Elsevier

Journal of Environmental Management

Volume 128, 15 October 2013, Pages 83-91
Journal of Environmental Management

Production of extracellular polymeric substances (EPS) by Serratia sp.1 using wastewater sludge as raw material and flocculation activity of the EPS produced

https://doi.org/10.1016/j.jenvman.2013.04.039Get rights and content

Highlights

  • Bioflocculants were produced from Serratia sp. incubating in the sterilized sludge.

  • Bioflocculants produced in the sterilized sludge were growth associated.

  • Kaolin flocculation study revealed flocculation potential of bioflocculants.

  • Capsular, broth and slime were the effective forms of bioflocculants, respectively.

Abstract

Growth profile and extracellular polymeric substances (EPS) production of Serratia sp.1 was studied in shake flask fermentation for 72 h using wastewater sludge as raw material. Maximum cell concentration of 6.7 × 109 cfu/mL was obtained at 48 h fermentation time. EPS dry weight, flocculation activity and dewaterability of different EPS (tightly bound or TB-EPS, loosely bound or LB-EPS and broth-EPS or B-EPS) were also measured. The highest concentration of LB-EPS (2.45 g/L) and TB-EPS (0.99 g/L) were attained at 48 h of fermentation. Maximum flocculation activity and dewaterability (ΔCST) of TB-EPS (76.4%, 14.5s and 76.5%, 15.5s), LB-EPS (67.8%, 8.1s and 64.7%, 7.6s) and broth EPS (61%, 6.1s and 70.4%, 6.8s) were obtained at 36 and 48 h of growth. Higher flocculation activity and dewaterability were achieved with TB-EPS than with the two other EPS. Characterization of TB-EPS and LB-EPS was done in terms of their protein and carbohydrate content. Protein content was much higher in TB-EPS where as carbohydrate content was only slightly higher in TB-EPS than LB-EPS. Morphology of the Serratia strain after fermentation in sludge and TSB was observed under a scanning electron microscope and the cell size was found to be bigger in the sludge medium than the TSB medium.

Introduction

During the treatment of the sludge, sludge settling and dewaterability are the main obstacles faced by wastewater treatment plants (Neyens et al., 2004; Wakeman, 2007; Qi et al., 2011). These problems arise mainly from poor settling with sludge bulking by both filamentous and non-filamentous microorganisms contained in the sludge (Bala Subramanian et al., 2010a; Martins et al., 2004). Normal practice in wastewater treatment plants is to employ the use of synthetic polymers for enhancement of sludge settling. These synthetic polymers have many disadvantages however, namely that they are expensive, toxic and can pollute the environment (Abu-Orf et al., 2001). When dewatered sludge containing the synthetic polymers is applied to agricultural land, they negatively affect the soil's microorganisms (Hébert, 2004). Moreover, dewatered sludge with chemical polymers can adversely impact the environment through its effect on natural microorganisms present in the composting and receiving soil environments during agriculture spreading (Bala Subramanian et al., 2010a; Gagnon and Ziadi, 2004). Therefore, the use of synthetic polymers should be minimized in wastewater treatment plants by replacing with biopolymers/bioflocculants. The biopolymers are biodegradable, non-hazardous, free from secondary pollution, sustainable and environmentally friendly. These qualities of bioflocculants have recently become the main focus of many researchers (Bala Subramanian et al., 2010a; Jorand et al., 1998; Houghton et al., 2001; Sobeck and Higgins, 2002).

Extracellular polymeric substances (EPS) are complex high molecular weight mixtures of polymers that are secreted from microorganisms (Sheng et al., 2010). EPS are the main components of the biological aggregates responsible for degradation of organics during wastewater treatment, including activated sludge and biofilms (Martin-Cereceda et al., 2001). EPS foster the formation of bioflocs by modifying the interactions among microbial aggregates, filamentous bacterial strains, and organic and inorganic particles. EPS essential function is to hold the cells together (Novak et al., 2003; Bala Subramanian et al., 2010b). Carbohydrates and proteins are the major components of the EPS, along with nucleic acids, lipids and other cellular components (Sobeck and Higgins, 2002; Sheng et al., 2010). In general, EPS is present in two forms: as tightly bound to the cell wall (TB-EPS) or weakly (loosely) bound to the cell wall (LB-EPS). EPS of either variety is usually separated by centrifugation (Sheng et al., 2010). EPS that is not removed from the cell wall during the centrifugation is called capsular EPS and the EPS that is released into the supernatant during centrifugation is referred to as slime EPS.

Though various researchers are working on EPS production and its applications (Jorand et al., 1998; Houghton et al., 2001; Sobeck and Higgins, 2002), few researches focused on production of EPS in low-cost medium. There are still many gaps of information regarding the complete growth profile of EPS producing microorganisms in a sludge medium and their correlation with EPS production and fermentation time. Consequently, the objective of the current research is to study the correlation between growth of Serratia sp.1, EPS production using sludge as sole raw material and EPS activity (flocculation activity and dewaterability) while realizing the optimization of fermentation time required to achieve the maximum concentration and activity of the EPS.

Section snippets

Microorganism

Serratia sp.1 (EU031758), which was isolated from wastewater sludge and identified in our laboratory (INRS-ETE) was used in the present study.

Inoculum and cultural conditions

To prepare the inoculum for EPS production, 50 mL of tryptic soy broth (TSB) and secondary wastewater sludge with suspended solids of 20 g/L were taken in two separate 250 mL flasks. The pH of the content in both the flasks was adjusted to 7.0. The flasks with TSB and sludge were sterilized at 121 °C for 15 and 30 min, respectively. After sterilization,

EPS production and characterization

Growth and EPS production capacity of Serratia sp.1 were evaluated and results were presented in Fig. 1. Sludge characteristics are provided in Table 1. Exponential growth was observed until 24 h, stationary growth phase started after 24 h. The maximum cell concentration (6.7 × 109 cfu/mL) was attained at 48 h of fermentation. Concentration of both EPS increased with fermentation time and reached maximum at 48 h where the cell concentration (6.7 × 109 cfu/mL) of the bacteria was also maximum (

Conclusions

Growth and EPS production of Serratia sp.1 was studied in shake flask using sterilized wastewater sludge. From the above discussed results, the following conclusions are drawn:

  • 1

    .EPS production by Serratia sp.1 is growth associated. Maximum EPS concentration was observed at 48 h of batch fermentation time.

  • 2

    .Morphology of the Serratia sp.1 using a scanning electron microscope in TSB and sludge after fermentation was found to be different. Size of the cells in sludge medium was bigger than cells in

Acknowledgments

The authors are sincerely thankful to Natural Sciences and Engineering Research Council of Canada (Grants A4984, and Canada Research Chair) for financial support. The views and opinions expressed in this paper are those of the authors.

References (45)

  • E. Neyens et al.

    A review of thermal sludge pre-treatment processes to improve dewaterability

    Journal of Hazardous Materials

    (2003)
  • E. Neyens et al.

    Advanced sludge treatment affects extracellular polymeric substances to improve activated sludge dewatering

    Journal of Hazardous Materials

    (2004)
  • J.T. Novak et al.

    Mechanisms of floc destruction during anaerobic and aerobic digestion and the effect of conditioning and dewatering of biosolids

    Water Research

    (2003)
  • T.L. Poxon et al.

    Extracellular polyanions in digested sludge: measurement and relationship to dewaterability

    Water Research

    (1997)
  • Y. Qi et al.

    Application of filtration aids for improving sludge dewatering properties – a review

    Chemical Engineering Journal

    (2011)
  • L. Shao et al.

    Effect of proteins, polysaccharides, and particle sizes on sludge dewaterability

    Journal of Environmental Sciences

    (2009)
  • G.-P. Sheng et al.

    Extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems: a review

    Biotechnology Advances

    (2010)
  • D.C. Sobeck et al.

    Examination of three theories for mechanisms of cation-induced bioflocculation

    Water Research

    (2002)
  • V. Urbain et al.

    Bioflocculation in activated sludge: an analytical approach

    Water Research

    (1993)
  • R.J. Wakeman

    Separation technologies for sludge dewatering

    Journal of Hazardous Materials

    (2007)
  • S.G. Wang et al.

    Production of a novel bioflocculant by culture of Klebsiellamobilis using dairy wastewater

    Biochemical Engineering Journal

    (2007)
  • J.Y. Wu et al.

    Characterization and flocculating properties of an extracellular biopolymer produced from a Bacillus subtilis DYU1 isolate

    Process Biochemistry

    (2007)
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