Nitrification during extended co-composting of extreme mixtures of green waste and solid fraction of cattle slurry to obtain growing media

Evolution of microbiome composition, antibiotic resistance gene loads, and nitrification during the on-farm composting of the solid fraction of pig slurry using two bulking agents

Composting is a nature-based method used to stabilize organic matter and to transform nitrogen from animal farm manure or solid fraction of slurry (SFS). The use of composted material as source of nutrients for agriculture is limited by its potential to facilitate the propagation of biological hazards like pathogens and antibiotic-resistant bacteria and their associated antibiotic-resistance genes (ARG). We show here an experimental on-farm composting (one single batch) of pig SFS, performed under realistic conditions (under dry continental Mediterranean climate) for 280 days, and using two different bulking agents (maize straw and tree pruning residues) for the initial mixtures. The observed reduction in potentially pathogenic bacteria (80-90%) and of ARG loads (60-100%) appeared to be linked to variations in the microbiome composition occurring during the first 4 months of composting, and concurrent with the reduction of water-soluble ammonium and organic matter loads. Nitrification during the composting has also been observed for both composting piles. Similar patterns have been demonstrated at small scale and the present study stresses the fact that the removal can also occur at full scale. The results suggest that adequate composition of the starting material may accelerate the composting process and improve its global performance. While the results confirm the sanitization potential of composting, they also issue a warning to limit ARG loads in soils and in animal and human gut microbiomes, as the only way to limit their presence in foodstuffs and, therefore, to reduce consumers' exposure.

Microbial agents obtained from tomato straw composting effectively promote tomato straw compost maturation and improve compost quality

Appropriate management of agricultural organic waste (AOW) presents a significant obstacle in the endeavor to attain sustainable agricultural development. The proper management of AOW is a necessity for sustainable agricultural development. This can be done skillfully by incorporating microbial agents in the composting procedure. In this study, we isolated relevant bacteria strains from tomato straw AOW, which demonstrated efficient degradation of lignocellulose without any antagonistic effects in them. These strains were then combined to create a composite microbial agent called Zyco Shield (ZS). The performance of ZS was compared with a commercially effective microorganism (EM) and a control CK. The results indicate that the ZS treatment significantly prolonged the elevated temperature phase of the tomato straw pile, showing considerable degradation of lignocellulosic material. This substantial degradation did not happen in the EM and CK treatments. Moreover, there was a temperature rise of 4-6 ℃ in 2 days of thermophilic phase, which was not the case in the EM and CK treatments. Furthermore, the inoculation of ZS substantially enhanced the degradation of organic waste derived from tomato straw. This method increased the nutrient content of the resulting compost and elevated the enzymatic activity of lignocellulose-degrading enzymes, while reducing the urease enzyme activity within the pile. The concentrations of NH4+-N and NO3--N showed increases of (2.13% and 47.51%), (14.81% and 32.17%) respectively, which is again very different from the results of the EM and CK treatments. To some extent, the alterations observed in the microbial community and the abundance of functional microorganisms provide indirect evidence supporting the fact that the addition of ZS microbial agent facilitates the composting process of tomato straw. Moreover, we confirmed the degradation process of tomato straw through X-ray diffraction, Fourier infrared spectroscopy, and by scanning electron microscopy to analyze the role of ZS microbial inoculum composting. Consequently, reinoculation compost strains improves agricultural waste composting efficiency and enhances product quality.

Brown sugar as a carbon source can make agricultural organic waste compost enter the secondary thermophilic stage and promote compost decomposition

To enhance the efficiency of composting agricultural organic waste (AOW), this study aimed to examine the impact of inoculating tomato straw compost with two distinct microbial agents: ZymoZone (ZZ), a composite microbial agent derived from the straw compost and Effective Microorganisms (EM), a commercial microbial agent. Furthermore, in order to reactivate the microorganisms within the compost during the initial high temperature phase, 10% brown sugar was introduced as a carbon source. The objective of this addition was to assess its influence on the composting process. The findings revealed that compared to the control (CK) group, the ZZ and EM treatments extended the first high-temperature phase by 2 and 1 day, respectively. Furthermore, with the addition of 10% brown sugar, the ZZ and EM treatments remained in the second high-temperature phase for 8 and 7 days, respectively, while the CK treatment had already entered the cooling stage by then. Notably, the inoculation of microbial agents and the addition of brown sugar substantially augmented the activity of lignocellulose-related hydrolases, thereby promoting the degradation of lignocellulose in the ZZ and EM treatment groups. This was confirmed by FTIR analysis, which demonstrated that the addition of microbial agents facilitated the degradation of specific substances, leading to reduced absorbance in the corresponding spectra. XRD analysis further indicated a notable reduction in cellulose crystallinity for both the ZZ (8.00%) and EM (7.73%) treatments. Hence, the incorporation of microbial agents and brown sugar in tomato straw compost effectively enhances the composting process and improves the quality of compost products.

Incorporation of Substrates and Inoculums as Operational Strategies to Promote Lignocellulose Degradation in Composting of Green Waste—A Pilot-Scale Study

Composting is a sustainable alternative for green waste (GW) valorization contributing to the circular bioeconomy. However, the processing time must be reduced and the end-product quality must be improved. This study determined the effect of the incorporation of processed food waste (PFW), unprocessed food (UPFW), sawdust (SW), phosphate rock (PR) and a specific bacterial inoculum on GW-composting process parameters and product quality. Three treatments were evaluated in 120 kg piles: (i) TA: (GW + UPFW + PFW + inoculum), (ii) TB (GW + UPFW + PFW), and (iii) TC (GW). An inoculum of Bacillus sp. and Paenibacillus sp. was incorporated in the cooling phase for TA. On the other hand, the effect of the inoculum at the laboratory scale (20 kg reactors) was compared with that found at the pilot scale (120 kg piles). The incorporation of FW, SW, PR and the inoculum increased the amount of lignocellulose biodegradation (TA: 29.1%; TB: 22.7%; TC: 18.2%), which allowed for a reduction of up to 14 days of processing time. The product obtained for TA had a similar quality to the other two treatments, although a lower phytotoxicity was determined according to the germination index (TA: 95%; TB: 85%; and TC: 83%). The final product of TA showed the best agricultural characteristics with pH 8.3, TOC of 24.8%, TN of 1.32%, and GI of 98.8%. Finally, the scaling effect with the bacterial inoculum was shown to affect parameters such as the TOC, TN, GI, and, to a lesser extent, temperature and pH. The results obtained in this paper highlight the importance of optimizing the composting of GW, specifically with the use of co-substrates and specific inocula, which can be of interest for composting materials with a high content of lignocellulose such as GW.

Optimization of lignocellulolytic bacterial inoculum and substrate mix for lignocellulose degradation and product quality on co-composting of green waste with food waste

The present study evaluates the effect of the mixing ratio of substrates and inoculation with lignocellulolytic bacteria on green waste (GW) and food waste (FW) co-composting. A Box-Behnken design was used to simultaneously optimize the lignocellulose degradation (%LD) and end-product quality. The best operational conditions were 4.85*10⁵ CFU g^-1 of Bacillus sp. F3X3 and 1.44*10⁶ CFU g^-1 of Paenibacillus sp. F1A5 with a substrate mixture containing 50% GW, 32.5% unprocessed FW, 2.5% processed FW, 13% sawdust, and 2% phosphate rock; with a C/N ratio of 27. Under these conditions, the %LD was 33% and the end-product has pH 8.3, TOC 22,4%, TN 1,7%, and a germination index of 103%. Therefore, the product complies with quality standards for organic fertilizers. The results of this study allow the identification of appropriate strategies to optimize GW composting, increasing the degradation of lignocellulose and improving the end-product quality.

Promoting lignocellulose degradation during green waste composting by maintaining a specific temperature through heap size control

Owing to its high lignocellulose content, the recalcitrance of green waste is a technical challenge obstructing the composting process. This study aimed to identify a temperature that could facilitate efficient lignin and cellulose degradation during green waste composting, and maintain this temperature by controlling the heap size to enhance the degradation. The optimum temperature was determined by conducting a laboratory-scale cultivation experiment under controlled temperatures, and a pilot-scale experiment was conducted to explore heap size control and its influence on green waste composting. The results showed that efficient lignin and cellulose degradation was achieved when the temperature was between 45 and 60 ℃, and maintaining this temperature for at least 150 days maximized the lignin and cellulose degradation rates. This was achieved by constraining the heap size at 0.8 m³ at the beginning of composting; 1.56, 2.60, and 4.00 m³ on days 15, 39, and 96; and then enlarging the heap as much as possible on day 156. Following this approach, the duration of the target temperature was extended by over six times, the lignin and cellulose degradation rates were increased by 18.82-21.38 % and 9.54-11.55 %, and nitrification and humification were enhanced. Correlation analysis showed that lignocellulose degradation, nitrification, and humification were positively and significantly correlated with the duration of the target temperature. Generally, heap size control is an ecological and economic method of enhancing the efficiency and quality of green waste composting and compost, respectively.

Evaluation of Co-Composting as an Alternative for the Use of Agricultural Waste of Spring Onions, Chicken Manure and Bio-Waste Produced in Moorland Ecosystems

Composting is an adequate method for treating and valorizing agricultural waste such as those from spring onion (SO) cultivation and chicken breeding (chicken manure–CM). However, the low content of Total Organic Carbon in the waste from SO and the high concentration of total nitrogen in CM are limitations for the composting process. This research studied the co-composting of SO and CM in a moorland ecosystem, together with locally available co-substrates such as biowaste (BW) and woodchips (WC), focusing on the effect of co-composting in process development and end-product quality. A pilot-scale experiment was carried out using three treatments in triplicated composting piles: (i) Treatment A: 43% CM + 41% BW + 16% WC; (ii) Treatment B: 52% CM + 32% SO + 16% WC, and (iii) Treatment C: 70% SO + 30% WC. Treatments A and B reached thermophilic temperatures after two days of the process start and remained at that level for 17 days. However, treatment B reached environmental temperature during curing in a shorter time (43 days) than treatment A (53 days). Treatment C did not achieve thermophilic temperatures. Tests carried out at the end of the process showed end-product stability and non-phytotoxic characteristics (germination indexes 80%). The fertility index of the products showed that treatments A and B presented values of 4.3 (over 5.0) while treatment C obtained a value of 2.5. From the perspective of agricultural use, products from the three treatments had limitations due to deficiencies in essential nutrients like phosphorus. Still, they had potential as a soil amendment for restoration processes. In summary, we have demonstrated that this waste, in combination with other organic materials, could be a good amendment for the composting process and the end product.

Insight into the evolution of antibiotic resistance genes and microbial community during spiramycin fermentation residue composting process after thermally activated peroxydisulfate pretreatment

Previous research has been demonstrated that the residual unextracted antibiotics in spiramycin fermentation residue (SFR) could be efficiently removed by thermally activated peroxodisulfate (TAP) pretreatment, indicating the improvement of biodegradability. This study aimed to investigate the effect of TAP pretreatment on the succession of bacterial community and fate of antibiotic resistance genes (ARGs) during SFR composting. Results indicated that TAP pretreatment increased the composting temperature and promoted the decomposition of organic matters. Furthermore, TAP pretreatment could increase bacterial alpha diversity and significantly reduce the relative abundance of ARGs (1.13-1.75 times) and mobile genetic elements (MGEs) (1.13-1.32 times) after composting. The compost of pretreated SFR by TAP could reduce the enrichment of ARGs and MGEs in the bacterial community, especially the rRNA methylase genes of ermB (4-142-folds). Redundancy analysis showed that Actinobacteria, Bacteroidetes, Proteobacteria and horizontal gene transfer mediated by MGEs (intI1) was positively related to the changes in ARGs (accounted for 97.4%). Network analysis showed that Firmicutes was the main bacterial hosts of ARGs and MGEs. These findings demonstrated that TAP pretreatment combined composting was a promising strategy for SFR safe treatment and disposal that could reduce the proliferation and transfer of ARGs.

Food waste composting based on patented compost bins: Carbon dioxide and nitrous oxide emissions and the denitrifying community analysis

Mature compost and rice bran were used as bulking agents to perform Food Waste Rapid Composting (FWRC) in a patented composting bin. The characteristics of CO₂ and N₂O emission and the denitrifying community were investigated. The release of CO₂ and N₂O concentrated in the early composting stage and reduced greatly after 28 h, and the N₂O emission peak of the treatment with mature compost was 8.5 times higher than that of rice bran. The high N₂O generation resulted from massive denitrifying bacteria and NO_x^--N in the composting material. The relative abundances of denitrifiers, correspondingly genes of narG and nirK were much higher in the treatment with mature compost, which contributed to the N₂O emission. Moreover, the correlation matrices revealed that N₂O fluxes correlated well with moisture, pH, temperature, and the abundances of nirK and nosZ genes during FWRC.

Adding an appropriate proportion of phosphogypsum ensured rice husk and urea composting to promote the compost as substrate utilization

To explore the effectiveness of urea replacing poultry manure as the nitrogen source in the rice husk composting system, and to promote the utilization of compost products as substrates, 0%, 10%, 20%, and 30% of phosphogypsum were added respectively in the urea composting system, and were compared with the chicken manure composting (RCP0). Finally, the fermentation and maturation of RCP0 were achieved, but high EC value limited the utilization of compost products as the substrate. Urea, as an N source, could lower the EC value, but the C/N ratio was uncoordinated during the initial stage of composting. Adding an appropriate proportion of phosphogypsum could ensure a proper C/N ratio to promote smooth fermentation and enable the products to be ideal substrates. When the added proportion was 30%, the thermophilic stage was shortened significantly but this may increase heavy metals. 10%-20% were concluded to be the recommended proportion.

Effect of biochar combined with a biotrickling filter on deodorization, nitrogen retention, and microbial community succession during chicken manure composting

The high-nitrogen content and dense structure of poultry manure compost cause volatilization of N to ammonia (NH₃). This study evaluated the combined application of biochar and biotrickling filtration (BTF) to remove of odor in chicken manure mixed straw compost (w/w, 2.5:1). Adding of 10% biochar reduced NH₃, hydrogen sulfide (H₂S), and total volatile organic compounds (TVOCs) contents by 20.04%, 16.18%, and 17.55% respectively, and decreased the N loss rate by 8.27%, compared with those observed in control. The organic matter content decreased by 28.11% and germination index reached 97.36% in the experimental group. Meanwhile, the N-cycling microorganisms such as Pusillimonas and Pseudomonas became more active, and the relative abundance of sulfur-cycling microorganisms Hydrogenispora decreased in the experimental group. Following BTF application, the NH₃, H₂S, and TVOCs removal rates reached 95%, 97%, and 53%, respectively.

Composting-a solution of eliminating a nitrite-rich wastewater by reusing it as a moisture conditioning agent

Composting could be applied to dispose various organic solid wastes and liquid wastes. Literature suggested that reusing a nitrogen-rich wastewater as a composting moisture conditioning agent could promote the maturity and nitrogen content of compost. However, it's unclear whether a nitrite-rich wastewater could be eliminated by composting because of the toxicity of nitrite. In this study, a nitrite-rich wastewater (STL, pH = 7.9) was reused as a composting moisture conditioning agent. The influence of STL reusing period (i.e., adding STL from the first day of mesophilic, thermophilic, and cooling period, and the addition lasted for 10 days) on composting performance was also discussed. Results revealed that organic matter decomposition was strongly suppressed by high concentration of free nitrous acid when STL was added in mesophilic period, whereas the organic matter hydrolysis was prompted when STL was added in thermophilic and cooling period. STL addition enhanced nitrification at high temperatures during composting, thus increasing the nitrate content of compost by 2-10 times compared with that of the control group (using tap water as a moisture conditioning agent). Nitrite addition also stimulated nitrous oxide emissions yielded by biotic or chemical processes during STL addition, especially under the transient condition at 50°C-55 °C, and resulted in a 28%-39% increase in greenhouse gas emissions compared with that of the control group. Therefore, the composting could be a solution of eliminating a nitrite-rich wastewater by reusing it as a moisture conditioning agent when nitrous oxide emission issue was properly addressed.

Effect of Microbial Inoculation on Carbon Preservation during Goat Manure Aerobic Composting

Carbon is the crucial source of energy during aerobic composting. There are few studies that explore carbon preservation by inoculation with microbial agents during goat manure composting. Hence, this study inoculated three proportions of microbial agents to investigate the preservation of carbon during goat manure composting. The microbial inoculums were composed of Bacillus subtilis, Bacillus licheniformis, Trichoderma viride, Aspergillus niger, and yeast, and the proportions were B1 treatment (1:1:1:1:2), B2 treatment (2:2:1:1:2), and B3 treatment (3:3:1:1:2). The results showed that the contents of total organic carbon were enriched by 12.21%, 4.87%, and 1.90% in B1 treatment, B2 treatment, and B3 treatment, respectively. The total organic carbon contents of B1 treatment, B2 treatment, and B3 treatment were 402.00 ± 2.65, 366.33 ± 1.53, and 378.33 ± 2.08 g/kg, respectively. B1 treatment significantly increased the content of total organic carbon compared with the other two treatments (p < 0.05). Moreover, the ratio of 1:1:1:1:2 significantly reduced the moisture content, pH value, EC value, hemicellulose, and lignin contents (p < 0.05), and significantly increased the GI value and the content of humic acid carbon (p < 0.05). Consequently, the preservation of carbon might be a result not only of the enrichment of the humic acid carbon and the decomposition of hemicellulose and lignin, but also the increased OTU amount and Lactobacillus abundance. This result provided a ratio of microbial agents to preserve the carbon during goat manure aerobic composting.

Changes in physicochemical properties and microfauna community during vermicomposting of municipal sludge under different moisture conditions

The present study aimed to explore the effect of a range of moisture content levels, including 65%, 72%, and 78%, on physicochemical properties and microfauna communities during vermicomposting of municipal sludge. As a result, death of perishable microfauna together with the degradation of organic matter was the dominant response in all groups in the early period of vermicomposting, while the effects of moisture content levels on various physiochemical parameters did not appear until the mid-later period. After the treatment with 78% moisture content, the content of mineral nitrogen was 1.186 g/kg in the sludge, with a 9.36 × 103 ind./g of microfauna quantity and 663.01 g of earthworm biomass. The values of these three measurements in 78% group were significantly higher than other two groups (p < 0.05), indicating that the effects of 78% moisture content were more pronounced for promoting nitrogen mineralization as well as microfauna and earthworms growth during vermicomposting. Specifically, testate amoebae were strongly associated with nitrification process, while nematodes were related to ammonification and phosphorus mineralization, of which testate amoebae had great potential of being bioindicators during vermicomposting of municipal sludge.

Reducing odor emissions from feces aerobic composting: additives

Aerobic composting is a reliable technology for treating human and animal feces, and converting them into resources. Odor emissions in compost (mainly NH₃ and VSCs) not only cause serious environmental problems, but also cause element loss and reduce compost quality. This review introduces recent progresses on odor mitigation in feces composting. The mechanism of odor generation, and the path of element transfer and transformation are clarified. Several strategies, mainly additives for reducing odors proven effective in the literature are proposed. The characteristics of these methods are compared, and their respective limitations are analyzed. The mechanism and characteristics of different additives are different, and the composting plant needs to be chosen according to the actual situation. The application of adsorbent and biological additives has a broad prospect in feces composting, but the existing research is not enough. In the end, some future research topics are highlighted, and further research is needed to improve odor mitigation and element retention in feces compost.

Aerobic composting is a reliable technology for treating human and animal feces, and converting them into resources. The addition of additives can reduce the production of odor during the composting process.

Insight to nitrification during cattle manure-maize straw and biochar composting in terms of multi-variable interaction

This study investigated nitrification process during cattle manure-maize straw (CM) and biochar (CMB) composting in terms of multi-variable interaction (MVI) among environmental parameters, ammonia-oxidizing archaea (AOA) and bacteria (AOB) community structure, nitrogen-related enzymes as well as substrates using structural equation model (SEM). Results showed that adding biochar significantly reduced potential ammonia oxidation rates. SEM analysis revealed that AOB was affected by temperature and pH, which stimulated the release of urease, increased NH₄⁺-N concentration and finally exerted influence on nitrification in CM. Temperature (0.755) and NO₂^--N (-0.994) were identified as the main factors mediating nitrification in CM and CMB, respectively. Moreover, MVI analysis indicated that nitrification and denitrification occurred simultaneously. Mutual verification of SEM and quantitative analyses (RNA level) confirmed that AOB predominated nitrification. The above results indicated that nitrification could be better explained by MVI using SEM during composting.

Biotransformation of paper mill sludge and tea waste with cow dung using vermicomposting

Vermicomposting of paper mill sludge (PMS) and tea waste (TW) using cow dung (CD) in five different combinations was carried out using Eisenia fetida. The aim of this study was to manage the waste disposal problem of PMS using the environment-friendly technology of vermiconversion. The changes in physico-chemical parameters were observed at 30-day intervals up to 90 days. The final pH was within 6.09-6.95 among all units. The TN, TP and TK contents increased 0.30-0.87, 0.53-3.23, 0.33-0.63 times, respectively in all mixtures after vermicomposting with increase in EC and ash Content. Maximum reduction in Total Organic Carbon (23.91%) was observed in treatment with highest PMS content, attributed to earthworm activity. Reduction in C: N ratio (38.63%-54.05%) was significantly observed in all the treatments. It was finally inferred that the paper mill sludge and tea waste in combination with cow dung can be successfully biotransformed into useful manure employing earthworms.

From anaerobic to aerobic treatment: upcycling of digestate as a moisturizing agent for in-vessel composting process

In Tunisia, there are crucial challenges facing both urban and rural areas, the most prominent of which are the production of organic waste, the need for waste treatment, the demand for water and energy and the need for a circular economy. To this end, the study was designed to develop a technical concept on closed cycle ‘biowaste to bioenergy’ treating, basically food waste (FW) through combined biological processes. In this approach, the generated digestate from FW anaerobic reactors was used successfully as a moisturizing agent for FW in-vessel composting. Four types of digestate were examined to be used as moisturizing agent (MA). The selection of the appropriate MA was achieved based on technical criteria; moisture content (MC), C:N ratio and heavy metals concentrations. The findings showed that the digestate obtained from anaerobic co-digestion of food waste and wheat straw (D1) was the most efficient AD-effluent to be added. In terms of composting process performance, the thermophilic phase of the amended reactor (A1) lasted 16 days and reached higher temperatures of about 72 °C, while the unamended one (A1) was characterized by a thermophilic temperature of around 66 °C indicating that the end products were of a pathogen-free compost. When it comes to the physico-chemical factors examined demonstrating that the biological conditions were sufficiently developed. The findings showed overall decreasing profiles during the composting period for moisture, C:N ratio as well as nitrification index (NI). From the quality-point of view, it was found that heavy metal concentrations had lower limits than those values set by German standards. Moreover, all the compost samples appeared to be stable and classified as class IV and V end product.

Vermicomposting of duckweed (Spirodela polyrhiza) by employing Eisenia fetida: Changes in nutrient contents, microbial enzyme activities and earthworm biodynamics

This study investigated the vermicomposting of duckweed (DW) mixed with cow dung in 25 (T₂₅), 50 (T₅₀), 75 (T₇₅), 100% (T₁₀₀) ratio using Eisenia fetida under a 35 d trail. Decrease in pH, organic carbon (33.54-38.25%), C/N ratio (43.6-56.6%), but increase in total N (18.2-42.4%), P_aval (137-187%), and TK (7.76-79.4%) was recorded. Macro-elements (Mg, Fe, Zn, Mn, and Cu) also showed a many-fold increase in vermicomposts. T₅₀ and T₇₅ showed the highest mineralization rates. Activities of enzymes (proteases; dehydrogenases; β-galactosidase; acid phosphatase; and alkali phosphatases) and soil respiration rate was also higher in DW-rich waste mixtures. Seed bioassay test indicates the high agronomic application of DW-based vermicomposts. High earthworm biomass (975-1395 mg) and fecundity rate (1.53-4.07 cocoons worm^-1) was recorded in all vermi-setups suggesting the suitability of DW as a substrate for E. fetida culture.

Maintaining the ratio of hydrosoluble carbon and hydrosoluble nitrogen within the optimal range to accelerate green waste composting

The recalcitrance of green waste, caused by its high lignocellulose content, is a technical challenge for accelerating green waste composting. Adjusting the initial ratio of total carbon and total nitrogen (TC/TN) to the optimal range of 25-30:1 is a common strategy to accelerate the composting process. However, because microorganisms can only utilize hydrosoluble nutrients directly, we investigated whether maintaining the ratio of hydrosoluble carbon and hydrosoluble nitrogen (HC/HN) within the optimal range through continuous urea addition can better accelerate green waste composting. We conducted a pilot-scale composting experiment, in which the aforementioned maintaining started at the beginning of composting, or after the thermophilic phase. The results demonstrate that maintaining the optimal HC/HN ratio starting at both periods can, to some extent, direct the TC/TN ratio toward 25-30:1, and can also significantly improve heat generation, pH, lignocellulose degradation, and humification. Moreover, lignin degradation was improved by 3.15-7.33%, cellulose degradation was improved by 6.48-8.15%, and carbon content of humus was increased by 7.19-16.13%. Although the maturity assessment showed that none of the final compost reached maturity within the limited experimental period (48 days), based on the promoted lignocellulose degradation and humification, we conclude that maintaining the HC/HN ratio within the optimal range is a more efficient method to accelerate green waste composting, compared to the initial TC/TN adjustment only once.

Monitoring of Fruit and Vegetable Waste Composting Process: Relationship between Microorganisms and Physico-Chemical Parameters

The aim of this study was to investigate and evaluate the composting potential of fruit and vegetable waste with sawdust in different combinations and to establish the relationship between microorganisms and physico-chemical parameters. Three samples were made with the C/N ratios of 50 (sample 1), 45 (sample 2), and 30 (sample 3) by adding fruit waste (apple, banana, orange, and kiwi peels) and vegetable waste (cabbage leaves, potato and carrot peels). The total amount of fruit and vegetable waste was approximately 2 kg in each sample to which different quantities of sawdust were added (1.23, 0.14, and 0.203 kg) in order to obtain the C/N ratios proposed and to limit the odor. Composting process was monitored over 70 days, while physico-chemical and microbiological analyses were performed. Results showed that in the first week pH is acidic and electrical conductivity values are high for all three samples, and then the pH values increase during the composting process, while electrical conductivity values decrease. The nitrogen content is low in all samples and will decrease during the first five weeks of the composting process, then begin to increase slightly. Cr, Cu, Ni, and Zn values in the all three compost samples are below threshold values. During the composing process the microbial communities are constantly changing. The compost was successfully obtained and meets the requirement standards for agricultural use. It can be concluded that there is statistically significant association between the microorganisms and physico-chemical indicators.

Spent mushroom substrate and cattle manure amendments enhance the transformation of garden waste into vermicomposts using the earthworm Eisenia fetida

Garden wastes (GW) having high lignin contents could hinder the growth of earthworms and microorganisms in vermicomposting. This study investigated the Eisenia fetida-based vermicomposting of GW mixed with cattle manure (CM) and/or spent mushroom substrate (SMS) at different ratios of GW alone (control), 3:1 GW:SMS, 1:1 GW:SMS, 3:1 GW:CM, 1:1 GW:CM and 2:1:1 GW:SMS:CM to promote earthworm growth and improve the final vermicompost quality. In general, treatments with the addition of SMS and/or CM increased the survival rate, biomass, cocoon and juvenile numbers of E. fetida compared to the control. The addition of SMS and/or CM also significantly increased the activities of dehydrogenase, cellulase, urease, and alkaline phosphatase compared to the control. Furthermore, the addition of SMS and/or CM facilitated the decomposition of organic matter, cellulose and lignin, increased nutrient (N, P and K) concentrations, and accelerated nitrification compared to the control. The addition of SMS and CM led to greater chemical changes of the substrate compared to control. Heavy metal concentrations were increased in the final vermicomposts comparatively to the initial materials, but none of them exceeded the permissible limits. The highest germination index of Chinese cabbage and tomato seeds were both observed in the treatment of 2:1:1 GW:SMS:CM which reached 146.9 and 148.1. Overall, the 2:1:1 GW:SMS:CM treatment had the highest growth and reproduction rates of E. fetida, higher percentage degradation of organic matter, cellulose and lignin, as well as the best quality of the final vermicompost.

Evaluation of mixing ratio and frequency of turning in the co-composting of biowaste with sugarcane filter cake and star grass

This work studied the effect of mixing ratio (MR) and turning frequency (TF) in biowaste composting (BW) with sugarcane filter cake (SFC) and star grass (SG), both on process performance (temperature, static respiration index, total organic carbon, total nitrogen and total phosphorus) and on product quality (pH, cation exchange capacity, electrical conductivity, organic matter, nutrients, stability, maturity, total coliforms and faecal coliforms), through the Principal Components Analysis (PCA). The Pearson correlation coefficients were calculated for all the quality parameters. A joint effect of mixing ratio and turning frequency was demonstrated, highlighting the importance of studying the operational parameters simultaneously. The results of the PCA showed that the best operating conditions and therefore higher product quality is achieved with a TF of twice a week and MR between 20 and 30% of SFC or SG. Additionally, it was found that a frequency of one turn per week generates the lowest product quality, regardless the co-substrate and the MR. The best treatment corresponded to BW composting with MR of 20% SFC and TF of two turnings per week. The obtained results allow to optimize the operation in composting facilities.

Removal and dissipation pathway of typical fluoroquinolones in sewage sludge during aerobic composting

To observe the effect of aeration strategies on the dissipation of fluoroquinolones (FQs) during aerobic composting and explore their dissipation pathways, 60-L composting and 0.5-L incubation experiments were carried out in this study. Three aeration strategies (windrow, static aeration, feedback aeration) were applied to remove two typical FQs (Norfloxacin (NOR) and Ofloxacin (OFL)) during the 60-L composting of sewage sludge with 5 mg kg^-1 of FQs added. Then, three 0.5 L-sample groups were taken during the three phases of the 60-L composting matrixes without FQs under static aeration, and were inoculated separately at 35 °C, 55 °C and 40 °C after being added with 5 mg kg^-1 of FQs. In each group, incubation was carried out for three treatments (sterilization + no aeration, sterilization + aeration, and no sterilization + aeration). The FQs in the sewage sludge were mainly removed in the mesophilic and thermophilic phases in all the aeration strategies. The removal efficiencies were high for the whole process: 89.6-95.4% for NOR and 87.2-95.4% for OFL. The order of removal efficiency of FQs was static aeration > feedback aeration > windrow. The combination of composting phases facilitated to the rapid dissipation of FQs, which reduced the half-life to about 1/6 to 1/5 of the values in each phase. In the mesophilic and thermophilic compost, biodegradation was the main pathway for the dissipation of FQs followed by irreversible adsorption. Irreversible adsorption and biodegradation provided similar removal efficiencies for the curing compost. The volatilization of FQs was non-negligible in all phases.

Application of seasonal freeze-thaw to pretreat raw material for accelerating green waste composting

The recalcitrance of green waste, caused by its high lignocellulose content, is a technical challenge for accelerating green waste composting. However, because lignocellulose degradation in litter (similar to green waste) can be promoted during the freeze-thaw season, and the composting is difficult to implement in this period (due to the low temperature); seasonal freeze-thaw was intended to be used as a pretreatment strategy for the existing technical challenge in the winter of cold regions. In this process, green waste was pretreated with seasonal freeze-thaw to enhance its lignocellulose degradation for subsequent composting. To verify this assumption, two strategies for the pretreatment were used: the green waste was either drenched or immersed in water during the freeze-thaw season, and the effects on subsequent composting were evaluated. The results demonstrated that both strategies can significantly promote the mineralization of TOC (total organic carbon, by 2.73%-8.01% compared with the control, the following comparisons were all based on the control), TN (total nitrogen, by 0.21%-0.52%), and lignocellulose (lignin degradation was promoted by 3.52%-3.73%, cellulose degradation was promoted by 13.23%-14.26%) during composting and that the synthesis of humus was also enhanced (by 19.19%-21.43%). Furthermore, since the loss of NH₄⁺N and NO₃^-N was significantly less in the drenched treatment than in the immersed treatment (by 9.15% for the loss of NH₄⁺N and 7.66% for the loss of NO₃^-N), drenching the green waste during the freeze-thaw season might be a better strategy than immersing for nitrogen conservation. An additional advantage of drenching compared to immersing is water conservation.

Application of quadratic regression orthogonal design to develop a composite inoculum for promoting lignocellulose degradation during green waste composting

The aims of this study are to determine the feasibility of applying QROD (quadratic regression orthogonal design) to optimize a combination of microorganisms and to develop a composite inoculum for promoting lignocellulose degradation during GWC (green waste composting). This feasibility was studied in a laboratory scale experiment, using three lignocellulolytic microorganisms, isolated from the mature phase of GWC by the dilution plating method. After the feasibility was confirmed, a composite inoculum was developed through the results of the optimization, whose effect was evaluated by comparing it with Phanerochaete chrysosporium and EM (Effective Microorganisms) in a pilot scale experiment of GWC. The use of QROD to finish this optimization was proven feasible, because the p value of the regression equation was less than 0.05 (0.0108), meaning that the quadratic regression model is suitable for describing the relationship between the combination of the three microorganisms and their ability to degrade lignocellulose. Additional proof of this feasibility is that the composite inoculum in the quadratic regression orthogonal experiment demonstrated lignocellulose degradation ability similar to the GWC experiment. Although the lignin degradation ability of the composite inoculum did not surpass Phanerochaete chrysosporium, it was stronger than EM. Meanwhile, cellulose degradation ability and humus synthesis ability of the composite inoculum were stronger than for Phanerochaete chrysosporium and were close to EM. It is hard to tell which inoculum is the best since each inoculum had advantages in different aspects, while the composite inoculum still showed a considerable effect of lignocellulose degradation during GWC.

A systematic review on the composting of green waste: Feedstock quality and optimization strategies

Green waste (GW) is an important fraction of municipal solid waste (MSW). The composting of lignocellulosic GW is challenging due to its low decomposition rate. Recently, an increasing number of studies that include strategies to optimize GW composting appeared in the literature. This literature review focuses on the physicochemical quality of GW and on the effect of strategies used to improve the process and product quality. A systematic search was carried out, using keywords, and 447 papers published between 2002 and 2018 were identified. After a screening process, 41 papers addressing feedstock quality and 32 papers on optimization strategies were selected to be reviewed and analyzed in detail. The GW composition is highly variable due to the diversity of the source materials, the type of vegetation, and climatic conditions. This variability limits a strict categorization of the GW physicochemical characteristics. However, this research established that the predominant features of GW are a C/N ratio higher than 25, a deficit in important nutrients, namely nitrogen (0.5-1.5% db), phosphorous (0.1-0.2% db) and potassium (0.4-0.8% db) and a high content of recalcitrant organic compounds (e.g. lignin). The promising strategies to improve composting of GW were: i) GW particle size reduction (e.g. shredding and separation of GW fractions); ii) addition of energy amendments (e.g. non-refined sugar, phosphate rock, food waste, volatile ashes), bulking materials (e.g. biocarbon, wood chips), or microbial inoculum (e.g. fungal consortia); and iii) variations in operating parameters (aeration, temperature, and two-phase composting). These alternatives have successfully led to the reduction of process length and have managed to transform recalcitrant substances to a high-quality end-product.

Nitrification within composting: A review

Composting could be regarded as a process of processes because it entails a number of complex chemical and microbiological reactions and transformations. Nitrification is one of such processes that normally takes place during the curing phase. This process has been studied in detail for wastewater treatment, and it is becoming an extensively studied topic within composting. In the past, nitrate presence in compost has been clearly perceived as a maturation indicator; however, nowadays, nitrate formation is also conceived as a way of conserving nitrogen in compost. Nitrification is a process closely linked to other processes such as ammonification and the possible loss of ammonia (NH₃). Nitrification is defined as conversion of the most reduced form of nitrogen (NH₃) to its most oxidized form (i.e. nitrate) and it is performed in two steps which are carried out by two different groups of microorganisms: the ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB). The objectives of this review are: a) to gather relevant information on nitrification, which can specifically occur during composting, b) to outline ultimate findings described by the literature in order to increase the understanding and the application of nitrification within composting, and c) to outline future research direction.

Using cow dung and spent coffee grounds to enhance the two-stage co-composting of green waste

The objective of this study was to determine the effects of cow dung (CD) (at 0%, 20%, and 35%) and/or spent coffee grounds (SCGs) (at 0%, 30%, and 45%) as amendments in the two-stage co-composting of green waste (GW); the percentages refer to grams of amendment per 100g of GW based on dry weights. The combined addition of CD and SCGs improved the conditions during co-composting and the quality of the compost product in terms of composting temperature; particle-size distribution; mechanical properties; nitrogen changes; low-molecular weight compounds; humic substances; the degradation of lignin, cellulose, and hemicellulose; enzyme activities; the contents of total Kjeldahl nitrogen, total phosphorus, and total potassium; and the toxicity to germinating seeds. The combined addition of 20% CD and 45% SCGs to GW resulted in the production of the highest quality compost product and did so in only 21days.

Biochar to reduce ammonia emissions in gaseous and liquid phase during composting of poultry manure with wheat straw

Composting of poultry manure which is high in N and dense in structure can cause several problems including significant N losses in the form of NH₃ through volatilization. Biochar due to its recalcitrance and sorption properties can be used in composting as a bulking agent and/or amendment. The addition of a bulking agent to high moisture raw materials can assure optimal moisture content and enough air-filled porosity but not necessarily the C/N ratio. Therefore, amendment of low C/N composting mixtures with biochar at low rates can have a positive effect on composting dynamics. This work aimed at evaluating the effect of selected doses of wood derived biochar amendment (0%, 5% and 10%, wet weight) to poultry manure (P) mixed with wheat straw (S) (in the ratio of 1:0.4 on wet weight) on the total ammonia emissions (including gaseous emissions of ammonia and liquid emissions of ammonium in the collected condensate and leachate) during composting. The process was performed in 165L laboratory scale composting reactors for 42days. The addition of 5% and 10% of biochar reduced gaseous ammonia emission by 30% and 44%, respectively. According to the obtained results, the measure of emission through the condensate would be necessary to assess the impact of the total ammonia emission during the composting process.

Biochar amendment for integrated composting and vermicomposting of sewage sludge - The effect of biochar on the activity of Eisenia fetida and the obtained vermicompost

Sewage sludge derived biochar (SSDB) was used as a supplementary material for municipal sewage sludge (SS) and wood chips mixtures (WC) treated by combined composting and vermicomposting. SSDB added to the mixture before composting resulted in significantly higher reproduction rate: on week 4 the number of cocoons increased by 213% when compared to the mixture with no biochar. On week 6 the average number of juveniles increased 11-fold in the mixture with biochar added before composting and 5-fold in the mixtures with biochar added after composting when compared to the mixture with no biochar. Biochar added before composting reduced bioavailability of Cd and Zn to E. fetida. The biochar-added vermicomposts showed good fertilizing properties except for elevated concentrations of Cr. The pH of all vermicomposts was in the range of 5.27-5.61. The obtained vermicomposts can be used as a growing medium for horticultural purposes or as an amendment in calcareous soils.