The use of respiration indices in the composting process: a review

Oxygen uptake rate versus CO2 based respiration rate for assessment of the biological stability of peat, plant fibers and woody materials with high C:N ratio versus composts

The biological stability of organic materials predicts their performance when used as either a soil improver or as an ingredient in growing media. CO₂ release in a static measurement and O₂ consumption rate (OUR) were compared for seven groups of growing media components. The ratio between CO₂ release and OUR was matrix-specific. This ratio was highest for plant fibers high in C:N and with a high risk of N immobilization, intermediate for wood fiber and woody composts, and lowest for peat and other compost types. The effect of variable test conditions in the OUR setup was assessed for plant fibers, where addition of mineral N and/or nitrification inhibitor had no effect on the OUR measurements. Testing at 30 °C instead of 20 °C resulted in higher OUR values as expected, but did not change the effect of mineral N dose. A strong increase in the CO₂ flux was measured when plant fibers were mixed with mineral fertilizer; in contrast, addition of mineral N or fertilizer before or during the OUR test had no effect. The present experimental setup did not allow for differentiation between a higher CO₂ release as a result of increased microbial respiration after adding mineral N versus an underestimation of stability due to N limitation in the dynamic OUR setup. Results indicate that type of material, C:N ratio and risk of N immobilization all appear to affect the OUR results. The OUR criteria may therefore require clear differentiation based on the different materials used in horticultural substrates.

A Review on Remediation of Iron Ore Mine Tailings via Organic Amendments Coupled with Phytoremediation

Mining operations degrade natural ecosystems by generating a large quantity of mine tailings. Mine tailings remain in dams/open ponds without further treatment after valuable metals such as iron ore have been extracted. Therefore, rehabilitation of tailings to mitigate the negative environmental impacts is of the utmost necessity. This review compares existing physical, chemical and amendment-assisted phytoremediation methods in the rehabilitation of mine tailings from the perspective of cost, reliability and durability. After review and discussion, it is concluded that amendment-assisted phytoremediation has received comparatively great attention; however, the selection of an appropriate phytoremediator is the critical step in the process. Moreover, the efficiency of phytoremediation is solely dependent on the amendment type and rate. Further, the application of advanced plant improvement technologies, such as genetically engineered plants produced for this purpose, would be an alternative solution. Further research is needed to determine the suitability of this method for the particular environment.

Insight to maturity during biogas residue from food waste composting in terms of multivariable interaction

This study used biogas residue produced by anaerobic fermentation of food waste as the raw material in large-scale windrow composting. The effects of the addition of a microbial consortium on the physical and chemical properties and stability of composting of biogas residue were studied. The maturity of food waste biogas residue during composting was investigated by multivariate interaction of environmental, maturity, and nutrient parameters, using structural equation modeling (SEM). Results showed that the temperature of T2 compost with the microbial consortium increased more rapidly. The pH ranges of T1 (without the microbial consortium) and T2 were 8.75-9.15 and 8.42-9.27, respectively; the electrical conductivity (EC) ranges of T1 and T2 were 2.74-3.95 mS/cm and 2.81-3.85 mS/cm, respectively; the degradation rates of organic matter (OM) in T1 and T2 were 21.74% and 33.62%, respectively; and the total nitrogen (TN) ranges of T1 and T2 were 1.93-3.10% and 1.80-3.21%, respectively. By the end of composting, the germination indices (GI) of T1 and T2 were 20.57% and 64.24%, respectively. The total oxygen consumption after 4 days (AT₄) was 1.88 mg-O₂/g and 1.2 mg-O₂/g in T1 and T2, respectively. SEM of T1 showed that compost temperature and EC were important factors affecting compost maturity. These factors highly significantly affected OM, which in turn affected AT₄ of the biogas residue composting. SEM of T2 showed that compost temperature, pH, and EC affected OM, which in turn affected compost maturity. Temperature affected compost maturity by affecting AT₄ and GI. Principal component analysis (PCA) showed that the overall score of T2 was higher than that of T1, indicating that the addition of the microbial consortium was beneficial for industrial-scale composting of biogas residue produced by anaerobic digestion of food waste.

Protocol of conjugate evaluation of the biological activity of soils in terms of cellulolytic activity and biological consumption of oxygen

The article presents protocols for determining the biological activity of kerosene-contaminated soils in terms of two indicators, i.e. cellulolytic activity and biological consumption of oxygen. A method for determining the cellulolytic activity of soils is based on measuring the rate of cellulose decomposition in situ. Model test objects (linen fragments 10 × 20 cm weighing 4–6 g) were put in the root layer of soil. A month later, the linen was removed from soil and its weight loss was measured. Cellulolytic activity was estimated by the weight loss of readily hydrolysable organic matter (RHOM) per day (mg/g RHOM per day). The method for determining the biological consumption of oxygen of water was adapted for soils. The indicator characterizes the ability of microorganisms to oxidize organic substances using oxygen for 5 days. The analytic procedure includes taking a soil sample, preparing the suspension (the ratio of soil to distilled water is at least 1:10) and after 5 days measuring the concentration of unspent dissolved oxygen using the oxygen meter. The proposed methods give reproducible and reliable results on the biochemical activity of soil microorganisms in a wide range of soils, e.g. Retisols, Arenosols and Histosols, including those under hydrocarbon pollution.

A plant-like battery: a biodegradable power source ecodesigned for precision agriculture

The natural environment has always been a source of inspiration for the research community. Nature has evolved over thousands of years to create the most complex living systems, with the ability to leverage inner and outside energetic interactions in the most efficient way. This work presents a flow battery profoundly inspired by nature, which mimics the fluid transport in plants to generate electric power. The battery was ecodesigned to meet a life cycle for precision agriculture (PA) applications; from raw material selection to disposability considerations, the battery is conceived to minimize its environmental impact while meeting PA power requirements. The paper-based fluidic system relies on evaporation as the main pumping force to pull the reactants through a pair of porous carbon electrodes where the electrochemical reaction takes place. This naturally occurring transpiration effect enables to significantly expand the operational lifespan of the battery, overcoming the time-limitation of current capillary-based power sources. Most relevant parameters affecting the battery performance, such as evaporation flow and redox species degradation, are thoroughly studied to carry out device optimization. Flow rates and power outputs comparable to those of capillary-based power sources are achieved. The prototype practicality has been demonstrated by powering a wireless plant-caring device. Standardized biodegradability and phytotoxicity assessments show that the battery is harmless to the environment at the end of its operational lifetime. Placing sustainability as the main driver leads to the generation of a disruptive battery concept that aims to address societal needs within the planetary environmental boundaries.

On-Farm Composting of Hop Plant Green Waste—Chemical and Biological Value of Compost

Green agro waste can be turned into compost, which can then be used as an organic fertilizer, thus reducing the environmental impact of food and feed production. This research is focused on finding a feasible on-farm composting treatment of plant biomass to produce high-quality compost. Three different composting treatments were prepared and followed (with different additives at the start—biochar (BC) and effective microorganisms (EM), no additive (CON); covering and not covering the pile; different start particles size). Samples were analysed for nutrient concentrations, phytotoxicity and bacterial and fungal presence after seven months of composting. In 100 g of dry matter, the average compost contained 2.7 g, 0.38 g and 1.08 g of N, P and K, respectively. All investigated treatments contained more than 2% of total nitrogen in dry mass, so they could be used as a fertilizer. The highest nutrient content was observed in compost of small particle size (˂5 cm) and added biochar (11 kg/t fresh biomass). However, this compost had the least bacteria and fungi due to very high temperatures in the thermophilic phase of this pile. According to the radish germination index, the prepared composts have no phytotoxic properties and are stable and ready to use in plant production. Taking the cress germination test into consideration, they provided a nutrient-rich and biostimulative soil amendment. All three final composts were stable in terms of respiration rate, growth and germination tests. Results have shown that hop biomass after harvest has great potential for composting.

Oriented conversion of agricultural bio-waste to value-added products - A schematic review towards key nutrient circulation

Agriculture bio-waste is one of the largest sectors for nutrient circulation and resource recovery. This review intends to summarize the possible scheme through coupling chemical conversion of crop straws to biochar and biological conversion of livestock waste to value-added products thus reaching key nutrient circulation. Chemical conversion of crop straws to biochar was reviewed through summarizing the preparation methods and functional modification of biochar. Then, high-solid two-phase anaerobic conversion of agriculture bio-waste to value-added products and improved performance of bio-conversion through byproduct gases reuse and biochar supplementation were reviewed. Finally, high quality compost production through amendment of biochar and residual digestate was proposed with analysis of reduced nitrogen emission and carbon balance. The biological mechanism of synergistic regulation of carbon and nitrogen loss during bio-conversion with biochar was also reviewed. This will provide a model for synergistic conversion of agricultural wastes to value added products pursuing key nutrient circulation.

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.

The microbial metabolic activity on carbohydrates and polymers impact the biodegradability of landfilled solid waste

Biological waste degradation is the main driving factor for landfill emissions. In a 2-year laboratory experiment simulating different landfill in-situ aeration scenarios, the microbial degradation of solid waste under different oxygen conditions (treatments) was investigated. Nine landfill simulation reactors were operated in triplicates under three distinct treatments. Three were kept anaerobic, three were aerated for 706 days after an initial anaerobic phase and three were aerated for 244 days in between two anaerobic phases. In total, 36 solid and 36 leachate samples were taken. Biolog® EcoPlates™ were used to assess the functional diversity of the microbial community. It was possible to directly relate the functional diversity to the biodegradability of MSW (municipal solid waste), measured as RI₄ (respiration index after 4 days). The differences between the treatments in RI₄ as well as in carbon and polymer degradation potential were small. Initially, a RI₄ of about 6.5 to 8 mg O₂ kg^-1 DW was reduced to less than 1 mg O₂ kg^-1 DW within 114 days of treatment. After the termination of aeration, an increase 3 mg O₂ kg^-1 DW was observed. By calculating the integral of the Gompertz equation based on spline interpolation of the Biolog® EcoPlates™ results after 96 h two substrate groups mainly contributing to the biodegradability were identified: carbohydrates and polymers. The microbial activity of the respective microbial consortium could thus be related to the biodegradability with a multilinear regression model.

Evaluation of the bio-drying process of municipal solid waste using rotating drums Bio-drying rotary drum

Most of the municipal solid waste collected is disposed of in landfills and controlled landfills. However, efficient ways of recovering these wastes have emerged, such as bio-drying. This technique uses the exothermic degradation reaction of organic matter carried out by microorganisms along with aeration to reduce the moisture of the waste. The objective of the research was to test the bio-drying technique in a rotary drum. For this purpose, three rotary drums were built, and the tested residue was synthetically produced. The aeration rate tested was 1 liter per kilogram per minute, and rotation was performed for one minute every three hours. The analyses performed on the residues were moisture content, volatile solids, calorific value, particle size, and temperature profile. The residues entered the bio-drying process with a moisture content of 52%, 49%, and 54% and went out with 15%, 13%, and 10% for drum 1, 2, and 3, respectively, a reduction of more than 70%. The calorific value increased by 95%, 88%, and 122% for drum 1, 2, and 3, respectively. During the process, no leachate generation was observed.

Biodegradation of bio-sourced and synthetic organic electronic materials towards green organic electronics

Ubiquitous use of electronic devices has led to an unprecedented increase in related waste as well as the worldwide depletion of reserves of key chemical elements required in their manufacturing. The use of biodegradable and abundant organic (carbon-based) electronic materials can contribute to alleviate the environmental impact of the electronic industry. The pigment eumelanin is a bio-sourced candidate for environmentally benign (green) organic electronics. The biodegradation of eumelanin extracted from cuttlefish ink is studied both at 25 °C (mesophilic conditions) and 58 °C (thermophilic conditions) following ASTM D5338 and comparatively evaluated with the biodegradation of two synthetic organic electronic materials, namely copper (II) phthalocyanine (Cu-Pc) and polyphenylene sulfide (PPS). Eumelanin biodegradation reaches 4.1% (25 °C) in 97 days and 37% (58 °C) in 98 days, and residual material is found to be without phytotoxic effects. The two synthetic materials, Cu-Pc and PPS, do not biodegrade; Cu-Pc brings about the inhibition of microbial respiration in the compost. PPS appears to be potentially phytotoxic. Finally, some considerations regarding the biodegradation test as well as the disambiguation of "biodegradability" and "bioresorbability" are highlighted.

Evaluation on maturity and stability of organic fertilisers in semi-arid Ethiopian Rift Valley

Case studies that have comprehensively examined local organic fertilisers (OFs) for their maturity and stability are rare in sub-Saharan Africa. Farmers in the semi-arid Ethiopian Rift Valley use indigenous compost (kosi) and household wastes for OFs. With the entry of fast compost that was introduced by the administration, maturity and stability of these OFs were assessed. Their maturity was assessed by: monitoring pile temperature and volume, pH, organic matter and total nitrogen contents, and carbon to nitrogen ratio; determination of NO₃^– to NH₄⁺ ratio; and respirometric measurement of CO₂ evolution. Their stability was assessed by weed seed germination tests and phytotoxicity bioassays. Weed seeds that were originally contained in the feedstock of the kosi and fast compost samples became inactive during the composting process. The CO₂ evolution tests and phytotoxicity bioassays indicated a probable presence of some phytotoxic compounds in the kosi. Mature kosi and immature kosi in a kosi pile should be mixed before the field application. Some samples (15%) of the household wastes contained weed seeds. The combination of several assessment methods used in this study and determination methods for nitrogen components using RQ-flex is considered to be effective for on-site quality assessment of OFs in sub-Saharan Africa.

Detection of Alternaria alternata in tomato juice and fresh fruit by the production of its biomass, respiration, and volatile compounds

Tomato is widely consumed and marketed as juice, puree, or fresh product. Nevertheless, 30% of its harvest volume is lost because of the fungus Alternaria alternata. This research aimed to provide early detection methods for this fungal decay on tomato juice and fresh fruit. Biomass content, CO₂, O₂ and volatile compounds (VOCs) during A. alternata growth in tomato juice and fruit at two ripening stages (breaker and red colour) were evaluated. Additionally, CO₂ and VOCs data set were analysed with a hierarchical cluster technique (HCA) to explore the differences between inoculated and non-inoculated samples. Biomass was determined by gravimetry, CO₂ and O₂ by gas chromatography (GC), and VOCs by GC-mass spectrometry. Biomass content was not drastically modified by tomato's ripening stage (3-6 mg of dry weight). CO₂ in tomato juice was considerably higher in the inoculated samples with A. alternata (27-63%) than in the non-inoculated ones (2.8-6.6%), regardless of the ripeness stage; while in tomato fruit CO₂ was higher at breaker stage and inoculated with A. alternata (33-41%) than the remaining treatments (9-23%). It was also observed that, except for limonene, trans-sabinene hydrate, and rhodovibrin, VOCs' release during the interaction between tomato juice and A. alternata was different from the fresh tomato and A. alternata interaction. Only the HCA based on CO₂ data showed clear differences between the inoculated and non-inoculated tomato juice and fruit at both ripening stages.

Composting Hydrochar-OFMSW Digestate Mixtures: Design of Bioreactors and Preliminary Experimental Results

An increasing number of industrial plants integrate the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) with a subsequent composting phase. To improve the plant productivity, a fraction of OFMSW digestate can be converted into a carbonaceous material, called hydrocar (HC), through Hydrothermal Carbonization (HTC), and then composted together with the OFMSW digestate itself, to produce “hydrochar co-compost”. The aim of this paper is to present the design and assembly of batch bioreactors, built in-house to investigate the co-composting process of OFMSW digestate and its HC, and to provide some preliminary results. The OFMSW digestate from an industrial plant was carbonized at 200 °C for 3 h in a 2 L HTC reactor, to produce wet HC after filtration. The ratio of OFMSW digestate and green waste (1:1) used as bulking medium was reproduced in four bioreactors with an increasing percentage of HC substituting the OFMSW digestate (0, 25, 50, 75%). The bioreactors managed to effectively compost the solid wet biomasses in a wet environment with temperature and oxygen control, while measuring online the oxygen consumption and thus the dynamic respirometric index (DRI). The DRI24,max measured with AIR-nl solid respirometer (standardized offline measurement) started from values above 800 mg O2 kgVS−1 h−1 before composting and dropped at the end of the process to values in the range 124–340 mg O2 kgVS−1 h−1 for the four mixes, well below the recommended limit of 500 mg O2 kgVS−1 h−1 for high-quality compost stability. These offline DRI values were confirmed by the online DRI measurements. This research is part of the international C2Land Project funded by the European Institute of Innovation and Technology Climate Knowledge and Innovation Community (EIT Climate-KIC), which is greatly acknowledged.

Biological denitrification potential as an indicator for measuring digestate stability

Biological stability is an essential parameter for assessing the environmental impact from the land application of digestate as organic amendment. In this paper, a new indicator, biological denitrification potential (BDP), was developed for evaluating the biological stability of digestate. Digestate samples collected along the digestion process from a mesophilic anaerobic batch digester fed with food waste were investigated under different solid retention time. The value of BDP based on nitrate removal ranged from 176.3 to 48.3 mg-N/g-VS_digestate, corresponding well to the digestion time, and strongly correlated with total organic carbon content. Evolution trends similar to respiration index (RI) and biochemical methane potential (BMP) can be also observed for BDP, indicating that values presented of these stability indices decreased with the degree of digestate stabilization. The mass balance of the BDP process indicated that nitrate was mainly converted into N₂ gas with mineralizing organic carbon from digestate, implying that biostability evaluated by BDP depends on carbon source and denitrification activity in digestate. The denitrifying bacteria Thiopseudomonas and Pseudomonas accounted for the majority of microorganisms. These findings of this study concluded that BDP can be an efficient indicator to assess the bio-stability of digestate planned for agricultural or land use. Compared with the existing biostability index, BDP has the additional advantage of no exogenous inoculum addition, homogenous test condition and possibility of shortening incubation time.

Root Biomass Distribution of Populus sibirica and Ulmus pumila Afforestation Stands Is Affected by Watering Regimes and Fertilization in the Mongolian Semi-arid Steppe

Desertification of the semi-arid steppe of Mongolia is advancing very rapidly, motivating afforestation efforts. The "Green Belt" joint project (Government of Mongolia and Republic of Korea), which aims to mitigate soil degradation and develop agroforestry activities through the planting of a forest shelterbelt, is one such response. In these plantations, tree growth has been supported by different watering regimes (no watering, 2, 4, and 8 L h^-1) and by two types of soil fertilization (NPK and Compost). The present paper analyses the effect of these techniques on soil chemistry and root biomass partitioning of Populus sibirica (Horth ex Tausch) and Ulmus pumila (L.) tree species. In July 2019, at the plantation site in Lun Soum, Tuv province (Mongolia), six trees were excavated by hand in each treatment, the root system was divided into taproot and five diameter classes (0-2; 2-5; 5-10; 10-20; > 20 mm), and the biomass was measured. Soil organic matter, macronutrients, and pH were also measured. The addition of fertilizers in the long-term did not enhance the soil chemical properties. The build-up of root biomass in both species correlated positively with increasing levels of the watering, while the application of fertilizers led to root growth suppression. For most of the root classes and both species, an irrigation level of 4 L h^-1 was sufficient to yield the highest biomass and could be recommended for afforesting the semi-arid steppe of Mongolia. The root biomass of P. sibirica was more dependent on the watering regimes and of U. pumila was more negatively influenced by the application of fertilizers, indicating that U. pumila, due to the its lower water need, could be suitable for afforesting semi-arid environments. Our experiments suggest that afforestation practices in the semi-arid steppe of Mongolia should be supported by a prior analysis of plants' needs, soil type, dose, and type of fertilizers to be applied. Knowledge of the root response to the supporting techniques is necessary for choosing the best one for the plantation and, thus, to develop a sustainable and successful strategy to restore these degraded lands.

Uncovering new indicators to predict stability, maturity and biodiversity of compost on an industrial scale

Currently, the metagenomic study of the composting process has gained great importance since it has allowed the identification of the existence of microorganisms that, until now, had not been isolated during the process by traditional techniques. However, it is still complex to determine which bioindicators could reveal the degree of maturity and stability of a particular compost. Thereby, the main objective of this work was to demonstrate the possible correlation between traditional parameters of maturity and stability of compost, with other indicators of biodiversity in products highly heterogeneous from composting processes on an industrial scale. The results demonstrated the enormous influence of the raw materials in characterizing the products obtained. Even so, important relationships were established between the Chao1 and Shannon indexes, and certain parameters related to the maturity, stability and toxicity of the samples, such as nitrification index, humification rate, phenolic content, germination index or oxygen consumption.

Physico-chemical and spectroscopic quality assessment of compost from date palm (Phoenix dactylifera L.) waste valorization

Organic matter (OM) is a vital component for a healthy soil, its lack arise a major problem for farmers who need to use commercialized fertilizers with high costs. Considering circular economy approach and for increasing OM availability, water soaked date palm waste was co-composted with goat manure in aerated windrow to produce a soil organic amendment. The OM biodegradation was mainly controlled based on biological parameters and spectroscopic techniques. The results showed a rapid temperature increase during the first week, and a relatively long compost maturity phase. The OM content reduction was of 36% and C/N ratio shifted from 60 to 20 at the process end. During the composting process, the specific ultraviolet absorbance SUVA₂₅₄, SUVA₂₆₉ and the SUVA₂₈₀ values increase confirmed the OM and hydrophilic compounds degradation, as well as substrate content oxidation into aromatic compounds. The Fourier Transform Infrared Spectroscopy (FTIR) analyses of the different samples collected during the process exhibited both OM biodegradation and mineralization. The 3 absorption ratios 1650/2845, 1525/2925 and 2920/1640 confirmed an aromaticity increase by aromatic structures biosynthesis, such as humic-like and fulvic-like substances, with the decomposition/transformation of aliphatic components, polysaccharides, and alcohols. Fluorescence excitation-emission matrix (FEEM) spectroscopy coupled with parallel factor analysis (PARAFAC) evidenced the dissolved organic matter (DOM) humification. A four-component model was obtained, i.e. humic-like component (S1, S2 and S3) and fulvic-like component (S4). The produced compost didn't exhibit any phytotoxicity evidenced by cress seed germination index exceeding 80%. All the analyses confirmed the good quality of the compost issued from mixed date palm waste and goat manure.

Methods for Bioaerosol Characterization: Limits and Perspectives for Human Health Risk Assessment in Organic Waste Treatment

Bioaerosol characterization represents a major challenge for the risk assessment and management of exposed people. One of the most important bioaerosol sources is the organic waste collection and treatment. This work analyzed and discussed the literature with the purpose of investigating the main techniques used nowadays for bioaerosol monitoring during organic waste treatment. The discussion includes an overview on the most efficient sampling, DNA extraction, and analysis methods, including both the cultural and the bio-molecular approach. Generally, an exhaustive biological risk assessment is not applied due to the organic waste heterogeneity, treatment complexity, and unknown aerosolized emission rate. However, the application of bio-molecular methods allows a better bioaerosol characterization, and it is desirable to be associated with standardized cultural methods. Risk assessment for organic waste workers generally includes the evaluation of the potential exposition to pathogens and opportunistic pathogens or to other microorganisms as biomarkers. In most cases, Saccharopolyspora rectivirgula, Legionella spp., Aspergillus spp., and Mycobacterium spp. are included. Future perspectives are focused on identifying common composting biomarkers, on investigating the causality process between chronic bioaerosol exposure and disease onset, and finally, on defining common exposure limits.

Selection of Mediterranean plants biomass for the composting of pig slurry solids based on the heat production during aerobic degradation

Heat recovery from composting processes and its use as a source of bioenergy have come into prominence in recent years. In this study, the selection of an adequate bulking agent for the composting of the solid fraction of pig slurry has been based on the heat produced by the microbial activity during aerobic degradation of the organic matter. Residues of five plant species typical of the Mediterranean area were mixed with the solid fraction of pig slurry, as bulking agents. The residues were: the prunings of three common cultivated tree species (orange, palm, and olive) and the biomass of two herbaceous species (milk thistle and sunflower). Self-heating tests were run for 18 days in thermally insulated laboratory-scale reactors; the energy released as heat was calculated from the temperature increase inside the reactors. The mixtures were sampled at the beginning and end of the experiment, and the microbial stability was evaluated by aerobic respiration tests. The heat energy produced was highest in the mixture with milk thistle (18.3 ± 1.78 MJ kg^-1 of total solids -TS), followed by that with orange tree prunings (16.0 ± 1.094 MJ kg^-1 TS), and was lowest with olive tree prunings (6.3 ± 0.23 MJ kg^-1 TS). The microbial biodegradability of the mixtures and the physico-chemical characteristics (mainly the C/N ratio, cellulose concentration, and density) of the different bulking agents controlled the heat energy produced. The orange tree prunings were considered the most suitable bulking agent for composting of pig slurry solids as they showed high degradability and energy recovery potential.

Biodrying of the Light Fraction from Anaerobic Digestion Pretreatment in Order to Increase the Total Recovery Rate

Two pilot-scale tests were carried out to assess if biodrying could be an effective process for the treatment of light fraction produced by an hydromechanical pre-treatment in an anaerobic digestion plant. The trials were performed using two pilot-scale stainless steel cylindrical reactors of 750 L capacity. Two tests were performed: in Test 1, only the light fraction was used; in Test 2, the light fraction was mixed with a bulking agent composed of garden and pruning waste. In Test 2, the highest temperature (71 °C) in a short time (8 days) was reached. An average water content reduction of 78% in Test 1 and 61% in Test 2 was measured, leading to similar reductions of weight (47–48%) and volume (27–29%). A high biological stability was measured on the final light fraction samples collected from both the tests. Furthermore, the lower heating value obtained after the biodrying treatment complies with the quality specification of the European standard on refuse-derived fuels.

A new liquid-phase method and its comparison to two solid-phase microbial respiration activity methods to assess organic waste stability

Goal of the work was to compare the respiration activities, as measured via oxygen consumption with three different organic waste stability methods so that to propose the optimal one. The novelty of the work is that there exists no comparison of solid-phase with liquid-phase stability assessment techniques in the literature. The respiration activities were assessed using two solid-phase methods and a manometric liquid-phase method (MANLIQ) performed on twenty-seven organic substrates. The methods rely on measuring oxygen consumption (uptake) via pressure drops (liquid-phase test, static solid-phase test) or via direct O₂ measurements on the gaseous phases at the inlet and outlet of the respirometer (solid-phase dynamic test). A positive statistically significant correlation was calculated between the MANLIQ and the static solid-phase indices. The maximum rate MANLIQ index for the raw substrates was 2900 mg O₂ kg^-1 VS h^-1, while most of the processed substrates had cumulative MANLIQ indices below 160 g O₂ kg^-1 VS. The ratio of the liquid indices to the static solid-phase indices ranged from 1.6 to 2.7 and the ratio of the liquid indices to the dynamic solid-phase indices ranged from 0.2 to 0.4. The MANLIQ method failed to result in a good correlation of the processing time with the respiration indices. On the other hand, a correlation was more visible in the two solid-phase tests, despite the large variability of the types and sources of the substrates. Therefore, the solid-phase methods should be preferred over the liquid-phase method to assess stability for various organic substrates.

Decomposition characteristics of indigenous organic fertilisers and introduced quick compost and their short-term nitrogen availability in the semi-arid Ethiopian Rift Valley

Case studies on the assessment of local organic fertilisers (OFs) in their quality (decomposition characteristics and nutrient availability for crops) are few in sub-Saharan Africa (SSA). This study assessed the quality of local OFs from the Ethiopian Rift Valley. The decomposition characteristics were assessed by acid detergent fibre analysis methods, while the short-term nitrogen availability was assessed by a combination of laboratory incubations and inorganic nitrogen and acid detergent soluble nitrogen determinations. A commercial hand-held reflectometer (RQFlex) was used for determining nitrogen components. The mean acid detergent soluble organic matter contents exceeded 250 mg g⁻¹, indicating the OF feedstock contained much of the readily decomposable organic matter. Some of the indigenous compost (kosi) samples showed net nitrogen immobilisation during the initial period of incubation, followed by net nitrogen mineralisation in one month of incubation with 4% of the nitrogen mineralisation rate. Kosi should be applied to a field one month before seeding. Short-term nitrogen availability from kosi was too low to substitute for inorganic fertilisers. The combination of the simple analysis methods shown in this study is a quick, cost-saving, and accurate quality assessment approach for OFs, which can be useful in the field and at experimental stations in SSA.

Exhausted grape marc and organic residues composting with polyethylene cover: Process and quality evaluation as plant substrate

In Argentina, wine production is one of the most important economic activities, producing a large quantities of organic wastes. Composting is a viable alternative to treat these residues, with the possibility to obtain high-quality products. The objective of the present study was to evaluate the effect of the addition of goat manure, leaves from garden raking and alfalfa to exhausted grape marc and the influence of plastic cover on the composting process and the quality of the finished product. Composting was carried out in turned piles in a total randomized design. Temperature, moisture, pH, electrical conductivity, micro and macro elements, biological parameters, stability and structure were determined with the goal to assess product quality. Mixture compost presented higher macro and micro elements content (especially P, Mn and Zn) than grape marc compost. Plastic cover showed no significant effect on physico-chemical parameters, while microorganisms were affected, with higher cellulolytic and nitrifying content in uncovered piles. In all composts, parameters indicated stability and no pathogens (Salmonella sp.) were detected. Pot assay with Lactuca sativa suggested that all compost revealed adequate substrate quality, with higher plant biomass values than commercial substrate and sand (Control), even with fertilization. Mixture compost showed significantly higher biomass and nutrient absorption values relative to the remaining evaluated substrates, suggesting that the use of goat manure and leaves added to exhausted grape marc, as raw material resulted in higher compost quality. All together indicated that the use of polyethylene cover negatively affect microorganisms content and a higher diversity of organic residues composted would result in higher microbiological activity and nutritional grade product.

A method for the rapid evaluation of leather biodegradability during the production phase

Advances in technological-industrial processes have led to the development of new materials that generate different impacts on the environment when presented as waste. The application of sustainable manufacturing practices in order to improve the environmental behaviour of materials, including in the waste stage, is now an important industry responsibility. This study developed a new method for the rapid evaluation of leather biodegradability that can easily be operated by the tannery industry during the production phase. The method uses the OxiTop® system within which a solid sample is suspended in a liquid medium with no nutritional limitations at a constant temperature and stirring conditions. Ten leather samples were tested based on the existing methodology for determining aerobic biological activity (EN 16087-1: 2011), ultimate aerobic biodegradability of plastic materials in an aqueous medium (ISO 14851: 2004), and OECD 301F guidelines for testing of chemicals. The developed method has been shown to reliably distinguish (over 7 days) between samples produced using different manufacturing processes/treatments. Starch proved to be a better standard reference material for checking inoculum activity and the proper functioning of the measurement system than cellulose. Skin without treatment was shown to be a suitable reference material for defining the maximum biodegradation of leather materials. Double exponential and Gompertz mathematical models closely described the biodegradation of the tested samples. This method offers a way for industry to test and produce leather materials with higher levels of biodegradability, thus reducing the adverse environmental impacts of the final products when presented as solid waste.

Enhancement of pig bristles waste bioconversion by inoculum of keratinolytic bacteria during composting

The objective of this study was to evaluate the effect of keratinolytic B. cereus PCM 2849 inoculum on the process of composting pig bristles, in the mixture with sawdust and lignite dust. The process was conducted in closed, static and dynamic reactors. The impact of the composting technique and inoculum on the mineralization and maturity indices during active stage of composting was evaluated. A beneficial effect of the inoculum was confirmed during composting with the application of a static technique and with the dynamic technique. The introduction of bacterial inoculum enhanced transformation of mineral compounds and had a positive effect on maturity, as established with maturity indexes i.e. C/N ratio, carbon solubility, oxidation index of mineral forms of nitrogen, humification ratio or content of humic and fulvic acids. Products after the active stage of composting, especially inoculated compost variants, were characterized by beneficial contents of minerals and met safety standards regarding occurrence of heavy metals. Moreover, inoculated variants, left on prisms for further maturation, reached a more advanced level of matter decomposition and stabilization, as compared to composts obtained after the active phase of composting. The use of B. cereus inoculum for composting pig bristles turned out to be an effective method for accelerating the biodegradation of this hard-to-degrade waste and enabled to produce a valuable fertilizing product.

Valorisation of digestate from biowaste through solid-state fermentation to obtain value added bioproducts: A first approach

Digestate from biowaste was assessed as a potential source of bioproducts of commercial and industrial interest through solid-state fermentation. The targeted bioproducts were hydrolytic enzymes (cellulases and proteases from autochthonous microbiome), biosurfactants (sophorolipids produced from Starmella bombicola) and biopesticides (produced from Bacillus thuringiensis). Low cellulase production was observed within the range of 0.5-1.5 FPU g^-1 DM while protease production showed two discrete peaks of 66 ± 8 and 65 ± 3 U g^-1 DM at 3.5 and 48 h, respectively. Low sophorolipids production was also obtained, with a maximum yield of 0.02 g g^-1 DM using hygienised digestate supplemented with external sugar and fat sources. Biopesticides produced by B. thuringiensis were successfully at 72 h of operation, reaching a maximum spore production of 8.15 ± 0.04 (10⁷) CFU g^-1 DM and 2.85 ± 0.22 (10⁷) CFU g^-1 DM using sterile and hygienised digestate, respectively. These biopesticides could contribute to the substitution of chemically produced pesticides, moving towards a sustainable digestate management in a circular economy scheme.

Characterization of composted sewage sludge during the maturation process: a pilot scale study

This paper determines the impact of the maturation process of composted sewage sludge on the quality of the final product and assesses the stabilization effect. The samples of composted sewage sludge were taken from a wastewater treatment plant located in Pomerania in northern Poland. The sewage sludge was composted in an open windrow composting plant with the addition of straw and wood chips in the turning windrow. The aeration of the sewage sludge mixture was conducted based on two methods. The first phase (intensive degradation phase of 6 to 8 weeks) was characterized by frequently turning; the second phase for maturation used aeration channels (2 to 3 months). In three sampling campaigns samples were taken from the same windrow after 2 (no. 1), 8 (no. 2), and 12 weeks (no. 3) of maturation. Fresh samples were used for analyzing the stabilization parameter as static respiration activity (AT₄). Furthermore, the values of pH, organic matter (OM), total organic carbon (TOC), elementary composition, nutrients, total content, and mobile forms of heavy metals were analyzed in the compost samples. A significant decrease was found in the stabilization parameter (AT₄) during the maturation of tested materials. In turn, no significant differences were found in the elementary composition. The concentration of most metals increased in the final product. The total content of heavy metals in the final product did not exceed the limit values for the agricultural use of sewage sludge, compost from municipal waste, and for organic fertilizers. There were no significant changes in the percentage of bioavailable and mobile forms of heavy metals during compost maturation. Zinc was characterized by the highest level of mobile and bioavailable forms, which may cause bioaccumulation after the fertilization of soil. The study has shown that the process of maturation of compost from sewage sludge not affects changes in the content of heavy metal forms. The scope of this study has been planned on a wider scale for different variants of sewage sludge composting, in order to evaluate the process.

Characterization of selected municipal solid waste components to estimate their biodegradability

Biological treatments of Residual Municipal Solid Waste (RMSW) allow to divert biodegradable materials from landfilling and recover valuable alternative resources. The biodegradability of the waste components needs however to be assessed in order to design the bioprocesses properly. The present study investigated complementary approaches to aerobic and anaerobic biotests for a more rapid evaluation. A representative sample of residual MSW was collected from a Mechanical Biological Treatment (MBT) plant and sorted out into 13 fractions according to the French standard procedure MODECOM™. The different fractions were analyzed for organic matter content, leaching behavior, contents in biochemical constituents (determined by Van Soest's acid detergent fiber method), Biochemical Oxygen Demand (BOD) and Bio-Methane Potential (BMP). Experimental data were statistically treated by Principal Components Analysis (PCA). Cumulative oxygen consumption from BOD tests and cumulative methane production from BMP tests were found to be positively correlated in all waste fractions. No correlation was observed between the results from BOD or BMP bioassays and the contents in cellulose-like, hemicelluloses-like or labile organic compounds. No correlation was observed either with the results from leaching tests (Soluble COD). The contents in lignin-like compounds, evaluated as the non-extracted RES fraction in Van Soest's method, was found however to impact negatively the biodegradability assessed by BOD or BMP tests. Since cellulose, hemicelluloses and lignin are the polymers responsible for the structuration of lignocellulosic complexes, it was concluded that the structural organization of the organic matter in the different waste fractions was more determinant on biodegradability than the respective contents in individual biopolymers.

Inside the small-scale composting of kitchen and garden wastes: Thermal performance and stratification effect in vertical compost bins

Decentralized composting has been proposed as a best available practice, with a highly positive impact on municipal solid wastes management plans. However, in cold climates, decentralized small-scale composting performance to reach thermophilic temperatures (required for the product sanitization) could be poor, due to a lack of critical mass to retain heat. In addition, in these systems the composting process is usually disturbed when new portions of fresh organic waste are combined with previous batches. This causes modifications in the well-known composting evolution pattern. The objective of this work was to improve the understanding of these technical aspects through a real-scale decentralized composting experience carried out under cold climate conditions, in order to assess sanitization performance and to study the effects of fresh feedstock additions in the process evolution. Kitchen and garden organic wastes were composted in 500 L-static compost bins (without turning) for 244 days under cold climate conditions (Bariloche, NW Patagonia, Argentina), using pine wood shavings in a ratio of 1.5:1 v: v (waste: bulking agent). Temperature profile, stability indicators (microbial activity, carbon and nitrogen contents and ratio) and other variables (pH and electrical conductivity), were monitored throughout the experience. Our results indicate that small-scale composting (average generation rate of 7 kg d^-1) is viable under cold weather conditions, since thermophilic sanitization temperatures (> 55 °C) were maintained for 3 consecutive days in most of the composting mass, according to available USEPA regulations commonly used as a reference for pathogens control in sewage sludge. On the other hand, stability indicators showed a differentiated organic matter degradation process along the compost bins height. Particularly, in the bottommost composting mix layer the process took a longer period to achieve compost stability than the upper layers, suggesting that differential organic matter transformation appears not to be necessarily associated to the order of the waste batches incorporation in a time line, as it could be expected. These findings suggest the need to discuss new ways of studying the composting process in small-scale compost bins as well as their commercial design.

Insight into effects of mature compost recycling on N2O emission and denitrification genes in sludge composting

Mature compost recycling is widely used to reduce the dosage of organic bulking agent in actual composting process. In this study, the effects of mature compost amendment on N₂O emission and denitrification genes were investigated in 47 days composting of sewage sludge and rice husks. The results showed that mature compost amendment dramatically augmented N₂O emission rate in mesophilic phase and CO₂ emission rate in thermophilic phase of composting, respectively. The cumulative amount of N₂O emission increased by more than 23 times compared to the control. Mature compost amendment not only reduced moisture and pH, but also significantly increased NO₃^--N and NO₂^--N concentrations. The correlation matrices indicated that NO₃^--N, narG and norB were the main factors influencing N₂O emission rate in sludge composting with mature compost recycling, but the N₂O emission rate was significantly correlated to NO₂^--N, nirK and norB in the control.

Relationship between maturity and microbial communities during pig manure composting by phospholipid fatty acid (PLFA) and correlation analysis

The dynamic of microbial community plays vital role during composting. We therefore conducted a combined study on the maturity of compost (by pig manure composting with covering matured compost) and the successions of microbial communities (via phospholipid fatty acid (PLFA)). Our results showed that pH, electrical conductivity (EC), NH₄-N, and germination index (GI) were suitable indicators for compost maturity evalument. In addition, there was a closer correlation between maturity indexes (NH₄-N and GI) and the microbial compositions (as evaluated by microbial PLFA). The regression predicting model for NH₄-N used bacteria PLFA 15:0 and fungi PLFA 18:1ω9t (R² = 0.98, P < 0.01) and for GI used fungi PLFA 18:1ω9t and 18:1ω9, 12 (R² = 0.94, P < 0.01) as the evidences of good predictive ability. It also indicated that PLFA 18:1ω9t has a good relationship with the changes of NH₄-N and GI during the composting. Our results revealed the potential of using microbial PLFA for evaluating the maturity during pig manure composting.

Composting of food wastes: Status and challenges

This review analyses the main challenges of the process of food waste composting and examines the crucial aspects related to the quality of the produced compost. Although recent advances have been made in crucial aspects of the process, such composting microbiology, improvements are needed in process monitoring. Therefore, specific problems related to food waste composting, such as the presence of impurities, are thoroughly analysed in this study. In addition, environmental impacts related to food waste composting, such as emissions of greenhouse gases and odours, are discussed. Finally, the use of food waste compost in soil bioremediation is discussed in detail.

Investigating the efficiency of co-composting and vermicomposting of vinasse with the mixture of cow manure wastes, bagasse, and natural zeolite

Fermentation of ethanol as a product of sugarcane agro-industry causes the discharge of large amounts of a liquid waste called vinasse into the environment. In this study, co-composting followed by vermicomposting process of the mixtures of vinasse, cow manure, and chopped bagasse was performed for 60days using earthworms of Eisenia fetida species. The results showed that the trend of changes in C/N was decreasing. The pH of the final fertilizer was in alkaline range (8.1-8.4). The total potassium decreased during the process, ranging from 0.062 to 0.15%, while the total phosphorus increased and its values ranged from 0.06 to 0.10%. The germination index (GI) for all samples was 100%, while the cellular respiration maturity index was<2mg C-CO₂g^-1 organic carbon day^-1, confirming a very stable compost. The results of this study indicate that the compost obtained from the co-composting-vermicomposting process could be used as a sound soil amendment.

Analysis of MSW full-scale facilities based on anaerobic digestion and/or composting using respiration indices as performance indicators

The Landfill Directive (1999/31/EC) forces European States to reduce the amount of biodegradable municipal waste landfilled to 35% of 1995 levels. Mechanical-Biological Treatment (MBT) plants are the main alternative to waste incineration and landfilling. In this work, the waste treatment efficiency of six full-scale MBT facilities has been analysed using respiration indices (Dynamic Respiration Index and Cumulative Oxygen Consumption) to monitor plant performance. MBTs relying on anaerobic digestion plus composting achieved a high grade of stability on final compost (0.24±0.09mgO₂g^-1DMh^-1 and 20±9mgO₂g^-1DM for dynamic respiration and cumulative consumption, respectively). On the contrary, MBTs relying only on composting showed a poor performance (1.3±0.2mgO₂g^-1DMh^-1 and 104±18mgO₂g^-1DM for dynamic respiration and cumulative consumption, respectively). These results highlight the usefulness of respirometric balances to assess the performance of MBT full-scale plants.

Composting of pig manure and forest green waste amended with industrial sludge

The aim of this research was to study the composting of chestnut forest green waste (FGW) from short rotation chestnut stands amended with sludge resulting from the manufacture of Medium Density Fibreboard (MDFS) and pig manure (PM). Both FGW and MDFS presented low biodegradation potential but different characteristics in granulometry and bulk density that make its mixture of interest to achieve high composting temperatures. PM decreased the C/N ratio of the mixture and increased its moisture content (MC). Three mixtures of MDFS:FGW at volume ratios of 1:1.3 (M2), 1:2.4 (M3) and 0:1 (M4) were composted after increasing its MC to about 70% with PM. A control with food waste (OFW) and FGW (1:2.4 in volume) (M1) was run in parallel. Watering ratios reached 0.25 (M1), 1.08 (M2) 1.56 (M3) and 4.35 (M4) L PM/kg TS of added solids wastes. Treatments M2 and M3 reached a thermophilic phase shorter than M1, whilst M4 remained in the mesophilic range. After 48days of composting, temperature gradients in respect to ambient temperature were reduced, but the mineralization process continued for around 8months. Final reduction in total organic carbon reached 35-56%, depending mainly on the content in MDFS. MDFS addition to composting matrices largely reduced nitrogen losses, which range from 22% (M2) to 37% (M3) and 53% (M4). Final products had high nutrient content, low electrical conductivity and low heavy metal content which make it a valuable product for soil fertilization, right to amend in the chestnut forests and as a pillar of their sustainable management.

In Vitro and In Vivo Assessment of Aqueously Extractable Estrogens in Poultry Manure after Pilot-scale Composting

Poultry manure contains free and conjugated forms of the natural estrogens 17β-estradiol and estrone, which can be transported to receiving waters via runoff when land-applied. Previous studies have demonstrated estrogens in runoff from poultry manure-amended fields but have not tracked changes in estrogenicity within this water over time. Microbial conversion of conjugated estrogens (a major portion of water-extractable estrogens) to parent forms may result in temporary increases in estrogenicity in natural water bodies. The present study created 80-L batches of simulated poultry manure runoff, which were investigated over 10 d for estrogenicity by bioluminescent yeast estrogen screen assay and fathead minnow () vitellogenin induction model. The efficacy of different compost conditions (in-vessel aeration ± turning, and piling) on reduction/elimination of aqueously extractable estrogens in poultry manure was also investigated. Results indicate 3- to 10-fold increases in estrogenicity in various poultry manure mixtures during 10-d observations. Estrogenicity returned to low levels in postcompost treatments but remained elevated in the precompost treatment. Aerated compost resulted in >75% reductions in initial, peak, and 10-d mean estrogenicity in aqueous mixtures (0.3, 0.8, and 0.5 ng 17β-estradiol equivalents [EEQ] L, respectively) compared with the precompost mixture (1.4, 4.8, and 2.1 ng EEQ L, respectively). Estrogenicity was significantly higher in the aqueous extract from the piled treatment than the aerated treatment, and 10-d exposure of male fish to the piled treatment resulted in statistically significant vitellogenin induction. Collectively, our results suggest a need to investigate estrogenicity in surface waters for several days after receiving manure-influenced runoff.

Optimization of waste combinations during in-vessel composting of agricultural waste

In-vessel composting of agricultural waste is a well-described approach for stabilization of compost within a short time period. Although composting studies have shown the different combinations of waste materials for producing good quality compost, studies of the particular ratio of the waste materials in the mix are still limited. In the present study, composting was conducted with a combination of vegetable waste, cow dung, sawdust and dry leaves using a 550 L rotary drum composter. Application of a radial basis functional neural network was used to simulate the composting process. The model utilizes physico-chemical parameters with different waste materials as input variables and three output variables: volatile solids, soluble biochemical oxygen demand and carbon dioxide evolution. For the selected model, the coefficient of determination reached the high value of 0.997. The complicated interaction of agricultural waste components during composting makes it a nonlinear problem so it is difficult to find the optimal waste combinations for producing quality compost. Optimization of a trained radial basis functional model has yielded the optimal proportion as 62 kg, 17 kg and 9 kg for vegetable waste, cow dung and sawdust, respectively. The results showed that the predictive radial basis functional model described for drum composting of agricultural waste was well suited for organic matter degradation and can be successfully applied.

Wastewater Biosolid Composting Optimization Based on UV-VNIR Spectroscopy Monitoring

Conventional wastewater treatment generates large amounts of organic matter-rich sludge that requires adequate treatment to avoid public health and environmental problems. The mixture of wastewater sludge and some bulking agents produces a biosolid to be composted at adequate composting facilities. The composting process is chemically and microbiologically complex and requires an adequate aeration of the biosolid (e.g., with a turner machine) for proper maturation of the compost. Adequate (near) real-time monitoring of the compost maturity process is highly difficult and the operation of composting facilities is not as automatized as other industrial processes. Spectroscopic analysis of compost samples has been successfully employed for compost maturity assessment but the preparation of the solid compost samples is difficult and time-consuming. This manuscript presents a methodology based on a combination of a less time-consuming compost sample preparation and ultraviolet, visible and short-wave near-infrared spectroscopy. Spectroscopic measurements were performed with liquid compost extract instead of solid compost samples. Partial least square (PLS) models were developed to quantify chemical fractions commonly employed for compost maturity assessment. Effective regression models were obtained for total organic matter (residual predictive deviation-RPD = 2.68), humification ratio (RPD = 2.23), total exchangeable carbon (RPD = 2.07) and total organic carbon (RPD = 1.66) with a modular and cost-effective visible and near infrared (VNIR) spectroradiometer. This combination of a less time-consuming compost sample preparation with a versatile sensor system provides an easy-to-implement, efficient and cost-effective protocol for compost maturity assessment and near-real-time monitoring.

Artemia salina as a new index for assessment of acute cytotoxicity during co-composting of sewage sludge and lignocellulose waste

Considering the necessity to constantly monitor the safety of use of sewage sludge, we have focused on evaluating the toxicity of raw sludge and sludge treated by co-composting with date palm waste using an in vitro assessment of cytotoxicity based on Artemia salina larvae as a simple new sensitive and reliable routine test. The efficiency of co-composting in decreasing sludge toxicity was evaluated in terms of cytotoxicity abatement reaching 100% by the second month of composting for mixture A (1/3 sludge+2/3 date palm waste) and the third month for mixture B (1/2 sludge+1/2 date palm waste). Cytotoxicity abatement was confirmed by the increase of germination index, which reached over 100% with positive correlation for lettuce (R(2)=0.81 and 0.86) and for turnip (R(2)=0.87 and 0.74) for mixtures A and B respectively. A strong correlation between the proposed cytotoxicity test and the evolution of regulatory physical-chemical approaches was found, (R(2)=0.88 and 0.89) for NH4(+)/NO3(-) and (R(2)=0.80 and 0.88) for C/N respectively for mixture A and B. These findings allow the inexpensive bioassay reported to be used as a highly sensitive test to determine the cytotoxicity and maturity of composts.

Immobilisation of lead and zinc in contaminated soil using compost derived from industrial eggshell

This study aims to evaluate the capacity of a compost obtained by co-composting of industrial eggshell (CES) to immobilise lead (Pb) and zinc (Zn) in an acidic soil contaminated by mining activities. Mature compost without eggshell (CWES) and natural eggshell (ES) were also tested as soil amendments for comparison purposes. Three different application rates were used for each material, ensuring the same quantity in terms of neutralizing capacity. Incubation experiments were conducted under controlled conditions and CO2 emissions monitored for 94 days. The environmental availability of Pb and Zn in the amended soil was assessed and bioassays were performed at the end of the incubation period. When eggshells were present, the CES compost raised the soil pH to values higher than 6 and reduced the soil mobile fraction for both Pb and Zn, in more than 95%. Soil toxicity towards Vibrio fischeri was also suppressed and environmental risk decreased to "low level". However, the immobilisation in the acid insoluble soil component was significantly achieved only for Zn. In addition, regarding soil carbon dynamics the CO2-C emissions were enhanced, mainly in the case of the highest rate of amendment. Both first order-E and parallel first order models may adequately describe the kinetic data of CO2-C cumulative release. Without eggshells, the CWES compost revealed limited effect on heavy metals immobilisation, likely due to its small capacity to correct soil acidity, at lower application rates. Using solely eggshells, the ES waste had similar outcomes when compared with CES, but at the higher application rate, CO2 emissions were enhanced with the eggshell compost due to the contribution of biotic carbon present therein. Therefore, this study points out that CES is an effective liming material and may be used for in situ remediation of contaminated soil with Pb and Zn.

The use of organic wastes at different degrees of maturity as carbon sources for denitrification of landfill leachate

In this study different garden refuses were investigated to ascertain their efficiency to act as carbon sources in a denitrification system. Six different garden refuse materials were studied: commercial and domestic garden refuse raw (CGR RAW, DGR RAW), immaturely composted domestic and commercial garden refuse (DGR 10 and CGR 10 respectively), commercial garden refuse composted by Dome Aeration Technology and by "turned windrow" technology (DAT and TW). Different concentrations of synthetic nitrate solution were used to assess the efficiency of each substrate. The results demonstrate that all substrates were able to sustain the denitrification process. However, due to its higher C/N ratio the CGR RAW was the better performing of the materials, reaching 100% removal after 8 and 12h for the 100 and 500 mg L(-1) respectively and after 11 days for 2000 mg L(-1). Kinetic studies revealed that the zero-order reaction better describes the process indicating a denitrification rate independent from the nitrate concentrations investigated when 100 and 500 mg L(-1) of nitrate were used. The study demonstrated the suitability of organic municipal solid wastes to sustain denitrification, opening a new scenario towards a low cost and in situ solution for treatment of landfill leachate by using wastes, otherwise disposed of in landfill.

Physico-chemical and biological characteristics of compost from decentralised composting programmes

Composts that originated from small-scale composting programmes including home, community and canteen waste composters were studied. Heavy metals concentration indicated compliance with current regulations for conventional and organic agriculture. Compost from canteen waste showed high organic matter content (74% VS), while community (44 ± 20% VS) and home composts (31 ± 16% VS) had moderate levels. N content increased from home compost (1.3 ± 0.9% dm) to community (2.0 ± 0.9%) and canteen compost (2.5-3.0%) while P content ranged from 0.4% to 0.6% dm. C/N, absorbance E4/E6 and N-NH4(+)/N-NO3(-) ratios as well as respiration index indicated well-stabilized final products. Culturable bacterial and fungal cfu linkage to composting dynamics were identified and higher diversity of invertebrates was found in the smaller scale static systems. With similar process evolution indicators to industrial systems, overall results support the sustainability of these small-scale, self-managed composting systems.

Evaluation of Optimum Moisture Content for Composting of Beef Manure and Bedding Material Mixtures Using Oxygen Uptake Measurement

Moisture content influences physiological characteristics of microbes and physical structure of solid matrices during composting of animal manure. If moisture content is maintained at a proper level, aerobic microorganisms show more active oxygen consumption during composting due to increased microbial activity. In this study, optimum moisture levels for composting of two bedding materials (sawdust, rice hull) and two different mixtures of bedding and beef manure (BS, Beef cattle manure+sawdust; BR, Beef cattle manure+rice hull) were determined based on oxygen uptake rate measured by a pressure sensor method. A broad range of oxygen uptake rates (0.3 to 33.3 mg O₂/g VS d) were monitored as a function of moisture level and composting feedstock type. The maximum oxygen consumption of each material was observed near the saturated condition, which ranged from 75% to 98% of water holding capacity. The optimum moisture content of BS and BR were 70% and 57% on a wet basis, respectively. Although BS’s optimum moisture content was near saturated state, its free air space kept a favorable level (above 30%) for aerobic composting due to the sawdust’s coarse particle size and bulking effect.

The importance of aeration mode and flowrate in the determination of the biological activity and stability of organic wastes by respiration indices

The aim of this study was to assess the effect of different air flowrates and different aeration modes on the respiration activity of three organic substrates of different stability degree: (i) a constant flowrate and (ii) a continuously adjusted air flowrate that optimized the oxygen uptake rate (OUR). Above 20L air kg(-1)DMh(-1), at the constant flow regime, the resulting dynamic respiration index at 24h (DRI24) and the cumulative respiration at four days (AT4) were statistically similar. At the OUR based aeration regime, the DRI24 and AT4 were statistically similar at all initial flowrates tested. Above a minimum threshold, cumulative air flow of around 3000Lairkg(-1) DM during a 5day period, the respiration activity was similar, particularly for the two less active substrates. This study highlights the importance of selecting the aeration to obtain reliable measures of biological activity and stability in organic wastes.

Stability and maturity of biowaste composts derived by small municipalities: Correlation among physical, chemical and biological indices

Stability and maturity are important criteria to guarantee the quality of a compost that is applied to agriculture or used as amendment in degraded soils. Although different techniques exist to evaluate stability and maturity, the application of laboratory tests in municipalities in developing countries can be limited due to cost and application complexities. In the composting facilities of such places, some classical low cost on-site tests to monitor the composting process are usually implemented; however, such tests do not necessarily clearly identify conditions of stability and maturity. In this article, we have applied and compared results of stability and maturity tests that can be easily employed on site (i.e. temperature, pH, moisture, electrical conductivity [EC], odor and color), and of tests that require more complex laboratory techniques (volatile solids, C/N ratio, self-heating, respirometric index, germination index [GI]). The evaluation of the above was performed in the field scale using 2 piles of biowaste applied compost. The monitoring period was from day 70 to day 190 of the process. Results showed that the low-cost tests traditionally employed to monitor the composting process on-site, such as temperature, color and moisture, do not provide consistent determinations with the more complex laboratory tests used to assess stability (e.g. respiration index, self-heating, volatile solids). In the case of maturity tests (GI, pH, EC), both the on-site tests (pH, EC) and the laboratory test (GI) provided consistent results. Although, stability was indicated for most of the samples, the maturity tests indicated that products were consistently immature. Thus, a stable product is not necessarily mature. Conclusively, the decision on the quality of the compost in the installations located in developing countries requires the simultaneous use of a combination of tests that are performed both in the laboratory and on-site.