Estimation of maturity of compost from food wastes and agro-residues by multiple regression analysis

Co-composting of green waste and biogas waste: physical, chemical parameters and quality of ripe compound

The impact of adding biogas waste (BW) to green waste (GW) composting to increase nitrogen supplementation and improve mature compost quality was investigated. Conducted over 90 days using static windrows, the experiment compared treatments with GW alone (T1) and GW supplemented with BW (T2 and T3). The results showed that the addition of BW increased temperatures, improved the C/N ratio, and expedited the stabilization process compared to T1. Furthermore, the addition of BW led to significant degradation of hemicellulose (up to 39.98%) and cellulose (up to 27.63%) compared to GW alone. Analysis of Fourier-transform infrared (FTIR) spectra revealed the presence of aromatic, phenolic, aliphatic, and polysaccharide structures in the compost, with BW supplementation enhancing these characteristics. Importantly, the germination index (GI) assessment indicated that the compounds produced were not toxic and instead exhibited stimulatory effects on seed germination. Overall, the findings suggest that supplementing GW composting with BW can enhance the quality and efficacy of the composting process, resulting in compost with desirable properties for agricultural use.

Application of Multivariate Regression and Artificial Neural Network Modelling for Prediction of Physicochemical Properties of Grape-Skin Compost

The reusability of by-products in the food industry is consistent with sustainable and greener production; therefore, the aim of this paper was to evaluate the applicability of multiple linear regression (MLR), piecewise linear regression (PLR) and artificial neural network models (ANN) to the prediction of grape-skin compost's physicochemical properties (moisture, dry matter, organic matter, ash content, carbon content, nitrogen content, C/N ratio, total colour change of compost samples, pH, conductivity, total dissolved solids and total colour change of compost extract samples) during in-vessel composting based on the initial composting conditions (air-flow rate, moisture content and day of sampling). Based on the coefficient of determination for prediction, the adjusted coefficient of determination for calibration, the root-mean-square error of prediction (RMSEP), the standard error of prediction (SEP), the ratio of prediction to deviation (RPD) and the ratio of the error range (RER), it can be concluded that all developed MLR and PLR models are acceptable for process screening. Furthermore, the ANN model developed for predicting moisture and dry-matter content can be used for quality control (RER >11). The obtained results show the great potential of multivariate modelling for analysis of the physicochemical properties of compost during composting, confirming the high applicability of modelling in greener production processes.

Determining the extraction conditions and phytotoxicity threshold for compost maturity evaluation using the seed germination index method

The phytotoxicity of the compost aqueous extracts determines the maturity. To improve the accuracy of compost maturity evaluation using the seed germination index (GI) method, different extraction methods (different moisture content and extraction ratio) were designed to obtain samples with various phytotoxic level. This study analyzed the effects of different extraction condition of compost samples on GI, and established the relationship between phytotoxicity and GI. The results showed that the moisture content and extraction ratio of the compost significantly affected the GI. The extraction ratio for the compost with 60-70 % moisture content was 1:10 (ratio of compost mass to extract volume). However, commercial compost, which must have a moisture content of 30-45 %, had an extraction ratio of 1:30 (w:v). More importantly, compost extraction based on dry weight, with a moisture content of 10-15 %, more effectively reflected the phytotoxicity variations during composting. In such cases, the extraction ratio should be at least 1:30 (w:v) but not exceed 1:50 (w:v). The relationship between phytotoxicity and GI showed that dissolved organic carbon and dissolved nitrogen were the most important factors influencing GI, followed by NH4+, electrical conductivity, K, volatile fatty acids, Zn, and Cu. For composts with a GI greater than 70 %, the dissolved organic carbon, dissolved nitrogen, and NH4+ concentrations were below 257, 164, and 73 mg/L, respectively. These findings provide an optimized standard method for compost maturity evaluation using GI and a concentration threshold of key phytotoxicity is proposed to achieve accurate control of compost maturity.

Effects of oxygen supply rate on organic matter decomposition and microbial communities during composting in a controlled lab-scale composting system

The study aimed to elucidate the effect of oxygen supply rate (OSR) on the composting of model organic waste independently from other factors by using a controlled laboratory-scale reactor system. Four OSRs, 96.2, 24.2, 13.7, and 3.45 mL-O₂/min/kg-WS (wet solid), were tested. The delay of organic matter degradation was observed temporarily in the early stage of composting with 13.7 mL-O₂/min/kg-WS and severe oxygen deficiency was observed in lower OSR, indicating that the critical OSR existed around this value. Composting with 3.45 mL-O₂/min/kg-WS resulted in constantly low CO₂ evolution rate and remarkably low degree of organic matter degradation. Under deficient oxygen, all enzymes measured, such as phosphatases, esterases, lipases, proteases, and sugar degrading enzymes, showed lower activities. High-throughput sequencing revealed Caldibacillus and Ureibacillus became dominant in the later stages of the oxygen deficiency composting, while Geobacillus was the most dominant microorganism throughout composting with OSR higher than 13.7 mL-O₂/min/kg-WS.

Mitigating gas emissions from poultry litter composting with waste vinegar residue

The composting process is important in the recycling of organic wastes produced in agriculture, food, and municipal waste management. This study explored the suitability of using waste vinegar residue (WVR) as an amendment in poultry litter (PL) composting. Four treatments, including poultry litter (CK), poultry litter+vinegar residue (VR), poultry litter+vinegar residue+lime (VR_Ca) and poultry litter+vinegar residue+biochar (VR_B), were conducted. During a 42-day composting period, the dynamics of carbon dioxide (CO₂), ammonia (NH₃), nitrous oxide (N₂O) and methane (CH₄) emissions, as well as the physicochemical properties and abundances of the bacteria and fungi of the feedstock were tracked to examine the potential barriers in the co-composting of WVR and PL. Compared to those of the CK, using a WVR amendment lowered the pH, increased the electrical conductivity significantly at the early stage, resulted in a strong inhibition of bacterial and fungal growth and delayed the thermophilic period of poultry litter composting while significantly reducing NH₃ and N₂O and GHG (CO₂-e) emissions. A preadjustment of the WVR with alkaline biochar or lime lengthened the thermophilic period and increased the germination index (GI) by alleviating the inhibitory effect of the WVR on bacterial and fungal growth during composting. However, such preadjustment might reduce the mitigation effect on NH₃. In conclusion, WVR can be recycled through co-composting with poultry litter, and the additional mitigation of N losses and N conservation can be achieved without halting compost quality.

Critical Factors and Emerging Opportunities in Food Waste Utilization and Treatment Technologies

Globally, approximately one-third of food produced for human consumption is lost or discarded, comprising 1. 3 billion tons annually. Factors contributing to food waste from the food manufacturer to the consumer level are numerous. Events that may result in food waste include, but are not limited to, manufacturing food by-products, improper handling within the supply chain (e.g., cold chain deviations), misunderstood food date labels, over-purchasing, and consumer-level temperature abuse. From the manufacturer to consumer, each node in the food supply requires concerted efforts to divert food waste from entering municipal landfills. Depending on the state of the food waste, it is diverted to various outlets, from food donation for consumption to composting for soil amendment. To better understand the opportunities in the United States to divert food waste from landfills, current and emerging federal policies as well as the causes of food waste generation must be understood. Unfortunately, information on both the composition of food waste in the U.S. and how it impacts critical factors in food waste treatment, especially in food waste composting, is limited. Specifically, this review aims to: (1) discuss and compare critical factors that impact the fate of food waste and (2) examine emerging opportunities to advance the processing and products of food waste.

Effect of C/N ration on disposal of pig carcass by co-composting with swine manure: experiment at laboratory scale

Disposal of animal carcasses by co-composting with animal waste usually selected conventional carbon to nitrogen (C/N) ratio around 25:1, in which the compost is widely used throughout the world. In this study, the pig carcass tissue blocks were sampled for composting at a laboratory scale to evaluate the effect of C/N ratio on the pig carcass compost. The time of thermophilic phase between 60 °C - 70 °C at a lower C/N ratio of 20:1 was significantly longer than that at the conventional C/N ratio, and it was the only one with the temperature beyond 70 °C that lasted for 2 days. Germination index and T value (the final C/N ratio / the initial C/N ratio) of the treatment with a C/N ratio of 20:1 were 94.67% and 0.69, respectively, meeting the standards of animal carcass compost. The degradation rate was 75.67%, and no significant difference was obtained as compared to the conventional C/N ratio groups. Organic fertilizer produced from the treatment with a C/N ratio of 20:1 was selected to evaluate the fertility by pot experiment of Cayenne pepper compared with chemical fertilizer. The results showed that organic fertilizer from this treatment could significantly improve the growth of Cayenne pepper. Overall, the use of the lower C/N ratio of 20:1 in the disposal of pig carcass by co-composting with swine manure could achieve the similar degradation rate as well as the maturity and stability of organic fertilizer as compared with the traditional C/N ratio at lab scale.

Enhanced depletion of antibiotics and accelerated estabilization of dissolved organic matter by hydrothermal pretreatment during composting of oxytetracycline fermentation residue

In this study, the feasibility of employing hydrothermal pretreatment (HTPT) to improve the composting of oxytetracycline fermentation residue (OFR) was evaluated by investigating the depletion of oxytetracycline (OTC) and evolution of dissolved organic matter (DOM). HTPT drastically declined the final content of OTC and its main transformation intermediates in OFR compost from 89.96 to 2.61 mg/kg. Although HTPT slightly increased the DOM content and significantly decreased the contents of biodegradable and humified compounds in OFR compost, it did not significantly change the germination index of OFR compost. Nevertheless, the time required for the overall pattern of DOM parameters to reach stabilization was shortened from 28 to 14 days by HTPT. Taken together, although HTPT did not change the maturity degree of OFR compost, it obviously shortened the OFR composting cycle and lowered the potential risk of OFR compost, confirming that HTPT could efficiently improve the OFR composting.

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.

Changes in Arsenic and Copper Bioavailability and Oxytetracycline Degradation during the Composting Process

This research focuses on the effects of the composting process on oxytetracycline antibiotic degradation and the bioavailability of arsenic and copper. A compost experiment was conducted using cow and pig manure contaminated with oxytetracycline, and copper and arsenic salts. The changes in physicochemical properties, oxytetracycline concentration, and the germination index were measured. Copper and arsenic were estimated by sequential chemical extraction. We also detected the effects of compost properties, oxytetracycline concentration, and heavy metal (loid)s on the germination index through simple regression analysis. The results showed that the composting process positively and significantly affected heavy metal(loid)s bioavailability, oxytetracycline degradation, and the germination index. Oxytetracycline concentration declined in all treatments, and the decline was more evident in cows' manure. The copper and arsenic bioavailable fraction decreased significantly, while the low bioavailability fraction increased. The germination index increased above 50%, which showed that the compost was free of toxic substances. This result also showed that the compost properties had the most significant impact on the germination index, and their regression had the highest R2 values (0.84 and 0.99) in the cow and pig manure treatments, respectively. In conclusion, the composting process provides an economical method for oxytetracycline degradation and heavy metal(loid)s bioavailability reduction.

The distinctive microbial community improves composting efficiency in a full-scale hyperthermophilic composting plant

The application of conventional thermophilic composting (TC) is limited by poor efficiency. Newly-developed hyperthermophilic composting (HTC) is expected to overcome this shortcoming. However, the characterization of microbial communities associated with HTC remains unclear. Here, we compared the performance of HTC and TC in a full-scale sludge composting plant, and found that HTC running at the hyperthermophilic and thermophilic phases for 21 days, led to higher composting efficiency and techno-economic advantages over TC. Results of high-throughput sequencing showed drastic changes in the microbial community during HTC. Thermaceae (35.5-41.7%) was the predominant family in the hyperthermophilic phase, while the thermophilic phase was dominated by both Thermaceae (28.0-53.3%) and Thermoactinomycetaceae (29.9-36.1%). The change of microbial community could be the cause of continuous high temperature in HTC, and thus improve composting efficiency by accelerating the maturation process. This work has provided theoretical and practical guidance for managing sewage sludge by HTC.

Co-composting of Olive Mill Waste and Wine-Processing Waste: An Application of Compost as Soil Amendment

In order to decrease the environmental harm produced by the agro industries’ wastes’, an investigation of the co-composting of olive mill waste (olive mill wastewater (OMW), olive mill sludge (OMS)) and wine by-products (grape marc and winery wastewater) was done. Three aerated windrows of variable compositions were performed; these windrows differ in terms of their initial composition and the liquid used for their humidification; OMW and wastewater winery were used for humidification to replace water for windrow moistening. Moreover, the main physicochemical parameters (temperature, pH, electrical conductivity, and C/N) were monitored to evaluate the co-composting process. The latter lasted around three months. The elaborated composts were characterized by low C/N ratio, and they were rich in fertilizing and nutriment elements and of low heavy metal contents. The humidification of the windrows with OMW showed effectiveness in improving the windrows temperature, reflected by the high temperatures monitored during the composting process in comparison with the windrow humidified with winery wastewater. Furthermore, a longer thermophilic phase was held in windrows carrying OMS. The valorization of the produced composts for soil amendment significantly improved the soil fertility. Indeed, field experiments showed an increase in radish yield by 10%, the composts were harmless and did not have any phytotoxic effect on radish growth.

Dynamics of organic matter decomposition during vermicomposting of banana stem waste using Eisenia fetida

A better understanding of how dynamics of physical and chemical changes occur during vermicomposting process would be helpful for determining the stability and maturity of vermicompost. For improving the knowledge about this issue several instrumental techniques were used in the present study to analyse the physical and chemical changes as a function of vermicomposting time of banana stem waste (BS) spiked with cow dung (CD) in different proportions using earthworm Eisenia fetida. Chemical analysis by ICP-AES showed gradual increase in the plant nutrients (P, Ca, K, Mg, Fe) up to 60 day of vermicomposting in all the treatments. But among different treatments, K, Mg and Fe were considerably higher in the BS2CD1 blend. The FTIR showed strong NO stretching vibration with increasing BS content signifying the presence of nitrate in the final compost. The TG analysis of final BS-CD composts described the lower mass loss (52-55%) in the final compared to the initial stage due to high level of humification by earthworms. The maturity of the final compost was confirmed by DSC analysis which exhibited lowering of relative intensity of exothermic peaks related to the easily degradable material at 320-330 °C and complex organic moieties at 495-530 °C. Decrease in the humification index (Q_4/6, Q_2/4, Q_2/6) at 60 day confirmed the stability of vermicomposts. All the treatments showed <2 mg CO₂-C g^-1 vermicompost C day^-1 respiration rates and >70% germination indices (GI) for rice and pea seeds. These findings defined a clear comparison between the treatments during vermicomposting in terms of stability and maturity and revealed that BS2CD1 can be utilized as nutrient-rich stable compost for enhanced crop production.

Transformation of organic nitrogen fractions with different molecular weights during different organic wastes composting

This study aimed to investigate different transformation mechanisms of organic nitrogen (N) fractions during composting with different raw materials, and the contributions of bacterial communities and environmental factors to organic N fractions transformation. The results showed that high molecular weight organic N was first degraded to low molecular weight organic N and then turned into NH₄⁺ during chicken manure composting. In comparison, organic N fractions were stored in composts rather than mineralization during garden waste and municipal solid waste composting. Meanwhile, bacterial communities, environmental factors and the combination of them were the main drivers of N transformation during chicken manure, municipal solid waste and garden waste composting, respectively. In conclusion, the proposed organic N transformation mechanisms in this study provided a theoretical basis for improving the quality of compost products.

Ammonia emission mitigation in food waste composting: A review

Composting is a reliable technology to treat food waste (FW) and produce high quality compost. The ammonia (NH₃) emission accounts for the largest nitrogen loss and leads to various environmental impacts. This review introduced the recent progresses on NH₃ mitigation in FW composting. The basic characteristics of FW from various sources were given. Seven NH₃ emission strategies proven effective in the literature were presented. The links between these strategies and the mechanisms of NH₃ production were addressed. Application of hydrothermally treated C rich substrates, biochar or struvite salts had a broad prospect in FW composting if these strategies were proven cost-effective enough. Regulation of nitrogen assimilation and nitrification using biological additive had the potential to achieve NH₃ mitigation but the existing evidence was not enough. In the end, the future prospects highlighted four research topics that needed further investigation to improve NH₃ mitigation and nitrogen conservation in FW composting.

Seed germination test for toxicity evaluation of compost: Its roles, problems and prospects

Compost is commonly used for the growth of plants and the remediation of environmental pollution. It is important to evaluate the quality of compost and seed germination test is a powerful tool to examine the toxicity of compost, which is the most important aspect of the quality. Now the test is widely adopted, but the main problem is that the test results vary with different methods and seed species, which limits the development and application of it. The standardization of methods and the modelization of seeds can contribute to solving the problem. Additionally, according to the probabilistic theory of seed germination, the error caused by the analysis and judgment methods of the test results can be reduced. Here, we reviewed the roles, problems and prospects of the seed germination test in the studies of compost.

Evaluation of integrated ammonia recovery technology and nutrient status with an in-vessel composting process for swine manure

The study investigated the effect of different initial moisture (IM) content (55, 60, 65, and 70%) of composting mixtures (swine manure and sawdust) for the production of nutrient rich manure, and the recovery of ammonia through a condensation process using a vertical cylindrical in-vessel composter for 56days. The composting resulted in a significant reduction in C:N ratio and electrical conductivity (EC), with a slight increase in pH in all products. The NH₃ were emitted notably, and at the same time the NO₃^--N concentration gradually increased with the reduction of NH₄⁺-N in the composting mixtures. The overall results confirmed, the 65% IM showed the maximum nutritional yield, maturity and non-phytotoxic effects (Lycopersicon esculentum L.), with the results of ideal compost product in the following order of IM: 65%>60%>70%>55%. Finally, the recovered condensed ammonia contained considerable ammonium nitrogen concentrations and could be used as fertilizer.

The effects of biochar, compost and their mixture and nitrogen fertilizer on yield and nitrogen use efficiency of barley grown on a Nitisol in the highlands of Ethiopia

The effects of organic amendments and nitrogen (N) fertilizer on yield and N use efficiency of barley were investigated on a Nitisol of the central Ethiopian highlands in 2014. The treatments were factorial combinations of no organic amendment, biochar (B), compost (Com), Com+B and co-composted biochar (COMBI) as main plots and five N fertilizer levels as sub-plots, with three replicates. Application of organic amendment and N fertilizer significantly improved yield, with grain yield increases of 60% from Com+B+69kgNha(-1) at Holetta and 54% from Com+92kgNha(-1) at Robgebeya, compared to the yield from the maximum N rate. The highest total N uptake was obtained from Com+B+92kgNha(-1) at Holetta (138kgha(-1)) and Com+92kgNha(-1) at Robgebeya (101kgha(-1)). The agronomic efficiency (yield increase per unit of N applied, AE), apparent recovery efficiency (increase in N uptake per unit of N applied, ARE) and physiological efficiency (yield increase per unit of N uptake, PE) responded significantly to organic amendments and N fertilizer. Mean AE and ARE were highest at B+23kgNha(-1) at Holetta and at B+23 and B+46kgNha(-1) at Robgebeya. The PE ranged from 19 to 33kggrainkg(-1) N uptake at Holetta and 29-48kggrainkg(-1) N uptake at Robgebeya. The effects of organic amendments and N fertilizer on AE, ARE and PE were greater at Robgebeya than at Holetta. The enhancement of N use efficiency through application of organic amendments emphasizes the importance of balanced crop nutrition, ensuring that barley crops are adequately supplied with N and other nutrients. Overall, the integration of both organic and inorganic amendments may optimize N uptake efficiency and reduce the amount of N fertilizer required for the sustainable barley production in the long-term.

Effects of added polyacrylamide on changes in water states during the composting of kitchen waste

The effects of adding polyacrylamide (PAM), to attempt to delay the loss of capillary water and achieve a better level of organic matter humification, in the composting of kitchen waste were evaluated. Four treatments, with initial moisture content of 60 % were used: 0.1 % PAM added before the start of composting (R1), 0.1 % PAM added when the thermophilic phase of composting became stable (at >50 °C) (R2), 0.1 % PAM added when the moisture content significantly decreased (R3), and no PAM added (R4). The introduction of PAM in R1 and R2 significantly increased the capillary force and delayed the loss of moisture content and capillary water. The introduction of PAM in R2 and R3 improved the composting process, in terms of the degradation of biochemical fractions and the humification degree. These results show that the optimal time for adding PAM was the initial stage of the thermophilic phase.

Monitoring and characterization of compost obtained from household waste and pine sawdust in a facultative reactor by conventional and spectroscopic analyses

This study proposes a new facultative reactor configuration for the treatment of organic household waste and pine sawdust. The process was monitored and the compost characterized by conventional (temperature, moisture, pH, ash content and ratio C/N) conjugated with spectroscopic analyses (ultraviolet (UV)/visible (Vis) and infrared (IR)) and germination index. The spectroscopy results revealed enrichment of carbon-carbon unsaturation structures and a degradation of the aliphatic structures. The results showed that stability of the final product was reached after 90 days and that the compost obtained presents substantial richness of stabilized organic matter and an absence of toxicity, so it may be considered as an organic fertilizer. Finally, this study led to the conclusion that the reactor proposed can be a promising technology for the management of organic household waste and sawdust.

Evaluation of thermophilic fungal consortium for organic municipal solid waste composting

Influence of fungal consortium and different turning frequency on composting of organic fraction of municipal solid waste (OFMSW) was investigated to produce compost with higher agronomic value. Four piles of OFMSW were prepared: three piles were inoculated with fungal consortium containing 5l each spore suspensions of Trichoderma viride, Aspergillus niger and Aspergillus flavus and with a turning frequency of weekly (Pile 1), twice a week (Pile 2) and daily (Pile 3), while Pile 4 with weekly turning and without fungal inoculation served as control. The fungal consortium with weekly (Pile 1) turning frequency significantly affected temperature, pH, TOC, TKN, C/N ratio and germination index. High degradation of organic matter and early maturity was observed in Pile 1. Results indicate that fungal consortium with weekly turning frequency of open windrows were more cost-effective in comparison with other technologies for efficient composting and yield safe end products.

Experimental and modeling approaches for food waste composting: a review

Composting has been used as a method to dispose food waste (FW) and recycle organic matter to improve soil structure and fertility. Considering the significance of composting in FW treatment, many researchers have paid their attention on how to improve FW composting efficiency, reduce operating cost, and mitigate the associated environmental damage. This review focuses on the overall studies of FW composting, not only various parameters significantly affecting the processes and final results, but also a number of simulation approaches that are greatly instrumental in well understanding the process mechanism and/or results prediction. Implications of many key ingredients on FW composting performance are also discussed. Perspects of effective laboratory experiments and computer-based simulation are finally investigated, demonstrating many demanding areas for enhanced research efforts, which include the screening of multi-functional additives, volatile organiccompound emission control, necessity of modeling and post-modeling analysis, and usefulness of developing more conjunctive AI-based process control techniques.

Characterization of olive mill wastes composts and their humic acids: stability assessment within different particle size fractions

Compost stability assessment within different particle size fractions was studied. Humic acids (HAs) were extracted from two kinds of co-composts prepared using evaporated olive mill wastewater (OMSW) or solid waste from olive oil extraction (OC) and poultry manure (PM). The elemental composition, Fourier-transform infrared spectroscopy (FTIR) and 13C-NMR (nuclear magnetic resonance) analysis and molecular weight distribution were investigated to assess the composted organic matter stability in different fractions. In both composts, organic matter content was higher in the > 2 mm fractions than in the < 2 mm fractions, because of fractions' richness in hardly biodegradable compounds. Spectroscopic analysis revealed that OMSW compost fraction < 2 mm and OC compost 2-4 mm fraction were rich in aromatic compounds and oxygenated groups but poor in aliphatic structure. Moreover, the HA distribution reflected a high stabilized compost < 2 mm fraction, especially from evaporated effluent known as phytotoxic. However, the 4-6 mm fraction included high aliphatic compounds besides aromatic structures and did not exhibit any phytotoxicity, confirming compost fraction maturity. However, the low C/N ratio, the high OMSW compost mineral nutritive elements and the high aromatic C rate reflected highly stabilized products. Consequently, the performance of both prepared organic fertilizers for agriculture use contested the previous negative effect ascribed to olive mill wastewater.

Vermicomposting of food waste: assessing the stability and maturity

The vermicompost using earthworms (Eisenia Fetida) was produced from food waste and chemical parameters (EC, pH, carbon to nitrogen contents (C/N)) and germination bioassay was examined in order to assess the stability and maturity indicators during the vermicomposting process. The seed used in the germination bioassay was cress. The ranges of EC, pH, C/N and germination index were 7.5-4.9 mS/cm, 5.6-7.53, 30.13-14.32% and 12.8-58.4%, respectively. The germination index (GI) value revealed that vermicompost rendered as moderate phytotoxic to cress seed. Pearson correlation coefficient was used to evaluate the relationship between the parameters. High statistically significant correlation coefficient was calculated between the GI value and EC in the vermicompost at the 99% confidence level. The C/N value showed that the vermicompost was stable. As a result of these observations, stability test alone, was not able to ensure high vermicompost quality. Therefore, it appears that determining vermicompost quality requires a simultaneous use of maturity and stability tests.

Nitrogen conservation in simulated food waste aerobic composting process with different Mg and P salt mixtures

To assess the effects of three types of Mg and P salt mixtures (potassium phosphate [K3PO4]/magnesium sulfate [MgSO4], potassium dihydrogen phosphate [K2HPO4]/MgSO4, KH2PO4/MgSO4) on the conservation of N and the biodegradation of organic materials in an aerobic food waste composting process, batch experiments were undertaken in four reactors (each with an effective volume of 30 L). The synthetic food waste was composted of potatoes, rice, carrots, leaves, meat, soybeans, and seed soil, and the ratio of C and N was 17:1. Runs R1-R3 were conducted with the addition of K3PO4/ MgSO4, K2HPO4/MgSO4, and KH2PO4/MgSO4 mixtures, respectively; run R0 was a blank performed without the addition of Mg and P salts. After composting for 25 days, the degrees of degradation of the organic materials in runs R0-R3 were 53.87, 62.58, 59.14, and 49.13%, respectively. X-ray diffraction indicated that struvite crystals were formed in runs R1-R3 but not in run R0; the gaseous ammonia nitrogen (NH3-N) losses in runs R0-R3 were 21.2, 32.8, 12.6, and 3.5% of the initial total N, respectively. Of the tested Mg/P salt mixtures, the K2HPO4/ MgSO4 system provided the best combination of conservation of N and biodegradation of organic materials in this food waste composting process.

Response of compost maturity and microbial community composition to pentachlorophenol (PCP)-contaminated soil during composting

Two composting piles were prepared by adding to a mixture of rice straw, vegetables and bran: (i) raw soil free from pentachlorophenol (PCP) contamination (pile A) and (ii) PCP-contaminated soil (pile B). It was shown by the results that compost maturity characterized by water soluble carbon (WSC), TOC/TN ratio, germination index (GI) and dehydrogenase activity (DA) was significantly affected by PCP exposure, which resulted in an inferior degree of maturity for pile B. DGGE analysis revealed an inhibited effect of PCP on compost microbial abundance. The bacteria community shifts were mainly consistent with composting factors such as temperature, pH, moisture content and substrates. By contrast, the fungal communities were more sensitive to PCP contamination due to the significant correlation between fungal community shifts and PCP removal. Therefore, the different microbial community compositions for properly evaluating the degree of maturity and PCP contamination were suggested.

Quantitative effects of composting state variables on C/N ratio through GA-aided multivariate analysis

It is widely known that variation of the C/N ratio is dependent on many state variables during composting processes. This study attempted to develop a genetic algorithm aided stepwise cluster analysis (GASCA) method to describe the nonlinear relationships between the selected state variables and the C/N ratio in food waste composting. The experimental data from six bench-scale composting reactors were used to demonstrate the applicability of GASCA. Within the GASCA framework, GA searched optimal sets of both specified state variables and SCA's internal parameters; SCA established statistical nonlinear relationships between state variables and the C/N ratio; to avoid unnecessary and time-consuming calculation, a proxy table was introduced to save around 70% computational efforts. The obtained GASCA cluster trees had smaller sizes and higher prediction accuracy than the conventional SCA trees. Based on the optimal GASCA tree, the effects of the GA-selected state variables on the C/N ratio were ranged in a descending order as: NH₄+-N concentration>Moisture content>Ash Content>Mean Temperature>Mesophilic bacteria biomass. Such a rank implied that the variation of ammonium nitrogen concentration, the associated temperature and the moisture conditions, the total loss of both organic matters and available mineral constituents, and the mesophilic bacteria activity, were critical factors affecting the C/N ratio during the investigated food waste composting. This first application of GASCA to composting modelling indicated that more direct search algorithms could be coupled with SCA or other multivariate analysis methods to analyze complicated relationships during composting and many other environmental processes.

Evaluation of the maturity of organic waste composts

Olive-mill wastes represent a significant environmental problem in Mediterranean areas due to their significant production during a short period of time. Their high polyphenol, lipid and organic acid concentrations make them phytotoxic wastes. Composting is one of the technologies used for the valorization of those wastes, producing a fertilizer useful for poor soils. The present study is an attempt to elaborate upon organic matter transformations and define the parameters for product maturity by adapting chemical and spectroscopic methods during composting. The aim of this work was to study the changes involved in the composting process of four piles during 200 days, and follow up the maturity of the final product during composting. Fourier transform infrared (FTIR) spectroscopy has been proven to be an appropriate analytical method for the qualitative assessment of compost stability. FTIR spectroscopy results revealed enrichment in aromatic structures and a degradation of the aliphatic and alcoholic structures indicating stabilization of the final compost. The results showed that stability of the final product was reached after 7 months of composting. The phytotoxic effects of olive mill wastes and animal manures was assessed by germination index. Indeed, the germination indices of piles 1, 2, 3 and 4 reached 131.31%, 72%, 90.56%, and 105.37%, respectively, at the end of the process. This demonstrated the absence of phytotoxicity in the majority of mature composts.

A stepwise-cluster microbial biomass inference model in food waste composting

A stepwise-cluster microbial biomass inference (SMI) model was developed through introducing stepwise-cluster analysis (SCA) into composting process modeling to tackle the nonlinear relationships among state variables and microbial activities. The essence of SCA is to form a classification tree based on a series of cutting or mergence processes according to given statistical criteria. Eight runs of designed experiments in bench-scale reactors in a laboratory were constructed to demonstrate the feasibility of the proposed method. The results indicated that SMI could help establish a statistical relationship between state variables and composting microbial characteristics, where discrete and nonlinear complexities exist. Significance levels of cutting/merging were provided such that the accuracies of the developed forecasting trees were controllable. Through an attempted definition of input effects on the output in SMI, the effects of the state variables on thermophilic bacteria were ranged in a descending order as: Time (day)>moisture content (%)>ash content (%, dry)>Lower Temperature ( degrees C)>pH>NH(4)(+)-N (mg/Kg, dry)>Total N (%, dry)>Total C (%, dry); the effects on mesophilic bacteria were ordered as: Time>Upper Temperature ( degrees C)>Total N>moisture content>NH(4)(+)-N>Total C>pH. This study made the first attempt in applying SCA to mapping the nonlinear and discrete relationships in composting processes.

Continuous thermophilic composting (CTC) for rapid biodegradation and maturation of organic municipal solid waste

Fewer and fewer municipal solid wastes are treated by composting in China because of the disadvantages of enormous investment, long processing cycle and unstable products in a conventional composting treatment. In this study, a continuous thermophilic composting (CTC) method, only a thermophilic phase within the process, has been applied to four bench-scale composting runs, and further compared with a conventional composting run by assessing the indexes of pH, total organic carbon (TOC), total Kjeldahl nitrogen (TKN), C/N ratio, germination index (GI), specific oxygen uptake rate (SOUR), dissolved organic carbon (DOC) and dehydrogenase activity. After composting for 14 days, 16 days, 18 days and 19 days in the four CTC runs, respectively, mature compost products were obtained, with quality similar to or better than which had been stabilized for 28 days in run A. The products from the CTC runs also showed favorable stability in room temperature environment after the short-term composting at high temperature. The study suggested CTC as a novel method for rapid degradation and maturation of organic municipal solid wastes.

Comparison of organic matter degradation and microbial community during thermophilic composting of two different types of anaerobic sludge

Changes in organic matter degradation and microbial communities during thermophilic composting were compared using two different types of anaerobic sludge, one from mesophilic methane fermentation, containing a high concentration of proteins (S-sludge), and the other from thermophilic methane fermentation, containing high concentrations of lipids and fibers (K-sludge). The difference in the organic matter degradation rate corresponded to the difference in the organic matter constituents; the CO(2) evolution rate was greater in the composting of S-sludge than of K-sludge; moreover, the NH(3) evolution resulting from the protein degradation was especially higher in the composting of S-sludge. Then the differences in the microbial communities that contributed to each composting were determined by the PCR-DGGE method. Ureibacillus sp., which is known as a degrader with high organic matter degradation activity, was observed during the composting of S-sludge, whereas Thermobifida fusca, which is a well known thermophilic actinomycete that produces enzymes for lignocellulose degradation, were observed during the composting of K-sludge.

Evaluation of composting as a strategy for managing organic wastes from a municipal market in Nicaragua

A pilot-scale study was undertaken to evaluate alternatives to the solid waste management of a Central American municipal market located in Estelí, Nicaragua. The municipal solid waste from the local market is the second largest contributor to the municipal solid waste (MSW) stream. Waste from the market without any previous sorting or treatment is open dumped. The options evaluated in this study were windrow composting, windrow composting with yard waste, bokashi and vermicompost. Significant differences between the properties of composts produced were found; however, all of them reduce the initial waste volume and are potential useful agronomic products for a survival agrarian milieu.

Co-composting of oil exhausted olive-cake, poultry manure and industrial residues of agro-food activity for soil amendment

The co-composting of exhausted olive-cake with poultry manure and sesame shells was investigated. These organic solid wastes were watered by the confectionary wastewater which is characterized by its high content of residual sugars raising its COD. Four aerated windrows were performed to establish the effects of confectionary by-products on the compost process. Different mixtures of the agro-industrial wastes were used. During the composting process, physico-chemical parameters (temperature, moisture, pH, electrical conductivity, total carbon and total nitrogen) were studied. The stability of the biological system was noticed after 70 days. The final products were characterized by their relatively high organic matter content, and low C/N ratio of 14-17. The humidification of the windrows with the wastewater seemed to have accelerated the composting process in comparison to a windrow humidified with water. In addition, the organic matter degradation was enhanced to reach 55-70%. The application of the obtained composts to soil appeared to significantly improve the soil fertility. Indeed, field experiments showed an increase in potato yield; the production was 30.5-37.5 tons ha(-1), compared to 30.5 tons ha(-1) with farm manure.

An electrochemical on-field sensor system for the detection of compost maturity

A maturity sensor system was developed, based on the combination of three electrically measured parameters, pH, NH(4)(+) concentration, and phosphatase activity in the water extracts of compost samples. One of these parameters, the apparent phosphatase activity in crude test solutions was determined using screen-printed carbon strips (SPCSs) coated with alpha-naphthyl phosphate (alpha-NP) in Nafion film. The phosphatase activity was monitored in connection with differential pulse voltammetry (DPV) with an aliquot (30 microL) of the test solution on SPCS. The phosphatase activity sensor was validated using alkaline phosphatase (ALP) in Tris-HCl buffer (pH 8.0) and acid phosphatase (ACP) in citric acid buffer (pH 5.0). The activity of the spiked enzymes in the water extract of the compost sample could be confirmed with the change of corresponding oxidation peak current signal of the product, alpha-naphthol. The water extracts of compost samples (n=24) collected in various composting days were applied to our compost maturity sensor system, and the conventional germination tests. Using multiple regression analysis, the germination index (GI) was expressed by the multi-linear regression equation consisting of pH, NH(4)(+) concentration, and the phosphatase activity. The calculated GI from the regression equation had a good correlation with the measured GI of the corresponding composts (r=0.873). As a result, we have determined an equation for the determination of the compost stability using our portable sensor system rapidly at the composting site.