Daniela Pezzolla

Chemical and spectroscopic characterization of organic matter during the anaerobic digestion and successive composting of pig slurry

In this work, anaerobic digestion of pig slurry and successive composting of the digestate after centrifugation were studied by means of chemical analysis, FTIR and fluorescence spectroscopy as excitation-emission matrix (EEM). Chemical analysis highlighted the organic matter transformation occurring during the processes. A decrease of volatile solids and total organic carbon were observed in the digestate with respect to the fresh pig slurry as a consequence of the consumption of sugars, proteins, amino acids and fatty acids used by microorganisms as a C source. Water Extractable Organic Matter (WEOM) was obtained for all samples and fractionated into a hydrophilic and a hydrophobic fraction. The highest WEOM value was found in the pig slurry indicating a high content of labile organic C. The digestate centrifuged and the digestate composted showed lower hydrophilic and higher hydrophobic contents because of the decrease of labile C. Total phenolic content was lower in the digestate with respect to fresh pig slurry sample (36.7%) as a consequence of phenolic compounds degradation. The strong decrease of total reducing sugars in the digestate (76.6%) as compared to pig slurry confirmed that anaerobic process proceed mainly through consumption of sugars which represent a readily available energy source for microbial activity. FTIR spectra of pig slurry showed bands indicative of proteins and carbohydrates. A drop of aliphatic structures and a decrease of polysaccharides was observed after the anaerobic process along with the increase of the peak in the aromatic region. The composted substrate showed an increase of aromatic and a relative decrease of polysaccharides. EEM spectra provided tryptophan:fulvic-like fluorescence ratios which increased from fresh substrate to digestate because of the OM decompostion. Composted substrate presented the lowest ratio due to the humification process.

Greenhouse gas (GHG) emissions from soils amended with digestate derived from anaerobic treatment of food waste

RATIONALE The application of organic materials to agricultural lands is considered good practice to improve soil organic matter content and recycle nutrients for crop growth. The anaerobic treatment of food waste may have environmental benefits, particularly with regard to greenhouse gases (GHGs) mitigation and enhancement of carbon sequestration. METHODS This work presents the results from a field experiment to evaluate CO(2) , CH(4) and N(2) O emissions from grassland amended with digestate produced by anaerobic fermentation of food waste. Experimental plots, located close to Rothamsted Research-North Wyke, were established using a randomized block design with three replicates and two treatments, added digestate (DG) and the unamended control (CNT). The digestate was applied on three occasions at an equivalent rate of 80 kg N ha(-1) . RESULTS The application of digestate led to an increase in CO(2) emissions, especially after the 2(nd) application (74.1 kg CO(2) -C ha(-1)  day(-1) ) compared with the CNT soil (36.4 kg CO(2) -C ha(-1)  day(-1) ), whereas DG treatment did not affect the overall CH(4) and N(2) O emissions. The total grass yield harvested on a dry matter basis was greater in the DG treated plots (0.565 kg m(-2) ) than in the CNT plots (0.282 kg m(-2) ), as was the (15)  N content in the harvest collected from the DG plots. CONCLUSIONS The results suggest that the digestate can be applied to agricultural land as a fertilizer to grow crops. Our study was conducted in an exceptionally dry growing season, so conclusions about the effect of digestate on GHG emissions should take this into account, and further field trials conducted under more typical growing seasons are needed.

Solid anaerobic digestion batch of bio-waste as pre-treatment for improving amendment quality: The effect of inoculum recirculation.

The effect of solid anaerobic digestion batch (SADB) on bio-waste performed with and without inoculum on the quality of the final amendment was investigated by means of determining the content of organic carbon, humic and fulvic acids and the degree of humification. Two different processes were compared: composting and SADB with post-composting. Six parallel tests were performed. In three of these tests the SADB was inoculated mixing the bio-waste with the digestate from the previous run in a 1:1 ratio by weight. The amendment obtained by the SADB with post-composting treatment, in which the SADB was not inoculated, had an organic carbon content ranging from 15.5% TS to 30.3% TS resulting from 1% up to 14% higher than that of the corresponding composting processes. Similar results were achieved for the degree of humification. On the other hand SADB in which the inoculum was used generated about 300NL/kgVS of biogas instead of about 267NL/kgVS for non-inoculated runs.

Short-term Variations in Labile Organic C and Microbial Biomass Activity and Structure After Organic Amendment of Arable Soils

Abstract Although the application of organic amendments to arable soils is considered to be a suitable tool for improving soil fertility and enhancing carbon (C) stocks, more research is required on the influence of input of organic matter on the activity and structure of the soil’s microbial community. The aim of this work was therefore to make a comparative study of the effects of organic materials with different degrees of stabilization and source (an untreated pig slurry, the solid fraction of the digestate from the anaerobic fermentation of pig wastes, a livestock-derived organic matter compost, and an urban waste compost) on the size, activity, and structure of the microbial community in two arable soils. These effects, studied through a laboratory incubation experiment, were related to the quantity and quality of organic matter added, as well as to the rapid changes in the more labile water-soluble organic matter fraction. Particular attention was devoted to the short-term variations after organic amendment, during which changes in CO2 emissions, microbial biomass C, and water-extractable organic C pools were most pronounced. Phospholipid fatty acid profiles and 16S rDNA sequence analyses evidenced changes in the microbial community structure of amended soils. Modifications of the structure of bacterial communities after amendment, generally involving declining proportions of Gram-positive bacteria (Actinobacteria and Firmicutes) and an increase in abundance of Gram-negative bacteria (Acidobacteria, Bacteriodetes, and Proteobacteria), were both quality and quantity dependent, with effects being proportional to the mineralizable organic C content of the added materials.

Evaluation of benefits and risks associated with the agricultural use of organic wastes of pharmaceutical origin

Industrial fermentations for the production of pharmaceuticals generate large volumes of wastewater that can be biologically treated to recover plant nutrients through the application of pharmaceutical-derived wastes to the soil. Nevertheless, benefits and risks associated with their recovery are still unexplored. Thus, the aim of the present work was to characterize three potential organic residues (sludge, anaerobic digestate and compost) derived from the wastewater generated by the daptomycin production process. The main parameters evaluated were the physico-chemical properties, potential contaminants (heavy metals, pathogens and daptomycin residues), organic matter stabilization and the potential toxicity towards soil microorganisms and plants. The results showed that all the studied materials were characterized by high concentrations of plant macronutrients (N, P and K), making them suitable for agricultural reuse. Heavy metal contents and pathogens were under the limits established by European and Italian legislations, avoiding the risk of soil contamination. The compost showed the highest organic matter stabilization within the studied materials, whereas the sludge and the anaerobic digestate were characterized by large amounts of labile organic compounds. Although the pharmaceutical-derived fertilizers did not negatively affect the soil microorganisms, as demonstrated by the enzymatic activities, the sludge and the anaerobic digestate caused a moderate and strong phytotoxicity, respectively. The compost showed no toxic effect towards plant development and, moreover, it positively affected the germination and growth in lettuce and barley. The results obtained in the present study demonstrate that the valorization of pharmaceutical-derived materials through composting permits their agricultural reuse and also represents a suitable strategy to move towards a zero-waste production process for daptomycin.

Valorization of a pharmaceutical organic sludge through different composting treatments

Nowadays, the agricultural reuse of pharmaceutical sludge is still limited due to environmental and agronomic issues (e.g. low stabilization of the organic matter, phytotoxicity). The aim of the present study was to evaluate the characteristics of a pharmaceutical sludge derived from the daptomycin production and to study the possibility of improving its quality through composting. The pharmaceutical sludge showed high content of macronutrients (e.g. total Kjeldahl N content was 38 g kg-1), but it was also characterized by high salinity (7.9 dS m-1), phytotoxicity (germination index was 36.7%) and a low organic matter stabilization. Two different mixtures were prepared (mixture A: 70% sludge + 30% wood chips w/w, mixture B: 45% sludge + 45% wood chips + 10% cereal straw w/w) and treated through static composting using two different aeration systems: active and passive aeration. The mixtures resulted in the production of two different compost, and the evolution of process management parameters was different. The low total solids and organic matter content of mixture A led to the failure of the process. The addition of cereal straw in mixture B resulted in increased porosity and C/N ratio and, consequently, in an optimal development of the composting process (e.g. the final organic matter loss was 54.1% and 63.1% for the passively and actively aerated treatment, respectively). Both passively and actively aerated composting of mixture B improved the quality of the pharmaceutical sludge, by increasing its organic matter stabilization and removing phytotoxicity.

Changes in the Composition of Soil Dissolved Organic Matter After Application of Poultry Manure

The aim of this study is to investigate if and how the fertilisation with poultry manure can affect the composition of dissolved organic matter (DOM) in soil solution. Moreover, these effects were studied in relation with different soil depths and time. In this study, the profiles and vertical distribution of selected biomarker compounds were also investigated to provide a fingerprint of manure contribution DOM. The results showed that the application of poultry manure affected the DOM content of soil immediately after the poultry manure application at different soil depths. Moreover, it was demonstrated, by studying the organic compounds in the soil solution, that sterol compounds as cholesterol and coprostanol might be used as biomarkers of animal manure amendment.

Multi-approach characterization of organic sediment produced by an anaerobic digestion plant fed with pig slurry and stored for a long term in a lagoon

This study combined different approaches to characterize organic sediments produced by an anaerobic digestion plant feed with pig slurry, and accumulated for many years in a lagoon. The results of all analyses identified a certain homogeneity of the sediments. As a consequence of the pig diet, the sediment contained an high concentration of Zn (about 4gkg-1) and Cu (about 1.2gkg-1), which were mostly associated to the particles with a size ranging from 2 to 53μm. The sediment was made of large amount of organic matter, mostly cellulose and recalcitrant molecules, and 30-40% mineral fraction. XANES and XES spectroscopies indicated the presence of zinc phosphate (38%), zinc sulfide (32%), zinc carbonate (19%), and zinc oxide (11%). The presence in the sediment of forms characterized by a very scarce solubility, as also confirmed by the Zn and Cu chemical speciation, indicated a low bioavailability of these metals. However, although their low mobility, the high concentrations of Zn and Cu allowed to consider the sediment not suitable to use as a fertiliser due to the potential risk of metal interaction with the food chain.

Use of agricultural by-products in the development of an agro-energy chain: A case study from the Umbria region

Use of agricultural and livestock by-products for anaerobic digestion (AD), in total or partial substitution of the maize silage was evaluated from an environmental and economical point of view. The evaluation process included three methodological interdependent and consequential steps: the chemical stage at laboratory and plant level, the environmental and economic steps developing the Life Cycle Assessment and Life Cycle Costing jointly. The laboratory test showed that the two mixtures prepared with by-products, in partial (MIX A) and total (MIX B) substitution of maize silage, did not show differences in bio-methane production compared to a reference mixture with the 33% of maize silage. All mixtures tested at full-scale plant, showed the same performances, resulting in a similar energy production. Environmentally, MIX B increased greenhouse gas credits derived from the avoided production of mineral fertiliser for the energetic crops, resulting also in better economic performances. The break-even transport distances follow the positive environmental pattern result, in contrast to what was found for the break-even transport distances from the economic point of view.