Keywords

1.1 Background

Water quality poses a significant challenge worldwide as industrialization, urbanization, and climate change continue to escalate. In mitigating urban water pollution, nature-based solutions (NbS) for water treatment have emerged as a promising approach, offering multiple co-benefits that enhance the livability and resilience of cities. Several pilot and demonstration projects across Asian cities have explored the potential of NbS; however, there is a dearth of comprehensive documentation on their effectiveness and impacts. Additionally, the sustainability, replication, and upscaling of these solutions remain poorly understood. To address this knowledge gap, the Asia Pacific Network for Global Change Research funded a two-year project (October 2021 to September 2023) involving an international research team from Australia, Sri Lanka, the Philippines, Vietnam, and Spain, which includes the authors of this chapter (source: https://doi.org/10.30852/p.18686). The project’s objective is to conduct an integrated assessment of existing practices and explore pathways for the effective integration of nature-based water treatment in urban areas of Sri Lanka, the Philippines, and Vietnam. This book draws upon the research conducted within the framework of the project.

Nature-based approaches to water management and treatment have experienced a renewed interest in recent decades, although the concept itself is not new. It is essential to revisit the definition of nature-based solutions (NbS). According to the European Commission (EC), NbS encompass solutions that address socio-environmental challenges such as climate change, water security, water pollution, food security, human health, biodiversity loss, and disaster risk management. These solutions are inspired by and aligned with nature, offering cost-effective means to simultaneously provide environmental, social, and economic benefits while enhancing local resilience. NbS aim to integrate a greater diversity of nature and natural features and processes into urban areas, landscapes, and seascapes through locally adapted, resource-efficient, and systemic interventions. Notably, the EC updated its definition in 2020, underscoring the importance of NbS in benefiting biodiversity and supporting the delivery of various ecosystem services.

NbS, such as roof gardens, vertical gardens, sustainable drainage systems, ponds, constructed floating wetlands (CFWs), and constructed wetlands (CWs), offer significant opportunities for decentralized water management, particularly in areas where centralized solutions are limited or economically impractical. These solutions typically require less energy than conventional systems while delivering a multitude of ecosystem services.

The implementation of NbS brings forth a range of regulating services, which encompass improved air quality, favorable local climatic conditions, reduced stormwater run-off, prevention of soil erosion, mitigation of natural hazards, increased pollination, and the creation of new habitats to support urban biodiversity. In addition, these solutions generate supporting ecosystem services that contribute to nutrient cycling, water cycling, soil formation, and photosynthesis, thereby enhancing the overall ecological balance. This, in turn, leads to provisioning ecosystem services, increasing the availability of food, fiber, fuel, biomass, freshwater, and natural medicines within the urban environment.

Moreover, the adoption of NbS also has positive implications for cultural ecosystem services. It enhances opportunities for recreation and ecotourism and fosters the development of ethical values and recognition of existence values, further strengthening the connection between communities and their natural surroundings.

Within the scope of the aforementioned project, extensive research on NbS identified constructed wetlands (CWs), green roofs (GRs) for water treatment, and constructed floating wetlands (CFWs) as promising approaches in the local context. For a considerable period, lakes in Sri Lanka have served as vital sources of drinking water and popular recreational spots. However, with the rapid urbanization and the associated by-products, these lakes are experiencing pollution, posing significant environmental challenges. In order to address this issue, the implementation of floating wetlands has emerged as an effective and cost-efficient solution for treating the incoming water in these lakes. As a result, the study focuses on the placement of CFWs in lakes, recognizing their potential to mitigate pollution and safeguard the ecological balance. Similarly, in densely populated urban areas of Vietnam, the lack of proper treatment for septic tank effluents has led to significant pollution in canals and rivers. To tackle this problem, the study proposes a twofold approach. First, by treating the septic tank effluent at its source using GRs, the study aims to prevent the introduction of pollutants into the canals. Additionally, CFWs are considered a suitable choice to address the pollutants already present in the canals, thus providing a comprehensive solution for water treatment in these urban areas. In the Philippines, constructed wetlands have been identified as crucial components in the treatment of septic tank effluents. These wetlands play a significant role in effectively treating and purifying the wastewater generated by septic systems, contributing to overall water quality improvement. By recognizing the specific challenges faced in each country and exploring the appropriate NbS, the project aims to contribute to the preservation of water resources and the protection of the environment in Sri Lanka, Vietnam, and the Philippines.

Thus, to assess their effectiveness and impacts, pilot studies were conducted in Vietnam, Sri Lanka, and the Philippines. These studies focused on a green roof system and a floating wetland in Vietnam, two floating wetlands in Sri Lanka, and two constructed wetlands in the Philippines. Detailed findings and insights from these studies, as documented by Jegatheesan et al. (2022), Dang et al. (2022), Velasco et al. (2022), and Weragoda et al. (2022), form the basis for the guidelines included in this book.

The book provides comprehensive guidelines for the establishment, operation, and maintenance of green roofs for water treatment, floating wetlands, and constructed wetlands. Additionally, it offers selected examples that delve deeper into technical, economic, social, and policy/governance aspects considered crucial for the successful implementation and maintenance of NbS, as well as their replication. Table 1.1 summarizes the key factors considered in the development of these guidelines, ensuring a comprehensive and practical resource for practitioners and policymakers alike.

Table 1.1 Aspects considered in the NbS guides
Full size table

1.2 Organization of Chapters

While the primary focus of the book revolves around three specific types of NbS for water treatment, it is worth noting that various other solutions have been implemented in the past across the countries under examination. Chapter 2, titled “Mapping of Existing NbS for Water Treatment in the Philippines, Sri Lanka, and Vietnam,” aims to capture these diverse approaches, providing insights into the tested NbS in each country, their performance, and the lessons learned from those experiences. This chapter sets the stage and provides a broader context for the subsequent chapters.

Chapter 3 delves into the “Suitability Mapping of Constructed Wetlands,” presenting a framework for evaluating locations suitable for the application of constructed wetlands. While the chapter draws on the experiences and context of the Philippines, it offers a generic process that can be adapted by users in other countries with relevant modifications to the local context.

Moving forward, Chap. 4 focuses on the “Economic Analysis of NbS for Wastewater Treatment Under Uncertainties,” while Chap. 5 examines the “Social Acceptability Assessment of NbS for Water Treatment.” These chapters present methodologies employed in the Philippines but can be replicated in other contexts with necessary adaptations.

Chapter 6 provides a “Guide to Constructed Wetlands: A Philippine Perspective,” followed by Chap. 7, which presents a “Guide to Green Roofs: A Vietnam Perspective.” Chapters 8, 9, and 10 are dedicated to floating treatment wetlands, with Chap. 8 offering a guide based on relevant experiences from Sri Lanka, and Chap. 10 providing a guide based on experiences from Vietnam. In Chap. 9, a guide is presented for selecting plants suitable for floating treatment wetlands.

Chapter 11 explores “Pathways for the Scaling of NbS for Water Treatment: Examples from the Philippines, Sri Lanka, and Vietnam,” discussing strategies to facilitate the broader adoption of NbS. It also outlines directions for future applications and research, providing a comprehensive conclusion to the book.

We anticipate that this book will serve as a valuable guide for establishing, operating, and maintaining constructed wetlands, green roofs, and floating treatment wetlands not only in the examined countries but also in other locations within the broader region. By addressing not only the technical aspects but also the relevant economic, social, and policy factors, we aim to facilitate the transition of these NbS from research pilots, which currently dominate the field, to practical applications that can contribute to achieving the targets outlined in Sustainable Development Goal 11—“Sustainable Cities and Communities.”

Our hope is that the implementation of these NbS will foster inclusive, safe, resilient, and sustainable urban environments across the South/Southeast Asian region. By providing guidance that goes beyond technical considerations, we aspire to support the transformation of urban landscapes, promoting the well-being and quality of life for all residents while working toward a more sustainable future.