Role of extracellular polymeric substances from Chlorella vulgaris in the removal of ammonium and orthophosphate under the stress of cadmium

• Cd2+ increased the contents of S-EPS and B-EPS.
• Cd2+ increased the contents of tryptophan-like and tyrosine-like substances.
• The increased EPS contents (e.g., B-EPS) enhanced the interactions with Cd2+.
• The interactions between EPS and Cd2+ reduced the toxicity of Cd2+ for algae.
• Algae-based technique was a stable sewage treatment coexisted with heavy metals.

The interactions between the soluble extracellular polymeric substances (S-EPS), bound EPS (B-EPS) of algae and heavy metal, would affect the removal of ammonium (NH4+-N) and orthophosphate (PO43−-P) from wastewater by algae-based techniques. This study investigated the role of Cd2+-mediated EPS from Chlorella vulgaris on NH4+-N and PO43−-P removal. The results showed that the removal efficiencies of NH4+-N and PO43−-P still separately remained 62.6% and 64.9% under 1.0 mg/L Cd2+, compared to those without Cd2+, mainly attributing to enhanced S-EPS and B-EPS contents of the algae. The increased of PS (polysaccharides) and PN (proteins, e.g., tryptophan-like and tyrosine-like components) led to accelerated interactions of Cd2+ with PS and PN in EPS fractions, especially for B-EPS, due to a higher detected distribution of Cd2+ (e.g., about 55.4% in B-EPS). Thus, algae-based techniques are stable treatment methods for wastewater in which NH4+-N and PO43−-P coexist with heavy metals.

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