Feasibility and Carbon Footprint Analysis of Lime-Dried Sludge for Cement Production

Use of bacterial binder in repair mortar for micro-crack remediation

Micro-cracks are one of the types of stone deterioration which can propagate and lead to surface detachments and larger cracks in the long run. The present study developed a sustainable and environmentally friendly infill material-biological mortar (BM), as an alternative to conventional approaches. Using a biomineralization approach, this BM was explicitly designed for healing micro-cracks (less than 2 mm) in historic travertines. To this end, the mortar was prepared using a calcifying Bacillus sp. isolated from thermal spring water resources in Pamukkale Travertines (Denizli), stone powder gathered from travertine quarries in the vicinity, and a triggering solution specifically designed to set off calcium carbonate precipitation reaction. After setup, BM was applied to micro-cracks of artificially aged test stones for testing. Scanning electron microscopy revealed calcium carbonate-coated Bacillus sp. bodies in the BM matrix, optical microscopy showed secondary calcite minerals throughout the BM applied micro-cracks, and stereomicroscopy and nanoindentation analyses demonstrated bonding of BM with stone due to microbial calcification activities. Furthermore, BM and original material contact showed a continuous and coherent structure in all samples. Within this context, BM could be considered a promising and alternative approach for the remediation of micro-cracks of historic stones. KEY POINTS: A binder was produced by the MICP of Bacillus sp. Pamukkale. Physical, mineralogical, and nanomechanical characterization demonstrated microbial calcite precipitates in BM. A significant bond was determined between the grains and matrix of BM due to Bacillus sp. calcite production activities.

Upgradation of sludge deep dewatering conditioners through persulfate activated by ferrous: Compatibility with sludge incineration, dewatering mechanism, ecological risks elimination and carbon emission performance

Serious loss of organic substances and notable release of refractory intracellular organics and cell-free antibiotic resistance genes (ARGs) caused by cell lysis are found when quick lime, FeCl₃, and cationic polyacrylamide (CPAM) were used as sludge conditioners, which is not feasible to sludge separate incineration and increases ecological risks. Therefore, persulfate oxidation through ferrous (Fe²⁺-Na₂S₂O₈) activation was applied for the upgradation of sludge conditioner in China, the specific resistance to filtration (SRF) and capillary suction time (CST) significantly decreased and the removed water increased from 40% to 54%, implying that the persulfate activated by ferrous (PAF) conditioner presents good performance in sludge dewatering. Organic matter content and heating value of sludge merely decreased, and Cl^- content in sludge simultaneously decreased with the use of the PAF conditioner, thereby effectively reducing the corrosion risk to the incinerator and showing good compatibility with sludge separate incineration. In accordance with ferrous activation, sulfate radical plays an important role in sludge dewatering process because remarkable decrease in polysaccharides and protein contents from tightly bound extracellular polymeric substances (TB-EPS) was discovered. Based on flow cytometry analysis, slight cell lysis presented better filtrate quality by the use of PAF conditioner, 49.3% of refractory intracellular organics was removed and the respective ermB, tetW and blaTEM decreased by factors of 37.3%, 54.5% and 63.6% due to the strong oxidizing property of sulfate radical. The intensive decrease in refractory intracellular organics and cell-free ARGs will reduce the ecological risks. The total carbon emission significantly decreases to 1771.1 kgCO₂/tDS when PAF conditioner was employed, which is beneficial to the upgradation of sludge deep dewatering conditioners.

Structural Equation Model of Factors Influencing the Selection of Industrial Waste Disposal Service in Cement Kilns

Industrial waste disposal in a cement kiln is an operation that includes waste disposal as well as the conversion of waste into renewable energy, which is a cement industry in many countries. This research studied business factors related to the intention to use co-processing industrial waste disposal service in cement kilns by surveying the data with questionnaires from 1251 customers nationwide. The objectives of this research were to study the relationship of business factors by using structural equation modeling to analyze factors influencing the selection of industrial waste disposal service in cement kilns. The study results found that customer attitude towards the following factors, including perceived ease of use, perceived usefulness, disposal price, service provider location, promotion, people, and a service provider’s infrastructure, influenced intention to use the service. The variables that customers gave importance to were the industrial waste disposal with zero wastes to landfill and the use of industrial waste relevant to the circular economy by using the industrial waste, which has a quality of renewable fuel in cement kiln as the renewable fuel of the cement furnace. According to the research results, service providers in cement kilns can potentially plan service strategies to achieve sustainability for further business operations in a highly competitive market.

The Tapio Decoupling Principle and Key Strategies for Changing Factors of Chinese Urban Carbon Footprint Based on Cloud Computing

The expansion of Xi’an City has caused the consumption of energy and land resources, leading to serious environmental pollution problems. For this purpose, this study was carried out to measure the carbon carrying capacity, net carbon footprint and net carbon footprint pressure index of Xi’an City, and to characterize the carbon sequestration capacity of Xi’an ecosystem, thereby laying a foundation for developing comprehensive and reasonable low-carbon development measures. This study expects to provide a reference for China to develop a low-carbon economy through Tapio decoupling principle. The decoupling relationship between CO₂ and driving factors was explored through Tapio decoupling model. The time-series data was used to calculate the carbon footprint. The auto-encoder in deep learning technology was combined with the parallel algorithm in cloud computing. A general multilayer perceptron neural network realized by a parallel BP learning algorithm was proposed based on Map-Reduce on a cloud computing cluster. A partial least squares (PLS) regression model was constructed to analyze driving factors. The results show that in terms of city size, the variable importance in projection (VIP) output of the urbanization rate has a strong inhibitory effect on carbon footprint growth, and the VIP value of permanent population ranks the last; in terms of economic development, the impact of fixed asset investment and added value of the secondary industry on carbon footprint ranks third and fourth. As a result, the marginal effect of carbon footprint is greater than that of economic growth after economic growth reaches a certain stage, revealing that the driving forces and mechanisms can promote the growth of urban space.

Valorization of Tropical Biomass Waste by Supercritical Fluid Extraction Technology

The inception of sustainable and cleaner extraction technology has paved the way for the innovative development of nonconventional extractions, such as supercritical fluid extraction, apart from conventional extraction counterparts. The concept of biomass waste-to-wealth for the conversion of biomass waste or by-products into value-added products for diversified applications had piqued the prominent interest of researchers and industry players, especially with the abundance of biomass resources readily available in tropical regions that have yet to be tapped into to reach their full potential. In this paper, a critical review of the developments of supercritical fluid technology from its initial inception up to commercialized scalability, including its limitations, extraction of potential tropical biomass wastes for various types of applications, such as biopesticides, bio-repellents, phenolics, and lipids for biofuel, and its role in circular bioeconomy and sustainable development approaches, are discussed in detail.