A comparative estimate of life cycle greenhouse gas emissions from two types of constructed wetlands in Tianjin, China

Identifying a sustainable rice-based cropping system via on-farm evaluation of grain yield, carbon sequestration capacity and carbon footprints in Central China

Greenhouse gas emission in constructed wetlands for wastewater treatment: A review

Life cycle assessment of primary energy demand and greenhouse gas (GHG) emissions of four propylene production pathways in China

Life cycle assessment of vertical and horizontal flow constructed wetlands for wastewater treatment considering nitrogen and carbon greenhouse gas emissions

Aluminum production is a major energy consumer and important source of greenhouse gas (GHG) emissions globally. Estimation of the energy consumption and GHG emissions caused by aluminum production in China has attracted widespread attention because China produces more than half of the global aluminum. This paper conducted life cycle (LC) energy consumption and GHG emissions analysis of primary and recycled aluminum in China for the year 2020, considering the provincial differences on both the scale of self-generated electricity consumed in primary aluminum production and the generation source of grid electricity. Potentials for energy saving and GHG emissions reductions were also investigated. The results indicate that there are 157,207 MJ of primary fossil energy (PE) consumption and 15,947 kg CO2-eq of GHG emissions per ton of primary aluminum ingot production in China, with the LC GHG emissions as high as 1.5–3.5 times that of developed economies. The LC PE consumption and GHG emissions of recycled aluminum are very low, only 7.5% and 5.3% that of primary aluminum, respectively. Provincial-level results indicate that the LC PE and GHG emissions intensities of primary aluminum in the main production areas are generally higher while those of recycled aluminum are lower in the main production areas. LC PE consumption and GHG emissions can be significantly reduced by decreasing electricity consumption, self-generated electricity management, low-carbon grid electricity development, and industrial relocation. Based on this study, policy suggestions for China’s aluminum industry are proposed. Recycled aluminum industry development, restriction of self-generated electricity, low-carbon electricity utilization, and industrial relocation should be promoted as they are highly helpful for reducing the LC PE consumption and GHG emissions of the aluminum industry. In addition, it is recommended that the central government considers the differences among provinces when designing and implementing policies.

Treatment of fishpond water by recirculating horizontal and vertical flow constructed wetlands in the tropics

New insights in correlating greenhouse gas emissions and microbial carbon and nitrogen transformations in wetland sediments based on genomic and functional analysis

Abstract. The removal efficiency of carbon (C) and nitrogen (N) in constructed wetlands (CWs) is very inconsistent and frequently does not reveal whether the removal processes are due to physical attenuation or whether the different species have been transformed to other reactive forms. Previous research on nutrient removal in CWs did not consider the dynamics of pollution swapping (the increase of one pollutant as a result of a measure introduced to reduce a different pollutant) driven by transformational processes within and around the system. This paper aims to address this knowledge gap by reviewing the biogeochemical dynamics and fate of C and N in CWs and their potential impact on the environment, and by presenting novel ways in which these knowledge gaps may be eliminated. Nutrient removal in CWs varies with the type of CW, vegetation, climate, season, geographical region, and management practices. Horizontal flow CWs tend to have good nitrate (NO3−) removal, as they provide good conditions for denitrification, but cannot remove ammonium (NH4+) due to limited ability to nitrify NH4+. Vertical flow CWs have good NH4+ removal, but their denitrification ability is low. Surface flow CWs decrease nitrous oxide (N2O) emissions but increase methane (CH4) emissions; subsurface flow CWs increase N2O and carbon dioxide (CO2) emissions, but decrease CH4 emissions. Mixed species of vegetation perform better than monocultures in increasing C and N removal and decreasing greenhouse gas (GHG) emissions, but empirical evidence is still scarce. Lower hydraulic loadings with higher hydraulic retention times enhance nutrient removal, but more empirical evidence is required to determine an optimum design. A conceptual model highlighting the current state of knowledge is presented and experimental work that should be undertaken to address knowledge gaps across CWs, vegetation and wastewater types, hydraulic loading rates and regimes, and retention times, is suggested. We recommend that further research on process-based C and N removal and on the balancing of end products into reactive and benign forms is critical to the assessment of the environmental performance of CWs.

Application of a full-scale newly developed stacked constructed wetland and an assembled bio-filter for reducing phenolic endocrine disrupting chemicals from secondary effluent

Greenhouse gas (GHG) arising from the treatment of domestic sewage in the developed world is known to contribute to GHG emissions in the atmosphere – principally carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Accounting protocols exist that allow development of emissions inventories on a geographic, utility, or facility-specific basis using uniform methodologies and assumptions. This thesis develops new, improved methodologies for estimating direct GHG emissions sources from: 1) Sewer CH4, 2) Anthropogenic CO2 from methanol use for nutrient removal, and 3) CH4 from incomplete digester gas combustion. The significance of these GHG sources is estimated herein on a national scale for centralized wastewater treatment in the United States (US). Current GHG-emissions-inventorying protocols consistently ignore sewer CH4.However, by the methods in this thesis, sewer CH4 is estimated to represent between 26% and 35% of DC Water’s and more than 54% of centralized-wastewater-related direct GHG emissions in the US. A new sewer CH4 methodology developed in this thesis uses sewer hydraulic models at average flow rates to classify pipe segments as either gravity or surcharged sewers. CH4 generation in surcharged segments is derived using a prior forcemain algorithm while gravity sewers are modelled using a new algorithm. After method verification using exhaust-CH4 mass fluxes from an odour-control fan evacuating air from a regional sewer, the methodology is applied to the entire DC Water (Washington, DC - US) collection system to estimate utility-wide sewer CH4 emissions, which are found to be substantial.Similarly, until recently, GHG-accounting protocols also ignored CO2 emissions attributable to methanol addition for nutrient removal. As most methanol is derived from natural gas, its carbon represents an anthropogenic CO2 emission when released. In this thesis, a site-specific method is developed for DC Water and used to determine that methanol CO2 represents 40% and 60% of DC Water’s direct GHG emissions, before and after anaerobic-digestion upgrades, respectively. When applied to the US treated wastewater flows, considering likely effluent-nitrogen requirements and presence of and/or lack of digestion that would influence methanol use, methanol CO2 is estimated to account for nearly 12% of the country’s centralized-wastewater-treatment GHG emissions.A new method is also developed to account for fugitive CH4 from digester-gas combustion based on a specific end uses of the biogas. This method contrasts with current protocols which uniformly suggest that 1 to 2% of all produced digester gas is vented to the atmosphere (whether through incomplete combustion or simply leakage is unclear). Use of the new methodology could, depending on the biogas-use technologies in operation, more accurately replace a 1% protocol-based estimation of 4,200 MT CO2e/year for DC Water with emission rates ranging from 60 to over 21,000 MT CO2e/year. Accordingly, current protocol-based simplifications are shown to result in an actual 70-time overestimation for DC Water or a possible 5-times underestimation for the poorest-efficiency biogas-combustion devices: conventional, candle-stick flares.As the final subject of this thesis, electricity use, which comprises the largest portion of centralized-treatment GHG emissions inventories, is reviewed. GHG emissions from electricity consumption occur at the power plant, and their make-up and carbon intensity is a function of how that plant produces electricity. While local electricity carbon intensity is normally beyond the control of the wastewater utility, how much is purchased is largely under its control. Aeration-blower and total-plant power consumption over one or two years for 13 large to very-large facilities in New York City (NY - US) are correlated to average flow and total-oxygen-demand loading and removal to evaluate electricity-use metrics. Additionally, the local carbon intensity of power is shown to dramatically impact the magnitude of GHG emissions and to have surprising effects on an example “sustainability-enhancing” upgrade.This research discusses these improved GHG-accounting methodologies and evaluates their significance using large-scale utility process and GHG data. When combined, application of new sewer CH4 and methanol CO2 methods herein would roughly triple direct GHG emissions attributed to an industry that already represents a significant GHG source and energy consumer. An improved understanding of emissions intensity and the significance of various emissions sources would allow an already proactive wastewater industry to better target or incorporate intervention strategies that mitigate GHG emissions. This thesis offers these improved methodologies while providing evidence that: 1) GHG accounting science is far from fully understood; 2) additional research is warranted; so that 3) the industry’s understanding and GHG emissions baselines are accurate and thereby support almost-certain eventual regulation.

Three pilot-scale two-stage hybrid constructed wetlands were evaluated in order to compare their efficiency for total coliforms (TCol) and Escherichia coli removal and to analyze their performances in two 1-year periods of experimentation. System I consisted of a horizontal flow (HF) constructed wetland (CW) followed by a stabilization pond. System II was also configured with a HF CW as a first stage which was then followed by a vertical flow (VF) CW as a second stage. System III was configured with a VF CW followed by a HF CW. In the first year of evaluation, the HF-VF system was the most effective for TCol removal (p < 0.05) and achieved a reduction of 2.2 log units. With regard to E. coli removal, the HF-VF and VF-HF systems were the most effective (p < 0.05) with average reductions of 3.2 and 3.8 log units, respectively. In the second year, the most effective were those with a VF component for both TCol and E. coli which underwent average reductions of 2.34-2.44 and 3.44-3.74 log units, respectively. The reduction achieved in E. coli densities, in both years, satisfy the World Health Organization guidelines that require a 3-4 log unit pathogen reduction in wastewater treatment systems.

A review on the main affecting factors of greenhouse gases emission in constructed wetlands

A review on the occurrence, fate and removal of steroidal hormones during treatment with different types of constructed wetlands

Carbon footprint of a conventional wastewater treatment plant: An analysis of water-energy nexus from life cycle perspective for emission reduction

Introducing demand to supply ratio as a new metric for understanding life cycle greenhouse gas (GHG) emissions from rainwater harvesting systems