Mechanical Filtration in RAS – A Detailed Overview

A Recirculating Aquaculture System (RAS) is a closed-loop fish farming method designed to maximize water efficiency and maintain optimal water quality. In this system, water is reused repeatedly, with minimal discharge. This makes the buildup of solid waste a major challenge. These solids, if not promptly removed, decompose and increase the biological oxygen demand (BOD) and total ammonia nitrogen (TAN) load on the system. Accumulated solids can also clog biofilters, reduce oxygen levels, and serve as breeding grounds for pathogenic bacteria. A well-designed mechanical filtration system can remove up to 60–90% of total suspended solids (TSS) in the first stage of filtration, greatly reducing the downstream load on biofilters and improving overall system performance. Mechanical filtration is the first stage of water treatment in a Recirculating Aquaculture System (RAS) and plays a pivotal role in maintaining optimal water quality. Its primary function is to remove suspended solids—including uneaten feed, fish feces, and organic debris—from the culture water before they break down into harmful dissolved substances such as ammonia and nitrite.