STUDY ON WASTE WATER TREATMENT PROCESS AND ASSESSMENT OF HEAVY METAL CONCENTRATION IN DIFFERENT TYPES OF ETP AND STP IN SOME INDUSTRIES AT CHATTOGRAM REGION

Abstract

This study delves into a comprehensive assessment of Wastewater Treatment Plants including Effluent Treatment Plants (ETPs) and Sewerage Treatment Plants (STPs) within diverse industries in Chattogram Division, Bangladesh. The investigation was mainly focused on the analysis of ETP samples obtained from the steel and paint industries located in Mirsharai, Sitakunda, Karnaphuli, and Kalurghat industrial areas of Chattogram, as well as STP samples collected from hotels in Cox's Bazar of Chattogram Division. These industries release complex liquid waste rich in dissolved solids, suspended particles, and heavy metal ions. Considering the economic and environmental significance of Chattogram and the detrimental effects of water pollution on ecosystems, the assessment of the discharge of effluents from those industries into water bodies becomes imperative. Thus, this study aims to find out the operational maintenance practices in wastewater treatment plants and to analyze the water quality in ETP samples and STP samples from the industries mentioned above in terms of studying various physio-chemical parameters before and after discharge from the treatment plants. Effluent samples were collected from the ETPs and STPs bi-annually during the dry season (D.S., January- February) and monsoon season (M.S., July- August) using systematic and standardized analytical methods. Sampling procedures involved collecting effluent samples from both the inlet and outlet points of the industrial ETPs and STPs. The water quality was evaluated based on five physio-chemical parameters, namely pH, dissolved oxygen (DO), biological oxygen demand (BOD5), chemical oxygen demand (COD), total dissolved solids (TDS), as well as the concentration of heavy metals including Fe, Cu, Cr, Ni, and Cd. The results were compared to national and international regulations, such as the Bangladesh Standard for Industrial Effluent (BSIE) of Department of Environment (DoE), World Health Organization (WHO) guidelines, European Union Directives (EU-DIR), and US Environmental Protection Agency (US EPA). It was observed that steel-galvanizing industries generate complex wastewater rich in highly dissolved solids and heavy metal ions. Although pH, BOD5, and COD values were within acceptable ranges in these industries, high TDS values were observed. The Fe concentration of discharged stream areas ranged from 0.992 mg/L to 16.89 mg/L, exceeding the guideline limits. Additionally, the Cr concentration in both the inlet and outlet exhibited high concentrations, surpassing the standard limits, particularly those set by the US EPA. Thus, steel-galvanizing industries are likely contributing to water pollution through the discharge of wastewater, particularly in terms of Fe and Cr. In the case of the Paint Industries, after treatment, Fe concentration of discharged stream areas ranged from 2.333 mg/L to 5.117 mg/L exceeded the guideline limits of WHO and BSIE standards and indicated probable water pollution by Fe. Ni in those samples was under the safe limit, and Cd was found under the detectable limit. This study examined the operation of STPs in three Hotel Industries and assessed their impact on water quality in Cox's Bazar, Chattogram Division. Notably, pH levels remained relatively stable, while DO levels fluctuated. The fluctuations of COD levels reflect the presence of various pollutants and similar trends were observed for BOD5. Additionally, TDS indicated the presence of dissolved substances and solid particles. Furthermore, elevated nitrate and phosphate levels raised concerns about nutrient pollution and eutrophication. Fe concentrations remained within regulatory limits, but Cu exceeded limits in specific areas, requiring further investigation. Cr concentrations were within acceptable ranges, while Mn levels significantly exceeded defined limits. Finally, the findings of this study underscore the importance of adopting comprehensive measures and optimizing wastewater treatment processes to address pollution in different industries.