**3.2 Life cycle impact assessment of the operation stage**

**Figure 4** shows the impact assessment results for the wastewater treatment operation stage for all micromixer devices. The total impact of each micromixer, in this stage, was determined by the summation of all impacts during ten work cycles. **Figure 4** compiles the results of all evaluated impact categories for the six devices under study. Overall, the LCIA results showed that in the operation stage, circular and rectangular-3D micromixers presented 30% more impact than the other micromixers. This finding can be explained by the high retention of these devices and the Lac-magnetite amount required for each work cycle. Two vertical loops and multiple layers micromixers presented the lowest impact in all impact categories, due to their high retentions per work cycle. Impact assessment was measured in four general categories: human health, ecosystem quality, climate change and resource depletion.

**Figure 4A**–**C** show impacts on human toxicity, non-cancer effects category, human toxicity-cancer effects category, and photochemical ozone formation category, respectively. Results indicate that human toxicity impacts are mainly related to ABTS use. This is a chemical compound used to track the reaction kinetics of specific enzymes such as laccases [24]. In this study, ABTS is used in the enzymatic activity assay of the obtained Lac-magnetite bionanocompounds. Assessment of toxicological effects of ABTS emitted into the environment were considered by estimating a specific characterization factor, i.e., comparative toxic units (CTUh). This factor provides an estimate of increase morbidity for the human population per unit mass of an emitted chemical (cases per kilogram) by assuming equal weighting between cancer and non-cancer situations [25]. However, some studies have


**101**

**Figure 4.**

*dissipated water.*

*Micromixers for Wastewater Treatment and Their Life Cycle Assessment (LCA)*

proposed the calculation of human health effect factors for cancer and non-cancer effects via ingestion and inhalation exposure, respectively. Additionally, toxic effects models have been considered to determine impacts on human health per kilogram substance emitted [26]. These calculations have been developed through steps, such as environmental fate, exposure, and effects of chemicals, which implies

*Impact assessment results for the operation stage: A) human toxicity, non-cancer effects, B) human toxicity, cancer effects, C) photochemical ozone formation, D) Ecotoxicity freshwater, E) freshwater and terrestrial acidification, F) climate change, G) resource depletion, minerals and metals, H) resource depletion,* 

a cause–effect chain that links emissions to impacts.

*DOI: http://dx.doi.org/10.5772/intechopen.96822*

#### **Table 2.**

*Lac-magnetite amount per work cycle for the six micromixer devices.*

## *Micromixers for Wastewater Treatment and Their Life Cycle Assessment (LCA) DOI: http://dx.doi.org/10.5772/intechopen.96822*

**Figure 4.**

*Advances in Microfluidics and Nanofluids*

*Micromixer Two* 

*vertical loops*

*Lac-magnetite amount per work cycle for the six micromixer devices.*

*One loop*

*Two horizontal loops*

*Cycle 1 5 5 5 5 Cycle 2 0.65 1 3 5 Cycle 3 0.0845 0.2 1.8 5 Cycle 4 0.0109 0.04 1.08 5 Cycle 5 0.0014 0.008 0.648 5 Cycle 6 0.00018 0.0016 0.3888 5 Cycle 7 2.4E-05 0.00032 0.2332 5 Cycle 8 3.1E-06 6.4E-05 0.1399 5 Cycle 9 4.08E-07 1.28E-05 0.0839 5 Cycle 10 5.3E-08 2.5E-06 0.0503 5*

*Retention rate 87% 80% 40% 0%*

*Triangular Circular Rectangular-3D*

**3.2 Life cycle impact assessment of the operation stage**

the corresponding environmental impacts. Therefore, we considered the operation stage of each micromixer from its use in the first cycle until the completion of a total of ten work cycles. The initial input of the Lac-magnetite bionanocompound was 5 mg during all the operation process in the wastewater treatment. Then, this amount was different for each microsystem and work cycle. The total amounts of Lac-magnetite per work cycle for each micromixer are summarized in **Table 2**.

**Figure 4** shows the impact assessment results for the wastewater treatment operation stage for all micromixer devices. The total impact of each micromixer, in this stage, was determined by the summation of all impacts during ten work cycles. **Figure 4** compiles the results of all evaluated impact categories for the six devices under study. Overall, the LCIA results showed that in the operation stage, circular and rectangular-3D micromixers presented 30% more impact than the other micromixers. This finding can be explained by the high retention of these devices and the Lac-magnetite amount required for each work cycle. Two vertical loops and multiple layers micromixers presented the lowest impact in all impact categories, due to their high retentions per work cycle. Impact assessment was measured in four general categories: human health, ecosystem quality, climate change and resource depletion. **Figure 4A**–**C** show impacts on human toxicity, non-cancer effects category, human toxicity-cancer effects category, and photochemical ozone formation category, respectively. Results indicate that human toxicity impacts are mainly related to ABTS use. This is a chemical compound used to track the reaction kinetics of specific enzymes such as laccases [24]. In this study, ABTS is used in the enzymatic activity assay of the obtained Lac-magnetite bionanocompounds. Assessment of toxicological effects of ABTS emitted into the environment were considered by estimating a specific characterization factor, i.e., comparative toxic units (CTUh). This factor provides an estimate of increase morbidity for the human population per unit mass of an emitted chemical (cases per kilogram) by assuming equal weighting between cancer and non-cancer situations [25]. However, some studies have

**100**

**Table 2.**

*Lacmagnetite amount (mg)*

*Impact assessment results for the operation stage: A) human toxicity, non-cancer effects, B) human toxicity, cancer effects, C) photochemical ozone formation, D) Ecotoxicity freshwater, E) freshwater and terrestrial acidification, F) climate change, G) resource depletion, minerals and metals, H) resource depletion, dissipated water.*

proposed the calculation of human health effect factors for cancer and non-cancer effects via ingestion and inhalation exposure, respectively. Additionally, toxic effects models have been considered to determine impacts on human health per kilogram substance emitted [26]. These calculations have been developed through steps, such as environmental fate, exposure, and effects of chemicals, which implies a cause–effect chain that links emissions to impacts.

Regarding the ecosystem quality, **Figure 4D** and **E** present impacts on the ecotoxicity freshwater category and the freshwater and terrestrial acidification category. According to Aurisano et al. [27], assessing ecotoxicological impacts on freshwater ecosystems after chemical exposure is an important component of various environmental and chemical management frameworks. These impact categories were considered here because we needed to determine impacts associated with compounds from our process that potentially come into contact with aquatic organisms and human beings [28]. Results showed that ABTS had the highest impact contribution on these categories due to its potential impact on aquatic ecosystems. Many authors have agreed that freshwater acidification is mainly caused by protons resulting from the mineralization of nitrogen and sulfur deposition, while carbon dioxide is the main cause of (coastal) marine acidification [29, 30]. These environmental impacts directly compromised the operation stage of micromixers in wastewater treatment.

**Figure 4F** shows impacts on the climate change category. Emissions of CO2 and other greenhouse gases (GHGs), aerosols, and ozone precursors are thought to be responsible for detrimental climate impact [31]. In this study, energy use in operation processes of micromixers had the highest contribution to this impact category, which agrees well with previous studies [32]. This energy along with the energy used during the life span of a micromixer comprise the life-cycle energy and emissions footprint. According to Yousefi et al. [33], in addition to the energy consumption issue, greenhouse gas (GHG) emission issues and an understanding of emissions in a production process based on the kilogram of carbon equivalent (CO2eq) are also critical in any production process. Several studies have reported some greenhouse gas removal technologies that will be needed to balance residual emissions and meet the emission targets [34]. Overall, most of these technologies proposed involve carbon dioxide removal or conversion of a higher global warming potential (GWP) gas to a lower GWP gas [35]. However, some removal technologies require significant amounts of energy for both installation and operation. Therefore, it is necessary to continue investigating in this field to assess potential environmental tradeoffs, including those related to energy use and climate change.

Finally, **Figure 4G** and **H** show the impact assessment results for the resource depletion of minerals and metals category and resource depletion of dissipated water category, respectively. Results in these categories are mainly associated with the energy consumption due to the use of non-renewables such as fossil fuels. According to Klinglmair et al. [36], resources could be evaluated according to their depletion (consumption related to geological or natural reserve), scarcity (economic availability) and their criticality (a resource that is scarce and crucial for society). Hence, depletion refers to the decrease of the physical amount of a resource that is available for future human use [37]. Minerals and metals depletion are considered within the abiotic depletion potential (ADP) method, which is recommended by the ILCD handbook and the Product Environmental Footprint (PEF) as the best available practice for assessing resource depletion on a midpoint level [37, 38]. Therefore, here we considered this impact category to determine the potential impacts associated with resource use when operating wastewater treatment processes enabled by the developed micromixers. However, both environmental and human health impacts related to extraction or use, such as toxic emissions, are kept as separate environmental impact categories, and resource depletion directly impacting ecosystem health was disregarded in importance.

#### **3.3 Total impact assessment**

**Figure 5** shows the impact assessment results of manufacturing and operation stages for each micromixer. The manufacturing stage had the highest contribution

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*Micromixers for Wastewater Treatment and Their Life Cycle Assessment (LCA)*

to the total impact of each micromixer in the photochemical ozone formation category, representing 87% in the two vertical loops micromixer, 69% in the rectangular-3D micromixer, 77% in the one loop and two horizontal loop micromixers, 66% in the triangular micromixer, and 58% the in circular micromixer. Similar results were also obtained in other impact categories due to the energy spent for laser cutting to manufacture the device in addition to the use of raw materials, such as PMMA. Regarding the operation stage, results showed that although ten work cycles for each micromixer were considered, this stage had the lowest contribution in all impact categories. This can be explained by the use of low impact raw materials in the enzyme activity assay, the preparation of artificial wastewater, and

*Impact assessment of manufacturing and operation stages in the photochemical ozone formation category.*

Specifically, the two vertical loops micromixer presented, on average, 56% more impact in all categories than other micromixers, considering the manufacturing and operation stages. In contrast, the circular micromixer had the lowest impact in the manufacturing stage due to a significant reduction in the use of PMMA. Also, this micromixer had the highest impact during the operation stage due to its low retention of Lac-Magnetite, which leads to an increased requirement of the bionanocompound per cycle. However, total impact of circular micromixer is one of the lowest compared to other designs. This result showed that to calculate the impact assessment, it is necessary to consider all stages of a micromixer from its manufacture to

Results from this study showed that six prototypes of micromixers for wastewater treatment can be analyzed in terms of impacts to human health and environment using the LCA methodology. This tool confirmed to be useful for this early research stage as it allows to identify potential impacts during the different phases

According to the four general impacts categories considered in this study, we successfully identified the main flows that contributed to each one. The ABTS chemical for enzyme activity assays significantly contributed to human health and ecosystem quality categories. Assessment of potential toxicological effects of this compound on human health were determined in several impact categories including

*DOI: http://dx.doi.org/10.5772/intechopen.96822*

the micromixer operation.

**Figure 5.**

its final operation.

**4. Conclusions**

required to implement these technologies.

*Micromixers for Wastewater Treatment and Their Life Cycle Assessment (LCA) DOI: http://dx.doi.org/10.5772/intechopen.96822*

**Figure 5.** *Impact assessment of manufacturing and operation stages in the photochemical ozone formation category.*

to the total impact of each micromixer in the photochemical ozone formation category, representing 87% in the two vertical loops micromixer, 69% in the rectangular-3D micromixer, 77% in the one loop and two horizontal loop micromixers, 66% in the triangular micromixer, and 58% the in circular micromixer. Similar results were also obtained in other impact categories due to the energy spent for laser cutting to manufacture the device in addition to the use of raw materials, such as PMMA. Regarding the operation stage, results showed that although ten work cycles for each micromixer were considered, this stage had the lowest contribution in all impact categories. This can be explained by the use of low impact raw materials in the enzyme activity assay, the preparation of artificial wastewater, and the micromixer operation.

Specifically, the two vertical loops micromixer presented, on average, 56% more impact in all categories than other micromixers, considering the manufacturing and operation stages. In contrast, the circular micromixer had the lowest impact in the manufacturing stage due to a significant reduction in the use of PMMA. Also, this micromixer had the highest impact during the operation stage due to its low retention of Lac-Magnetite, which leads to an increased requirement of the bionanocompound per cycle. However, total impact of circular micromixer is one of the lowest compared to other designs. This result showed that to calculate the impact assessment, it is necessary to consider all stages of a micromixer from its manufacture to its final operation.
