Analysis methods for Lifecycle Assessment of Energy Systems and Nutrient Recovery, in relevance to environmental policies
Authors:   , Kar Saurajyoti , Gurian Patrick L. , Spatari Sabrina 
Published: July 2021

Life Cycle Assessment (LCA) is a multi-faced analytical approach targeted to assess environmental and economic sustainability approaches. LCA is used to evaluate challenges faced by industrial processes objectively while identifying environmental, energy, and economic hot spots. Performing LCA, researchers face several challenges: data collection and missing data, spatial and temporal variability, selection of assessment metrics, and uncertainty. This thesis evaluates three different approaches to LCA applicable for bioenergy and marginal supply of nutrients for agriculture. Economic assessment is performed along with LCA to consider the feasibility of bioenergy and nutrient recovery pathways. Three primary objectives define the thesis consisting of: (a) combining LCA and economic assessment of air-stripping technology to evaluate the cost-effectiveness of producing ammonium sulfate (AS) fertilizer from anaerobic digestor effluent at wastewater treatment plants, (b) developing an optimization framework to assess barley-to-ethanol biofuel pathway for its relevance as an advanced fuel under the federal Renewable Fuel Standard (RFS2), and (c) evaluating forest residue and willow short-rotation crop feedstocks for residential heating as alternatives to the use of heating oil and natural gas. The study estimates a reduction of 83% in greenhouse gas emissions from AS if produced by air-stripping technology at Philadelphia's WWTP compared to the conventional Haber Bosch process. Significant energy savings are observed for the ammonia recovery process compared to nitrogen and hydrogen's catalytic reaction to form ammonia in the Haber Bosch process. Economic evaluation considering capital and operational costs for Philadelphia's WWTP flow capacities estimates a break-even selling price of $0.11 per gallon AS (100% w/w concentration). This study demonstrates a point estimation of LCA methodology to identify a prospective future technology's economic and environmental feasibility based on local parameters. In the second objective, an optimization framework is developed to minimize upstream feedstock costs of producing ethanol, which selects winter fallow cropland for growing barley for ethanol production. The framework uses simulations of soil greenhouse gas emissions and crop yield estimated from the DAYCENT biogeochemical model, where parameters related to weather cycle, soil properties, and fertilizer management options affect emissions and crop yield. A generalized additive mixed modeling approach is used to accommodate temporal and spatial autocorrelation and variation. A mixed-integer optimization approach is used to minimize upstream production cost while maximizing the cropland acreage per choice selection. As a case study, for a biorefinery producing 2.08 x 108 liters of barley-ethanol per year, the average carbon intensity is estimated at 0.74 gCO₂e MJ-1 when all co-products are used. This shows that winter barley-to-ethanol can be classified as an advanced biofuel under RFS2. Credit incentives such as California state's Low Carbon Fuel Standard are found to have a negligible effect on cropland selection. The study also found that the favored management approaches for reducing greenhouse gas emissions largely match the farmers' choices to choose the most economical fertilizer management option. The third study implements Bern cycle modeling of atmospheric greenhouse gas retention and decomposition for estimating radiative forcing of alternative residential heating infrastructures over 30 production years and a total of 100 observation years. Natural gas and biomass feedstock-based heating scenarios are significantly more environmentally efficient than conventional heating oil. District heating (DH) infrastructure is similarly efficient as decentralized (CH) infrastructure for natural gas use. The study suggests using forest residues when available because if kept unused, it undergoes natural decay, emitting greenhouse gas emissions, which adversely affects radiative forcing for the 100 observed years. When forest residues are not available as feedstock, alternative bio-feedstock such as willow short rotation crop grown on marginal land can be planned for use in residential heating infrastructures. In addition, carbon capture and storage technology implementation can facilitate further reduction of radiative forcing when forest residues or willow short rotation crops are used as feedstocks. The study demonstrates the radiative forcing-based analytical framework that implements time-heterogenous greenhouse gas accounting of biomass-based residential heating. Keywords: Biomass for bioenergy, Life cycle assessment, Nutrient recovery, Portfolio optimization, Temporal GHG emissions