Bioenergy Potential from Food Waste in California

Food waste makes up approximately 15% of municipal solid waste generated in the United States, and 95% of food waste is ultimately landfilled. Its bioavailable carbon and nutrient content makes it a major contributor to landfill methane emissions, but also presents an important opportunity for energy recovery. This paper presents the first detailed analysis of monthly food waste generation in California at a county level, and its potential contribution to the state’s energy production. Scenarios that rely on excess capacity at existing anaerobic digester (AD) and solid biomass combustion facilities, and alternatives that allow for new facility construction, are developed and modeled. Potential monthly electricity generation from the conversion of gross food waste using a combination of AD and combustion varies from 420 to 700 MW, averaging 530 MW. At least 66% of gross high moisture solids and 23% of gross low moisture solids can be treated using existing county infrastructure, and this fraction increases to 99% of high moisture solids and 55% of low moisture solids if waste can be shipped anywhere within the state. Biogas flaring practices at AD facilities can reduce potential energy production by 10 to 40%

Greenhouse Gas and Air Pollutant Emissions from Composting

Composting can divert organic waste from landfills, reduce landfill methane emissions, and recycle nutrients back to soils. However, the composting process is also a source of greenhouse gas and air pollutant emissions. Researchers, regulators, and policy decision-makers all rely on emissions estimates to develop local emissions inventories and weigh competing waste diversion options, yet reported emission factors are difficult to interpret and highly variable. This review explores the impacts of waste characteristics, pretreatment processes, and composting conditions on CO2, CH4, N2O, NH3, and VOC emissions by critically reviewing and analyzing 388 emission factors from 46 studies. The values reported to date suggest that CH4 is the single largest contributor to 100-year global warming potential (GWP100) for yard waste composting, comprising approximately 80% of the total GWP100. For nitrogen-rich wastes including manure, mixed municipal organic waste, and wastewater treatment sludge, N2O is the largest contributor to GWP100, accounting for half to as much as 90% of the total GWP100. If waste is anaerobically digested prior to composting, N2O, NH3, and VOC emissions tend to decrease relative to composting the untreated waste. Effective pile management and aeration are key to minimizing CH4 emissions. However, forced aeration can increase NH3 emissions in some cases

Greenhouse Gas and Air Pollutant Emissions from Composting

Composting can divert organic waste from landfills, reduce landfill methane emissions, and recycle nutrients back to soils. However, the composting process is also a source of greenhouse gas and air pollutant emissions. Researchers, regulators, and policy decision-makers all rely on emissions estimates to develop local emissions inventories and weigh competing waste diversion options, yet reported emission factors are difficult to interpret and highly variable. This review explores the impacts of waste characteristics, pretreatment processes, and composting conditions on CO2, CH4, N2O, NH3, and VOC emissions by critically reviewing and analyzing 388 emission factors from 46 studies. The values reported to date suggest that CH4 is the single largest contributor to 100-year global warming potential (GWP100) for yard waste composting, comprising approximately 80% of the total GWP100. For nitrogen-rich wastes including manure, mixed municipal organic waste, and wastewater treatment sludge, N2O is the largest contributor to GWP100, accounting for half to as much as 90% of the total GWP100. If waste is anaerobically digested prior to composting, N2O, NH3, and VOC emissions tend to decrease relative to composting the untreated waste. Effective pile management and aeration are key to minimizing CH4 emissions. However, forced aeration can increase NH3 emissions in some cases

Achieving Deep Cuts in the Carbon Intensity of U.S. Automobile Transportation by 2050: Complementary Roles for Electricity and Biofuels

Passenger cars in the United States (U.S.) rely primarily on petroleum-derived fuels and contribute the majority of U.S. transportation-related greenhouse gas (GHG) emissions. Electricity and biofuels are two promising alternatives for reducing both the carbon intensity of automotive transportation and U.S. reliance on imported oil. However, as standalone solutions, the biofuels option is limited by land availability and the electricity option is limited by market adoption rates and technical challenges. This paper explores potential GHG emissions reductions attainable in the United States through 2050 with a county-level scenario analysis that combines ambitious plug-in hybrid electric vehicle (PHEV) adoption rates with scale-up of cellulosic ethanol production. With PHEVs achieving a 58% share of the passenger car fleet by 2050, phasing out most corn ethanol and limiting cellulosic ethanol feedstocks to sustainably produced crop residues and dedicated crops, we project that the United States could supply the liquid fuels needed for the automobile fleet with an average blend of 80% ethanol (by volume) and 20% gasoline. If electricity for PHEV charging could be supplied by a combination of renewables and natural-gas combined-cycle power plants, the carbon intensity of automotive transport would be 79 g CO₂e per vehicle-kilometer traveled, a 71% reduction relative to 2013

Dynamic Geospatial Modeling of the Building Stock To Project Urban Energy Demand

In the United States, buildings account for more than 40% of total energy consumption and the evolution of the urban form will impact the effectiveness of strategies to reduce energy use and mitigate emissions. This paper presents a broadly applicable approach for modeling future commercial, residential, and industrial floorspace, thermal consumption (heating and cooling), and associated GHG emissions at the tax assessor land parcel level. The approach accounts for changing building standards and retrofitting, climate change, and trends in housing and industry. We demonstrate the automated workflow for California and project building stock, thermal energy consumption, and associated GHG emissions out to 2050. Our results suggest that if buildings in California have long lifespans, and minimal energy efficiency improvements compared to building codes reflective of 2008, then the state will face a 20% or higher increase in thermal energy consumption by 2050. Baseline annual GHG emissions associated with thermal energy consumption in the modeled building stock in 2016 is 34% below 1990 levels (110 Mt CO_2eq/y). While the 2020 targets for the reduction of GHG emissions set by the California Senate Bill 350 have already been met, none of our scenarios achieve >80% reduction from 1990 levels by 2050, despite assuming an 86% reduction in electricity carbon intensity in our “Low Carbon” scenario. The results highlight the challenge California faces in meeting its new energy efficiency targets unless the State’s building stock undergoes timely and strategic turnover, paired with deep retrofitting of existing buildings and natural gas equipment

Role of Lignin in Reducing Life-Cycle Carbon Emissions, Water Use, and Cost for United States Cellulosic Biofuels

Cellulosic ethanol can achieve estimated greenhouse gas (GHG) emission reductions greater than 80% relative to gasoline, largely as a result of the combustion of lignin for process heat and electricity in biorefineries. Most studies assume lignin is combusted onsite, but exporting lignin to be cofired at coal power plants has the potential to substantially reduce biorefinery capital costs. We assess the life-cycle GHG emissions, water use, and capital costs associated with four representative biorefinery test cases. Each case is evaluated in the context of a U.S. national scenario in which corn stover, wheat straw, and Miscanthus are converted to 1.4 EJ (60 billion liters) of ethanol annually. Life-cycle GHG emissions range from 4.7 to 61 g CO_2<i>e</i>/MJ of ethanol (compared with ∼95 g CO_2<i>e</i>/MJ of gasoline), depending on biorefinery configurations and marginal electricity sources. Exporting lignin can achieve GHG emission reductions comparable to onsite combustion in some cases, reduce life-cycle water consumption by up to 40%, and reduce combined heat and power-related capital costs by up to 63%. However, nearly 50% of current U.S. coal-fired power generating capacity is expected to be retired by 2050, which will limit the capacity for lignin cofiring and may double transportation distances between biorefineries and coal power plants

Life-Cycle Greenhouse Gas and Water Intensity of Cellulosic Biofuel Production Using Cholinium Lysinate Ionic Liquid Pretreatment

Cellulosic biofuels present an opportunity to meet a significant fraction of liquid transportation fuel demand with renewable, low-carbon alternatives. Certain ionic liquids (ILs) have proven effective at facilitating hydrolysis of lignocellulose to produce fermentable sugars with high yields. Although their negligible vapor pressure and low flammability make ILs attractive solvents at the point of use, their life-cycle environmental impacts have not been investigated in the context of cellulosic biorefineries. This study provides the first life-cycle greenhouse gas (GHG) and water use inventory for biofuels produced using IL pretreatment. We explore two corn stover-to-ethanol process configurations: the conventional water-wash (WW) route and the more recently developed integrated high gravity (iHG) route, which eliminates washing steps after pretreatment. Our results are based on the use of a representative IL, cholinium lysinate ([Ch]­[Lys]). We find that the WW process results in unacceptably high GHG emissions. The iHG process has the potential to reduce GHG emissions per megajoule of fuel by ∼45% relative to gasoline if [Ch]­[Lys] is used. Use of a protic IL with comparable performance to [Ch]­[Lys] could achieve GHG reductions up to 70–85%. The water intensities of the WW and iHG processes are both comparable to those of other cellulosic biofuel technologies

Environmental and Economic Impacts of Managing Nutrients in Digestate Derived from Sewage Sludge and High-Strength Organic Waste

Increasingly stringent limits on nutrient discharges are motivating water resource recovery facilities (WRRFs) to consider the implementation of sidestream nutrient removal or recovery technologies. To further increase biogas production and reduce landfilled waste, WRRFs with excess anaerobic digestion capacity can accept other high-strength organic waste (HSOW) streams. The goal of this study was to characterize and evaluate the life-cycle global warming potential (GWP), eutrophication potential, and economic costs and benefits of sidestream nutrient management and biosolid management strategies following digestion of sewage sludge augmented by HSOW. Five sidestream nutrient management strategies were analyzed using environmental life-cycle assessment (LCA) and life-cycle cost analysis (LCCA) for codigestion of municipal sewage sludge with and without HSOW. As expected, thermal stripping and ammonia stripping were characterized by a much lower eutrophication potential than no sidestream treatment; significantly higher fertilizer prices would be needed for this revenue stream to cover the capital and chemical costs. Composting all biosolids dramatically reduced the GWP relative to the baseline biosolid option but had slightly higher eutrophication potential. These complex environmental and economic tradeoffs require utilities to consider their social, environmental, and economic values in addition to present or upcoming nutrient discharge limits prior to making decisions in sidestream and biosolids management