Biomonitoring detoxification efficiency of an algal-bacterial microcosm system for treatment of coking wastewater: Harmonization between Chlorella vulgaris microalgae and wastewater microbiome

Abstract

Nowadays, due to worldwide water shortage, water utilities are forced to re-evaluate treated wastewater. Consequently, wastewater treatment plants need to conduct biomonitoring. Coking wastewater (CWW) has toxic, mutative and carcinogenic components with threatening effect on the environment. CWW was selected as a model for complex highly toxic industrial wastewater that should be treated. CWW from Egypt was treated in a nine-liter photobioreactor using an algal-bacterial system. The photobioreactor was operated for 154 days changing different parameters (toxic load and light duration) for optimization. Optimized conditions achieved significant reduction (45%) in the operation cost. The algal-bacterial system was monitored using chemical assays (chemical oxygen demand and phenol analysis), bioassays (phytotoxicity, Artemia-toxicity, cytotoxicity, algal-bacterial ratio and settleability) and Illumina-MiSeq sequencing of 16S rRNA gene. The algal-bacterial system detoxified (in terms of phytotoxicity, cytotoxicity and Artemia-toxicity) CWW introduced as influent through all phases. A significant difference was recorded in the microbial diversity between influent and effluent samples. Four phyla dominated influent samples; Proteobacteria (77%), Firmicutes (11%), Bacteroidetes (5%) and Deferribacteres (3%) compared to only two in effluent samples; Proteobacteria (66%) and Bacteroidetes (26%). The significant relative-abundance of versatile aromatic degraders (Comamonadaceae and Pseudomonadaceae families) in influent samples conformed to the nature of CWW. Microbial community shifted and promoted the activity of catabolically versatile and xenobiotics degrading families (Chitinophagaceae and Xanthomonadaceae). Co-culture of microalgae had a positive effect on the biodegrading bacteria that was reflected by enhanced treatment efficiency, significant increase in relative abundance of bacterial genera with cyanide-decomposing potential and negative effect on waterborne pathogens.