construction of a refrigerator system for leachate collection to study mineral weathering

Enhancing CO&lt;sub&gt;2&lt;/sub&gt; Sequestration: A Soil Biota Approach to Boost Mineral Weathering

Enhanced weathering (EW) is a relatively new and low-tech carbon dioxide removal (CDR) technology with a significant potential to mitigate climate change1,2,3. The principle of this technology relies on accelerating the natural mineral weathering process in soils, leading to the sequestration of carbon dioxide (CO2) as inorganic carbon (IC)3. Enhanced weathering aims at increasing IC sequestration by artificially optimizing the factors governing mineral weathering, thereby enhancing the speed through which weathering occurs to humanly relevant time scales3. For EW to be most effective, fast-weathering silicate minerals are ground into a powder with a grain size distribution in the micrometers to millimeters range to reach a high reactive surface area in the ~1 m2&#183;g-1 range3,4.
So far, knowledge about EW has been mainly provided by experiments that focus on abiotic factors governing the rates at which minerals are dissolved5. These include mineral reactivity and surface area, temperature, solution composition, water residence time, and acidity4,6,7, but research still needs to be done within this context. Besides being influenced by abiotic factors, natural systems, and soils in particular, are shaped by a vast number of organisms, ranging from microbes to macrofauna such as earthworms. Despite some studies having shown little or no influence of the biotic activity of mineral dissolution8,9,10, other studies have provided evidence that soil organisms such as bacteria11,12, fungi13,14, and earthworms15,16 could increase mineral weathering rates. Therefore, biotic components could be key to understanding the actual IC sequestration potential of EW5.
The first common mechanism through which soil organisms could accelerate mineral dissolution is via CO2 release during respiration,which increases soil acidification17. Besides, bacteria and fungi could increase mineral weathering by exuding protons, chelates, organic acids, and enzymes, all of which enhance mineral dissolution18,19,20,21. For example, chelation through carboxyl and hydroxyl groups can create ion imbalances, transporting elements away from the surfaces of minerals and lowering saturation states20,22. This could lead to less secondary mineral formation and higher efficiency of EW. Moreover, by feeding on soil particles, the strong actions of earthworms&#39; body walls could break down mineral grains into finer particles, increasing their available reactive surface area23. Microbes dwelling in earthworms&#39; intestines and fresh droppings could further attack these smaller particles, which further exudate organic acids and enzymes24,25. Through their burrowing activity, in addition to contributing to the mixing of organic and mineral particles, earthworms also create macropores that could allow water flow to bypass saturated pore space17. This could enable the water to interact with different mineral surfaces and enhance the water-rock contact rate.
Until now, no setup has been built to study EW rates and therefore IC sequestration using soil organisms while ensuring the possibility to optimize different relevant abiotic conditions, such as water inputs, temperature, mineral type, and mineral grain size. Here, the design and explanation of the construction steps of an innovative setup that aims at increasing EW rates through the activity of soil organisms in small mesocosms are presented. The experimental setup consists of 203 columns (length 15 cm, diameter 7 cm) placed in a climate chamber (4.54 m x 2.72 m) at 25 &#176;C for 8 weeks. The 203 columns are divided into 10 groups of 18 and 2 groups of 10 to fit in the climate chamber. One of the two groups of 10 columns is used to allow the insertion of three more columns which are used as blanks. Each group is placed above a fridge and is topped by a remotely controllable irrigation system, which allows for variable irrigation rates within and between fridges. The leachate of each column is collected in a jerrycan kept at a constant temperature in the fridge (Figure 1). One fridge collects the leachate of a group of columns, meaning that one fridge can be considered as a single system of either 18 or 10 columns. Therefore, the number of columns in this experimental setup can be adjusted according to experimental requirements with a maximum of 203 columns.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65563/65563fig01.jpg" /> 
Figure 1: Schematic side-view of the setup showing 5 columns but considering a system of 18 columns. The frame holding the columns is made of stainless-steel plates, stainless steel screws and acrylic plates. Columns are positioned in the middle of the frame and are topped by an irrigation system. Below the columns, funnels are connected to jerrycans through pipes to collect the leachate. Jerrycans are in a fridge that holds the whole system. The fridge can be opened by lifting the lid. <a href="https://www.jove.com/files/ftp_upload/65563/65563fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In this setup, the use of silicate rock powders of specific grain sizes ensures that high weathering rates can be reached, while the inoculation with specifically selected bacteria, fungi, and earthworms grants the biotic activity in this artificial system. The setup enables concurrent quantification of carbon sequestered in the solid and in the liquid samples by measuring both dissolved and solid IC, as well as total alkalinity (TA). Besides, other parameters such as pH, electrical conductivity (EC), and ions can be measured in the leachate as indicators of weathering. This setup also allows the assessment of the impact of soil organisms&#39; survival and activity. Representative results are shown to prove the suitability of this protocol to build a setup where increases in weathering rates are derived not only from abiotic factors but also from biotic ones.

Author Spotlight: Unraveling the Role of Earthworms in Enhancing Mineral Weathering for CO2 Removal 

Design and Construction of an Experimental Setup to Enhance Mineral Weathering through the Activity of Soil Organisms

Enhanced weathering is a carbon dioxide removal technology that involves the reaction of silicate rock with carbon dioxide and water. Microbes and other soil biota can stimulate this weathering reaction, but their potential impact on enhanced weathering is yet unknown. Here, we aim to unravel the impact of various soil biota on enhanced weathering.One of the soil biota we're interested in is earthworm. Earthworms play a fundamental role in soil. They can increase weathering by respiration, ingestion of soil, production of mucus, or stimulation of microbial activity.Here, we're interested in testing if earthworms can enhance weathering in an artificial system primarily made of minerals. Accurately quantifying weathering rates and associated carbon dioxide capture is the biggest experimental challenge. Different indicators show different weathering rates and do not always scale with carbon dioxide capture.In this experimental setup, we can measure multiple indicators. Our aim of the protocol is to understand the impacts of earthworms, bacteria, and fungi on weathering rates, while also studying the abiotic factors boosting it. However, the ultimate aim of the protocol is to find the optimal combination of biotic and abiotic factors to maximize carbon dioxide removal.The main benefits relate to scale and level of control, and we are now able to test a much larger number of combinations of soil biota and minerals, all under the same experimental conditions, and that allows us to pick up synergies, interactions that we would never have picked up in more conventional, smaller experimental designs. Our results will showcase the potential of soil biota to draw CO2 from the atmosphere, and if we can prove that, that would be a huge step in finding ways to help mitigate global warming.

Watch this Scientific Journal Video about Construction of a Refrigerator System for Leachate Collection to Study Mineral Weathering at JoVE.com

Construction of a Refrigerator System for Leachate Collection to Study Mineral Weathering  

To begin, set up the refrigerator and the frame holding the columns in the climate chamber. Lift the lid to open the fridge and move Acrylic Plate Four forward. Take pipes of different lengths that have been previously cut to reach the jerrycans and insert them in Acrylic Plate Four, according to their numbers.Move the Acrylic Plate Four backward. Take the clean funnels, insert them carefully into position in Acrylic Plate Three and connect them to the corresponding pipes as per their designated numbers. Then take high density polyethylene jerrycans inside the chamber inside.Stack these jerrycans in the refrigerator in two layers according to the scheme shown here. And simultaneously connect the tubes to the jerrycans. After completing the refrigeration setup, close the fridge.

construction-refrigerator-system-for-leachate-collection-to-study

Research

JoVE Journal

Biochemistry

418 Views.  Wageningen University & Research. To begin, set up the refrigerator and the frame holding the columns in the climate chamber. Lift the lid to open the fridge and move Acrylic Plate Four forward. Take pipes of different lengths that have been previously cut to reach the jerrycans and insert them in Acrylic Plate Four, according to their numbers.Move the Acrylic Plate Four backward. Take the clean funnels, insert them carefully into position in Acrylic Plate Three and connect them to the corresponding pipes as per their ...

Video: Construction of a Refrigerator System for Leachate Collection to Study Mineral Weathering  

Enhanced weathering (EW) is an emerging carbon dioxide (CO2) removal technology that can contribute to climate change mitigation. This technology relies on accelerating the natural process of mineral weathering in soils by manipulating the abiotic variables that govern this process, in particular mineral grain size and exposure to acids dissolved in water. EW mainly aims at reducing atmospheric CO2 concentrations by enhancing inorganic carbon sequestration. Until now, knowledge of EW has been mainly gained through experiments that focused on the abiotic variables known for stimulating mineral weathering, thereby neglecting the potential influence of biotic components. While bacteria, fungi, and earthworms are known to increase mineral weathering rates, the use of soil organisms in the context of EW remains underexplored. 
 This protocol describes the design and construction of an experimental setup developed to enhance mineral weathering rates through soil organisms while concurrently controlling abiotic conditions. The setup is designed to maximize weathering rates while maintaining soil organisms' activity. It consists of a large number of columns filled with rock powder and organic material, located in a climate chamber and with water applied via a downflow irrigation system. Columns are placed above a fridge containing jerrycans to collect the leachate. Representative results demonstrate that this setup is suitable to ensure the activity of soil organisms and quantify their effect on inorganic carbon sequestration. Challenges remain in minimizing leachate losses, ensuring homogeneous ventilation through the climate chamber, and avoiding flooding of the columns. With this setup, an innovative and promising approach is proposed to enhance mineral weathering rates through the activity of soil biota and disentangle the effect of biotic and abiotic factors as drivers of EW.

Here we present the construction and operation of an experimental setup to enhance mineral weathering through the activity of soil organisms while concurrently manipulating abiotic variables known to stimulate weathering. Representative results from the functioning of the setup and sample analyses are discussed together with points for improvement.

Enhanced weathering (EW) is an emerging carbon dioxide (CO2) removal technology that can contribute to climate change mitigation. This technology relies ...

Constructing the Columns and the Mesh System for Leachate Collection to Study Mineral Weathering

To begin, construct the refrigerator setup for the leachate collection. Take the PVC column to incubate rock powder and soil organisms. Also, acquire middle rings to hold columns above the funnels.Position the rings a few centimeters from the bottom of the columns. Acquire material to create a mesh system at the bottom of the columns to filter the leachate. Place the 20-micrometer mesh at the bottom of the column and add a one-centimeter layer of plastic beads over this mesh.Next, place a 10-micrometer mesh on top of the 20-micrometer mesh. Secure the meshes in place using two cable ties. Tighten them firmly and remove excess ties by cutting their edges.The setup is now ready to be filled with the organomineral mixture and inoculated with soil organisms.

Filling the Columns and Inoculating the Biota for Leachate Collection to Study Mineral Weathering

To begin, construct the refrigeration for leachate collection and the mesh system at the bottom of the columns. Weigh 400 grams of minerals and 10 grams of organic materials in a bowl according to the desired treatment. Then, calculate the water holding capacity using the equation shown here.Adjust the water holding capacity to 80%based on the mineral type, grain size, and organic source. Mix all the components cautiously using a metal spoon, and fill the columns with the thoroughly blended mixture. Position the filled columns in the climate chamber.Then, take the prepared microbial cultures. Using a pipette, inoculate the selected culture on the surface of the columns as per the desired treatment. Acquire earthworms as per the desired density, and carefully place them on the surface of the columns as per the desired treatment.Place the mesh on top of the columns to avoid earthworms'escape once they are introduced, and to columns without earthworms to maintain the same conditions. Then, insert the columns at the respective places in the acrylic sheet too. After setting up the irrigation and control system, click the Edit button to edit the settings of each task.To activate the relay, simply click on the task that requires the relay to be turned on. Then, insert the preferred settings in the Start Date and Start Time fields to set the start date and time for the operation. Click Set Repeat and Repeat Every to set the watering frequency.To specify the date and time when the relay should stop operating, click on the End Repeat Date and End Repeat Time fields. After entering the desired values, click the Save Changes button. To turn off the relay, click on the task for which the action is to set the specific relay off.Set the time at which the relay must stop working depending on the water irrigation rate and the watering frequency following the same commands as to set the relay on. Once each relay is set, click on Save Changes. The irrigation system will then start watering the columns according to the set flow rates and frequencies.The irrigation system allowed water adjustments in the columns, leading to small differences in irrigation rates. The average amount of water was lower for irrigation rates of 50 and 150 milliliters per day, while it was higher for an irrigation rate of 100 milliliters per day. Values for dissolved inorganic carbon measured at the end of the experiment ranged from 7.352 C to 259.279 milligrams carbon.At the end of the experimental period, earthworms successfully survived in this organomineral system, and visual signs of microbial growth could be detected.