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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.

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.

Anaerobic digestion (AD) is one of the most important technologies for converting organic waste into bioenergy, mostly in the form of biogas, and offers a wide range of environmental, economic, and public health benefits. This review provides a detailed description of the process of AD and its key biological phases, namely, hydrolysis, acidogenesis, acetogenesis, and methanogenesis, and emphasizes why microbial consortia are important in the breakdown of organic matter. The review analyzes the different pretreatment methods that enhance substrate digestibility and increase biogas yield, along with the key operational parameters that affect the operation of a process, including operating temperature, organic loading rate (OLR), pH, mixing efficiency, and hydraulic retention time (HRT). Moreover, there are metabolic difficulties associated with the choice of feedstock, feedstock stability, interference by product, and also the economic viability. The scalability and versatility of the technology are evidenced by several case studies used to show successful applications of AD systems in various fields, such as the treatment of olive pomace and livestock waste. Moreover, the inclusion of AD in the circles of the economic system is also deliberated as a good avenue towards the sustainable management of waste. The growing environmental use of this technology is evidenced by the growing innovations in the field, including membrane‐based AD systems to control pathogens and odors. Overall, AD is one of the sustainable solutions to the issues of waste treatment, the production of renewable energy, and the reduction of the impact of climate change on the entire world.

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.

Background n-Caproic acid (CA), as a medium-chain carboxylic acid, is a valuable chemical feedstock for various industrial applications. The fermentative production of CA from renewable carbon sources has attracted a lot of attentions. Lactate is a significant intermediate waste in the anaerobic breakdown of carbohydrates that comprise 18-70% of the chemical oxygen demand (COD) in municipal and some industrial wastewaters. Recently, researchers (including our own group) reported the CA production using lactate as electron donor with newly identified microbiome systems. However, within such processes, it was hard to determine whether the CA production was completed by a single strain or by the co-metabolism of different microorganisms. Results Here, we report the CA production using lactate as electron donor using the strain CPB6, which we isolated from a microbiome for CA production as described previously. Strain CPB6 is affiliated with Clostridium cluster IV of the family of Ruminococcaceae based on 16S rRNA gene sequence analysis. The strain prefers acidic initial pH condition (pH 5.0-6.5), and the temperature ranging from 30 to 40 °C for CA production. In a fed-batch fermentation with non-sterilized lactate-containing organic wastewater as feedstock, strain CPB6 produced 16.6 g/L CA (from 45.1 g/L lactate) with a maximum productivity of 5.29 g/L/day. Enzyme assays with crude cell extract showed that CPB6 can metabolize acetate and butyryl-CoA to produce n-butyric acid, and acetate/n-butyrate and caproyl-CoA to produce CA, respectively. Conclusion This study demonstrated that high concentration of CA production can be obtained by a newly isolated pure culture CPB6. This strain can be employed as a powerful workhorse for high-efficient CA recovery from lactate-containing waste streams. Our preliminary investigation suggested that the CA production from lactate in strain CPB6 might be via the chain elongation pathway of the reverse β-oxidation; the detailed mechanism, however, warrants further investigation using various molecular microbiology techniques.

In this current investigation, the experimental performance of a solar still basin was significantly enhanced by incorporating snail shell biomaterials. The outcomes of the snail shell-augmented solar still basin (SSSS) are compared with those of a conventional solar still (CSS). The utilization of snail shells proved to facilitate the reduction of saline water and enhance its temperature, thereby improving the productivity of the SSSS. Cumulatively, the SSSS productivity was improved by 4.3% over CSS. Furthermore, the SSSS outperformed in energy and exergy efficiency of CSS by 4.5 and 3.5%, respectively. Economically, the cost per liter of distillate (CPL) for the CSS was 3.4% higher than SSSS. Moreover, the SSSS showed a shorter estimated payback period (PBP) of 141 days which was 6 days less than CSS. Considering the environmental impact, the observed CO2 emissions from the SSSS were approximately 14.6% higher than CSS over its 10-year lifespan. Notably, the SSSS exhibited a substantial increase in the estimated carbon credit earned (CCE) compared to the CSS. Ultimately, the research underscores the efficacy of incorporating snail shells into solar still basins as a commendable approach to organic waste management, offering economic benefits without compromising environmental considerations.

With increases in global population and urbanization, the production of Municipal Solid Waste (MSW) is growing rapidly, thus contributing to social and environmental concerns for sustainable waste management. This study addresses the research gap in optimizing composting, hypothesizing that integrating best practices and recent innovations can enhance the efficiency of the process. Data were collected through a systematic review of existing literature using Google Scholar and Scopus databases. The review provides an overview of municipal organic waste composting, outlining its processes, benefits, and challenges with the aim of identifying key area of further improvement and possibilities of adopting recent technological innovations. The analysis emphasized that technological advances in composting, as microbial inoculants or in-vessel composting have greatly improved the efficiency and quality of the resulting compost. However, several challenges remain, including managing contaminants such as heavy metals and microplastics, ensuring the compost quality and safety and addressing socioeconomic barriers that prevent widespread adoption. Moreover, process optimization, environmental and economic evaluation, as well as political and public involvement are essential to unlock the whole potential of composting systems.

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.

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.

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.