Strategies for PHA production by mixed cultures and renewable waste materials.
ABSTRACT Production of polyhydroxyalkanoates (PHA) by mixed cultures has been widely studied in the last decade. Storage of PHA by mixed microbial cultures occurs under transient conditions of carbon or oxygen availability, known respectively as aerobic dynamic feeding and anaerobic/aerobic process. In these processes, PHA-accumulating organisms, which are quite diverse in terms of phenotype, are selected by the dynamic operating conditions imposed to the reactor. The stability of these processes during long-time operation and the similarity of the polymer physical/chemical properties to the one produced by pure cultures were demonstrated. This process could be implemented at industrial scale, providing that some technological aspects are solved. This review summarizes the relevant research carried out with mixed cultures for PHA production, with main focus on the use of wastes or industrial surplus as feedstocks. Basic concepts, regarding the metabolism and microbiology, and technological approaches, with emphasis on the kind of feedstock and reactor operating conditions for culture selection and PHA accumulation, are described. Challenges for the process optimization are also discussed.
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ABSTRACT: Simultaneous nitrate-N, phosphate and COD removal was evaluated from synthetic waste water using mixed microbial consortia in an anoxic environment under various initial carbon load (ICL) in a batch scale reactor system. Within 6 hours of incubation, enriched DNPAOs (Denitrifying Polyphosphate Accumulating Microorganisms) were able to remove maximum COD (87%) at 2g/L of ICL whereas maximum nitrate-N (97%) and phosphate (87%) removal along with PHB accumulation (49 mg/L) was achieved at 8 g/L of ICL. Exhaustion of nitrate-N, beyond 6 hours of incubation, had a detrimental effect on COD and phosphate removal rate. Fresh supply of nitrate-N to the reaction medium, beyond 6 hours, helped revive the removal rates of both COD and phosphate. Therefore, it was apparent that in spite of a high carbon load, maximum COD and nutrient removal can be maintained, with adequate nitrate-N availability. Denitrifying condition in the medium was evident from an increasing pH trend. PHB accumulation by the mixed culture was directly proportional to ICL; however the time taken for accumulation at higher ICL was more. Unlike conventional EBPR, PHB depletion did not support phosphate accumulation in this case. The unique aspect of all the batch studies were PHB accumulation was observed along with phosphate uptake and nitrate reduction under anoxic conditions. Bioinformatics analysis followed by pyrosequencing of the mixed culture DNA from the seed sludge revealed the dominance of denitrifying population, such as Corynebacterium, Rhodocyclus and Paraccocus (Alphaproteobacteria and Betaproteobacteria). Rarefaction curve indicated complete bacterial population and corresponding number of OTUs through sequence analysis. Chao1 and Shannon index (H') was used to study the diversity of sampling. "UCI95" and "LCI95" indicated 95% confidence level of upper and lower values of Chao1 for each distance. Values of Chao1 index supported the results of rarefaction curve.PLoS ONE 02/2015; 10(2):e0116230. DOI:10.1371/journal.pone.0116230 · 3.53 Impact Factor
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ABSTRACT: A pilot-scale process was operated over 22months at the Brussels North Wastewater Treatment Plant (WWTP) in order to evaluate polyhydroxyalkanoate (PHA) production integration with services of municipal wastewater and sludge management. Activated sludge was produced with PHA accumulation potential (PAP) by applying feast-famine selection while treating the readily biodegradable COD from influent wastewater (average removals of 70% COD, 60% CODsol, 24% nitrogen, and 46% phosphorus). The biomass PAP was evaluated to be in excess of 0.4gPHA/gVSS. Batch fermentation of full-scale WWTP sludge at selected temperatures (35, 42 and 55°C) produced centrate (6-9.4gCODVFA/L) of consistent VFA composition, with optimal fermentation performance at 42°C. Centrate was used to accumulate PHA up to 0.39gPHA/gVSS. The centrate nutrients are a challenge to the accumulation process but producing a biomass with 0.5gPHA/gVSS is considered to be realistically achievable within the typically available carbon flows at municipal waste management facilities. Copyright © 2015 Elsevier Ltd. All rights reserved.Bioresource Technology 01/2015; 181C:78-89. DOI:10.1016/j.biortech.2015.01.046 · 5.04 Impact Factor
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ABSTRACT: Abstract Lignocellulosic fibres obtained by dry grinding of three different solid agro-residues, i.e. wheat straw, brewing spent grains and olive mills, were compared regarding their potential use as fillers in poly(3-hydroxybutyrate-co-valerate) (PHBV) for food packaging applications. Differences found in their composition might have influenced their grinding ability, as observed with the difference of sizes, i.e. 109 μm, 148 μm and 46 μm, respectively. Thereafter, composites structure was characterized regarding their morphology, fibre/matrix interaction, matrix molecular weight and crystallization behaviour. Poor fibre/matrix adhesion, degradation of PHBV polymer chains, and decrease of PHBV’s crystallinity were evidence. Consequently, mechanical properties were degraded in presence of the fibres. Water vapour transfer rate of composites was increased with wheat straw fibres introduction while it was decreased for olive mills-based materials. Regarding the food packaging applications, PHBV/wheat straw fibres composites appeared as promising materials to reach the requirements of respiring food products, whereas PHBV/olive mills composites would be more adapted for water sensitive products.Industrial Crops and Products 07/2015; 69:110 - 122. DOI:10.1016/j.indcrop.2015.01.028 · 3.21 Impact Factor