Environmental Impacts of Secondarily Treated Wastewater Discharge on the Coastal Water Quality of Al-Awda Beach, Tobruk, Libya

Aims: This study aimed to assess the environmental impacts of wastewater discharge from the Tobruk wastewater treatment plant on the coastal water quality of Al-Awda Beach, northeastern Libya. Study Design: A spatio-temporal observational field study. Place and Duration of Study: Al-Awda Beach, Tobruk City, Libya, during autumn 2022 and winter 2023. Methodology: Seawater samples were collected in triplicates from six coastal sites representing a spatial gradient relative to the wastewater outfall. The treatment plant applies secondary treatment with low operational efficiency and an average daily discharge rate of approximately 18,000 m³/day. Site (5) was considered a relative reference site due to its distance from the direct discharge point. Physical, chemical, and microbiological parameters were analyzed following standard APHA and EPA methods. Statistical analyses included one-way ANOVA and Pearson correlation coefficients (R) using SPSS (version 25). Results: Most physicochemical and microbiological parameters showed significantly elevated concentrations at sites close to the discharge point compared with the reference site (P ≤ .05). Ammonia, nitrite, phosphate, BOD, COD, and heavy metals (Cd, Cr, Pb, Fe) exceeded international coastal water quality guidelines. Strong positive correlations were observed between nutrients and oxygen-demand parameters, indicating wastewater as the dominant pollution source. Microbial indicators (E. coli and total coliforms) consistently exceeded recreational water standards, reflecting a substantial public health risk. Conclusion: The discharge of secondarily treated wastewater with low treatment efficiency has caused marked degradation of coastal water quality at Al-Awda Beach. The findings highlight the urgent need for upgrading the treatment system and implementing sustainable coastal management strategies to mitigate environmental and health risks.