November 2, 2016
However hard we try, it will always appear sooner or later…. Yes, it’s biowaste — but luckily, it can be now processed into very useful compounds and products. Hard to believe?
This is a repost of Bioodpady i innowacyjne sposoby ich przetwarzania, originally published by Janusz Mizerny (Facebook, Instagram, Google+) after the European Week of Regions and Cities, which he attended as one of the three Winners of the Europe in My Region 2016 blogging competition.
Let’s start with a few words on why we chose this topic. Apart from continuing our waste theme (see our posts on wasting food (English version) and the zero-waste concept), this post was also inspired by our visit to Brussels for the European Week of Regions and Cities. While there, we attended a session called From bio-waste to bio-based products: the potential for regional innovation development. We learned of a number of promising technologies for biowaste processing that generate valuable bioproducts for various applications.
From Biowaste to Bioproducts
A variety of organic waste products may be used as raw materials. These include municipal biowaste (such as normal household rubbish), industrial biowaste (e.g. from paper mills and the food industry, including animal by-products), and agricultural waste (such as manure). What’s more, the same technology can be used to process sewage sludge and fermentation waste from biogas and bioethanol plants.
Now that we have our biowaste, we need to process it into useful products. This is done using Thermo-Catalytic Reforming, or TCR for short (it’s a trademark, so we will put ® after it). The diagram shows how a TCR® installation works.
Whatever biowaste we are processing first needs to be dried until we have 70–90% of dry mass. Once dried, the waste goes through a special auger conveyor, where it decomposes in the absence of oxygen at a temperature of around 400–500°C. At this stage, biochar and volatile organic compounds (VOCs) are formed.
Next comes catalytic reforming — a process where catalysts are used to further transform the intermediate products (biochar and VOCs) in the 600–750°C temperature range. This stage produces the final biochar, and the process gases are condensed and refined to obtain syngas and biooil (plus some water). Yes, it all sounds very chemical, technical and complicated, but TCR® allows waste to be transformed into useful products with very practical applications.
Utilizing Biochar, Biooil and Syngas
Biochar is the first product in this technological process. It is essentially a kind of charcoal. Biochar is not in itself a new invention — native Amazonians were producing it hundreds of years ago. Of course, they didn’t use advanced technologies, but just slowly charred organic waste under a layer of earth at a low temperature and without smoke. So, what are its practical uses?
First and foremost, it is an excellent soil enhancer. Biochar greatly improves soil water retention, making it easier for plants to access the nutrients they need to grow. If nothing else, it can be used as fuel for biomass power plants — we don’t like to burn anything, but at least it’s CO2-neutral.
Biooil extracted using the TCR® process not only is a high-calorie fuel in itself, but also mixes well with plant oils, biodiesel, petrol and diesel oil. This means it can be used in vehicle fuels or burnt in suitably adapted boilers.
Syngas generated in the final stages of the process is 50% hydrogen. This means that after further processing, it can provide fuel for hydrogen vehicles — cars, city buses or even trains. Syngas is also an important product for the chemical industry, used in processes to make methanol (and derivative compounds), ammonia and nitrogen compounds.
Though still only a technology demonstrator, TCR® is already a working solution, as you can see in this video. A containerized installation is currently in operation, processing some 750 kg of biowaste a day. Next year, Susteen plans to launch a full commercial version of the containerized installation, followed by much larger industrial installations capable of processing 2,200 tons of waste a year. All that’s left to do is wait for this innovative technology to spread.
Bioplastics Made by Bacteria
Plastic production accounts for 6% of all fossil fuel consumption, so curbing that demand would be highly beneficial to the climate and the environment. For that very reason, we were intrigued by a presentation from Paques, who claimed during the same session to have a technology for converting sewage and biowaste to biopolymers. We decided to investigate further.
The method works by using specially selected bacteria. The first installation was the result of scientific collaboration between four Dutch universities, Paques, and other companies. During 2012–2014, a test installation was set up at a Mars bar factory to process the plant’s sewage, generating about 1 kg of some very interesting compounds every day (before you ask: it wasn’t chocolate).
The compounds in question are polyhydroxyalkanoates (PHAs for short) — a group of biodegradable polymers produced by bacteria (typically E. Coli) through sugar and lipid fermentation, and used by the bacteria to store energy for leaner times (a sort of bacterial fat tissue). However, this description only applies to costly PHA production in limited laboratory conditions.
Much more interesting for us is the production of PHA from industrial sewage and biowaste. In this case, the first stage is fermentation using bacteria that convert sugars in sewage and other waste into various fatty acids, including butyric and capric acid.
The mixture of fatty acids then enters a tank populated by over 90 types of special bacteria that can generate PHA. The bacteria are fed in a feast-famine system, which in this instance means they are provided with food for one hour and then have to wait 11 hours for their next meal. Scientists discovered that this feeding system supports natural selection among the bacteria. Only bacteria capable of converting a lot of fatty acids into PHA reserves in a short time can survive.
In the third and final stage, the bacteria are fattened as much as possible to obtain maximum mass. Biopolymers stored inside the bacteria can then theoretically make up some 90% of their total mass, though currently 75% is the best result (and impressive nonetheless).
Biopolymers For All Occasions
The bacteria have done their job, so let’s see how we can use their produce. Polyhydroxyalkanoates are polymers with very similar properties to ubiquitous conventional plastics such as polypropylene (PP) and polyethylene terephthalate (PET).
Unsurprisingly, they are thermoplastic, and with suitable processing can be made ductile or elastic. They are also resistant to UV radiation and insoluble in water, though they are not resistant to acids or bases. However, they are permeable to oxygen, and combine well with other biocomponents. Most importantly, PHA polymers are biodegradable, unlike conventional plastics littering every corner of the globe.
With so many useful properties, we should expect PHAs to have a vast array of applications… as, in fact, they do. They can be used to make food packaging, both rigid and elastic. Packing film can also be made of PHA. Because they resist temperatures up to 110°C, these biopolymers can be used to make hot drinks cups. And there’s more.
Beyond packaging, PHAs can also be used in medical applications. For many years now, they have been used to make all sorts of implants, fasteners, bone grafts and many other items you’d probably prefer not to read about here. PHA-based substances can be used to produce medicines or even destroy cancer cells (yes, really).
Biopolymers may also be useful as raw materials in various chemical processes and in materials engineering. After suitable processing and mixing with other compounds, they can be used as biofuel. As you can see, the potential for using these polymers is enormous, so it’s no surprise that more and more test installations are being built. Between 2014 and 2015 bacteria were successfully used to process sewage from a cardboard factory, and at the end of 2015 a new installation for processing biowaste was set up at the Orgaworld plant in Holland.
Time for Mass Production
Bioproducts made from processed biowaste are not only useful, but above all highly ecological. In making them, we are closing the lifecycle of many products which would otherwise go to waste. After all, many products end up in a landfill or an incinerator, or at best get composted or processed into biogas.
What we have here are innovative technologies that make maximum use of various kinds of biowaste. And the best thing is that the new products have many practical applications. All that remains to do is to scale up existing test installations. As with most emergent technologies, it’s going to take a lot of money (though luckily the EU supports such projects) and time (which is, unfortunately, beyond EU control). However, we firmly believe that these eminently sensible and ecological technologies will soon be successful.
Sources: Presentations during the EUWRC session From bio-waste to bio-based products (…), Susteen Technologies GmbH, Delta TU Delft, Plastics Completely Synthesized by Bacteria: PHA, bioplasticsinfo.comMathew Lowry