Muteero Farms Sustainability Assessment
1. Background
There is little doubt today that climate change is a pressing global issue with severe consequences to both the global economy and the natural world and its ecosystems. Recently, there have been several developments within the agricultural sector seeking to minizine agricultural emissions and produce crops in a more sustainable manner, such as the Terraton initiative and the rise of urban aquaponic and hydroponic farms. However, there is lack of consensus regarding the sustainability of these new approaches and their environmental impacts.
In this report, we will investigate certain aspects of the aquaponic infrastructure installed at Muteero Farms to better understand the carbon footprint of the current facilities, and therein explore the stainability of aquaponic crop production as a possible means to reduce the carbon emissions of the global agricultural sector.
2. Scope of Assessment
This sustainability assessment will focus primarily on three main sources of carbon emissions at Muteero Farms; the base footprint of the facilities currently constructed, the energy footprint required to operate the current facilities, and finally the footprint of the current distribution model of the finished goods. In conjunction with these emissions sources, we will also consider the offsetting footprint of Muteero Farms and determine the impacts the farm has at sequestering carbon from the atmosphere. After determining the footprint of the farm at current and full operating capacity, a brief comparison to the footprint of a soil-based farm of similar output scale will be provided.
3. Methodology
In order to determine the total footprint of Muteero Farms at both current and full operating capacity, we must determine the individual footprints of each of the three emissions sources outlined above.
Base Footprint
To determine the base footprint of the current facilities, we will consider the combined carbon footprint of materials used in the construction of the farm. Within this, we will consider the emissions resulting from the main construction materials used at the farm, namely metal, plastic and wood.
Energy Footprint
As Muteero Farms mainly relies on gravity-fed systems to control the flow of wastewater from the fish tanks to the growing area, there are only a few components of the aquaponics system that require energy inputs. Specifically, these include the compressors responsible for the aeration of both the fish tanks and growing troughs and the main circulation pump moving water from the sump tank to the fish tanks. Miscellaneous energy demands such as powering the office space and the processing room will be discarded as negligible compared to the main aquaponics infrastructure.
Distribution Model Footprint
The current distribution model’s footprint used by Muteero Farms will be analyzed based on the fuel consumed during normal delivery routes. This will also be expanded to determine the projected footprint at full operating capacity. Furthermore, the footprint will be compared to that of an equivalent vehicle running on biogas, given the possibility to switch delivery modes.
Sequestration & Offset Footprint
For both the current and full capacity, the annual offset footprint will be determined based on standard literature estimates for the average CO2 consumption of greenhouse crops.
4. Footprint
Base Footprint - Materials
In order to determine the approximate base footprint of the farm, the primary materials used for the construction of the current structures were considered, as outlined in the table below.
Table 1
However, as the values for CO2 emissions for each material are given in kg CO2 emitted per kg of material produced, the total mass of all materials used in the construction process had to be determined. This was performed by finding the standard volume of material for each item and multiplying by the density in kg/m³:
These results are in Table 2.
Table 2
Using values for mean kg CO2 per kg of material, the mean carbon footprint of the materials of Table 2 could be determined as follows:
Where Production Emissions is in kgCO2/kg. These results can be found in Table 3.
The total footprint shown in the last row of the table the carbon footprint associated with the production of these materials and thus is counted as a single emission of 12.95 tons of CO2. The following chart shows a breakdown of the materials footprint by material type.
Base Footprint - Transportation
In addition to the materials footprint, the carbon emissions from shipping the container of XPS from China to Nairobi should also be included in the base footprint calculations. For the first part of the journey, the container travelled by sea from Qingdao to Mombasa, and then was trucked from Mombasa to the site.
The sea route distance from the port of Qingdao to the port of Mombasa is 6981 nautical miles (12928.81km). (Ports.com, 2018) Given that the average emissions of a deep-sea container ship is 8.4g CO2 per ton-km, and assuming the container had a net weight of 2t carrying the XPS board and additional equipment, we can determine the total sea footprint below. (European Chemical Transport Association, 2011, p. 9).
Table 4
Then, for the land journey from Mombasa to the site (a distance of 503km) and using value of 62g CO2 per ton-km for land shipping, we can determine the total shipping emissions. (European Chemical Transport Association, 2011, p. 6).
Table 5
Thus, we can see that the total combined shipping footprint for the container is approximately 0.28t CO2.
Base Footprint - Total
In summary, combining both the footprint associated with the production of the primary construction materials with that of the transportation of imported materials yields a total carbon footprint of 13.23t CO2. This is summarized in the pie chart on the following page.
Energy Footprint
The bulk of the current annual carbon footprint comes from the operation of the aquaponics system at the farm. Within this, there are three main components which consume the greatest power on site; air compressors for the troughs, air compressors for the fish tanks, and the water pump to move water from the sump tank to the fish tanks.
The 12 troughs currently require four 300W compressors running continuously to aerate the water in the growing area. Thus, we can calculate the energy consumption of this system using the following formula:
Where the power of the compressors is in kW and operating time is in hours. The consumption for the trough compressors is shown in the following table.
Table 6
Likewise, the fish tanks require six 300W compressors and one 160W compressor to aerate the water. The energy consumption of this system is outlined below as well.
Table 7
Finally, the 700W main sump pump runs for approximately 8.5 minutes every hour, 24 hours a day.
Table 8
Therefore, the combined daily energy consumption of the farm can be determined from the sum of these components. Using the emission rate 0.274 t/MWh for Kenyan grid energy, we can also determine the footprint of each of these systems and the total energy footprint. (World Agroforestry Center, 2012, p. 15).
Table 9
Therefore, annually Muteero Farms produces 7.82 tons of CO2 annually from grid energy consumption. A pie-chart breakdown of the energy footprint can be found on the following page.
Distribution Model Footprint
In addition to the energy footprint from the operation of the farm, the distribution of finished goods to retailers has an associated footprint from the vehicles used to transport the products.
Currently, Muteero Farms operates a single mid-sized vehicle to deliver approximately 80 boxes of product to 3 retailers biweekly. The estimated length of the route round-trip is 7km, and operating year-round gives a total annual distance of 1092 km. As of 2012, the average CO2 emissions of vehicles in Kenya was 0.1854kg/km. (University of Nairobi Enterprises and Services LTD & Energy Regulatory Commission, 2014, p. 28).
Therefore, at the current distribution volume, Muteero Farms emits a further 0.1t of CO2 annually. However, as Muteero Farms estimates that it is currently operating at 50% of its full capacity, scaling up distribution accordingly will emit 0.3t of CO2 annually. This data is summarized below, with the estimated footprint of a similar-sized vehicle fueled with biogas. (MyClimate, 2019).
Table 10
Sequestration Footprint
Although Muteero Farms has emitted a large amount of CO2 to date, the growing of crops removes CO2 from the atmosphere through photosynthesis. Therefore, some operations of the farm also have an offsetting effect. The active sequestration effect of the farm will be calculated in this section.
At current capacity, Muteero Farms has 12 full troughs of dimensions 19m by 1.2m, constituting a growing area of 417.6 m2. A mean estimated average CO2 consumption rate of 0.18 kg/hour/100m2 of growing area (Blom, Straver, Ingratta, Khosala, & Brown, 2019). Using these values, we can estimate the possible sequestration footprint of the greenhouse space at current and full capacity, assuming the average batch stays at the farm for 7 weeks and is 20% efficient at retaining CO2.
These results are summarized below.
Table 11
However, it should be noted that the sequestration footprint is not comprehensive, as actual CO2 consumption rates differ based on crop, canopy cover area, humidity, incident sunlight, temperature, and a range of other factors not accounted for here. (Wheeler et al., 1994, pp. 610-615) Furthermore, actual carbon fixation efficiencies from the crops may differ from this estimate.
Moreover, this estimate does not account for the sequestration footprint from microalgae and other aquatic microorganisms, which has much higher efficiency of carbon sequestration. (Bao, Lu, Zhao, & Bi, 2018, p. 183).
5. Combined Footprint
In the previous sections we looked at a specific aspect of Muteero Farms’ carbon footprint. In this section we will combine the footprints of the previous sections to determine both the total footprint of the farm and the net annual emissions.
The total footprint of Muteero Farms includes both the one-time emissions from constructing the current infrastructure as well as the ongoing emissions derived from continuous operation and distribution. Muteero Farms has emitted approximately 13.23 tons of CO2 from construction alone, and annually emits a further 6.65 tons from production and distribution at current capacity, post-sequestration. These are summarized in the table below.
Table 12
From Table 12, it is evident that at current capacity, production processes have the greatest carbon emissions annually at Muteero Farms. The crops are quite good at sequestering carbon from the atmosphere, resulting in lower net annual emissions.
6. Offsetting Capabilities
In addition, as Muteero Farms grows its crops using aquaponics, Muteero Farms’ total footprint may offset the carbon emissions from soil farms of similar output scales. In order to determine an estimate for a similar output scale soil farm, we will assume the farm has 5 times the growing area of Muteero Farms and is located 100km from its retailers.[1]
In Kenya, the total cropland in 2016 was 2566.62 hectares and had a net carbon emission (post removals) of 88.20 gigagrams of CO2. (Food and Agriculture Organization of the United Nations, 2018) Using these values, we can determine the net emission tonnage per square meter and determine the annual emissions from raising a similar crop volume on the specified farm.
Table 13
Multiplying the current and full-capacity growing area of Muteero Farms by five, we can determine the growing area of a similar output scale soil farm and hence the net annual emissions from production.
Table 14
In addition, we must consider the annual emissions from distribution. Using a 200km round trip with one weekly delivery, we can determine the annual distribution footprint using the same value of 0.1854kg/km from 4. (University of Nairobi Enterprises and Services LTD & Energy Regulatory Commission, 2014, p. 28).
Table 15
Finally, we can determine the total net annual emissions of the similar-scale farm by combining the production and distribution footprints.
Table 16
From these estimates of the net annual emissions of a soil-based farm, we can determine the offsetting capabilities of Muteero Farms by finding the difference in emissions for the same output volume.
Table 17
Based on this, we can determine the offsetting ability per head produced. We will assume current capacity is 3000 heads annually, and full capacity is 5000 heads annually.
Table 18
7. Evaluation & Conclusions
As outlined above in 5, Muteero Farms has emitted 13.23 tons of CO2 from construction and continues to emit a further 6.65 tons annually from production and distribution at current capacity. However, it should be noted that this footprint assessment is not fully representative of the emissions at Muteero Farms; notably, the emissions from pumping water, composting and using processed fish food have not been included in this assessment, nor has the total emissions from all construction materials been determined. Therefore, it is likely that the final footprint is much higher than this estimate.
Values for full-capacity output are linearly scaled from the current capacity – including distribution. As such, true full capacity footprints will differ; it is likely that the energy footprint will increase as more aeration is needed with increased fish and troughs, while the distribution footprint will be slightly lower as the number of deliveries will likely not double as assumed.
In addition, the sequestration abilities of the crops were estimated by using an average consumption rate, which varies significantly based on crop type and meteorological conditions, and therefore is not very accurate. (Wheeler et al., 1994, pp. 610-615) Additional research would be required to determine the true sequestration ability of the crops at the farm. Furthermore, this analysis neglects the sequestration from aquatic algae, which may play a significant role in absorbing atmospheric carbon.
The comparison model used for a similar output scale soil farm was not rigorously investigated, rather based on averages across the entire cropland of Kenya, thus the true emissions of a farm of this scale may differ. Additionally, the full-capacity model was scaled linearly from the current capacity model; more research would be required to assess whether this assumption is indeed accurate.
Consequently, it must be noted that the values for offsetting capabilities are simply estimates based on average emission rates in Kenya for certain processes (eg. energy consumption), of a select number of systems at Muteero Farms. Thus, the stated values in the tables above may not be fully representative of Muteero Farms’ true annual emissions, nor its offsetting capabilities.
However, from this assessment, we can draw multiple important conclusions. For example, based on the provided model, it is evident that Muteero Farms emits less carbon annually than a similar soil-based farm, not to mention has a far smaller physical footprint. As a result, the aquaponic crops grown at Muteero Farms appear to emit less than crops grown using traditional methods, as well as are located physically closer to their retailers, thus emitting less through distribution each year.
Furthermore, switching the distribution vehicles from standard gasoline to biogas would further reduce the annual distribution model’s footprint, allowing Muteero Farms to offset more per annum.
Currently, Muteero Farms’ energy comes directly from the Kenyan grid. As the energy consumption of the farm is relatively fixed, a possible means to reduce the energy footprint would be to install renewables such as solar or wind on-site to power the farm. With this comes the added challenge of ensuring redundancy and continuous, reliable power supply, but this would nevertheless have a positive impact and increase the offsetting capabilities of Muteero Farms.
Assuming the current offsetting capability to be on the order of 2 tons, Muteero Farms would be able to offset their estimated construction footprint within 7 years. However, as Muteero Farms is still carbon-positive annually, with the current facilities and production volume, it is not currently possible for the site to become carbon negative based on this assessment. After fully offsetting the construction footprint, Muteero Farms would offset 2 tons less annually after year 7.
Given that power consumption does not scale linearly with increased output and that a linear scale of a soil-based farm are accurate assumptions, then based on Table 17 an increasing output volume would also increase offsetting capabilities. Extrapolating these trends would suggest that there may be a critical output volume where Muteero Farms can become carbon-neutral or possibly carbon-negative. After offsetting the entire construction footprint, at this volume it would be possible for Muteero Farms to act as a carbon sink and actively remove carbon from the atmosphere each year rather than emitting it. Further research would be required to determine the validity of these assumptions as well as the critical output volume.
Overall, it appears that Muteero Farms is able to produce their crops in a more sustainable fashion than a traditional soil-based farm, yet with positive annual emissions. Nonetheless, reducing the energy and distribution footprints of the farm would reduce net annual emissions, and possibly offer a pathway to net-zero or net-negative carbon emissions. An additional pathway to net-zero emissions could be scaling up output, but more research would be required to assess the feasibility of this approach. Thus, although Muteero Farms is still emission-positive annually, the aquaponic method of growing crops offers promising results for reducing agricultural carbon emissions and sustainably combating climate change.
Assessment conducted by Franklin Lurie while on an Internship at Muteero Farms in Nairobi, Kenya