Lecture 4 - Organic Waste Treatment

Organic Waste is the largest fraction of the household Waste. In Germany it was 39,3% in 2017 (study conducted by INFA GmbH, published in UBA 2020, see slide 7 in the ppt element below). In low-, middle and upper-middle income countries it takes up more than half of the waste. Look at the slides below to see some statistics.

Hence it is important to bring the organic waste to a place, where through proper treatment the health hazard is reduced (e. g. through self-heating in the composting process bacteria are killed-of). Organic Waste that was degraded by microorganismns in aerobic and anerobic processes however, matures into a fine fertilizer for soils which is important to bring back onto the fields as otherwise food security is put into jeopardy and the soil degrades and becomes infertile and also erosive. In a way, it is natures example of how a circular economy should work. 

It is however also important where the nutrients are introduced back into the environment. If a large amount of fertilizer is bought out onto the fields in one place and a strong rain follows, the nutrients are washed out and lead to eutriphication in the water-bodies (e. g. rivers). This is of course also the case if all waste is disposed of in form of open dumping as the organic waste degrades and leachate gets uncontrolled into the environment; concentrated in one place. Naturally large amount of food waste would not accumulate in one place as there would be not living being other than the human collecting large amount of residues in one spot. 

Also the atmosphere is burdend by improperly disposed of organic waste. In large piles too little oxygen is present, so anerobic degradation takes place, where methane and nitrous oxide are formed, which are stronger greenhouse gases than carbon dioxide which is formed in composting processes. In controlled biogas the production of methane can be utilized to win energy but in open dumpings it is not only harmfull to the climate but also dangerous as it might lead to uncontrolled fires. 

Taking everything into account, the proper disposal and treatment of organic waste decides over it being a harmful and hazardous substance or it ensuring food security as a fertilizer and contributing to the green energy mix. This makes it undeniable that learning about organic waste is of utmost important, so let's start by learning about the differnt pathways organic waste can take into the environment. 

Organic Waste can be collected together with another fraction like residual waste or segregated at source and then treated seperately. Look at the Graphic below to find out more about the pathways organic waste can take around the world and which of these are more preferable.

Of course measurements should also be put in place to avoid food waste (such as suitable storage,  sufficient logistics and especially in high-income countries sufficiency and less pressure to accomodate to customer wishes). 

Plants are extremly important to regulate the climate and water management in living areas as they cool down cities, have recreational value for the inhabitants and prevent flooding by containg water in place; which also is valuable in dry areas as the water does not simply run-off. Thus keeping fertile lands in and outside of cities is essential. Without nutrients and humus recirculation this is not possible. 

For this reason, let's take a closer look at aerobic and anerobic waste treatment. 

As you learned in part 2 the most preferable treatment option for organic waste is to collect it seperately and than either treat it aerobically (with elemental oxygen) or anerobically (without elemental oxgen) in order to make use of the nutrients inside as a fertiliser and/or generate energy. A combination of both treatment forms is also possible. 

Find out more about aerobic and anerobic treatment in the next sections. 

3.1 Aerobic Treatment (Composting)

Composting describes a controlled process, where microorganisms use molecular oxygen to decompose organic matter into a humuslike product while they produce energy in form of heat. 

Look at the slides below to learn more about the composting process and different compsosting facility types. Afterwards try answering the quiz on the ideal parameters needed for rapid composting. 

Quiz time - Which parameters are ideal for a quick composting process? 

A good and usable compost can only be produced out of separately collected organic wastes. Please collect the right fractions.

The anerobic degradation of organic waste can be described through four distinct steps: Hydrolysis, Acidogenisis, Acetogenesis, Methanogenesis

These steps are described in the Hot-spot-Graphik below.

The technology used to utilised the above described process to win biogas is shown below.

This project “German MENA University Network for Waste Management and Circular Economy”, implemented by the University Rostock (UR), Hamburg University of Technology (TUHH) and University of Technology Dresden (TUD), Jordan University of Science and Technology (JUST), Constantine university 3 Algeria, Ain Shams University Egypt and Cadi Ayyad University Morocco is funded by the PREVENT Waste Alliance, an initiative of the German Federal Ministry for Economic Cooperation and Development (BMZ). The contents of the Wastepedia course are the sole responsibility of German-MENA University Network and do not necessarily reflect the positions of all PREVENT Waste Alliance members or official policy positions of the governments involved. More information: https://prevent-waste.net/en/.

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