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This study explores the potential of utilizing tannery sludge for short-chain fatty acids (SCFAs) production through fermentation, incorporating zeolites in the process. The study involved a mild thermal pretreatment of the sludge as well, aimed at enhancing the subsequent fermentation process by increasing the solubilization of the organic matter. Six thermophilic continuously stirred tank reactor runs with varying hydraulic retention times (HRT) and zeolite addition are conducted. Zeolites, known for their low cost and absorption properties, significantly impacted chromium concentrations. SCFA production levels remain relatively consistent across tests. However, the acidification efficiency, as reflected in the SCFAs/sCOD ratios, shows improvement in the presence of Chabazite. Specifically, the acidification efficiency is highest in test RB8 (0.92 COD/COD). This suggests that the addition of Chabazite enhances acidification efficiency in tannery sludge applications. The findings highlight zeolites' potential to absorb heavy metals and improve acidification efficiency, indicating promising practical applications for tannery sludge treatment. [ABSTRACT FROM AUTHOR]

The disposal of sewage sludge potentially reaches the 50-60% of WWTP’s total operation cost. Such stream can be considered a renewable carbon source to produce added-value products. Different pre-treatment methods have been applied on thickened sewage sludge (SS) coming from the domestic wastewater treatment plant (WWTP) of Treviso (northeast Italy) to favour its acidogenic fermentability. Alkaline (pH 9-11) and thermal (50-70°C) hydrolysis were applied separately and in combination The following fermentation process was addressed to the recovery of volatile fatty acids (VFA) as valuable building blocks substances. Batch fermentation tests were conducted at lab-scale under controlled temperature (T): 20, 37, 55 and 70°C by using an available mixed fermentative consortium as inoculum. Thermophilic T (55°C) was chosen in the following semi-continuous fermentation process (fill and draw), carried out with three different hydraulic retention time (HRT; 4-5-6 days). In terms of organic matter solubilisation, the thermal hydrolysis (70°C) allowed to obtain a soluble chemical oxygen demand (CODSOL) concentration around 10.0 g/L, with no additional benefits from the combined alkaline treatment. The batch acidogenic fermentation tests highlighted the T effect on acidification performances; thermophilic trials (55°C) showed the highest CODVFA/CODSOL ratio (0.81). The three semi)continuous tests (HRT 4-5-6 days) were followed for 45 days (roughly), under the chosen thermophilic condition (55°C). The highest fermentation rate was obtained at 4.0 d as HRT (22 mgCODVFA/gVS d); on the contrary, the highest fermentation yield (0.30 gCODVFA/gVS) and CODVFA/CODSOL ratio (0.73) were obtained at 6.0 d as HRT. In practice, low HRT selected for a mixed consortium with high fermentation rate, but less efficient in the conversion of the organic matter into VFA. No HRT’s effect was instead observed in the VFA composition, always rich in acetic (29-31% COD basis) and butyric acid (31-32%), and poorer in propionic (14-15%), valeric (12-13%) and caproic acid (11-12%). [ABSTRACT FROM AUTHOR]

Biorefinery represents an innovative approach for waste management, where products at the end of their service life are seen as valuable resources for the production of high added value bio-products or bio-fuels. In this context, acidogenic fermentation is gaining scientific and commercial interest, since it allows to improve waste/wastewater treatability as well as additional recovery of volatile fatty acids (VFA), the building blocks for the chemical industry or precursors of reduced chemicals in conventional organic chemistry. This work illustrates the results of a study aimed at highlighting the effects of different inputs (feedstock composition and pre-treatment; temperature) on process performance and safety. The fermentation process was applied on a mixture of food waste and sewage sludge (FWs-SS) within the contest of Treviso municipality (northeast Italy). The VFA production and relative ratio respect to soluble chemical oxygen demand (CODSOL) were evaluated, as well as the variation of lower flammability limit (LFL) of flammable gaseous mixture, produced during the acidogenic fermentation. Thermal pre-treatment (72°C, 48 h) enhanced the solubilization of the organic matter, which was converted into VFA in batch mode under mesophilic conditions (37°C). The VFA level increased up to 30 ± 3 g COD/L, with high CODVFA/CODSOL ratio (0.86 ± 0.05). This condition was also characterized by the lowest level in volumetric percentage of flammable gases such as H2, CH4 and H2S. Variation of LFL of gaseous mixture as function of fermenter operating parameters has been investigated by Le Chatelier's Law. The high concentration of CO2 (greater than 80% v/v) increased the LFL and therefore the flammable mixture was considered poorly hazardous. In practice, the variation of fermenter operating parameters to the final optimized protocol caused a continuous LFL growth, up to 29.3%, corresponding to a safer operation of fermentation reactor. [ABSTRACT FROM AUTHOR]

In recent years, the attention to organic wastes as a new feedstock for the production of PHA is increased based on the idea that this is the only way to reduce their high cost and to increase their sustainability. For this reason, a pilot platform has been designed to produce PHA from the source-sorted organic fraction of municipal solid waste (OFMSW). The cost-effective system consists in the three-steps anaerobic-aerobic process: the fermentation step was performed in a 200 L CSTR (OLR 20.0 kgVS/m³.d, HRT 3.3 d) in thermophilic conditions (55°C). The VFA-rich mixture was used for the two following aerobic steps: a first sequencing batch reactor (SBR, 100 L) for the production of functionalized PHA-producing biomass (mixed consortium, MMC), and a second batch reactor (50 L) for production of PHA and its maximization inside cell walls. The SBR was operated at 1.2-2.5 kgCOD/m³.d as OLR, and HRT of 1 d (equal to SRT); dynamic feeding regime (feast-famine) was used for consortium selection. The fermentation conditions allowed obtaining a significant COD conversion into VFA. Acetic, propionic and butyric acids accounted for more than 80% of total VFA and the relative yield was 0.45 ± 0.03 CODVFA/VS. The necessary buffering capacity was provided by anaerobic digestate addition, which increased the system alkalinity (2.8 ± 0.2 gCaCO3/L at pH 5.75). In SBR, a strong selective pressure favouring PHA-accumulating organisms was easily reached, as demonstrated by the short feast-to-cycle length ratio (often below 0.12). In the second aerobic accumulation reactor, the biomass was able to accumulate up to 49% gPHA/gVSS. Both aerobic steps were performed without temperature (T) control, avoiding additional consumption of energy; the applied OLR was chosen based on biomass kinetic in order to have a constantly short feast phase and a stable selection/enrichment of PHA-accumulating consortium. [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]

• Acidogenic fermentation process was optimized for urban bio-waste valorisation. • Thermal pre-treatment favoured the urban bio-waste organic matter solubilisation. • Mesophilic alkaline fermentation enhanced VFA production yields. • Higher HRTs and lower OLRs gave the best performance in a CSTR with 39 g COD VFA /L. • Alkaline urban bio-waste fermentation increased the HV precursors concentrations. The problem of waste disposal has recently focused on practices for waste recycling and bio-resources valorization. Organic waste produced in urban context together with biological sludge produced in wastewater treatment plants (WWTPs) can be used as renewable feedstock for the production of building blocks of different products, from biopolymers to methyl esters. This paper deals with the optimization of the fermentation process in order to transform urban organic waste (a mixture of pre-treated food waste and biological sludge) into added-value volatile fatty acid (VFA) rich stream, useful for biological processes within a biorefinery technology chain. Different temperatures, pH, hydraulic retention times (HRTs) and organic loading rates (OLRs) were tested both in batch and continuous trials. Batch tests showed the best working conditions at 37 °C and pH 9, using the bio-waste feedstock thermally pre-treated (76 h at 72 °C). These conditions were applied in continuous process, where higher HRT (6.0 d) and lower OLR [7.7 kg VS/(m3 d)] gave the best performances in terms of process yield and maximum VFA level achieved: 0.77 COD VFA /VS (0) and 39 g COD VFA /L. An optimized fermentation process is crucial in a biorefinery perspective since it has to give a final stream of constant composition or tailored products suitable for further applications. [ABSTRACT FROM AUTHOR]

The aim of this study was to verify the efficiency of a separate hydrolysis step by testing different working temperatures (37–55 °C) and hydraulic retention times (two, four and six days) and by evaluating readily biodegradable carbon production. The fermentation products included primarily acetic, propionic and butyric acids. These acids can be easily converted into biogas or can be recovered in a biorefinery approach, for example, to produce polyhydroxyalkanoates. The optimal condition was found by applying an organic loading rate of 17.9 gTVS m −3 with a four-day retention time at 37 °C for an acidification yield of 183.2 gCOD VFA kgVS fed −1 . [ABSTRACT FROM AUTHOR]

Abstract A combined acidic fermentation and anaerobic digestion (AD) treatment has been developed on pilot scale for urban bio-waste conversion into volatile fatty acid (VFA) and biogas. The specific waste mixture was composed by the pre-treated organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS), both produced inside the Treviso (northeast Italy) municipality. The effect of temperature (37 °C and 55 °C) was investigated in both steps. Only the mesophilic fermentation process provided a VFA-rich stream (19.5 g COD VFA /L) with stable physical-chemical features, with no need of chemicals addition for pH control. The sludge buffering capacity made this step technically feasible. The AD step was performed on the solid-rich fraction of fermented bio-waste, after dilution with excess WAS. No relevant differences were observed under the two investigated temperature: in the steady state (organic loading rate of 2.5 kg VS/m3 d), the specific biogas production was 0.40 and 0.45 m3/kg VS at 37 °C and 55 °C respectively, with similar CH 4 content (63–64% v/v). The scaled-up version of the system (in an average urban municipality of 170,000 Person Equivalent) revealed that the whole process is thermally sustainable if both reactors are operated at mesophilic temperature: 36% of surplus thermal energy and 13,03 MWh/d of produced electricity, which corresponds to a revenue of 609,605 €/year. In addition, 2,262 kg COD VFA /d are available for parallel purposes, such as the synthesis of bio-products with higher added value than bio-methane (e.g. biopolymers). Highlights • An innovative route for feasible and profitable urban bio-waste management. • OFMSW-WAS fermentation does not require pH-control at mesophilic temperature. • The overall urban bio-waste treatment process is energetically sustainable at 37 °C. • A surplus of 2,262 kg COD VFA /d is produced for bio-products synthesis. [ABSTRACT FROM AUTHOR]

The present study describes the microbial production of polyhydroxyalkanoates (PHA) from thermally pre-treated sewage sludge at pilot scale level, investigating for the first time the effect of the organic loading rate (OLR) under oxygen limitation on biomass storage properties and kinetics. Polymer characteristics have been also evaluated. The selection/enrichment of PHA-storing biomass was successfully achieved in a Sequencing Batch Reactor (SBR) under short hydraulic retention time (HRT; 2 days). Low OLR (2.05 g COD/L d) was ideal for the selection of an efficient PHA-producing consortium cultivated under limited oxygen availability. In the fed-batch accumulation conducted under high DO regime, such biomass was characterized by 51% of PHA content on cell dry weight, with a related storage yield (Y P/S batch) of 0.61 COD PHA /COD S. On the contrary, medium OLR (4.56 g COD/L d) was not technically feasible to sustain the required consortium's selection under low DO regime. The PHA produced by biomass cultivated under low DO regime was characterized higher thermal stability and crystalline domain compared to PHA traditionally produced under high DO regime. The mass balance assessment highlighted a global yield of 51 g PHA/kg VS (volatile solids of thickened sludge), which was 9% lower than yield obtained under high DO regime, in the face of a realistic reduction of the energy cost of the process. [Display omitted] • Low DO regime sustained the PHA-storing biomass selection in SBR at low OLR. • High OLR was not technically suitable to select PHA-storing biomass at low DO. • Butyrate and valerate were preferentially consumed in the fed-batch accumulations. • The extracted PHA had high thermal stability and crystalline domain. • An overall PHA yield of 51 g PHA/g VS from sewage sludge was quantified. [ABSTRACT FROM AUTHOR]

Biohythane is a hydrogen-methane blend with hydrogen concentration between 10 and 30% v/v . It can be produced from different organic substrates by two sequential anaerobic stages: a dark fermentation step followed by a second an anaerobic digestion step, for hydrogen and methane production, respectively. The advantages of this blend compared to either hydrogen or methane, as separate biofuels, are first presented in this work. The two-stage anaerobic process and the main operative parameters are then discussed. Attention is focused on the production of biohythane from household food wastes, one of the most abundant organic substrate available for anaerobic digestion: the main milestones and the future trends are exposed. In particular, the possibility to co-digest food wastes and sewage sludge to improve the process yield is discussed. Finally, the paper illustrates the developments of biohythane application in the automotive sector as well as its reduced environmental burden. [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]