Evaluation of Solids Thickening Technologies (Gravity Thickening Cone, Geotextile Filter, Belt Filter) for Treating Backwash from RecirculatingAquaculture Systems

摘要

Solids that accumulate in recirculating aquaculture systems (RAS) are comprised of a dilute mixture of uneaten feed, fish feces, and biological floe shed from either nitrification reactors or from pipe and vessel surfaces. Consequently, efficient removal and treatment of biosolids from RAS can be challenging. Typical means employed to capture biosolids from fish culture process water are rotating microscreen drum filters and gravity settling units. In our experience, the backwash and underflow generated by these removal mechanisms typically results in a waste stream with a solids concentration of 0.1 -0.2 %. Rapid separation of these biosolids from water can allow for efficient capture of suspended solids and carbonaceous biological oxygen demand (cBODs), and prevent mineralization and leaching of dissolved nitrogen and phosphorus. The corollary also hold true as solids will mineralize and leach dissolved nutrients and CBOD5 if they are stored for days within the system. For example, storing solidswithin a plastic-bead filter between 24 hour backwash cycles can cause 30-40% of the total suspended solids generated within a recirculating system to decay within that same time period (Chen et al., 1993).