The prawn cracker industry is one of the most common types of food industry in Indonesia. The existence of this industry has a positive impact in maintaining and improving the Indonesian economy, but it can also have a negative impact on the environment in particular, because this industry produces wastewater which can have a negative impact on the aquatic environment if the wastewater is directly discharged into the river. Based on the results of the analysis of the quality of wastewater from one of the shrimp cracker industries, it is known that wastewater contains Chemical Oxygen Demand (COD) which is 3446 mg/L, Biological Oxygen Demand (BOD) 1118.9 mg/L and acidity (pH) 5.88 – 6.13. Referring to the wastewater quality standards for the shrimp cracker industry, namely COD: 120 mg/L, BOD: 50 mg/L, and acidity pH: 6-9, the shrimp cracker industrial wastewater must be treated first before being channeled into the body. river receiving water. In this study, the treatment process used is an aerobic biological process with a modified contact-stabilization method. This method is the development of the contact-stabilization method, where in this modified method the wastewater from the treatment is recycled to the stabilization tank and together with the bacteria is transferred to the contact tank. Variations carried out in this study are the incoming wastewater flow rate (liters/hour): 4,5 ; 5.5; 6.5 ; 7.5 and 8.5 and flow rate of recycled water from treatment to stabilization tank (%) : 10 ; 20 ; 30 of the incoming wastewater flow rate. The best results were obtained at the wastewater flow rate of 5.5 liters/hour and the recycled water flow rate from the treatment to the stabilization tank 20% with a decrease in the COD value of 97.3% and BOD of 98.4% and the pH of the treated water 6.9.

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