Fabrizio Adani

Assessing amendment and fertilizing properties of digestates from anaerobic digestion through a comparative study with digested sludge and compost

Digestate, with biogas represents the final products of anaerobic digestion (AD). The methane-rich biogas is used to produce electricity and heat, whereas the digestate could be valorized in agriculture. Contrarily to well-recognized biomasses such as digested sludge and compost, the properties of the digestate are not well known and its agricultural use remains unexplored. In this work, a first attempt to study the agronomic properties of digestates was performed by comparing the chemical, spectroscopic, and biological characteristics of digestates with those of compost and digested sludge, used as reference organic matrices. A total of 23 organic matrices were studied, which include eight ingestates and relative digestates, three composts, and four digested sludges. The analytical data obtained was analyzed using principal component analysis to better show in detail similarities or differences between the organic matrices studied. The results showed that digestates differed from ingestates and also from compost, although the starting organic mix influenced the digestate final characteristics. With respect to amendment properties, it seems that biological parameters, more than chemical characteristics, were more important in describing these features. In this way, amendment properties could be ranked as follows: compost≅digestate>digested sludge≫ingestate. As to fertilizer properties, AD allowed getting a final product (digestate) with very good fertilizing properties because of the high nutrient content (N, P, K) in available form. In this way, the digestate appears to be a very good candidate to replace inorganic fertilizers, also contributing, to the short-term soil organic matter turnover.

Assessing amendment properties of digestate by studying the organic matter composition and the degree of biological stability during the anaerobic digestion of the organic fraction of MSW.

The transformation of organic matter during anaerobic digestion of mixtures of energetic crops, cow slurry, agro-industrial waste and organic fraction of municipal solid waste (OFMSW) was studied by analysing different samples at diverse points during the anaerobic digestion process in a full-scale plant. Both chemical (fiber analysis) and spectroscopic approaches ((13)C CPMAS NMR) indicated the anaerobic digestion process proceeded by degradation of more labile fraction (e.g. carbohydrate-like molecules) and concentration of more recalcitrant molecules (lignin and non-hydrolysable lipids). These modifications determined a higher degree of biological stability of digestate with respect to the starting mixture, as suggested, also, by the good correlations found between the cumulative oxygen uptake (OD(20)), and the sum of (cellulose+hemicellulose+cell soluble) contents of biomasses detected by fiber analysis (r=0.99; P<0.05), and both O-alkyl-C (r=0.98; P<0.05) and alkyl-C (r=-0.99; P<0.05) measured by (13)C CPMAS NMR.

The effect of commercial humic acid on tomato plant growth and mineral nutrition

Abstract The effects of humic acids extracted from two commercially‐available products (CP‐A prepared from peat and CP‐B prepared from leonardite) on the growth and mineral nutrition of tomato plants (Lycopersicon esculentum L.) in hydroponics culture were tested at concentrations of 20 and 50 mg L‐1. Both the humic acids tested stimulated plants growth. The CP‐A stimulated only root growth, especially at 20 mg L‐1 [23% and 22% increase over the control, on fresh weight basis (f.w.b.), and dry weight basis (d.w.b.), respectively]. In contrast, CP‐B showed a positive effect on both shoots and roots, especially at 50 mg L‐1 (shoots: 8% and 9% increase over the control; roots: 18% and 16% increase over the control, on f.w.b. and d.w.b., respectively). Total ion uptake by the plants was affected by the two products. In particular, CP‐A showed an increase in the uptake of nitrogen (N), phosphorus (P), iron (Fe), and copper (Cu), whereas, CP‐B showed positive effects for N, P, and Fe uptake. The change in the F...

The influence of biomass temperature on biostabilization-biodrying of municipal solid waste.

A laboratory study was carried out to obtain data on the influence of biomass temperature on biostabilization-biodrying of municipal solid waste (initial moisture content of 410 g kg wet weight (w.w.)(-1)). Three trials were carried out at three different biomass temperatures, obtained by airflow rate control (A = 70 degrees C, B = 60 degrees C and C = 45 degrees C). Biodegradation and biodrying were inversely correlated: fast biodrying produced low biological stability and vice versa. The product obtained from process A was characterized by the highest degradation coefficient (166 g kg TS0(-1); TS0(-1) = initial total solid content) and lowest water loss (409 g kg W0(-1); W0 = initial water content). Due to the high reduction of easily degradable volatile solid content and preservation of water, process A produced the highest biological stability (dynamic respiration index, DRI = 141 mg O2 kg VS(-1); VS = volatile solids) but the lowest energy content (EC = 10,351 kJ kg w.w.(-1)). Conversely, process C which showed the highest water elimination (667 g kg W0(-1)), and lowest degradation rate (18 g kg TS0(-1)) was optimal for refuse-derived fuel (RDF) production having the highest energy content (EC = 14,056 kJ kg w.w.(-1)). Nevertheless, the low biological stability reached, due to preservation of degradable volatile solids, at the end of the process (DRI = 1055 mg O2 kg VS(-1)), indicated that the RDF should be used immediately, without storage. Trial B showed substantial agreement between low moisture content (losses of 665 g kg W0(-1)), high energy content (EC = 13,558 kJ kg w.w.(-1)) and good biological stability (DRI = 166 mg O2 kg VS(-1)), so that, in this case, the product could be used immediately for RDF or stored with minimum pollutant impact (odors, leaches and biogas production).

In search of a reliable technique for the determination of the biological stability of the organic matter in the mechanical-biological treated waste

The biological stability determines the extent to which readily biodegradable organic matter has decomposed. In this work, a massive estimation of indices suitable for the measurement of biological stability of the organic matter content in solid waste samples has been carried out. Samples from different stages in a mechanical-biological treatment (MBT) plant treating municipal solid wastes (MSW) were selected as examples of different stages of organic matter stability in waste biological treatment. Aerobic indices based on respiration techniques properly reflected the process of organic matter biodegradation. Static and dynamic respirometry showed similar values in terms of aerobic biological activity (expressed as oxygen uptake rate, OUR), whereas cumulative oxygen consumption was a reliable method to express the biological stability of organic matter in solid samples. Methods based on OUR and cumulative oxygen consumption were positively correlated. Anaerobic methods based on biogas production (BP) tests also reflected well the degree of biological stability, although significant differences were found in solid and liquid BP assays. A significant correlation was found between cumulative oxygen consumption and ultimate biogas production. The results obtained in this study can be a basis for the quantitative measurement of the efficiency in the stabilization of organic matter in waste treatment plants, including MBT plants, anaerobic digestion of MSW and composting plants.

Predicting anaerobic biogasification potential of ingestates and digestates of a full-scale biogas plant using chemical and biological parameters

The aim of this work was to develop simple and fast tests to predict anaerobic biogasification potential (ABP) of ingestates and digestates from a biogas plant. Forty-six samples of both ingestates and digestates were collected within an eight-month observation period and were analyzed in terms of biological and chemical parameters, namely, ABP test, oxygen demand in a 20-h respirometric test (OD20), total solids (TS), volatile solids (VS), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonia, cell solubles (CS), acid detergent fibers (ADF), lignin (ADL), cellulose, and hemicellulose. Considering both quantitative (VS and TOC) and qualitative aspects (OD20 and CS) of organic matter (OM), four models (linear regressions; 0.80<R2<0.913; 16%<standard errors<23%) were proposed to predict ABP. The models were chosen according to the needed accuracy of the evaluation in terms of time schedule and the availability of the required laboratory analyses.

Odours and volatile organic compounds emitted from municipal solid waste at different stage of decomposition and relationship with biological stability

Odours (OU(E)) and volatile organic compounds (VOC) emission during biological process used to treat MSW were studied under standardized conditions in order to detect potential risk for workers and population. Results obtained indicated that odours and VOCs emitted depend on the biological stability of waste measured by the dynamic respiration index (DRI) and a very good correlation were found between these parameters (OU(E) vs. DRI, r=0.96, p<0.001, n=6; VOC vs. DRI, r=0.97, p<0.001, n=6). GC-MS study of the VOCs indicated the presence of a group of molecules that were degraded during the process. On the other hand, a second group of molecules, i.e. aromatic and halogenated compounds, and furan persisted in the waste sample, although molecule concentrations were always lower than Threshold Limit Value-Time Weighted Average (TLV-TWA).

Substituting energy crops with organic wastes and agro-industrial residues for biogas production.

In this study, industrial and agro-industrial by-products and residues (BRs), animal manures (AMs), and various types of organic wastes (OWs) were analyzed to evaluate their suitability as substitutes for energy crops (ECs) in biogas production. A comparison between the costs of the volume of biogas that can be produced from each substrate was presented with respect to the prices of the substrates in the Italian market. Furthermore, four different feeding mixtures were compared with a mixture of EC and swine manure (Mixture A) used in a full-scale plant in Italy. Swine manure is always included as a basic substrate in the feeding mixtures, because many of the Italian biogas plants are connected to farms. When EC were partially substituted with BR (Mixture B), the cost (0.28 euro Nm(-3)) of the volume of biogas of Mixture A dropped to 0.18 euro Nm(-3). Furthermore, when the organic fraction of municipal solid waste (OFMSW) and olive oil sludge (OS) were used as possible solutions (Mixtures C and D), the costs of the volume of biogas were -0.20 and 0.11euroNm(-3), respectively. The negative price signifies that operators earn money for treating the waste. For the fifth mix (Mixture E) of the OFMSW with a high solid substrate, such as glycerin from biodiesel production, the resulting cost of the volume of biogas produced was -0.09 euro Nm(-3). By comparing these figures, it is evident that the biogas plants at farm level are good candidates for treating organic residues of both municipalities and the agro-industrial sector in a cost-effective way, and in providing territorially diffused electric and thermal power. This may represent a potential development for agrarian economy.

Determination of Biological Stability by Oxygen Uptake on Municipal Solid Waste and Derived Products

A new scientific apparatus and method are proposed for determining biological stability by oxygen uptake (respiration index, RI), on municipal solid waste (MSW) and derived products. For measuring the RI, a dynamic approach (with continuous aeration) was demonstrated to be more effective than the static approach (without aeration). The validity of the method was tested by comparing carbon losses calculated using both respirometric (carbon lossesresp) and analytical data (carbon lossesanal) during four trials performed on MSW and products derived from it. Carbon losses (expressed as g kg−1Ci, in which Ci represents initial carbon content) were: 219.0 and 248.0, 67.9 and 57.1, 39.6 and 36.4, and 250.7 and 280.3, using respirometric and analytical data alternately for Trials 1,2,3, and 4. The comparison between respirometric data using continuous or no aeration showed, for the latter, an underestimation of RI of between 70% and 90% that was more evident for unstable biomass leading to more similar values when stabilization occurred. The scientific apparatus proposed made it possible to measure oxygen uptake under autothermal conditions and avoid problems connected with the use of a preset temperature, biomass temperature being a consequence of the microbial activity, as is also suggested by the significant linear regression of T versus RI (R2 = 0.84, 0.73, 0.82, and 0.90 for the four trials, respectively). The methods proposed could be used with advantage in the future for biological stability measurements, above all for heterogeneous material such as MSW and its products, thus obtaining respirometric data that better reflect what happens during an aerobic process.

Organic Matter Evolution Index (OMEI) as a Measure Of Composting Efficiency

The significance of the organic matter evolution index (OMEI) related to the composting process degree was tested on a full-scale windrow process for 239 days. Analytical data from many samples collected during the process and kinetics were in agreement regarding the insufficient degree of stability and maturity reached by the compost obtained. As expected, the OMEI at the end of the process was low (OMEI = 0.46) confirming its validity to composting degree evaluation. New analytical methods for humic substances quantification were developed by monitoring humic acids concentration versus composting time and ligno-humic fraction.