Environmental Performance in the Production and Use of Recovered Fertilizers from Organic Wastes Treated by Anaerobic Digestion vs Synthetic Mineral Fertilizers

Advancing sustainable wastewater management: A comprehensive review of nutrient recovery products and their applications

Wastewater serves as a vital resource for sustainable fertilizer production, particularly in the recovery of nitrogen (N) and phosphorus (P). This comprehensive study explores the recovery chain, from technology to final product reuse. Biomass growth is the most cost-effective method, valorizing up to 95 % of nutrients, although facing safety concerns. Various techniques enable the recovery of 100 % P and up to 99 % N, but challenges arise during the final product crystallization due to the high solubility of ammonium salts. Among these techniques, chemical precipitation and ammonia stripping/ absorption have achieved full commercialization, with estimated recovery costs of 6.0-10.0 EUR kgP-1 and 4.4-4.8 £ kgN-1, respectively. Multiple technologies integrating biomass thermo-chemical processing and P and/or N have also reached technology readiness level TRL = 9. However, due to maturing regulatory of waste-derived products, not all of their products are commercially available. The non-homogenous nature of wastewater introduces impurities into nutrient recovery products. While calcium and iron impurities may impact product bioavailability, some full-scale P recovery technologies deliver products containing this admixture. Recovered mineral nutrient forms have shown up to 60 % higher yield biomass growth compared to synthetic fertilizers. Life cycle assessment studies confirm the positive environmental outcomes of nutrient recycling from wastewater to agricultural applications. Integration of novel technologies may increase wastewater treatment costs by a few percent, but this can be offset through renewable energy utilization and the sale of recovered products. Moreover, simultaneous nutrient recovery and energy production via bio-electrochemical processes contributes to carbon neutrality achieving. Interdisciplinary cooperation is essential to offset both energy and chemicals inputs, increase their cos-efficiency and optimize technologies and understand the nutrient release patterns of wastewater-derived products on various crops. Addressing non-technological factors, such as legal and financial support, infrastructure redesign, and market-readiness, is crucial for successfully implementation and securing the global food production.

Techno-economic analysis of biogas production from domestic organic wastes and locally sourced material: the moderating role of social media based-awareness

Management of organic waste addresses the issue of cleanliness and sanitation in developing nations such as Pakistan, where improper waste management usually leads to significant health problems and early mortality. The control of organic waste in rural regions of Pakistan and other developing nations needs to be undertaken using effective solutions. This study contributes to satisfying local needs such as cooking, lighting, and maintaining a comfortable temperature in anaerobic locations and works as a guideline for converting to biogas. This research aims to ascertain households' most substantial challenges concerning biogas production using domestic organic waste and locally sourced materials. The analysis is conducted on data from 81 respondents gathered using a comprehensive questionnaire assessment. Respondents were carefully chosen with the purposive sampling process. Primary data were collected from a structured questionnaire and partial least squares structural equation modeling (PLS-SEM) to evaluate the formulated assumptions. The results indicate that managing organic waste positively influences the sustainable improvement of biogas using human organic waste and locally resourced materials. The selected variables and their moderating effect significantly and favorably influence this conceptual model. Furthermore, all manipulating influences are constructively connected with implementing biogas technology using organic waste and locally resourced material, minimizing household energy expenses, and satisfying local needs. This study concludes that the government's green energy policy and economic incentives encourage households to use biogas energy produced from organic waste and locally resourced material. The government should use modern technology, resident training, and expert methodological assistance to induce households into biogas production using domestic organic waste and locally resourced material. Finally, the study's limitations and suggestions for further research are also addressed.

Life cycle assessment of fermentative production of lactic acid from bread waste based on process modelling using pinch technology

Bread waste (BW), a rich source of fermentable carbohydrates, has the potential to be a sustainable feedstock for the production of lactic acid (LA). In our previous work, the LA concentration of 155.4 g/L was achieved from BW via enzymatic hydrolysis, which was followed by a techno-economic analysis of the bioprocess. This work evaluates the relative environmental performance of two scenarios - neutral and low pH fermentation processes for polymer-grade LA production from BW using a cradle-to-gate life cycle assessment (LCA). The LCA was based on an industrial-scale biorefinery process handling 100 metric tons BW per day modelled using Aspen Plus. The LCA results depicted that wastewater from anaerobic digestion (AD) (42.3-51 %) and cooling water utility (34.6-39.5 %), majorly from esterification, were the critical environmental hotspots for LA production. Low pH fermentation yielded the best results compared to neutral pH fermentation, with 11.4-11.5 % reduction in the overall environmental footprint. Moreover, process integration by pinch technology, which enhanced thermal efficiency and heat recovery within the process, led to a further reduction in the impacts by 7.2-7.34 %. Scenario and sensitivity analyses depicted that substituting ultrapure water with completely softened water and sustainable management of AD wastewater could further improve the environmental performance of the processes.

Measuring the environmental impacts of sewage sludge use in agriculture in comparison with the incineration alternative

This study compares two scenarios for sewage sludge treatment i.e., agricultural-land application (LA) and incineration (INC), in an Italian context (Pavia province, Po Valley). The study was realised within a regional project aiming to obtain useful data to better address future sludge management policies. To do so, an attributional Life Cycle Assessment (LCA) approach was chosen and the multi-functionality was addressed by using system expansion. Results indicated that the scenario INC had higher impacts than scenario LA for the categories linked to process inputs and to the direct emissions of incineration, such as Global warming potential (= + 60 %)., Stratospheric Ozone Depletion, Ozone Formation, Mineral Resource Scarcity and Fossil Resource Scarcity. System expansion i.e., the production of non-renewable fertilisers, played a large role (higher impacts) in the categories related to resource scarcity in the INC scenario. On the other hand, LA scenario showed higher impacts than INC for direct emissions due to fertilisation (Marine and Freshwater Eutrophication, and Particulate Matter). In conclusion, the use of sewage sludge in agriculture seemed to be competitive with the alternative of incineration but both sludge quality and emission reduction during sludge distribution in the field play an important role in the reduction of environmental impacts.

Nutrient recovery and recycling from fishery waste and by-products

The circular bio-based economy offers great untapped potential for the food industry as possible valuable products and energy can be recovered from food waste. This can promote more sustainable and resilient food systems in Europe in follow-up of the European Commission's Farm to Fork strategy and support the global transition to more sustainable agri-food systems with the common agricultural and fisheries policies. With its high nutrient content, waste and by-products originating from fish and seafood industry (including aquaculture) are one of the most promising candidates to produce alternative fertilising products which can play a crucial role to replace synthetic mineral fertilisers. Whereas several studies highlighted the opportunities to recover valuable compounds from fishery waste, study towards their potential for the production of fertilising products is still scarce. This study presents an extensive overview of the characteristics of fishery waste and by-products (i.e., fish processing waste, fish sludge, seafood waste/by-products), the state-of-the-art nutrient recovery technologies and recovered nutrients as fertilising products from these waste streams. The European Commission has already adopted a revised Fertilising Products Regulation (EU) 2019/1009 providing opportunities for fertilising products from various bio-based origins. In frame of this opportunity, we address the quality and safety aspects of the fishery waste-derived fertilising products under these criteria and highlight possible obstacles on their way to the market in the future. Considering its high nutrient content and vast abundance, fish sludge has a great potential but should be treated/refined before being applied to soil. In addition to the parameters currently regulated, it is crucial to consider the salinity levels of such fertilising products as well as the possible presence of other micropollutants especially microplastics to warrant their safe use in agriculture. The agronomic performance of fishery waste-derived fertilisers is also compiled and reported in the last section of this review paper, which in most cases perform equally to that of conventional synthetic fertilisers.

Centralization of wastewater treatment in a tourist area: A comparative LCA considering the impact of seasonal changes

Nowadays, environmental protection has become a topic of primary importance, and the interest in wastewater treatment plants (WWTPs) has increased due to the need for a paradigm shift from linear to circular economy. The centralization level of wastewater infrastructure is the basis for a successful system. The aim of this study was to investigate the environmental impacts generated from the centralized treatment of wastewater in a tourist area in central Italy. The combined use of BioWin 6.2 simulation software and life cycle assessment (LCA) methodology was implemented to evaluate the potential connection of a small decentralized WWTP to a medium-size centralized facility. Two different scenarios (decentralized system, corresponding to the current situation, and centralized) were evaluated in two separate periods: high season (HS), corresponding to the main tourist season, and low season (LS), which is the period before the main tourist season. Two sensitivity analyses were conducted, assuming different N2O emission factors, and considering the period at the end of tourist season, respectively. Although with modest advantages (up to -6 % in pollutant emissions), WWTP connection was the best management option in 10 out of 11 indicators in HS, and 6 out of 11 categories in LS. The study showed that wastewater centralization was promoted by scale factors in HS, as the most impactful consumptions decreased as the degree of centralization increased; on the other hand, the decentralized system was less penalized in LS, as small WWTP was less stressed and energy consuming in this period. Sensitivity analysis confirmed the results obtained. Site-specific conditions can lead to conflicting circumstances, as key parameters may have different behaviors depending on seasonal variations, and the degree of centralization in tourist areas should be addressed by distinguishing separate periods, based on changes in tourist flows and pollution loads.

A Critical Review of Data Science Applications in Resource Recovery and Carbon Capture from Organic Waste

Municipal and agricultural organic waste can be treated to recover energy, nutrients, and carbon through resource recovery and carbon capture (RRCC) technologies such as anaerobic digestion, struvite precipitation, and pyrolysis. Data science could benefit such technologies by improving their efficiency through data-driven process modeling along with reducing environmental and economic burdens via life cycle assessment (LCA) and techno-economic analysis (TEA), respectively. We critically reviewed 616 peer-reviewed articles on the use of data science in RRCC published during 2002-2022. Although applications of machine learning (ML) methods have drastically increased over time for modeling RRCC technologies, the reviewed studies exhibited significant knowledge gaps at various model development stages. In terms of sustainability, an increasing number of studies included LCA with TEA to quantify both environmental and economic impacts of RRCC. Integration of ML methods with LCA and TEA has the potential to cost-effectively investigate the trade-off between efficiency and sustainability of RRCC, although the literature lacked such integration of techniques. Therefore, we propose an integrated data science framework to inform efficient and sustainable RRCC from organic waste based on the review. Overall, the findings from this review can inform practitioners about the effective utilization of various data science methods for real-world implementation of RRCC technologies.

Life cycle assessment of a novel strategy based on hydrothermal carbonization for nutrient and energy recovery from food waste

In this work, a novel strategy for food waste valorization was evaluated from an environmental life-cycle perspective. A system based on acid-assisted hydrothermal carbonization of food waste combined with the exploitation of hydrochar by combustion and process water through nutrient recovery stage and subsequent anaerobic digestion, was assessed and compared with stand-alone anaerobic digestion as the reference system. This combination of processes aims to recover both nutrients in a stage of struvite precipitation from process water and energy through hydrochar and biogas combustion. Both systems were modeled in Aspen Plus® to identify and quantify their most relevant input and output flows and subsequently evaluate their environmental performance through the life cycle assessment methodology. The novel combined system was found to generally involve a more favorable environmental performance than the reference stand-alone configuration, which would be closely linked to the substitution of hydrochar for fossil fuels. In addition, the impacts associated with soil application of the struvite produced in the integrated process would also be reduced compared to the use of the digestate generated in the stand-alone anaerobic digestion process. Following these results and the evolving regulatory framework for biomass waste management, mainly in the field of nutrient recovery, combined process based on acid-assisted hydrothermal treatment plus nutrient recovery stage and anaerobic digestion is concluded to be a promising circular economy concept for food waste valorization.

Rice straw for energy and value-added products in China: a review

The rise of global waste and the decline of fossil fuels are calling for recycling waste into energy and materials. For example, rice straw, a by-product of rice cultivation, can be converted into biogas and by-products with added value, e.g., biofertilizer, yet processing rice straw is limited by the low energy content, high ash and silica, low nitrogen, high moisture, and high-quality variability. Here, we review the recycling of rice straw with focus on the global and Chinese energy situations, conversion of rice straw into energy and gas, biogas digestate management, cogeneration, biogas upgrading, bioeconomy, and life cycle assessment. The quality of rice straw can be improved by pretreatments, such as baling, ensiling, and co-digestion of rice straw with other feedstocks. The biogas digestate can be used to fertilize soils. The average annual potential energy of collectable rice straw, with a lower heating value of 15.35 megajoule/kilogram, over the past ten years (2013-2022) could reach 2.41 × 109 megajoule.

Pig Slurry Management Producing N Mineral Concentrates: A Full-Scale Case Study

Manure treatment to recover nutrients presents a great challenge to delocalize nutrients from overloaded areas to those needing such nutrients. To do this, approaches for the treatment of manure have been proposed, and currently, they are mostly under investigation before being upgraded to full scale. There are very few fully operating plants recovering nutrients and, therefore, very few data on which to base environmental and economic studies. In this work, a treatment plant carrying out full-scale membrane technology to treat manure to reduce its total volume and produce a nutrient-rich fraction, i.e., the concentrate, was studied. The concentrate fraction allowed the recovery of 46% of total N and 43% of total P. The high mineral N content, i.e., N-NH₄/total-N > 91%, allowed matching the REcovered Nitrogen from manURE (RENURE) criteria proposed by the European Commission to allow the potential substitution of synthetic chemical fertilizers in vulnerable areas characterized by nutrient overloading. Life cycle assessment (LCA) performed by using full-scale data indicated that nutrient recovery by the process studied, when compared with the production of synthetic mineral fertilizers, had a lower impact for the 12 categories studied. LCA also suggested precautions which might reduce environmental impacts even more, i.e., covering the slurry to reduce NH₃, N₂O, and CH₄ emissions and reducing energy consumption by promoting renewable production. The system studied presented a total cost of 4.3 € tons^-1 of slurry treated, which is relatively low compared to other similar technologies.

Maximizing agricultural reuse of recycled nutrients: A spatially explicit assessment of environmental consequences and costs

Recovering nutrients from organic materials to reduce artificial fertilizer inputs requires the implementation of processing technologies and can involve considerable logistics and transportation costs. Reducing such costs by directly applying organic materials to agricultural land can contribute to pollution due to potential contaminants and unbalanced nutrient ratios. Assessing the cost of increased recycling requires a spatially explicit approach because availability of organic materials, nutrient demand and agro-ecosystem properties vary spatially. A multi-objective model was developed to estimate the trade-offs between costs of nutrient recovery and improvements in nutrient distribution for a case study area in The Netherlands. The evaluated recovery processes included solid-liquid separation followed by reverse osmosis to recover nutrients from pig manure which was compared to a conventional process via hygienisation and export. Results indicate that, even in a nutrient saturated area, replacement potential of artificial nitrogen (N) and phosphorus (P) fertilizers through locally reclaimed nutrients is limited to about 17% N and 55% P. A cost optimum was found when about 48% of the initial pig manure quantities were processed via nutrient recovery and directed to land. Increasing manure processing for nutrient recovery led to a redistribution of nutrients and trace metals (zinc (Zn) and copper (Cu)), resulting in more localized concentration. Zn and Cu were enriched by about 8% and 2%, respectively, when maximizing nutrient recovery. Our generic model offers a methodology to assess the trade-offs between increased recycling and associated spatial effects to facilitate sustainable recycling infrastructures for achieving more circular agriculture.

Nitrogen dynamics in soils fertilized with digestate and mineral fertilizers: A full field approach

Highly stabilized digestate from sewage sludge and digestate-derived ammonium sulphate (RFs), were used in a comparison with synthetic mineral fertilizers (SF) to crop maize in a three-year plot trial in open fields. RFs and SF were dosed to ensure the same amount of mineral N (ammonia-N). In doing so, plots fertilized with digestate received much more N (+185 kg ha^-1 of organic N) because digestate also contained organic N. The fate of nitrogen was studied by measuring mineral and organic N in soil at different depths, ammonia and N₂O emissions, and N uptake in crops. Soil analyses indicated that at one-meter depth there was no significant difference in nitrate content between RF, SF and Unfertilized plots during crop season indicating that more N dosed with digestate did not lead to extra nitrate leaching. Ammonia emissions and N content in plants and grains measured were also similar for both RF and SF. Measuring denitrification activity by using gene makers resulted in a higher denitrification activity for RF than SF. Nevertheless, N₂O measurements showed that SF emitted more N₂O than RF (although it was not statistically different) (7.59 ± 3.2 kgN ha^-1 for RF and 10.3 ± 6.8 kgN ha^-1 for SF), suggesting that probably the addition of organic matter with digestate to RF, increased the denitrification efficiency so that N₂ production was favoured. Soil analyses, although were not able detecting N differences between SF and Rf after three years of cropping, revealed a statistical increasing of total carbon, suggesting that dosing digestate lead to carbon (and maybe N) accumulation in soil. Data seem to suggest that N₂O/N₂ emission and organic N accumulation in soil can explain the fate of the extra N dosed (organic-N) in RF plots.

A comparative LCA of three WWTPs in a tourist area: Effects of seasonal loading rate variations

Although the wastewater treatment is a fundamental utility for the protection of human health and the environment, non-evident drawbacks are associated with it. Wastewater treatment plants (WWTPs) located in tourist areas generally suffer from the seasonal increase in wastewater flow-rate and associated pollution loads. In this study, a Life Cycle Assessment (LCA) of three medium-size urban WWTPs, located in a tourist area in central Italy, was carried out. The study compared the environmental impacts generated by 1 m³ of treated wastewater in low season (LS) and high season (HS). All the material and energy flows involved in the operational phase of wastewater treatment were considered within the system boundaries, including the disposal or recovery treatment of the waste streams generated by the WWTPs, namely screenings, waste from grit removal and wastewater sludge. The analysis was conducted using almost only real data from full-scale plants. In each WWTP, the environmental impacts produced in HS were higher than those generated in LS; therefore, the environmental impacts increased as the loading rate increased. Furthermore, a correlation between WWTP size and environmental performance was observed. Indeed, in 8 out of 11 environmental indicators, the percentage increase in pollutant emissions due to wastewater treatment in HS decreased as the WWTP size increased. Results revealed that larger WWTPs suffered less from seasonal loading rate variations, showing greater flexibility. The existence of a scale factor suggests that the centralization of WWTPs in tourist areas can be an option to enable better treatment performance in terms of environmental impacts. A sensitivity analysis was performed, increasing N₂O emission factors from wastewater treatment in LS: considering a 75 % increase, the outcomes found in default LCA were not confirmed. Future research should investigate the operational factors and biological mechanisms that most affect wastewater treatment when significant seasonal variations are present.

Life cycle assessment of Parmigiano Reggiano PDO cheese with product environmental footprint method: A case study implementing improved slurry management strategies

The environmental impact of Parmigiano Reggiano PDO cheese was quantified using the Product Environmental Footprint Category Rules (PEFCRs) in a Traditional System (TS) and in an Improved Management System (IMS). The TS differs from IMS with respect to slurry management (raw slurry storage vs anaerobic digestion and storage of the liquid fraction of digestate) and application of nutrients to the field (by slurry tanker with a diverter plate vs soil injection at pre-sowing and side dressing). Two additional scenarios were evaluated by considering the possible environmental enhancement achievable by reducing enteric methane production and by using soybean grain produced in Italy as the protein source for animals' diets. The environmental impact was quantified both for 1 kg of fat and protein corrected milk (FPCM) and for the production of 10 g dry matter equivalent of cheese as single score. For the first assessment, the environmental impact results were 124 and 112 μPt kg FPCM^-1 for TS and IMS, respectively. In the second case, it was 10.8 μPt and 9.9 μPt 10 g dry matter equivalent^-1 of cheese, for TS and IMS, respectively. The specific cost for reducing the GHG emissions in this production chain was equal to 34 € Mg^-1 milk produced. Finally, although specific studies should consider the reduction of enteric methane emissions and the use of soybean grain nationally produced as feed source, the scenarios evaluated in this study highlighted some potential for environmental improvements. Even small environmental improvements to the Parmigiano Reggiano PDO cheese supply chain can bring substantial improvements to the sustainability of the food market, because of the widespread demand on the global market of Parmigiano Reggiano and of its chance of attracting consumers who are sensitive to environmental problems.