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Background: Agronomic uses of biochar have been intensely explored in the last 15 years. Recently, a new generation of biochar-based fertilizers has been developed. Raw biochar (BCH), nitrogen-enriched biochar (N + BCH) or urea were added to a coir fiber-based substrate for tomato cultivation, to assess seed germination, growth and fruiting of two cultivars (Cuarenteno and Moneymaker)., Results: BCH stimulated seed germination and early radicle growth, possibly because of the presence of karrikins detected in both BCH and N-BCH (0.039 and 0.044 mg kg -1 , respectively). However, BCH reduced growth in adult plants in both cultivars, probably because of ammonium retention, causing low-N-stress-related symptoms such as accumulation of flavonoids in the leaf. Urea was toxic for seed germination because of the fast release of ammonium, but caused a positive effect on adult plant growth and yield, increasing chlorophyll in both cultivars, quantum yield and ascorbic acid in cv. Cuarenteno, and decreasing flavonoids and peroxide in leaves of both cultivars. Unlike urea, N + BCH showed a positive impact on plant growth and yield, but without releasing high amounts of ammonium or negatively affecting seed germination. Nitrogen-rich amendments reduced phosphorus and increased iron leaf content in both cultivars., Conclusion: BCH can be effectively used as a growth medium constituent in nurseries for seedling production, whereas N + BCH offers a promising alternative to urea or other nitrogen mineral fertilizers for crop cultivation. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry., (© 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.)

The agronomic use of compost and biochar as soil amendments may exhibit contrasting results in terms of soil fertility and plant nutrition. The effects of the biennial application of biochar, compost and a blend of compost:biochar (90:10; % dw:dw) on the agronomical performance of an organically managed and well established 25-year-old olive orchard was assessed 5 years after the initial application. The agronomical evaluation was based on the assessment of the soil physical, chemical, and biological characteristics, and the assessment of the soil fertility by both crop production and nutritional status of the orchard, and the bioassay with olive plantlets. Biochar mainly benefited the physical properties (bulk density, total porosity, aeration, water retention capacity) of soil, especially in the top 0-5 cm. Compost and its blend with biochar improved microbial activity, soil nutritional status (increasing the content of soluble organic C, N, and P) and favoured the formation of aggregates in soil. The bioassay conducted with young plantlets confirmed the enhanced soil fertility status in the three amended treatments, particularly in the case of biochar and its blend with compost. However, this effect was not significantly observed in the adult plants after 5 years of application, reflecting the slow response of adult olive trees to changes in fertilization. Based on these results, alongside the desirable long-residence time of biochar in soil and the ready availability of compost, the blend of biochar with compost assayed in this study is defined as a valid strategy for preparing high quality soil organic amendments., (© 2024. The Author(s).)

Different activation and N-doping treatments were used to produce biochar-based fertilizers (BBFs) with increased N concentration and slow N release. Pristine biochars were produced by pyrolysis of olive tree pruning feedstock at low and high temperatures (400 and 800 °C). These biochars were activated either by ultrasonication, or oxidation with hydrogen peroxide (H 2 O 2 ) or nitric acid (HNO 3 ) to increase their N retention potential. Subsequently biochars were enriched with N with either urea or ammonium sulfate. The activation of low-temperature biochars with HNO 3 was the most effective treatment leading to new surface carboxylic groups that facilitated the later enrichment with N. When treated with urea, BBFs reached 7.0 N%, whereas the H 2 O 2 activation only allowed an increase up to 2.0 N%. The use of urea as the external N source was the most efficient for incorporating N. Urea treated biochars had a water-soluble fraction that represented up to 14.5 % of the total N. The hydrolyzable N fraction, composed by amides and simple N heterocycles originated by the N-doping treatments, and nitro groups generated from HNO 3 activation, represented up to 60 % of the total N. This study relates the N chemical forms in the new BBFs to potential N availability in soil. The presence of water-soluble, hydrolyzable and non-hydrolyzable N implied that these BBFs may supply N that would be progressively available for plants, acting as slow-release fertilizers., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Little is known about the effect of biochar on the degradation of paracetamol in soil, considering the ubiquity of this pollutant in the environment. Given the importance of the electrochemical properties of biochar for contaminant remediation, we investigated the influence of raw and designer redox-active biochars on paracetamol degradation in soil. Metabolite quantification indicated that a minimum of 53% of the spiked paracetamol was transformed in biochar-amended soil, resulting in the accumulation of different degradation products. The identification of these products allowed us to chart paracetamol degradation pathways in soil with and without biochar amendment. Some of the major degradation routes were observed to proceed via catechol and phenol, despite being previously described as having only a minor role in paracetamol metabolism. Additionally, a new transformation route from paracetamol to NAPQI was discovered in anaerobic soil originating from direct redox reactions on the surface of the designer biochars. These results may contribute to change our understanding of the environmental fate of paracetamol in soil and the role of biochar in its biodegradation., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In this study, we produced modified biochars with enhanced electrochemical properties to increase PCP remediation in soil. Although all biochars enhanced PCP remediation in aerobic conditions, only a few did in anaerobic soil. The most successful modifications were (i) the preloading of biomass with 10% w/w FeCl 3 , to obtain a biochar rich in redox-active metals (B-Fe); (ii) the oxidation of a conductive biochar pyrolyzed at 1000 ºC with 0.025 M KMnO 4 , to produce a biochar with both moderate conductivity and redox capacity (B-1000-KMnO 4 ); and (iii) KMnO 4 oxidation of an amorphous biochar pyrolyzed at 400 ºC to obtain a biochar with very high redox capacity (B-KMnO 4 ). B-Fe reduced extractable PCP to almost zero after 50 days in both incubations, but showed slow kinetics of remediation in aerobic soil. B-1000-KMnO 4 had the highest rate of remediation under aerobic conditions, but no significant effect under anaerobic conditions. B-KMnO 4 , however, presented high rates of remediation and high removal of extractable PCP under both conditions, which made it the recommended modification strategy for increased PCP remediation. We found that the degree of remediation primarily depends on the redox capacity, while the rate of remediation was determined by both the conductivity and redox capacity of biochar., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

The demand for biostimulants has been growing at an annual rate of 10 and 12.4% in Europe and Northern America, respectively. The beneficial effects of humic substances (HS) as biostimulants of plant growth have been well-known since the 1980s, and they can be supportive to a circular economy if they are extracted from different renewable resources of organic matter including harvest residues, wastewater, sewage sludge, and manure. This paper presents an overview of the scientific outputs on application methods of HS in different conditions. Firstly, the functionality of HS in the primary and secondary metabolism under stressed and non-stressed cropping conditions is discussed along with crop protection against pathogens. Secondly, the advantages and limitations of five different types of HS application under open-fields and greenhouse conditions are described. Key factors, such as the chemical structure of HS, application method, optimal rate, and field circumstances, play a crucial role in enhancing plant growth by HS treatment as a biostimulant. If we can get a better grip on these factors, HS has the potential to become a part of circular agriculture., (Copyright © 2020 Jindo, Olivares, Malcher, Sánchez-Monedero, Kempenaar and Canellas.)

The efficiency of biochar for reducing the levels of volatile organic compounds (VOC) was investigated in a composting mixture containing 90% poultry manure and 10% straw (with and without 3% biochar addition) at three different stages of the process. The use of a low application rate of biochar reduced the concentration of VOC during the thermophilic phase. Biochar significantly reduced the levels of nitrogen volatile compounds, which are the most abundant VOC family, originated from microbial transformation of the N-compounds originally present in manure. The most efficient VOC reduction was observed in oxygenated volatile compounds (ketones, phenols and organic acids), which are intermediates of organic matter degradation, whereas there was no effect on other VOC families (aliphatic, aromatic and terpenes). These results suggest the importance of not only the sorption capacity of biochar but also its impact in the composting progress as main drivers for VOC reduction., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Composting operations taking place at municipal solid waste (MSW) treatment plants represent a source of volatile organic compounds (VOC) to the atmosphere. Understanding the variables governing the release of VOC at these facilities is crucial to assess potential health risks for site workers and local residents. In this work the changes in the VOC composition of a composting pile were monitored and compared to the VOC emmited from the same pile in order to understand the impact of composting operations on the release of VOC. More than one hundred VOC were indentified in the solid phase of the composting piles, which were dominated by terpenes (about 50% of the total amount of VOC) and in a lower quantity alcohols, volatile fatty acids and aromatic compounds. There was a reduction in the total concentration of VOC in the pile during composting, from 45 to 35 mg/kg, but the compostion and distribution of VOC families remained stable in the pile even in the mature compost. However, there was no correlation between the emitted VOC and their concentration in the composting pile. The VOC emission pattern was affected by the biological activity in the pile (measured by temperature, CO 2 evolution and the presence of CH 4 emissions). The highest VOC emissions were detected at early stages of the process, alongside with the generation of CH 4 in the pile, and then decreased sharply in the mature compost as a consequence of biodegradation and volatilisation. These results pointed to the importance of composting operation rather than the composition of the raw materials on the release of VOC in composting plants., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Biochar production and use are part of the modern agenda to recycle wastes, and to retain nutrients, pollutants, and heavy metals in the soil and to offset some greenhouse gas emissions. Biochars from wood (eucalyptus sawdust, pine bark), sugarcane bagasse, and substances rich in nutrients (coffee husk, chicken manure) produced at 350, 450 and 750°C were characterized to identify agronomic and environmental benefits, which may enhance soil quality. Biochars derived from wood and sugarcane have greater potential for improving C storage in tropical soils due to a higher aromatic character, high C concentration, low H/C ratio, and FTIR spectra features as compared to nutrient-rich biochars. The high ash content associated with alkaline chemical species such as KHCO3 and CaCO3, verified by XRD analysis, made chicken manure and coffee husk biochars potential liming agents for remediating acidic soils. High Ca and K contents in chicken manure and coffee husk biomass can significantly replace conventional sources of K (mostly imported in Brazil) and Ca, suggesting a high agronomic value for these biochars. High-ash biochars, such as chicken manure and coffee husk, produced at low-temperatures (350 and 450°C) exhibited high CEC values, which can be considered as a potential applicable material to increase nutrient retention in soil. Therefore, the agronomic value of the biochars in this study is predominantly regulated by the nutrient richness of the biomass, but an increase in pyrolysis temperature to 750°C can strongly decrease the adsorptive capacities of chicken manure and coffee husk biochars. A diagram of the agronomic potential and environmental benefits is presented, along with some guidelines to relate biochar properties with potential agronomic and environmental uses. Based on biochar properties, research needs are identified and directions for future trials are delineated.

The use of biochar has been revealed to have beneficial effects during the composting of manures and other N-rich materials by reducing N losses and enhancing the rate of the process. However, the impact of biochar has not been explored in other complex organic matrices with low N nitrogen that may hinder the composting process. The main novelty of this work was to study the impact of a small amount of biochar (4%) on the composting process of olive mill wastes, which are characterised by a recalcitrant lignocellulosic composition with reduced nitrogen (N) availability. Two treatments: (i) control (olive mill waste 46%+sheep manure 54%, dry weight) and (ii) the same mixture treated with biochar (4%), were composted during 31 weeks. The incorporation of a small amount of biochar improved N cycling by increasing NO3(-)-N content, indicating a higher nitrifying activity, and reducing N losses by 15% without affecting the amount of N2O released. The use of biochar as an additive for composting could improve the value of olive mill waste composts by reducing N losses and increasing N availability in lignocellulosic and N-poor materials., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Two experiments were conducted where three biochars, made from macadamia nutshell (MS), hardwood shaving (WS) and chicken litter (CL), were co-composted with chicken manure and sawdust, and also incubated with a chicken litter based commercial compost. Biochars were added at the rates of 5% and 10% in the co-composting and 10% and 20% in the incubation experiment. The rates of biochar had no consistent effect on the change in element contents of composted- or incubated-biochars. The biochar C demonstrated recalcitrance in both composting and incubation systems. Composting increased the CEC of biochars probably due to thermophilic oxidation. The increases in CEC of WS and CL were 6.5 and 2.2 times, respectively, for composting. Translocation of elements, between biochar and compost medium, occurred in both directions. In most cases, biochars gained elements under the influence of positive difference of concentrations (i.e., when compost medium had higher concentration of elements than biochar), while in some cases they lost elements despite a positive difference. Biochar lost some elements (WS: B; CL: B, Mg and S) under the influence of negative difference of concentrations. Some biochars showed strong affinity for B, C, N and S: the concentration of these elements gained by biochars surpassed the concentration in the respective composting medium. The material difference in the biochars did not have influence on N retention: all three netbag-biochars increased their N content. The cost of production of biochar-compost will be lower in co-composting than incubation, which involves two separate processes, i.e., composting and subsequent incubation., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A composting study was performed to assess the impact of biochar addition to a mixture of poultry manure and barley straw. Two treatments: control (78% poultry manure + 22% barley straw, dry weight) and the same mixture amended with biochar (3% dry weight), were composted in duplicated windrows during 19 weeks. Typical monitoring parameters and gaseous emissions (CO2, CO, CH4, N2O and H2S) were evaluated during the process as well as the agronomical quality of the end-products. Biochar accelerated organic matter degradation and ammonium formation during the thermophilic phase and enhanced nitrification during the maturation phase. Our results suggest that biochar, as composting additive, improved the physical properties of the mixture by preventing the formation of clumps larger than 70 mm. It favoured microbiological activity without a relevant impact on N losses and gaseous emissions. It was estimated that biochar addition at 3% could reduce the composting time by 20%., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The presence of polycyclic aromatic hydrocarbons (PAHs) has been postulated as a mechanism by which biochar might mitigate N(2)O emissions. We studied whether and to what extent N(2)O emissions were influenced by the three most abundant PAHs in biochar: naphthalene, phenanthrene and pyrene. We hypothesised that biochars contaminated with PAHs would show a larger N(2)O mitigation capacity and that increasing PAH concentrations in biochar would lead to higher mitigation potentials. Our results demonstrate that the high-temperature biochar (550 °C) had a higher capacity to mitigate soil N(2)O emissions than the low-temperature biochar (350 °C). At low PAH concentrations, PAHs do not significantly contribute to the reductions in soil N(2)O emissions; while biochar stimulated soil N(2)O emissions when it was spiked with high concentrations of PAHs. This study suggests that the impact of biochar on soil N(2)O emissions is due to other compositional and/or structural properties of biochar rather than to PAH concentration., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Several maturity indices were evaluated for in-vessel co-composting of chicken manure and pine sawdust with three different biochars. All the seven mixtures (piles) contained chicken manure and sawdust. Six of these piles contained biochar; each biochar was added at two rates, 5% and 10% wet weight. The maturity of composts was assessed by C/N, dissolved organic carbon (DOC), seed germination, NO3(-)-N/NH4(+)-N, and the Solvita test. The C/N values of finished composts were from 31.5 to 35.7, which were much higher than the optimum value of 21 for matured compost. Nevertheless, the rest of the parameters indicated that the composts were matured. The C/N values were high because of the high amount of recalcitrant carbon present in the feedstocks: biochar and sawdust. Biochar treated piles showed higher respiration as well as decomposition of DOC indicating higher microbial activity. Use of biochar in composting may reduce NH3 emission and nitrate leaching., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Composting is a method for preparing organic fertilizers that represents a suitable management option for the recycling of two-phase olive mill waste (TPOMW) in agriculture. Four different composts were prepared by mixing TPOMW with different agro-industrial by-products (olive pruning, sheep manure and horse manure), which were used either as bulking agents or as N sources. The mature composts were added during six consecutive years to a typical "Picual" olive tree grove in the Jaén province (Spain). The effects of compost addition on soil characteristics, crop yield and nutritional status and also the quality of the olive oil were evaluated at the end of the experiment and compared to a control treated only with mineral fertilization. The most important effects on soil characteristics included a significant increase in the availability of N, P, K and an increase of soil organic matter content. The application of TPOMW compost produced a significant increase in olive oil content in the fruit. The compost amended plots had a 15% higher olive oil content than those treatment with inorganic fertilization. These organics amendments maintained the composition and quality of the olive oil., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Traditional methods to evaluate the stability and maturity of organic wastes and composting matrices are laborious, time-consuming and generate laboratory chemical wastes. This study focused on the development of partial least square (PLS) regression models for the prediction of the stability and maturity of compost-based substrates based on Fourier transform infrared (FTIR) spectroscopy. The following parameters, selected as conventional maturity indexes, were modeled and used as dataset: dissolved organic carbon (DOC), C/N and NH4(+)/NO3(-) ratios, cation exchange capacity (CEC), degree of polymerization (DP), percentage of humic acid (PHA), humification index (HI) and humification ratio (HR). Models were obtained by using data from a wide range of compost based growing media of diverse origin and composition, including 4 commercially available substrates and 11 substrates prepared in our facilities with varying proportions of different organic wastes. The PLS models presented correlation coefficient of calibration (R(2)cal) close to 0.90 and correlation coefficient (R(2)) of cross validation (R(2)cv) presented acceptable values (>0.6), ranging from 0.67 (HR) to 0.92 (C/N). The good performance of the method was also confirmed by the low correlation obtained from the Y-randomization test. R(2) for test samples (R(2)pred) ranged from 0.66 (C/N) to 0.97 (HI) confirming the good correlation between measured and PLS predicted maturity indexes. FTIR spectroscopy combined with PLS regression represents, after modeling process, a fast and alternative method to assess substrate maturity and stability with reduction of time, lower generation of laboratory chemical wastes residues and lower cost per sample than conventional chemical methods. All models adjusted for maturity indexes are predictive, robust and did not present chance correlation., (© 2013 Elsevier B.V. All rights reserved.)

Solid phase microextraction (SPME) is a fast, cheap and solvent free methodology widely used for environmental analysis. A SPME methodology has been optimized for the analysis of VOCs in a range of matrices covering different soils of varying textures, organic matrices from manures and composts from different origins, and biochars. The performance of the technique was compared for the different matrices spiked with a multicomponent VOC mixture, selected to cover different VOC groups of environmental relevance (ketone, terpene, alcohol, aliphatic hydrocarbons and alkylbenzenes). VOC recovery was dependent on the nature itself of the VOC and the matrix characteristics. The SPME analysis of non-polar compounds, such as alkylbenzenes, terpenes and aliphatic hydrocarbons, was markedly affected by the type of matrix as a consequence of the competition for the adsorption sites in the SPME fiber. These non-polar compounds were strongly retained in the biochar surfaces limiting the use of SPME for this type of matrices. However, this adsorption capacity was not evident when biochar had undergone a weathering/aging process through composting. Polar compounds (alcohol and ketone) showed a similar behavior in all matrices, as a consequence of the hydrophilic characteristics, affected by water content in the matrix. SPME showed a good performance for soils and organic matrices especially for non-polar compounds, achieving a limit of detection (LD) and limit of quantification (LQ) of 0.02 and 0.03 ng g(-1) for non-polar compounds and poor extraction for more hydrophilic and polar compounds (LD and LQ higher 310 and 490 ng g(-1)). The characteristics of the matrix, especially pH and organic matter, had a marked impact on SPME, due to the competition of the analytes for active sites in the fiber, but VOC biodegradation should not be discarded in matrices with active microbial biomass., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Agricultural soils represent the main source of anthropogenic N2O emissions. Recently, interactions of black carbon with the nitrogen cycle have been recognized and the use of biochar is being investigated as a means to reduce N2O emissions. However, the mechanisms of reduction remain unclear. Here we demonstrate the significant impact of biochar on denitrification, with a consistent decrease in N2O emissions by 10-90% in 14 different agricultural soils. Using the (15)N gas-flux method we observed a consistent reduction of the N2O/(N2 + N2O) ratio, which demonstrates that biochar facilitates the last step of denitrification. Biochar acid buffer capacity was identified as an important aspect for mitigation that was not primarily caused by a pH shift in soil. We propose the function of biochar as an "electron shuttle" that facilitates the transfer of electrons to soil denitrifying microorganisms, which together with its liming effect would promote the reduction of N2O to N2.

Nitrogen availability plays a critical role in the biodegradation of organic matter during composting. Although the optimal initial C/N is known to be around 25-30, the chemical form in which N is present influences microbial activity and therefore degradation rate and gaseous losses. This study was conducted to evaluate the influence of N availability on the composting of a mixture of lignocellulosic materials. Three composting piles were made of a mixture of wheat straw and cotton waste, each pile containing different N-rich animal by-products. The evolution of the main physico-chemical parameters was monitored (temperature, pH, electrical conductivity, C/N, NH(4)(+), NO(3)(-), water soluble C and N) as well as the enzymatic activity related to the cycle of the main nutrients (β-glucosidase, protease, alkaline phosphatase and fluorescein diacetate hydrolysis). Additionally, fluxes of CO(2), CH(4) and N(2)O emitted from the composting piles were measured by the closed-chamber technique. Cumulative CO(2) emissions were fitted to five different kinetic models with biological significance to C mineralization data. The application of the different N-rich residues had a significant effect on the C and N dynamics during composting. However, most enzymatic activities followed similar patterns in the three piles. The major CO(2) fluxes were recorded during the thermophilic phase, showing a direct relationship with temperature peaks. No CH(4) fluxes were detected for any of the composting piles during the whole trial, whereas low N(2)O emissions were found at the early beginning and during the maturation stage., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The low degradation rate of two-phase olive mill wastes (TPOMW) during composting and after soil application is a characteristic feature of these materials. The aim of this work was to evaluate the relationship between the lignocellulosic fraction of TPOMW and the organic matter (OM) degradation rate in three agricultural soils amended with four TPOMW composting mixtures at different degree of stabilisation and prepared with different bulking agents and N sources. The mineralisation kinetics of TPOMW composting mixtures in soil reflected a large amount of slowly mineralisable C even in the starting mixtures (I and T1) where this fraction represented up to 85% of the total potentially mineralisable C pool. The effect of rich lignocellulosic composition was confirmed by the study of the DTS (50% dry TPOMW + 50% sheep manure) mixtures prepared with dry TPOMW, which had undergone partial degradation in a storage pond for one year before composting. These DTS samples showed a more similar kinetic behaviour in soil than the more transformed composting mixtures as reflected in the principal component analysis (PCA) diagram, where they were grouped in the same quadrant dominated by the lignin/holocellulose ratio. Soils amended with mature composts evolved very low amounts of C (between 2 and 6% of the added C) after two months of incubation, which highlights the suitability of these materials as a suitable C source for the soil to promote long term soil C stabilisation.

The influence of biochar derived from a hardwood tree (Quercus serrate Murray) on the dynamics of the microbial community during the composting of poultry manure (PM) and cow manure (CM) was evaluated by phospholipid fatty acid analysis (PLFAs). Changes in the PLFA patterns were related to key composting properties (C/N ratio, temperature, and bulk density) as the major drivers of the dynamics of the microbial community. At the beginning of the process, the fungal biomass was significantly greater in PM and CM than in the respective co-composted materials with biochar (PMB and CMB); this difference declined gradually during the process. In contrast, the Gram+ to Gram- ratio was increased by the presence of biochar. After 12 weeks of composting, factor analysis based on the relative abundances of single PLFAs revealed changes in the microbial community structure which depended on the original organic wastes (CM vs PM)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

One of the main disadvantages in the composting of two-phase olive mill wastes (TPOMW) is the long time required for its transformation (up to 40 weeks). The aim of this work was to evaluate the relationship between the degradation of the lignocellulosic fraction of TPOMW and the organic matter (OM) mineralisation rate in four composting piles prepared with different bulking agents and N-sources used to enhance OM degradation. The kinetics of degradation of the lignocellulosic fraction was compared to conventional maturation and stability indices to evaluate its impact on the duration of the composting process. The composition of bulking agents mainly affected the water-soluble fraction which influenced the OM degradation rate (linear or exponential OM degradation pattern) at early stages of the composting process but it neither modified the duration of the process (between 34 and 36 weeks) nor the total OM degradation underwent by the piles. The high initial mineral N availability was a key factor to significantly enhanced microbial activity. The mixture with urea as N-source registered the most efficient degradation of hemicellulose, cellulose and lignin, reducing the thermophilic phase and the total duration of TPOMW composting., ((c) 2010 Elsevier Ltd. All rights reserved.)

The evolution of CO(2), CH(4) and N(2)O were monitored in five composting mixtures prepared from two-phase olive mill waste (TPOMW) and different agroindustrial by-products in order to assess the effect of the initial composition and the N source on greenhouse gas emission. Surface gas fluxes were measured using a closed static chamber and compared to the changes in different organic matter fractions (organic and watersoluble C) and N forms (NH(4)(+) and NO(3)(-)). CH(4) emissions depended on the organic matter mineralisation dynamics and the incorporation of manure in the starting mixture. The highest CH(4) fluxes were registered during the intense degradation at early stages of the process (up to 100 g Cm(-2)d(-1)). The emission of N(2)O (0-0.9 g Nm(-2)d(-1)) occurred from 6th to 10th wk of composting (bioxidative phase), coinciding with an intense nitrification in the pile. The use of urea enhanced the N(2)O emission up to 3.7 g Nm(-2)d(-1), due to an increase in available mineral N in the pile. Even though well managed TPOMW composting piles only represent a minor source of CH(4) and N(2)O emissions, the addition of urea and easily available C fractions to the starting mixtures can significantly increase the environmental impact of TPOMW composting as far as greenhouse gas emissions are concerned., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated by the olive oil industry. Its recycling as a soil amendment, either unprocessed or composted, is being promoted as a beneficial agricultural practice in the Mediterranean area. One of the major difficulties when composting TPOMW is the compaction of the material due to its dough-like texture, which leads to an inadequate aeration. For this reason, the addition of bulking agents is particularly important to attain a proper composting process. In this study we followed the evolution of two composting mixtures (A and B) prepared by mixing equal amounts of TPOMW and sheep litter (SL) (in a dry weight basis). In pile B grape stalks (GS) were added (10% dry weight) as bulking agent to study their effect on the development of the composting process and the final compost quality. The incorporation of grape stalks to the composting mixture changed the organic matter (OM) degradation dynamics and notably reduced the total amount of lixiviates. The evolution of several maturation indices (C/N, germination index, water soluble carbon, humification indices, C/N in the leachates) showed a faster and improved composting process when GS were added. Moreover, chemical (NH4+, NO3(-), cation exchange capacity, macro and micronutrients, heavy metals) and physical properties (bulk and real densities, air content, total water holding capacity, porosity) of the final composts were analysed and confirmed the superior quality of the compost where GS were added.

The aim of this study was to evaluate the use of biochar (produced by slow pyrolysis of Eucalyptus grandis biomass) as bulking agent for the composting of poultry manure. Three composting mixtures were prepared by the turned-pile system by mixing poultry manure with different organic wastes used as bulking agent (biochar, coffee husk and sawdust) in a proportion of 1:1 (fresh weight). Despite the inert nature of biochar, the composting mixture prepared with biochar underwent an organic matter degradation of 70% of the initial content. The organic matter of the poultry manure-biochar mixture was characterised by a high polymerisation degree of the humic-like substances, with a relative high proportion of humic acids in relation to fulvic acids. At the end of the composting process, the humic acid fraction represented more than 90% of the alkali extractable fraction, reflecting the intense humification of this material. Enrichment of poultry manure with biochar reduced the losses of nitrogen in the mature composts, although the use of sawdust would be more efficient in preserving the organic matter and nitrogen in the mature compost.

Six different wastewater treatment plants were monitored in order to identify the main bioaerosol sources and to evaluate the effect of the aeration system used in the biological treatment (air diffusion, horizontal rotors and surface turbine aerators) on the airborne microorganism levels to which workers may be exposed. Air samples were collected by using a single stage impactor. Total count of mesophilic bacteria was used as the monitoring parameter to compare the impact of the aeration system on generic bacterial bioaerosols rather than a quantitative estimation for pathogens or fecal indicator microbes. In this study, pre-treatment, biological treatment and sludge thickening were the processes that generated the highest amount of bioaerosols. Aeration systems involving mechanical agitation of the wastewater, such as horizontal rotors and surface turbines, generated a larger amount of bioaerosols (between 450 and 4580CFU/m(3)) than air diffuser aerators (between 22 and 57CFU/m(3)). The levels of airborne bacteria generated by air diffusers were very similar to those registered at the background locations (lower than 50CFU/m(3)), unaffected by the activities taking place in the wastewater treatment plant. The use of air diffusers as an aeration system for the biological treatment would significantly minimise the potential biological hazard that wastewater treatment plant workers may be exposed to.

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated during the extraction of olive oil by the two-phase centrifugation system. Among all the available disposal options, composting is gaining interest as a sustainable strategy to recycle TPOMW for agricultural purposes. The quality of compost for agronomical use depends on the degree of organic matter stabilization, but despite several studies on the topic, there is not a single method available which alone can give a certain indication of compost stability. In addition, information on the biological and biochemical properties, including the enzymatic activity (EA) of compost, is rare. The aim of this work was to investigate the suitability of some enzymatic activities (beta-glucosidase, arylsulphatase, acid-phosphatase, alkaline-phosphatase, urease and fluorescein diacetate hydrolysis (FDA)) as parameters to evaluate organic matter stability during the composting of TPOMW. These enzymatic indices were also compared to conventional stability indices. For this purpose two composting piles were prepared by mixing TPOMW with sheep manure and grape stalks in different proportions, with forced aeration and occasional turnings. The composting of TPOMW followed the common pattern reported previously for this kind of material with a reduction of 40-50% of organic matter, a gradual increase in pH, disappearance of phytotoxicity and formation of humic-like C. All EA increased during composting except acid-phosphatase. Significant correlations were found between EA and some important conventional stability indices indicating that EA can be a simple and reliable tool to determine the degree of stability of TPOMW composts.

The present work deals with the potential of olive mill wastes as a C source for soil C sequestration strategy, which is based on the high lignocellulosic content that makes these wastes to degrade slowly during composting and after land application. A C balance was performed during the whole life cycle of two different two-phase olive mill wastes (TPOMW): C losses were calculated during the composting process and after soil application of the composting mixtures under laboratory conditions. The effect of the degree of stabilization of TPOMW on the overall C waste conservation efficiency was also evaluated. C losses after 34 weeks of TPOMW composting ranged from 40.58% to 45.19% of the initial C, whereas the amount of C evolved as CO2 after 8 months of incubation of soil amended with mature composts only represented between 20.6% and 21.9% of the added C. The total C losses considering the whole life cycle of the TPOMW showed lower losses compared to composts prepared with organic residues of different origin. Conversely to the typical behaviour of other organic wastes, the stabilisation degree of the TPOMW composting mixtures did not show any significant effect on the total C losses measured during composting and later land application. The low rate of degradation of TPOMW both during composting and after soil application makes the use of TPOMW as a C source an attractive strategy for soil C sequestration.

Extracted organic C and microbial biomass were evaluated as stability parameters in 3 different ligno-cellulosic waste composts. Organic C was extracted by both water and alkali and further separated in humic-like carbon (HLC) and nonhumic carbon (NHC). Conventional humification parameters, such as humification index and degree of humification were calculated from NHC and HLC. Microbial biomass carbon (B(C)) was determined as an indicator of the degree of biochemical transformation, whereas ninhydrin reactive N (B(NIN)) was measured to obtain the stability parameter B(NIN)/N(TOT) (N(TOT), total N). The water-extracted organic C did not provide reliable information on the transformations underwent by the ligno-cellulosic wastes during composting, since its content remained almost unaltered during the whole process. In contrast, parameters based on the alkali-extracted organic C and microbial biomass clearly reflected organic matter (OM) changes during the process. There was an increase in the net amount of HLC in the alkali extracts throughout composting, especially in the first 7 to 12 wk of the process, as well as a relative enrichment of HLC with respect to NHC. Values of humification index and degree of humification in end products were consistent with an adequate level of compost stability. The stability parameter B(NIN)/N(TOT) showed to be a reliable indicator of stability in ligno-cellulosic wastes. Parameters based on the alkali-extracted C and microbial biomass clearly reflected the transformation of the OM during composting and can be used as stability parameters in ligno-cellulosic waste composts.

Olive mill wastes represent an important environmental problem in Mediterranean areas where they are generated in huge quantities in short periods of time. Their high phenol, lipid and organic acid concentrations turn them into phytotoxic materials, but these wastes also contain valuable resources such as a large proportion of organic matter and a wide range of nutrients that could be recycled. In this article, recent research studies for the valorisation of olive mill wastes performed by several authors were reviewed: second oil extraction, combustion, gasification, anaerobic digestion, composting and solid fermentation are some of the methods proposed. Special attention was paid to the new solid waste generated during the extraction of olive oil by the two-phase system. The peculiar physicochemical properties of the new solid waste, called two-phase olive mill waste, caused specific management problems in the olive mills that have led to the adaptation and transformation of the traditional valorisation strategies. The selection of the most suitable or appropriate valorisation strategy will depend on the social, agricultural or industrial environment of the olive mill. Although some methods are strongly consolidated in this sector, other options, more respectful with the environment, should also be considered.

Bioaerosol release from composting plants is a cause of concern because of the potential health impacts on site workers and local residents. A one-year monitoring was undertaken in a typical composting plant treating green wastes by windrowing in the open. Aspergillus fumigatus spores and mesophilic bacteria were used as monitoring parameters and were collected in a six-stage Andersen sampler impactor from the air at different locations and during different operational activities. Background concentrations of both microorganisms were generally below 1000 colony-forming units m(-3) when no vigorous activity was taking place. Shredding of fresh green wastes, pile turning, and screening of mature compost were identified as the activities generating the highest amounts of both bioaerosols 40 m downwind of the composting pad. These air concentrations were approximately 2 log units higher than background levels. Screening of mature compost generated lower amounts of A. fumigatus than the other two activities (an average of 1 log unit higher than background levels). Workers were identified as the main potential receptors of high bioaerosol concentrations in areas close to the composting pad, whereas no major risk for local residents was expected because the concentrations recorded at distances of 200 and 300 m downwind of the operational area were not significantly different from background levels.

High values of pH may represent a limitation for the agricultural use of the composts, not only when used as soil-less substrate but also as soil amendment in high pH soils. The addition of elemental S during the maturation phase of the composting process was evaluated as suitable method to reduce pH of the composts under the organic agriculture regulations. A compost prepared with two phase olive mill waste (OMW) and sheep litter (SL) was used to study the effect of elemental sulphur addition on the pH of the composting mixture. Initially, different bench scale experiments were designed in order to study the influence of moisture, sulphur concentration, and incubation temperature on the sulphur oxidation rate and thus on the pH of the compost. A concentration of 0.5% in sulphur (dry weight basis) and moisture of 40% were proposed as the optimum conditions to decrease the compost pH by 1.1 units without increasing in EC to levels that may suppose a limitation for its agricultural use. Finally, these optimum experimental conditions found at bench scale were tested at full scale in a commercial composting plant treating the same organic materials by windrowing. The pH values of the composting mixture were reduced by one unit after 2 weeks following the addition of elemental S causing no negative effects on the final compost quality.

The effect of land application of biosolids on an agricultural soil was studied in a 2-month incubation experiment. The soil microbial biomass and the availability of heavy metals in the soil was monitored after the application of four different composting mixtures of sewage sludge and cotton waste, at different stages of composting. Land application caused an increase of both size and activity of soil microbial biomass that was related to the stabilization degree of the composting mixture. Sewage sludge stabilization through composting reduced the perturbance of the soil microbial biomass. At the end of the experiment, the size and the activity of the soil microbial biomass following the addition of untreated sewage sludge were twice those developed with mature compost. For the mature compost, the soil microbial biomass recovered its original equilibrium status (defined as the specific respiration activity, qCO2) after 18 days of incubation, whereas the soil amended with less stabilized materials did not recover equilibrium even after the two-month incubation period. The stabilization degree of the added materials did not affect the availability of Zn, Ni, Pb, Cu, Cr and Cd in the soil in the low heavy metal content of the sewage sludge studied. Stabilization of organic wastes before soil application is advisable for the lower perturbation of soil equilibria status and the more efficient C mineralization.

The effects of the composting process on the chemical and structural properties of humic acids have been studied in seven different organic waste mixtures from different origin. Only slight changes in elemental composition have been found in the humic acids after the composting process pointing to a more aromatic structure with higher proportions of oxygen and nitrogen. Functional groups were the most sensitive to the changes caused by the composting process showing a marked increase in the total acidity and phenolic, carboxyl and carbonyl groups. Gel permeation chromatography showed a slight increase in the average molecular weight of the humic acids. Infrared spectroscopy did not show important differences in humic acid structure but a clear decrease in the intensity of the bands in the region 3000-2850 cm(-1) corresponding to the aliphatic fractions. As a general result, the composting process yields humic acids in which the elemental and functional composition are closer to that of the more humified soil humic acids.

The evolution of the different forms of nitrogen during the composting of several wastes was studied, as well as its relation to the pH, electrical conductivity and parameters of maturity of the composts obtained. Four mixtures were prepared from different organic materials: sewage sludge, municipal solid waste, brewery sludge, sorghum bagasse, cotton waste and pine bark. The evolution of the different forms of nitrogen during composting depended on the material which supplied the nitrogen to the mixtures and the organic matter (OM) degradation rate during composting. The greatest concentration of ammonium was observed during the first weeks of composting, coinciding with the most intense period of OM degradation, and ammonium then decreased gradually to reach final values of below 0.04%. The use of urea as a nitrogen source in the mixtures led to high ammonium levels during the first weeks as a result of its rapid hydrolysis. The nitrification process began only when the temperature of the mixtures had dropped below 40 degrees C and its intensity depended on the quantity of ammonium present when the process began. The highest concentrations of NO3-N were always produced at the end of maturation, reaching values of 0.52%, 0.53%, 0.12% and 0.20% in the four mixtures studied. Nitrogen losses during composting depended on the materials used and on the pH values of the mixtures. Mixtures with the highest lignocellulose content showed the lowest losses (below 25%), while those containing municipal solid waste lost more than 40% of the initial content. Statistically significant correlations at a high probability level were found between the NO3-N concentration and pH and electrical conductivity. confirming that nitrification was responsible for the falling pH values and increasing electrical conductivity. The ratio of NH4-N and NO3-N concentrations was shown to be a clear indicator of the maturity of the mixtures during composting, the final values of 0.08, 0.04, 0,16 and 0.11 for the four mixtures being equal to, or below the maximum value established as a maturity index in other materials.