Bio-assessment of wastewater effluent conditions with algal pollution index and multivariate approach

Abstract

Water scarcity and water pollution are important issues in the world. Therefore, reusing treated wastewater for irrigation can be a crucial approach in arid and semi-arid regions. There are still some concerns about the sustainability of wastewater irrigated agriculture. Thereby, the present study is aimed to evaluate responses of algal species to stressors in the central wastewater treatment plant using the modified algae pollution index and multivariate approaches to assess healthy sustainability of wastewater effluent quality and to give the suggestion for reusing such kind of waters, especially for irrigation. Samplings of water and algae were carried out twice a month between October 2019 and August 2020. Canonical correspondence analysis (CCA) explained 94.1% of the relationships between environmental factors and species. Water and air temperatures, precipitation, chemical oxygen demand (COD), electrical conductivity (EC), pH, and NO3 played important roles in the temporal occurrence/succession of algae composition in the wastewater treatment plant. Ordination of commonly encountered algae species relatively near the center of the CCA indicates their wide range of tolerance levels to the changes in environmental conditions in the system. Of the species, Navicula aitchelbee, Nitzschia fonticola, and Euglena oxyuris preferred high EC levels; Brachysira exilis, Chlorella vulgaris, G. parvulum, and C. ovata associated with high COD levels, and Navicula tripunctata, Nitzschia umbonata and C. vulgaris related to high NO3 levels (>75% of the percentile). The modified pollution index developed in the present study indicated that the wastewater treatment plant had mainly high organic pollution (>3.00) in the summer and fall seasons, when it had moderate organic pollution (>2.50) in the winter and spring seasons. Results of the study suggest that crucial algae-stressors relationships can be used as an assessment tool to ensure sustainable water supply for the irrigation purpose in arid and semi-arid regions.