Recovery of polyhydroxyalkanoates from municipal secondary wastewater sludge
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:where 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.
References (23)
- et al.
Polyhydroxyalkanoate (PHA) production by a mixed microbial culture using sugar molasses: effect of the influent substrate concentration on culture selection
Water Res.
(2010) - et al.
Production of polyhydroxyalkanoates by activated sludge treating a paper mill wastewater
Bioresour. Technol
(2008) - et al.
A crossroads for bioplastics: exploring product developers challenges to move beyond petroleum-based plastics
J. Clean. Prod.
(2016) - et al.
Morphological and 13C-nuclear magnetic resonance studies for polyhydroxyalkanoate biosynthesis in Pseudomonas sp. 61–3
FEMS Microbiol. Lett.
(1998) - et al.
Enhanced removal of COD and color from landfill leachate in a sequential bioreactor
Bioresour. Technol.
(2014) - et al.
Biodiesel production from municipal secondary sludge
Bioresour. Technol.
(2016) - et al.
Carbon dioxide sequestration by chemolithotrophic oleaginous bacteria for production and optimization of polyhydroxyalkanoate
Bioresour. Technol.
(2016) - et al.
Characterization of carbon dioxide concentrating chemolithotrophic bacterium Serratia sp. ISTD04 for production of biodiesel
Bioresour. Technol.
(2017) - et al.
Increased recovery and improved purity of PHA from recombinant Cupriavidus necator
Bioengineered
(2013) - European Bioplastics., 2013. Bioplastics Facts and Figures. European Bioplastics,...
Pseudomonas putida KT2442 cultivated on glucose accumulates poly (3-hydroxyalkanoates) consisting of saturated and unsaturated monomers
Appl. Environ. Microbiol.
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Pooja Ghosh and Khushboo Khosla have contributed equally to this work.