Prediction of moisture variation during composting process: A comparison of mathematical models

Alternating ventilation accelerates the mineralization and humification of food waste by optimizing the temperature-oxygen-moisture distribution in the static composting reactor

Traditional unidirectional ventilation often leads to the loss of heat and moisture during composting, disrupting the favorable microenvironment required for aerobic microbes. This study developed a pulse alternating ventilation composting reactor and investigated the effects of alternating ventilation on composting efficiency compared with upward ventilation and downward ventilation. The results demonstrated that alternating ventilation stabilized the moisture content at approximately 60 % while reducing the temperature and oxygen concentration range within the reactor. Moreover, it extended the duration of high-temperature (>50 °C) by 31 % and 75 % compared to other two groups. It improved the microbial cooperation intensity and stimulated the core microbe (Tepidimicrobium). Seed germination index (GI) of the compost was improved (GI = 91.27 %), and the humic acid content was 1.23 times and 1.37 times higher than other two groups. These results showed that alternating ventilation can be used for efficient resource disposal of food waste.

Comprehensive evaluation on effect of planting and breeding waste composts on the yield, nutrient utilization, and soil environment of baby cabbage

Treatment of the planting and breeding waste is becoming a big issue due to their significant quantities. Composting could be an effective alternative for planting and breeding waste management which could be used as fertilizer. The purpose of this research was to evaluate the effect of planting and breeding waste on baby cabbage growth and soil properties, to establish a suitable agricultural cycle model for semi-arid area in central Gansu Province. The planting and breeding wastes [sheep manure (SM), tail vegetable (TV), cow manure (CM), mushroom residue (MR) and corn straw (CS)] were used as the raw materials in this study, which were designed 8 compost formulas for composting fermentation. With no fertilization (CK1) and local commercial organic fertilizer (CK2) as the control, the comprehensive evaluation of planting and breeding waste composts on the yield of baby cabbage, fertilizer utilization rate, soil physical and chemical properties and microbial diversity were studied to select the best compost formula suitable for the growth of baby cabbage. And the material flow and energy flow analysis of the circulation model established by the formula were carried out. The results showed that the biological yield and economic yield of baby cabbage, absorption and recycling utilization of total phosphorus (TP) and total potassium (TK) reached the maximum under the formula of SM: TV: MR: CS = 6:2:1:1. Compared with CK2, the formula of SM: TV: MR: CS = 6:2:1:1 significantly increased the richness of soil bacteria and beneficial bacteria Proteobacteria, and decreased the relative abundance of harmful bacteria Olpidiomycota. Principal component analysis showed the comprehensive score of SM: TV: MR: CS = 6:2:1:1 was the best organic compost formula suitable for producing high-quality and high-yield baby cabbage and improving soil environment. Therefore, this formula can be used as a reference organic fertilizer formula for field cultivation of baby cabbage.

Toxicity and physicochemical parameters of composts including distinct residues from agribusiness and slaughterhouse sludge

Composting is useful for treatment of residues from agribusiness, but the potential toxicity of the final compost should be evaluated before its agricultural destination. The objective of this study was to evaluate the physicochemical characteristics and the toxicity of agribusiness residues using onion seeds as bioindicators. All tested treatments were composed by sludge from a swine slaughterhouse and sawdust. Besides the control, which included no additional materials, the other treatments included aviary bedding, rice husk and residue from tobacco industries as structuring materials. After 120 days of composting, for all treatments, the temperature inside the composting piles approached the environmental temperature, the physicochemical parameters indicated that the composts were stabilized and, except for the treatment including tobacco residues, that could be used for agriculture without impairing plant germination. Although the treatments including tobacco residues and rice husk showed evidence of cytotoxicity and genotoxicity at the beginning of the composting period, that was not observed for the treatment including aviary bedding. Such potential toxicity was not observed at the end of composting for any of the tested treatments.

A Review of Composting Process Models of Organic Solid Waste with a Focus on the Fates of C, N, P, and K

To foster a circular economy in line with compost quality assessment, a deep understanding of the fates of nutrients and carbon in the composting process is essential to achieve the co-benefits of value-added and environmentally friendly objectives. This paper is a review aiming to fill in the knowledge gap about the composting process. Firstly, a systematic screening search and a descriptive analysis were conducted on composting models involving the fates of Carbon (C), Nitrogen (N), Phosphorus (P) and Potassium (K) over the past decade, followed by the development of a checklist to define the gap between the existing models and target models. A review of 22 models in total led to the results that the mainstream models involved the fates of C and N, while only a few models involved P and K as target variables. Most of the models described the laboratory-scale composting process. Mechanism-derived models were relatively complex; however, the application of the fractionation of substrates could contribute to reducing the complexity. Alternatively, data-driven models can help us obtain more accurate predictions and involve the fates of more nutrients, depending on the data volume. Finally, the perspective of developing composting models for the fates of C, N, P, and K was proposed.

Gasification filter cake reduces the emissions of ammonia and enriches the concentration of phosphorous in Caragana microphylla residue compost

Nutrient loss is a major problem during agricultural waste composting. This study investigated the impact of gasification filter cake (GFC) addition on gaseous emissions and nutrient loss during composting of chicken manure mixed with Caraganna microphylla straw. The GFC was added to the composting mix at dry weight rates of 0% (GFC₀), 6.25% (GFC_6.25), 12.5% (GFC_12.5), 25% (GFC₂₅) and 50% (GFC₅₀). Overall, GFC_12.5 and GFC₂₅ efficiently enhanced organic matter decomposition, reduced N loss and enriched P and K concentrations during composting, as compared to GFC₀. However, GFC_6.25 did not show a significant effect on organic matter decomposition, while GF_C50 had no effect on N loss. As a result, an overall enhancement of nutrient contents was observed in the final composts of GFC_12.5 and GFC₂₅. These results suggest that the addition of GFC at moderate-rates (i.e. 12.5% and 25%) can enhance nutrient retention and thereby result in a nutrient-rich compost.

Effects of moisture and carbon/nitrogen ratio on gaseous emissions and maturity during direct composting of cornstalks used for filtration of anaerobically digested manure centrate

This study investigated the maturity and gaseous emission during direct composting of cornstalks used as organic media for filtration of anaerobically digested manure centrate. Effects of moisture and carbon/nitrogen (C/N) ratio on composting performance were evaluated. Results show that cornstalks could effectively retain suspended solids and organic matter in digested manure centrate to lower their C/N ratio and attain microbial inoculation. Filtered cornstalks became more compostable when their moisture decreased from 76% to 60% or C/N ratio increased from 12 to 24. Nevertheless, such adjustment aggravated the emission of greenhouse and odours gases during composting. Regardless of composting conditions, the phylum Firmicutes was the most dominant with reduced abundance during composting. Similar reduction also occurred to several abundant phyla, including Atribacteria, Synergistetes and Euryarchaeota. By contrast, the phylum Bacteroidetes, Chloroflexi, Proteobacteria and Actinobacteria enriched as composting progressed. In addition, compost maturity was insignificantly affected by matrix moisture and C/N ratio.

Recalcitrant carbon for composting of fibrous aquatic waste: Degradation kinetics, spectroscopic study and effect on physico-chemical and nutritional properties

Biochar, a recalcitrant carbon, is known to enhance organic matter degradation and improve physical properties. The objective of the study is to examine the probable effect of biochar addition during composting of a fibrous aquatic waste, i.e., water hyacinth though degradation kinetics and spectroscopic (FTIR and PXRD) analysis. Four dosages of biochar (0, 2.5, 5, and 10% w/w) were mixed to a mixture of water hyacinth, cow-dung and saw-dust comprising a total weight of 150 kg and composted using rotary drum composter for 20 days in batch mode. The study outcomes indicated that the amendment of biochar prolonged the duration of the thermophilic temperatures, reduced salinity, and promoted nutritional quality of compost. Moreover, biochar amendment enhanced the organic matter degradation with a rate constant of 0.029 day^-1 and increased the total Kjeldahl nitrogen content up to 1.75% from an initial value of 1.10% in the reactor with 2.5% biochar amendment. Concurrently, biochar amendment aided in reducing Cu and Cr in the final product inferring 2.5% biochar is best suited for composting of water hyacinth. However, future studies are encouraged to decipher the microbial shifts and bioavailability of metals due to biochar dosage during composting for mitigating and managing the menace of such fibrous waste like water hyacinth by converting it to a soil conditioner.

Combining pre-treatment strategies for broilers industry waste valorization

aiming at expanding the possibilities for broiler slaughter wastes valorization, composting piles were submitted, at different time points (T₀, T₁₀, T₂₀, T₃₀ and Control) representing the treatments, to a solid-liquid fraction separation (FS), after being submerged in water (2:1, water:compost, in the fresh weight). After FS, solid material separated with a strain was again placed in piles for the final stage of composting, being evaluated the organic composts obtained after the stabilization phase (65 days) and maturation (95 days), in the different treatments. Reductions in mass (60–62%) and volume (56–64%) were greater in piles submitted to FS in comparison to control piles (52% and 54%). On the other hand, the FS induced greater losses of C (70.3–71.3%), N (55–62%), P (41.7–54.4%) and K (62.3–72.1%) in comparison to the control (65.2%, 48.0%, 28.1%, and 37.6%, respectively). We conclude that, as a way of integrating bioprocesses, FS does not have negative effects on the composting process. Moreover, compost mixtures from FS-treated piles, when used as substrate, yield better seedlings in comparison to mixtures from control.

Improving municipal solid waste compost process by cycle time reduction through inoculation of Aspergillus niger

A lack of understanding about the effect of microorganism inoculation on compost production and relatively expensive downstream processing are the main obstacles towards an economic compost production. Our work tries to fill this gap. For this, influence of inoculation on the composting of organic fraction of municipal solid waste (OFMSW) to produce compost with higher agronomic value was evaluated. Three similar aerated bioreactors (A, B and C) with the same size and shape in laboratory scale designed. Reactor A was inoculated with the Aspergillus niger IBRC-M 30095, reactor B was inoculated with old compost and reactor C was used as a control. During the composting process temperature, moisture, pH, and electrical conductivity (EC) were evaluated. Also, the ratio of carbon to nitrogen (C/N) and germination index (GI) were measured in during process to evaluate compost maturity. The results of this study showed that the C/Ns decreased to about 63.37%, 59.6% and 46% for bioreactors B, A and control, respectively. Also maximum GI and temperature reached to about 138% and 59 °C in reactor B. Furthermore, our results showed that inoculation with this microorganism reduces process time to 18 days that is better than the results of other researchers and thus results in cost savings. However, we think, Aspergillus niger is appropriate candidate for compost production as a model. Graphical abstractSchematic diagram of experimental reactors: Reactor A was inoculated with the Aspergillus Niger IBRC-M 30095, reactor B was inoculated with old compost and reactor C used as a control without inoculation; (1) composting tank; (2) air compressor; (3) gas flow meter; (4) air regulator; (5) thermal probe; (6) exhausted gas; (7) mixer; (8) effluent; (9) moisture content probe; (10) sampling; (11) electric motor; (12) pump.

Clarifying configurations of reaction rate constant for first-order and Monod-type kinetics: A comparative manner and a pursuit of parametric definition

The mechanisms of first-order and Monod-type kinetics describes degradation in distinct manner and yet too little attention is paid on the fact that first-order kinetic was derived from pure elementary reaction while Monod-type degradation was based on microbial uptake. Both mechanisms are basic theories in developing sophisticated degradation models and there are needs to give more guidance on selection of kinetics. The objective of this study was to compare the two kinetics when used for modeling degradation and biodegradability during composting. With both experimental data, from reactor composting of swine manure/wheat straw, and simulated results, it was found that Monod-type kinetic was more capable of modeling the lag phase, while first-order kinetic could explain the fast oxygen uptake rate for the oxidation of soluble substrate. Comparison of growth rate constants, based on Monod-type equation, with maximum degradation rate constants, based on first-order kinetic, showed that the former was generally one magnitude greater, which could be explained with the fact that part of growth of cell weight was from water consumption.

Characterization of lignocellulosic compositions' degradation during chicken manure composting with added biochar by phospholipid fatty acid (PLFA) and correlation analysis

Biorefractory high polymer lignocellulosic compositions may limit rapid composting and stable decomposition. Because their degradation during composting is not well understood, the correlation with microbial community profiles was assessed to reveal degradation mechanism of lignocellulosic compositions. Testing of chicken manure aerobic composting with added biochar was performed using phospholipid fatty acid (PLFA) and correlation analysis. Results demonstrated a good composting effect with good dynamic correlation between microbial characteristic (PLFA) and lignocellulosic compositions' degradation ratio. The prediction model for hemicellulose degradation ratio (R²=0.97, SEP=3.24) and the prediction model for cellulose degradation ratio (R³=0.94, SEP=3.09), built using PLFA 16:0-18:2ω6c and PLFA 18:2ω6c-18:3ω3 as the arguments had good predictive ability. Based on microbial analysis and quantitative characterization of the degradation ratio, the prediction models provided methodological support for delineating the mechanism of lignocellulosic compositions' degradation during chicken manure aerobic composting with added biochar.

Composting technology in waste stabilization: On the methods, challenges and future prospects

Composting technology has become invaluable in stabilization of municipal waste due to its environmental compatibility. In this review, different types of composting methods reportedly applied in waste management were explored. Further to that, the major factors such as temperature, pH, C/N ratio, moisture, particle size that have been considered relevant in the monitoring of the composting process were elucidated. Relevant strategies to improve and optimize process effectiveness were also addressed. However, during composting, some challenges such as leachate generation, gas emission and lack of uniformity in assessing maturity indices are imminent. Here in, these challenges were properly addressed and some strategies towards ameliorating them were proffered. Finally, we highlighted some recent technologies that could improve composting.

Application of Contois, Tessier, and first-order kinetics for modeling and simulation of a composting decomposition process

An integrated model was developed by associating separate degradation kinetics for an array of degradations during a decomposition process, which was considered as a novelty of this study. The raw composting material was divided into soluble, hemi-/cellulose, lignin, NBVS, ash, water, and free air-space. Considering their specific capabilities of expressing certain degradation phenomenon, Contois, Tessier (an extension to Monod kinetic), and first-order kinetics were employed to calculate the biochemical rates. It was found that the degradation of soluble substrate was relatively faster which could reach a maximum rate of about 0.4perhour. The hydrolysis of lignin was rate-limiting with a maximum rate of about 0.04perhour. The dry-based peak concentrations of soluble, hemi-/cellulose and lignin degraders were about 0.9, 0.2 and 0.3kgm(-3), respectively. Model developed, as a platform, allows degradation simulation of composting material that could be separated into the different components used in this study.

Integrating particle physical geometry into composting degradation kinetics

The study was carried out to integrate physical geometry of compost particle with degradation kinetics to model biological reactions, which revealing additional dynamic approaches. A sphere and its circumscribing cube were used to represent compost particles. An inner sphere, representing anaerobic zone, was introduced to describe variations of substrate volume without sufficient oxygen supply. Degradation of soluble substrates and hydrolysis of insoluble substrates were associated with the particle geometry. Transportation of soluble substrates produced from hydrolysis was expressed using Fick's law. Through the integration of degradation kinetics with geometry models, degradation models could describe varying volume of composting materials involving aerobic or anaerobic digestion and transportation of soluble substrates in a unit compost particle.

Mathematical model of organic substrate degradation in solid waste windrow composting

Organic solid waste composting is a complex process that involves many coupled physical, chemical and biological mechanisms. To understand this complexity and to ease in planning, design and management of the composting plant, mathematical model for simulation is usually applied. The aim of this paper is to develop a mathematical model of organic substrate degradation and its performance evaluation in solid waste windrow composting system. The present model is a biomass-dependent model, considering biological growth processes under the limitation of moisture, oxygen and substrate contents, and temperature. The main output of this model is substrate content which was divided into two categories: slowly and rapidly degradable substrates. To validate the model, it was applied to a laboratory scale windrow composting of a mixture of wood chips and dog food. The wastes were filled into a cylindrical reactor of 6 cm diameter and 1 m height. The simulation program was run for 3 weeks with 1 s stepwise. The simulated results were in reasonably good agreement with the experimental results. The MC and temperature of model simulation were found to be matched with those of experiment, but limited for rapidly degradable substrates. Under anaerobic zone, the degradation of rapidly degradable substrate needs to be incorporated into the model to achieve full simulation of a long period static pile composting. This model is a useful tool to estimate the changes of substrate content during composting period, and acts as a basic model for further development of a sophisticated model.