Evolution of enzyme activities during composting of tobacco waste

Tobacco as bioenergy and medical plant for biofuels and bioproduction

Tobacco, a widely cultivated crop, has been extensively utilized by humans for an extended period. However, the tobacco industry generates a significant amount of organic waste, and the effective utilization of this tobacco waste has been limited. Currently, most tobacco waste is either recycled as reconstituted tobacco sheets or disposed of in landfills. However, tobacco possesses far more potential value than just these applications. This article provides an overview of the diverse uses of tobacco waste in agriculture, medicine, chemical engineering, and energy sectors. In the realm of agriculture, tobacco waste finds primary application as fertilizers and pesticides. In medical applications, the bioactive compounds present in tobacco are fully harnessed, resulting in the production of phenols, solanesol, polysaccharides, proteins, and even alkaloids. These bioactive compounds exhibit beneficial effects on human health. Additionally, the applications of tobacco waste in chemical engineering and energy sectors are centered around the utilization of lignocellulosic compounds and certain fuels. Chemical platform compounds derived from tobacco waste, as well as selected fuel sources, play a significant role in these areas. The rational utilization of tobacco waste represents a promising prospect, particularly in the present era when sustainable development is widely advocated. Moreover, this approach holds significant importance for enhancing energy utilization.

Isolation of starch and protein degrading strain Bacillus subtilis FYZ1-3 from tobacco waste and genomic analysis of its tolerance to nicotine and inhibition of fungal growth

Aerobic fermentation is an effective technique for the large-scale processing of tobacco waste. However, the specificity of the structure and composition of tobacco-derived organic matter and the toxic alkaloids in the material make it currently difficult to directly use microbial agents. In this study, a functional strain FYZ1-3 was isolated and screened from thermophilic phase samples of tobacco waste composting. This strain could withstand temperatures as high as 80°C and grow normally at 0.6% nicotine content. Furthermore, it had a strong decomposition capacity of tobacco-derived starch and protein, with amylase activity of 122.3  U/mL and protease activity and 52.3  U/mL, respectively. To further understand the mechanism of the metabolic transformation of the target, whole genome sequencing was used and the secondary metabolite gene cluster was predicted. The inhibitory effect of the strain on common tobacco fungi was verified using the plate confrontation and agar column methods. The results showed that the strain FYZ1-3 was Bacillus subtilis, with a genome size of 4.17  Mb and GC content of 43.68%; 4,338 coding genes were predicted. The genome was annotated and analyzed using multiple databases to determine its ability to efficiently degrade starch proteins at the molecular level. Moreover, 14 functional genes related to nicotine metabolism were identified, primarily located on the distinct genomic island of FYZ1-3, giving a speculation for its nicotine tolerance capability on the molecular mechanism. By mining the secondary metabolite gene cluster prediction, we found potential synthetic bacteriocin, antimicrobial peptide, and other gene clusters on its chromosome, which may have certain antibacterial properties. Further experiments confirmed that the FYZ1-3 strain was a potent growth inhibitor of Penicillium chrysogenum, Aspergillus sydowii, A. fumigatus, and Talaromyces funiculosus. The creation and industrial use of the functional strains obtained in this study provide a theoretical basis for its industrial use, where it would be of great significance to improve the utilization rate of tobacco waste.

Nutrient uptake, yield and taste of oilseed rape (Brassica napus L.) and soil chemical properties following amendment with uncomposted and composted tobacco waste and cattle manure

The inadequacy of the nutrient supply of most tropical and sub-tropical soils may be curbed through organic material recycling, thus reducing the need for mineral fertiliser use. To promote tobacco waste recycling in a smallholder food-cash crop production system, nutrient uptake, dry biomass yield and taste of oilseed rape (Brassica napus L.) and soil chemical properties were determined on a sandy loam soil under field conditions. The experiment was a randomised complete block design with three blocks and eight treatments, namely, control (no amendment), mineral fertiliser (121, 30.8, 24.6 kg/ha N, P and K, respectively), uncomposted tobacco leaf scrap (TSC) and compost of TSC and cattle manure (TSC-CM) at 5, 20 and 40 t/ha. N, P and K uptake and dry biomass yield of oilseed rape were higher (p<0.05) than control with 40 t/ha TSC-CM and mineral fertiliser application at 3 weeks after transplanting (WAT), while significant improvements with TSC were observed from 5 WAT. Mineral N, extractable P and exchangeable K were higher than control with TSC-CM at 20 t/ha and 40 t/ha at 3 WAT, and higher with TSC at 9 WAT. Soil organic carbon was more improved with TSC application than TSC-CM at 9 WAT. Organoleptic testing revealed an intensely bitter taste in oilseed rape with mineral fertiliser, 20 t/ha and 40 t/ha TSC at 3 WAT, although it diminished with time. A trade-off of nutrient uptake, yield, taste of oilseed rape and soil properties improvement is attainable with application of TSC-CM at 40 t/ha, while if composting is not feasible, TSC application at 20 t/ha is a viable alternative. Thus, judicious utilisation of tobacco waste offers a viable solution to the problem of low soil fertility on sandy soils and can reduce the need for mineral fertiliser use, while promising sustainable soil management.

Effects of drying pretreatment and particle size adjustment on the composting process of discarded flue-cured tobacco leaves

The main characteristic of discarded flue-cured tobacco leaves is their high nicotine content. Aerobic composting is an effective method to decrease the nicotine level in tobacco leaves and stabilize tobacco wastes. However, high levels of nicotine in discarded flue-cured tobacco leaves complicate tobacco waste composting. This work proposes a drying pretreatment process to reduce the nicotine content in discarded flue-cured tobacco leaves and thus enhance its carbon-to-nitrogen ratio to a suitable level for composting. The effect of another pretreatment method, particle size adjustment, on composting efficiency was also tested in this work. The results indicated that the air-dried (nicotine content: 1.35%) and relatively long discarded flue-cured tobacco leaves (25 mm) had a higher composting efficiency than damp (nicotine content: 1.57%) and short discarded flue-cured tobacco leaves (15 mm). When dry/25 mm discarded flue-cured tobacco leaves mixed with tobacco stems in an 8:2 ratio was composted at a temperature above 55 °C for 9 days, the nicotine content dropped from 1.29% to 0.28%. Since the discarded flue-cured tobacco leaves was successfully composted to a fertile and harmless material, the germination index values increased to 85.2%. The drying pretreatment and particle size adjustment offered ideal physical and chemical conditions to support microbial growth and bioactivity during the composting process, resulting in efficient conversion of discarded flue-cured tobacco leaves into a high quality and mature compost.

Design of experiment (DOE) based screening of factors affecting municipal solid waste (MSW) composting

A design of experiment (DOE) based methodology was adopted in this study to investigate the effects of multiple factors and their interactions on the performance of a municipal solid waste (MSW) composting process. The impact of four factors, carbon/nitrogen ratio (C/N), moisture content (MC), type of bulking agent (BA) and aeration rate (AR) on the maturity, stability and toxicity of compost product was investigated. The statistically significant factors were identified using final C/N, germination index (GI) and especially the enzyme activities as responses. Experimental results validated the use of enzyme activities as proper indices during the course of composting. Maximum enzyme activities occurred during the active phase of decomposition. MC has a significant effect on dehydrogenase activity (DGH), β-glucosidase activity (BGH), phosphodiesterase activity (PDE) and the final moisture content of the compost. C/N is statistically significant for final C/N, DGH, BGH, and GI. The results provided guidance to optimize a MSW composting system that will lead to increased decomposition rate and the production of more stable and mature compost.

Stocking Density Optimization for Enhanced Bioconversion of Fly Ash Enriched Vermicompost

Although it is widely agreed that stocking density critically affects the rate of vermicomposting, there is no established stocking density for mixtures of fly ash and other waste materials. This study sought to optimize (Savigny, 1826) stocking density for effective biodegradation and nutrient release in a fly ash-cow dung-waste paper (FCP) mixture. Four stocking densities of 0, 12.5, 25, and 37.5 g worms kg were evaluated. Although the 12.5, 25, and 37.5 g worms kg treatments all resulted in a mature vermicompost, stocking densities of 25 and 37.5 g worms kg resulted in faster maturity, higher humification parameters, and a significantly lower final C/N ratio (range 11.1-10.4). The activity of β-glucosidase and fluorescein diacetate hydrolysis enzymes showed faster stabilization at stocking densities of 25 and 37.5 g worms kg, indicating compost stability and maturity. Similarly, a stocking density of 25 g worms kg resulted in the highest release of Olsen-extractable P and (NO + NO)-N contents. The 0-, 12.5-, 25-, and 37.5-g treatments resulted in net Olsen P increases of 16.3, 38.9, 61.0, and 53.0%, respectively, after 10 wk. Although compost maturity could be attained at stocking densities of 12.5 g worms kg, for faster production of humified and nutrient-rich FCP vermicompost, a stocking density of 25 g worms kg seems most appropriate.

Potential of Effective micro-organisms and Eisenia fetida in enhancing vermi-degradation and nutrient release of fly ash incorporated into cow dung-paper waste mixture

The interactions between earthworms and microorganisms activity has prompted several researchers to evaluate the potential of artificially inoculating vermicomposts with additional specific microbes, with the intention of enhancing the vermicomposting process. This study evaluated the potential of inoculating fly ash (F)-cow dung-paper waste (CP) mixture (F-CP) with a specialized microbial cocktail called Effective micro-organisms (EM) during vermicomposting using Eisenia fetida earthworms. Inoculation with EM alone did not result in significantly (P>0.05) different changes in C/N ratio and dissolved organic matter (DOC) compared to the control with no EM and E. fetida. A significant interaction between EM and E. fetida presence resulted in greater changes in C/N ratio and DOC, which were not statistically different from the E. fetida alone treatment. It was also noteworthy that the activity of ß-Glucosidase was not influenced by the presence of EM, but was significantly influenced (P=0.0014) by the presence of E. fetida. However, the EM+E. fetida treatment resulted in a rate of weekly Olsen P release of 54.32mgkg(-1) which was 12.3%, 89.2% and 228.0% more that the E. fetida alone, EM alone and control treatments, respectively. Similarly, though higher in the E. fetida plus EM treatment, the phosphate solubilizing bacteria counts were not significantly different (P>0.05) from the E. fetida alone treatment. It is concluded that inoculation of F-CP composts with EM alone may not be beneficial, while combining EM with E. fetida results in faster compost maturity and significantly greater Olsen P release. It would be interesting to evaluate higher optimized rates of EM inoculation and fortifying EM cocktails with phosphate solubilizing bacteria (PSB) on F-CP vermicompost degradation and phosphorus mineralization.