Submitted:
05 March 2023
Posted:
06 March 2023
You are already at the latest version
Abstract

Keywords:
1. Introduction
2. Materials and methods
2.1. Materials
2.2. Methods
- proficient communication in the same language of the potential clients to make them feel comfortable during the primary market research, to build a clear picture of their problems handling manure and slurry,
- manage several secondary sources of information in different languages to be informed about how other countries are dealing with the global challenge of mitigating the GHG emissions from agriculture,
- calculate mass and energy balances (Woolfolk and Pineda-Alaya, 2014, pp. 48–53) to optimize the performance of the artifact and to minimize the cost of treating the slurry,
- take advantage of the convenience of paper-based and online tools for sharing information (Gamage et al., 2023) and maximize the coordination with the teacher for the operation of the artifact in-between session throughout the whole PBL (Make it happen!): the adapted BMC template is also telematically available,
- get used to the cognitive conflict and appreciate the usefulness of the metacognition during the filling the Rumsfeld’s matrix (top right corner of the adapted BMC template; Figure 2),
- propose novel and original ideas to be assessed by the other group members and improve the own conceptualization of the artifact by considering the feedback and feedforward of peers.
3. Results
4. Discussion
5. Conclusions
Supplementary Materials
Author Contributions
Acknowledgements
References
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| Quantity | Item description | Price/(EUR) |
|---|---|---|
| 2 | 150-L boxes of high resistance plastic resin for the soil organic amendment stabilization tank and the condensed brine of calcium chloride (Figure 1). | 81.34 |
| 1 | Pack of mineral wool panels (1.35 x 0.6 x 0.04 m) for insulation of the stabilization tank (preserving the high temperature) and the condensation vessel (preventing the increase of the temperature). | 96.37 |
| 2 | 3-m flexible aluminum pipes of 150 mm diameter to connect the 2 vessels and allow the convective transport of moisture from the stabilizing manure to the condensation tank. | 32.00 |
| 2 | 25-kg sacks of lentils of calcium chloride for the operation of the prototype for 3 months. | 45.82 |
| 1 | 150-mm diameter tubular fan inline duct ventilator (45 W) to promote the movement of the air between the headspace of the 2 vessels. | 33.30 |
| 1 | 2-m stainless steel bar to prepare the cradle for the calcium chloride in the condensation vessel. | 8.29 |
| 1 | 3-m glass fiber mosquito netting roll (1 m wide) to use as trays and ensure the better contact of the calcium chloride lentils with the moisture in the air (Figure 4b). Also, to avoid flies reaching the condensation vessel by covering the air conducts. | 6.00 |
| 1 | 100-m carbon fiber heating cable (33ohm/m) coated with silicone gum to operate the stabilization vessel above room temperature. | 57.69 |
| 1 | Cutter and hot melt glue gun (Figure 3b) to modify the plastic boxes as per the requirements of the prototype in Figure 1. | 20.53 |
| 2 | Aluminum tape to seal the connections of the flexible aluminum pipe and the plastic boxes. | 3.15 |
| Block | Didactic unit | Details of the sessions of the PBL (Make it happen!) |
|---|---|---|
| B1: The scientific activity | DU1: The research process | Based on the data available by secondary sources of information (Alejandro Moure Abelenda, 2022; Moure Abelenda et al., 2022; Moure Abelenda and Amaechi, 2022), students share with their working group members their understanding of the situation that the agroindustry is facing, and they start to hypothesize what are the possible solutions. Kahoot! and Socratic method to develop the understanding, increase the intrinsic motivation, and refine hypotheses. |
| B2: Matter | DU2: Aggregation states and separation of mixtures | Prediction, Observation, and Explanation (POE) experience: Appraisal of the underlying phenomenon of the calcium chloride deliquescence, which is widely used as home dehumidifier, particularly in small cupboards and dress rooms. Elucidation of the law of (water) mass conservation. Introduction to the design of a prototype for the dehydration (and stabilization) of a complex blend: Students play with the surface area to volume ratio to obtain a quicker drying and stabilization of manure and slurry (Moure Abelenda and Aiouache, 2022). |
| DU3: Formulation and nomenclature of binary and ternary compounds | Study the role of anhydrous salts in the operation of the artifact: Calcium chloride as dehydrating agent and additive to untreated slurry; Calcium carbonate as pasteurizing agent to keep under control the biological activity as well as enhancing the dehydration. Students can observe the self-hardening effect of quicklime and slaked lime and they can prepare pellets of limed slurry to enhance the rate of drying (greater surface to volume ratio) and prepare a granular fertilizer. | |
| B3: Phenomena | DU4: Physical phenomena and chemical phenomena | By this session of the PBL (Make it happen!), students are able to have an idea of the scientific background of the prototype and they can think about how to improve it: Cooperatively understanding of the kinetic and the equilibrium of the exothermic reaction and the mechanism associated to the colligative properties of ionic solutions. Determination of the reaction stoichiometry: maximum amount of water that calcium chloride is able to retain and the lowest concentration attainable for the condensed brine (< 1 M CaCl2). |
| DU5: The importance of the chemistry in the society and the environmenta | IBL: Double session (100 minutes) for the pedagogic outing associated with the primary market research with key stakeholders of the agroindustry. Initial training to elaborate the questions about the logistics of managing animal slurry at farm level (small and medium size < 500 cattle) and to check whether the POC being developed fits with the current infrastructure for manure management (Market Business News, n.d.; MScTE48, 2015). | |
| B4: Movement and Forces | DU6: Forces and Movement | Understanding how fan propellers promote turbulence and the convective movement of air: inductive convection (behind the fan) and forced convection (in front of the fan). Elucidate how the air flow enhances the rate of drying and stabilization of the organic manure, based on the kinetic-molecular theory that explains the behavior of gases and the mass transfer of substances (e.g. moisture). Students can suggest the best location of the fan in the prototype (Figure 1) and test different flowrates to determine the best performance considering the power consumption. |
| DU7: Simple machines | Assess the possibility of including a screw conveyor or other type of automatic conveyor in the stabilization vessel and/or a centrifugal pump in the condenser, to enable the continuous operation of the prototype. Feeding the equipment with fresh materials is as necessary as periodically purging the stabilized organic amendment and the condensed brine. In order to decrease the residence time of the organic manure a propeller would need to be designed for the stabilization tank, to enable faster kinetics due to continuous mixing. | |
| B5: Energy | DU8: Electricity and electric circuits | The students have the opportunity to design the heating system of the stabilization tank using carbon fiber cable and determining the optimum power consumption, by making use of Ohm’s law and Watt’s law. They need to consider the runaway effect could lead to ignition, as the substrate becomes drier. Consideration of the different mechanisms of heat transfer (via conduction, convection, and radiation) to increase the rate of evaporation, deliquescence, and stabilization. |
| DU9: Transformation and conservation of energy | By this point, the working groups could start to apply modifications to the original prototype before understanding very well all the involved mechanisms or even the opinion of the stakeholders. Since students have limited chances for amelioration of the prototype (as this constrain represents their budget in the project), they need to optimize the whole system considering that the liming of the slurry and the deliquescence process of calcium chloride are exothermic processes. Determination of the overall energy balance and justification of the power consumption of the prototype. The cost of the type of lime (quicklime, slaked lime, or limestone) also needs to be inputted. | |
| B1: The scientific activity | UD10: Sharing and roundtablea | Double session (100 minutes) to allow each group to sell the advances made on the prototype and how these address the demands of the potential clients (15 minutes per group). Discussion on the best approach and best practices. Subsequently, metacognition is promoted with a self-assessment form to assist them on their evaluation of the cognitive conflict experience throughout the whole PBL (Make it happen!), and to understand how their project management skills have improved with this didactic experience. |
| Components | Parameters | Targeted conditions |
|---|---|---|
| Incubator (Stabilization tank) | Length of the heating cable of carbon fiber | Maximum operating temperature avoiding runaway of the system leading to ignition. |
| Intensity/voltage/power consumption | Design as per the domestic (220/240 V) or industrial application (if 3-phase electric power available). | |
| Temperature/heating requirements | Accounting the exothermic reactions of lime hydration and carbonation, and brine formation. | |
| Rate of drying/stabilization | Targeted stabilized soil organic amendment: 50 wt.% moisture content or below. | |
| Dose of lime | Just enough to prevent excessive biological activity, which could be indicated by the presence of flies. Assess the use of quicklime, slaked lime, and limestone. | |
| Automatic conveyor | Suitable for the stabilization vessel without decreasing the working volume (i.e. inner space) and the loading rate of fresh slurry. | |
| Recirculation loop | Optimum feeding ratio of fresh slurry to coarse fraction of the stabilized manure obtained by 2-mm sieving. | |
| Condenser (Brine collecting vessel) | Temperature of the vessel and insulation with mineral wool | Based on Le Chatelier’s principle, exothermic reactions are more spontaneous under low temperatures (i.e. room temperature or below). |
| Air flowrate | Fastest retention of moisture and other gases while minimizing the electric power consumption of the blower. | |
| Feeding rate of CaCl2 | Optimum ratio of solid CaCl2 to liquid brine to maximize the absorption of moisture and other gases in the condenser. Targeted brine concentration: < 1 M. | |
| Clean brine | Clear and free of biomass (including flies). In optimum concentration for commercialization and use large scale slurry lagoon at a rate of 1 L brine additive per tonne of slurry. | |
| Centrifugal pump and conveyor | Continuous operation of the prototype: removal of the condensed brine and feeding of CaCl2 lentils. |
| Helpful | Harmful | |
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