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Anaerobic digestion allows for the proper management of agro-waste, including manure. Currently, more than 18,000 anaerobic digestion plants are under operation in EU, 80% of which are employed in the rural context. Tariff schemes for power generation from biogas produced during anaerobic digestion of agricultural feedstocks in Germany, Italy and Austria are coming to an end and new approaches are needed to exploit the existing infrastructures. Digesters in the rural context can be implemented and modified to be transformed into sustainable multi-feedstock and multi-purpose biorefineries for the production of energy, nutrients, proteins, bio-chemicals such as carboxylic acids, polyesters and proteins. This paper describes how the transition of agricultural anaerobic digesters into multi-products biorefineries can be achieved and what are the potential benefits originating from the application of a pilot scale platform able to treat cow manure and other crop residues while producing volatile fatty acids, polyhydroxyalkanoates, microbial protein material, hydrogen, methane and a concentrated liquid stream rich in nitrogen, potassium and phosphorus. [ABSTRACT FROM AUTHOR]

The updated Bioeconomy Strategy document "A sustainable bioeconomy for Europe: strengthening the connection between economy, society and the environment", which was issued by the European Commission in October 2018, encourages the exploitation of organic wastes according to a pyramidal hierarchy in which the extraction of valuable biomolecules, which will be used as they are or as precursors of high‐added‐value compounds, is a priority in biofuel production. This review considers a biorefinery platform in which food waste and sewage sludge are adopted to produce volatile fatty acids (VFAs) through a dark fermentation process. VFA fermentation is optimized by slightly acid pH (6–7), short hydraulic retention time (1–7 days) and high organic load rate (more than 10 gTS L−1 d−1). Attention has been focused on VFA exploitation for polyhydroxyalkanoate (PHA) production via a 'feast and famine' strategy performed in sequencing batch reactors. The obtained PHA yields are around 0.4–0.5 gPHA gCOD−1. Moreover, VFAs allow for the production of biofuels, such as hydrogen and methane, through single‐ or double‐staged anaerobic digestion. Innovative bioelectrochemical upgrade strategies for biogas helps producers to obtain biomethane for the automotive sector. Moreover, biogas has recently been tested for the production of polyhydroxybutyrate, a biodegradable and biocompatible thermoplastic made by microorganisms from C1 carbon sources (CO2 and CH4). Digestates from anaerobic bioreactors are still rich in nitrogen and phosphorus compounds. These latter compounds have been identified as critical raw materials due to their low availability in the European Union and to increasing demand from the growing global population. Thus, nutrient recovery from digestate allows users to close the loop of the 'circular economy' approach. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

50.3 M tons of wastes are annually produced at urban level in the EU-27. Sewage sludge, Organic Fraction of Municipal Solid Wastes (OFMSW) and food industrial wastewaters, are the major typologies of wastes produced at urban level. OFMSW and sewage sludge account for the 28 % and 23 % of the EU-27 wastes streams, respectively. Their abundance and the high content of nutrients (nitrogen and phosphorous) make them very interesting as substrates in a biorefinery loop to produce biofuels and bio-based products. This review provides an overview on the conversion of urban wastes into Volatile Fatty Acids (VFAs) at different operational conditions, from small laboratory scales to full industrial plants. Mono-fermentation of no pretreated substrates OFMSW and Thickened Primary Sludge (TPS) led to low VFAs yields of 0.25–0.30 and 0.50 g VFA-COD /g COD , respectively. The co-fermentation of OFMSW and sewage sludge achieved higher VFAs yields (0.38 g VFA-COD /g COD). Co-fermentation yields was further improved (0.85 g VFA-COD /g COD) by the adoption of thermophilic temperature (55 °C). Regarding VFAs profile, it was observed that substrates with lower VFAs yields presented a higher concentration of acetic acid, while the improvement of the acidogenic fermentation's yield had as consequence the increasing of propionic and butyric acids' concentrations. Finally, innovative electro-driven approaches, electro-fermentation and electrodialysis, employing polarized electrodes have been investigated to favor the production of desired VFAs or to enhance acids separation from the fermentation broth. [Display omitted] • EU-27 produces more than 50 Mtons of wastes every year. • OFMSW and Sewage Sludge account for the 23 % and 28 % of the EU-27 wastes. • Mono-fermentation of OFMSW leads to achieve about 40 % of VFAs yield. • Co-fermentation of OFMSW with Sewage sludge improves the VFAs yield up 80 %. • Digestate recirculation and thermophilic temperature allow to increase the yields. [ABSTRACT FROM AUTHOR]

The anaerobic digestion in double stage is a known and adopted system, but the process productivity and optimization still remain an aspect to investigate. The accumulation of organic acids (produced during fermentative metabolism) in the first stage generally decrease the pH below the optimal values (5.5). A pre-evaluation strategy by control charts for further pH control is proposed. The process combines in series the 1st Fermentation process and the 2nd Anaerobic Digestion process, using the recirculation of the anaerobic digestion effluent, rich in buffer agents, to control the pH in the 1st stage. The recycle ratio becomes a further operating parameter that should be properly managed. A proper management as dynamic recirculation flow allows to maintain the pH of the first phase to values higher than 5. Specific hydrogen production, specific methane production and volatile fatty acid production; 170 L/kgTVS at 40% H 2 , 750 L at 67% CH 4 and 14 gCOD/L VFA were obtained respectively. [ABSTRACT FROM AUTHOR]

Abstract Volatile fatty acids (VFAs) are a class of largely used compounds in the chemical industry, serving as starting molecules for bioenergy production and for the synthesis of a variety of products, such as biopolymers, reduced chemicals and derivatives. Because of the huge amounts of food waste generated from household and processing industry, 47 and 17 million tons per year respectively only in the EU-28 Countries, food wastes can be the right candidate for volatile fatty acids production. This review investigates all the major topics involved in the optimization of VFAs production from food wastes. Regarding the best operative conditions for the anaerobic fermenter controlled pH in the neutral range (6.0–7.0), short HRT (lower than 10 days), thermophilic temperatures and an organic loading rate of about 10 kgVS/m3d, allowed for an increase in the VFAs concentration between 10 and 25%. It was also found that additions of mineral acids, from 0.5 to 3.0%, and thermal pretreatment in the range 140–170 °C increase the organic matter solubilisation. Applications of VFAs considered in this study were biofuels and bioplastics production as well as nutrients removal in biological wastewater treatment processes. Graphical abstract Image Highlights • Dark fermentation by Microbial Mixed Cultures for VFAs production was considered. • The adoption of Food Wastes for VFAs production has been investigated. • Acid and thermal pretreatments are the best pretreatments for VFAs production from FW. • The higher operative conditions (pH, Temperature, HRT, OLR) have been presented. • The main applications (PHAs, biogas, nutrients removal) of VFAs has been investigated. [ABSTRACT FROM AUTHOR]

Pasta is one of the most appreciated Italian products around the world. The 31% of the global production of pasta is made by Italian companies: here, about 120 companies assure an annual production of 5.3 million tons of pasta. The pasta not compliant with the required selling standards (for example size, weight) is usually crushed, grounded to power, and used for animals feeding. This study offered a more advantageous alternative for the valorization of pasta by-products, whose mono-fermentation for Volatile Fatty Acids (VFAs) production was not investigated before. In particular, we considered pasta residues to optimize the operational parameters both in batch and in continuous conditions. The first round consisted in batch tests at different Total Solids (TS) concentration (1.5–10% TS w/w). The 2% TS w/w emerged as the best one, able to assure a VFAs yield close to the 80%. Consequently, this concentration was chosen for the conduction of continuous tests dedicated to the optimization of the best HRT and SRT for the process. The HRT of 3 d and a SRT of 4.4 d allowed the best process performances with a VFAs productivity of 3.48 g VFAs_COD per L of reactor and per day. The optimization of the process conditions for VFAs production led to a greater concentration of butyric acids (about 10% w/w) instead of the mere acetic acid production. Because of the economic value of butyric acid, this result is of particular interest. [Display omitted] • Low solid content led to a very high pasta conversion into VFAs (80%) in batch test. • The highest VFAs productivity of 2 g/Ld was obtained with a HRT of 3 days. • The recirculation of 50% of the solid improved the pasta residues' hydrolysis. • HRT of 3 days and SRT of 4.4 days led to a VFAs productivity of 3.5 g/Ld. [ABSTRACT FROM AUTHOR]

The performance parameters of volatile fatty acids (VFAs) measurements were assessed for the first time by a multi-laboratory validation study among 13 laboratories. Two chromatographic techniques (GC and HPLC) and two quantification methods such as external and internal standard (ESTD/ISTD) were combined in three different methodologies GC/ESTD, HPLC/ESTD and GC/ISTD. Linearity evaluation of the calibration functions in a wide concentration range (10–1000 mg/L) was carried out using different statistical parameters for the goodness of fit. Both chromatographic techniques were considered similarly accurate. The use of GC/ISTD, despite showing similar analytical performance to the other methodologies, can be considered useful for the harmonization of VFAs analytical methodology taking into account the normalization of slope values used for the calculation of VFAs concentrations. Acceptance criteria for VFAs performance parameters of the multi-laboratory validation study should be established as follows: (1) instrument precision (RSD INST ≤ 1.5%); (2) linearity ( R 2 ≥ 0.998; RSD SENSITIVITY ≤ 4%; RE MAX ≤ 8%; RE AVER ≤ 3%); (3) precision (RSD ≤ 1.5%); (4) trueness (recovery of 97–103%); (5) LOD (≤3 mg/L); and (6) LOQ (10 mg/L). [ABSTRACT FROM AUTHOR]

• The influence of different Household Food Wastes fractions on VFA was investigated. • Fractions rich in proteins and starch led to the highest VFA yield (12–15 g/L). • Fractions rich in cellulose, fibers, and sugars showed low VFA production (<2 g/L). • Metagenomic analysis of the different HFW fractions on VFAs production was conducted. • The bacterial community compositions and VFAs profile was correlated. This research investigated for the first time the influence of the single fractions (proteins, lipids, starch, cellulose, fibers and sugars) composing Household Food Wastes on Volatile Fatty Acids (VFA). A production at different pH (uncontrolled, 5.5 and 7.0): both the amount and profile of VFA were investigated. It was found that fractions rich in proteins and starch led to the greatest VFA productions (12–15 g/L), especially at neutral pH condition. On the contrary, fractions rich in cellulose, fibers, and sugars showed a very low VFA production (<2 g/L). The chemical nature of HFW influenced the speciation of the microbial communities too. Lactobacillaceae family was highly represented in proteins-, starch-, fibers and sugars-rich substrates and Atopobiaceae, Eggerthellaceae, Acidaminococcaceae and Veillonellaceae displayed positive correlation to VFAs production. Instead, Comamonadaceae showed high relative abundance in lipids- and cellulose-rich fraction and was negatively correlated to the VFAs generation. [ABSTRACT FROM AUTHOR]