Bioremediation potential of macroalgae gracilaria edulis and gracilaria changii co-cultured with shrimp wastewater in an outdoor water recirculation system

Abstract

Effluent from the aquaculture industry discharged into water bodies and it impacts the environment severely. The shrimp industry is one of the developing aquacultures that releases a high amount of organic matters in the form of wastewater. As an effort to reduce the environmental impact, an integrated system with shrimp and macroalgae researched abundantly as the macroalgae are naturally capable of removing nutrient from wastewater. As a bioremediation potential, this study investigates the nutrient uptake and macroalgal growth performance in short term (21 days) using an outdoor recirculating water system stocked with two local macroalgae species Gracilaria edulis and Gracilaria changii as biofilter. The stocking density of 3 kg/m2with the flow rate of the water system set to 200 L/hr during the operation. The temperature, pH, dissolved oxygen (DO) and salinity was measured daily throughout the experimental period. Water temperature in all tanks were almost constant and ranged between 28.5 °C to 29.1 °C. The higher mean of pH of around 8.26 ± 0.15 and 8.28 ± 0.05 was observed in tanks with G. edulis and G. changii respectively. In the control tanks, mean pH was 7.87 ± 0.09. The mean concentrations of dissolved oxygen in G. edulis, G. changii and control tanks were 6.89 ± 0.05 mg/L, 6.84 ± 0.06 mg/L, and 6.10 ± 0.03 mg/L respectively. The mean growth rates of Gracilaria edulis and Gracilaria changii were found to be 4.3% day−1, 4.1% day−1 with carbon to nitrogen (C:N) ratio of 8.3 to 8.5 respectively. The removal rate of ammonium and nitrate by the two species were found to be 72.5%, 71.0%, and 58.8%, 56.8% respectively. The macroalgal biofilter is found to be an ecologically sustainable that has improved the shrimp water quality to an acceptable level that in turn ultimately enhanced shrimp and macroalgae productivity.