ZTANK is a compact underground wastewater treatment system designed for decentralized locations without access to municipal sewer networks, such as villages, resorts, and small communities. Engineered for flexibility and reliability, it is available in both Multistage A/O (Anoxic/Oxic) and SND (Simultaneous Nitrification and Denitrification) series, providing stable and efficient nitrogen removal for a variety of scenarios. Constructed with reinforced PPH composite material, ZTANK offers up to 30 years of durability while minimizing operational complexity. Its innovative design reduces sludge production and features a desludging cycle of 4–12 months, complemented by a chemical-free electrolytic phosphorus removal process that simplifies operation and reduces environmental impact. With a treatment capacity of 20–100 m³/d, ZTANK can serve communities of approximately 130–670 people, delivering reliable, long-term, and eco-friendly wastewater treatment where conventional infrastructure is unavailable.