Optimization of Rotary Algae Biofilm Reactor (RABR) Using Ulva Sp. for Batik Liquid Waste Management : Effects of Algal Suspension Concentration, CO2 Tablet Mass, and Rotation Speed

Abstract

The batik industry is a vital part of Indonesia’s cultural heritage, but generates significant liquid waste containing high levels of pollutants. Batik wastewater often exhibits excessive suspended solids, Chemical Oxygen Demand (COD), and Biological Oxygen Demand (BOD), which surpass permissible discharge standards. For instance, the batik industry in Ambulu produced effluent with a COD of 1,011 mg/L and a BOD of 511.79 mg/L, far exceeding environmental limits. Conventional treatment methods are generally costly, energy-intensive, and often generate secondary waste, making them less suitable for small-scale industries. Therefore, sustainable and affordable alternatives are urgently needed. This study investigates the use of a Rotary Algae Biofilm Reactor (RABR) integrated with Ulva sp. macroalgae as a natural biofilter for batik wastewater treatment. Optimization was conducted using Response Surface Methodology with Central Composite Design (RSM-CCD), focusing on three operational parameters: Ulva sp. suspension concentration (4-6%), CO2 tablet mass (1-3 tablets), and rotation speed (40-60 rpm), with a contact time of 1 day. The optimal condition was identified at a 5.991% Ulva sp. suspension, 1 CO2 tablet, and a rotation speed of 60 rpm. Under these conditions, the COD was reduced to 42.923 mg/L (96% removal) and the BOD to 55.330 mg/L (89% removal), both of which meet the Indonesian wastewater discharge standards (COD < 100 mg/L, BOD 100 mg/L). The findings confirm that the RABR-Ulva sp. system provides a cost-effective, eco-friendly, and scalable solution for batik wastewater treatment. This approach minimizes operational costs, avoids secondary waste, and supports the principles of sustainable development, particularly SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production).