Effect of calcium peroxide dosage on organic matter degradation, humification during sewage sludge composting and application as amendment for Cu (II)-polluted soils

Microbial inoculant accelerated pig slurry maturation at low-temperature anaerobic digestion: Performance and mechanism

This study investigated the impact of microbial inoculants on maturing pig slurry during anaerobic digestion (AD) at psychrophilic temperatures (10 °C). A simulation experiment was conducted with two treatments: pig slurry alone (CK) and pig slurry supplemented with microbial inoculants (MA). The MA treatment achieved faster maturity than CK, as evidenced by an improved germination index (achieving 70 % in advance) and a reduced content of organic pollutants, which was attributed to an increased relative abundance of hydrolytic microorganisms (7-21 %) and decreased pathogens (6-9 %) at the early stage (<42 (d)). Microbial inoculants influenced pig slurry microorganisms by serving as keystone taxa (B_OTU229 (f_Ruminococcaceae) and F_OTU76 (s_Acremonium alcalophilum)), and stimulating new keystone taxa (B_OTU423 (g_NK4A214) and F_OTU25 (g_Clavulina)) through associative interactions, thereby intensifying saprotrophic and carbon cycling processes, and accelerating maturation. These results provide a biological strategy for maturing pig slurry and help elucidate the mechanisms underlying microbial effects.

Improved humification and Cr(VI) immobilization by CaO2 and Fe3O4 during composting

The current research studied how Fe3O4 nanomaterials (NMs) and CaO2 affect humification and Cr(VI) immobilization and reduction during the composting of oil-tea Camellia meal and Cr-contaminated soil. The results showed that Fe3O4 NMs and CaO2 successfully construct a Fenton-like reaction in this system. The excitation-emission matrix-parallel factor (EEM-PARAFAC) demonstrated that this Fenton-like treatment increased the generation of humic acids and accelerated the humification. Meantime, RES-Cr increased by 5.91 % and Cr(VI) decreased by 16.36 % in the treatment group with CaO2 and Fe3O4 NMs after 60 days. Moreover, the microbial results showed that Fe3O4 NMs and CaO2 could promote the enrichment of Cr(VI) reducing bacteria, e.g., Bacillus, Pseudomonas, and Psychrobacter, and promote Cr(VI) reduction. This study gives a novel view and theoretical reference to remediate Cr(VI) pollution through composting.

Performance evaluation and microbial community succession analysis of co-composting treatment of refinery waste activated sludge

Refinery waste activated sludge (RWAS) is riched in organic matter with energy recovery value, while unique petroleum components in RWAS may pose challenges to the recycling process. Aerobic composting technology is an effective means of organic solid waste resource treatment, which can convert organic solid waste into fertilizer for agriculture. This study explores the effect of petroleum components on the performance of RWAS composting by co-composting it with chicken manure. The results showed that more than 65% of petroleum was removed by aerobic composting. After composting, germination index (GI) exceeded 80%, and a humic acid to fulvic acid ratio (HA/FA) was greater than 1. These results signified that the petroleum components slightly affect the harmless and recycling of RWAS. The microbial community succession found that Firmicutes (54.11-91.96%) and Ascomycota (82.35-97.21%) emerged as the dominant phyla during the thermophilic phase of composting. Thermobifida, norank_f__Limnochordaceae and Kernia were the key microorganism in the degradation of petroleum and the humification of composting, and reduced the phytotoxicity of composting products. Redundancy analysis found that the degradation of petroleum was conducive to the formation of humic acid. These findings indicate that aerobic composting technology can remove petroleum components in RWAS and convert them into composted fertilizers, providing key technical support for managing RWAS in a sustainable and environmentally friendly manner.

Mitigating greenhouse gas emission and enhancing fermentation by phosphorus slag addition during sewage sludge composting

During the composting of sewage sludge (SS), a quantity of greenhouse gases has been produced. This study aimed to clarify the microbial mechanisms associated with the addition of industrial solid waste phosphorus slag (PS) to SS composting, specifically focusing on its impact on greenhouse gas emissions and the humification. The findings indicated that the introduction of PS increased the temperature and extended the high-temperature phase. Moreover, the incorporation of 10% and 15% PS resulted in a decrease of N2O emissions by 68.9% and 88.6%, respectively. Microbial diversity analysis indicated that PS improved waste porosity, ensuring the aerobic habitat. Therefore, the environmental factors of the system were altered, leading to the enrichment of various functional bacterial species, such as Firmicutes and Chloroflexi, and a reduction of pathogenic bacterium Dokdonella. Consequently, incorporating PS into SS composting represents an effective waste treatment strategy, exhibiting economic feasibility and promising application potential.

Biochar, phosphate, and magnesium oxide in seaweed and cornstarch dregs co-composting: Enhancing organic matter degradation, humification, and nitrogen retention

Seaweed waste, abundant and rich in plant-stimulating properties, has the potential to be transformed into valuable soil amendments through proper composting and utilization management. Given its low carbon-to-nitrogen ratio, co-composting seaweed with carbon-rich cornstarch dregs is an effective strategy. However, the potential application of co-composting largely depends on the efficiency of the composting and the quality of the product. This study explores the effects of adding 10 % corn stalk biochar to a co-composting system of seaweed and cornstarch dregs, alongside varying buffering capacities of phosphates (KH2PO4 and K2HPO4·3H2O-KH2PO4) and MgO, on the degradation efficiency of organic matter, nitrogen transformation, and humification. The results indicate that the addition of biochar and salts enhances the oxygen utilization rate (OUR) and cellulase activity during the thermophilic phase. Additionally, X-ray diffraction (XRD) and parallel factor analysis (PARAFAC) demonstrate more intense solubilization and transformation of proteinaceous substances, along with cellulose degradation. These processes are crucial for enhancing organic matter degradation and humification, significantly boosting degradation (with an increase of 28.6 % to 33.8 %) and humification levels (HA/FA increased by 37.1 % to 49.6 %). Specifically, groups with high buffering capacity significantly promote the formation of NO3--N and NH4+-N, and a higher degree of humification, creating an optimal environment for significantly improving nitrogen retention (increased by 4.80 %). Additionally, this treatment retains and slightly enhances the plant-stimulating properties of seaweed. These findings underscore the potential of integrating biochar with specific ratios of phosphates and MgO to enhance composting efficiency and product quality while preserving the plant-stimulating effects of seaweed.

Effects of agricultural mulch film on swine manure composting: Film degradation and nitrogen transformation

The utilization of biodegradable mulch films (bio-MFs) is essential for agricultural safety. This study explored the effects of no MF (CK), aging bio-MF (BM), non-aging bio-MF (NBM), and aging polyethylene (PE)-MF (PEM) on swine manure composting. The results demonstrated that outdoor aging (45 days) accelerated the macroscopic degradation of bio-MF in the BM. A reduction in NH4+-N and NH3 emissions in the initial composting was observed owing to an increase in the carbon source or the bulking effect provided by the MFs. N2O emissions from days 9 to 21 were higher in the PEM than other treatments because of the formation of anaerobic zone in the MF-based aggregates. An obvious increase of amoA in PEM indicated a promoted nitrification during the maturation phase, meanwhile the increase of NO2--N and aggregate promoted denitrification. Altogether, MF influenced composting through the synergistic effects of increasing the carbon source, bulking effect, and aggregates.

Exploring the promoting effect of nitrilotriacetic acid on hydroxyl radical and humification during magnetite-amended composting of sewage sludge

The OH production by adding magnetite (MGT) alone has been reported in composting. However, the potential of nitrilotriacetic acid (NTA) addition for magnetite-amended sludge composting remained unclear. Three treatments with different addition [control check (CK); T1: 5 % MGT; T2: 5 % MGT + 5 % NTA] were investigated to characterize hydroxyl radical, humification and bacterial community response. The NTA addition manifested the best performance, with the peak OH content increase by 52 % through facilitating the cycle of Fe(Ⅱ)/Fe(Ⅲ). It led to the highest organic matters degradation (22.3 %) and humic acids content (36.1 g/kg). Furthermore, NTA addition altered bacterial community response, promoting relative abundances of iron-redox related genera, and amino acid metabolism but decreasing carbohydrate metabolism. Structural equation model indicated that temperature and Streptomyces were the primary factors affecting OH content. The study suggests that utilizing chelators is a promising strategy to strengthen humification in sewage sludge composting with adding iron-containing minerals.

Diverse Applications of Two-Dimensional Correlation Spectroscopy (2D-COS)

This second of the two-part series of a comprehensive survey review provides the diverse applications of two-dimensional correlation spectroscopy (2D-COS) covering different probes, perturbations, and systems in the last two years. Infrared spectroscopy has maintained its top popularity in 2D-COS over the past two years. Fluorescence spectroscopy is the second most frequently used analytical method, which has been heavily applied to the analysis of heavy metal binding, environmental, and solution systems. Various other analytical methods including laser-induced breakdown spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, capillary electrophoresis, seismologic, and so on, have also been reported. In the last two years, concentration, composition, and pH are the main effects of perturbation used in the 2D-COS fields, as well as temperature. Environmental science is especially heavily studied using 2D-COS. This comprehensive survey review shows that 2D-COS undergoes continuous evolution and growth, marked by novel developments and successful applications across diverse scientific fields.

Enhancing bioavailable carbon sources and minimizing ammonia emissions in distillery sludge and distiller's grains waste co-composting through deep eutectic solvent addition

This study introduced two deep eutectic solvents, ChCl/oxalic acid (CO) and ChCl/ethylene glycol (CE), into a 34-day co-composting process of distillery sludge and distiller's grains waste to address challenges related to NH3 emissions. The addition of DES increased dissolved organic carbon by 68% to 92%, offering more utilizable carbon for microorganisms. SYTO9/PI staining and enzyme activity tests showed the CE group had higher bacterial activity and metabolic levels during the thermophilic phase than the control. Bacterial community analysis revealed that early dominance of Lactobacillus and Lysinibacillus in CE accelerated the onset of the thermophilic phase, reduced pile pH, and significantly decreased urease production by reducing Ureibacillus. Consequently, CE treatment substantially dropped NH3 emissions by 73% and nitrogen loss by 54%. Besides, CE fostered a more abundant functional microbial community during the cooling and maturation phases, enhancing deep degradation and humification of organic matter.

Occurrence, spatiotemporal trends, fate, and treatment technologies for microplastics and organic contaminants in biosolids: A review

This review provides a comprehensive overview of the occurrence, fate, treatment and multi-criteria analysis of microplastics (MPs) and organic contaminants (OCs) in biosolids. A meta-analysis was complementarily analysed through the literature to map out the occurrence and fate of MPs and 10 different groups of OCs. The data demonstrate that MPs (54.7% occurrence rate) and linear alkylbenzene sulfonate surfactants (44.2% occurrence rate) account for the highest prevalence of contaminants in biosolids. In turn, dioxin, polychlorinated biphenyls (PCBs) and phosphorus flame retardants (PFRs) have the lowest rates (<0.01%). The occurrence of several OCs (e.g., dioxin, per- and polyfluoroalkyl substances, polycyclic aromatic hydrocarbons, pharmaceutical and personal care products, ultraviolet filters, phosphate flame retardants) in Europe appear at higher rates than in Asia and the Americas. However, MP concentrations in biosolids from Australia are reported to be 10 times higher than in America and Europe, which required more measurement data for in-depth analysis. Amongst the OC groups, brominated flame retardants exhibited exceptional sorption to biosolids with partitioning coefficients (log Kd) higher than 4. To remove these contaminants from biosolids, a wide range of technologies have been developed. Our multicriteria analysis shows that anaerobic digestion is the most mature and practical. Thermal treatment is a viable option; however, it still requires additional improvements in infrastructure, legislation, and public acceptance.

Field application of hydroxyapatite and humic acid for remediation of metal-contaminated alkaline soil

The quality of soil is essential for ensuring the safety and quality of agricultural products. However, soils contaminated with toxic metals pose a significant threat to agricultural production and human health. Therefore, remediation of contaminated soils is an urgent task, and humic acid (HA) with hydroxyapatite (HAP) materials was applied for this study in contaminated alkaline soils to remediate Cd, Pb, Cu, and Zn. Physiochemical properties, improved BCR sequential extraction, microbial community composition in soils with superoxide dismutase (SOD), peroxidase (POD), and chlorophyll content in plants were determined. Among the studied treatments, application of HAP-HA (2:1) (T7) had the most significant impact on reducing the active forms of toxic metals from soil such as Cd, Pb, Cu, and Zn decreased by 18.59%, 9.12%, 11.83%, and 3.33%, respectively, but HAP and HA had a minor impact on metal accumulation in Juncao. HAP (T2) had a beneficial impact on reducing the TCleaf/root of Cd, Cu, and Zn, whereas HAP-HA (T5) showed the best performance for reducing Cd and Cu in EFleaf/soil. HAP-HA (T5 and T7) showed higher biomass (57.3%) and chlorophyll (17.9%), whereas HAP (T4) showed better performance in POD (25.8%) than T0 in Juncao. The bacterial diversity in soil was increased after applying amendments of various treatments and enhancing metal remediation. The combined application of HAP and HA effectively reduced active toxic metals in alkaline soil. HAP-HA mixtures notably improved soil health, plant growth, and microbial diversity, advocating for their use in remediating contaminated soils.

Enhancing humification and microbial interactions during co-composting of pig manure and wine grape pomace: The role of biochar and Fe2O3

Phenol-rich wine grape pomace (WGP) improves the conversion of pig manure (PM) into humic acid (HA) during composting. However, the impact of using combinations of Fe2O3 and biochar known to promote compost maturation remains uncertain. This research explored the individual and combined influence of biochar and Fe2O3 during the co-composting of PM and WGP. The findings revealed that Fe2O3 boosts microbial network symbiosis (3233 links), augments the HA yield to 3.38 by promoting polysaccharide C-O stretching, and improves the germination index to 124.82 %. Limited microbial interactions, increased by biochar, resulted in a lower HA yield (2.50). However, the combination weakened the stretching of aromatics and quinones, which contribute to the formation of HA, resulting in reduced the humification to 2.73. In addition, Bacillus and Actinomadura were identified as pivotal factors affecting HA content. This study highlights Fe2O3 and biochar's roles in phenol-rich compost humification, but combined use reduces efficacy.

Effect and its mechanism of potassium persulfate on aerobic composting process of vegetable wastes

Vegetable waste (VW) is a potential organic fertilizer resource. As an important way to utilize vegetable wastes, aerobic composting of VW generally has the problems of long fermentation cycle and incomplete decomposition of materials. In this study, 0.3-1.2% of potassium persulfate (KPS) was added to promote the maturity of compost. The results showed that the addition of KPS promoted the degradation of materials, accelerated the temperature rise of compost. KPS also promoted the formation of humic substances (HS). Compared with the control, HS contents of treatments with KPS addition increased by 7.81 ~ 17.52%. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) analysis reveal the mechanism of KPS affecting the composting process: KPS stimulated the degradation of various organic substances such as lignin at high temperature stage, and the degradation of lignin could accelerate the release and decomposition of other components; KPS made the structure of the material looser, with more voids and pores, and more specific surface area of the material, which was more suitable for microbial degradation activities. Therefore, the addition of KPS can promote the decomposition of organic matter in the early stage of composting, accelerate the process of thermophilic phase, and shorten the composting process and improve product maturity.

Simultaneous passivation of heavy metals and removal of antibiotic resistance genes by calcium peroxide addition during sewage sludge composting

This research evaluated the effects of calcium peroxide (CP) at 0% (CK, w/w), 5% (T1, w/w), and 10% (T2, w/w), on heavy metals (HMs) mobility and prevalence of antibiotic resistance genes (ARGs) during sludge composting. T1 and T2 significantly reduced (p < 0.05) the mobility of Cu (29.34%, and 32.94%, respectively), Ni (24.07%, and 31.48%, respectively) and Zn (33.28%, and 54.11%, respectively) compared to CK after the composting. CP addition resulted in a decrease in mobile genetic elements (MGEs) and ARGs during composting. Together with structural equation model and random forest analysis depicted MGEs had a primary association with total ARGs variations during composting. Microbial analysis indicated CP downregulated the expression of the genes associated with two-component and type IV secretion system, thus reducing the prevalence of ARGs. This study demonstrates that application of CP is a feasible strategy to mitigate both ARGs and HMs hazards during composting.

Organic amendments for in situ immobilization of heavy metals in soil: A review

There is a growing need for soil remediation due to the increase in heavy metals (HMs) migrating into the soil environment, especially those from man-made sources dominated by industry and agriculture. In situ immobilization technology, because of its lower life cycle environmental footprint, can achieve "green and sustainable remediation" of soil heavy-metal pollution. Among the various in situ immobilization remediation agents, organic amendments (OAs) stand out as they can act as soil conditioners while acting as HMs immobilization agents, and therefore have excellent application prospects. In this paper, the types and remediation effects of OAs for HMs in situ immobilization in soil are summarized. OAs have an important effect on the soil environment and other active substances in soil while interacting with HMs in soil. Based on these factors, the principle and mechanism of HMs in situ immobilization in soil using OAs are summarized. Given the complex differential characteristics of soil itself, it is impossible to determine whether it can remain stable after heavy-metal remediation; therefore, there is still a gap in knowledge regarding the compatibility and long-term effectiveness of OAs with soil. In the future, it is necessary to develop a reasonable HMs contamination remediation program for in situ immobilization and long-term monitoring through interdisciplinary integration techniques. These findings are expected to provide a reference for the development of advanced OAs and their applications in engineering.

A Review on Remediation of Iron Ore Mine Tailings via Organic Amendments Coupled with Phytoremediation

Mining operations degrade natural ecosystems by generating a large quantity of mine tailings. Mine tailings remain in dams/open ponds without further treatment after valuable metals such as iron ore have been extracted. Therefore, rehabilitation of tailings to mitigate the negative environmental impacts is of the utmost necessity. This review compares existing physical, chemical and amendment-assisted phytoremediation methods in the rehabilitation of mine tailings from the perspective of cost, reliability and durability. After review and discussion, it is concluded that amendment-assisted phytoremediation has received comparatively great attention; however, the selection of an appropriate phytoremediator is the critical step in the process. Moreover, the efficiency of phytoremediation is solely dependent on the amendment type and rate. Further, the application of advanced plant improvement technologies, such as genetically engineered plants produced for this purpose, would be an alternative solution. Further research is needed to determine the suitability of this method for the particular environment.

Effects of potassium persulfate on nitrogen loss and microbial community during cow manure and corn straw composting

Strong oxidants can reduce the emission of NH₃ during composting. But as a commonly used oxidant, the influence of persulfate on nitrogen transformation during composting is unclear. In this study, the effects of 0.3 %-1.2 % potassium persulfate (PS) on nitrogen losses and microbial community during air-dried cow manure composting were investigated. The results showed that PS could reduce nitrogen losses compared to the control. This was because it decreased pH and the maximum NH₄⁺-N content of treatments, which was beneficial to nitrogen retention. In addition, Pseudoxanthomonas and Chelativorans were enriched compared to the control, which might be associated with NH₄⁺-N transformation and nitrogen fixation. Meanwhile, PS increased the abundance of thermophilic lignocellulose degrading bacteria, and 0.3 % and 0.6 % PS increased the maximum temperature and the duration of the thermophilic period. This study indicated that PS could reduce nitrogen losses in composting and greatly influence nitrogen transforming and lignocellulose degrading bacteria.