<p>This review paper highlights bio-carriers’ vital role in Moving Bed Biofilm Reactors (MBBRs), which provide the required surfaces for biofilm formation that are super important for improving MBBR performance. Traditional bio-carrier types have several weaknesses concerning the surface area, structural complexity, nature of the used materials, and overall efficiency in the MBBRs. So, this review investigates the potential of employing 3D-printing technology in the design of bio-carriers to mitigate these challenges, enabling the fabrication of intricate geometries that are unachievable using conventional manufacturing methods. This review revealed that 3D printing allows for complete control over geometries, shapes, and materials, so bio-carriers can be designed and fabricated with proper porosity and surface texture, which increases biofilm growth and enhances mass transfer and flow dynamics in MBBRs. This research dives into challenges that come up during the 3D-printed biocarrier fabrication on a larger scale. Although 3D printing is preferable for its complex design options, producing large amounts of biocarriers can become time-consuming. To tackle this scalability issue, emerging strategies such as high-speed printing techniques and post-processing optimizations were investigated in order to enhance feasibility and improve effectiveness and adoption of 3D-printed biocarriers in wastewater treatment.</p>