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

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 sector's new requirements and saving on raw materials.

Enhanced polyhydroxyalkanoate (PHA) production from the organic fraction of municipal solid waste by using mixed microbial culture.

BACKGROUND: In Europe, almost 87.6 million tonnes of food waste are produced. Despite the high biological value of food waste, traditional management solutions do not consider it as a precious resource. Many studies have reported the use of food waste for the production of high added value molecules. Polyhydroxyalkanoates (PHAs) represent a class of interesting bio-polyesters accumulated by different bacterial cells, and has been proposed for production from the organic fraction of municipal solid waste (OFMSW). Nevertheless, until now, no attention has been paid to the entire biological process leading to the transformation of food waste to organic acids (OA) and then to PHA, getting high PHA yield per food waste unit. In particular, the acid-generating process needs to be optimized, maximizing OA production from OFMSW. To do so, a pilot-scale Anaerobic Percolation Biocell Reactor (100 L in volume) was used to produce an OA-rich percolate from OFMSW which was used subsequently to produce PHA. RESULTS: The optimized acidogenic process resulted in an OA production of 151 g kg-1 from fresh OFMSW. The subsequent optimization of PHA production from OA gave a PHA production, on average, of 223 ± 28 g kg-1 total OA fed. Total mass balance indicated, for the best case studied, a PHA production per OFMSW weight unit of 33.22 ± 4.2 g kg-1 from fresh OFMSW, corresponding to 114.4 ± 14.5 g kg-1 of total solids from OFMSW. PHA composition revealed a hydroxybutyrate/hydroxyvalerate (%) ratio of 53/47 and Mw of 8∙105 kDa with a low polydispersity index, i.e. 1.4. CONCLUSIONS: This work showed how by optimizing acidic fermentation it could be possible to get a large amount of OA from OFMSW to be then transformed into PHA. This step is important as it greatly affects the total final PHA yield. Data obtained in this work can be useful as the starting point for considering the economic feasibility of PHA production from OFMSW by using mixed culture.

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 compost's 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.

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.