Membrane filtration for removal of fine solids from aquaculture process water

Abstract

In recirculating aquaculture systems (RASs), fine solids (diameters <20–25 μm) often escape conventional treatment processes such as sedimentation and microscreen clarification and thus, accumulate over time. Consequently, alternative means to remove fine solids from RASs must be developed in an effort to improve water quality and fish health, which is expected to enhance production yield and decrease cost. Thus, the objective of this study was to assess the technical feasibility of utilizing cross-flow microfiltration to remove fine particulate matter from RASs. Based on tests conducted using a synthetic aquaculture process water as a controlled feed solution in a dead-end filtration module, the 0.05 μm membrane yielded the best water quality with >94% TSS rejection and 76% biochemical oxygen demand rejection. In cross-flow membrane filtration using a 0.05 μm pore size hollow fiber membrane, permeate flux increased with increasing feed temperature. Flux also increased with and transmembrane pressure up to a limit after which a pressure independent flux was observed. On average, pressure independent flux was found to increase with cross-flow rate approximately linearly. Based on a preliminary assessment of process economics, it was determined that membrane filtration was not a cost effective alternative to coarse solids removal processes such as microscreen clarification. However, membrane filtration for fine solids removal has potential niche applications in areas such as rearing high-value products.