Vermicomposting of cow manure: Effect of time on earthworm biomass and chemical, physical, and biological properties of vermicompost

Cheese whey and dairy manure anaerobic co-digestion at psychrophilic conditions: Technical and environmental evaluation

Cheese whey (CW) and dairy manure (DM) are the main residues from the dairy industry, both of which can led to significant negative environment impacts if not properly managed. However, their combined anaerobic digestion represents an opportunity to obtain bioenergy and a stabilised material as a soil improver on the farm. Biochemical potential of methane (BMP) assays were carried out at psychrophilic conditions (20 °C) to analyse the influence on biomethane production of different CW:DM mixtures (% w/w) at different of inoculum-to-substrate ratios (ISR). Based on the BMP results, a life cycle assessment (LCA) of the cheese manufacturing process was carried out considering two scenarios (i) considering the current process, where propane gas and electricity are used for cheese production (ii) the incorporation of the biogas generated in the cheese production process in the company. BMP results showed that the best mixture between CW and DM was 65:35 (weight basis) at an organic load of 0.6 gVS/L (ISR of X). The LCA showed that CW and DM anaerobic digestion allowed to reduce the cheese manufacturing carbon footprint from through the substitution of propane by the biogas produced, changing from 5.5 to 3.1 kg CO2-eq/kg cheese produced, which indicates that according to the monthly production (633.6 kg) it would stop emitting about 1519 kg CO2-eq, i.e. a saving in terms of emissions of approximately 43,6% of the total currently generated.

Effect of conventional and biodegradable microplastics on earthworms during vermicomposting process

The potential effect of microplastics is an increasingly growing environmental issue. However, very little is known regarding the impact of microplastics on the vermicomposting process. The present study explored the effect of non-biodegradable (low density polyethylene; LDPE) and biodegradable (polybutylene succinate-co-adipate; PBSA) microplastics on earthworm Eisenia fetida during vermicomposting of cow dung. For this, earthworms were exposed to different concentrations (0, 0.5, 1 and 2%) of LDPE and PBSA of 2 mm size. The cow dung supported the growth and hatchlings of earthworms, and the toxicity effect of both LDPE and PBSA microplastics on Eisenia fetida was analyzed. Microplastics decreased the body weight of earthworms and there was no impact on hatchlings. The body weight of earthworm decreased from 0 to 60th day by 18.18% in 0.5% of LDPE treatment, 5.42% in 1% of LDPE, 20.58% in 2% of LDPE, 19.99% in 0.5% of PBSA, 15.09% in 1% of PBSA and 16.36% in 2% of PBSA. The physico-chemical parameters [pH (8.55-8.66), electrical conductivity (0.93-1.02 (S/m), organic matter (77.6-75.8%), total nitrogen (3.95-4.25 mg/kg) and total phosphorus (1.16-1.22 mg/kg)] do not show much significant changes with varying microplastics concentrations. Results of SEM and FTIR-ATR analysis observed the surface damage of earthworms, morphological and biochemical changes at higher concentrations of both LDPE and PBSA. The findings of the present study contribute to a better understanding of microplastics in vermicomposting system.

Understanding vermicompost and organic manure interactions: impact on toxic elements, nitrification activity, comammox Nitrospira inopinata, and archaea/bacteria

Vermicompost is a substantial source of nutrients, promotes soil fertility, and maintains or increases soil organic matter levels. Potentially toxic elements (PTEs) in vermicompost impact on nitrification activity. However, it is yet unknown how vermicompost affects nitrifying bacteria and archaea, comammox Nitrospira inopinata (complete ammonia oxidizers), net nitrification rates (NNRs), and PTEs. The effects of vermicompost application on NNRs, potential nitrification rates (NPs), PTEs, and the abundances of comammox N. inopinata bacteria, nitrite-oxidizing bacteria (NOB), and ammonia-oxidizing bacteria (AOB)/archaea (AOA) were studied. NNRs and NPs were significantly higher (p < 0.05) in fresh cow-dung vermicompost (stored for 40 days) as compared with other organic manure. The level of PTEs (Cu2+, Fe2+, Pb2+, Cd2+, and Zn2+) was significantly lower (p < 0.05) in vermicompost as compared with compost of waste material with Trichoderma and cow dung. Comammox N. inopinata, NOB, AOB, and AOA were significantly higher (p < 0.05) in stored cow-dung vermicompost (more than 1 year) as compared with other organic manure. The results of the scatterplot matrix analysis suggested that Fe2+, total nitrogen (TN), soil organic carbon (SOC), and total carbon (TC) were linearly correlated (p < 0.001) with NNRs and NPs in vermicompost and organic manure. Similarly, comammox N. inopinata bacteria, NOB, AOB, and AOA were linearly correlated (p < 0.001) with NNR and NP. These results indicated that vermicompost promoted nitrification activity by increasing microbial diversity and abundance, supplying nutrients and organic matter for microbial growth, and facilitating complex microbial interactions. It may be concluded that the influence of vermicompost, which played a great role in PTE concentration reduction, increased chemical, and biological properties, increased the growth rate of nitrifying bacteria/archaea and the nitrogen cycle.

Application of life cycle assessment to high quality-soil conditioner production from biowaste

The recent large-scale urbanization and industrialization resulted in an impressive growth of solid waste generation worldwide. Organic fraction generally constitutes a large fraction of municipal solid waste and its peculiar chemical properties open to various valorization strategies. On this purpose, life cycle assessment is applied to an innovative industrial system that processes 18 kt/y of agricultural and livestock waste into a high-quality soil conditioner. The high-quality soil conditioner production system consists of a series of processes, including anaerobic digestion and vermicomposting, allowing the generation of a peat-like material with high carbon content, porosity, and water-holding capacity. The presence of a photovoltaic plant and a cogeneration plant, fed with the biogas produced in the anaerobic digestion, makes the system entirely self-sufficient from the national grid and generating a surplus of electricity of 1177MWh/y. The high-quality soil conditioner showed better environmental performances in 15 out of 18 impact categories when compared to alternative scenarios. In particular, the high-quality soil conditioner and the related biowaste management resulted in a carbon saving of around 397 kg CO2 eq/ton compared with a scenario involving the employment of peat in place of the high-quality soil conditioner and a traditional biowaste management, and 165 kg CO2 eq/ton compared with a scenario where cogeneration is replaced by biomethane upgrading. This study demonstrates the possibility of using organic waste as an environmentally sustainable and renewable source for energy and carbon to soil conditioning.

Organic fertilization and mycorrhization increase copper phytoremediation by Canavalia ensiformis in a sandy soil

Organic fertilization and mycorrhization can increase the phytoremediation of copper-contaminated soils. The time of vermicomposting alters the properties of vermicompost, which can affect copper's availability and uptake. Therefore, this study sought to evaluate the effect of different organic fertilizers and mycorrhization on copper-contaminated soil phytoremediation. The soil was contaminated with 100 mg Cu kg^-1 dry soil and received mineral fertilizer (MIN), bovine manure (CM), and vermicompost produced in 45 days (V45) or 120 days (V120), all in doses equivalent to 40 mg kg^-1 dry soil of phosphorus. Half of the jack bean (Canavalia ensiformis) plants were inoculated with the arbuscular mycorrhizal fungus Rhizophagus clarus. At plant flowering, the dry mass and concentrations of Cu, Zn, Mn, Ca, Mg, P, and K in the soil, solution, and plant tissue were determined, in addition to mycorrhizal colonization, nodulation, photosynthetic pigments, and oxidative stress enzyme activity. Organic fertilization increased plant growth and copper accumulation in aerial tissues. These effects were more evident with the V120, making it suitable for use in copper phytoextraction. Mycorrhization increased root and nodule dry mass, making it recommended for phytostabilization. C. ensiformis nodulation in Cu-contaminated soils depends on vermicompost fertilization and mycorrhization. Hence, the copper phytoremediation by C. ensiformis is increased by using organic fertilization and mycorrhization.

Towards a circular economy in virgin olive oil production: Valorization of the olive mill waste (OMW) "alpeorujo" through polyphenol recovery with natural deep eutectic solvents (NADESs) and vermicomposting

Virgin olive oil (VOO) production generates large amounts of a harmful by-product, olive mill waste (OMW) or alpeorujo, which has a strong environmental impact and that must be recycled to adapt VOO production to a circular economy model. Here, the valorization of OMW was studied by considering three consecutive stages: Stage 1 involves the generation of OMW; Stage 2 the recovery of bioactive phenolic compounds from the fresh OMW using natural deep eutectic solvents (NADESs), generating a valuable phenolic extract and a new by-product, a dephenolized OMW named "alpeoNADES"; and Stage 3 involves vermicomposting alpeoNADES with Eisenia fetida earthworms. Six NADES were formulated and tested, selecting a NADES composed of citric acid and fructose (CF) derived from food grade and biodegradable substances. CF was the most effective solvent to obtain phenolic extracts for nutraceutical and agronomical purposes, extracting 3988.74 mg/kg of polyphenols from fresh OMW. This alpeoNADES is a non-palatable substrate for E. fetida earthworms, as the residual CF gives it an acidic pH (pH 2). Its palatability was improved by mixing it with horse manure and straw for vermicomposting, in a 1:1 and 3:1 dry weight ratio. When these substrates were precomposted for 3 weeks they reached pH 5.5-6 and they could then be vermicomposted for 23 weeks (using OMW as a control). The best substrate for vermicomposting was determined by the worm biomass, growth rate, carbon to nitrogen (C:N) ratio, and N and P content. AlpeoNADES and manure 3:1 produced the highest quality vermicompost in the shortest time, generating a product that complied with European standards for organic fertilizers. Hence, alpeoNADES was recycled to a low-cost, organic balanced fertilizer in Stage 3, enabling the olive oil industry to transition to sustainable production through this integrated circular economy design.

Reactive oxygen species accelerate humification process during iron mineral-amended sludge composting

The production of hydroxyl radicals (OH) has been documented during composting. However, the effect of OH on composting efficiency remains unclear. Here, iron mineral supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing OH production and accelerating the maturation of composting. The results indicated that the maximum OH production of imTC was 1922.74 μmol·kg^-1, which increased by 1.39 times than that of ordinary thermophilic composting (oTC). Importantly, the increase of OH could greatly enhance organic matter degradation and humic substances formation during imTC, resulting in shorting the maturity time by 25 %. Enrichment of laccase-producing bacteria resulted in higher laccase activity (31.85 U·g^-1) in imTC compared with oTC (23.82 U·g^-1), which may have contributed to the higher level of humification in imTC treatment. This work, for the first time, proposes a feasible strategy for improving composting efficiency through the regulation of OH production during aerobic composting.

Assessment of the eco-toxicological effects in zoxamide polluted soil amended with fertilizers-An indoor evaluation

Zoxamide is a benzamide fungicide applied to control diseases caused by oomycete fungi. Fertilizers are important agricultural supplies to adjust soil properties and increase nutrition. To investigate the impact of zoxamide and seven fertilizers urea, phosphate fertilizer, potash fertilizer, compound fertilizer, organic fertilizer, vermicompost and soya bean cakes on the soil environment, the enantioselective dissipation characteristics of zoxamide, soil enzyme activities, pH and N, P nutrition changes were comprehensively analyzed in our present study. The enantioseparation method was successfully validated to quantify the zoxamide enantiomers in soil by HPLC using Chiral NQ (2)-RH column. Our results demonstrated that the R-(-)- and S-(+)-zoxamide half dissipated in the range of 10.88-17.81 and 8.05-14.41 days, respectively. S-(+)-zoxamide disappeared faster in soil. The vermicompost accelerated the dissipation rate of S-(+)-zoxamide, while urea, phosphate, organic and vermicompost fertilizer increased the dissipation selectivity. Zoxamide and fertilizers other than urea caused soil acidification during 80 days. Zoxamide was beneficial to soil catalase, instead inhibited soil urease, dehydrogenase activities and available phosphorus content. No significant effects on sucrase activity and available nitrogen content were found by zoxamide. Vermicompost and soya bean cakes had lasting and outstanding performance in efficiently improving soil enzyme activity and N, P nutrition. The comprehensive understanding of the ecological impact induced by chiral pesticide enantiomers and fertilizers on soil is vital to ensure the sustainable development and safety of agricultural production.

Feasibility of vermicomposting combined with room drying for enhancing the stabilization efficiency of dewatered sludge

Vermicomposting is characterized by transforming organic waste into nutrient-rich organic fertilizer through the action of different earthworms and microorganisms. Although vermicomposting can recycle the excess sludge in an eco-friendly manner, the longer stabilization period has limited its industrial application. The present study sought to investigate a novel operation process of vermicomposting combined with room drying (VD) to improve the stabilization efficiency of dewatered sludge. Subsequently, the performance and efficiency of vermicomposting without room drying, room dry without vermicomposting, and VD for sludge stabilization were compared simultaneously. In the VD process, the sludge water content reduced from 60.8% to 1.64%, showing the highest electrical conductivity and lowest organic matter content, making the humus substances abundant in the final product. Moreover, the vermicomposting achieved the highest ammonia and nitrate content in final product. Additionally, the bacterial and eukaryotic abundances in the VD product were significantly higher (P < 0.01, i.e., 15.6% and 180.7%) than the vermicomposting product. The specific bacterial genus of Glutamicibacter, Chitinibacter, and Acidobacteria was dominated in the VD product. The Partial least squares-Path modeling (PLS-PM) results revealed that the maturity degree in the VD product was significantly associated with microbial component, and the organic form was strongly driven by the change in the physicochemical properties, which was contradictory to vermicomposting model. The study suggests that the VD process could shorten the vermicomposting period by rapidly accelerating the physical, chemical, and biological stabilization of sludge.