria, WSPs have been installed in some