The invisible world
Producing conventional plastics from petroleum costs a lot of energy and generates a lot of greenhouse gases. PLA bioplastic produced by lactic acid bacteria is a sustainable alternative. Production is CO2 neutral, and PLA is better suited for recycling, composting, and reusing. A new installation at ARTIS-Micropia shows how these lactic acid bacteria work and how they could reduce some of our plastics problems.
We live in a world of plastics, from the plastic bag to packaging material, from furniture to electronics. In 2014, we produced more than 311 million tonnes of plastic worldwide and this figure will double in the next 20 years. Petroleum is used in the production of these huge quantities of plastic. The extraction and processing of this finite fossil fuel costs a lot of energy and causes major CO2 emissions. On top of that, plastic degrades poorly. The vast majority of plastic products are not collected and end up polluting the natural environment.
This makes plastic a major problem. But microbes could perhaps help us out. The PLA (polylactic acid) bioplastic is produced using lactic acid bacteria (Lactobacillus). With sugars used as a raw material, there is no need for petroleum. The bacteria eat the sugars, excreting lactic acid (also called lactate). These sugars (e.g. cellulose) were originally extracted from food crops, such as maize, sugar cane, and sugar beet. But this is not convenient if you need these crops for food. For this reason, second-generation raw materials, such as wood chips, straw, and other plant debris, are increasingly being used nowadays. Many industries have such plant waste streams. Agriculture and the cotton industry are examples. This is a way of producing a valuable raw material from a worthless waste product.
Lactic bacteria are present in our bodies, but they are also used in the production of yoghurt, buttermilk, sauerkraut, and olives. Here, they perform the same function as in the production of PLA: converting sugars into lactic acid. As this lowers the pH, they inhibit the growth of pathogens, in our bodies for example, or lend food a unique flavour. Lactic acid bacteria can also work anaerobically. This means that, if need be, they can live with in both oxygenated (in our mouth) and anaerobic (in our intestines) conditions. In PLA production, the conditions for the growth of lactic acid bacteria are therefore similar to those in our intestines: a pH of 5.4-6.4, a temperature of 38 to 42 °C, and a low oxygen concentration.
Different types of lactic acid bacteria make different types of lactic acid, namely D-lactate or L-lactate. These lactic acids in themselves are not yet useful. They are first condensed into different lactides, and those lactides then combine to produce the final product: polylactic acid (PLA). Various types of PLA are created by combining various lactides in other ways. Each has its unique properties and applications: heat-resistant, durable, compostable, but also safe for health and for use as food packaging. In addition, the PLA can be biocompatible (‘friendly to our bodies’). This means that surgical sutures and screws used to repair fractures do not need to be removed: they are metabolised in the body and broken down into lactic acid.
Using bacteria ensures four times less energy is used in the production of PLA than in that of conventional plastic. Coupled with organic waste as a raw material, this ensures PLA production is virtually CO2 neutral. But it is also very efficient: 1.6 kg of biomass produces 1 kg of PLA. Provided it is properly collected and processed, PLA is also more recyclable, compostable, and reusable than conventional plastic. This is how lactic acid bacteria contribute to a circular economy. Want to know more about bacteria that produce bioplastics? If you do, make sure you visit the installation developed by Micropia and its partner Corbion, and take part in the special ‘the lab talk’.
