Abstract: The aim of this work was to evaluate the impact of different N-rich animal wastes on the composting of ligno-cellulosic wastes by a range of classical and novel methods, with particular emphasis on microbial community composition. Two composting mixtures were prepared by adding to a mixture of cotton carding wastes and wheat straw: (i) meat and bone meal and (ii) blood meal and horn and hoof meal. Composts were analyzed using physico-chemical and biochemical properties, as well as nucleic acid microarrays. Results showed that physico-chemical and biochemical parameters differentiated composts depending on their degree of stability, while microarray hybridization discriminated compost samples according to the starting materials used in the compost production. Microarray analysis indicated not only the presence in the composts of bacteria involved in N(2) fixation and plant disease suppression, but also the presence of Acinetobacter calcoaceticus that is suspected to trigger an autoimmune response related to bovine spongiform encephalopathy. The present work highlights the importance of using parameters addressing different properties of the composting matrix for a proper evaluation of the process performance.
Abstract: 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.
Abstract: Soil organic matter (SOM) is the largest C stock of the continental biosphere with 1550Pg. The size of C reservoir in the soil and environmental concerns on climate change have recently attracted the attention of scientist and politicians on C sequestration as an effective strategy to tackle greenhouse gas (GHG) emissions. It has been estimated that the potential for C storage in world cropland is relevant (about 0.6-1.2PgCy(-1)). However, there are several constraints of C sequestration that raise concern about its effectiveness as a strategy to offset climate change. C sequestration is finite in quantity and time, reversible, and can be further decreased by socio-economic restrictions. Given these limitations, C sequestration can play only a minor role in the reduction of emissions (2-5% of total GHG emission under the highest emission scenarios). Yet, C sequestration is still attractive for two main reasons: it is likely to be particularly effective in reducing atmospheric CO2 levels in the first 20-30yr of its implementation and presents ancillary benefits for environment and sustainability that make it a real win-win strategy. These beneficial implications are discussed in this paper with emphasis on the need of C sequestration not only to offset climatic changes, but also for the equilibria of the environment and for the sustainability of agriculture and of entire human society.
Abstract: 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.
Abstract: Meat and bone meal (MBM) is obtained from the wastes produced during slaughtering operations. Its high concentration of N and P makes it interesting as an organic fertiliser but its use in soil has been barely studied previously. In this work four laboratory experiments were performed to study the influence of different variables (MBM composition, rate of application, temperature of incubation and the type of soil) on C mineralization dynamics of MBM in agricultural soils. The total CO2-C evolved (as % of added C) after 2 weeks ranged between 10% and 20%. The kinetics of mineralization were rapid, with C evolved as CO2 within the first 4 days representing more than 50% of total C mineralized. A linear correlation was found between the rate of application (added-C) and CO2-C evolved (r2: 0.997; P<0.001). A temperature coefficient (Q10) was used to assess the difference in biological activity at 5 degrees C intervals. Q10, which ranged from 1.0 to 2.7 (250h), was higher for the lower temperature range (Q10 (15-20 degrees C)>Q10 (20-25 degrees C)) and it was found to be related to the soil properties. Finally, the mineralization process was found to be highly dependent upon the different soil factors, although no simple linear correlation was found between mineralization and soil properties.
Abstract: Soil organic matter comprises all dead plant and animal residues, from the most recent inputs to the most intensively humified. We have found that traces of fresh substrates at microg g(-1) soil concentrations (termed 'trigger molecules') activate the biomass to expend more energy than is contained in the original 'trigger molecules'. In contrast, we suggest that the rate limiting step in soil organic matter mineralisation is independent of microbial activity, but is governed by abiological processes (which we term the Regulatory Gate theory). These two findings have important implications for our understanding of carbon mineralisation in soil, a fundamental process in the sequestration of soil organic matter.
Abstract: 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.
Abstract: Biofiltration was evaluated as a method to control the airborne microorganisms released at composting facilities. Seven commercial composting plants were selected for this study because of their different operating conditions and biofilter designs. In all plants, the biofilters were originally designed for odor control. The concentrations of both Aspergillus fumigatus and mesophilic bacteria were measured in the air stream before and after passing through the biofilters and compared with the background concentrations in the surrounding area. Results showed that biofiltration achieved an average reduction greater than 90% and 39% in the concentrations of A. fumigatus and mesophilic bacteria, respectively. In all the plants, the airborne A. fumigatus concentration after the biofilter was lower than 1.2 x 10(3) cfu m(-3), independent of the inlet concentration, whereas the mesophilic bacteria concentration was dependent on the inlet concentration. The different behaviors of the two microorganism groups were thought to be due to the different aerodynamic characteristics of the particles that affected the capture by impact in the biofilter bed. The fungus, whose spores had a maximum of diameter size distribution between 2.1 and 3.3 microm, were more effectively captured in the biofilter than the bacteria, which had diameters mainly between 1.1 and 2.1 microm.
Abstract: The evaluation of compost stability is of the utmost importance for the reliability of composting as a recycling strategy. To date there is no single parameter that can give a sure indication of the stability of composts from different starting materials. This paper investigates different methods of evaluating the dynamics of transformation of materials and the stability level of the end products in a composting process. The following parameters were determined on compost samples of different ages from cotton (Gossypium herbaceum L.) cardings and yard wastes: humification index (HI), degree of humification (DH), thermogravimetry (TG) microbial biomass C (B(C)), and ninhydrin-reactive N (B(NIN)). Finally, from TG, derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) thermal stability parameters were deduced. Humification parameters in the end products (0.2 and 81% for HI and DH, respectively) showed the effective stability reached by the organic matter (OM). Thermal analysis evidenced the presence of two main organic pools with different thermal stability. During composting a relative increase in the more stable organic pool was indicated by the variation of the thermostability index R1 from 0.41 to 0.74. The parameter R1 was significantly correlated with both HI (r = -0.94; P < 0.05) and DH (r = 0.97; P < 0.05). Microbial biomass content dynamics reflected the availability of readily decomposable substrates. The ratio between B(NIN) and total N in the end product was 0.96%, indicating a good stability level. The simultaneous application of different approaches, considering different properties of composting materials, provides a more complete description of the stability and quality reached by the organic materials.
