Fossil organic carbon in wastewater and its fate in treatment plants

This study reports the presence of fossil organic carbon in wastewater and its fate in wastewater treatment plants. The findings pinpoint the inaccuracy of current greenhouse gas accounting guidelines which defines all organic carbon in wastewater to be of biogenic origin. Stable and radiocarbon isotopes (¹³C and ¹⁴C) were measured throughout the process train in four municipal wastewater treatment plants equipped with secondary activated sludge treatment. Isotopic mass balance analyses indicate that 4–14% of influent total organic carbon (TOC) is of fossil origin with concentrations between 6 and 35 mg/L; 88–98% of this is removed from the wastewater. The TOC mass balance analysis suggests that 39–65% of the fossil organic carbon from the influent is incorporated into the activated sludge through adsorption or from cell assimilation while 29–50% is likely transformed to carbon dioxide (CO₂) during secondary treatment. The fossil organic carbon fraction in the sludge undergoes further biodegradation during anaerobic digestion with a 12% decrease in mass. 1.4–6.3% of the influent TOC consists of both biogenic and fossil carbon is estimated to be emitted as fossil CO₂ from activated sludge treatment alone. The results suggest that current greenhouse gas accounting guidelines, which assume that all CO₂ emission from wastewater is biogenic may lead to underestimation of emissions.     

Natural versus wastewater derived dissolved organic carbon: implications for the environmental fate of organic micropollutants

The interaction of organic micropollutants with dissolved organic carbon (DOC) can influence their transport, degradation and bioavailability. While this has been well established for natural organic carbon, very little is known regarding the influence of DOC on the fate of micropollutants during wastewater treatment and water recycling. Dissolved organic carbon-water partition coefficients (K_DOC) for wastewater derived and reference DOC were measured for a range of micropollutants using a depletion method with polydimethylsiloxane disks. For micropollutants with an octanol-water partition coefficient (log K_OW) greater than 4 there was a significant difference in K_DOC between reference and wastewater derived DOC, with partitioning to wastewater derived DOC over 1000 times lower for the most hydrophobic micropollutants. The interaction of nonylphenol with wastewater derived DOC from different stages of a wastewater and advanced water treatment train was studied, but little difference in K_DOC was observed. Organic carbon characterisation revealed that reference and wastewater derived DOC had very different properties due to their different origins. Consequently, the reduced sorption capacity of wastewater derived DOC may be related to their microbial origin which led to reduced aromaticity and lower molecular weight. This study suggests that for hydrophobic micropollutants (log K_OW > 4) a higher concentration of freely dissolved and thus bioavailable micropollutants is expected in the presence of wastewater derived DOC than predicted using K_DOC values quantified using reference DOC. The implication is that naturally derived DOC may not be an appropriate surrogate for wastewater derived DOC as a matrix for assessing the fate of micropollutants in engineered systems.     

装配式建筑施工阶段碳排放测算研究

根据碳排放系数法构建模型,结合工程量清单对装配式建筑施工阶段的碳排放进行测算, 探讨预制率对施工阶段碳排放的影响, 深入探究工程造价、总建筑面积与碳排放总量的关系。以漳州某住宅楼为例, 探讨施工阶段碳排放的排放规律并提出减排路径。 结果表明: 施工阶段的碳排放主要来自一般土建工程;单位面积的碳排放在 671 kgCO2/m2左右波动,单位造价的碳排放在 2749.33 kgCO2/万元左右波动; 混凝土工程和钢筋工程的碳排放随着预制率的升高而增加; 碳排放总量与工程造价、建筑面积存在显著的线性关系。     

An embodied carbon and energy analysis of modern methods of construction in housing: A case study using a lifecycle assessment framework

There is a growing interest in comparing the energy and consequential carbon embodied in buildings using different methods of construction and alternative materials. This paper compares the embodied carbon in a low energy, affordable house constructed using a novel offsite panellised modular timber frame system, in Norfolk UK with two traditional alternative scenarios. A lifecycle assessment (LCA) framework is used to conduct a partial LCA, from cradle to site, of the construction. An inventory of the materials and fossil fuel energy utilised in the construction was used to calculate the primary energy consumed and the associated embodied carbon. The embodied carbon was found to be 34.6 tonnes CO₂ for a 3 bedroom semi-detached house, 405 kgCO₂ per m² of useable floor area. When compared with traditional methods of construction the modern methods of construction (MMC) house resulted in a 34% reduction in embodied carbon. Despite timber being the predominant structural and cladding material, concrete is the most significant material (by proportion) in embodied carbon terms, responsible for 36% of materials related embodied carbon.     

办公建筑物化阶段CO_2排放研究

建筑物化阶段的CO2排放时间集中、绝对量大,是建筑节能减排的研究重点。构建了办公建筑物化阶段CO2排放的计算模型,包括建材、设备生产与运输的CO2排放,以及施工过程的CO2排放。利用该计算模型,分析计算了78栋办公建筑物化阶段的CO2排放量。平均来看,物化阶段的碳排放量为326.75kg/m2;随着建筑高度的增加单位面积碳排放明显增加,超高层建筑的单位面积碳排放量是多层建筑的1.5倍;土建工程的碳排放量占到物化阶段的75%左右,而钢筋、混凝土、砂浆、墙体材料的碳排放量占到了土建工程的80%以上。分别以建筑层数和建材用量为自变量做了办公建筑物化阶段CO2排放量的预测模型,通过统计学的分析对比,发现以钢筋、混凝土和墙体材料为自变量的预测公式可以很好地预测建筑物化阶段的碳排放。     

Sheep grazing in ‘lawnscape’ management: an emissions comparison with conventional ‘lawnscape’ management

The use of sheep in lawnscape management is touted as a low-carbon alternative to conventional lawnscaping; however this claim remains unsubstantiated. While conventional lawnscaping generates greenhouse gas (GHG) emissions, primarily through fuel combustion, sheep grazing produces methane (CH₄) as well as manure which releases embodied nitrogen as nitrous oxide (N₂O) as it degrades. These gases have a carbon equivalency of 25 and 298 respectively, indicating their much greater potency as GHGs relative to carbon dioxide (CO₂). This paper is the first to critically profile and compare GHG emissions produced by grazing and conventional lawnscape management. It discusses critical factors affecting the carbon footprint of both practices, and develops a framework for evaluating lawnscape management emissions. This study finds that replacing lawnmowers and the treatment and application of compost with a grazing regime can reduce net lawnscape management emissions by 34–37%, or 980 kgCO₂e/ha/year.     

Life cycle emissions analysis of two nZEB concepts

The net-zero emissions building (nZEB) performance is investigated for building operation (EO) and embodied emissions in materials (EE) for Norway's cold climate. nZEB concepts for new residential and office buildings are conceived in order to understand the balance and implications between operational and embodied emissions over the building's life. The main drivers for the CO₂ equivalent (CO₂e) emissions are revealed for both building concepts through a detailed emissions calculation. The influence of the CO₂e factor for electricity is emphasized and it is shown to have significant impact on the temporal evolution of the overall CO₂e emissions balance. The results show that the criterion for zero emissions in operation is easily reached for both nZEB concepts (independent of the CO₂e factor considered). Embodied emissions are significant compared to operational emissions. It was found that an overall emissions balance including both operational and embodied energy is difficult to reach and would be unobtainable in a scenario of low carbon electricity from the grid. In this particular scenario, the net balance of emissions alone is nonetheless not a sufficient performance indicator for nZEB.     

Post‐construction liability and insurance

A new method for stochastic embodied greenhouse gas emissions modelling of construction materials is proposed. The method progressively integrates process analysis data into a prior probability distribution of embodied greenhouse gas emissions for a given material drawn from a disaggregated expansion of the UK Environmental Accounts. Current analyses of embodied CO_2eq emissions, whether performed at the economic sector or individual building system boundary level, are deterministic. Such deterministic models do not allow for the easy analysis of potential CO_2eq emissions reductions obtainable through preferential selection of low embodied CO_2eq material suppliers within material supply chains. Such analyses are important for assessing the extent to which emissions reductions can be achieved through economic mechanisms which drive preferential selection of low embodied carbon materials back through the supply chain - such as carbon taxes. It is argued that the need for estimating both the uncertainty, and the variability, in embodied CO_2eq data is best addressed through the development of a fully stochastic modelling framework, and that such frameworks are methodologically more appropriate for Kyoto Protocol compliance policy formulation. Cet article traite d'une nouvelle méthode de modélisation stochastique des émissions de gaz à effet de serre intrinsèque applicable aux matériaux de construction. Elle intègre progressivement des données résultant d'analyses de procédés dans une distribution de probabilité préalable d'émissions de gaz à effet de serre intrinsèque pour un matériau donné tiré d'une expansion désaggrégée des Environmental Accounts du Royaume Uni. Les analyses actuelles des émissions de CO_2eq intrinsèque, réalisées soit au niveau du secteur économique soit à celui de la limite des systèmes de construction individuels, sont déterministes. De tels modèles déterministes ne permettent pas d'analyser facilement les réductions des émissions de CO_2eq potentielles que l'on pourrait obtenir via une sélection préférentielle de fournisseurs de matériaux à faible CO_2eq intrinsèque au sein de chaônes d'approvisionnement de matériaux. De telles analyses sont importantes pour évaluer dans quelle mesure ces réductions d'émissions peuvent être réalisées au moyen de mécanismes économiques qui renvoient la sélection préférentielle de matériaux à faible teneur en carbone intrinsèque vers la chaône d'approvisionnement, comme la taxe sur les hydrocarbures. On prétend que le besoin d'estimer à la fois l'incertitude et la variabilité dans les données relatives au CO^2eq intrinsèque est mieux appréhendé par le développement d'un cadre de modélisation entièrement stochastique et que de tels cadres sont méthodologiquement plus appropriés pour la formulation de principes conformes au Protocole de Kyoto.     

Assessing the marginal cost of reducing greenhouse gas emissions in the English and Welsh water and sewerage industry: A parametric approach

Reducing greenhouse gas (GHG) emissions involves effort from different sectors of the economy, including the water and sewerage industry. This study estimates the marginal cost of curtailing GHG emissions in the water and sewerage industry using stochastic frontier analysis techniques for a sample of ten English and Welsh water and sewerage companies over the 2010–2019 period. Results illustrated that the average marginal cost of reducing GHG emissions was 0.181 £/Kg CO₂ equivalent. The marginal cost estimated notably differs across companies and over time. Findings further illustrate the impact of water companies' operating characteristics on the marginal cost of reducing carbon emissions.     

An environmental assessment of wood and steel reinforced concrete housing construction

Wooden type of housing is ubiquitous in Japan. It is the main structure for housing; however, due to the increase in residential developments, steel reinforced concrete houses are also on the rise. This paper assesses the environmental impacts of these two types of construction. An evaluation of the two types of construction in terms of energy usage and air emissions is done. A comparison of the damage costs due to the generated emissions is also considered. Four types of emissions generated are evaluated, namely carbon emissions (CO₂), nitrogen oxides (NO_x), sulfur oxides (SO_x) and suspended particulate matter (SPM). The life cycle of the two different housing construction types is traced and environmental impacts are determined. External costs are also calculated. Furthermore, different improvement assessment scenarios are simulated to ascertain several emission reduction possibilities. The study looks into the emitted emissions from the housing construction to its final disposal of a typical residential development in Saga, Japan. Results show that much of the environmental impacts from building a house are on the Global Warming Potential due to high carbon emissions. Moreover, the construction phase generated the highest pollutant emissions from nitrogen oxides, sulfur oxides and suspended particulate matter. Steel reinforced concrete (SRC) construction has a higher environmental impact compared to the wooden type of housing construction. A longer design life for a residential house gives a reduction of about 14% in carbon emissions. Using solar energy for the operation phase has gained a reduction of 73% in the total life cycle carbon emissions.     

基于BIM和云技术的建筑物化阶段碳排放协同管理研究

建筑物化阶段是建筑节能减排的重点,首先界定建筑物化阶段碳排放核算范围,然后基于协同工作原理,利用BIM和"云"技术进行建筑物化阶段碳排放体系设计。最后阐述建筑物化阶段建设单位、设计单位、施工单位和监理单位等参建方碳排放的协同管理,为建筑项目全生命周期碳排放协管理提供参考。     

Understanding embodied greenhouse gas emissions in the water and sewerage sectors

Embodied (or embedded) greenhouse gas emissions are commonly overlooked in corporate carbon accounting, although they can represent a large proportion of overall emissions. In this paper, we utilise embodied emission data submitted to Ofwat, the economic regulator of water and sewerage companies in England and Wales, as part of their review of price limits. This is the first time that water and sewerage companies have presented embodied emissions associated with their capital programmes. In total, embodied emissions add an extra 50% on top of companies' operational greenhouse gas emissions. We consider the drivers for embodied emissions and show that capital maintenance programmes are the largest source. We highlight the relationship between capital expenditure and embodied emissions, and discuss why there are significant differences in embodied emission intensities between companies. Many of the differences arise from the way the common methodology for estimating embodied emissions is applied.     

Estimation of greenhouse gas emissions from municipal wastewater treatment systems in India

Greenhouse gas (GHG) emissions generated from municipal wastewater treatment plants in India is estimated in this study. The emissions from the wastewater treatment process as well as from the electricity used during the treatment process are estimated by using the methodology of Intergovernmental Panel on Climate Change. The present treatment plants of capacity 15 997 million litres per day (MLD) contributes towards GHG emissions of 7.3 Mt of CO₂‐eq/year. The future GHG emissions would depend upon the treatment technology used for treating 34 109 MLD of untreated wastewater. The highest GHG emissions would occur if all new wastewater treatment plants are based on upflow anaerobic sludge blanket technology, 19.66 Mt CO₂‐eq/year and lowest if sequential batch reactor technology is adopted, 2.93 MtCO₂‐eq/year.     

Embodied energy analysis of the indirect solar drying unit

The increase in cost of fossil fuel and unavailability of electricity are the barrier for farmers to run their farm machineries and their development. Solar drying is a technique that not only helps in reducing fossil fuels and greenhouse gas emission by avoiding the use of machines in this sector, but also reduces the post-harvest food losses too. In present study, embodied energy analysis has been done for indirect solar dryer unit. Fenugreek leaves of 02?kg were put in each tray inside indirect solar dryer unit for drying purposes. Various environmental and economic parameters have been evaluated, which includes the payback period by cost, the energy payback time (EPBT), embodied energy, CO₂ emission and the earned carbon credit. The total embodied energy of the system is 1081.83?kWh. The EPBT and CO₂ emission are found to be 4.36 years and 391.52?kg per year, respectively.     

Towards a common carbon footprint assessment methodology for the water sector

This paper describes the carbon footprint methodology used in assessing the global warming potential of the Dutch water sector. The assessment includes CO₂ emissions from energy consumption and methane and nitrous oxide emissions from water treatment processes. There is, however, debate on the amounts and mechanism of greenhouse gas (GHG) emissions, and a standardised approach is discussed. As a result of this approach, the contribution of GHG emissions to the total carbon footprint of the Dutch water sector appeared to be relatively high. Next to the lack of common emission factors for GHG and chemicals used, there is also no agreed‐upon approach related to the system boundaries and scope of carbon footprinting of the water cycle. For reasons of benchmarking and monitoring of climate change reduction targets, a common carbon footprint assessment methodology for the water sector will be required.     

Embodied and operational carbon dioxide emissions from housing: A case study on the effects of thermal mass and climate change

A 100-year lifecycle carbon dioxide (CO₂) emissions analysis is reported for a two-bedroom, 65 m² floor area, semi-detached house in south-east England. How the balance between the embodied (ECO₂) and operational CO₂ emissions of the building are affected by the inclusion of thermal mass and the impacts of climate change is quantified. Four ‘weights’ of thermal mass were considered, ranging from lightweight timber frame to very heavyweight concrete construction. For each case, total ECO₂ quantities were calculated and predictions for operational CO₂ emissions obtained from a 100-year dynamic thermal modelling simulation under a medium-high emissions climate change scenario for south-east England. At the start of the lifecycle, the dwellings were passively cooled in summer, but air conditioning was installed when overheating reached a certain threshold. The inclusion of thermal mass delayed the year in the lifecycle when this occurred, due to the better passive control of summertime overheating. Operational heating and cooling energy needs were also found to decrease with increasing thermal mass due to the beneficial effects of fabric energy storage. The calculated initial ECO₂ was higher in the heavier weight cases, by up to 15% (4.93 t) of the lightweight case value, but these difference were offset early in the lifecycle due to the savings in operational CO₂ emissions, with total savings of up to 17% (35.7 t) in lifecycle CO₂ found for the heaviest weight case.     

基于离散仿真的钢结构工程施工碳排放计量研究

施工过程碳排放是建筑物全生命周期碳排放的重要组成部分,对施工碳排放的优化控制可带来较大的减排效应。通过对施工过程的动态碳排放特性分析,构建了基于离散事件仿真的施工碳排放计量模型和方法,选用某展馆钢结构桁架拼吊装工程进行实例分析,设计了 3 种施工方案情景,共 36 种机械配置方案,分别进行离散仿真模拟,从碳排放、成本、进度3 个目标分别进行了统计和情景对比分析,实现了施工碳排放的准确测评以及低碳约束下施工方案的优选,是对传统碳排放计量方法的补充和完善。     

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

Life cycle assessment (LCA) is used to compare the environmental impacts of vertical flow constructed wetlands (VFCW) and horizontal flow constructed wetlands (HFCW). The LCAs include greenhouse gas (N₂O, CO₂ and CH₄) emissions. Baseline constructed wetland designs are compared to different treatment performance scenarios and to conventional wastewater treatment at the materials acquisition, assembly and operation life stages. The LCAs suggest that constructed wetlands have less environmental impact, in terms of resource consumption and greenhouse gas emissions. The VFCW is a less impactful configuration for removing total nitrogen from domestic wastewater. Both wetland designs have negligible impacts on respiratory organics, radiation and ozone. Gaseous emissions, often not included in wastewater LCAs because of lack of data or lack of agreement on impacts, have the largest impact on climate change. Nitrous oxide accounts for the increase in impact on respiratory inorganic, and the combined acidification/eutrophication category. The LCAs were used to assess the importance of nitrogen removal and recycling, and the potential for optimizing nitrogen removal in constructed wetlands.     

Construction sector views on low carbon building materials

As is the case in a number of countries, the UK construction industry faces the challenge of expanding production whilst making ambitious greenhouse gas emission reductions. Embodied carbon constitutes a growing proportion of whole-life carbon emissions and accounts for a significant share of total UK emissions. A key mitigation strategy is increasing the use of alternative materials with lower embodied carbon. The economic, technical, practical and cultural barriers to the uptake of these alternatives are explored through a survey of construction professionals and interviews with industry leaders. Perceptions of high cost, ineffective allocation of responsibility, industry culture, and the poor availability of product and building-level carbon data and benchmarks constitute significant barriers. Opportunities to overcome these barriers include earlier engagement of professionals along the supply chain, effective use of whole-life costing, and changes to contract and tender documents. A mounting business case exists for addressing embodied carbon, but has yet to be effectively disseminated. In the meantime, the moral convictions of individual clients and practitioners have driven early progress. However, this research underscores the need for new regulatory drivers to complement changing attitudes if embodied carbon is to be established as a mainstream construction industry concern.     

Using dynamic simulation to quantify the effect of carbon-saving measures for a UK supermarket

A standard UK supermarket design is used to simulate the energy performance, and subsequent CO₂ emissions, of a modern-day UK supermarket building. Retrofit measures are proposed to reduce these CO₂ emissions by over 50%, mostly due to demand-side measures but also accounting for likely onsite supply-side solutions. The influence of refrigeration and lighting in such buildings is explored and the possible use of heat recovery systems discussed. The air-tightness of supermarket buildings is also highlighted as a potential area for significant energy savings. Finally, the reliance on grid electricity is demonstrated for non-domestic buildings with a high electrical energy use. A combined approach of energy efficiency and low-carbon offsite electrical generation is suggested from the described case study as the most successful strategy to achieve large carbon savings (i.e. >50%) in existing supermarket buildings.