Food losses and food waste has been addressed in a number of scientific research papers in recent years. Peter Alexander write about ‘Losses, inefficiencies and waste in the global food system’ (In: Agricultural Systems, Volume 153, May 2017, Pages 190-200,

The article contains two beautiful Sankey diagrams. The first depicts the global food system in 2011. Flows are shown as dry mass. Flows are not individually labelled with the underling quantity, but rather a scale at the bottom shows 5 representative flow quantities and their corresponding width.

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Crop (yellow) and grassland (green) net primary production (NPP) are shown as sources for the global food system. Losses are branching out as grey arrows. These “inefficiencies” of the system are described in detail in the article. The authors observe that “44% of harvested crops dry matter are lost prior to human consumption” and that “the highest loss rate can be found in livestock production”.

The second Sankey diagram shows a section of the above figure, just the dry matter flows from crop harvest and processing, without any losses. This is interesting because it allows us seeing the share of processed and non-processed food being consumed by humans worldwide, and the the share of crop-based food intake (dark blue) compared to animal-based food intake (red). You could call this the veggie / non-veggie split. Based on dry matter that is.

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If you want to see the corresponding global food system wet mass, protein and energy Sankey diagrams check out this interesting article. A recommended read for all of us eaters.

The French region Auvergne-Rhône-Alpes in the south-east of the Hexagone borders with Switzerland and Italy. Lyon and Grenoble are located in this region, known for skiing, lush pastures … and great cheese!

Auvergne-Rhône-Alpes Énergie Environnement (AUR-EE) is a regional agency that works to bring together players in the renewable energy field and to promote RE projects.

Given the agricultural character of Auvergne-Rhône-Alpes, biomass use for energy generation has been going strong in recent years. The agency has created energy flow Sankey diagrams for existing biogas installations, as well as a projection for the ones being under development.

Data is for 2017 and for the scenario where all projects currently under development would already completed. The yellow stream (‘déchets ménagers’) is household waste, providing 374 GWh of energy. Manure and other side-products from agriculture (green arrow) contributes another 260 GWh.
The stacked bar on the left hand side of the diagram indicates the potential availability of biomass by 2035, and one can see that only a small fraction of it is currently being taken advantage of.
Biogas is produced in anaerobic digesters (‘méthanisation’) and the region yields some 271 GWh electricity and 200 GWh heat per year from cogeneration plants. Already almost 100 GWh of biogas could be injected to the natural gas network, allowing for storage of the energy.

Note that smaller or even negligible flows are still shown with a minimum width in order to make them visible (these thinner arrows are not to scale with the others).

Javier Dufuor on the madrid+d Energía y Sostenibilidad blog reports about a novel lignocellulose biorefinery process developed by Prof. James A. Dumesic at the University of Wisconsin-Madison. This so-called TriVersa process can yield up to 80% of biomass from birch wood as marketable products.

The Sankey diagram for the TriVersa process shows carbon in biomass flows. Values are in percent, starting with the 100% C molecules in birch wood being used as feedstock.

An interesting detail about this Sankey diagram is that it additionally uses the process “nodes” or “boxes” to indicate operating cost and annualized capital cost. No numbers are given here, but the height of the process box indicates the overall cost (in a kind of stacked bar chart).

The European research project CASCADES’ objective was “to define the cascading use of wood and assess the environmental and socio-economic impacts of cascading, to identify and analyse the barriers preventing cascading”. As a central element of the project a wood flow analysis was conducted.

From page 26 the 2016 final report [Vis M., U. Mantau, B. Allen (Eds.) (2016) Study on the optimised cascading use of wood. No 394/PP/ENT/RCH/14/7689. Final report. Brussels 2016. 337 pages)] comes this Sankey diagram depicting wood flows in the European Union (EU-28).

All flows are in Mm³ swe (solid wood equivalent). No absolute numbers are given to quantify the flows, instead three sample arrows serve a reference to the scale (“Legend of dimensions”).

The wood biomass is either used as material (left branches) or as energy (right branch). On the material side wood industry (yellow path) and paper industry (blue path) take up most of the biomass. Residues of both industries along with a good chunk of the post-consumer paper waste are being recovered and led in a cascading loop, until they eventually shift to the energetic side.

A complex and interesting Sankey diagram with much to discover. The CASCADES report describes all the areas of the wood flow system, identifies hotspots and describes measures for optimization.

What happens to yard waste and biowaste in Germany? This Sankey diagram from a 2014 PowerPoint presentation titled ‘Flächendeckender Ausbau der Biotonne in Deutschland’ by Peter Krause and Rüdiger Oetjen-Dehne (u.e.c. Berlin) shows how these flows were distributed.

In 2012 there were 14.5 mio. tonnes of yard waste andd 6.6 mi. tonnes of bio waste (kitchen/food waste) were disposed of in Germany. Much of it was collected and treated or – such as in the case of yard waste – composted (7.8 mio. tonnes).

In addition to the absolute quantities the labels along the Sankey arrows show the average per inhabitant (kg/E, a).

A large potential is still in bio waste (orange-coloured arrow) being disposed of in regular household waste (“Restabfall”). Calls for separate collection of bio waste for energy recovery are being made.

Interesting comparative Sankey diagram on page 16 of the 2012 environmental declaration of Rosenheim Stadtwerke (Rosenheim City Power?).

The city is building or already running a wood gasification plant. Instead of just using the heat from directly burning wood (with 30% energy loss), they decided to work with a wood gas carburetor and use the wood gas to run a gas motor. This is somewhat similar to CHP where heat and electric power can be produced. Overall loss of energy (“Verluste”) in the system is only 23%.

The green box at the bottom displays the avoided fossil GHG emissions per tonne of wood for both technologies.

Flows are in MWh, but only some selected arrows are labeled. Unfortunately the flows are not always to scale: yellow arrow “Wärme” (heat) in figure at top representing 3,15 MWh, but shown as half the width of the blue arrow 4,5 MWh. I reckon the diagram was build manually from rectangles and triangles.

Browsing my previously bookmarked Sankey diagram samples I came across this one which I find interesting. The diagram was shown in a Green Cars Congress blog entry in 2010 and illustrates a study that finds that “large scale biofuel production can be successfully reconciled with food production through the use of land-efficient animal feed technologies and double-cropping”. The authors of the study are Dr. Bruce Dale and colleagues at Michigan State University.

As always I refrain from commenting the underlying content as I am not a domain expert. Rather I would like to focus on what makes this Sankey diagram special.

These are actually two diagrams that are “flipped” over at a vertical center line. The left half of the diagram has a right-to-left orientation and shows the “114 million ha of cropland used now to produce animal feed, corn ethanol, and exports”. Some cropland sits idle and is not used productively. The right half is a second Sankey diagram and shows a different use of the cropland with “major crops and outputs for the maximum ethanol production scenario”. No units in the Sankey diagram but the central columns seems to represent the land area (million ha), while the two outer vertical columns (Crops, Output) show mass (tonnes?) on a different scale.

In contrast to the first scenario it can be observed that “30% of total US cropland, pasture and range, up to 400 billion liters (106 billion gallons US) of ethanol can be produced annually”. Ethanol can be used as an alternative non-fossil car fuel. CO2 emissions are also higher but this is from biogenic sources.

This one is from a presentation (download) by Roberts from Cornell University titled “Life cycle assessment of biochar production from corn stover, yard waste, and switchgrass” held in in Boulder, CO in August 2009.

I admit it is all new to me and I had to lookup stover and biochar on Wikipedia to understand what it is all about. So, apparently the slow pyrolysis process has several advantages: It works with waste biomass (waste management), it produces biochar that can improve soil, it produces energy (syngas) and it captures carbon.

The Sankey diagram in the presentation shows the energy flows: 16,000 MJ of energy is contained in a tonne of stover; more than a fourth of it can be approved of as syngas from the pyrolysis process. The main objective however seems to be carbon dioxide capture, and biochar presents a viable alternative to other (more energy intensive) carbon sequestration technologies.

The diagram has a slight downwardish slope and some of the arrows have superfluous bends. Heat flows and heat recovery are in orange, losses in yellow, the feedstock and syngas in green.

Edit: I received a sample of biochar from a friend. Looks like small pieces of coal indeed. After taking the photo I disposed of the biochar in one of the flower pots on my balcony…

A sample of biochar