1. From biowaste to energy
Valorização energética de resíduos orgânicos
Energy valorization of organic residues
3. Biowaste
Jorge C. Oliveira
Invited Professor, Instituto Superior Tecnico
Head of Dpt., University College Cork
From biowaste to energy
So we found that biomass waste is actually a very interesting source to produce biofuels, particularly biogas (hydrogen or methane), by using bioprocesses. Lets us then see what they are and how to characterise them

2. Where are we? technology biowaste biofuel
We established that learning how to turn biowaste to energy was a worthwhile objective for our profession.
For this to ever work, we need to make sure that we can make money out of it (it has to pay for itself at least). So we started by considering biofuels as an option for our money-making concept and we concluded that biowaste was actually an excellent idea for a raw material to make the biofuels. So now let’s look at the biowaste, what it is, and what technologies we might find to turn it to fuel in a cost-feasible way

3. Yes, we can run things on biogas
Reading 2015
Reached 80 mph
Autonomy of about 160 miles
The technologies exist and there are examples. For instance, here’s the so-called “Cow Poop Bus” that Reading city council (UK) put to work that used methane produced by cow dung

4. Guess what moves this one...
Bristol, 2015
By the way, it doesn’t have to be cow... The digestive system of animals (in which we are included) produces methane (by anaerobic digestion). The digestate expelled by the animals still has methane production going on, and can go on further.

5. Hydrogen buses also exist
Vancouver, Olympic games. 2010
But methane is not the only waste-to-fuel option. There are several car manufacturers that have developed models that run with hydrogen fuel cells, and hydrogen can be produced by biological means, such as photosynthesis, and also from waste. Here you see one of the Vancouver buses that the municipality put in place for the Olympic games (Winter) 2010.

6. However Trickier issues of safety in people’s minds
Cost about 4 times the price of a normal diesel bus
That didn’t last though... Their angle was not the biowaste, but an engine with zero emissions (burning hydrogen produces nothing but water). It just costed too much, so after the Olympics they “parked the buses”. There was also concern with Hydrogen because of memories of the Hindenburg disaster, but actually hydrogen is not the only fuel to explode... All vehicles must have safety measures to handle fuel !
“Vancouver ends hydrogen bus program amid high costs”, 2014,
Buses were costing twice as much to run than diesel vehicles because Vancouver had no source of hydrogen

7. Biowaste sources are ...
Cow dung (and other animals, including poultry)
Municipal Solid Waste
Water treatment waste
Waste from food businesses (dairy, meat, etc)
Slaughterhouses
Straws, husks (non edible parts of plants)
Sawdust, wooden chips from wood industry
Paper industry effluents
So, let’s list the sources of biowaste that we might be able to turn to biogas. This is the list we came up with in class

8. Biowaste sources Municipal Agricultural Industrial OF-MSW
grass cuttings, leaves, woody masses
sewage
Agricultural
Straws and husks
Abattoirs (slaughter houses)
Farm dung (specially cows)
Industrial
brewing (inc. spirits)
paper industry
textiles
wood/carpentry
And this is a list I had thought about before. There actually is a quite wide variety of biowastes that we may be able to use !

9. Are people really pigs?
Looking into the statistics of how much of which is produced, household waste stands out. Even though quantities have been decreasing, it still is a lot more than anything else

10. A mountain of waste
Ireland produces about 1 million ton of food waste per year, 1/3 of which is household (around 80 kg per capita)
If you think the Irish waste too much, the average figure for food waste in Europe is 180 kg per capita (89 million tons a year)
US throws away around 45 million tons per year
Check the statistics on household waste, and how much of it is organics, and you’ll be surprised. In addition to this, don’t forget the tons that “go to the bin” in the distribution centres of large retailers because the supermarkets couldn’t sell it in their shelf-life windows. Good news is that fruits & vegetable waste is among the best to turn into energy

11. The EU said enough is enough
Council Directive 1999/31/EC of 26 April 1999 limits organic fraction of waste allowable in landfills to 3%
States have been pushed to sort out organics from other waste
what can be recycled
is to be recycled
what can’t should
go to biogas
There are actually policies in place to limit this enormity of waste. When you throw away food leftovers, all the energy and water that went into it was lost. Of course, there are things you need to discard, like peels, fat strips, etc. But a lot is food that just goes off because you didn’t consume it in time. EU directive forbids landfills to accept more than 3% of organic waste. Thus, EU states have been pushed to start thinking about separating waste, recycling what can be recycled, and biowaste (which is not recyclable...) can, if nothing else, be turned to biogas

12. Some countries are more enthusiastic than others
Waste treatment in EU-27 in 2010
Some countries are more enthusiastic than others. Belgium only actually disposes of 10% of its waste, Denmark does not incinerate, they just don’t (note: this is incineration for disposal, not combustion to produce energy). Germany already has around 9,000 plants producing biogas, with a capacity of circa 4GW of electricity: that’s enough to power 9 million homes, generating about 9 billion Euro of sales (the progression: 9 thousand plants, 9 million homes, 9 billion Euro)

13. The German biogas story – why go nuclear?
That’s not just biowaste, but remember that the cost of biowaste as a raw material is negative (that is, it is actually an income), whereas some of the others you have to pay for !
So there’s lot to do in Germany still; only around 2% of the feed is household biowaste and 48% still is crops that could otherwise be used for food (44% manure and 6% industrial and agricultural effluents). Of the 9,000 biogas units, only around 300 do anaerobic digestion of biowaste alone

14. What distinguishes waste streams?
Volatile solids are those that ignite at 550 C
it’s mostly the organics
The most important features of a waste stream are:
the elemental analysis (Carbon and Nitrogen of particular interest, and potential contaminants, the main ones being Sulphur, Chlorine, Phosphorus, Potassium and Magnesium, but others can also be an issue, like Lead, Heavy metals, etc) – the table above is an example for a particular waste stream analysed in one study
the total solids and the fraction of them that are combustible, called the volatile solids; they are determined by taking the whole mass to 550 C and then weigh how much was lost

15. Most important VS/TS ratio Carbon Nitrogen Sulphur Chlorine
of particular importance will be the C/N ratio
Sulphur
Chlorine
other possible contaminants (K, Mg, Ph)
Water content
remember difference between HHV and LHV?
The ratio of volatile to total solids is very important, as the remaining is the ash left after combustion. A low VS/TS means a lot of ash, which is not suitable for combustion.
For energy production reasons (which we will explore later), the C/N ratio is very important, not just how much C and N there is in themselves. Nitrogen comes mostly from proteins, so biowaste from food tends to have low C/N ratio, whereas biowaste from digestates for instance has a lot less nitrogen (most proteins were absorbed by the animal’s digestive system), so a higher C/N ratio (same goes for lignocellulosic materials)
Various contaminants could be a problem, Sulphur quite obviously, as we know from conventional oil refinery that it is the very first thing that we need to do with oil when it enters the refinery: get rid of that sulphur. Not only it produces terrible smells (like H2S) but also very strong acids (like H2SO4). Although C/N is important for some uses, if the waste was to be burnt as is, then Nitrogen is a very important contaminant as well, it leads to noxious nitrous oxides (are you familiar with the Volkswagen emissions scandal?). Environmental regulations will have limits for these contaminants in anything purporting to be a fuel.
Another important characteristic is the water content. Remember the difference between HHV and LHV? A waste stream with a lot of water has an effective lower heating value if you’re thinking about burning it straight away

16. What can we do with this? Just dry and burn
Produce hydrogen with appropriate micro-organisms and operating conditions
without light, some bacteria digest organic matter and produce hydrogen
Produce methane with appropriate micro-organisms and operating conditions
under aerobic conditions, some bacteria break down organics and produce CO2
under anaerobic conditions, some bacteria break down organics and produce CH4
So what can we do with this waste?
1 - Just burn it, it will probably be more efficient to dry it first, but that’s it, it generates energy. You can sell this as a biofuel, just dry and compress into briquettes or pellets, just like you do with sawdust and things like that. Drying is a good idea to increase its combustion properties, but also removes volatiles, which in some cases is really necessary to avoid nauseous smells.
2 – We know from microbiology that there are some bacteria that digest biomasses in the absence of light and produce hydrogen, so we can actually produce a very good fuel out of biowaste by using these.
3 – Just like we do every day in our own digestive system, we can use the type of micro-organisms that our own guts have to digest the biomass to produce methane. The bacteria that do this are anaerobic, so this requires no oxygen. In the presence of oxygen, as you can guess very easily from the stoichiometries of oxidation, the aerobic bacteria would just produce water vapour and carbon dioxide

17. let’s fill up our knowledge sink
info source for your study: Extract from HJXW study
Review paper: EU-27 tech potential of organic streams
There are many sources of biowaste
One of the most promising is household organic waste
Sewage (mostly farms) also seems interesting
Critical factors are contents in:
volatiles solids (VS) versus total solids
carbon and C/N ratio
Problems from contaminants such as
sulphur
chlorine
potassium, etc...
They can be dried, fermented (in dark) to produce hydrogen or digested anaerobically to produce methane
So looking back at what we learned at this stage of our journey, these are the take-home messages
For more details, I leave two texts. One is a recent review of the status of production and usage of waste in the EU-27 (delete the UK column in 2 years...), and the other some details of a briquetting process that we will talk about next, but it also has an interesting review about waste streams and waste policies in the EU