Guest Column | January 7, 2025

8 Trends In Decentralized Wastewater Treatment: Shaping A Sustainable Future

By Ashley Donnelly and Dennis F. Hallahan

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Centralized wastewater treatment is sometimes not an option — and sometimes simply not the best choice, considering the expanding capabilities of decentralized systems.

For onsite wastewater professionals looking ahead, there are several new up-and-coming trends in the industry, including a focus on environmentally sensitive areas, advancements in treatment technologies, and concerns over water scarcity. Decentralized wastewater treatment systems have always been vital to our infrastructure and the communities they serve, providing system designers with the flexibility to tailor a wastewater system to meet the needs of the community. Much of the public still views a decentralized wastewater treatment system as a single-family septic system. However, these systems are more complex. They can offer solutions for commercial and community systems, and at times, work in conjunction with centralized systems. At the intersection of technology, sustainability, and resilience, decentralized wastewater treatment systems — and their ability to meet the unique needs of the communities, challenging sites, and facilities they serve — are indispensable solutions for modern wastewater infrastructure. The following are some examples of the emerging trends and innovative design approaches that are shaping the future of decentralized wastewater treatment systems.

Addressing Nutrients

Nitrogen management, eutrophication, and nutrient removal are critical challenges due to increasingly stringent discharge limits. Elevated nitrogen levels contribute to eutrophication in waterbodies, posing serious threats to ecosystems. Decentralized wastewater treatment systems offer flexible solutions, capable of integrating advanced technologies to enhance nitrogen reduction and nutrient removal. These systems can be designed to meet stringent regulatory requirements.

PFAS — The Forever Chemicals

The emergence of per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals,” presents a daunting challenge. Decentralized systems will have to be modified to incorporate treatment technologies such as granular activated carbon (GAC), ion exchange resins, and advanced oxidation processes to reduce PFAS contamination. This will allow localized treatment, reducing the need for costly, large-scale interventions. As regulations develop for PFAS management, decentralized systems will meet the challenge.

Advanced Treatment

Advanced treatment systems are revolutionizing decentralized wastewater treatment systems for challenging sites such as small lots, areas with tight soils, high water tables, and fast-moving soils. Specifying advanced treatment systems offers an innovative solution by using compact, efficient designs. Systems such as suspended growth aerobic treatment units and fixed film textile filters provide higher levels of treatment in limited spaces, improving effluent quality while minimizing the footprint. These systems can also allow sites that have high water tables and fast-moving soils to be buildable by ensuring reliable performance even in difficult conditions. For engineers, these technologies provide the tools to design systems that meet stringent environmental standards, while addressing the unique challenges of complex site conditions.

Scalability And Customization For Community Systems

Decentralized systems are no longer one-size-fits-all solutions. Modular designs and scalable technologies allow systems to grow with community needs. Pre-engineered, plug-and-play units allow ease of installation and future expansion. Communities can customize treatment configurations to address specific challenges, such as nutrient removal, water reuse, and seasonal or intermittent flows, making these systems adaptable and future-ready — all while recharging local aquifers.

A modular treatment plant shipped to site and specified to meet permit limits. Plumbing is attached and electrical service provided to begin treating effluent.

Creative Solutions For Challenging Sites

From rocky terrain to steep slopes, difficult sites require innovative engineering and products. Combined treatment and dispersal (CTD) systems allow treatment and dispersal within the same footprint. These systems can meet NSF40 levels of treatment with no power inputs, providing a sustainable solution.

Septic Tank Effluent Pumping (STEP), Septic Tank Effluent Gravity (STEG), And Liquid-Only Sewer Systems

These systems use septic tanks to provide primary treatment which removes solids. Then the treated effluent (liquid only) is pumped to a decentralized community system or centralized facility. These systems offer flexibility, cost efficiency, and improved water quality management, making them ideal choices for communities seeking decentralized alternatives or hybrid systems.

Aquifer Recharge

Water scarcity is driving the adoption of decentralized systems to address water reuse and aquifer recharge. These systems treat wastewater to high standards, enabling their use for irrigation, industrial processes, or potable applications. Managed aquifer recharge (MAR) is another promising approach, whereby treated water is stored in underground aquifers for future use. Advanced filtration and disinfection technologies, such as UV and reverse osmosis, are integral to these applications, ensuring safety and reliability.

Large subsurface dispersal systems are practical solutions for communities. These systems provide additional benefits of polishing and aquifer recharge.

Operation And Maintenance

The success of decentralized systems hinges on effective operation and maintenance (O&M). Advances in contractor equipment and automation are making O&M more accessible and less labor-intensive. Mobile apps and remote monitoring provide operators with real-time insights, enabling proactive management. Additionally, the development of compact, user-friendly equipment reduces the need for specialized training, empowering local contractors to manage systems effectively.

The Road Ahead

Decentralized wastewater treatment systems are at the forefront of innovation, providing adaptable, sustainable, and scalable solutions for diverse communities and industries. From advanced nutrient removal to PFAS management and water reuse, these systems are redefining wastewater management. To fully unlock their potential, continued investment in research, regulation development, and public education are essential. By embracing these trends, decentralized systems can play pivotal roles in achieving a sustainable water future, addressing environmental challenges while supporting community resilience and growth.

About The Authors

As Technical Training and Sales Development Manager at Infiltrator Water Technologies (IWT), Ashley Donnelly manages the inside sales team and is responsible for maintaining and building customer relationships, including assisting engineers, contractors, and regulators with technical and design information, training, installation, and O&M. She serves on several industry committees, including TOWA, NOWRA Emerging Professionals, and NEWEA Small Communities Committee.

Dennis F. Hallahan, PE, is the technical director of Infiltrator Water Technologies. Hallahan has over 30 years of experience with the design and construction of decentralized wastewater treatment systems. He has written numerous articles for onsite industry magazines and regularly gives presentations nationally on the science and fundamentals of onsite wastewater treatment systems. Hallahan also serves on various national industry association wastewater committees.