LCA Goals and Scope of the Study

The goal of this LCA is to provide SBI with information on how their operations impact the environment:

1. In comparison with operations before adding the anaerobic digestion system (Base Case) 2. Upon application of different scenarios of digestate disposal

3. Upon application of several scenarios of biogas utilization 4. Upon application of various scenarios of AD byproduct utilization

This will provide quantitative results that can assist SBI in making well-informed decisions on how their business operations will impact the environment. The LCA will also allow SBI to communicate

14 SNRE. "Reimagining Chevy in the Hole." University of Michigan School of Natural Resources and Environment. 2 Apr. 2012. Web. <http://www.thelandbank.org/Landuseconf/Reimagining_Chevy_in_the_Hole.pdf>.

15Amon, Thomas, Vitaliy Kryvoruchko, Barbara Amon, Werner Zollitsch, Erich Potsch. "Biogas Production from Maize and Clover Grass Estimated With the Methane Energy Value System." Web.

<http://www.boku.ac.at/fileadmin/_/H93/H931/AmonPublikationen/biogas_production_maize_and_clover.pdf>.

16 USDA. “2007 Census of Agriculture.” U.S. Department of Agriculture. 2007. Web.

<http://www.agcensus.usda.gov/Publications/2007/Full_Report/usv1.pdf>.

17 Oslaj, Matjaz, Bogomir Mursec, and Peter Vindis. "Biogas Production from Maize Hybrids." Biomass and Bioenergy 34.11 (2010). Web. <http://www.sciencedirect.com/science/article/pii/S0961953410001431>.

quantitatively the environmental benefits and tradeoffs associated with AD to the City of Flint and future clients.

As outlined in Section 2, the product system under investigation includes the anaerobic digestion process, handling of resulting biogas and other AD byproducts such as digestate and centrate.

2.3.1. FUNCTION AND FUNCTIONAL UNIT

The function of SBI’s anaerobic digestion system is to produce biogas for sale in the form of either electricity or biomethane. The functional unit for this product system is one thousand standard cubic feet (MCF) of biogas produced in the digester.

Functional Unit = 1000 Standard Cubic Feet (SCF) of biogas or 1MCF

2.3.2. SYSTEM BOUNDARIES

For the biogas production system, we performed a cradle-to-grave LCA. We consider the sludge and food waste used for biogas production to be acquired in lieu of disposal by the wastewater treatment plant and food vendors, and therefore do not include upstream processes in our analysis. Materials acquisition, manufacture and transport of equipment used in the product system are outside the system boundaries due to their minimal impact per unit of biogas created over the lifetime of the equipment.

We also did not include material and energy inputs to the support structures for the system, e.g. the heating and lighting of the buildings housing the anaerobic digestion equipment or SBI’s offices and laboratory, due to the level of aggregation of the available data.

2.3.2.1. BASE CASE

As seen in Figure 1 the system boundary for the Base Case LCA includes dewatering, incineration of the sludge, and transport of the ash to the landfill is outside the system boundaries. The wastewater treatment plant is not included since we assume its operations are not affected by the method of handling and disposing of the biosolids.

2.3.2.2. CURRENT OPERATIONS

As seen in Figure 2 the system boundary for the current operations LCA includes all processes associated with anaerobic digestion including sludge thickening, digestion, operation of the boiler, digestate storage, digestate dewatering, and incineration. As in the Base Case, handling and transport of the ash to the landfill is outside the system boundaries.

2.3.2.3. FULLY OPERATIONAL

Figure 3, the system boundary for the fully operational LCA includes all processes associated with anaerobic digestion as well as transport of food waste from food vendors, operation of the electrical

generator, operation of the biogas upgrading system, transportation of digestate to Chevy in the Hole, and spreading digestate at Chevy in the Hole. Transmission of electricity or biomethane to the point of end-use is not included. Emissions from biomethane combustion were included to allow comparison between biogas use for electricity and biomethane production.

System expansion was used to allocate credit for avoided emissions from the Michigan electricity grid due to electricity generated from biogas. More on system expansion for electricity generation can be found in Section 3.7.3.

2.3.2.4. ALTERNATIVE AND SUPPLEMENTAL OPERATIONS

As seen in Figure 4, the boundary for the alternative and supplemental operations includes the boundaries associated with the future operations boundaries in addition to alternative and supplemental operations chosen by the master’s project team to investigate. The three additional boundary systems include, kiln drying, phosphorus recovery, and energy crops.

2.3.2.4.1. KILN DRYING

The system boundaries for kiln drying biosolids to produce of Class A fertilizer are in conjunction with the operations analyzed in the fully operational case.

The following additional life-cycle stages were included:

- Use of equipment for treating biosolids to be used as fertilizer

- Storage of Class A organic fertilizer prior to transportation to distribution centers and customers

- System expansion was used to evaluate the available nitrogen in the resulting Class A biosolids and compare with synthetic nitrogen production.

The following life-cycle stages were excluded:

- Construction of storage facility and infrastructure - The sequestration of nutrients

More on system expansion for kiln drying can be found in Section 3.7.1.

2.3.2.4.2. PHOSPHORUS RECOVERY

The system boundaries for phosphorus recovery to produce fertilizer are in conjunction with the operations analyzed in the Fully Operational case.

The following additional life-cycle stages were included:

- Electricity required for heating drying and pelletizing the centrate

- System expansion of available phosphorus in fertilizer product offsetting the same amount of phosphorus being produced from mining.

The following life-cycle stages of were excluded:

- Transportation of product away from the SBI plant - Construction of nutrient recovery system

- The reduced loading impact on the Flint wastewater treatment facility More on system expansion for phosphorus recovery can be found in Section 3.7.2.

2.3.2.4.3. ENERGY CROPS

The system boundaries for growing maize at CitH are in conjunction with the operations analyzed in the Fully Operational case.

The following life cycle stages were included:

- Production of maize at CitH

- Transportation of maize to the biogas plant - Processing of additional input at the plant The following are life cycle stages were excluded:

- Material acquisition, construction, and transportation to SBI of the buildings, vehicles, and equipment used in maize production

- The ensiling process

No land change at CitH was accounted for in this analysis since the area was deforested prior to the temporal boundaries of the cases analyzed.

2.3.3. ALLOCATION METHODS

All impacts within the system boundaries are allocated to the biogas produced by the system. In addition we used system expansion to account for the emissions avoided from the reduction in fossil fuels combusted to generate electricity for the Michigan grid and the emissions avoided in the kiln drying and phosphorus recovery scenarios by reducing the amount of synthetic fertilizer production.

2.3.3.1. SYSTEM EXPANSION

Using system expansion involves taking the amount of environmental burdens and material inputs to produce the outputs that are not used within the product system and then subtracting environmental burdens and material inputs using the process that only produces these materials. For the purposes of this study we established the environmental benefit of biogas byproducts by the nutrients recovered or returned to the ecosystem. The analysis conducted in this study used system expansion in the kiln drying

and the phosphorus recovery scenarios as well as for electricity generated to evaluate the

environmental benefits of each process. Details on the methodology used for system expansion in the kiln drying and phosphorus recovery scenarios and for electricity generation is found in Section 3.7.

2.3.4. DATA REQUIREMENTS

Much of the data for the Base Case LCA and current operations LCA are measurements or estimations based on operations at the Flint Wastewater Treatment Plant. Data for Base Case were from 2009-2011, and data for current operations were from June 2011 through February 2012. Although it would be ideal to have at least one entire year of data for the current operations LCA in order to account for seasonal variations, time constraints on the project made that impossible. We assume that the data averages would not change much as the time range for the data we do have includes the two most extreme seasons, summer and winter. Data for the LCAs in which we investigate potential impacts from different scenarios for future operations are estimates based on current operations, literature, and equipment specifications indicated by SBI’s Director of Operations to be representative of equipment that will be used in future operations. We used data specific to the United States from literature when available.

However, in some cases the data was European, as many studies on anaerobic digestion have been conducted in Germany, Austria, and Sweden.

2.3.5. IMPACT METHODS

We assessed environmental impact based on three U.S. EPA TRACI midpoint impact categories. These impact categories are global warming potential, acidification potential, and smog formation potential.

While we expect eutrophication potential to be an important impact of this system, we did not model this impact category. We expect that much of the nitrogen and phosphorus emissions would occur from land application of digestate. Modeling the eutrophication potential from these non-point sources was not possible due to time and data limitations.