Evaluation of Water Quality Degradation Associated with an Ethanol/Wastewater Spill in Bais City, Negros Oriental Using Quantitative Water Quality Variables

Abstract

The quantitative research method assessed changes in water quality before and after the ethanol and wastewater spill in Negros Oriental using secondary data from the government and publicly available reports. The major discharge from the Universal Robina Corporation’s ethanol distillery facility occurred on October 24, 2025, followed by the collapse of a containment dike on the evening of October 26, 2025. This incident released an estimated 255,000 cubic meters (67 million gallons) of wastewater into North Bais Bay and the Tañon Strait Protected Seascape, a critical marine habitat. The environmental disaster significantly affected the livelihoods of communities in Bais City and the adjacent municipality of Manjuyod, both of which declared a state of calamity due to extensive fish kills. Government agencies, including the Similar spill incidents had been recorded in previous years, including one in 2015, indicating a recurring issue. Comparable approaches have been applied in both local and international studies to evaluate the effects of industrial wastewater discharges on water quality. In the United States, the effects of the Gold King Mine wastewater spill on water quality were assessed using secondary data in monitoring the changes in water quality (U.S. Environmental Protection Agency, 2019). Likewise, in Vancouver, Canada, monitoring data supported assessments of untreated wastewater releases into coastal waters. The results of this study revealed detectable post-spill changes in selected water quality parameters, indicating a decline in water quality. Overall, the findings demonstrate that secondary data analysis is an effective method for assessing the environmental impacts of wastewater spill incidents.