Decision making for the Circular Economy: Life Cycle Assessment

Post by Shauhrat Chopra (Assistant Professor, City University of Hong Kong, formerly a Post-Doctoral Researcher at University of Illinois Chicago) and Weslynne Ashton (Associate Professor, Illinois Institute of Technology Stuart School of Business). Here, Shauhrat and Weslynne present a Life-Cycle Assessments of bread baking, considering wood versus Plant Chicago biobricks as fuel. 

In a facility-scale industrial symbiosis system like The Plant, the ideal is for one business to utilize the waste or by-product streams as raw materials for their own process. This practice not only allows businesses to minimize their production costs but also reduces the utilization of virgin materials. Such resource exchanges aim to use resources more effectively compared to the traditional linear production model. However, to truly transition into a circular economy, it is imperative to make decisions that maximize the value at every stage of the material’s life cycle. In order to create sustainable resource exchanges, businesses within The Plant need information to compare technical functionality, economic viability and environmental impacts associated for different waste utilization options.

Life Cycle Assessment (LCA), a popular methodology used to account for environmental burden, can play a major role in comparing alternate strategies of utilizing a waste resource. LCA-informed decision-making will help determine which resource exchange scenarios truly maximizes the value of the waste material by understanding the trade-offs between benefits and impacts. In this post, we highlight the utility of this approach for businesses in deciding how best to use their waste, well before a new exchange is developed.

Currently, spent grain from Whiner Brewery and coffee chaff from 4 Letter Word Coffee together constitutes a large portion of organic waste material being generated at the Plant. At present, these resources are composted on-site, and later used to grow vegetables, greens, and potentially an orchard(!) on site. However, as these businesses grow, so does their waste, and it is becoming increasingly difficult to compost all of it given the space constraint. To deal with this challenge, Plant Chicago has been working on innovative solutions with the aim of maximizing the value of this resource. Recently, they proposed developing bio-bricks from the mixture of spent grain and coffee chaff, and using them as a fuel source for firing the oven at the Pleasant House bakery. While bio-bricks may provide a higher value as a fuel source in comparison to the compost, it is not clear how performance and environmental impacts for different bio-brick recipes compare with traditionally used wood. For this reason, we conducted a comparative cradle-to-gate LCA to compute the environmental impacts for baking using different fuel sources – wood or bio-brick. We modeled how much of each fuel is needed and the associated environmental concerns to produce 1 loaf of sourdough bread (730 grams).


Figure 1. Comparing cradle-to-gate impacts for producing 1 loaf of sourdough bread under four scenarios

Figure 1 above compares four alternate scenarios for producing a loaf of bread based on ten environmental impact categories. One of the scenarios (blue-colored bar) assesses the impacts associated with the use of wood from Indiana as a fuel source. The other three scenarios focus on the production and use of bio-bricks. The process flow diagram for producing the bio-brick at The Plant is presented in Figure 2, and the red-colored bar in Figure 1 represents the environmental impacts for this scenario.


Figure 2. Process flow diagram for the standard bio-brick production system

The other two scenarios evaluate the environmental impacts of making improvements to this production system. One of the scenarios consider drying of bio-bricks with excess heat from the oven (green-colored bar), the other scenario modeled burning of loose bio-material in the oven to avoid the energy use and related impacts associated  with the press machine (violet-colored bar).

Based on the results from Figure 1 it is clear that any of the three production systems that use bio-bricks as fuel have considerably lower impacts in comparison to the wood. The fact that these bio-bricks will be produced on-site provide an added advantage. The wood that is transported in trucks from over 200 miles contributes the largest share of the emissions.

When we remove the scenario that uses wood as a fuel source, we are able to observe the variation between the three bio-brick based production systems. On comparing the three bio-brick scenarios (Figure 3), we notice that the production strategy where bio-material is co-dried with the excess heat from the oven tends to perform by far the best. Moreover, the results show that, contrary to expectation, the loose burn of bio-material has the highest environmental impacts due to lower energy efficiency, which suggests more bio-material is needed to produce a comparable amount of energy.


Figure 3. Comparison of cradle-to-gate environmental impacts for producing 1 MJ of energy from three alternate production systems of Bio-bricks

These insights equip Plant Chicago and businesses at The Plant with environmental information that supplements the decision-making for creating new exchanges, which tend to be either unplanned or based on financial incentive alone. Moving forward, in addition to considering environmental impacts, we would like to compare the social benefits of alternate scenarios of utilizing excess raw material, such as the potential for creating new jobs in the community.

For more information on the material and energy impacts of bread baking, see our posts on Material Flow Analysis and the chemistry of wood-burning.

Other posts by the Plant Chicago Research Steering Committee can be found here:

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