The impact of silver and titanium dioxide nanoparticles on the in-vessel composting of municipal solid waste

Microbial bioprocess performance in nanoparticle-mediated composting

Microbial composting is one of the most cost-effective techniques for degradation, remediation, nutrition, etc. Currently, there is faster growth and development in nanotechnology in different sectors. This development leads nanoparticles (NPs) to enter into the composts in different ways. First, unintentional entry of NPs into the composts via: waste discharge, buried solid waste, surface runoff, direct disposal into wastes (consumer goods, food, pharmaceuticals, and personal care products). Second, intentional mediation of the NPs in the composting process is a novel approach developed to enhance the degradation rate of wastes and as a nutrient for plants. The presence of NPs in the composts can cause nanotoxicity. Conversely, their presence might also be beneficial, such as soil reclamations, degradation, etc. Alternatively, metal NPs are also helpful for all living organisms, including microorganisms, in various biological processes, such as DNA replication, precursor biosynthesis, respiration, oxidative stress responses, and transcription. NPs show exemplary performance in multiple fields, whereas their role in composting process is worth studying. Consequently, this article aids the understanding of the role of NPs in the composting process and how far their presence can be beneficial. This article reviews the significance of NPs in: the composting process, microbial bioprocess performance during nano composting, basic life cycle assessment (LCA) of NP-mediated composting, and mode of action of the NPs in the soil matrix. This article also sheds insight on the notion of nanozymes and highlights their biocatalytic characterization, which will be helpful in future composting research.

A review on biological methodologies in municipal solid waste management and landfilling: Resource and energy recovery

Rapid industrialization and urbanization growth combined with increased population has aggravated the issue of municipal solid waste generation. MSW has been accounted for contributing tremendously to the improvement of sustainable sources and safe environment. Biological processing of MSW followed by biogas and biomethane generation is one of the innumerable sustainable energy source choices. In the treatment of MSW, biological treatment has some attractive benefits such as reduced volume in the waste material, adjustment of the waste, economic aspects, obliteration of microorganisms in the waste material, and creation of biogas for energy use. In the anaerobic process the utilizable product is energy recovery. The current review discusses about the system for approaching conversion of MSW to energy and waste derived circular bioeconomy to address the zero waste society and sustainable development goals. Biological treatment process adopted with aerobic and anaerobic processes. In the aerobic process the utilizable product is compost. These techniques are used to convert MSW into a reasonable hotspot for resource and energy recovery that produces biogas, biofuel and bioelectricity and different results in without risk and harmless to the ecosystem. This review examines the suitability of biological treatment technologies for energy production, giving modern data about it. It likewise covers difficulties and points of view in this field of exploration.

Nanobiotechnological Approaches to Enhance Drought Tolerance in Catharanthus roseus Plants Using Salicylic Acid in Bulk and Nanoform

Drought has a detrimental effect on crop production, affecting economically important plants’ growth rates and development. Catharanthus roseus is an important medicinal plant that produces many pharmacologically active compounds, some of which have significant antitumor activity. The effect of bulk salicylic acid (SA) and salicylic acid nanoparticles (SA-NPs) were evaluated on water-stressed Catharanthus roseus plants. The results showed that SA and SA-NPs alleviated the negative effects of drought in the treated plants by increasing their shoot and root weights, relative water content, leaf area index, chlorophyll content, and total alkaloids percentage. From the results, a low concentration (0.05 mM) of SA-NPs exerted positive effects on the treated plants, while the best results of the bulk SA were recorded after using the highest concentration (0.1 mM). Both treatments increased the expression level of WRKY1, WRKY2, WRKY40, LEA, and MYC2 genes, while the mRNA level of MPKK1 and MPK6 did not show a significant change. This study discussed the importance of SA-NPs in the induction of drought stress tolerance even when used in low concentrations, in contrast to bulk SA, which exerts significant results only at higher concentrations.

Effects of TiO2 and ZnO nanoparticles on vermicomposting of dewatered sludge: studies based on the humification and microbial profiles of vermicompost

Nanoparticles (NPs) are prevalent in dewatered sludge, and their presence increases the environmental risks associated with the subsequent sludge treatment process. However, until now, their potential effects on sludge vermicomposting have not been clarified. This study investigated the effects of NPs on sludge humification and microbial profiles during vermicomposting by comparing fresh dewatered sludge substrates with substrates mixed with 0 mg/kg NPs (control), 100 mg/kg TiO₂, 500 mg/kg TiO₂, 100 mg/kg ZnO, and 500 mg/kg ZnO. The results showed that addition of TiO₂ and ZnO NPs to sludge did not significantly affect the growth rate of earthworms and the superoxide dismutase activity in their guts during vermicomposting. Moreover, higher concentrations of the selected NPs promoted the humification index of sludge by 20.7-49.6%, through the formation of polysaccharides, aromatic substances, and organic acids in final vermicomposts. Compared with the control without NP addition, bacterial community diversity was enhanced in treatments with TiO₂ and ZnO NPs, and dominant genera differed according to the type and concentration of NPs. This study suggests that the presence of TiO₂ and ZnO NP residuals modify the microbial community of sludge, thus promoting sludge humification during vermicomposting.

Evaluation of silver nanoparticles (AgNPs) penetration through a clay liner in landfills

Most products containing engineered nanomaterials are disposed at landfills in the final stage of their lifecycle. This study aims to assess landfill liners as a final barrier of disposed silver nanoparticles (AgNPs). Sorption and transport of AgNPs were investigated in the laboratory-scale simulation of landfill liner conditions. Field soil (silt loam) and bentonite were tested in batch sorption experiments respectively. To test transportation, 3 cm thick mixture of the field soil and the bentonite constituted the porous media to meet the criteria for compacted clay liner of landfill. Mathematical modeling in the experimental and actual landfill conditions was also conducted. The results demonstrated considerable extent of sorption by both types of sorbents. The breakthrough of AgNPs was not observed for 200 days (over 20 pore volume). In general, the experimental results indicated that AgNPs cannot easily pass through the landfill clay liner under present standards. Modeling results also showed that AgNPs could be blocked effectively. Although long-term tests are still required, these results clearly show resistance to current sanitary landfill liners against AgNP penetration. As the trial to assess the safety of landfills against AgNP migration, this work provides insights into the fate and transport of nanomaterials in the landfill environment.

Evolutions of different microbial populations and the relationships with matrix properties during agricultural waste composting with amendment of iron (hydr)oxide nanoparticles

This study investigated the evolutions of different microbial populations and multivariate relationships between their abundances and environmental variables during composting with amendment of Fe (hydr)oxide nanoparticles. Piles treated with nanohematite and nanomagnetite were denoted as T-nanohematite and T-nanomagnetite, and another one was T-control. It was found that nanohematite more effectively increased bacteria and fungi abundances with 1.24∼1.58 times average value of T-control, while nanomagnetite was more useful to actinomycetes. As the most significant variable, the total effect of temperature in T-control and T-nanomagnetite was increased to 0.87 and 0.92, respectively, because both the direct and indirect effects were positive, while it in T-nanohematite was reduced to 0.18 by the negative indirect effect. Partial redundancy analysis suggested that each microbial abundance shared different relationships with composting parameters. Overall, actinomycetes was more sensitive to changes of composting parameters than bacteria and fungi.

Influence of FeONPs amendment on nitrogen conservation and microbial community succession during composting of agricultural waste: Relative contributions of ammonia-oxidizing bacteria and archaea to nitrogen conservation

Composting amended with iron oxide nanoparticles (FeONPs, α-Fe₂O₃ and Fe₃O₄ NPs) were conducted to study the impacts of FeONPs on nitrogen conservation and microbial community. It was found that amendment of FeONPs, especially α-Fe₂O₃ NPs, reduced total nitrogen (TN) loss, and reserved more NH₄⁺-N and mineral N. Pearson correlation analysis revealed that decrease of ammonia-oxidizing bacteria (AOB) in FeONPs treatments played more important role than ammonia-oxidizing archaea (AOA) in reserving more NH₄⁺-N and mineral N, and reducing TN loss. Bacterial community composition at phylum level did not shift with addition of FeONPs. Firmicutes, Actinobacteria, and Proteobacteria were the three most dominant phyla in all treatments. Overall, this study provides a method to reduce TN loss and improve mineral N reservation during composting, and gives a deep insight into the role of AOB and AOA in nitrogen transformation.

Impacts of iron oxide nanoparticles on organic matter degradation and microbial enzyme activities during agricultural waste composting

The effects of iron oxide nanoparticles (IONPs, including Fe₂O₃ NPs and Fe₃O₄ NPs) on composting were investigated through evaluating their influences on organic matter (OM) degradation, dehydrogenase (DHA) and urease (UA) activities, and quality of the final compost product. Results showed that composting amended with Fe₂O₃ NPs was more effective to facilitate OM degradation. At the end of composting, the total OM loss in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs was 66.19%, 75.53% and 61.31%, respectively. DHA and UA were also improved on the whole by the amendment of IONPs, especially Fe₂O₃ NPs. Although relationships between enzyme activities and environmental variables were changed by different treatments, temperature was the most influential to variations of both DHA and UA in all treatments, which independently explained 75.1%, 34.7% and 38.4% of variations in the two enzyme activities in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs, respectively. Compared with DHA, UA was more closely related to the environmental parameters. The germination index in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs was 134.49%, 153.64% and 146.76%, and the average shoot length was 3.16, 3.87 and 3.45 cm, respectively, indicating that amendment of IONPs, especially Fe₂O₃ NPs, could promote seed germination and seedling growth. Therefore, composting amended with IONPs was a feasible and promising method to improve composting performance, enzyme activities as well as quality of the final compost product.

Untapped potential of zeolites in optimization of food waste composting

This study aims to examine the effect of zeolites in optimizing the process of food waste composting. A novel method of sequential hydrothermal was introduced to modify the natural zeolite and apply to in-vessel compost bioreactors. Raw and modified natural zeolites were applied at 10 and 15% (w/w) of the total waste and compared with un-amended control trial. Both raw and modified zeolites affected the composting process, but the notable results were observed for modified natural zeolite. The results for compost stability parameters were prominent at 15% modified natural zeolite concentration. The rapid and long-term thermophillic temperature and moisture content reduction to the optimum range was observed for modified natural zeolite. Furthermore, the total ammonium (NH₄⁺) and nitrate (NO₃^-) concentration in modified natural zeolite were increased by 11.1 and 21.5% respectively as compared to raw zeolite. Compost stability against moisture contents (MC), electrical conductivity (EC), organic matters (OM), total carbon (TC), mineral nitrogen, nitrification index (NI) and germination index (GI) was achieved after 60 days of composting that was in accordance with the international compost quality standards. The findings of this study suggested the suitability of modified natural zeolite addition at 15% to the total waste as the optimum ratio for the composting of food waste in order to achieve a stable nutrient-rich compost.

Multivariate relationships between microbial communities and environmental variables during co-composting of sewage sludge and agricultural waste in the presence of PVP-AgNPs

This study evaluated the contributions of environmental variables to the variations in bacterial 16S rDNA, nitrifying and denitrifying genes abundances during composting in the presence of polyvinylpyrrolidone coated silver nanoparticles (PVP-AgNPs). Manual forward selection in redundancy analysis (RDA) indicated that the variation in 16S rDNA was significantly explained by NO₃^--N, while nitrifying genes were significantly related with pH, and denitrifying genes were driven by NO₃^--N and TN. Partial RDA further revealed that NO₃^--N solely explained 28.8% of the variation in 16S rDNA abundance, and pH accounted for 61.8% of the variation in nitrifying genes. NO₃^--N and TN accounted for 34.2% and 9.2% of denitrifying genes variation, respectively. The RDA triplots showed that different genes shared different relationships with environmental parameters. Based on these findings, a composting with high efficiency and quality may be conducted in the future work by adjusting the significant environmental variables.

A review of the fate of engineered nanomaterials in municipal solid waste streams

Significant knowledge and data gaps associated with the fate of product-embedded engineered nanomaterials (ENMs) in waste management processes exist that limit our current ability to develop appropriate end-of-life management strategies. This review paper was developed as part of the activities of the IWWG ENMs in Waste Task Group. The specific objectives of this review paper are to assess the current knowledge associated with the fate of ENMs in commonly used waste management processes, including key processes and mechanisms associated with ENM fate and transport in each waste management process, and to use that information to identify the data gaps and research needs in this area. Literature associated with the fate of ENMs in wastes was reviewed and summarized. Overall, results from this literature review indicate a need for continued research in this area. No work has been conducted to quantify ENMs present in discarded materials and an understanding of ENM release from consumer products under conditions representative of those found in relevant waste management process is needed. Results also indicate that significant knowledge gaps associated with ENM behaviour exist for each waste management process investigated. There is a need for additional research investigating the fate of different types of ENMs at larger concentration ranges with different surface chemistries. Understanding how changes in treatment process operation may influence ENM fate is also needed. A series of specific research questions associated with the fate of ENMs during the management of ENM-containing wastes have been identified and used to direct future research in this area.

Resource recovery of food waste through continuous thermophilic in-vessel composting

In the Kingdom of Saudi Arabia (KSA) and Gulf region, a very small amount of municipal solid waste (MSW) is treated for compost production. The produced compost through traditional methods of compost piles and trenches does not coincide with the international standards of compost quality. Therefore, in this study, a continuous thermophilic composting (CTC) method is introduced as a novel and efficient technique for treating food waste into a quality compost in a short period of time. The quality of the compost was examined by degradation rates of organic matter (OM), changes in total carbon (TC), ash contents, pH, dynamics in ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N), and nitrification index (NI). The results showed that thermophilic treatment at 60 °C increased the pH of the substrate and promoted degradation and mineralization process. After 30 days of composting, the degree of OM degradation was increased by 43.26 and 19.66%, NH₄-N by 65.22 and 25.23%, and NO₃-N by 44.76 and 40.05% as compared to runs treated at 25 and 40 °C, respectively. The stability of the compost was attained after 30 to 45 days with quality better than the compost that was stabilized after 60 days of the experiment under mesophilic treatment (25 °C). The final compost also showed stability at room temperature, confirming the rapid degradation and maturation of food waste after thermophilic treatment. Moreover, the quality of produced compost is in line with the compost quality standard of United States (US), California, Germany, and Austria. Hence, CTC can be implemented as a novel method for rapid decomposition of food waste into a stable organic fertilizer in the given hot climatic conditions of KSA and other Gulf countries with a total net saving of around US $70.72 million per year.

The impact of nanoparticles on aerobic degradation of municipal solid waste

The amount of nanoparticles released from industrial and consumer products has increased rapidly in the last decade. These products may enter landfills directly or indirectly after the end of their useful life. In order to determine the impact of TiO₂ and Ag nanoparticles on aerobic landfilling processes, municipal solid waste was loaded to three pilot-scale aerobic landfill bioreactors (80 cm diameter and 350 cm height) and exposed to TiO₂ (AT) and Ag (AA) nanoparticles at total concentrations of 100 mg kg^-1 of solid waste. Aerobic landfill bioreactors were operated under the conditions about 0.03 L min^-1 kg^-1 aeration rate for 250 days, during which the leachate, solid waste, and gas characteristics were measured. The results indicate that there was no significant difference in the leachate characteristics, gas constituents, solid quality parameters, and temperature variations, which are the most important indicators of landfill operations, and overall aerobic degradation performance between the reactors containing TiO₂ and Ag nanoparticles, and control (AC) reactor. The data also indicate that the pH levels, ionic strength, and the complex formation capacity of nanoparticles with Cl^- ions can reduce the toxicity effects of nanoparticles on aerobic degradation processes. The results suggest that TiO₂ and Ag nanoparticles at concentrations of 100 mg kg^-1 of solid waste do not have significant impacts on aerobic biological processes and waste management systems.

The impact of silver nanoparticles on the co-composting of sewage sludge and agricultural waste: Evolutions of organic matter and nitrogen

This study evaluated the influence of silver nanoparticles (AgNPs) on evolutions of organic matter and nitrogen during co-composting of sewage sludge and agricultural waste. Two co-composting piles were conducted, one was treated without AgNPs (pile 1) and the other with AgNPs (pile 2). Results showed that the AgNPs affected the quality of final composts. Less organic matter (OM) losses were determined in pile 2 (57.96%) than pile 1 (61.66%). 27.22% and 30.1% of the initial total organic matter (TOC) was decomposed in pile 1 and pile 2, respectively. The final water soluble carbon (WSC) concentration in pile 2 was 23559.27mg/kg DW compost which was significantly lower than pile 1 (25642.75mg/kg DW compost). Changes of different forms of nitrogen in the two piles showed that AgNPs could reduce the losses of TN but increase the losses of mineral N.