Compact GRP-enabled sewage treatment plant (STP) with a horizontal flow activated sludge system, designed to serve a school in Manaus, Amazonas. The system includes screening, a 5,000-L anaerobic/aerobic module, a 310-L chlorinator tank, booster pumps, sludge return, an aeration turbine, and an electrical control panel. The solution includes manufacturing, installation, and technical documentation (memorandum, manual, and ART). Treatment capacity: 15 m³/day .