Digestion of settleable solids from recirculating fish tank as nutrients source for the microalga Scenedesmus sp. cultivation

Abstract

The high concentration of nitrogen and phosphorus in wastewater incorporated with the ability to use carbon dioxide as the carbon source make the microalgae become more attractive in wastewater treatment process. This study evaluates the optimal conditions for the digestion of settelable solids from the recirculating aquaculture system to produce the biomass of the green microalga Scenedesmus sp. After solids separation, aerobic digestion of settleable solids under disperse condition produced nitrate as the final product of consequently ammonification and nitrification processes. With the optimal digestion procedure, nitrate concentration during aerobic digestion in 2000 mL vessel increased from 9.63±0.65 mg N/L to 58.66±0.06 mg N/L in 10 days. Thereafter, cultivation of Scenedesmus sp. was performed in 1000 mL Duran bottle with air bubbling. The highest Scenedesmus sp. specific growth rate of 0.321±0.01/d was obtained in treatment using liquid fraction after aerobic digestion as the whole culture medium for Scenedesmus sp. cultivation. With this study, digestion of 8,800±128.12 mg dry weight/L of settleable solids from fish pond finally produced 1,235±21 mg dry weight/L of Scenedesmus sp. biomass.

Repeated phosphate removal from recirculating aquaculture system using cyanobacterium remediation and chitosan flocculation

“…The results demonstrated that the efficiency of chitosan flocculation was over 90% even with cell concentration in the photobioreactor as high as 6 mg Chl-a/L (OD 730 5 1.5). As the water from the fish tank could provide nutrients for algal growth (Rotthong et al 2015), the flocculated Synechocystis cells retained in the photobioreactor were able to grow and remove phosphate effectively over 10 cycles of water treatment from a single inoculation. The concentration of phosphate in RAS water after treatment was lower than 0.08 mg P/L in every treatment cycle with an average of 0.03 mg P/L from all 12 treatment cycles, that is, 98.6 6 0.8% phosphate was removed.…”

“…With this process, single inoculation of cyanobacterium can be used with several cycles of phosphate treatment as the algae are able to grow in the water from the recirculating aquaculture system (RAS) without the need of extra nutrients (Rotthong et al . ). Algal cells containing high phosphate concentration are finally removed from the photobioreactor by flocculation.…”

“…Therefore, this study demonstrates an alternative technique of phosphate removal from recirculating fish culture tanks by cyanobacterial uptake in the photobioreactor followed by chitosan induced cell flocculation. With this process, single inoculation of cyanobacterium can be used with several cycles of phosphate treatment as the algae are able to grow in the water from the recirculating aquaculture system (RAS) without the need of extra nutrients (Rotthong et al 2015). Algal cells containing high phosphate concentration are finally removed from the photobioreactor by flocculation.…”