Comparative study on production and characterisation of extracellular polymeric substances (EPS) using activated sludge fortified with crude glycerol from different biodiesel companies

Abstract

Extracellular polymeric substances (EPS) are eco-friendly and economical biopolymers with a significant role in pollutant removal, bio-flocculation, settling and dewatering of activated sludge. In this study, growth profile and EPS production by an EPS-producing microbial strain (isolated from wastewater sludge or WWS) was studied using activated sludge fortified with glycerol. The study compared three crude glycerol samples as carbon sources from different biodiesel companies (BIO-LIQ, BIOCARDEL, ROTHSAY) and their effect on EPS production and characterisation was observed. The maximum slime EPS (S-EPS) concentration (12.34 g/L) was produced when sludge fortified with BIO-LIQ crude glycerol was used, higher than pure glycerol (10 g/L) at 72 h. The S-EPS was enhanced (16 g/L) when purified BIO-LIQ glycerol (by acid treatment) was used. It was also observed that S-EPS concentration increased 1.6–2.6 times by using sludge fortified with glycerol as compared to only glycerol (no sludge) as EPS production medium. In addition, the S-EPS produced from different glycerol samples yielded different characteristics in terms of protein-carbohydrate content, flocculation activity and dewaterability. The S-EPS from purified BIO-LIQ glycerol (with sludge) gave maximum flocculation activity and dewaterability i.e. 93.71% and 60.2% respectively. The comparison between Ca(OH)2 and NaOH used as alkaline sludge pre-treatment methods revealed that the EPS produced from Ca(OH)2-treated sludge fortified with glycerol solutions to be better in terms of protein content, flocculation activity and dewaterability. Structural composition analysis using Fourier Transform Infrared Spectroscopy (FT-IR) revealed the presence of distinct functional groups (carboxyl, hydroxyl, amine groups) in the produced S-EPS.