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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2010.07.024 Byline: David Bolzonella, Francesco Fatone, Silvia di Fabio, Franco Cecchi Abstract: The Mediterranean Region is a semi-arid area whose land is facing serious erosion, causing adverse impacts on agriculture. To improve the water availability, researchers have proposed the reclamation and reuse of treated wastewater. In this paper, we report the main findings of 10 years of research on the efficiencies of a conventional activated sludge process and a submerged membrane bioreactor, with particular emphasis on the removal of non-conventional pollutants. The studies showed that the membrane bioreactor produced a virtually solids-free, high-quality permeate: most nutrients, heavy metals, and persistent organic pollutants were removed, and in particular, dioxins, furans, and polychlorinated biphenyls were typically present at concentrations below the detection limit. Moreover, the total coliforms count decreased by 4-5log and Escherichia coli was absent from the membrane bioreactor permeate. These results, combined with the continuing reduction of the capital and operating costs for this approach, suggest that membrane bioreactors are an increasingly cost-effective technology to produce treated effluents that are suitable for reuse. Author Affiliation: Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy Article History: Received 2 September 2009; Revised 19 June 2010; Accepted 19 July 2010

As the world population continues to grow, alternative protein sources must be sought to meet increased protein needs and avoid the detrimental effects of traditional protein production. Microbial proteins (MP) are a low-carbon footprint alternative suitable for manufacturing food and feed. Bacterial-based MP can be produced at moderate costs using agro-waste, which is already utilised by anaerobic digestion (AD) plants to produce biogas and fertilisers. At present, there is the opportunity to turn existing AD plants into biorefineries for bio-based products like MP destined for fish feed. In this work, we evaluated the feasibility of biogas production coupled with MP production in the same medium-sized European biogas plant through mass and energy balances and basic economic assessment. The liquid phase rich in volatile fatty acids resulting from agro-waste fermentation was used to obtain MP by mixed cultures in a continuous stirred tank reactor, with the highest VSS productivity (1.21 g/L day) obtained at hydraulic retention times of 2–3 days. The obtained MPs were rich in proteins (74.0% of TVS), PHAs (22.5%) and essential amino acids, useable as feed ingredients in aquaculture. An initial economic analysis showed that the production of 590 tMP/year could yield a break-even price of 1300 €/t of MP, taking into account the investments in the new technology and additional operating costs. This analysis illustrates the competitiveness of a combined plant when evaluated against established market benchmarks and highlights a promising prospect for the expansion of MP production capacity. [Display omitted] • MP were produced in a bioreactor with a maximum productivity of 1.21 g/L day. • MP were rich in proteins (74%), polyhydroxyalkanoates (22.5%), essential amino acids. • Plants for biogas production could be upgraded to produce MP for aquaculture. • The calculated break-even point for combined MP-biogas plants is 1300 €/t for MP. • A medium-sized biogas plant has the potential to host cost-competitive MP production. [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]

• Cheese whey, olive oil wastes and winery wastewaters are about 300 M tons worldwide. • About 85 kg of food wastes are annually produced by each people in the world. • VFA and PHA conversions can reach 0.9 gVFAs/gCOD and 0.7 gPHA/gVSS, respectively. • Wine wastes have the highest PHA yield (0.7 gPHA/gVSS), olive ones the lowest (0.3) • These yields allow to estimate the global annual PHAs production of about 260 M tons. Dairy products, extra virgin olive oil, red and white wines are excellent food products, appreciated all around the world. Their productions generate large amounts of by-products which urge for recycling and valorization. Moreover, another abundant waste stream produced in urban context is the Organic Fraction of Municipal Solid Wastes (OFMSW), whose global annual capita production is estimated at 85 kg. The recent environmental policies encourage their exploitation in a biorefinery loop to produce Volatile Fatty Acids (VFAs) and polyhydroxyalkanoates (PHAs). Typically, VFAs yields are high from cheese whey and OFMSW (0.55–0.90 g COD_VFAs /g COD), lower for Olive Mill and Winery Wastewaters. The VFAs conversion into PHAs can achieve values in the range 0.4–0.5 g PHA /g VSS for cheese whey and OFMSW, 0.6–0.7 g PHA /g VSS for winery wastewater, and 0.2–0.3 g PHA /g VSS for olive mill wastewaters. These conversion yields allowed to estimate a huge potential annual PHAs production of about 260 M tons. [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 status of treated wastewater reuse as experienced in some Mediterranean Basin countries such as Greece, Israel, Italy and Cyprus is examined. General background information is given for each of these Mediterranean countries, including natural water resources, climatic conditions (temperature, rainfall), generated wastewater, crops cultivated and irrigated with effluent, and related aspects of reuse. The examined parameters include treatment strategies, wastewater reuse standards applied in each country, effluent reuse research in progress in the above target countries related to the treatment technologies, water quality, regulations, economics, public acceptance, risk assessment, benefits, keys for potential success and main constraints. Emphasis has been given to the benefits of treated wastewater reuse in integrated water resources management systems and its role for water cycle management, solving water scarcity issues mainly in arid and semi-arid regions of the Mediterranean basin. The experience presented can be implemented in other water scarce regions around the world. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the results of a pilot- and full-scale experimental campaign on the anaerobic co-digestion of waste activated sludge and biowaste both in mesophilic and thermophilic conditions. The study demonstrated the possibility to increase the specific biogas production from 0.34 to 0.49 m3/kgTVS and the gas production rate from 0.53 to 0.78 m3per m3 of reactor per day changing the reactor temperature from the mesophilic (37 °C) to the thermophilic (55 °C) range. The experimental work was carried out at pilot-scale, and the results match the full-scale behaviour. Ammonia nitrogen recycled from the anaerobic digestion section to the wastewater treatment plant accounted for about 4% of the total nitrogen loading. Digestate characteristics in terms of biological stability and heavy metals content suggested the opportunity of a short time post-aerobic stabilisation, leading to a high quality compost product. [Copyright &y& Elsevier]

Abstract: The paper reports the findings of a two-year pilot scale experimental trial for the mesophilic (35°C), thermophilic (55°C) and temperature phased (65+55°C) anaerobic digestion of waste activated sludge. During the mesophilic and thermophilic runs, the reactor operated at an organic loading rate of 2.2kgVS/m3d and a hydraulic retention time of 20days. In the temperature phased run, the first reactor operated at an organic loading rate of 15kgVS/m3d and a hydraulic retention time of 2days while the second reactor operated at an organic loading rate of 2.2kgVS/m3d and a hydraulic retention time of 18days (20days for the whole temperature phased system). The performance of the reactor improved with increases in temperature. The COD removal increased from 35% in mesophilic conditions, to 45% in thermophilic conditions, and 55% in the two stage temperature phased system. As a consequence, the specific biogas production increased from 0.33 to 0.45 and to 0.49m3/kgVSfed at 35, 55, and 65+55°C, respectively. The extreme thermophilic reactor working at 65°C showed a high hydrolytic capability and a specific yield of 0.33gCOD (soluble) per gVSfed. The effluent of the extreme thermophilic reactor showed an average concentration of soluble COD and volatile fatty acids of 20 and 9g/l, respectively. Acetic and propionic acids were the main compounds found in the acids mixture. Because of the improved digestion efficiency, organic nitrogen and phosphorus were solubilised in the bulk. Their concentration, however, did not increase as expected because of the formation of salts of hydroxyapatite and struvite inside the reactor. [Copyright &y& Elsevier]

Petrochemical wastewater treatment is a new sector for the possible widespread application of membrane bioreactor technology. In this field, hard to degrade compounds such as amines and nitrogen residuals were generally the major issues. In addition, over the last years the irregular operation of the manufacturing plants involved drastic variability of the wastewater's loadings and characteristics, so as to call for more flexible schemes of the treatment plants. This paper compares two different schemes of a continuously fed membrane bioreactor to adequate the nitrification potential to the influent loadings. These are: a) controlled and continuous external ammonia dosage; b) sequencing batch nitrifier enrichment. On the basis of lab and pilot-scale treatment of real petrochemical wastewater, the cyclic batch enrichment process proved to be reliable, cost-effective, and easy to control, being more flexible with respect to changeable influent loadings. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the results of a study focused on the occurrence and removal of dioxins and furans (PCDD/F) and poly-chlorinated biphenyls (PCB) in both conventional and membrane wastewater treatment processes. It was found that the conventionally activated sludge process could perform a good removal of PCDDs/Fs and PCBs, but the relatively low solid retention time applied and the presence of suspended solids in the effluent limited the removal capability of the system. On the other hand, the membrane bioreactor was capable of perfectly removing PCDDs/Fs and PCBs giving an effluent characterised by concentrations under the limit of detection for most of the tested compounds. This efficiency was the result of both the solids removal from the effluent (permeate) and the application of prolonged solid retention times which enabled the bioconversion of those compounds as demonstrated by the mass balances. A mathematical model was developed to predict the final fate of a given molecule according to the operational conditions applied in the wastewater treatment process. [ABSTRACT FROM AUTHOR]

Abstract: The performance of mesophilic anaerobic digesters of four large Italian wastewater treatment plants without primary sedimentation were studied. Only the waste activated sludge is stabilised by means of the mesophilic (35–37°C) anaerobic digestion process. The anaerobic digesters generally worked with a hydraulic retention time in a range of 20–40 days and an organic loading rate of some 1kgVS/day. The solids content of the sludge fed to the digesters was in the range 2.6–3.9% and the gas produced per kilogram of volatile solids added was in the range 0.07–0.18m3/kgVSfed. The specific gas production per kilogram of volatile solids destroyed was in the range 0.5–0.9m3/kgVSdestroyed and the reduction of the volatile solids concentration was in the range 13–27% (average 18%). These figures are particularly significant when designing anaerobic digesters for the treatment of waste activated sludge as single substrate. Moreover, it was observed that the higher the applied solid retention time in the activated sludge process for wastewater treatment, the lower the gas production. In particular, the specific gas production decreased from 0.18 to 0.07m3/kgVSfed when increasing the solid retention time in the wastewater treatment line from 8 to 35 days. Finally, a mathematical model for the prediction of biogas production on the solid retention time applied in the wastewater treatment process was developed. [Copyright &y& Elsevier]

The bio-based production of added-value products and energy from waste streams while minimizing environmental impacts is a crucial aspect within the circular economy's principles. A two-phases anaerobic digestion process to produce volatile fatty acids (VFA) and biogas production in an energetically feasible manner from the organic fraction of municipal solid waste (OFMSW) has been investigated. Mesophilic temperature (T) coupled to 5.0 days as hydraulic retention time (HRT) gave a VFA-rich stream with an overall concentration of 24.4 ± 0.2 g COD VFA /L, dominated by propionic and valeric acids, and high acidification yield, being VFA close to 90% of the soluble COD. The pH was maintained around 7.0 by the digestate recirculation from the second methanation reactor (HRT of 20 days) where biogas production was quantified under mesophilic and thermophilic T. The assessment of energy balance showed the benefits to carry out the second methanation stage under thermophilic condition, having more income from electricity generation without losing the thermal sustainability of the two-phases process as a whole. [Display omitted] • Two-phases anaerobic OFMSW fermentation-digestion for bio-refinery development. • Mesophilic temperature and high HRT enhanced VFA production and process stability. • Neutral pH favours the short chain fatty acid with even number of carbon's atom. • Major economic income with methanation stage conducted at thermophilic temperature. [ABSTRACT FROM AUTHOR]

• Three anaerobic digestates (ADs) and two animal effluents were studied via SCE. • These were compared for soil P release and ryegrass P uptake in pot. • AD (bovine slurry + energy crops) and swine slurry were alternative to chemical P. • 31P NMR revealed that PO− 4 was the main factor in their P fertilization capacity. • SCE can be helpful to assess potentially available P from ADs and animal slurries. Recycled organic wastes (OW) can be a valuable P source; however, their P-fertilising capacity is still poorly known. In this study, we selected three anaerobic digestates [wastewater sludge (D 1), winery sludge (D 2), and bovine-slurry/energy crops (BD)] and two animal effluents [bovine slurry (BS) and swine slurry (SS)] to test their P-release and P-fertilising capacities via sequential chemical extraction (SCE), X-ray diffraction (XRD), and 31P-nuclear magnetic resonance (31P NMR). Subsequently, the three digestates (30 mg P kg−1 of soil) were compared for the release of Olsen-P during a soil incubation and for plant-P apparent recovery (ARF) in a pot experiment using ryegrass (112 days) in a soil with poorly available-P (Olsen-P < 5 mg kg−1), under a non-limiting N environment. The amount of labile-P (H 2 O + NaHCO 3), as determined from SCE, related well to the Olsen-P following OW addition to the soil. It was shown via 31P NMR spectroscopy that orthophosphate was the leading P-form in highly P-releasing OW. The amount of labile-P, however, was affected by soil adsorption, thereby reducing plant-P uptake. The plant-P ARF (%) showed that the recycled P-sources were clustered in highly (BD and SS: ≈20%), intermediately (D 1 and BS: ≈15%), and poorly performing OWs (D 2 : ≈10%) vs. chemical P-source (P-chem: 20%). Therefore, only BD and SS were effective alternatives to P-chem; however, the other OW can be efficient P-sources in soils with higher Olsen-P. Thus, crop fertilisation can be tailored on a P-basis by SCE as a function of soil adsorption capacity and on an N-basis according to the demand. [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]

Wastewater treatment plants in many countries use anaerobic digesters for biosolids management and biogas generation. Opportunities exist to utilise the spare capacity of these digesters to co-digest food waste and sludge for energy recovery and a range of other economic and environmental benefits. This paper provides a critical perspective for full-scale implementation of co-digestion of food waste and wastewater sludge. Data compiled from full-scale facilities and the peer-reviewed literature revealed several key bottlenecks hindering full- scale implementation of co-digestion. Indeed, co-digestion applications remain concentrated mostly in countries or regions with favourable energy and waste management policies. Not all environmental benefits from waste diversion and resource recovery can be readily monetarised into revenue to support co- digestion projects. Our field surveys also revealed the important issue of inert impurities in food waste with significant implication to the planning, design, and operation of food waste processing and co-digestion plants. Other pertinent issues include regulatory uncertainty regarding gate fee, the lack of viable options for biogas utilisation, food waste collection and processing, impacts of co-digestion on biosolids reuse and downstream biogas utilisation, and lack of design and operation experience. Effort to address these bottlenecks and promote co-digestion requires a multi-disciplinary approach. [ABSTRACT FROM AUTHOR]

The global CO 2 emissions are above 35 GtCO 2 /year. Recently, the European Commission approved the Green Deal with the aim to reduce the greenhouse gases emissions. Hydrogen, because of its capacity to burn without CO 2 formation, is considered one of principal energy option for the future to obtain decarbonization. In 2020, total hydrogen demand was estimated at 8.6 Mt but over 90% of all hydrogen production plants use fossil fuels as feedstock. In perspective, a relatively small part of this hydrogen can be of biological origin. Anaerobic digestion, in particular two stages processes, can assure biological hydrogen and methane productions using organic waste and waste effluents as feedstock. Carbon dioxide in biogas can be removed to obtain a gas blend of methane and hydrogen with typical concentrations of 90:10–70:30% v/v. This review aims to provide an overview on biohythane production in Europe at Technology Readiness Level greater or equal to 5 (technology validated in relevant environment). At the moment, there are few examples of biohythane plants at pilot or higher scales, mainly located in Italy, France and United Kingdom. Here reactors with volumes in the range 20–350 L and 300-1000 L were able to assure a stable hydrogen and methane, respectively, production. The highest volumes of 700 and 3800 L for acidogenic and methanogenic phases, respectively, were successfully tested close Milan (Italy). • European total hydrogen demand is about 8–9 Mt. • Over 90% of hydrogen produced comes from non-sustainable resources. • Anaerobic Digestion leads to biohydrogen and biomethane injectable in the gas grid. • Some TSAD pilot plants have reached a hydrogen yield of 100 LH 2 /kgTVS. • TSAD can be easily implemented in the 10,000 European biogas plants. [ABSTRACT FROM AUTHOR]

The increase in human population determines a higher proteins request to sustain the feed demand for animals and aquaculture. Single Cell Proteins (SCPs) consist of mixed protein from pure and mixed culture of bacteria, fungi, algae, and yeast, which are grown and harvested to accomplish the food requirement of human and animals. This work investigated the production of Saccharomyces cerevisiae to be used as SCPs for animal feeding. The effluent of candies production process, rich in sugars, about 40 g/L, and agricultural digestate rich in nitrogen and other macro and micronutrients, were used for the yeast's growth. Preliminary batch tests demonstrated that aerobic conditions optimized the biomass growth. Then, continuous aerobic tests were conducted at different dilution rates. The dilution rate of 0.50 d−1, corresponding to a hydraulic retention time of 2 days, optimized both the biomass productivity of 0.25 g/L per day and the protein content of 28% w/w. The analysis of the aminoacidic profile demonstrated that obtained SCPs could be used as an integrator of feed for fish and monogastric animals. On the contrary, they were not suitable for pet feed as all the amino acids concentrations were lower than required standards. These results suggested that anaerobic digesters in the agricultural sector can be transformed into small biorefineries for microbial protein production. [Display omitted] • Candy production effluent and digestate were used to produce Single Cell Proteins. • Aerobic condition was the best for the Saccharomyces cerevisiae growth. • Continuous tests were performed to find the best Hydraulic Retention Time. • The obtained SCPs were analyzed to determine the aminoacidic content. • SCPs can be used as supplements to produce fish monogastric animals' feed. [ABSTRACT FROM AUTHOR]

Abstract: We studied the occurrence, removal, and fate of 16 polycyclic aromatic hydrocarbons (PAHs) and 23 volatile organic compounds (VOCs) in Italian municipal wastewater treatment systems in terms of their common contents and forms, and their apparent and actual removal in both conventional activated-sludge processes (CASP) and membrane bioreactors (MBRs). We studied five representative full-scale CASP treatment plants (design capacities of 12 000 to 700 000 population-equivalent), three of which included MBR systems (one full-scale and two pilot-scale) operating in parallel with the conventional systems. We studied the solid–liquid partitioning and fates of these substances using both conventional samples and a novel membrane-equipped automatic sampler. Among the VOCs, toluene, ethylbenzene, xylenes, styrene, 1,2,4-trimethylbenzene, and 4-chlorotoluene were ubiquitous, whereas naphthalene, acenaphthene, fluorene, and phenanthrene were the most common PAHs. Both PAHs and aromatic VOCs had removal efficiencies of 40–60% in the headworks, even in plants without primary sedimentation. Mainly due to volatilization, aromatic VOCs had comparable removal efficiencies in CASP and MBRs, even for different sludge ages. MBRs did not enhance the retention of PAHs sorbed to suspended particulates compared with CASPs. On the other hand, the specific daily accumulation of PAHs in the MBR’s activated sludge decreased logarithmically with increasing sludge age, indicating enhanced biodegradation of PAHs. The PAH and aromatic VOC contents in the final effluent are not a major driver for widespread municipal adoption of MBRs, but MBRs may enhance the biodegradation of PAHs and their removal from the environment. [ABSTRACT FROM AUTHOR]

A combined two-levels control method has been developed and tested on a long term operation of a two-phases pilot-scale anaerobic process for the concurrent production of volatile fatty acids, hydrogen and methane. The latter was designed for the treatment of food waste of urban origin (namely, the organic fraction of municipal solid waste). The optimized control method was set on the base of the inputs of three online probes: a pH-meter in the fermentation reactor, a pH-meter and a conductivity probe in the digestion reactor. The first control level managed the pH in the fermentation reactor while the second control level managed the ammonia concentration in the digestion reactor. This combination established the volume of the digestate to be recycled from the digestion to the fermentation reactor, optimizing the yield of volatile fatty acid (0.31–0.32 kg COD VFA /kg COD fed) and the specific hydrogen production (SHP; 0.070–0.074 m3 H 2 /kg TVS fed) in the fermentation reactor and the specific methane production (SMP; 0.48–0.55 m3 CH 4 /kg TVS fed) in the digestion reactor. A new process configuration was also proposed and applied over the course of the long operation period. This configuration allowed to remove part of the volatile fatty acid-rich liquid stream from the fermenter effluent, maintaining the corresponding solid-rich effluent in the whole system (as feed for the digestion reactor) by using a solid/liquid separation unit. In this way, the concentration of volatile fatty acids in the digester was kept at a low level, even with high loading rates, so maintaining a satisfying efficiency of methane production and utilizing the excess volatile fatty acids (out of the system) as building blocks for other purposes. The optimized two-levels control method for the anaerobic treatment of food waste provides new perspectives for the valorisation of such waste stream; the production of building blocks namely volatile fatty acids supports new innovative bio-refinery platforms for the production of bio-products. Image 1 • It is possible to automatically control an anaerobic process to valorise food waste. • New perspectives for constant production of volatile fatty acids from organic waste. • A mathematical model prediction of the ammonia level in anaerobic digestion. • The system supports innovative bio-refineries for the production of bio-products. [ABSTRACT FROM AUTHOR]

This study focuses on the application of the concept of circular economy, with the creation of added-value marketable products and energy from organic waste while minimizing environmental impacts. Within this purpose, an urban biorefinery technology chain has been developed at pilot scale in the territorial context of the Treviso municipality (northeast Italy) for the production of biopolymers (polyhydroxyalkanoates, PHAs) and biogas from waste of urban origin. The piloting system (100–380 L) comprised the following units: a) acidogenic fermentation of the organic fraction of municipal solid waste (OFMSW) and biological sludge; b) two solid/liquid separation steps consisting of a coaxial centrifuge and a tubular membrane (0.2 μm porosity); c) a Sequencing Batch Reactor (SBR) for aerobic PHA-storing biomass production; d) aerobic fed-batch PHA accumulation reactor and e) Anaerobic co-digestion (ACoD). The thermal pre-treatment (72 °C, 48 h) of the feedstock enhanced the solubilization of the organic matter, which was converted into volatile fatty acids (VFAs) in batch mode under mesophilic fermentation conditions (37 °C). The VFA content increased up to 30 ± 3 g COD/L (overall yield 0.65 ± 0.04 g COD VFA /g VS (0)), with high COD VFA /COD SOL (0.86 ± 0.05). The high COD VFA /COD SOL ratio enhanced the PHA-storing biomass selection in the SBR by limiting the growth of the non-storing microbial population. Under fully aerobic feast-famine regime, the selection reactor was continuously operated for 6 months at an average organic loading rate (OLR) of 4.4 ± 0.6 g COD/L d and hydraulic retention time (HRT) of 1 day (equal to SRT). The ACoD process (HRT 15 days, OLR 3.0–3.5 kg VS/m3 d) allowed to recover the residual solid-rich overflows generated by the two solid/liquid separation units with the production of biogas (SGP 0.44–0.51 m3/kg VS) and digestate. An overall yield of 7.6% wt PHA/VS (0) has been estimated from the mass balance. In addition, a preliminary insight into potential social acceptance and barriers regarding organic waste-derived products was obtained. Image 1 • Multiple by-products (biopolymer and biogas) from a single urban biorefinery. • Feedstock thermal pre-treatment enhanced its the acidification process. • Mesophilic anaerobic co-digestion ensured a positive process thermal balance. • Overall yield of 7.6% biopolymer mass on the initial volatile solids was estimated. • Social survey indicated bin bags derived from organic waste as preferred product. [ABSTRACT FROM AUTHOR]

Six million tons of Coffee Spent Grounds (SCG) are produced every year all around the world. Their physical and chemical characterization, rich in high value molecules and organic compounds, make SCG ideal for the recovery of bioactive molecules and bioenergy production according to the "cascade biorefinery approach". This work investigates the effects of the implementation of sequential processes for the recovery of the coffee oil, rich in valuable molecules, and the productions of bioethanol and biogas from SCG. The use of a 50:50 (v/v) ethanol-iso-propanol mixture allowed a coffee oil recovery of about 16% w/w. In particular, the extracted coffee oil was rich in tocopherols (about 15 mg/100 g SCG). On the other hand, n-hexane showed a lower performance in terms of coffee oil extraction (10% w/w) but allowed for the extraction of different molecules: linoleic and palmitic acids (38% and 34% w/w of the coffee oil, respectively) and of Cafestol (383 mg/100g SCG) and Kahweol (194 mg/100g SCG). The extracted SCG underwent to an acid-enzymatic hydrolysis process followed by a solid/liquid separation. The liquid fraction was then used for the bioethanol production which reached the final concentration of 50 g/L, while the solid fraction was used for biogas production by Anaerobic Digestion. The final methane yield resulted in a production of about 250 NL CH4 /kg VS. A complete train of operations, composing a biorefinery approach, can be therefore adopted to fully valorise this particular organic waste. Image 1 • The innovative cascade biorefinery approach was applied on spent coffee grounds. • Ethanol/iso-propanol allowed to extract 16% w/w of coffee oil from coffee grounds. • Coffee oil is rich in high added value tocopherols, Cafestol, Kahweol and fatty acids. • Coffee grounds were treated for sugar production by enzymatic production. • High ethanol (50 g/L) and biomethane productions (250 LCH4/kgVS) were obtained. [ABSTRACT FROM AUTHOR]

Opuntia ficus-indica can grow in arid and semi-arid environments characterized by low water and nutrients availability. These features make it a more sustainable alternative to the common energy crops for biorefinery purposes. This work focused on the potential benefits of anaerobic processes applied to this plant. Specifically, it considered i) the substrate preparation, demonstrating the effect of the apparent viscosity on the process; ii) the evaluation of biomethane, Volatile Fatty Acids (VFAs), and caproic acid production in semi-continuous mode at different hydraulic retention times; iii) the purification of the Fatty Acids-rich output through pressure-driven membrane filtration. The rheology analysis found that a 5 %w/w water dilution of the substrate is needed to lower the apparent viscosity to 173 cP, which is below the acceptable apparent viscosity level of 200 cP for a good bioreactor mixing. Keeping this condition, the semi-continuous trials with the best biomethane performance was at HRT of 20 days, with 210 mLCH 4 /gVS and 232 mLCH 4 /gCOD in of production and specific yield, respectively. The VFAs and caproic acid production reached their best at Hydraulic Retention Time 5, with 26 and 7.9 gCOD/L of VFAs and caproic acid, corresponding to specific yields of 79 and 30 % respectively. Pressure-driven filtration at 330 kDa allowed to obtain a permeate with a VFAs and caproic acid content of 96.72%w/w. Finally, the adsorption and desorption tests allowed to separate caproic acid from the permeate and to concentrate it from about 7.5 g COD /L to about 26 g COD /L. [Display omitted] • Opuntia Ficus Indica was valorized for multiple bioproducts and biofuels productions. • Caproic acid and methane were maximized at HRT 5 and 20 days, respectively. • The yields of VFAs and caproic acid were of 79 % and 30 % on COD base, respectively. • 300 kDa filtration allowed to obtain a medium of about 97 % of only VFAs. • Activated carbons led to a complete separation of caproic acid from the other VFAs. [ABSTRACT FROM AUTHOR]

Anaerobic Digestion is largely applied in the rural context because of its capability of stabilizing the organic matter while recovering biogas, thus renewable energy, and a renewable fertilizer, the digestate. In the present study, the methane yield of a large number of organic biomasses generated in the agro-industrial sector was evaluated by biomethane potential trials. More than 50 different organic substrates were grouped according to their chemical characteristics or their application in 7 major categories: energy crops, lignocellulosic by-products, herbaceous by-products, vegetable by-products, fruits by-products, livestock effluents and miscellaneous food processing by-products. Results demonstrated that the concentration and the nature of the organic matter is able to influence the methane production. Energy crops are among the more diffused substrates with about 200 million tons/year. Its wide adoption is justified by relative high methane yields (250–350 L CH 4 /kg TVS) and mainly by the rapid degradation rates with hydrolysis constant of about 0.15 d−1. By-products characterized by high content of lignocellulosic materials showed slower kinetics (0.05–0.09 d−1) and a methane production in the range of 150–400 L CH 4 /kg TVS, which increased with cellulose content. Livestock effluents had generally a lower methane yield (50–200 L CH 4 /kg TVS) as effect of the higher ammonia inhibiting compounds. Finally, food by products were characterized by a large methane production's range, 150–700 L CH 4 /kg TVS, due to heterogeneous nature of these substrates. Food by products rich in lipids content had the higher methane yield (400–700 L CH 4 /kg TVS), but showed the slowest kinetics (k h lower than 0.1 d−1). P Substrates rich in proteins and carbohydrates had lower methane yields (300–450 L CH 4 /kg TVS) but higher hydrolysis constants, generally upper than 0.1 d−1. Considering the global biomass generation of these substrates at European level, it was determined that their valorisation could contribute with an annual potential energy output of 2584 PJ (61.7 Mtoe), representing 5.7% of total energy consumed in EU- 28 in 2015 or 34,1% of total renewable energy in the same year. Image 1 • The biogas potential of different agro-industrial byproducts was considered. • Agro-industrial wastes can produce the 5.7% of total energy consumed in EU. • Their abundance make manure and crops are the highest energy potential substrates. • The highest BMP belong to food wastes with 350–700 LCH 4 /kgTVS. • Anaerobic digestion contribute to boots economy of local farms and industries. [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]

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]

More sustainable scenarios in the bioenergy sector can be achieved when biomass exploitation is based on eco-efficient supply chains. Regarding this, grass as a by-product obtained from landscape management could provide a large quantity of biomass potentially utilizable in the Anaerobic Digestion (AD) supply chain. This study assessed the energy and greenhouse gases (GHG) impacts of grass obtained from the landscape management of riverbanks. A study area of a land reclamation authority was investigated by interpreting high resolution spatial data and determination of the biomass yield. In addition, an inventory was made of the grass production chain. An energy analysis was performed using the Cumulative Energy Demand method (CED), while the GHG balance of grass AD was calculated based on CO2 equivalents. Special attention was also given to the logistic approaches: two different supply systems were evaluated in order to determine the best supply chain for this feedstock. The results show that the biomass yield of riverbank grass amounts to 13 t f.m /ha (4.8 t d.m /ha) while the energy utilization of grass determines a saving on fossil energy of about 2.6–2.4 GJ/t f.m. (7.0–6.4 GJ/t d.m. ) and on GHG equivalent emissions of about 86–67 kg CO2eq /t f.m. (233–181 kg CO2eq /t d.m. ) depending on supply distance and logistic approach. In this regard, the Indirect Logistic Approach (ILA) achieves the best performance in terms of the reduction of fossil energy and GHG emissions. The results suggest positive prospects for the integration of grass from non-cultivated areas into the AD supply chain in order to mitigate the requirement for agricultural feedstock and obtain a positive return, in terms of energy and emissions saved, from landscape management operations. [ABSTRACT FROM AUTHOR]

This study compared the performances of single and two-stage anaerobic digestion processes of food waste. The processes were monitored by taking into account both the steady state process performances and the transient conditions. In addition to a conventional univariate analysis, a multivariate analysis to increase the validity of the results of the comparison study was also performed. The transient states caused peaks due to a high organic loading rate, simulating possible overloading events and the recovery capacity of both processes (resilience). The specific gas production of the methanogenic reactor of the two-stage process was higher (0.88 m 3 biogas /kg VS ) than for the single-stage process (0.75 m 3 biogas /kg VS ). This finding was related to the increase in the removal efficiency (of 17%). Considering the pilot-scale results, a comparison of mass and energy balance, and costs (assuming the upgrading of the biogas produced) was also discussed. [ABSTRACT FROM AUTHOR]

This paper deals with the optimization of anaerobic digestion of winery wastes considering the behavior of biogas production rate between two consecutive reactor feeds. Processes operating at different hydraulic retention times (23 and 40 d) were monitored and the specific biogas productions were comparable (0.386 and 0.378 m 3 /kgCOD fed for retention time of 23 and 40 d, respectively). The biogas production rate reduced after 11–14 h in both the processes, this time corresponds to the necessary period to consume readily biodegradable and easily hydrolysable COD. In order to maximize biogas production, a system able to increase feeding frequency was set-up. The system activated the feeding pump when a reduction of biogas production rate (below 0.4 m 3 biogas /(m 3 reactor d)) was detected. Consequently, hydraulic retention time decreased to 21 d and organic loading rate reached 6.2 kg COD/(m 3 reactor d). Moreover, these conditions favored the growth of microorganism involved into degradation of soluble COD fraction and faster kinetics were observed in this conditions. Finally, two kinetic models (first order and step-diffusional) were applied to manually and automatically fed processes, in order to understand how the retention time and automatic control affected the degradation rate of the different types of compounds and to confirm the results obtained from the preliminary kinetic study. Step-diffusional model better predicted the trend of degradation rates (R 2 0.97–1.00) because it considered three groups of compounds and the same number of parameters. [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]

Within the urban scenario, the application of a biorefinery technology value chain can foster the conversion of different organic substrates into marketable and added-value products. In this work, a pilot-scale dark fermentation (DF) process has been carried out as a key step for volatile fatty acids (VFA) and hydrogen production from the liquid fraction of sewage sludge and food waste mixture. Six operating conditions have been monitored in terms of yield and process stability, by changing the hydraulic retention time (HRT) from 4 to 6 days and applying a short-term hyper-thermophilic hydrolysis (70 °C, 8 h) on the same feedstock mixture. A tubular centrifugation was utilized to remove part of the biosolids (driven to biogas production) before the DF step, which was applied on the soluble and/or colloidal organic matter only. The hydrolysis step favored the following acidification process, in which a fermentation yield up to 0.42 g COD VFA /g VS 0 was achieved at 5 days as HRT. Hydrogen production (up to 34.4% v/v and 0.046 m3 H 2 /kg VS 0) was positively affected by the hydrolysis application and by the decrease of the HRT, highlighting the possibility to produce biohythane in the modeled two-phases anaerobic bioprocess. On the other hand, without the application of the hydrolysis, a selective production of butyric acid (up to 75% COD basin) was achieved, furnishing a different valorization route for the chosen urban organic feedstock. Changes in operating conditions and performances were also reflected by the adaptation of the microbial community, whose characterization highlighted the occurrence of several fermentative microorganisms (e.g., Clostridiaceae , Ruminococcaceae). [Display omitted] • Acidification yield increased with hydrolyzed FW and sludge mixture in DF process. • Shorter HRT and mild hydrolysis favored specific hydrogen yield and production. • Selective butyrate production was obtained with no hydrolyzed feedstock mixture. • The microbial community was heavily affected by the hydrolyzation step. • Hydrolysis step was necessary to reach H 2 content above 10% v/v in the biohythane. [ABSTRACT FROM AUTHOR]

Deep separate collection of the organic fraction of municipal solid waste generates streams with relatively low content of inert material and high biodegradability. This material can be conveniently treated to recovery both energy and material by means of simplified technologies like screw-press and extruder: in this study, the liquid fraction generated from pressed biowaste from kerbside and door-to-door collection was anaerobically digested in both mesophilic and thermophilic conditions while for the solid fraction composting is suggested. Continuous operation results obtained both in mesophilic and thermophilic conditions indicated that the anaerobic digestion of pressed biowaste was viable at all operating conditions tested, with the greatest specific gas production of 0.92 m 3 /kgVS fed at an organic loading rate of 4.7 kgVS/m 3 d in thermophilic conditions. Based on calculations the authors found that the expected energy recovery is highly positive. The contents of heavy metals and pathogens of fed substrate and effluent digestates were analyzed, and results showed low levels (below End-of-Waste 2014 criteria limits) for both the parameters thus indicating the good quality of digestate and its possible use for agronomic purposes. Therefore, both energy and material were effectively recovered. [ABSTRACT FROM AUTHOR]

The study reported in this paper considered the results of pilot-scale experiments on single and 2-phase anaerobic digestion of waste activated sludge at high rate. Both single and 2-phase digesters were conducted at the same conditions of organic loading and retention time. The 2-phase anaerobic system showed clear increases in terms of organic matter removal and biogas production compared to the single stage system. Particularly, the volatile solids removal rose from 34% in the single stage system to 38% in the 2-phase system. Hence, the global specific biogas production increased 32%, moving from 0.21 to 0.31 m 3 /kgTVS·d respectively for the single and 2-phase systems. The 2-phase system produced 15% more energy than the single stage system. Furthermore, the heat produced in a CHP unit satisfied all heat requirements insuring more than the complete energetic sustainability of the process. Finally, both single and 2-phase digestates showed to meet requirements established for sludge reuse in agriculture regarding pathogens, metals and organic contaminants. A preliminary economic analysis showed the possibility to pay back the investment for the implementation of a second anaerobic reactor in 3 years because of both the increased biogas production and reduced quantity of excess sludge to be disposed of. [ABSTRACT FROM AUTHOR]