CHAPTER 1
Introduction to decentralized wastewater management systems
This chapter will
• Introduce the subject and importance of decentralized wastewater management systems;
• Introduce the purpose, need and audience for this manual; and
• Present the terms and definitions common to these systems.
About Figure 1.1
The photos of Mr. Makara's latrine factory near Phnom Phen, Cambodia (Figure 1.1), illustrate how the power of markets can be used to scale up sanitation. Market-based sanitation means matching the ability to supply products with programs that enhance demand and provide incentives fostered by engaged local governments. The major components are:
(1) Demand generation: People are generally willing to pay for improved sanitation if they believe it will address their needs, wants, and desires. Understanding what these may be for a population means information must be gathered. Development specialists use tools such as customer surveys, focus group discussions, and interviews with key stakeholders to find out what people really want, what they think, and what they think they need related to sanitation. In some instances, their overriding desire is to improve the health of their children. In other areas, it might be the convenience of having indoor plumbing or the status of having a flush toilet. When sanitation technologies are promoted to address the needs, wants, and desires of people treated as customers, they will be more willing to pay for services. Also, it is important to note that to achieve sustainability, the sanitation improvement must fulfill the promises that are made, or people will find other uses for their money.
(2) The sanitation value chain: The value chain of decentralized wastewater management describes how technologies are manufactured, sold, delivered, installed, operated, and maintained. To sustain the value chain, products should be manufactured using local materials and labor, and service providers should be trained through strong capacity-building exercises. When demand is generated (as described above), the value chain produces sales, profits, jobs, and economic development.
(3) The enabling environment: This is the combination of incentives and the regulatory framework that promotes rather than inhibits participation in sanitation improvement programs. Good programs include incentives that offer tangible benefits to those that comply, as well as enforcement provisions for those that do not. It is also the way local governments interact with citizens and businesses. Frameworks that speed up and simplify a fair and transparent regulatory process can be powerful tools local governments can use to scale up sanitation using decentralized wastewater management.
Achieving sanitation improvements at scale requires evidence-based promotions campaigns, a robust value chain, and an enabling environment that works. When all three of these elements are present together, improving sanitation can be a strong force for major social and environmental change.
1.1 BACKGROUND
In the past several decades, many organizations have described the lack of basic sanitation for much of the world's population. Estimates put the number of unserved people at more than two billion, mostly in South and East Asia and sub-Saharan Africa. In those regions there are 45 countries where sanitation coverage is less than 50% (Figure 1.2).
While the estimates and definitions of access to basic (often referred to as 'improved') sanitation have been challenged, it is widely agreed that this problem represents a crisis given the strength of the link between poor sanitation and disease and death, especially in children. Poor sanitation results in a significant yet preventable health and financial burden on individuals, families, communities, and countries. The economic burden is quite significant. For example, in India it was estimated that in 2006 the cost of poor sanitation amounted to 6.4 percent of the country's gross domestic product (World Bank Water and Sanitation Program, 2010).
To meet the widespread need for wastewater treatment, centralized sewerage systems have been implemented as the norm for large, medium, and even small sized cities and municipalities in developed countries. However, it is unlikely that centralized wastewater treatment systems will be used in developing country settings except in the most densely populated urban centers.
The rest of the population, as well as the commercial, industrial, public, and other facilities lacking proper sanitation systems will need to rely on site-specific solutions using on-site and decentralized wastewater treatment, dispersal, and reuse technologies. The benefits of smaller, decentralized wastewater management systems are many, as they use simpler technologies, allow for more cost-effective reuse of treated effluent on or near the site where the wastewater was generated, are generally simpler to install and maintain, and can be a force for economic development. Indeed, they not only improve sanitation and environmental health, but they can also lead to job creation along the entire value chain, from equipment manufacturers to system designers, installers, and operators.
1.1.1 Combining Technologies to Form Systems
Decentralized wastewater management systems, like their centralized counterparts, use a variety of technologies that work together to achieve many goals. The major goals are to remove sewage away from humans, reduce the pollution from the collected wastewater, and safely disperse the treated effluent, or reuse it and other residuals for beneficial purposes. These are accomplished by linking appropriate technologies together to form systems that meet the specific needs of the end-users. These systems, which vary widely in both complexity and cost, can include:
• toilets, or the human interface that includes individual toilets, latrines, and community-based toilet blocks that serve as the first point of collection for human waste and help to remove it from potential human contact;
• sewers and wastewater collection technologies that collect wastewater from the interface and deliver it to locations for treatment;
• treatment technologies that treat wastewater to a level that is 'safe' for discharge, reuse, or dispersal; and
• reuse and recycling, which represent the technologies that allow for the safe reuse or recycling of the treated effluent or other residuals from the wastewater treatment process, such as biosolids and biogas.
Selecting the most appropriate technologies requires knowledge of the wastewater source and an understanding of the site conditions where the wastewater will be managed. Knowing this information will help service providers to optimize their systems as well as to avoid costly and time-consuming mistakes that could come from improper technology selection. Given their importance, the procedures for conducting wastewater source characterizations and site evaluations in support of decentralized wastewater management systems decision-making are the focus of this manual.
1.1.2 Evolution of the Concept
In recent years, many organizations have used different terminology to describe the concepts of on-site and decentralized wastewater management. The term 'on-site wastewater treatment systems' has been used widely in the United States for many years to describe septic systems and leach fields, or other wastewater systems that manage the wastewater on the site where it was generated. The United States Environmental Protection Agency (US EPA) popularized this term in their 'Onsite Wastewater Treatment Systems Manual', first published in 1980 and revised in 2002.
DEWATS, or Decentralized Wastewater Treatment Systems, is an acronym popularized by the Bremen Overseas Research and Development Association (BORDA) in the 1990s. BORDA considers DEWATS to be the various technologies for primary and secondary wastewater treatment that have relatively low-cost operation and maintenance requirements and are most suitable for low-income and sub-tropical regions (Sasse, 1998). The major example of their approach is their DEWATS model, which uses a biogas digester and anaerobic baffled reactor for primary treatment and a constructed wetland for secondary treatment.
The International Water Association (IWA) is also advancing the practice of decentralized wastewater management in developing countries and has recently introduced the concept of wastewater management as a more holistic approach. In their Conference on Decentralized Wastewater Management in Asia 2012, which occurred with the support of BORDA in Nagpur, India, that concept was widely promoted by including topics of wastewater collection, treatment, reuse, and recycling of the treated effluent, rather than just wastewater treatment and dispersal. Wastewater management also includes planning, financing, promotion, and regulation of all aspects of wastewater, from its generation to its ultimate reuse or final dispersal. For these reasons, the authors of this manual use the acronym DWM, which stands for decentralized wastewater management, and the related term DWMS, which is used in this manual to mean decentralized wastewater management system(s).
1.1.2.1 A Note on Scale
Defining DWMS is somewhat difficult because decentralization is a concept of scale. Unlike centralized systems that collect and manage sewage at one location, decentralized systems manage the sewage closer to where it is generated. Under this definition, a subdivision with 100 homes that uses individual septic tanks and leach fields for each house would be using a decentralized approach to wastewater management. But would a common system that manages the wastewater from all 100 homes be considered a DWMS? For the purposes of this manual, the answer is 'yes', as the management is closer to the sources than if it involved linkage to a single system that served an entire city. But what if 1,000 homes in different areas combined their wastewater flows into a common system? Would these still be considered DWMS? The answer is that for the purposes of this manual, it does not really matter. This manual's goal is to provide useful information on the step-by-step approach of source characterization and site evaluation to make informed technology decisions. When properly trained, local government officials, service providers, or private developers can utilize the process, which is applicable to wastewater projects of all size.
1.2 THE PURPOSE OF THIS MANUAL
People in developing regions of the world generally want improved sanitation and healthy children, and increasingly are seeing the link between improving wastewater management and achieving these goals. Just as important, they often have the ability to pay for wastewater management and the desire to do so. Also, there is often sufficient land available to install systems, and locally available materials, labor, and resources to construct and maintain them. The missing ingredient is the 'how to', meaning how to move from wanting proper wastewater management to implementing a system.
This manual aims to provide the needed information that will help communities that want to improve sanitation utilize the procedures and practices that can make DWMS a viable community-based solution. It details a process for making informed technology decisions based on the specific nature of the development project. This manual can serve as a handbook, field guide, text book, and resource for those with the desire to implement DWMS. In particular, it can serve as an important part of necessary long-term capacity-building programs involving activities such as training, 'twinning' where more advanced utilities (donors) join with less advanced utilities (recipients) for sharing of best practices, job sharing, mentoring, and apprenticeships. This manual's concepts serve as effective methods for teaching and certifying practitioners and may help institutions of higher education find donor funding for train-the-trainer programs or establish degrees, certificates, or in-service educational products.
Furthermore, this manual addresses the need for better methods of wastewater technology selection, which is achieved through promoting a 'context-specific' approach to DWMS technology selection. The process identifies which technologies are most appropriate given the source characteristics and site and other resource limitations. Once the data gathering process is complete, appropriate technologies may be selected to meet the specific needs of the owner.
This manual includes check lists and step-by-step procedures to help users track the data gathering activities, and case studies to illustrate practical applications. Tools, forms, and Internet links to additional information help the user organize the collected data so that it may be used to base sound decisions for positive results. Case studies highlight how other project implementers in similar settings have collected and used relevant information to address their wastewater management needs. These case studies and practical applications are presented to inspire the reader to action by showing that these tasks can be accomplished with available resources.
Finally, site evaluations and wastewater system designs are services that can be performed by the private sector and in many instances, local government. It is hoped that this manual serves as useful guidance to the practitioners doing this work, and that it simplifies tasks and improves results.
1.3 THE AUDIENCE FOR THIS MANUAL
This manual is intended to benefit three major audiences:
(1) Private-sector DWM service providers;
(2) Local and national government regulatory officials tasked with DWM oversight; and
(3) Development specialists and researchers, such as those within NGOs and civil society groups working to promote and scale up sanitation improvement.
Building the capacity of private sector DWM service providers (Figure 1.4) is critical in scaling up sanitation improvement. This core group of individuals and business owners are the first audience for this manual, and includes:
• engineers and service providers that will be tasked with planning the DWMS of the present and the future;
• contractors that will be required to install the system components using best installation practices;
• septic tank desludgers and general maintenance staff who will be paid to operate and maintain systems;
• plumbers and electricians who will be called upon to help the contractors properly install systems; and
• technology providers that must ensure that the components they sell to end-users are appropriate given the specific needs and conditions of the project.
The second audience for this manual is local government officials who are responsible for wastewater management in their communities. These officials may manage local sanitation plans, enforce local wastewater laws, or oversee planning and installation of DWMS. In many instances, local governments have yet to implement procedures for DWMS, but many are thinking about it. Agencies that apply the information in this manual to develop their DWMS programs will be more likely to see the real and sustainable benefits for their community.
The third audience for this manual is development workers who promote sanitation through the power of DWMS. Development projects are often the first sanitation interventions in a community or region. Development programs funded by international donors may, in many cases, begin by working with local public and private stakeholders to create pilot projects. Local pilot projects that follow a step-by-step approach and create systems that are appropriate for local conditions can be a model for other projects in the community or region.
1.4 THE DWMS DEVELOPMENT MODEL
The DWMS Development Model (Figure 1.5) provides the basis for the step-by-step process for making informed technology decisions. It also suggests a method for integrating wastewater decision-making into the local government's existing compliance structure. Each step in the process could be associated with officials' physical inspection, with plan review by trained specialists, or through self-compliance and reporting programs. The premise of the model is as follows:
In order to determine the most appropriate technology choices of a DWMS for managing a specific wastewater flow, it is first necessary to properly characterize the wastewater source. Then, the site where the wastewater will be managed must be evaluated. These two steps must follow the principles stated below.
• The source must be characterized to determine the:
* volume of wastewater to be treated, otherwise known as the hydraulic loading or design flow;
* concentration of organic matter and other contaminants in the wastewater, otherwise known as wastewater strength;
* variability of the source conditions as they change over time; and
* other constituents or parameters that define the wastewater source.
• The site must be evaluated. This involves determining the:
* conditions of the site, including soils properties, slope and topography, the presence of groundwater and surface water, land use, utility issues, accessibility, reuse and regulatory concerns, and other aspects that may restrict the site's capacity to receive and process wastewater. It also suggests the range of DWMS technologies appropriate for the site.
