A critical review on re-envisioning contemporary decentralized wastewater management through a holistic lens

Decentralized wastewater management (DWM) has rapidly advanced due to the increasing global demand for clean water, intensified by climate change-induced water scarcity. Today, a pool of well-documented literature on decentralized wastewater treatment systems (DWTS) exists, mostly comparing them over the centralized wastewater treatment systems (CWTS) through a discursive notion of good and bad, resulting in one-size-fits-all solutions for wastewater treatment. This critical review presents a comprehensive overview of DWTS as a “complementary-not-competing” solution to existing wastewater management approaches (centralized/onsite) and evaluates where CWTS is beneficial. The study explores multifaceted opportunities for effective and sustainable implementation of DWTS to provide prospects to holistically plan DWM. Research focused on innovating the core technologies, that form the foundation most DWTS design whether standalone or integrated, including constructed wetland (CW)-based systems, filter bed-based systems, decentralized wastewater treatment system (DEWATS), and membrane bioreactor (MBR)-based systems has been thoroughly discussed. Key factors that play a pivotal role in enhancing potential of DWTS such as intended end-use, targeted pollutants, site-specific characteristics, and implementation costs have been identified. The study also incorporates various techno-economic (TEA) and life cycle assessment (LCA) studies of DWTS. A conceptual model for integrated DWM and faecal sludge (FS) treatment to develop a perspective towards promoting sustainable waste-wastewater management has been introduced. By summarizing shared challenges between treatment approaches, this review offers a roadmap for harnessing the potential of DWTS in achieving energy-efficient and carbon-neutral solutions, while outlining future research directions to advance the circular economy (CE).