The anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) and food waste achieves both environmental and economic benefits. This bio-process, well-known for producing ...biogas, is used extensively for industrial applications all over the world. Despite the use of AD across the world, the overall sustainability of this process as a source of an alternate fuel (i.e., biomethane) is intrinsically linked to the successful management of one of its major byproducts, the digestate. In order for the digestate to be classified as a “product” rather than a “waste” and to achieve regulatory compliance, this liquid stream needs to undergo biological or physicochemical treatments. The most common treatment for digestate is the use as a soil amendment. Nutrients surplus, variable agricultural seasonal requirements, escalating transportation cost, and market acceptance (e.g., risk for food safety) represents the major obstacle for the use of digestate for agricultural applications. Therefore, it is necessary to study alternative approaches for digestate management and utilization options. One alternative concept is the Back to Earth Alternative (BEA) whose aim is to bring appropriately treated residues back to their non-mobile state, as they were extracted from the earth to be used as raw materials, which would achieve actual closing of the materials cycles. Similarly, the same concept can be introduced into the digestate management process, with the goal of reducing resource costs and mitigate potential impacts on climate change, by employing a more holistic circular economy model instead of linear economy model commonly referred to as “take-make-dispose”. The overarching aim of this study is to introduce the BEA and circular economy concepts into the digestate management process taking into consideration the initial quality of the digestate and the techniques and processes necessary to meet the specific regulatory and quality requirements for the utilization of this waste stream for different applications. Cost benefit analysis and environmental impact were also evaluated for each BEA.
•Digestate from a decentralized on-farm biogas plant was assessed by a battery of ecotoxicological tests including plants, earthworms and aquatic organisms.•Obtained ecotoxicological parameters were ...used to derive indicators for future application of LCA and ERA.•Ecotoxicological investigation was performed under the “matrix-based” approach.
Over the last decade, the number of decentralized farm biogas plants has increased significantly in the EU. This development leads not only to an increasing amount of biogas produced, but also to a higher amount of digestate obtained.
One of the most attractive options to manage the digestate is to apply it as biofertiliser to the soil, because this gives the opportunity of recovering the nutrients, primarily nitrogen and phosphorus, and of attenuating the loss of organic matter suffered by soils under agricultural exploitation.
Studies have claimed that digestates can present a residual biodegradability, and contain complex organic elements, salts or pathogenic bacteria that can damage terrestrial organisms. However few ecotoxicological studies have been performed to evaluate the ecological impact of digestate application on soil.
In this study, the use of digestate as biofertiliser in agriculture was assessed by a battery of ecotoxicological tests considering the potential pollutants present in the digestate as a whole by using the “matrix-based” approach (also known as “whole effluent toxicity” for eluates or wastewater effluents). The direct and indirect tests included plant bioassays with Lepidium sativum, earthworm bioassays with Eisenia fetida, aquatic organisms (Artemia sp. and Daphnia magna) and luminescent bacteria bioassays (Vibrio fischeri).
Direct tests occurred to be more sensitive than indirect tests. The earthworm bioassays did not show serious negative effects for concentrations up to 15% (dry weight/dry weight percent, w/w dm) and the plant bioassays showed no negative effect, but rather a positive one for concentrations lower than 20% (w/w dm), which encourages the use of digestate as a biofertiliser in agriculture provided that proper concentrations are used. The indirect tests, on the eluate, with the using aquatic organisms and luminescent bacteria showed an LC50 value of 13.61% volume/volume percent, v/v) for D. magna and no toxicity for Artemia sp. and V. fischeri.
The ecotoxicological parameters obtained from the experimental activity have been analyzed so that they could serve in both ecological risk assessment (ERA) and life cycle assessment (LCA) to assess the risks and impacts of using digestate as a biofertiliser in agriculture. An interim effect factor of 1.17E−3m3/kg-in-soil is advocated and can be used in life cycle impact assessment modelling of terrestrial ecotoxicity. A predicted non effect concentration for soil organisms was defined at 341mg-digestate/kg-soil and can be used for the dose–response assessment step in ERA. Although these values are recommended for use in ERA and LCA applications, it should be stressed that they underlie important uncertainties, which should be reduced by increasing the number of toxicological tests, in particular of chronic studies conducted at different trophic levels.
•The food web of the largest Italian river is modelled for the first time with AQUATOX.•We used the model to assess direct and indirect effects of two chemicals on biota.•The response to chemical ...discharge depends on the organism position in the food web.•Biota responses to chemicals are poorly correlated with lab-estimated direct toxicity.•The lack of biomonitoring data to develop river food web models remains a challenge.
Ecological modelling has the potential to increase the realism of chemical risk assessment for better informed risk management and decision making meeting the protection goals and requirements of the EU's chemicals- and water-related regulations. We developed a food web model of the final lowland section of the longest Italian river (Po) to assess the importance of ecological interactions in setting protective thresholds for river ecosystems exposed to chemicals discharged via wastewater. An integrated 14 compartment model was setup using AQUATOX 3.1, providing a dynamic, quantitative representation of the main functional groups in the food web. To our knowledge, this is the first time that the functioning of the Po ecosystem is quantitatively described. The model was calibrated against observations of biomass density of riverine biota, as typically available for a large lowland river in Europe. The role of ecological interactions on the response of the modelled organisms to chemical exposure was tested on realistic and hypothetical exposure scenarios for two compounds contained in home and personal care products: the anionic surfactant linear alkylbenzene sulphonate and the antimicrobial triclosan. At realistic exposure concentrations the model showed no significant effect compared to control simulations. At hypothetical higher exposure, effects resulting from complex ecosystem-scale interactions emerge. Depending on the organism's position in the food web, indirect effects due to ecological interactions can either amplify or mitigate the effect of direct toxicity. Model results indicate that organisms’ responses to chemicals in real ecosystems is poorly correlated to their direct toxicity (i.e. measured by L/ECX values) for a range of simulated exposure, including concentrations equal to the reported PNEC values. AQUATOX is a useful tool to investigate the relative importance of direct toxicity and ecological interactions, but at this stage it is difficult to use it for prospective chemical risk assessment, given the underlying model uncertainties and the practical limitations of field scale evaluations. An improvement of the quantitative monitoring of feeding preferences and abundance over time of the most representative species within each functional group would be of great help to refine the model parameterisation and calibration. Nonetheless, the development of river ecosystem model scenarios is a stepping stone towards the incorporation of ecological modelling in risk assessment. When extensively tested on different scenarios AQUATOX provides a useful platform, which can be linked to mechanistic effect models as long as this component can be evaluated in controlled settings (i.e. laboratory or mesocosm scale).
The inhalation of pesticide in air is of particular concern for people living in close contact with intensive agricultural activities. This study aims to develop an integrated modelling methodology ...to assess whether pesticides pose a risk to the health of people living near vineyards, and apply this methodology in the world-renowned Prosecco DOCG (Italian label for protection of origin and geographical indication of wines) region. A sample field in Bigolino di Valdobbiadene (North-Eastern Italy) was selected to perform the pesticide fate modellization and the consequent inhalation risk assessment for people living in the area. The modellization accounts for the direct pesticide loss during the treatment of vineyards and for the volatilization from soil after the end of the treatment. A fugacity model was used to assess the volatilization flux from soil. The Gaussian puff air dispersion model CALPUFF was employed to assess the airborne concentration of the emitted pesticide over the simulation domain. The subsequent risk assessment integrates the HArmonised environmental Indicators for pesticide Risk (HAIR) and US-EPA guidelines. In this case study the modelled situation turned to be safe from the point of view of human health in the case of non-carcinogenic compounds, and additional improvements were suggested to further mitigate the effect of the most critical compound.
•New approach for the evaluation of pesticide inhalation exposure nearby vineyards.•Volatilization from soil modelled with a fugacity model “Soil”.•Dispersion of pesticide modelled with CALPUFF.•No acute and chronic risk identified for residents.•Application of drift reduction technique has been investigated.
Introduction:
Compost heat recovery systems (CHRS) represent an emerging technology to recover residual woody biomass from agroforestry and forestry activities and use the heat that is naturally ...produced during aerobic biodegradation (composting). However, a low oxygen concentration in the gas phase and self-drying and compaction of the compost body often limit efficient oxidation by microbial communities. Woodchip-derived biochar has often been proposed as a bulking agent and improver of water retention and of oxygen accessibility in the composting process, but the literature reporting its effects in the CHRS is scarce.
Methods:
Here, biochar (average particle size of 10 mm) was added at 10% (on weight basis) to chipped pruning residues into two bench-scale-controlled reactors (0.2 m
3
), operated in parallel for 57 days.
Results and Discussion:
The addition of 10% (w/w) biochar to the composting body increased biodegradation yields by approximately 50% and improved oxidation rates over readily biodegradable organic fractions (addition of cheese whey). Temperatures were on average 1.34°C higher, and heat extraction flux was also improved in the presence of biochar (0.3 kW/m
3
) versus in its absence (0.1 kW/m
3
). The organic matter mass balance resulted in approximately 50% higher biodegradation yield and improved oxidation rates over readily biodegradable organic fractions. Microbial analysis highlighted a higher concentration of thermophilic species and a lower concentration of well-known pathogenic and antibiotic-resistant genera in the presence of biochar.
Efficient and economic reuse of waste is one of the pillars of modern environmental engineering. In the field of domestic sewage management,source separation of yellow（urine）,brown（faecal matter）and ...grey waters aims to recover the organic substances concentrated in brown water,the nutrients（nitrogen and phosphorous）in the urine and to ensure an easier treatment and recycling of grey waters. With the objective of emphasizing the potential of recovery of resources from sewage management,a lab-scale research study was carried out at the University of Padova in order to evaluate the performances of oleaginous plants（suitable for biodiesel production）in the phytotreatment of source separated yellow and grey waters. The plant species used were Brassica napus（rapeseed）,Glycine max（soybean）and Helianthus annuus（sunflower）. Phytotreatment tests were carried out using 20 L pots. Different testing runs were performed at an increasing nitrogen concentration in the feedstock. The results proved that oleaginous species can conveniently be used for the phytotreatment of grey and yellow waters from source separation of domestic sewage,displaying high removal efficiencies of nutrients and organic substances（nitrogen 〉 80%; phosphorous 〉 90%; COD nearly 90%）. No inhibition was registered in the growth of plants irrigated with different mixtures of yellow and grey waters,where the characteristics of the two streams were reciprocally and beneficially integrated.
•Compost Heat Recovery System (CHRS) for heat recovery from biomass was investigated.•CHRS turned out to be convenient in terms of cost and carbon dioxide (CO2) emission.•CHRS promotes the storage of ...carbon in soil while reducing CO2 emissions.•Sustainable heating for buildings and ecosystem services can be provided with CHRS.•CHRS provide sustainable energy, being also regenerative for the ecosystem.
Aerobic biodegradation of biomass can release considerable heat, reaching temperatures of up to 65 °C. This heat can be recovered and used for domestic purposes through the implementation of Compost Heat Recovery System (CHRS). In this study, data were collected from a full-scale CHRS, fed with tree-pruning residues, installed in a farmhouse located in Northern Italy. The CHRS (2.75 kW average heating power) worked in conjunction with a pellet combustor for one year.
Energy and carbon balances were analyzed and compared (over a 15-year life-time) with combinations of alternative heating systems (both traditional and green ones). The real case study provided a heat supply at a competitive cost (0.087 € kWh−1). A scenario with two CHRSs would further decrease costs (0.074 € kWh−1). In terms of the carbon balance, a CHRS can save up to 0.252 kgCO2-eq kWh−1 of energy produced, compared to a fossil-fuel alternative (natural-gas), while promoting carbon storage for around 0.05 kgCO2-eq kWh−1 in agricultural soils by compost amendment. Over a 15-year period, each module can potentially substitute fossil-derived heat for around 264 MgCO2-eq, while increasing soil carbon pool by around 20 MgCO2-eq, as C-stock calculated on a medium-term scenario (100-years).
CHRSs have great potential to furnish renewable heat at competitive prices, while providing other ecosystem services, such as carbon storage and nutrients cycling to soil. Economic valorization of tree-pruning residues could also be an incentive for the implementation of agroforestry practices and landscape features. Further studies are needed in this relatively unexplored field, which might be of interest in the context of EU regulatory frameworks such as the EU Directive 2018/2001 and the upcoming Common Agricultural Policy (CAP) 2021 – 2027.
•Inoculum pre-treatment technologies are aimed at suppressing H2 consumption in dark fermentation.•Inoculum pre-treatment methods have only temporary effects on H2 consuming populations.•Substrate ...pre-treatment methods enhance the hydrolysis of organic wastes.•Economic viability must be taken into consideration for either substrate or inoculum pre-treatment.
Hydrogen is regarded as a clean and non-carbon fuel and it has a higher energy content compared to carbon fuels. Dark fermentative hydrogen production from organic wastes is the most promising technology for commercialization among chemical and biological methods. Using mixed microflora is favored in terms of easier process control and substrate conversion efficiencies instead of pure cultures. However, mixed cultures should be first pre-treated in order to select sporulating hydrogen producing bacteria and suppress non-spore forming hydrogen consumers. Various inoculum pre-treatments have been used to enhance hydrogen production by dark fermentation including heat shock, acid or alkaline treatment, chemical inhibition, aeration, irradiation and inhibition by long chain fatty acids. Regarding substrate pre-treatment, that is performed with the aim of enhanced substrate biodegradability, thermal pre-treatment, pH adjustment using acid or base, microwave irradiation, sonication and biological treatment are the most commonly studied technologies. This article reviews the most investigated pre-treatment technologies applied for either inoculum or substrate prior to dark fermentation, the long-term effects of varying pre-treatment methods and the subsequently feasibility of each method for commercialization.
Two-stage anaerobic digestion of food waste was performed using four different inoculum pre-treatment methods to enrich hydrogen (H2) producing bacteria from sludge. The pretreatments used in this ...study included heat shock, alkaline treatment, aeration, and a novel pretreatment using waste frying oil (WFO). Alkaline pretreatment and aeration did not completely inhibit methanogens in the first stage while no methane (CH4) was detected in the reactors cultivated either with heat shock or WFO-pretreated inocula. The highest H2 and CH4 yields (76.1 and 598.2 mL/gVS, respectively) were obtained using the inoculum pretreated with WFO. The highest total energy yield (21.96 kJ/gVS) and total organic carbon (TOC) removal efficiencies (95.77%) were obtained using inoculum pretreatment with WFO. The total energy yield trend obtained using the different pretreatments was as follows: WFO > alkaline > heat > aeration > control.
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•Two-stage anaerobic digestion using a novel inoculum pre-treatment method.•The novel pre-treatment was compared with three common inoculum pre-treatment methods.•Highest H2 and CH4 productions were obtained using the novel pre-treatment.
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