Diurnal variation of the water quality parameters in the waste stabilization ponds (WSPs) for water treatment of integrated multi-trophic aquaculture (IMTA) ponds with closed re-circulation system

Abstract

Organic wastes from Floating Fish Cage Aquaculture (FCA) activities have polluted many inland water bodies, from small reservoirs to major lakes in Indonesia. It has become a national priority to restore ecosystem health in Lake Maninjau. The lake has suffered from the harmful effects of approximately 17,000 units of FCA on its surface area. Better FCA practices that would improve its adjacent water quality have been proposed. The FCA should utilize a more excellent net that would confine its waste. Using a connection pump, the wastewater within this net could then be circulated into a wetland system for its water quality improvement. The proposed wetland system consists of a series of Waste Stabilization Ponds (WSP) and Constructed Wetland Compartments. For the initial stage, a study has been conducted to test the performance of the WSP with approximately six days of hydraulic retention time (HRT) to improve water quality from the Integrated Multi-Trophic Aquaculture (IMTA) ponds in the Prototype Laboratory of Research Centre for Limnology-LIPI. Two major problems in IMTA, namely organic deposition and low of dissolved oxygen (DO), especially concerning its diurnal variations in the system, have not been studied yet. Water qualities of the WSP ponds were measured every 2 hours for three days (22-25 May 2019). Water quality parameters measured were pH, conductivity, dissolved oxygen (DO), turbidity, temperature, oxidation and reduction potential (ORP), and total dissolved solids (TDS). A closed re-circulation within the WSP system was then applied for the last two days of the study period. The result showed that DO values in the effluent pond during the day were significantly higher than the night. In the maturation and facultative ponds, DO values difference ranged from 2.5-3 mg/L and 1.1-4.4 mg/L, respectively. The highest DO (5.98 mg/L) was measured in the maturation pond at 3.00 PM and values were lowest almost to 0 mg/L during the first day in the anaerobic ponds. While for turbidity, the highest was observed in the anaerobic ponds for 41 NTU and were decreased to stable values of an average of 5.3 NTU in the maturation pond on the third day. At the end of the observation, marked increase of DO and decrease in turbidity have occurred in the system. A closed recirculation system within WSP can be used as an option to increase the performance of the wetland system.