Congratulations! You made it through week 3. In this third week of the course, we focused on the treatment of organic waste. We included technologies such as composting, anaerobic digestion, vermicomposting, Black Soldier Fly processing, and thermochemical conversion. We gave particular importance to composting and anaerobic digestion, since these are the technologies most commonly used in low- and middle-income settings. Remember, composting is a controlled decomposition of raw organic material into compost, which is carried out by microorganisms in the presence of oxygen. We distinguished the active phase, when temperatures can reach up to 70 degrees and thermophilic bacteria are active, and the curing phase, when both temperature and oxygen consumption drop and mesophilic bacteria are active. In a different module, we covered the main important operational parameters that need to be considered when composting is carried out. These are: Carbon/nitrogen ratio, particle size and porosity, moisture content, pH, and temperature and climate. We then introduced different composting technologies which are commonly used in low- and middle-income countries. Do you remember their names? For instance, which one is the one on the bottom right, or the one on the top left? I hope you remember! We compared these 5 technologies regarding 5 different criteria: Investment and maintenance cost, space and time required, as well as labour needed. In order to provide you with a more hands-on feeling of composting, we introduced 2 very interesting study cases. One from Dhaka in Bangladesh, shown on the picture on the left, and one from Temesi, Indonesia, shown on the picture on the right. We then moved to learn about anaerobic digestion, as a treatment technology for biomass. Anaerobic digestion is a collection of processes, where, similar to what happens during the composting, microorganisms break down biodegradable material. However, in this case, this happens in the absence of oxygen. Anaerobic decomposition happens in a 4-step biochemical process, which happen partly simultaneously. These are: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. This is an interesting technology, because it generates methane, which is flammable and can be used as source of energy. Similar to composting, the anaerobic digestion also has important operational parameters that need to be considered. In this case we have: feedstock characteristics, such as total solids or volatile matter content, organic loading rate, pH, temperature, hydraulic retention time, carbon/nitrogen ratio, and particle size. We then saw different anaerobic digestion technologies, which are suitable for a low- and middle-income country context; all of them wet, continuous feeding, and mesophilic. What about their names? Do you remember them? We then proceeded to learn some hints on how to operate and maintain anaerobic digestion plants. We looked at how to dewater, store, and make use of the produced biogas. And we also discussed important criteria, favouring the choice of anaerobic digestion as a treatment technology. In vermicomposting, we looked at the worm's cycle as a start. Here shown in this picture: eisenia fetida. And then we looked at the environmental conditions suitable for vermicomposting, such as aeration, moisture, also the need to be shaded, and the daily feed rates of about 50 percent of worm weight per day. We also looked at case studies and looked how this technology is constructed, such as the example here from the Philippines. Then we looked at the products of vermicomposting: the vermicompost, the worm tea, and the worms themselves. Then we looked at another approach of biowaste processing using blank soldier fly larvae. First, we looked again at the life cycle of the insect. Then on how to manage the colony and how to operate the treatment process. Then we looked a the BSF products, the residue which is similar to vermicompost and the larvae, which have a high protein content of 40 percent and fat content of 30 percent and are a high value product, especially for animal feed.
