Team:PuiChing Macau/Description

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Global Food Waste Issue:

Food waste has been one of the most challenging issues around the world. According to the FAO (Food and Agriculture Organization of United Nations survey), about 1.3 billion tons of food is wasted each year, which is about one-third of the world's total food production. Among the whole food supply chain, 14% of food is loss and 17% of food is wasted. [1] Being a global issue, the food waste problem has been affecting our city, Macau, and places nearby. In Hong Kong, according to statistics from the Hong Kong Environmental Protection Department, about 150,000 tons of food are wasted a year; while on the contrary, only 42,000 tons undergo the treatment processes, meaning that the food waste treatment rate is very low, down to 2.8%.[12] It has been mentioned that most of the food loss and waste come from retails and tourism (by Gretzel, U et al, 2019) [2]. The problem in Macau is more serious, as Macau is a city famous for tourism with all kinds of delicacies and local cuisines. Though research from the Macau Environmental Protection Bureau has shown that food waste in Macau is lower than in Hong Kong, about 200,000 tons, the food waste treatment rate is still very low. When 200,000 tons of food is wasted a year, only 440 tons of them have been treated, which means the food waste treatment rate accounts for only 0.2%. [3]

Treating Food Waste: From a Local perspective…

In Macau, there are two solutions to treat food waste. The more traditional one is processing with the Macau Refuse Incineration Plant. The heat generated by waste combustion is used to produce water vapor, hence driving the turbine generator to produce electricity. However, the Incineration Plant produces a large amount of carbon dioxide during the processing of food waste. Therefore, in 2019, the fertilizing machine was brought to Macau, processing 441,819 kg of food waste a year. However, the food waste treatment rate is still quite low due to the low efficiency.[3]Therefore, the commissioner of DSPA (Direcção dos Serviços de Protecção Ambiental), the environmental protection bureau in Macau, has announced the planning of an alternative solution in food waste treatment. The government is planning to build the central food waste treatment facility next year. The system works by producing biogas through fermentation of food waste, then the biogases are then converted into electricity. However, one downside is a large amount of carbon emission. This causes air pollution and aggravates the greenhouse effect, leading to global warming.[26]

Sustainable Approach in Food Waste Treatment:

In order to tackle this problem, we would like to find a solution to enhance the food waste treatment rate. We designed our project to improve the food waste treatment solution. Other than that, we have considered something more. Despite treating food waste, we also consider the sustainability of our project. We realized that lots of plastic meal box are generated due to the quarantine in Macau, turning out that the waste of non-biodegradable plastics has also becoming a more urgent problem. To tackling this issue, we would like to achieve a more sustainable approach. We would like to convert food waste into biodegradable bioplastics, and have chosen PLA and PHA due to their readily degradable under natural soil environment verified by research (by E. Rudnik et al, 2012).[23]

What are bioplastics?

Bioplastics are a special type of biomaterial. They are polyesters, produced by a range of microbes, cultured under different nutrient and environmental conditions.[13] In our project, we target converting food waste into two degradable bioplastics, PLA and PHA.
PHA, polyhydroxyalkanoates, are bio-based microbial biopolyesters; produced in nature by numerous microorganisms, including through bacterial fermentation of sugars or lipids.[15] They are biodegradable, and their degradation products do not exert any toxic or elsewhere negative effect to living cells or tissue of humans or animals.[14]
PLA, known as polylactic acid, is a degradable polymer. PLA is produced by the polymerization of lactic acid.[6] Lactic acid, which is often obtained from the fermentation of sugar, can be easily produced through the fermentation of food waste. In such a case, PLA is considered to be a potential bioplastic that can be converted from food waste. The degradation of PLA does not pollute the environment.[7] Hence, the most important thing is the combined use of PLA and PHA would provide better physical properties and shorten the degradable time when compared with other plastics.

Current Options:

One of the most common ways of food waste treatment is dumping them into the landfill. During these few decades, instead of letting food waste be trash lying in the landfill, new ways of treating food waste for upcycling reuse had been founded. The traditional treatment of food waste is the composting treatment.[8] However, throughout the industrial processes, large amounts of sewage have chemical reactions and then produced heavy metals.[9] This has an adverse effect on the ecosystem and humans. Heavy metals will also elaborate on some effects on humans. Another option nowadays is converting food waste into bioplastics in a chemical industrial way. It is a high-cost production process and unstable.[10] An alternative solution is anaerobic digestion, biogases are produced through fermentation of food waste, and are then converted into electricity. The one downside is a large amount of carbon emission. There is another option, which is producing biomaterials through bio feedstock. Yet, the solution is still not perfect. In our project, we would like to work on improving this option. The following paragraph will be introducing the problems and our solution to them.

CompostingHigh Efficiency & Low CostSewage produced (with heavy metal)
Bioplastic Production (after Anaerobic Digestion, Chemically synthesized)Eco-friendlyHigh Cost & Unstable
Biogas Production(Anaerobic digestion)Generating ElectricityCarbon Emission
Bioplastic Production(Biochemically Synthesized)Eco-friendly & StableLow Efficiency

Problems in Bioplastics Production:

However, the production of these biodegradable bioplastics is facing various problems. The cost of biodegradable plastics is higher than those non-biodegradable ones. As shown by research (Keith H. Coble et al), the cost of producing biodegradable plastics is 115 percent of non-biodegradable plastics, which many manufacturers are not willing to pay extra cost for environmental benefits.[16] Moreover, the low efficiency of PHA production and problems with PHA’s purification stops PHA’s large-scale production.[17] The same problem happens on polylactic acid, that its production was hard to be commercialized on large scale.[18] Recently, synthesizing plastics using microbial cultures has attracted much interest due to their simplified fermentation conditions and environmental advantages.[19] As PHA and PLA are produced by large-scale microbial fermentation, the environment then turns acidic after fermentation.[20][21] However, it is proved that the increasingly acidic conditions ultimately inhibit the growth of microorganisms, a low pH environment is not suitable for E.coli survival.[22] Thus, affecting the yield of bioplastic production. In our project, we would like to tackle these problems.

How can we solve problems in Macau?

Back to Macau, statistics (Report on the State of the Environment of Macao) have shown that Macau’s N2O emission has increased by 2.6% in a year, mainly from refuse incineration.[3] Moreover, the usage of fertilizer is very limited, which those fertilizers are not sold but given to the local restaurants. To figure out a better way, we decided to work on converting food waste into biodegradable bioplastics with more flexible usage.
Another significant issue is the low efficiency of food waste treatment, leading to low yield and high cost of the products. According to the data (O Martin et al), 36.2% of food waste can be recycled by converting it into composting.[7] An experiment (Davison, Brian H. et al) was carried out to investigate the conversion of food wastes into lactic acid by simultaneous saccharification and fermentation. As a result, the overall yield of lactic acid is 60% generated from food waste.[24] Hence, the yield of PLA from polylactic acid is about 81.3%. Hence, the yield of PLA from polylactic acid is about 81.3%. Therefore, by converting into PLA, 48.8% of food waste is recycled[25]. Comparing the two methods of food waste treatment, more food waste is treated when it is converted into bioplastic, meaning that the percentage of food waste recycled in bioplastic production is higher than composting treatment.

Our project:

Instead of treating food waste in traditional ways causing pollution to the ecological habitat and generating hazards to humans, we would like to develop an alternative way of treating food waste. Through synthetic biology, we aim to develop an engineered recombinant E.coli strain, to convert food waste into biodegradable and eco-friendly bioplastics, polylactic acid (PLA) and Polyhydroxyalkanoates (PHA). We have divided our system into different parts. First of all, we would like to convert food waste to monosaccharides with amylase and glucoamylase. Afterward, monosaccharides can be converted to lactic acid by fermentation. The problem is that due to the presence of lactic acid, the environment turns more acidic. In a lowered pH value environment, E.coli’s survival and growth will be inhibited. To tackle the issue, we have developed an acid-tolerant system using fabB genes to increase the production of unsaturated fatty acids. What comes next is the PLA and PHA production system, consisting of PhaC and PCT genes. At the same time, to tackle issues with the current biobricks, we have optimized the codon. We transform these two genes into the E.coli so that we are able to convert food waste into polylactic acid PLA(PCT) and polyhydroxyalkanoates PHA(PhaC). Therefore, we want to do more to enhance the rate of the production of PLA and PHA in our system. In order to promote the efficiency of our system, we would like to add Phasin to our PLA and PHA production system. Since phasin has been proven to be capable of increasing PHA production, and at the same time PHA and PLA share similar patterns in their chemical structures, we would like to apply phasin to our project to boost the PLA and PHA’s production rate of our system. All in all, we are building up our project with the bioplastic (PLA and PHA) production system and the acid-tolerant system, in order to achieve our goal of producing PLA and PHA in a one-step approach and promoting its efficiency.


  1. FAO, Browne and Murphy, (2013) (Food and Agriculture Organization of United Nations survey)
  2. Gretzel, U., Murphy, J., Pesonen, J. and Blanton, C., (2019), "Food waste in tourist households: a perspective article"
  3. Report on the State of the Environment of Macao, (2019)
  4. Poore, J., & Nemecek, T. (2018), Reducing food’s environmental impacts through producers and consumers.
  5. O Martin; L Avérous. Poly(lactic acid): plasticization and properties of biodegradable multiphase systems. , 42(14), 6209–6219.
  6. Rathin Datta; Shih-Perng Tsai; Patrick Bonsignore; Seung-Hyeon Moon; James R. Frank, Technological and economic potential of poly(lactic acid) and lactic acid derivatives.
  7. US Environmental protection agency, (
  8. Z. Chu et al. ,Quantitative evaluation of heavy metals’ pollution hazards and estimation of heavy metals’ environmental costs in leachate during food waste composting.
  9. Nielsen, Chad; Rahman, Asif; Rehman, Asad Ur; Walsh, Marie K.; Miller, Charles D. (2017), Food waste conversion to microbial polyhydroxyalkanoates.
  10. Zhao, Nana; Yu, Miao; Wang, Qunhui; Song, Na; Che, Shun; Wu, Chunfu; Sun, Xiaohong ,(2016), Effect of Ethanol and Lactic Acid Pre-fermentation on Putrefactive Bacteria Suppression, Hydrolysis, and Methanogenesis of Food Waste.
  11. Xu, F., Li, Y., Ge, X., Yang, L., Li, Y., Bioresource Technology ,(2017)
  12. Monitoring of Solid Waste in Hong Kong (Waste Statistics for 2019)
  13. José M Luengo; Belén Garcı́a; Angel Sandoval; Germán Naharro; Elı́as R Olivera (2003). Bioplastics from microorganisms. , 6(3), 0–260
  14. Koller, Martin (2018). Biodegradable and Biocompatible Polyhydroxy-alkanoates (PHA): Auspicious Microbial Macromolecules for Pharmaceutical and Therapeutic Applications. Molecules, 23(2), 362–.
  15. Lu, Jingnan; Tappel, Ryan C.; Nomura, Christopher T. (2009-08-05). "Mini-Review: Biosynthesis of Poly(hydroxyalkanoates)". Polymer Reviews. 49 (3): 226–248.
  16. Keith H. Coble, Ching-Cheng Chang, Bruce A. McCarl and Bobby R. Eddleman. Assessing Economic Implications of New Technology: The Case of Cornstarch-Based Biodegradable Plastics. Review of Agricultural Economics, 14(1), 33–43.
  17. Bajpai P. Biobased polymers: properties and applications in packaging. Elsevier; 2019.
  18. Sprajcar M, Horvat P, Kr zan A. Biopolymers and bioplastics: plastics aligned with nature. Ljubljana: National Institute of Chemistry; 2012.
  19. Chen, Zhiqiang; Huang, Long; Wen, Qinxue; Guo, Zirui (2015). Efficient polyhydroxyalkanoate (PHA) accumulation by a new continuous feeding mode in three-stage mixed microbial culture (MMC) PHA production process. Journal of Biotechnology, 209(), 68–75.
  20. Chen, Guo-Qiang (2009). A microbial polyhydroxyalkanoates (PHA) based bio- and materials industry. , 38(8), 2434–0.
  21. Piemonte V, Sabatini S, Gironi G. Chemical recycling of PLA: a great opportunity towards the sustainable development? J Polym Environ 2013;21:640e7.
  22. Janelle L Brown; Thomas Ross; Thomas A McMeekin; Peter D Nichols (1997). Acid habituation of Escherichia coli and the potential role of cyclopropane fatty acids in low pH tolerance. , 37(2-3), 163–173.
  23. E. Rudnik; D. Briassoulis (2011). Comparative Biodegradation in Soil Behaviour of two Biodegradable Polymers Based on Renewable Resources. , 19(1), 18–39.
  24. Davison, Brian H.; Lee, James W.; Finkelstein, Mark; McMillan, James D. (2003). Biotechnology for Fuels and Chemicals || Production of Lactic Acid from Food Wastes. , 10.1007/978-1-4612-0057-4(Chapter 53), 637–647.
  25. Zhao, Weirui; Ding, Huanru; Lv, Changjiang; Hu, Sheng; Huang, Jun; Zheng, Xiaodong; Yao, Shanjing; Mei, Lehe (2017). Two-step biocatalytic reaction using recombinant Escherichia coli cells for efficient production of phenyllactic acid from l-phenylalanine. Process Biochemistry, (), S1359511317307432–.