Different Approaches for the Separation of Suspended Solids in Aquaculture System

Abstract

The objective of this research is to propose the suitable suspended solid (SS) treatment process for the wastewater of the actual aquaculture systems (tilapia ponds). Sedimentation, coagulation, and depth filtration were chosen and applied in this study. Sand and anthracite were used as media in the depth filtration; while alum was used as a coagulant in jar tests. The results showed that, at the optimal operating condition, sedimentation (overflow rate of 0.8 m/hr) and coagulation (alum concentration of 15 mg/L) can provide treatment efficiencies of 90% and 99.25%, respectively. However, several drawbacks (high detention time, decrease of pH value, sludge generation) were observed. Therefore, the depth filtration processes with single and dual media were applied at different media configurations. The highest treatment efficiency (92%) and moderate filtration performance (80 minutes operating time and 12 m/hr filtration rate) can be obtained with the combination of media between anthracite (2 mm effective size and 0.15 m in depth) and sand (0.8 mm effective size and 0.55 m in depth). Finally, sedimentation as pretreatment and aeration in batch mode along the media depth were proven to significantly enhance the overall filtration performance. INTRODUCTION Recently, recirculating aquaculture system (RAS) is one of the well-liked methods for shrimp and fish cultivation farm in Thailand. Water quality management was required in order to control the amount of suspended solids or SS (e.g. fecal matter and uneaten feed) and nutrients (e.g. nitrogen, phosphorus, etc.) present in this system. Therefore, the removal of SS can be considered as one of the key processes in an RAS (Chen et al., 1993). The high solid concentrations in RAS have numerous impacts on fishes and water quality, such as damage of fish gills, increases in biochemical oxygen demand (BOD), reduction of nitrification in biofilters and increases of ammonia concentrations (Wong, 2001; Zhu and Chen, 2001). Typically, the common separation processes for removing SS in the system are sedimentation, coagulation-flocculation and filtration processes. These processes contained different pros and cons in practical applications, as well as, the design and operating conditions. To fulfill this gap, the objective of this research is to study and propose the suitable SS treatment process for the actual RAS wastewater (tilapia ponds). The processes were considered in different points of view: treatment efficiency, design and operating factors (retention time, system dimension,