Closed-loop organic waste management systems for family farmers in Brazil

A cascade approach to sustainable agriculture: From mushroom mycelium to lettuce harvest

Sustainable agriculture involves adopting best practices in food production to promote environmental and economic sustainability. Its implementation primarily aims to utilise organic residues to increase yield, diversify production, and reduce costs. In this context, the objective of this study was to investigate different substrates for Hypsizygus ulmarius production and, from its residual substrate, to develop formulations for lettuce seedling growth and subsequent greenhouse cultivation. For mushroom production, substrates were prepared from sawdust with the addition of wheat bran, rice bran, soybean meal, and calcite, resulting in four distinct substrate formulations. The spent mushroom substrate (SMS), obtained at the end of cultivation, was used for lettuce seedling production along with the commercial substrate Carolina Soil® and the soil conditioner BacSol®. The top five formulations were selected for transplanting in the greenhouse. Regarding mushroom production, substrates with higher carbon/nitrogen ratios, around 66: 1, resulted in higher yields. For seedling production, SMS showed lower efficiency compared to the commercial substrate Carolina Soil®, which also benefited from the addition of the soil conditioner BacSol®. However, after transplanting lettuce seedlings, the formulation containing SMS showed superior results in almost all evaluated parameters. Therefore, we concluded that despite the inefficiency of using H.ulmarius SMS for lettuce seedling production, it favours the establishment of seedlings in greenhouse cultivation environments.

Millipedes and earthworms: a comparison of their efficiency and the quality of the resulting products

ABSTRACTMillicomposting (MIL, with millipedes), vermicomposting (VER, with earthworms) and composting without invertebrates (CNT, control) were compared for the first time in a replicated controlled experiment to evaluate their efficiency and the quality of their products. Vegetal waste was degraded in small closed digesters to emulate household-scale composting. Temperature profiles were similar in the three composting types. Ninety-two days were enough to complete composting and obtain well-stabilized products (humus with C/N< 20; pH from 7 to 7.8). The mean final volume loss was about 8% higher in VER than MIL and CNT (P < 0.01) and it stabilized between the 32nd and 67th days (51.4% in VER, 43% MIL and 44% in CNT). Both invertebrates promoted gains in humus Ca content (about 34.5% higher compared to CNT), whereas the highest K and Mg contents were observed in VER humus. pH, P2O5, and S contents were also higher in VER humus than in CNT (all P < 0.05). The leachate volumes, electrical conductivity and Na+ and PO43- contents were similar (P > 0.05), while pH and contents of K+ and NH4+ were higher and NO3- was lower in VER than in MIL (all P < 0.01). This resulted in higher maturity degrees in MIL than VER (NH4+/NO3- = 0.01 and 0.93, respectively). Although all three composting types were efficient in producing mature high-quality organic fertilizers, this study showed that the addition of invertebrates improved the composting efficiency and the quality of the final products.

Advances, trends and challenges in the use of biochar as an improvement strategy in the anaerobic digestion of organic waste: a systematic analysis

A recently strategy applied to anaerobic digestion (AD) is the use of biochar (BC) obtained from the pyrolysis of different organic waste. The PRISMA protocol-based review of the most recent literature data from 2011-2022 was used in this study. The review focuses on research papers from Scopus® and Web of Knowledge®. The review protocol used permits to identify 169 articles. The review indicated a need for further research in the following challenges on the application of BC in AD: i) to increase the use of BC in developing countries, which produce large and diverse amounts of waste that are the source of production of this additive; ii) to determine the effect of BC on the AD of organic waste under psychrophilic conditions; iii) to apply tools of machine learning or robust models that allow the process optimization; iv) to perform studies that include life cycle and technical-economic analysis that allow identifying the potential of applying BC in AD in large-scale systems; v) to study the effects of BC on the agronomic characteristics of the digestate once it is applied to the soil and vi) finally, it is necessary to deepen in the effect of BC on the dynamics of nitrogen and microbial consortia that affect AD, considering the type of BC used. In the future, it is necessary to search for new solutions in terms of the transport phenomena that occurs in AD with the use of BC using robust and precise mathematical models at full-scale conditions.

Closed-loop agriculture systems meta-research using text mining

The growing global population and climate change threaten the availability of many critical resources, and have been directly impacting the food and agriculture sector. Therefore, new cultivation technologies must be rapidly developed and implemented to secure the world's future food needs. Closed-loop greenhouse agriculture systems provide an opportunity to decrease resource reliance and increase crop yield. Greenhouses provide versatility in what can be grown and the resources required to function. Greenhouses can become highly efficient and resilient through the application of a closed-loop systems approach that prioritizes repurposing, reusing, and recirculating resources. Here, we employ a text mining approach to research the available research (meta-research) and publications within the area of closed-loop systems in greenhouses. This meta-research provides a clearer definition of the term “closed-loop system” within the context of greenhouses, as the term was previously vaguely defined. Using this meta-research approach, we identify six major existing research topic areas in closed-loop agriculture systems, which include: models and controls; food waste; nutrient systems; growing media; heating; and energy. Furthermore, we identify four areas that require further urgent work, which include the establishment of better connection between academic research to industry applications; clearer criteria surrounding growing media selection; critical operational requirements of a closed-loop system; and the functionality and synergy between the many modules that comprise a closed-loop greenhouse systems.

Environmental advantages of coproducing beef meat in dairy systems

Beef meat, one of the more environmentally costly animal-based foods, can be produced in two general ways, as the main product on specialised farms or as a co-product on dairy farms. In this study, two cases (a semi-confinement dairy farm (A) and a pasture-based dairy farm (B)) have been analysed by means of LCA to evaluate the environmental impacts associated with the coproduction of beef meat. In both cases, purchased feed production was found to be the main cause of environmental impacts in most of the categories considered. Additionally, cow emissions to air were the main contributor for the global warming category. Comparing the two dairy systems, notably lower environmental impacts were obtained for B in 13 of the 18 categories analysed. Regarding CF, 8.10 and 8.88 kg CO₂eq/kg LW were obtained for A and B, respectively. These CF values were within the wide range found in the literature for beef meat (1.2-42.6 kg CO₂eq/kg LW). Beef calves and cull cows are an important output of dairy farming, so that coproduction enables milk and meat with lower CF and associated environmental impacts to be obtained. In addition, the variability of the data found in literature and the lack of LCA studies based on real data for beef meat coproduced on dairy farms evidence the importance of in-depth study of this interesting topic.

How Can Biodigesters Help Drive the Circular Economy? An Analysis Based on the SWOT Matrix and Case Studies

The use of biodigesters and the circular economy (CE) has been gaining attention in recent years. Both biodigesters and CE have the potential to minimize negative impacts—not only environmental, but also economic and social. However, little attention has been paid to the relationship between biodigesters and CE. Therefore, the objective of this paper is to identify and analyze the implications of the use of biodigesters in the light of a CE concept. To do this, a SWOT matrix was developed based on the opinion of experts and two case studies were conducted in companies operating in different sectors in Brazil. The results showed that the use of biodigesters can drive CE through biogas, which is a renewable energy source, closing the cycle of organic materials, increasing the economic power of companies and small producers, improving basic sanitation in remote areas, and stimulating industrial symbiosis. However, this study identified barriers in the use of biodigesters in the context of CE, such as lack of government incentives and composting being shown to be more cost-effective than the use of biodigesters for the treatment of solid waste.

Closed-Loop Biodigesters on Small-Scale Farms in Low- and Middle-Income Countries: A Review

Anaerobic digestion (AD) systems are prominent in low- and middle-income countries (LMICs), although their implementation within organic farms to enhance resource efficiency and “close the loop” has been limited. This paper thus reviewed existing literature on the potential of AD technologies as part of closed-loop rural family farming communities in LMICs. Data from eleven existing case studies matching this criterion was then collated to understand practical considerations of implementing and maintaining viable AD systems for small farmers. The case studies analyzed indicate that most, if not all, of the biogas produced in the AD process is used for household purposes such as cooking, lighting and heating. The AD systems are either based on the fixed biogas dome or the floating drum design, although the tubular flexible balloon model is mentioned as a low-cost alternative. Future research opportunities in this topic include studying the applicability of recommendations offered across different geographies, consideration of long-term sustainability and impact of biodigester technology, and sociocultural factors such as community ownership and indigenous practices.

Effects of a temporary increase in OLR and a simultaneous decrease in HRT on dry anaerobic digestion of OFMSW

The effects of the temporary increase of organic loading rate (OLR) combined with the simultaneous decrease of hydraulic retention time (HRT) on the stability of a pilot scale dry anaerobic digester were investigated. The separately collected organic fraction of municipal solid waste in mesophilic conditions (T = 40°C) was treated. The objective of this study was to verify whether it is possible to feed the digester for short periods, about three consecutive weeks, with higher OLRs and lower HRTs than those considered optimal without generating process failure or long-term instability. Starting from stable operation at a daily OLR of 10.0 kg of total volatile solids (TVS) for digester volume and an HRT of 23 d, the reactor was fed with an OLR of 10.8, 11.7 and 12.5 kg TVS m-3 d-1 corresponding to an HRT of 21, 19 and 18 d, respectively. It was observed that after using an OLR of 10.8 and 11.7 kg TVS m-3 d-1 for 3 weeks with satisfying results, it was possible to restore stable operating conditions at an OLR of 10.0 kg TVS m-3 d-1 in a short time. Otherwise, after using an OLR of 12.5 kg TVS m-3 d-1 the anaerobic digestion was deeply unbalanced and quickly failed. In this latter case, however, it was possible to fully recover and restore the stable conditions of the process within two months.