Effect of fine coal gasification slag on improvement of bacterial diversity community during the pig manure composting

Coal gasification crude slag based complex flocculants by two-step acid leaching process: synthesis, flocculation and mechanisms

Coal gasification crude slag (CGCS) is the side-product of the coal gasification process, and its effective utilization has attracted great attention. A novel flocculant of poly-aluminum-ferric-acetate-chloride (PAFAC) was synthesized based on the recovery of CGCS by a two-step acid leaching process, namely HCl-acid leaching and HAc-acid leaching, which was optimized by an acid leaching liquor volume ratio of HCl to HAc of 3 : 2, polymerization pH of 3.5, and reaction temperature and time of 70 °C and 3.0 h, respectively. The performance of PAFAC was further evaluated by kaolin simulated wastewater, domestic sewage, river water, and aquaculture wastewater. The results revealed that PAFAC was feasible for the removal of turbidity, chemical oxygen demand (COD) and total phosphorus (TP). Moreover, PAFAC was characterized by X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence spectrometry (XRF) and scanning electron microscopy (SEM), which proved that PAFAC was a kind of amorphous polyionic composite. Additionally, the acid leaching kinetics and flocculation mechanisms were further investigated. It was found that the acid leaching process was followed by the unreacted shrinkage core model, and the flocculation process was dominated by charge neutralization, adsorption bridging and precipitation net trapping. The work is expected to develop a new method for the safe disposal of CGCS and provide a novel way for the preparation of Fe-Al composite flocculants, especially, offering a potential strategy for the promotion of the additional value of the coal chemical industry.

Multitudinous components recovery, heavy metals evolution and environmental impact of coal gasification slag: A review

In recent years, the coal gasification industry has rapidly developed, becoming one of the most promising technologies in the advanced and clean coal chemical industry. As a result, the annual emission of coal gasification fine slag (CGFS) has continuously increased. The present situation of CGFS is regarded as a notorious waste in gasification plants and is rudely landfilled or deposited in slag yards, which leads to a large waste of land resources, the release of dangerous elements, and numerous pollution problems. Although CGFS is classified as industrial solid waste, its unique physical and chemical properties make it a valuable resource that cannot be overlooked. This paper focuses on the resource utilization technology and environmental impact of CGFS. The resource utilization of different components of CGFS has realized the evolution from waste to valuable substances. Moreover, during the disposal and utilization of CGFS, its environmental effects cannot be ignored. The main problems and future research directions are also further proposed. Efforts should be focused on the challenges of the technology, cost, and environmental protection in the application process to achieve industrial application, and ultimately committed to sustainable and green development goals, and promote the sustainable management and conservation of resources.

Basic characteristics of magnesium-coal slag solid waste backfill material: Part I. preliminary study on flow, mechanics, hydration and leaching characteristics

The environmental damage caused by surface subsidence and coal-based solid waste (CBSW) is a common problem in the process of coal mining. Backfill mining can control the mining-induced subsidence and solve the problem of bulk solid waste storage. In the present work, a magnesium-coal slag solid waste backfill material (MCB) with modified magnesium slag (MS) as binder and CBSW (fly ash (FA), flue gas desulfurization gypsum (FDG) and coal gasification slag (CGS)) as supplementary cementitious material/aggregate was proposed to meet the needs of coal mining in Northern Shaanxi, China, to realize the comprehensive treatment of goaf and CBSW. The results show that: (1) The rheological curve of the fresh MCB slurry is highly consistent with the Herschel-Bulkley (H-B) model, and its fluidity meets the basic requirements of mine backfill pumping. With the addition of FDG and MS, the yield stress, apparent viscosity and thixotropy of MCB slurry increase, while the pseudoplastic index and slump decrease. (2) The strength of MCB develops slowly in the early stage (0∼14 days) and increases rapidly in the later stage (14∼90 days). Except for the ratio of M20F1 and FDG = 0%, the strength of samples at other ratios (at 28 days) is between 6.06∼11.68 MPa, which meets the strength requirement of 6 MPa for coal mine backfill. The addition of MS and appropriate amount of FDG is beneficial to the development of strength. In contrast, MS exhibits a significant improvement in early strength, and FDG has a significant improvement in late-age strength. (3) Corresponding to the compressive strength, the hydration products C-S(A)-H and AFt of MCB are less in the early stage and greatly increased in the later stage. The active substance in FA/CGS will undergo pozzolanic reaction with the MS hydration product CH. The addition of FDG and MS can promote the reaction and increase the amount of hydration product, but in contrast, the promotion effect of FDG is more significant. (4) The amount of heavy metal leaching of MCB meets the requirements of national standards. The hardened MCB has a solidification/stabilization effect on heavy metal elements, which can significantly reduce the amount of heavy metal leaching. The results imply that MCB is a safe, reliable, and eco-friendly solid waste backfill material, and its application is conducive to the coordinated development of coal resource mining and environmental protection.

Recent trends and advances in composting and vermicomposting technologies: A review

Composting technologies have come a long way, developing from static heaps and windrow composting to smart, artificial intelligence-assisted reactor composting. While in previous years, much attention has been paid to identifying ideal organic waste streams and suitable co-composting candidates, more recent efforts tried to determine novel process-enhancing supplements. These include various single and mixed microbial cultures, additives, bulking agents, or combinations thereof. However, there is still ample need to fine-tune the composting process in order to reduce its impact on the environment and streamline it with circular economy goals. In this review, we highlight recent advances in integrating mathematical modelling, novel supplements, and reactor designs with (vermi-) composting practices and provide an outlook for future developments. These results should serve as reference point to target adjusting screws for process improvement and provide a guideline for waste management officials and stakeholders.

Black soldier fly larvae for organic manure recycling and its potential for a circular bioeconomy: A review

Livestock farming and its products provide a diverse range of benefits for our day-to-day life. However, the ever-increasing demand for farmed animals has raised concerns about waste management and its impact on the environment. Worldwide, cattle produce enormous amounts of manure, which is detrimental to soil properties if poorly managed. Waste management with insect larvae is considered one of the most efficient techniques for resource recovery from manure. In recent years, the use of black soldier fly larvae (BSFL) for resource recovery has emerged as an effective method. Using BSFL has several advantages over traditional methods, as the larvae produce a safe compost and extract trace elements like Cu and Zn. This paper is a comprehensive review of the potential of BSFL for recycling organic wastes from livestock farming, manure bioconversion, parameters affecting the BSFL application on organic farming, and process performance of biomolecule degradation. The last part discusses the economic feasibility, lifecycle assessment, and circular bioeconomy of the BSFL in manure recycling. Moreover, it discusses the future perspectives associated with the application of BSFL. Specifically, this review discusses BSFL cultivation and its impact on the larvae's physiology, gut biochemical physiology, gut microbes and metabolic pathways, nutrient conservation and global warming potential, microbial decomposition of organic nutrients, total and pathogenic microbial dynamics, and recycling of rearing residues as fertilizer.

Humic acid characterization and heavy metal behaviour during vermicomposting of pig manure amended with 13C-labelled rice straw

Aiming to reveal the humification process of organic waste and its contribution to the heavy metal behaviour affected by earthworm activity, it was studied about the variation of humic acid (HA) and heavy metal behaviour during vermicomposting of the mixed pig manure and ¹³C-labelled rice straw. The results showed that earthworms could well adapt to the culturing environment and feed organic matter for its growth and reproduction, the vermicomposting process increased the content of humic substances (HS), HA, and fulvic acid (FA) in substrate residues, but led to less transformation of HA into FA. The elemental, ultraviolet absorption spectroscopy, Fourier transform infrared (FTIR) and fluorescence excitation-emission matrix (EEM) analysis indicated that vermicomposting led to more aromatic structures and much higher humification degree in HA, whereas less protein, FA-like substances and plastein in HA. Vermicomposting could enhance the total Cu content and decrease Cu/Zn bioavailability in the substrate residues, and vermicomposting especially can help stabilize Cu in the substrate residues by forming more complexed HA-Cu.

Effects of further composting black soldier fly larvae manure on toxic metals and resistant bacteria communities by cornstalk amendment

Rapid composting by black soldier fly larvae (BSFL) may be insufficient to maturation and humification of composting and further composting is necessary. The purpose of this study was to explore cornstalk addition on toxic metals (Cu, Zn, Pb and Cd), toxic metals resistance bacterial (TMRB) destiny and their relationship with physicochemical factors during BSFL manure composting. High-throughput sequencing was performed by six treatments, namely T1 to T6, where T1 to T3 were BSFL manures from chicken, pig and dairy manure, respectively, and T4 to T6 were same manures and utilized cornstalk to adjust C/N to 25. The results showed that cornstalk amendment could enhance the toxic metals immobilization rate compared to control treatments in the ultimate product. TMRB indicated that the major potential hosts bacteria were Firmicutes, Bacteroidota, Proteobacteria, Acidobacteriota and Actinobacteriota, and the sum relative abundance were 63.33%, 90.62%, 83.62%, 69.38%, 50.66% and 90.52% in T1 to T6 at the end of composting. Bacteria diversity and heat map revealed composting micro-ecology with additive cornstalk to remarkably effect main resistant bacterial distribution via adjusting environmental factors and potential hosts bacterial. Finally, T5 treatment was able to greatly decrease the TMRB abundance, and improve the ability of composting and ultimate product quality.

Changes of fungal diversity in fine coal gasification slag amendment pig manure composting

The purpose of this study was to investigate fungal diversity and relative abundance (RA) during pig manure composting via high-throughput sequencing approach. Fine coal gasification slag (FCGS) (0%, 2%, 4%, 6%, 8% and 10%) were added into composting raw materials as additive and performed 42 days. Adjust C/N and moisture to 30 and 65%. Results showed that dominant phyla were Ascomycota (99.62%) and Basidiomycota (0.38%). The main genera were Epicoccum (1.26%), Alternaria (83.35%), Aspergillus (12.08%) and Gibberella (1.69%). 10% treatment got the higher abundance and operational taxonomic units number from rank abundance curve and petals diagram. Compared with control, FCGS amendment composting could increase the sanitary time (3-7 d) and total nitrogen (0.05-12.03%). The principal component analysis was considered that FCGS treatments and control had significantly difference. The RA of fungi varied among all treatments. Therefore, 10% treatment was a potential candidate to enhance fungal diversity and composting quality.

Linking microbial community structure with molecular composition of dissolved organic matter during an industrial-scale composting

This study explored the interactions between dissolved organic matter (DOM) composition and microbial community structure during an industrial-scale composting by Fourier transform ion cyclotron resonance mass spectrometry and 16S rRNA sequencing analysis. The results revealed that DOM from matured compost contained primarily lignins/carboxylic-rich alicyclic molecules (73.6%), the higher double bond equivalent (5.97) and aromaticity index (0.18), indicating that the molecular composition of DOM had changed substantially. Drastic changes in microbial community structure were also observed along with the DOM transformation process of composting. Network analysis further indicated that Caldicoprobacter, Bacillus, and Dechloromonas were associated with the most DOM subcategories. Caldicoprobacter could degrade carbohydrates, Bacillus accelerated the humification by transforming N-containing compounds, and Dechloromonas could degrade polycyclic aromatic hydrocarbons distributed in low O/C. These findings are helpful for understanding the molecular mechanisms of DOM transformation and humification of sludge composting.

Contributions of the biochemical factors and bacterial community to the humification process of in situ large-scale aerobic composting

Multiple types of biochemical parameters were determined in the course of the composting process with rice straw and Chinese traditional medicine residues as substrates. The water-soluble fractions (WSFs) were analyzed by excitation-emission-matrix fluorescence (EEM-FL), and the maximum P_V/III value (1.2) was observed in thermophilic phase (THP). Bacterial community analysis results indicated that the genera with the capacity of degrading lignocellulose dominated in mesophilic phase (MEP) and THP. The metabolic pathways based on KEGG analysis revealed that the amino acid, carbohydrate and energy metabolism pathways in THP were higher than the other two phases. The correlation analysis between EEM-FL and the bacterial community revealed that the genera with high abundances in the THP were significantly positively correlated with fulvic acid-like materials and humic acid-like organics. The quantification results of the lignocellulose-degrading genes in different phases further verified the key functional bacteria obtained by correlation analysis during the composting process.