Direct Greenhouse Gas Emissions Research Articles

Life Cycle Assessment of Nitrate and Compound Fertilizers Production—A Case Study

The production and utilization of fertilizers are processes with known and noteworthy environmental impacts. Direct greenhouse gas (GHG) emissions and a high contribution to water eutrophication due to the nitrogen (N) and phosphorus (P) derivatives are some of the most crucial impacts derived from the overall life cycle of fertilizer use. The life cycle assessment (LCA) has been reliable and analytical tool for the identification, quantification, and evaluation of potential environmental impacts of fertilizers related to the products, production processes, or activities throughout their lifecycle. In this paper, a gate-to-gate LCA approach was applied in order to identify and evaluate the impacts derived from the production processes of nitrate and compound fertilizers the production industry in Northeastern Greece. The results from this study prove that compound fertilizers have a greater impact compared with nitrate fertilizers, contributing up to 70% of the total production impacts. Furthermore, climate change, freshwater eutrophication, and fossil fuel depletion were identified as the most crucial impact categories. Finally, a comparison with relevant LCA studies was conducted, in order to identify the possibility of a consistency pattern of the fertilizer production impacts in general.

Key Considerations for the Use of Seaweed to Reduce Enteric Methane Emissions From Cattle.

Enteric methane emissions are the single largest source of direct greenhouse gas emissions (GHG) in beef and dairy value chains and a substantial contributor to anthropogenic methane emissions globally. In late 2019, the World Wildlife Fund (WWF), the Advanced Research Projects Agency-Energy (ARPA-E) and the Foundation for Food and Agriculture Research (FFAR) convened approximately 50 stakeholders representing research and production of seaweeds, animal feeds, dairy cattle, and beef and dairy foods to discuss challenges and opportunities associated with the use of seaweed-based ingredients to reduce enteric methane emissions. This Perspective article describes the considerations identified by the workshop participants and suggests next steps for the further development and evaluation of seaweed-based feed ingredients as enteric methane mitigants. Although numerous compounds derived from sources other than seaweed have been identified as having enteric methane mitigation potential, these mitigants are outside the scope of this article.

Driving factors of direct greenhouse gas emissions from China’s pig industry from 1976 to 2016

Livestock cultivation is a significant source of greenhouse gas (GHG) emissions, accounting for 14.5% of the total anthropogenic emissions. China is responsible for a considerable share of the global livestock emissions, particularly caused by pork production. We used the Kaya identity and the logarithmic mean Divisia index (LMDI) to decompose the national annual GHG emissions from enteric fermentation and manure management in pig farming in China from 1976 to 2016. We decomposed the sources of the emissions into five driving factors: (1) technological progress (e.g., feed improvement); (2) structural adjustment in the livestock sector; (3) structural adjustment in agriculture; (4) affluence; and (5) population growth. The results showed that the net GHG emissions from the pig sector in China increased 16 million tons (Mt) of carbon dioxide equivalents (CO2eq) during the study period. The decomposition analysis revealed that structural adjustment in agriculture, growing affluence, and population growth contributed to an increase of the GHG emissions of pork production by 23, 41, and 13 Mt CO2eq, respectively. The technological progress and structural changes in animal husbandry mitigated emissions by –51 and –11 Mt CO2eq, respectively. Further technological progress in pig production and optimizing the economic structures are critical for further reducing GHG emissions in China’s pig industry. Our results highlight the dominant role of technological changes for emission reductions in the pig farming.

Estimación de la huella de carbono en la industria de transformación primaria de la madera en El Salto, Durango

Introduction: The primary wood processing industry releases greenhouse gases (GHGs); their mitigation involves measuring the carbon footprint.Objective: To estimate the carbon footprint of two forestry companies dedicated to the primary transformation of wood.Materials and methods: Companies established as organizational boundaries L1 and L2 have two (Q1 and Q2) and one (D) sawmill, respectively. The operational limits were A1 (direct emissions from fossil fuel consumption), A2 (indirect emissions from electricity consumption) and A3 (emission sources not owned by L1 and L2). GHG emissions were calculated in two annuities with the method of using documented activity data and emission factors level 1. The annuities were compared with the Student’ t-test and Wilcoxon test, and the sawmills with the Kruskal-Wallis test.Results and discussion: The estimated carbon footprint for L1 was 480.06 tCO2e·year-1, where A1, A2 and A3 represented 29.32 %, 14.59 % and 56.09 %, respectively. L2 had a footprint of 230.56 tCO2e·year-1 of which 9.39 %, 11.78 % and 78.83 % corresponded to the categories A1, A2 and A3, respectively. The cumulative uncertainty was within a fair range of accuracy (±25 %). Only the direct GHG emissions between L1 annuities were statistically different (P < 0.05). Mechanical technology made the difference in GHG emissions among sawmills (P < 0.05).Conclusions: The carbon footprint is inherent to the energy used; energy management ensures the mitigation of GHG emissions.

Evaluation of Bursa metropolitan greenhouse Gas inventory and reduction targets

This study summarizes the greenhouse gas (GHG) emission levels and Sustainable Energy Action Plan (SEAP) of Bursa, where is an industrial, touristic, and historic metropolitan city with a dense population in Turkey. This study summarized direct (scope 1), indirect (scope 2), and other indirect (scope 3) GHG emissions. Urban GHG emissions including scope 1, 2, and 3 activities were determined as 14,148,597 tCO2e for 2016. Industrial fuel consumption, transportation, and residential heating activities were the main sources. GHG emission control sectors were determined according to the last consecutive workshops in 2017. Control actions, such as Energy efficiency/renewable energy applications in residential and commercial buildings, increasing the share of public transport in transportation, and reducing the number of private vehicles in traffic, were planned. Future projections for 2030 were estimated with and without reduction activities. Sectors (industry, agriculture, and animal husbandry) which are not within the jurisdiction of local governments or which cannot be intervened by local governments were excluded. It showed that with the mitigation measures to be implemented. Public transport problems, renewable energy conversion, and reduction of the green texture of the city are the main obstacles.

Environmental sustainability assessment of pig manure mono- and co-digestion and dynamic land application of the digestate

In this study, the environmental impacts of pig manure direct land application and anaerobic digestion (mono- and co-digestion) for biomethane production followed by digestate land application were evaluated by life cycle assessment, with a focus on the dynamic land application of digestate in terms of the nutrient profiles, soil nutrient status and environmental regulations. Ireland was used as a case study where co-digestion of manure with grass silage is viable, and an Irish emission inventory was established. The results indicate that pig manure and grass silage co-digestion performs best in 9 of the 11 impact categories assessed. Compared with direct land application, mono-digestion of pig manure decreases direct greenhouse gas emissions by 48% (190 tonne CO2e). Co-digestion with grass silage increases the total energy recovery by 226% (1592 MWh) than mono-digestion. The nitrogen available for plants in digestate (41.8%) is a little lower than that in raw pig manure (43.2%) due to the higher ammonia emissions after anaerobic degradation. The environmental impacts of the three pig manure management methods are greatly affected by soil nutrient conditions and regional environmental regulations, which determine the organic fertilizer application rates and consequently the required land areas and transport distances. In this case study, the land application area for digestate is determined by phosphorus acceptance of soils rather than nitrogen or potassium. This study provides practical insights to farmers, the gas industry, and policy makers to conduct effective organic fertilizer application, select optimal AD plant location, and maximize environmental benefits.

Improving the accuracy of electricity carbon footprint: Estimation of hydroelectric reservoir greenhouse gas emissions

Hydropower is usually considered as a low-carbon electricity source, as it does not lead to direct greenhouse gas (GHG) emissions, unlike producing electricity from fossil fuels. However, the flooding of lands following the construction of the dam generally leads to an increase in biogenic GHG emissions due to the degradation of biomass found in the newly created reservoir. The life cycle assessment (LCA) methodology is widely used to calculate and compare the carbon footprint of different electricity production pathways, while considering all life cycle stages. Net biogenic GHG emissions from hydropower reservoirs have been poorly considered in LCA because of the scarcity of data. These emissions are complex to quantify as several mechanisms are involved, and extrapolating observations from one reservoir to another is risky as emissions vary greatly depending on different parameters, such as climate, geographic location, age of impoundment, and watershed properties. The objective of this article is to compare different approaches to estimate hydropower reservoir emissions in LCA, to select the most appropriate one, and to apply it to the calculation of the carbon footprint of electricity distributed in the Canadian province of Québec. Net biogenic GHG emissions of all hydropower reservoirs in the province (with 2.5 and 97.5% confidence intervals), as estimated using the G-res model, are 16.5 (14.7–18.6) gCO2∙kWh−1 and 0.29 (0.23–0.35) gCH4∙kWh−1. Combined to ecoinvent data for other life cycle emissions, the carbon footprint of electricity distributed in the province in 2017 is 34.5 gCO2eq∙kWh−1.

Minimizing direct greenhouse gas emissions in livestock production: The need for a metabolic theory

Livestock production is one of the main contributors to global greenhouse gas (GHG) emissions. The tools provided by the Intergovernmental Panel on Climate Change to estimate GHG emissions (Tier 1 and Tier 2) cannot be used as a tool for advising farmers or national policy on how to minimize GHG emissions because these estimates are not explicitly related to any metabolic properties. For that, we need a metabolic model that obeys mass and energy balances and that models the trade-offs between different allocations of energy in the organism, throughout the life-cycle, as a function of environmental variables such as temperature and the amount and type of food. The Dynamic Energy Budget (DEB) Theory ensures mass conservation and models the transformations of state variable and product formation, allowing for explicit GHG emissions estimates. Therefore, we used this theory to build models for four bovine breeds – Alentejana, Angus, Charolais and Limousin. The goodness-of-fit of DEB models to data is good for all breeds. Differences in DEB breed specific parameters, such as the maximum reserve density and the maximum specific assimilation rate, explain differences in GHG emissions, ultimate lengths and weights and von Bertalanffy growth rates. Accumulated methane and nitrogen production ranges between 0.2 and 2, and 0.1 and 0.7 kg per kg of body weight, respectively. In terms of accumulated direct GHG emissions, there is a strong dependence on breed and age.

Carbon footprint of constructed wetlands for winery wastewater treatment

The aim of this study was to estimate the carbon footprint (CFP) of constructed wetlands for winery wastewater treatment. In particular, a constructed wetland scenario was compared to the previous scenario (third-party management) and to an activated sludge system. CFP considered both indirect and direct greenhouse gas (GHG) emissions measured on-site. Moreover, an economic analysis of the considered scenarios was also addressed. The results showed that the constructed wetland scenario had the lowest CFP (1.2 kg CO2eq mwater−3), while the third-party management was the worst scenario (52 kg CO2eq mwater−3) followed by the activated sludge system (4.5 kg CO2eq mwater−3). This was mainly due to the high GHG emissions generated by wastewater and sludge transportation as well as chemicals and electricity consumption in the third-party and activated sludge scenarios compared to the constructed wetlands. In terms of costs, the constructed wetland system was shown to be a low-cost technology which would reduce the capital, operation and maintenance costs associated with winery wastewater treatment up to 50% and 98%, respectively. Finally, constructed wetlands are low-cost and environmentally friendly technologies which constitute a sustainable alternative to conventional solutions for winery wastewater treatment.

Quantifying urban wastewater treatment sector's greenhouse gas emissions using a hybrid life cycle analysis method – An application on Shenzhen city in China

Substantial amounts of greenhouse gas (GHG) emissions generated at urban wastewater treatment plants (WWTP) are gaining increasing appreciation. Improving upon the commonly used Process-Based Life-Cycle Analysis (PLCA) and Environmentally-Extended Life-Cycle Analysis (EIO-LCA) models, we construct a Hybrid Life Cycle Analysis (HLCA) model and quantify both direct and indirect GHG emissions at the operational stage of WWTPs in Shenzhen, one of the fastest urbanizing cities in the world. Data are collected from 26 wastewater treatment plants in Shenzhen, out of all 32, covering 5 commonly used wastewater treatment technologies in China, i.e. Sequencing Batch Reactor, Oxidation Ditch, Biological Filter, AAO-MBR and AAO. The results show that WWTPs using AAO-MBR technology have the highest GHG emission intensity, averaging 0.79 tons per m3, primarily due to its large electricity intensity required. WWTPs using other technologies emit 0.27 to 0.39 tons of GHGs per m3 of wastewater treated. GHG emissions associated with electricity use occupy the largest share, ranging from 65 to 75%. Therefore, transforming the energy structure of the electric power sector to low-carbon sources can reduce WWTPs operational GHG emissions. In total, GHG emissions from Shenzhen's urban wastewater sector have increased from below 0.5 million tons in 2012 to over 0.6 million tons in 2017. Inter-model comparison shows that EIO-LCA substantially underestimates the urban wastewater sector's GHG emissions using the water sector's average parameters while PLCA also results in minor underestimations due the omission of indirect emissions in the production stage of chemicals and other material inputs.

Potentials and Limitations of the Bioconversion of Animal Manure Using Fly Larvae

Bioconversion of organic waste using fly larvae (such as Hermetia illucens and Musca domestica) is often presented as a promising and sustainable alternative because of its ability to generate high economic value products from excreta, waste or low value-added materials in short term, with the potential to promote a circular economy in agricultural systems. However, bioconversion of some organic waste, such as animal manure, could limit the use of bioconversion products because of contaminants presents in the substrate, offering risks of toxic substances entering the food chain and consequent effects on human health and the environment. This review provides an overview of the limitations and potentials of bioconversion process of cattle, swine, and chicken manure using fly larvae, focusing on nutrient recycling, environmental impacts, direct greenhouse gas emissions, heavy metals, antibiotics, and pathogenic organisms. Potential advantages identified include the ability to reduce manure volume and nutrients, produce biofertilizer and high protein and fat content larval biomass, and reduce environmental impact compared to composting and other protein and oil production sources, as well as, to reduce some metals, antibiotics and pathogenic organisms found in manure. On the other hand, some metals, antibiotics, bacteria, and parasites may be retained or bioaccumulated in larval biomass. Direct use of larval biomass from bioconversion of animal waste, as animal feed, is not recommended, and biofertilizer requires additional treatment before release to agricultural soil, aiming to ensure food and environmental safety.

Food systems in a zero-deforestation world: Dietary change is more important than intensification for climate targets in 2050

Global food systems contribute to climate change, the transgression of planetary boundaries and deforestation. An improved understanding of the environmental impacts of different food system futures is crucial for forging strategies to sustainably nourish a growing world population. We here quantify the greenhouse gas (GHG) emissions of global food system scenarios within a biophysically feasible “option space” in 2050 comprising all scenarios in which biomass supply – calculated as function of agricultural area and yields – is sufficient to cover biomass demand – derived from human diets and the feed demand of livestock. We assessed the biophysical feasibility of 520 scenarios in a hypothetical no-deforestation world.For all feasible scenarios, we calculate (in) direct GHG emissions related to agriculture. We also include (possibly negative) GHG emissions from land-use change, including changes in soil organic carbon (SOC) and carbon sinks from vegetation regrowth on land spared from food production. We identify 313 of 520 scenarios as feasible. Agricultural GHG emissions (excluding land use change) of feasible scenarios range from 1.7 to 12.5 Gt CO2e yr−1. When including changes in SOC and vegetation regrowth on spare land, the range is between −10.7 and 12.5 Gt CO2e yr−1. Our results show that diets are the main determinant of GHG emissions, with highest GHG emissions found for scenarios including high meat demand, especially if focused on ruminant meat and milk, and lowest emissions for scenarios with vegan diets. Contrary to frequent claims, our results indicate that diets and the composition and quantity of livestock feed, not crop yields, are the strongest determinants of GHG emissions from food-systems when existing forests are to be protected.

Improving energy and GHG performance of the rice-wheat rotation system: A life-cycle analysis based on a large-scale behavior investigation

Agricultural production is one of the crucial contributors to energy consumption and greenhouse gas (GHG) emissions. Understanding the various planting behaviors of farmers, instead of taking them as one, can be very helpful for improving crop management efficiency. This information can be used to relieve the pressures of direct and indirect energy use and GHG emissions. In this study, we took Jiangsu Province as an example to estimate the energy and GHG performance of the rice-wheat rotation system from a life-cycle perspective based on a large-scale behavior investigation of 409 samples in 2016. We further studied the influences of regional farmers’ planting characteristics on energy and GHG performance by regression models. The results indicated that farmers’ agricultural inputs varied widely among individuals and regions. Indirect energy consumption and GHG emissions, which are mainly caused by the use of fertilizers and pesticides and vary among farmers, contribute most to the life-cycle energy use and GHG emissions of the crop system in Jiangsu. The life-cycle energy consumption and GHG emissions of rice systems in Jiangsu can be effectively reduced by increasing the planting scales. Statistically, by controlling household characteristics such as the number of farmers involved in agricultural activities, age and education level of the household head, a 1-ha increase in the planting scale would lead to approximately 14.07 J/kcal and 1.676 kg CO2-e/kcal decreases in life-cycle energy consumption and GHG emissions, respectively, in Jiangsu. Policy implications are proposed to reduce and rationally use fertilizer as well as to enlarge the planting scale for sustainable agricultural development in Jiangsu.

Minimizing membrane bioreactor environmental footprint by multiple objective optimization

This paper presents a modelling study aimed at minimizing the environmental foot print of a membrane bioreactor (MBR) for wastewater treatment. Specifically, an integrated model for MBR was employed in view of the management optimization of an MBR biological nutrient removal (BNR) pilot plant in terms of operational costs and direct greenhouse gases emissions. The influence of the operational parameters (OPs) on performance indicators (PIs) was investigated by adopting the Extended-FAST sensitivity analysis method. Further, a multi-objective analysis was performed by applying the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The results show-up that the sludge retention time is the OP mostly affecting all the investigated PIs. By applying the set of optimal OPs, there was a reduction of 48% and 10% of the operational costs and direct emissions, respectively.

EMBODIED GREENHOUSE GAS EMISSIONS FOR TWO DIFFERENT TYPES OF TIRE TREAD MOLDS

In an assessment of the carbon footprint (CFP) of a tire product, embodied greenhouse gas (GHG) emissions of its tread mold are usually disregarded due to the absence of available information. This study presents embodied GHG emissions of a winter tire tread mold and evaluates its significance. We also provide a comparative study between two types of mold, namely the sector and the element mold, which are not different in terms of the tread forming in the production process, but subject to the customer’s utilization. The assessment was performed according to the international ISO/DIS 14067 standard, requirements, and guidelines for the quantification of the CFP of products. Required input data of the processes were collected and allocated based on a tread mold production plant located in Thailand. Direct GHG emissions and indirect emissions were calculated according to the 2006 IPCC guidelines. In other indirect processes, secondary data from process-based and input-output-based data were assigned to match the best site specificity, and closer fuel mix in upstream inputs. The results obtained in this study show that the embodied GHG emissions were 5,033.36 kg CO2e for the sector mold, whereas 53.73% additional emissions were found in the dataset using the element mold. The embodied emissions estimated for the aluminum input were found to significantly influence the mold CFP. Disregarding the embodied GHG emissions during the production of a single conventional tire could result in an underestimation of 0.03% for the sector type and 0.05% for the element type. Furthermore, appropriate lifetime utilization of the tread mold could increase the contribution of the tread mold CFP.

Forecast of energy consumption and greenhouse gas emissions by road transport in Russia up to 2050

The authors make a forecast for the base (inertial), innovative and decarbonization (“1.5 degrees”) scenarios related to the Russian motor vehicle fleet using the IPCC methodology (Tiers 1–3), EMEP/EEA and other methods with account for the following factors: demographic changes, economy transition from a resource-based to a low-carbon model of development, changes in the motorization level as well as in the number of fleet vehicles and the vehicle fleet structure in terms of power unit and (energy) types and the intensity of their use, identified trends of changes in the number, energy efficiency, and eco-friendliness of passenger cars, trucks, and buses with different power units (gasoline-, diesel-, gas- or electrically-powered, hybrid) as a result of the implementation of advanced materials, information, telecommunications or logistics technologies, and mobility management.It is expected that the consumption of gasoline and diesel fuel reaching a maximum in 2030–2035, may decrease by 2050 in comparison with 2015 under the innovative scenario by 5.4 times and 12%, respectively, and under the “1.5 degrees” scenario — by 13.6 times and 1.7 times. In the given period, according to the innovative scenario, natural gas consumption is expected to increase by 6.2 times. However, if the “1.5 degrees” scenario is implemented, the consumption of natural gas as a motor fuel may stop by 2050. At the same time, natural gas can be used for the production of environmentally friendly motor fuel — hydrogen, as well as electric energy for electric vehicles. The total gross greenhouse gas emissions of the motor vehicle fleet may reach a maximum in 2030 (194 million tons of CO2) but then they will decrease by 2050 according to the inertial scenario to 189.5 million tons, the innovative scenario — to 142.6 million tons and the “1.5 degrees” scenario — to 103.1 million tons of CO2. If the “1.5 degrees” scenario is implemented, in 2050, direct greenhouse gas emissions from the combustion of petroleum motor fuels by the motor vehicle fleet will be almost 2 times less than indirect CO2 emissions from the combustion of natural gas at thermal power plants in the production of electric energy for electric vehicles.It is expected that if the Russian economy and transport switch to a low-carbon development path, decarbonization of the vehicle fleet can be achieved after 2054.

Critical metals for electromobility: Global demand scenarios for passenger vehicles, 2015–2050

Electrification of future transport sector is important to reduce direct greenhouse gas emissions and the burden on fossil fuels. The modern clean energy technologies, such as electric vehicles (EVs), contain a number of hi-tech electronics and other components that depend on a wide range of metals for their functioning. A transition to large-scale deployment of such technologies might be constrained by the limited availability of these metals in future. This study is aimed at resource criticality assessment for passenger EVs, where three main scenarios are modelled considering future demand of EVs in five geographic regions by 2050. The focus metals are aluminium (Al), cobalt (Co), copper (Cu), iron (Fe), lithium (Li), manganese (Mn), nickel (Ni), and the two rare earth elements (REEs): neodymium (Nd) and dysprosium (Dy). The scenario results show an increase in total number of EVs from 1.13 billion in 2011 to 2.6 billion in the baseline scenario, 2.55 billion in the moderate scenario, and 2.25 billion in the stringent scenario by 2050. The geological reserves of cobalt, lithium and nickel seem to face higher pressure resulting from increasing demand of these metals by EVs’ batteries. Whereas, the geopolitical supply risk factor becomes important in case of REEs due to existing market concentration. Recycling and technology substitution at various levels seem to reduce the vulnerability of EVs to increasing geological and geopolitical supply risk of metals.

Carbon footprint accounts of Pakistan: an input-output life cycle assessment model.

The Paris agreement (2015) seems a significant achievement towards a global mitigation policy to climate change. However, implementing the promised Intended Nationally Determined Contribution (INDC) targets by the participating countries has become a real challenge. In this aspect, the input-output life cycle assessment (IO-LCA) model provides an important assessment mechanism to design suitable abatement policies limiting the rising greenhouse gas (GHG) emissions. The present paper develops an IO-LCA model for Pakistan and estimates all the direct and indirect GHG emissions caused by all the production activities during all the stages of production. This task is achieved in three phases. In phase 1, the Pakistan input-output table (IOT) is constructed. In phase 2, the GHG environmental satellite accounts are created for each sector in the economy. In phase 3, the GHG emissions are linked to different categories of final demand.

Land application of pulp and paper mill sludge may reduce greenhouse gas emissions compared to landfilling

Land application of pulp and paper mill sludge (PPMS) may replace landfilling in certain jurisdictions. However, the consequences of this change in management on greenhouse gas (GHG) emissions from PPMS are unknown. Land application may also entail temporary storage by landfilling due to a timing mismatch between PPMS production and application. We quantified direct GHG emissions from landfilled PPMS (pilot scale; N-rich and N-poor types) over two snow-free seasons, and after application of previously landfilled PPMS (LPPMS; < 6-month landfilled) to a clay loam soil cropped to wheat over one snow-free season. Landfilling of N-rich PPMS induced the highest GHG emission factor (EF; 0.26 Mg CO2-equivalent Mg−1 dry PPMS) and generated substantial N2O emissions (2% of landfilled N), which are neglected by the current assessment methods. Landfilling of N-rich PPMS also resulted in the highest CH4 emissions (0.6% of landfilled C). Replacing urea with LPPMS to fulfill wheat N requirements did not change field N2O-N EFs (1.1–3.5% of applied N) and did not generate CH4. Short-term (1–2 years) GHG (CO2-equivalent) EFs with landfilled N-rich PPMS were 0.54 to 4.48 times the EFs reported in the literature for land-applied PPMS. Long-term EF estimates suggest that landfilled PPMS may increase GHG emissions by up to three times compared to land application. Further research at the industrial scale is warranted to reduce uncertainty on GHG emissions from PPMS landfill sites, fulfill sustainable development goals and determine accurate carbon credits associated with changes in PPMS management practices.

Investigation of GHG emission sources and reducing GHG emissions in a municipal wastewater treatment plant

AbstractGlobal warming and the greenhouse effect are two of the most important environmental problems. Carbon dioxide, methane, and nitrous oxide emissions are the main greenhouse gas emissions in wastewater treatment plants. In this study, the greenhouse gas emission sources in a wastewater treatment plant were determined. Direct (from fossil fuel combustion, methane emissions, and process emissions of the other greenhouse gases) and indirect emissions (primarily from electricity use) in the plant were monitored. The optimum influent characteristics and operating conditions have been defined by using Monte Carlo simulation to minimize the emissions. The results revealed that the highest direct greenhouse gas emission was observed in August with the value of 23.328 kg CO2‐eq d–1 and the lowest emission was 7.56 kg CO2‐eq d–1 measured in January. The aeration tank is a major source of greenhouse gas emissions. Indirect emission has occurred because of the anaerobic digester but the biogas has been cogenerated in the plant, so it has been ignored for the calculation. According to the simulation study, if the plant is operated under optimum operating conditions, it can emit the lowest amount of greenhouse gas emissions. The optimum removal values required for the minimum greenhouse gas emissions are 79% for chemical oxygen demand, 75% for biochemical oxygen demand, and 82% for total suspended solid. The optimum operating conditions for the aeration tank, which is the major source of emission, are 5.33 h of hydraulic retention time, 0.215 d of solid retention time, and 0.999 for food/microorganisms. © 2019 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.