Abstract
Wastewater generated on ships and vessels is commonly stored onboard until the vessel reaches shore for treatment or is discharged into the marine environment when permitted by regulations. However, shipboard wastewater, particularly blackwater, can contain high concentrations of ammonium nitrogen, organic matter, and other nutrients that may negatively affect the marine environment. Therefore, treating wastewater directly onboard can provide a practical approach to reducing environmental impacts while improving the convenience of wastewater management. Conventional biological nutrient removal (BNR) systems typically require separate tanks or zones for different treatment conditions, such as anaerobic, anoxic, and aerobic processes. This requirement increases the space needed for treatment, which can be a major limitation for shipboard applications. This study investigates a low dissolved oxygen (DO) sequencing batch reactor–membrane bioreactor (SBR–MBR) system that combines different treatment conditions within a single reactor. The system operates in cycles, allowing the treatment phases to occur sequentially in the same tank, thus reducing the need for multiple treatment chambers. Additionally, the low DO aerobic phase will save blower costs in a full-scale operation. Each treatment cycle of the SBR–MBR system consisted of a 4.5-hour anoxic phase followed by a 6hour aeration phase. The mixed liquor was then allowed to settle for approximately 1 hour, after which the supernatant was passed through a membrane. Water quality of the membrane effluent, along with end of anoxic and aerobic phases, was monitored throughout for chemical oxygen demand (COD), ammonium nitrogen (NH₄+-N), nitrate nitrogen (NO₃--N), and nitrite nitrogen (NO₂--N). The system is currently showing steady performance in the removal of COD, NH₄+-N, NO₃--N, and NO₂--N. Although the experiment is ongoing, the results indicate consistent treatment performance under the current operating conditions. The overall removal trends, treatment efficiency, and supporting data will be discussed in detail.