Elsevier

Bioresource Technology

Volume 255, May 2018, Pages 111-115
Bioresource Technology

Recovery of polyhydroxyalkanoates from municipal secondary wastewater sludge

https://doi.org/10.1016/j.biortech.2018.01.031Get rights and content

Highlights

  • Municipal secondary wastewater sludge was found to be feedstock for extraction of PHAs.

  • Optimization by Response Surface Methodology enhanced the PHA recovery.

  • PHA yield under optimum conditions was 0.6081 g.

  • Analysis of PHA revealed dominance of mcl HAs (58%).

Abstract

In the current study, the feasibility of utilizing municipal secondary wastewater sludge for Polyhydroxyalkanoate (PHA) extraction was improved by optimization of various parameters (temperature, duration and concentration of sludge solids). Optimized process parameters resulted in PHA recovery of 0.605 g, significantly higher than un-optimized conditions. The characterization of PHA was carried out by GC–MS, FT-IR and NMR (1H and 13C) spectroscopy. The PHA profile was found to be dominated by mcl PHA (58%) along with other diverse PHA. The results of the present study show rich diversity of PHA extracted from a raw material which is readily available at minimal cost. In conclusion, exploring the potential of wastes for production of bioplastics not only reduces the cost of bioplastic production, but also provides a sustainable means for waste management.

Introduction

Rapid depletion of petroleum reserves and persistence of conventional synthetic plastics in the environment are considered important ecological problems. Thus, there is a need for alternatives to petroleum-based plastics. One such alternative is Polyhydroxyalkanoate (PHA), commonly known as bioplastic, which is a polymer produced by bacteria and has the advantage of being biodegradable and biocompatible. (Kumar et al., 2016b). It has been estimated that globally, production capacities of bioplastics till 2018 is going to increase by 300% (European Bioplastics, 2013). However, the main obstacle to the growth of bioplastic market is its high production cost, poor recycling facilities and inefficient waste handling technology (Brockhaus et al., 2016). There are innumerous reports of PHA production from pure bacterial cultures, but the major portion of the production cost is spent on media sterilization and maintenance of reactor (Reddy and Mohan, 2012). Hence, it has become imperative to search for worthwhile and cost effective feedstock alternatives for PHA production.

Wastewater treatment sludge containing mixed microbial consortia (MMC) is a potential feedstock for PHA production. Utilizing wastewater treatment sludge for producing PHA will also reduce the environmental burden of sludge disposal (Reddy and Mohan, 2012). Rapidly increasing population, urbanization and industrialization leads to production of excess amount of sludge every year, making it a readily available and more economical feedstock for bioplastic production (Bengtsson et al., 2008). Microbial species such as bacteria, yeasts, fungi present in sludge, synthesize the biopolymers triacylglycerol (TAG), wax esters (WEs) or PHA de novo with the availability of excess carbon source, particularly when nitrogen or phosphorus is limiting in the growth media (Kumar et al., 2017b).

Substantial efforts have gone towards PHA production using mixed culture of molasses (Albuquerque et al., 2010), sludge and municipal wastewater (Morgan-Sagastume et al., 2014), effluent of olive oil, designed synthetic wastewater (Reddy and Mohan, 2012). However, along with screening of low cost sustainable alternatives for PHA production, finding the optimum conditions for maximal PHA extraction is also essential. The solvent extraction method is not very environment friendly; apart from this it is economically more feasible when compared to green solvent extraction methods such as enzymatic digestion, mechanical cell disruption and the use of supercritical carbon dioxide, therefore making it an attractive method for PHA recovery (Anis et al., 2013). The action of the solvent at temperature above 50 °C will speed up the cell disruption, solubilize the intracellular PHA granules and ultimately increase the purity of polymer (Lee, 1996, Anis et al., 2013).

Response Surface Methodology (RSM) is one of the well known statistical techniques, commonly used for optimization. This optimization tool not only facilitates understanding of the interactions among different variables and estimate the maximum response generation, but also it is expeditious and cost-effective with lesser number of experiments and nominal utilization of resources (Ghosh et al., 2014).

Thus, the aim of present study is to explore the prospective use of municipal secondary wastewater sludge (MSWS) as a source for extraction of bioplastics in order to replace expensive feedstock for production of PHA. Further, statistical technique such as Box-Behnken design (BBD) model of RSM were opted to establish the optimum conditions for enhancing PHA extraction from municipal sewage sludge.

Section snippets

Chemicals

All the solvents (HPLC grade) such as chloroform, methanol, sulfuric acid were procured from Fisher Scientific, Hampton, New Hampshire (USA).

Sludge source

The sludge samples were acquired from secondary clarifier tank of Vasant Kunj wastewater Treatment Plant situated at Vasant Kunj (28°31′29.3″N latitude and 77°10′03.5″ E longitude), New Delhi, India. The collected sludge samples were kept in plastic containers and further transported in ice box to the laboratory. For recovery of sludge solid from watery

Regression models and their statistical testing

The correlation among independent factors and their response was evaluated by second-order polynomial equation. The coded equation derived from Box-Behnken design for determining the weight of recovered PHA as recommended by the software is given below:PHA Recovery=0.382+0.065A+0.014B+0.154C+0.017AB+0.041AC-0.0004BC-0.016A2+0.019B2-0.016C2where A = Temperature (°C), B = Duration (days) and C = Amount of sludge solids (% w/v) (Kumar et al., 2016a)

By comparing the above coded equation’s

Conclusions

Municipal secondary wastewater sludge is a potential feedstock for recovery of PHA since it contains MMC that have the ability to accumulate PHA as reserve food material. The results of the present study showed rich diversity of PHA from a readily available raw material, i.e. sewage sludge. The extraction conditions were optimized by successfully applying RSM. Direct recovery of PHA from MSWS using optimized extraction method without any upstream processing and carbon feeding; make it an ideal

Acknowledgements

We would like to express our sincere thanks to Department of Science and Technology, Govt. of India, Department of Biotechnology and University Grant Commission, Government of India, for financial assistance.

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    Pooja Ghosh and Khushboo Khosla have contributed equally to this work.

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