Michele Pognani

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.

Determination of the energy and environmental burdens associated with the biological treatment of source-separated Municipal Solid Wastes

Environmental burdens of four different full-scale facilities treating source-separated organic fraction of Municipal Solid Wastes (OFMSW) have been experimentally evaluated. The studied facilities include different composting technologies and also anaerobic digestion plus composting. Home composting, as an alternative to OFMSW management, was also included in the study. Energy (electricity and diesel), water consumption and emissions of volatile organic compounds (VOC), ammonia, methane and nitrous oxide have been measured for each process. Energy consumption ranged between 235 and 870 MJ Mg OFMSW−1 while the emissions of the different contaminants considered per Mg OFMSW were in the range of 0.36–8.9 kg VOC, 0.23–8.63 kg NH3, 0.34–4.37 kg CH4 and 0.035–0.251 kg N2O, respectively. Environmental burdens of each facility are also analyzed from the point of view of process efficiency (i.e. organic matter stabilization degree achieved, calculated as the reduction of the Dynamic Respiration Index (DRI) of the waste treated). This study is performed through two new indices: Respiration Index Efficiency (RIE), which includes the reduction in the DRI achieved by the treatment process and Quality and Respiration Index Efficiency (QRIE), which also includes the quality of the end product. Finally, a Life Cycle Assessment is performed using the Respiration Index Efficiency (RIE) as the novel functional unit instead of the classical LCA approach based on the total mass treated.

A complete mass balance of a complex combined anaerobic/aerobic municipal source-separated waste treatment plant

In this study a combined anaerobic/aerobic full-scale treatment plant designed for the treatment of the source-separated organic fraction of municipal solid waste (OFMSW) was monitored over a period of one year. During this period, full information was collected about the waste input material, the biogas production, the main rejects and the compost characteristics. The plant includes mechanical pre-treatment, dry thermophilic anaerobic digestion, tunnel composting system and a curing phase to produce compost. To perform the monitoring of the entire plant and the individual steps, traditional chemical methods were used but they present important limitations in determining the critical points and the efficiency of the stabilization of the organic matter. Respiration indices (dynamic and cumulative) allowed for the quantitative calculation of the efficiency of each treatment unit. The mass balance was calculated and expressed in terms of Mgy(-1) of wet (total) matter, carbon, nitrogen and phosphorus. Results show that during the pre-treatment step about 32% of the initial wet matter is rejected without any treatment. This also reduces the biodegradability of the organic matter that continues to the treatment process. About 50% of the initial nitrogen and 86.4% of the initial phosphorus are found in the final compost. The final compost also achieves a high level of stabilization with a dynamic respiration index of 0.3±0.1g O(2) per kg of total solids per hour, which implies a reduction of 93% from that of the raw OFMSW, without considering the losses of biodegradable organic matter in the refuse (32% of the total input). The anaerobic digestion process is the main contributor to this stabilization.

Evolution of organic matter in a full-scale composting plant for the treatment of sewage sludge and biowaste by respiration techniques and pyrolysis-GC/MS.

A full-scale composting plant treating in two parallel lines sewage sludge and the source-selected organic fraction of municipal solid waste (OFMSW or biowaste) has been completely monitored. Chemical routine analysis proved not to be suitable for an adequate plant monitoring in terms of stabilization and characterization of the process and final compost properties. However, the dynamic respiration index demonstrated to be the most feasible tool to determine the progression of the degradation and stabilization of organic matter for both sewage sludge and OFMSW lines. Both lines exhibited an important degree of stabilization of organic matter using rapid and cumulative respiration indices. Pyrolysis-GC/MS was applied to the most important inputs, outputs, and intermediate points of the plant. It proved to be a powerful tool for the qualitative characterization of molecular composition of organic matter present in solid samples. A full characterization of the samples considered is also presented.

Monitoring the organic matter properties in a combined anaerobic/aerobic full-scale municipal source-separated waste treatment plant

Respiration indices (dynamic and cumulative) and the anaerobic biogasification potential are applied to the quantitative calculation of the biodegradation efficiency in a combined anaerobic/aerobic treatment for the organic fraction of municipal solid waste (OFMSW). They also permit to observe possible deficiencies in some parts of the entire sequence of organic matter decomposition. On the contrary, chemical methods presented a limited utility. Dynamic respiration indices highlighted that anaerobic digestion was the most efficient step to reduce the respiration activity of the waste (61% calculated on a DRI(24h) basis). Respirometric activity of final compost was 93% lower than initial OFMSW confirming the overall efficiency of the plant studied and the stability of the final product (0.3g O(2) kg TS(-1)h(-1)). Finally, the use of an advanced methodology such as the Diffuse Reflectance Infrared Fourier Transformed (DRIFT) allows the determination of the main functional groups of organic matter, which significantly change during the biological treatment of organic matter.

Evaluation of hormone-like activity of the dissolved organic matter fraction (DOM) of compost and digestate

Biomasses are usually applied to soil for their agronomic properties (fertilization and amendment properties). Biomass can also have bio-stimulating effects on plants because of the presence of hormones and hormone-like molecules. Although compost has been the subject for studies of this aspect, no data have yet been reported on the extraction of this kind of molecule from digestate biomass. The aim of this work is to study the auxin- and gibberellin-like activity of pig slurry digestate in comparison with those of pruning and garden wastes composts dissolved organic fraction (DOM). DOM (i.e., fraction<0.45 μm) is the most reactive among the organic matter fractions readily available to microbial and plant metabolism. No gibberellin-like activities were found for either compost or digestate, whereas digestate showed auxin-like properties which were found to be located in its neutral hydrophobic (NHo) DOM fractions. Hormone activity was due principally to the presence of auxin coming from the anaerobic digestion of aromatic amino acids.

Effect of freezing on the conservation of the biological activity of organic solid wastes

To assess the effect of freezing on the indigenous biological activity of an organic waste, five types of organic wastes (raw sludge [RS], municipal solid waste [MSW], partially processed municipal solid waste [MSWpp], digested sludge [DS] and composted organic fraction of municipal solid waste [OFMSWc]) were frozen and stored during different times to identify if the interruption of the native biological activity was recovered. Respiration indices (DRI(24h) and AT(4)) were used to determine the biological activity expressed as oxygen consumption. ANOVA analysis was used to compare the results. Respiration indices of RS, DS, MSWpp and OFMSWc were not affected by freezing storage during 1 year. Contrarily, respiration indices of MSW samples were statistically different after 52 and 20 weeks of freezing storage (DRI(24h) and AT(4), respectively). Regarding the lag phase and the time to reach maximum respiration activity, frozen samples induced a significant change in the organic samples analyzed except for OFMSWc.

The anaerobic digestion process capability to produce biostimulant: the case study of the dissolved organic matter (DOM) vs. auxin-like property

Biostimulants improve plant growth by stimulating nutrient uptake and efficiency, improving tolerance to abiotic stress and raising crop quality. Biostimulants are currently only recognised in five categories. However, the recent interest in this sector has led to the identification of some new ones. The aim of this work was to study the auxin-like activity of digestate dissolved organic matter (DOM) obtained from full scale anaerobic digester plants. All DOMs had biostimulant capacity comparable with humic acid and amino acids. The auxin-like activities depended mainly on the hydrophobic DOM fractions for the presence of auxin-active and other auxin-like molecules. Significant correlations were found for the auxin-effect in relation to auxin-active molecules and fatty acids responsible for most of the auxin-like effects (67% of the total importance in giving auxin-like activity) while a minor or null contribution was attributable to the carboxylic acids and aminoacid categories. Therefore, the anaerobic digestion process seems to be a useful biotechnology to produce biostimulants. Basing on these first results, the expanding anaerobic digestion sector could become important for the production of new biostimulant classes to meet the agricultural sectors new requirements and saving on raw materials.

Environmental burdens of source-selected biowaste treatments: comparing scenarios to fulfil the European Union landfill directive. The case of Catalonia

The Organic Fraction of Municipal Solid Waste (OFMSW), or biowaste, can be valorized using different treatment technologies, such as anaerobic digestion and composting or the combination of them. The use of the end products (biogas and/or compost) generates benefits over the alternative of sending waste to landfill. The European Union regulations (i.e. Landfill Directive) encourage the diversion of untreated biodegradable waste from landfilling. However, OFMSW treatment installations also produce environmental impacts that must be assessed. This paper presents different future scenarios at regional scale proposed to accomplish the Landfill Directive and their environmental assessment in terms of environmental impact categories. The geographical area under study is Catalonia (Spain). Field data obtained in previous studies undertaken in the same geographical area are used to determine the environmental burdens of the present situation in order to compare them with different future scenarios. A combined scenario to treat 921 Gg of OFMSW source selected including the increase of the quantity of biowaste treated by anaerobic digestion (61.2% of the total biowaste), the modification of composting plants to ensure the treatment of all the gaseous emissions (25.3% and 8.1% of the total biowaste treated in in-vessel composting plants and in enclosed windrows composting plants respectively) and the incorporation of home composting as a waste treatment alternative (5.4% of total biowaste) results in the lowest impact scenario considered in the present study. Energy recovery through anaerobic digestion and benefits of gaseous emissions reduction are the key factors in the impact reduction of biowaste treatment.