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In modern agriculture, seeking eco-friendly ways to promote plant growth and enhance crop productivity is of priority. Biostimulants are a group of substances from natural origin that contribute to boosting plant yield and nutrient uptake, while reducing the dependency on chemical fertilizers. Developing biostimulants from by-products paves the path to waste recycling and reduction, generating benefits for growers, food industry, registration and distribution companies, as well as consumers. The criteria to select designated by-products for valorizing as biostimulant are: absence of pesticide residue, low cost of collection and storage, sufficient supply and synergy with other valorization paths. Over the years, projects on national and international levels such as NOSHAN, SUNNIVA, and Bio2Bio have been initiated (i) to explore valorization of by-products for food and agriculture industries; (ii) to investigate mode of action of biostimulants from organic waste streams. Several classes of waste-derived biostimulants or raw organic material with biostimulant components were shown to be effective in agriculture and horticulture, including vermicompost, composted urban waste, sewage sludge, protein hydrolysate, and chitin/chitosan derivatives. As the global market for biostimulants continues to rise, it is expected that more research and development will expand the list of biostimulants from by-products. Global nutrient imbalance also requires biostimulant to be developed for targeted market. Here, we review examples of biostimulants derived from agricultural by-products and discuss why agricultural biomass is a particularly valuable source for the development of new agrochemical products.

The composition of municipal wastewater and sewage sludge reflects the use and proliferation of elements and contaminants within society. In Sweden, official statistics show that concentrations of toxic metals in municipal sewage sludge have steadily decreased, by up to 90 %, since the 1970s, due to environmental programmes and statutory limits on metals in sludge and soil. Results from long-term field experiments show that reduced metal pollution during repeated sewage sludge application has reversed negative trends in soil biology. Despite this Swedish success story, organic waste recycling from Swedish towns and cities to arable land is still limited to only about 20 % of the total amount produced. Resistance among industries and consumers to products grown on land treated with sewage sludge may not always be scientifically grounded; however, there are rational obstacles to application of sewage sludge to land based on its inherent properties rather than its content of pollutants. We argue that application of urban organic wastes to soil is an efficient form of recycling for small municipalities, but that organic waste treatment from large cities requires other solutions. The large volumes of sewage sludge collected in towns and cities are not equitably distributed back to arable land because of the following: (i) The high water and low nutrient content in sewage sludge make long-distance transportation too expensive; and (ii) the low plant availability of nutrients in sewage sludge results in small yield increases even after many years of repeated sludge addition. Therefore, nutrient extraction from urban wastes instead of direct organic waste recycling is a possible way forward. The trend for increased combustion of urban wastes will make ash a key waste type in future. Combustion not only concentrates the nutrients in the ash but also leads to metal enrichment; hence, direct application of the ash to land is most often not possible. However, inorganic fertiliser (e.g. mono-ammonium phosphate fertiliser, MAP) can be produced from metalcontaminated sewage sludge ash in a process whereby the metals are removed. We argue that the view on organic waste recycling needs to be diversified in order to improve the urban-rural nutrient cycle, since only recycling urban organic wastes directly is not a viable option to close the urban-rural nutrient cycle. Recovery and recycling of nutrients from organic wastes are a possible solution. When organic waste recycling is complemented by nutrient extraction, some nutrient loops within society can be closed, enabling more sustainable agricultural production in future.

The sustainable transformation and management of dissolved organic matter (DOM) are crucial for advancing organic waste treatment towards resource-oriented processes. However, the intricate molecular complexity of DOM poses significant challenges, impeding a comprehensive understanding of the underlying biochemical processes. Here, we focus on the chemical “dark matter” mining using ultra-high resolution mass spectrometry technologies to elucidate the molecular diversity and transformation in anaerobic bioprocessing of food waste. We developed an analytical framework that reveals the persistence of DOM in the final effluent is mainly determined by its molecular properties, such as carbon chain length, aromaticity, unsaturation, and redox states. Our in-depth characterization and quantitative analysis of key biochemical reactions unveils the evolution of DOM composition, providing valuable insights into the targeted conversion of persistent molecules toward full utilization. Additionally, we establish a correlation between the redox state and energy density of a broad range of DOM molecules, enabling us to comprehend and evaluate their biodegradability. These insights enhance the mechanistic understanding of DOM transformation, guiding the rational design and regulation of sustainable organic waste treatment strategies. Sustainable management of dissolved organic matter (DOM) is essential for advancing organic waste treatment towards resource-oriented processes, but the molecular complexity of DOM hinders the understanding of the underlying biochemical processes. Here, the authors use ultra-high resolution mass spectrometry to explore the molecular transformation of DOM in anaerobic digestion.

This paper reports the results on the agronomic performance of organic amendments in the EU 7th FP project “FERTIPLUS—reducing mineral fertilizers and agro-chemicals by recycling treated organic waste as compost and bio-char”. Four case studies on field-scale application of biochar, compost and biochar-blended compost were established and studied for three consecutive years in four distinct cropping systems and under different agro-climatic conditions in Europe. These included the following sites: olive groves in Murcia (Spain), greenhouse grown tomatoes in Almeria (Spain), an arable crop rotation in Oost-Vlaanderen (Merelbeke, Belgium), and three vineyards in Friuli Venezia Giulia (Italy). A slow pyrolysis oak biochar was applied, either alone or in combination with organic residues: compost from olive wastes in Murcia (Spain), sheep manure in Almeria (Spain), and compost from biowaste and green waste in Belgium and Italy. The agronomical benefits were evaluated based on different aspects of soil fertility (soil total organic carbon (TOC), pH, nutrient cycling and microbial activity) and crop nutritional status and productivity. All amendments were effective in increasing soil organic C in all the field trials. On average, the increase with respect to the control was about 11% for compost, 20% for biochar-blended compost, and 36% for biochar. The amendments also raised the pH by 0.15–0.50 units in acidic soils. Only biochar had a negligible fertilization effect. On the contrary, compost and biochar-blended compost were effective in enhancing soil fertility by increasing nutrient cycling (25% mean increase in extractable organic C and 44% increase in extractable N), element availability (26% increase in available K), and soil microbial activity (26% increase in soil respiration and 2–4 fold enhancement of denitrifying activity). In general, the tested amendments did not show any negative effect on crop yield and quality. Furthermore, in vineyards and greenhouse grown tomatoes cropping systems, compost and biochar-blended compost were also effective in enhancing key crop quality parameters (9% increase in grape must acidity and 16% increase in weight, 9% increase in diameter and 8% increase in hardness of tomato fruits) important for the quality and marketability of the crops. The overall results of the project suggest that the application of a mixture of biochar and compost can benefit crops. Therefore, biochar-blended compost can support and maintain soil fertility.

This case study presents the experimental outcomes of a zero organic waste campus. Three hundred fifty families live on this academic campus, whose solid wastes from their homes were not being properly segregated. For easy segregation, 750 dustbins of two types (labeled as organic and inorganic waste) were distributed in the canteen, mess, and all residential apartments, holding capacity up to 13 kg of garbage. A total of 24 sample sets of household organic waste were studied in 12 months period with a sample size of 1620 waste bags. Seventy-three types of organic waste were found to be 518.53, 263.57, and 249.94 kg, respectively, in the form of raw vegetable waste (RVW), fruit waste (FW), and mixed cooked waste (MCW). Regression method is applied, and the result suggests that the coefficient of determination ( R 2 ) of these variables (RVW, FW), (RVW, MCW), and (FW, MCW) was observed to be 0.90, 0.91, and 0.94 , respectively, with p  < 0.05 . Compostable and digestible wastes demonstrate the great potential to generate compost and biogas, and each compostable waste contains nutrients such as nitrogen (N), phosphorus (P), and potassium (K), which are essential for the overall growth of plants. Our present study demonstrated that one ton of digested waste collected from the academic campus and transferred in the biogas plant could generate 50 m 3 of biogas/day, which can produce 160 kW of green electric energy and 200 kg of organic compost.

Treatment of biowaste, the predominant waste fraction in low- and middle-income settings, offers public health, environmental and economic benefits by converting waste into a hygienic product, diverting it from disposal sites, and providing a source of income. This article presents a comprehensive overview of 13 biowaste treatment technologies, grouped into four categories: (1) direct use (direct land application, direct animal feed, direct combustion), (2) biological treatment (composting, vermicomposting, black soldier fly treatment, anaerobic digestion, fermentation), (3) physico-chemical treatment (transesterification, densification), and (4) thermo-chemical treatment (pyrolysis, liquefaction, gasification). Based on a literature review and expert consultation, the main feedstock requirements, process conditions and treatment products are summarized, and the challenges and trends, particularly regarding the applicability of each technology in the urban low- and middle-income context, are critically discussed. An analysis of the scientific articles published from 2005 to 2015 reveals substantial differences in the amount and type of research published for each technology, a fact that can partly be explained with the development stage of the technologies. Overall, publications from case studies and field research seem disproportionately underrepresented for all technologies. One may argue that this reflects the main task of researchers—to conduct fundamental research for enhanced process understanding—but it may also be a result of the traditional embedding of the waste sector in the discipline of engineering science, where socio-economic and management aspects are seldom object of the research. More unbiased, well-structured and reproducible evidence from case studies at scale could foster the knowledge transfer to practitioners and enhance the exchange between academia, policy and practice.

Anaerobic digestion (AD) is a green biotechnology feed with various materials, including wastewater sludge and organic fraction of municipal solid waste (OFMSW). Even if a viral contamination of the organic materials is present, the persistence of the viruses in the effluent after the anaerobic treatment is not yet well known. This study aims to assess viral contamination in the influents and effluents of AD process combining innovative methods—digital polymerase chain reaction (ddPCR) and transmission electron microscope (TEM) observations—in a real-scale context. The research activity involved 2 wastewater treatment plants (WWTP) and 2 OFMSW treatment plants with an anaerobic digestion (AD) step. After a screening on 12 viral targets, including known pathogens and indicators, the 7 most present—adenovirus, norovirus genotype II (GII), SARS-CoV-2 and GII-GIII coliphages, pepper mild mottle virus (PMMoV), tomato mosaic virus (ToMV)—were investigated in 72 samples. Adenoviruses and the viral indicators were present in higher concentrations (> 5 log gene copies/kg sludge), lower values were observed forthe other viruses. SARS-CoV-2 RNA positivity was detected with a different prevalence in the samples (84% WWTP vs 36% OFMSW; p  < 0.01). AD produced limited viral decrease (≤ 1 Log) especially in WWTP sludges. ToMV was always observed when at least one viral pathogen was noted in the samples, supporting that it may be a promising viral marker. The innovative methods applied have produced useful evidence on the persistence of viruses in the sludges, valuable for the management and improvement of current waste treatments.

Solid waste management in Jordan is still following a linear model, where more than 90% of solid waste, including organic waste, is collected and disposed into landfills. Such practices are not sustainable and may lead to adverse public health and environmental impacts. Therefore, there is a pressing need to look for alternative organic waste management by adopting circular economy principles through which the adverse impacts are minimized and the benefits from the resources are maximized. The main objective of this study is to select the appropriate treatment technology for organic solid waste management in Jordan. To achieve this objective, an analytical hierarchy process was used as a decision making tool. A hierarchy model that consists of four levels was employed with 3 main criteria and 10 sub-criteria to assess 4 alternatives of organic waste treatment. Based on the experts’ opinions and the pairwise comparison, the AHP model results showed that the environmental and public health criterion is the most important. On the other hand, the most sustainable treatment option of the organic waste treatment is composting with a weight of 0.373, followed by landfilling with a weight of 0.203. Anaerobic digestion ranked third as an alternative, with a weight of 0.201, while the least-preferred treatment technology was found to be the mechanical biological treatment, with a weight of 0.193. Sensitivity analysis based on varying the main criteria weights under different scenarios showed the robustness of the AHP model, where composting continued to be the first ranked under most of the considered scenarios. Since the national solid waste management strategy is currently subject to review, the findings of the current study provide a valuable information for the decision makers in Jordan to update their strategic plans and move towards a circular economy option.

Anaerobic digestion is an efficient technology for a sustainable conversion of various organic wastes such as animal manure, municipal solid waste, agricultural residues and industrial waste into biogas. This technology offers a unique set of benefits, some of which include a good waste management technique, enhancement in the ecology of rural areas, improvement in health through a decrease of pathogens and optimization of the energy consumption of communities. The biogas produced through anaerobic digestion varies in composition, but it consists mainly of carbon dioxide methane together with a low quantity of trace gases. The variation in biogas composition are dependent on some factors namely the substrate type being digested, pH, operating temperature, organic loading rate, hydraulic retention time and digester design. However, the type of substrate used is of greater interest due to the direct dependency of microorganism activities on the nutritional composition of the substrate. Therefore, the aim of this review study is to provide a detailed analysis of the various types of organic wastes that have been used as a substrate for the sustainable production of biogas. Biogas formation from various substrates reported in the literature were investigated, an analysis and characterization of these substrates provided the pro and cons associated with each substrate. The findings obtained showed that the methane yield for all animal manure varied from 157 to 500 mL/gVS with goat and pig manure superseding the other animal manure whereas lignocellulose biomass varied from 160 to 212 mL/gVS. In addition, organic municipal solid waste and industrial waste showed methane yield in the ranges of 143–516 mL/gVS and 25–429 mL/gVS respectively. These variations in methane yield are primarily attributed to the nutritional composition of the various substrates.

Organic waste disposal contributes to 3.8% of GHG emissions to the atmosphere, yet 68.8% of this putrescible waste fraction is still disposed of, untreated, to landfills in South Africa. The implementation of a ban on disposal of organic waste to landfills at provincial level opens up the need to research best technology pathways and waste minimisation strategies to valorise and promote the circularity of diverted waste streams. The SARChI Chair in Waste and Climate Change has developed the WROSE™ (Waste Resource Optimization Scenario Evaluation) model to assist municipalities in selecting the most appropriate waste management solutions. A research gap has been identified in the lack of information on full-scale applications of two-stage anaerobic digestion (2-stage AD) for combined bio-hydrogen and bio-methane production from organic waste. In this review, we explore drivers and barriers to the implementation of 2-stage AD in South Africa and propose possible scenarios using the WROSE™ model for its insertion into an Integrated Waste Management System at municipal level. A literature analysis suggests that 2-stage AD is a potentially viable solution to recover the inherent value of organic waste and promote circularity using bio-hydrogen and bio-methane. However, the currently available organic fraction in the municipal solid waste streams is not a suitable feedstock, as it requires high levels of pre-treatment. Suitable scenarios using the WROSE™ model are proposed for South African municipalities, paving the way for future research towards the scale-up of this technology.