Sustainable Polyhydroxyalkanoates (PHA) Extraction Protocol Selection Using AHP-GRA


 In this study, a sustainable protocol for PHA extraction was methodically selected using two (2) multi-criteria decision analysis (MCDA) tools, the analytic hierarchy process (AHP) and grey relational analysis (GRA). AHP was first used to evaluate the proposed criteria categorized into technical, economic, and environmental aspects using a collected survey of pairwise comparisons. Based on the results of AHP, it was identified that both environmental and economic aspects were given higher priorities. Among the criteria, hazards and risks has the highest overall importance, followed by extraction cost and purity. Using GRA, twelve (12) protocol alternatives categorized into solvent extraction and precipitation, non-PHA cell mass (NPCM) digestion, and assisted extraction methods were graded according to the criteria. Overall, the highest priority weights were given to NPCM digestion protocols including sodium hydroxide, sodium hydroxide + sodium dodecyl sulfate, and ammonia water. The reagents involved in these protocols are ecologically benign and cheaper compared to other solvents; hence, the higher grades in the environmental and economic aspect. Sensitivity analysis also proved that these protocols are excellent, particularly if extraction cost is given a higher priority. However, if hazards and risks and purity were given more importance, butyl acetate is preferable than sodium hydroxide. Further investigations such as the validation and optimization of protocols, together with feasibility studies and life cycle analyses may be integrated with the results of this study to comprehensively determine a sustainable PHA extraction protocol.


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To combat the problem against petroleum dependency and plastic pollution, bioplastics that 63 are biodegradable, renewable, and biocompatible are receiving much attention as future 64 alternatives to conventional plastics. Among the bioplastics, there has been a growing production cost (Samori et al. 2012). Industrially, these attributes somewhat antagonize 85 sustainability and economic feasibility that the use of PHA promotes.

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Selecting an efficient, economical, and environment friendly PHA extraction protocol is 88 very important to reduce the cost of the polymer and minimize its impact. The protocol 89 must be operationally fast and simple and can improve polymer yield and purity using 90 minimal amounts of ecologically benign reagents. Nevertheless, choosing an appropriate 91 protocol is quite complicated due to conflicting relations of technical, economic, social, and 92 environmental attributes that must be taken into consideration and treated as an integrative 93 whole. Besides, the criteria to be considered for a PHA extraction protocol selection has not 94 been fully established. Researchers focus mostly on improving the feasibility of the process 95 by optimizing the polymer recovery and purity, but other important factors that can affect 96 protocol selection are often not evaluated. To make the selection process more strategic and 97 comprehensive, a multicriteria decision analysis (MCDA) can be employed. MCDA 98 methods differ from conventional decision techniques since they incorporate a decision-99 making that conforms with a synthetic numerical approach, leading to rankings and 100 identification of trends (Szabo et al. 2021). They are used to formally solve actual problems 101 by evaluating multiple conflicting criteria and identifying the "best" alternative from a pool Several papers had already employed the MCDA approach in decision-making. In selecting 108 a sustainable biomass crop for biofuel production, economic, environmental, and social 109 aspects subdivided into 16 sub-criteria were assessed using the stochastic analytic hierarchy 110 (AHP) methodology. Biomass crops considered were switchgrass, miscanthus, sugarcane, 111 corn, and wheat (Cobuloglu and Büyüktahtakin 2015). AHP was also applied to find the 112 most appropriate feedstock for biodiesel production in Vietnam among three possible Tobiszewski 2021). Upon ranking, results show that many solvents, synthesized by mixing 129 sugars alcohols, alcohols, sugars, and amides are promising solvents and more preferred than imidazolium-based ionic liquids. To the best of our knowledge, this paper is the only 131 existing study so far that utilizes MCDA in selecting a PHA extraction protocol.  Chloroform and dichloromethane are considered the best organic extraction solvents, but 150 are dangerous both for humans and the environment, rendering them as undesirable for 151 industrial applications (Samori et al. 2012). Greener non-halogenated solvents such as 1,2 152 propylene carbonate, 1,3-dioxolane, dimethyl carbonate, butyl acetate, and cyclohexanone were used to replace these compounds (Pérez-Rivero et al. 2019). After dissolution, PHA is 154 recovered with a precipitating agent (antisolvent) such as acetone, water, ethanol, and 155 methanol (Koller et al. 2013). These mild compounds polish the extract by solubilizing 156 lipids that coat the polymer granules. Alternatively, PHA can be precipitated by lowering 157 the temperature to a range where solubility of PHA in the solvent is not provided anymore.

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Although solvent and antisolvent systems often result in excellent polymer recoveries and 159 purities, the required low precipitation and high extraction temperatures entails additional 160 energy costs. Solvent extraction is operationally slow due to the nature of the solvents 161 utilized. Large amounts of these solvents, usually reaching up to 20-fold mass of the PHA-162 rich biomass are also undesirably required, making the process too costly to be considered a 163 feasible alternative (Koller et al. 2013 to these agents, leading to hydrolysis and degradation. Due to the lower purity of the 174 extracted polymer, an additional purification step is also often required. To improve polymer recovery from NPCM digestion, it can be coupled with physical 177 methods such as ultrasound (sonication) and microwave (Balakrishna Pillai et al. 2018;178 Martínez-Herrera at al. 2020). These tools help in speeding up the digestion process and 179 increase the recovery and purity of the extracted polymer. Sonication generates extreme 180 and rapid cyclic pressure changes in a fluid, generating microbubbles of gas and vapor.   At a given hierarchy level, elements were compared in pairs for their relative importance.

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In case of the criterion of each aspect, the assessment of the pairwise comparison was made 211 with respect to the former hierarchy level. The comparisons were made on an increasing 212 importance from a scale of 1 to 9. Values 1, 3, 5, 7, and 9 indicated equal, moderately 213 more, strongly more, very strongly, and extremely more importance, respectively, while the  The goal of the study was to determine a sustainable PHA extraction protocol. Nine (9) 218 proposed criteria were categorized into three (3) main aspects, namely technical, economic, 219 and environmental aspects. Technical aspect included recovery, purity, and product 220 degradation. For the economic aspect, extraction cost, recyclability, and ease of operation 221 were selected. Meanwhile, disposal management, hazards and risks, and carbon footprint were included in the environmental aspect. These sets of aspects and criteria were 223 compared pairwise by four (4) domain experts.
The CI value was calculated using the maximum eigenvalue (λmax) and order (n) of the  digestion, and assisted extraction methods were rated and ranked. The GRA scoring system 275 used to evaluate the proposed alternatives for feedstock selection is shown in Table 2. To 276 simplify calculations, scores ranging from 1 to 5 (with 5 as the highest score) were arranged 277 by incorporating the positive and negative criteria that will most likely give advantages to 278 the ranking of the protocol alternatives. For example, recovery and purity were considered 279 as positive criteria while product degradation and extraction cost were treated as negative 280 criteria. In effect, the scores were reversed for the negative criteria.

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( 1 , 2 , 3 , … , , … , ), where is the performance value of the attribute of 285 alternative . The could also be translated into a comparability sequence =

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Equations 4, 5, and 6 are used for the larger-the-better, smaller-the-better, and closer-to-the-292 desired-value- * -the-better, respectively (Kuo et al. 2008). This study used only Equation 4 293 prior to the pre-arranged scoring system shown in Table 3.

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Then, the grey relational coefficient was computed to determine the closeness of to 0 .

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The closer the to 0 , the larger the grey relational coefficient. In Equation 7 be set by the decision maker. In this study, the distinguishing coefficient was set at 0.5.
Finally, the grey relational grade was obtained using Equation 8.

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The integrated grey relational grade between reference sequence ( 0 ) and comparative  extract. An ideal protocol is similarly characterized by an average purity of 90% of higher.

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Lastly, product degradation pertains to the decomposition of long chains of PHA into smaller molecular counterparts. It is usually measured either by average molar mass or 340 polydispersity index of the extracted polymer. A minimal to negligible PHA degradation at 341 any extraction temperature is deemed desirable for an extraction process. Pairwise comparisons for the main aspects and criteria are summarized in Tables 4 to 7.

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AHP results indicate that both environmental and economic aspects are crucial in the 381 selection a sustainable PHA extraction protocol (Table 8). This is indicated by the closeness The final ranking of the protocols was then conducted using GRA. Initially, a decision 391 matrix was made using a scoring system (Table 3) Table 9. Scores were normalized and processed to obtain the grey relational 394 coefficients and grey relational grades.   in the technical aspect, but since the remaining two aspects were highly prioritized, they

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The study identified the best extraction protocol for sustainable PHA production by             Sensitivity analysis of the priority weights of protocol alternatives for PHA extraction and recovery at various criteria weight intervals of (A) hazards and risks, (B) extraction cost, and (C) purity

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