Isolation of Extra Cellular Biopolymer producing Microorganisms from Wastewater Sludge for Sludge Settling and Dewatering

Sludge settling and dewatering are carried out by employing cationic synthetic polymer (CSP) in municipal and industrial wastewater treatment plant. CSP are expensive and further pollute the environment, hence to address these problems bioflocculation of sludge was examined in this study. Microorganisms were isolated from municipal and industrial wastewater sludges and six extracellular polymeric substances (ECP) producing bacterial strains and one pellet forming fungal strain were screened for bioflocculation of sludge. Microbial strains were grown in tryptic soy broth (TSB) to produce ECP from bacterial strains and fungal pellets. Slime ECP was harvested by centrifugation at 6000g for 15 min and capsular ECP obtained from the bacterial pellet. Combination of both slime and capsular ECP was obtained from the fermented bacterial broth without centrifugation. Zeta potential characterization of ECPs carried out, all produced biopolymers showed anionic in nature. Sludge settling efficiency was evaluated by Sludge Volume Index (SVI). Results showed that slime ECP showed better performance in sludge settling than the capsular ECP and bacterial broth with and without addition of Ca++ ions. Fungal pellets were also harvested from the TSB broth after 5 days of growth at 25°C at 200 rpm. Produced pellets were incubated with different concentration of sludge suspended solids (1, 2.5, 5, 10 & 15 g/l) of sterilized (S) and non-sterilized (NS) sludge. Microbiological staining results revealed that the mechanisms of sludge solids and fungal mycelium interactions were mainly through physical adsorption or entrapment. Zeta potential value of fungal biomass also showed (− 49.42 mV) anionic in nature. SVI results revealed that sterilized sludge showed better settling index than the non-sterilized sludge at higher concentrations of sludge solids. Based on SVI results bacterial strains B1 (Slime ECP), B3 & B6 (Capsular ECP) were selected and fungal strains were also considered for further study.