Reduction in greenhouse gas emissions from sludge biodrying instead of heat drying combined with mono-incineration in China

Life cycle assessment of greenhouse gas emissions of typical sewage sludge incineration treatment route based on two case studies in China

The rapidly increasing amount of municipal sewage sludge generated in China necessitates a thorough examination and evaluation of available treatment options. In recent years, thermal-drying and incineration technology has gained popularity, however, it may lead to significant greenhouse gas (GHG) emissions. Nevertheless, the differences in boundary conditions and technological characteristic across various cases may affect emission levels significantly. Therefore, this study utilizes a life cycle assessment to estimate the GHG emissions associated with two typical sludge incineration routes in China: direct thermal-drying combined with coal co-incineration incinerator in Case 1 and indirect thermal-drying and self-sustain combustion in Case 2. The entire treatment processes, containing different functional units, were comprehensively investigated. The results demonstrate that Case 1 and Case 2 produce 1133.33 and 350.89 kg CO₂-eq/tDS (sludge dry solid) of GHG emissions, respectively. In Case 1, coal co-incineration produces 828.63 kg CO₂-eq/tDS of GHG emissions, accounting for 73.1% of the total GHG emissions. Moreover, the exhaust gas treatment is a significant GHG emission source, accounting for 9.2% and 16.9% of the total GHG emissions in Case 1 and Case 2, respectively. Additionally, the sludge thickening and dewatering unit in Case 2 produces 213.75 kg CO₂-eq/tDS of GHG emissions, accounting for 60.9% of the total GHG emissions. Analysis of energy flow and heat balance characteristics indicate that the indirect heat transfer method used in thermal-drying leads to significant heat loss, which limits heat recovery potential and hinders GHG emission reduction. This study proposed a scenario case based on Case 2, addressing the issues with the improvement of heat transfer process and reduction of electricity consumption, potentially reducing GHG emissions by 8.8%. Additionally, applying an exhaust gas heat recovery system could further offset up to 22.8% of the total GHG emission.

Freeze-thaw vacuum treatment of landfill sludge: Mechanism of uneven frost heaving and dewatering performance

The method of freeze-thaw combined with vacuum pretreatment for landfill sludge (LS) has attracted extensive attention. However, most of the existing approaches are based on small-scale laboratory testing, and further testing studies must be performed to realize in situ treatment. To enhance the practicality of such approaches, the range of temperature effects on LS was analysed after field freeze-thaw model testing. After the freeze-thaw model test, samples were transported to the laboratory for unidirectional oedometer tests, and the remaining samples were retained in the field to continue vacuum model testing for exploring the differences in the consolidation and drainage effect of the LS. Results show that temperature changes during freeze-thaw process affect the distribution of sludge and water in the model boxes, resulting in frost heave and the appearance of "extrusion rings". In addition, the coefficient of consolidation obtained from the unidirectional oedometer test shows that the consolidation coefficient is generally larger near the freezing tubes at a lower temperature. The settlement determined from the field vacuum preloading test shows that the subsequent vacuum consolidation settlement is larger at the position with a lower elevation of the frozen sludge surface. The comparison indicates that the consolidation and drainage effect in the field is not as significant as that in the laboratory. The findings can provide reference to optimize the field conditions during the in situ engineering practice of sludge treatment.

Multidimensional analysis of global climate change: a review

Even though climate change involves much more than warming, it is the name given to a set of physical phenomena. It is a long-term change in weather patterns that characterises different regions of the world. The warming effect in the earth's atmosphere has dramatically increased through the influence of some heat-taping gases emitted by various human activities, especially fossil fuel burning. The more the input of such gases, the more will be the warming effect in the coming times. Global climate change is already visible in various parts of the larger ecosystems like forests, fisheries, biodiversity, and agriculture; however, it is now also influencing the supply of freshwater, human health, and well-being. This paper reviews climate change drivers, its global scenario, major global events, and assessing climate change impacts. The most daunting problem of economic and ecological risks, along with the threats to humanity, is also discussed. The paper further reviews the species' vulnerability to climate change and the heat waves and human migration vis-à-vis climate change. Climate change politics and coverage of climate change episodes in mass media is the special focus of this review that concludes with a few mitigation measures.

Co-biodrying of sewage sludge and organic fraction of municipal solid waste: Role of mixing proportions

This study investigated the performance of co-biodrying sewage sludge and organic fraction of municipal solid waste (OFMSW) at different proportions. Cornstalk was added at 15% (of total wet weight) as the bulking agent. Results show that increasing OFMSW percentage promoted the biodegradation of organic matter, thus enhancing the temperature integration value and water removal to above 75% during sludge and OFMSW co-biodrying. In particular, adding more OFMSW accelerated the biodegradation of soluble carbohydrates, lignins, lipids, and amylums, resulting in more organic loss and thus lower biodrying index (3.3-3.7 for 55-85% OFMSW). Water balance calculation indicated that evaporation was the main mechanism for water removal. Heat used for water evaporation was 37.7-48.6% of total heat consumption during co-biodrying. Our results suggest that sludge and OFMSW should be mixed equally for their efficient co-biodrying.