Water Quality and Fluorescent Dissolved Organic Matter Dynamics of Dhaleshwari River

Mohammad Mohinuzzaman ^1* Jannatul Mowa ¹ Mohammad Mahbub Kabir ^1,2 Muhammed Alamgir Zaman Chowdhury ³ Meherun Nesha ³ Khan M.G Mostofa ⁴ Nahin Mostofa Niloy ^5,6 Mashura Shammi ⁵ Shafi M. Tareq ⁵

• ¹ Dept. of Environmental Science and Disaster Management, Noakhali Science and Technology University, Noakahli-3800, Noakhali, Bangladesh
• ² ARC Research Hub for Nutrients in a Circular Economy, School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, 15 Broadway, NSW 2007, Australia
• ³ Agrochemicals and Environmental Research Division, Institute of Food and Radiation Biology, Bangladesh Atomic Energy Commission, AERE, Savar, Dhaka-1349, Bangladesh
• ⁴ School of Earth System Science, Tianjin University, 92 Weijin Road, Tianjin 300072, Tianjin, China
• ⁵ Hydrobiogeochemistry and Pollution Control Laboratory, Department of Environmental Sciences, Jahangirnagar University, Dhaka 1342, Bangladesh
• ⁶ Faculty of Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia

The present study was designed to evaluate the status of the physiochemical properties and fluorescent dissolved organic matter (FDOM) characteristics of the Dhaleshwari River located in the peripheral Dhaka district, Bangladesh. Dhaleshwari River was selected as the study area due to the tannery industrial estate and different effluent discharging industries in the surrounding areas. The socioeconomic and ecological significance of the river is highly critical to the locality. Water samples were collected in the dry season for pH, electrical conductivity (EC), salinity, total dissolved solids (TDS), dissolved oxygen (DO), biochemical oxygen demand (BOD) chemical oxygen demand (COD) and FDOM analysis. The river water quality values were compared with the recommended values of the Environmental Conservation Rules (ECR) standards and the observed BOD and COD exceeded the limit. The water quality index (WQI) values showed that river water is extremely polluted and values significantly increased from upstream to Keraniganj BSCIC area. 3DEEM-PARAFAC analysis confirmed the presence of protein-like substances, terrestrial humic and fulvic acids, and degraded fulvic acids in the samples, which provided evidence of organic matter pollution. Relatively higher FDOMs were found in the upstream area of the river compared to the downstream area. Furthermore, we found that with the increase of the river depth, the FDOM substances decreased due to absorption of sunlight, microbial degradation, and photosynthesis. It is recommended that industrial estates operate proper wastewater treatment plants and the Department of Environment (DoE) should take political and legislative actions for an adequate water quality monitoring system.