From Waste to Fuel

In many regions of the developing and emerging markets, proper management of organic waste represents a significant and continued challenge. Bio-digestion, composting and waste to energy represent possible solutions to this problem. However due to technological, infrastructural, and logistical reasons these technologies have not hit the mark. Could the commercialisation of charcoal briquettes derived from organic waste be the answer? by Kevin Kung Proper organic waste management remains, despite various technological advances, a significant challenge in many developing nations. In these locations, where formal and centralised waste collection and treatment services are often unavailable, the entire organic waste value chain needs to be considered and evaluated for the feasibility of any given treatment technology, in addition to the viability of the technology itself. For treating organic waste, the most immediate solutions that come to mind are composting and biodigestion. While these techniques have met with some success, and are being implemented at various scales in countries such as India, the main challenges are that those techniques are generally only suitable for source-separated and homogeneous organic waste, and the treatment process is often quite sensitive to variations in the feedstock. Therefore, from the commercial perspective, it is often difficult to achieve a consistent biogas or fertiliser output. Furthermore, once the gas or fertiliser is produced, both packaging and distribution are non-trivial issues to consider, and may not be feasible. There are waste to energy (WtE) projects, but to be economically viable these are often only implemented at a very large scale, and these technologies are not an option for smaller locales. In India, for example, despite the extensive implementation of different biodigestion, composting, and WtE technologies to treat organic waste, currently 90.7% of organic waste is not being managed at all. Therefore, as a potentially complementary technique to address organic waste, we have been investigating the possibility of small-scale conversion of organic waste into charcoal briquettes through thermal treatment (pyrolysis or carbonisation) in the emerging markets. Case study Kenya Given the lack of formal, centralised waste management system in many countries, our scope is on creating and implementing low-cost, decentralised thermal treatment systems that at the same time have a commercialisation and dissemination potential. In Kenya there are three sources of main energy: wood, petroleum and electricity, accounting for 70%, 21%, and 9% of total energy use, respectively. Meanwhile, 82% of urban households use charcoal as the primary source of fuel - 34% in rural areas. Nairobi consumes 700 tonnes/day of charcoal. Kenya is rich in forest area, with 1.7 millionhectares of forests. However, continued reliance on wood-based charcoal has led to deforestation at an alarming rate. Additionally, proper organic waste management continues to be a challenge in both urban and rural areas. For the purposes of the study, Kenya represented the near-perfect environment to investigate the feasibility and viability of an organic waste driven charcoal briquette production. The main kiln has an open top and many holes at the bottom (a). The adapter has an alternatingly ridged/grooved bottom (b) as well as a star-shaped opening at the top (c). The biomass is lit from the top (d). Once the fire has spread the main kiln is covered with the adapter (e), immediately followed by the chimney (f). After about 20 minutes of pyrolysis and 1-2 hours cooling, charred biomass is recovered (g) There are three main types of low-cost carbonisation kilns that were developed and implemented in the course of the project. The first type, which we will call the open-drum kiln design, was developed by D-Lab at Massachusetts Institute of Technology, and is an open-source technology whose description and use is well-documented online. We introduced this design in Rumuruti, Kenya, where it was tested for 12 months. However, we found limited use for the design in an urban environment owing to excessive smoke emissions during the carbonisation process. In response to this limitation, a second version of the carbonisation kiln was developed, the top-lit kiln design, with reduced smoke emissions. In this design, there are three components: the main kiln, the adapter, and the chimney. To make this kiln requires two 200 liter oil drums that are sealed bottom and top are used. The drum body is checked for holes/leaks. One of these two drums will become the main drum, while the other one can be cut in half and made into two separate adapters. In addition, locate a smaller oil drum with an open end (bottom) and a closed end (top) to serve as the chimney. Combusting solid fuel may carry some health risks. From our interviews, we found more than 70% of Kenyan households cook indoors. The major risks include acute carbon monoxide poisoning (which is a known issue for wood charcoal), as well as chronic respiratory illnesses from particulate emissions. Therefore, it is of utmost importance for us to verify the health safety of the briquettes. Methodology There were two versions of the experimental set-up: laboratory and in-the-field. The laboratory set-up used the state-of-the-art instruments with high sensitivity: Bacharach ECA450 Combustion Efficient and Environmental Analyser for carbon monoxide measurements, and TSI DustTrak II Aerosol Monitor 8530 for total suspended particle (TSP) measurements. These instruments were installed in a controlled combustion chamber. However, these machines were not portable, and were unable to measure combustion emissions as the briquettes were being used for cooking in actual Kenyan households. In order to perform these in-the-field measurements the equipment needed to be portable and robust. For this purpose the UCB Particle Monitor, was used and for CO datalogging, the EL-USB-CO Carbon Monoxide Data Logger (Lascar, Erie, PA) was used. This verified that the readouts from the in-the-field instruments have a good correspondence with those from the state-of-the-art instruments. Particulate matter data We first measured the particulate matter emissions in different types of briquettes. Over a typical combustion time the briquettes ("Takachar recipe") had particulate emission levels that did not exceed those of the wood charcoal, illustrating that the charcoal briquettes, when made properly, do not pose an additional health risk to the households in terms of particulate emissions. Various briquetting techniques and binding agents were tested and the mean particulate emission levels for some 'recipes' recorded. While some binders (such as avocado and cloth) are unsuitable for briquetting purposes due to excessive smoke emissions, there are many briquetting recipes which offer safe levels of smoke emissions with respect to the traditional wood charcoal. Carbon monoxide data Carbon monoxide emissions were measured in different types of briquettes. Over a typical combustion time, the briquettes made using the 'Takachar' recipe developed for the project showed CO levels safer than those of the wood charcoal. Various briquetting techniques and binding agents (recipies) were tested. In general a correlation between the CO level and the total exposed surface area of the briquettes was qualitatively noted. In briquettes that had a higher surface area, there was a greater risk of incomplete combustion and hence CO emissions. Rural implementation Since 2012, we have implemented a charcoal project in partnership with the Rumuruti Forest Association in Rumuruti, Kenya, where charcoal-induced deforestation is severe. The community, consisting of around 5000 homes in seven villages, scaled the process up and now there are about 50 kilns in the community, amounting to a full-time production capacity of about 2 tonnes/day. In the Rumuruti area, corn cobs/husks are abundant, and this quantity far exceeds what is needed for competing purposes - such as chicken feed. However, the marketing of briquettes has been a significant challenge: many rural households are reliant upon firewood rather than charcoal as the cooking fuel of choice, and unlike the exorbitant prices (around $17/bag) in the urban area, charcoal is relatively low cost near the source of production (about $5/bag), so it is difficult for alternative briquettes to compete. The farmers are actively looking for an urban market to sell their carbonised biomass. The Rumuruti community, for example, plans to partner with a briquette seller to package and market the briquettes in the nearby town Nyahururu, where the price of charcoal doubled (about $9/bag) compared to that in Rumuruti. Therefore, while the rural farms are a reliable source of waste, the briquettes should be sold in urban areas. Urban implementation In many urban areas such as Nairobi, the waste is informally collected by waste-picker cooperatives, which also perform value-added sorting in order to sell plastics, metals, etc. Since all the municipal waste passes through their sorting procedure, our original hypothesis was that these groups could segregate organic waste for charcoal production, which they could run. Fig. 3. The left plot shows sample combustion time (on the x-axis) as well as the particulate emission readout (on the y-axis) inside a typical Kenyan household using the UCB Particle Monitor. The right plot (b) illustrates the mean particulate emission of various charcoal briquettes produced as described on the x-axis. Control 1 refers to regular wood charcoal. Control 2 to fragmented wood charcoal that are re-briquetted together using cassava as a binding agent. For the past 15 months, we have been working with such a cooperative in Kibera, Nairobi, Kenya. The first lesson learned was that it is very difficult to make use of household organic waste, unless there exists an incentive system to source separate (such as the model employed by Waste Ventures in India). For charcoal-making, the easier waste source to start would be marketplaces or informal food stalls, where such waste is available in large quantities without needing pre-sorting. Here the left plot shows combustion time (on the x-axis) as well as the carbon monoxide readout (on the y-axis) inside a typical Kenyan household using the Lascar CO Datalogger. The right plot illustrates the mean carbon monoxide levels of charcoal briquettes produced under various briquetting and binding conditions. Control 1 refers to regular wood charcoal. Control 2 to the combustion of fragmented wood charcoal pieces that are re-briquetted together using cassava as a binding agent. The cooperative was able to collect daily from the closest Toi Market, carbonise such waste, make briquettes at a small scale (about 10 kg/day), and sell such briquettes to households at a price that is 70% of that of regular wood charcoal. This project was subsequently demonstrated at the Nairobi International Trade Fair, and received certification from the Kenyan Ministry of Agriculture. Correspondence between measurement readouts of UCB Particle Monitor (which were employed in actual Kenyan households to test for briquette emissions) and of TSI DustTrak II Aerosol Monitor 8530, for one representative experiment during which carbonised briquettes using cassava as a binder was combusted in a chamber. The left figure shows the UCB Particle Monitor readout (red) and DuskTrak readout (blue) in time, with close correspondence between the two. The right figure shows a pairwise correlation plot between the readouts of UCB Particle Monitor (x-axis) and DustTrak (y-axis). While the UCB Particle Monitor is less sensitive compared to DustTrak, the correlation between the readout pairs is highly positive and statistically significant. However, the main operational challenge is the lack of scale: ultimately, charcoal is a low-margin, high-volume commodity, and we have seen that, in order for an operation to be financially sustainable in order to support a local micro-entrepreneur as well as three to four workers on site, it needs to quickly achieve a minimally viable scale of at least 500 kg/day. Groups that first started at a small scale of production often used crude presses or even hand-molded the briquettes, which offered poor quality control and low market pricing. Conclusions To overcome some of the challenges of implementing such organic waste charcoal-making projects, a micro-franchising model is proposed. This would see the 'outsourcing' of char-powder production to waste picker cooperatives or rural farmers. It also builds an incentive based structure to tackle the issues in sustainable operations of a green charcoal briquette production. Green charcoal producers do exist that are experimenting with some flavour of this model, such as ARTI-TZ in Dar es Salam, Tanzania, as well as EcoFuel-Africa in Kampala are in the early stages of this innovative approach. Kevin Kung is a fellow of the Waste Innovations Group at MIT-Tata Center for Technology and Design. Additional contributors include Ali Kamil, Carlo Ratti and Libby McDonald. Additional information and instructions on how to make the kiln are available in the online version of this article.