Design and Fabrication of 3D-Printed Gyroid Biocarriers for Biological Wastewater Treatment: Experimental and Pilot-Scale Evaluation

Inadequate domestic wastewater treatment remains a major environmental challenge due to the discharge of nitrogen compounds that originate primarily from human excreta, food residues, and household products, and are commonly present as ammonium and organic nitrogen. During biological processes, these compounds are converted to nitrite and nitrate, which are highly soluble and can easily migrate through soils, contaminating groundwater and posing risks to public health. Although Moving Bed Biofilm Reactors (MBBRs) are widely used for nitrogen removal, developing biocarriers with controllable geometry and optimized surface area for enhanced biofilm growth remains a challenge. This study aimed to design and fabricate gyroid-structured biocarriers using additive manufacturing (3D printing) from polylactic acid (PLA), acrylonitrile–butadiene–styrene (ABS), and polypropylene (PP), and to evaluate their performance in wastewater treatment for nitrogen removal. Bench-scale experiments showed significant chemical oxygen demand (COD) removal for all materials, with ABS and PP promoting the most stable biofilm formation. Pilot-scale tests with PP gyroid biocarriers achieved removal efficiencies of up to 87% for biochemical oxygen demand (BOD), 87% for ammonia, and 97% for nitrate. These results demonstrate that 3D-printed gyroid biocarriers provide a tunable geometry that enhances surface area and improves biological nitrogen removal in domestic wastewater treatment.