Biological treatment of organic materials for energy and nutrients production—Anaerobic digestion and composting

Unlocking the potential of biosurfactants: Production, applications, market challenges, and opportunities for agro-industrial waste valorization

Biosurfactants are eco-friendly compounds with unique properties and promising potential as sustainable alternatives to chemical surfactants. The current review explores the multifaceted nature of biosurfactant production and applications, highlighting key fermentative parameters and microorganisms able to convert carbon-containing sources into biosurfactants. A spotlight is given on biosurfactants' obstacles in the global market, focusing on production costs and the challenges of large-scale synthesis. Innovative approaches to valorizing agro-industrial waste were discussed, documenting the utilization of lignocellulosic waste, food waste, oily waste, and agro-industrial wastewater in the segment. This strategy strongly contributes to large-scale, cost-effective, and environmentally friendly biosurfactant production, while the recent advances in waste valorization pave the way for a sustainable society.

Community composting strategies for biowaste treatment: methodology, bulking agent and compost quality

The European Union's commitment to increase recycling and recovery rates of municipal solid waste requires significant changes in current waste management. Local governments are developing various strategies for treating the organic fraction of municipal waste (biowaste) via composting. Community composting centres (CCC), green waste collection, treatment points and community gardens are some of these new approaches. Population density and spatial distribution, together with the existence of community green areas, determine the location of the various infrastructures for recycling local biowaste. The composting process consumes high amounts of bulking agent (BA) necessary to provide the structure that allows, amongst other uses, biowaste aeration and microbial surface colonisation. Shredded green waste from parks, gardens and households can be used as BA in community composting and home composting. In this study, a total of 46 compost samples obtained from CCC with two types of handling were analysed: 22 samples treated by vertical flow (VF) and 24 samples treated by horizontal flow (HF). The HF model allowed better use of the volume of modular composting units and the VF model required less effort and time for the CCC operator. Mature, stable and high-nutrient-content composts were obtained with both models. These composts met the legal requirements to be used as an organic amendment, and they can be delivered to the participants or used in community gardens in the municipality.

Conversion of solid wastes and natural biomass for deciphering the valorization of biochar in pollution abatement: A review on the thermo-chemical processes

This overview addresses the formation of solid trash and the various forms of waste from a variety of industries, which environmentalists have embraced. The paper investigates the negative effects on the environment caused by unsustainable management of municipal solid trash as well as the opportunities presented by the formal system. This examination looks at the origins of solid waste as well as the typical treatment methods. Pyrolysis methods, feedstock pyrolysis, and lignocellulosic biomass pyrolysis were highlighted. Explain in detail the various thermochemical processes that take place during the pyrolysis of biomass. Due to its carbon content, low cost, accessibility, ubiquitousness, renewable nature, and environmental friendliness, biomass waste is a unique biochar precursor. This study looks at the different types of biomass waste that are available for treating wastewater. This study discussed a wide variety of reactors. Adsorption is the standard method that is used the most frequently to remove hazardous organic, dye, and inorganic pollutants from wastewater. These pollutants cause damage to the environment and water supplies, thus it is important to remove them. Adsorption is both simple and inexpensive to utilize. Temperature-dependent conversions explain the kinetic theories of biomaterial biochemical degradation. This article presents a review that explains how pyrolytic breakdown char materials can be used to reduce pollution and improve environmental management.

Study on the effect of different additives on the anaerobic digestion of hybrid Pennisetum: Comparison of nano-ZnO, nano-Fe2O3 and nano-Al2O3

The effects of three nanomaterials (ZnO, Al₂O₃, and Fe₂O₃) on the wet and dry anaerobic digestion (AD) processes of hybrid Pennisetum were assessed over 33 days, and the microbial communities of dry AD systems were studied. The results demonstrated that biogas production improved by 72.2% and 33.6% when nanoporous Al₂O₃ (nano-Al₂O₃) and nano-Fe₂O₃ were added during dry AD, respectively. However, biogas production decreased by 39.4% with nano-ZnO. Kinetic analysis showed that the three nanomaterials could shorten the lag phase of the AD sludge, while the 16S rRNA gene amplicon sequencing results demonstrated that microbes such as Longilinea and Methanosarcina were enriched in the nano-Al₂O₃ reactors and methanogenic communities community such as Methanobacterium sp., Methanobrevibacter sp., and Methanothrix sp., which were enriched in the nano-Al₂O₃ and nano-Fe₂O₃ reactors. However, the microbial community and some methanogenic communities diversity and richness were inhibited by the addition of nano-ZnO.

Rice Straw Utilisation for Bioenergy Production: A Brief Overview

Unsustainable rice straw management causes environmental impacts; hence, utilisation of rice straw for bioenergy is a promising strategy for sustainable rice straw management. Although rice straw has a high potential for bioenergy generation, the whole production cycle and application may cause environmental damage that is not fully understood. Hence, environmental performance studies are required to determine the most effective rice straw utilisation options. A comprehensive approach, such as life-cycle assessment (LCA), can give comprehensive information on the possible environmental effects of rice straw utilisation for bioenergy. Therefore, this study briefly overviews the LCA of rice straw utilisation for bioenergy production. It is found that utilisation of rice straw for bioenergy could reduce global warming potential compared to energy production from fossil fuels. However, it is suggested that other impact categories in LCA be evaluated in the bioenergy production from rice straw research to determine the overall sustainability of the production.

Patent Landscape of Composting Technology: A Review

Organic waste management is a major global challenge. It accounts for a significant portion of waste that ends up in landfills, where it gradually decomposes and emits methane, a harmful greenhouse gas. Composting is an effective method for potentially solving the problem by converting organic waste into valuable compost. Despite many studies focusing on the composting process, no study has reviewed the technological advancements in the composting fields from the perspective of patents. This review paper begins with background information on the composting process, specifically important factors affecting the process, problems associated with it, and the available technologies to facilitate the process. Different technologies are discussed, ranging from manual to automated methods. Subsequently, 457 patents are selected, classified into different categories, and reviewed in detail, providing a patent technology landscape of composting technology. Automatic composters are more prominent than manual ones as managing organic waste at the source has become more crucial in recent years. The need for a domestic composter creates an opportunity for the development of a compact and automated system for organic waste management, which is more suitable for urbanized settings. This technology has the potential to reduce the amount of organic waste that needs to be managed at an already overburdened landfill, as well as the environmental consequences associated with it.

Evaluation of methane production from the anaerobic co-digestion of manure of guinea pig with lignocellulosic Andean residues

The objective of this research was to evaluate anaerobic co-digestion of guinea pig manure (GP) with Andean agricultural residues such as amaranth (AM), quinoa (QU) and wheat (TR) in batch biodigesters under mesophilic conditions (37 ⁰C) for 40 days. As microbial inoculum, sewage treatment sludge was used in two inoculum/substrate ratios (ISR of 1 and 2). In terms of methane production, the best results occurred in treatments containing AM and QU as co-substrate and an ISR of 2. Thus, the highest methane production yield in the GP:AM biodigesters (25:75) and GP:QU (25:75) with 341.86 mlCH₄/g VS added and 341.05 mlCH₄/g VS added, respectively. On the other hand, the results showed that methane production with an ISR of 2 generated higher yields for guinea pig waste and the methane fraction of the biogas generated was in a range from 57 to 69%. Methane production kinetics from these raw materials was studied using five kinetic models: modified Gompertz, logistic equation, transfer, cone and Richards. The cone model adjusted best to the experimental values ​​with those observed with r² of 0.999 and RMSE of 1.16 mlCH₄/g VS added. Finally, the highest biodegradability (experimental yield/theoretical yield) was obtained in the GP-AM biodigesters (25:75) with 67.92%.

Solid state anaerobic digestion of food waste and sewage sludge: Impact of mixing ratios and temperature on microbial diversity, reactor stability and methane yield

Food waste (FW) and sewage sludge (SS) were anaerobically co digested under solid state conditions (Total solids >15%) and observed that mixing ratio of 3:1 and 2:1 is optimum for mesophilic and thermophilic conditions respectively. The VS reduction and methane yield at optimized ratio was 76% and 0.35 L CH₄/(g VS reduced) respectively at mesophilic temperature whereas it was 88% and 0.42 L CH₄/(g VS reduced) at thermophilic temperature. The metagenomic analysis for these cases were done and high throughput DNA sequencing revealed that diversified bacterial groups that participate in the different metabolisms (hydrolysis, acidogenesis and acetogenesis) were mainly dominated by the phylum Firmicutes and Bacteriodetes. Genus Methanothrix is found to be dominant which is capable of generating methane by any methanogenic pathway among all the archaeal communities in the reactors followed by Methanolinea and Methanoculleus. However, it was understood through metagenomic studies that acetotrophic pathway is observed to be the major metabolic pathway in the reactors.

Effect of decomposing oil palm trunk fibers on plant growth and soil microbial community composition

Oil palm trunks (OPT) are logged for replantation and the fiber residues are disposed of into the palm plantation area. The fiber residues are expected to increase soil fertility through recycling of carbon and minerals via fiber decomposition. This study investigated the effects of OPT fiber disposal and other lignocellulosic biomass on plant growth and microbial diversity in the soil environment. Four treatment plots were tested: (A) soil+OPT fiber (1:20), (B) soil+sugarcane bagasse (1:20), (C) soil+cellulose powder (1:20), and (D) unamended soil as a negative control. Low plant height, decreased chlorophyll content, and low biomass was observed in corn grown on soil mixed with OPT fiber, cellulose, and sugarcane bagasse, when compared with those of the control. The plants grown with OPT fiber were deficient in total nitrogen and magnesium when compared with those without fiber amendment, which suggested that nitrogen and minerals in soil might be taken up by changing microflora because of the OPT fibers presence. To confirm differences in the soil microflora, metagenomics analysis was performed on untreated soil and soil from each lignocellulose treatment. The microflora of soils mixed with OPT fiber, cellulose and sugarcane bagasse revealed substantial increases in bacteria such as families Cytophagaceae and Oscillospiraceae, and two major fungal genera, Trichoderma and Trichocladium, that are involved in lignocellulose degradation. OPT fiber resulted in a drastic increase in the ratios and amounts of Trichocladium in the soil when compared with those of cellulose and sugarcane bagasse. These results indicate that unregulated disposal of OPT fiber into plantation areas could result in nutrient loss from soil by increasing the abundance of microorganisms involved in lignocellulose decomposition.

Production of multienzyme by Bacillus aestuarii UE25 using ionic liquid pretreated sugarcane bagasse

The utilization of sugarcane bagasse (SB) in fermentation requires pretreatment processes to render fermentable components available to microorganisms. Pretreatment by using ionic liquids (ILs) is considered promising but the high cost is an impediment in its adoption, therefore, a mixture of IL pretreated and untreated SB was utilized to obtain bacterial multienzyme under solid-state fermentation (SSF). Bacillus aestuarii UE25, a thermophilic strain was utilized for that purpose. Fermentation conditions were optimized by adopting a central composite design. The model showed a good correlation between the predicted and the experimental values for amylase, xylanase, endoglucanase, and β-glucosidase. Volumetric and specific productivity of xylanase (4580 IU ml^-1  h^-1 , 244.25 IU mg^-1 substrate, and 50 IU mg^-1 protein) were higher than the other enzymes. Changes in lignin content and reduced cellulose crystallinity due to IL pretreatment, followed by fermentation, were visualized by scanning electron microscopy, Fourier transform infrared spectroscopy, and Nuclear magnetic resonance. The strategy adopted by utilizing a mixture of IL pretreated and untreated SB under SSF proved promising to obtain high titers of different enzymes simultaneously. Since the bacterial strain used is thermophilic, therefore, the multienzyme can find its application in commercial processes which are carried out at high temperatures.

A Conceptual Framework for Incorporation of Composting in Closed-Loop Urban Controlled Environment Agriculture

Controlled environment agriculture (CEA), specifically advanced greenhouses, plant factories, and vertical farms, has a significant role to play in the urban agri-food landscape through provision of fresh and nutritious food for urban populations. With the push towards improving sustainability of these systems, a circular or closed-loop approach for managing resources is desirable. These crop production systems generate biowaste in the form of crop and growing substrate residues, the disposal of which not only impacts the immediate environment, but also represents a loss of valuable resources. Closing the resource loop through composting of crop residues and urban biowaste is presented. Composting allows for the recovery of carbon dioxide and plant nutrients that can be reused as inputs for crop production, while also providing a mechanism for managing and valorizing biowastes. A conceptual framework for integrating carbon dioxide and nutrient recovery through composting in a CEA system is described along with potential environmental benefits over conventional inputs. Challenges involved in the recovery and reuse of each component, as well as possible solutions, are discussed. Supplementary technologies such as biofiltration, bioponics, ozonation, and electrochemical oxidation are presented as means to overcome some operational challenges. Gaps in research are identified and future research directions are proposed.

Effects of physicochemical properties of Au cyanidation tailings on cyanide microbial degradation

The initial cyanide (CN^-) concentration and amount of co-contaminants in GCTs can inhibit bacterial growth and reduce the CN^--degrading ability of bacteria. Several microorganisms can biotransform a wide range of organic and inorganic industrial contaminants into nontoxic compounds. However, active enzymatic CN^- metabolism processes are mostly constrained by the physical and chemical characteristics of GCTs. High concentrations of toxic metal co-contaminants, such as, Pb, and Cr, and factors, such as pH, temperature, and oxygen concentration create oxidative stress and limit the CN^--degrading potential of cyanotrophic strains. The effects of such external and internal factors on the CN^--degrading ability of bacteria hinder the selection of suitable microorganisms for CN^- biodegradation. Therefore, understanding the effects of the physicochemical properties of GCTs on cyanobacteria strains can help identify suitable microbes and favorable environmental conditions to promote microbial growth and can also help design efficient CN^- biodegradation processes. In this review, we present a detailed analysis of the physicochemical properties of GCTs and their effects on microbial CN^- degradation.

Performance evaluation of a small-scale digester for achieving decentralised management of waste

The performance of a small-scale prototype digestion plant (7.2 m³ working volume) intended for decentralised operation was evaluated considering energy efficiency and technical suitability for biogas valorisation in producing electrical and thermal energy. The digester operated in recirculation mode to enhance organic matter conversion and improve volatile solid degradation. An energy assessment of the process assumed the incorporation of a combined heat and power (CHP) unit. The coefficient of overall performance of the plant for electrical energy (COP_el) was 0.95 - this values was estimated at an electrical efficiency of 22.5% and represents the ratio between energy production and consumption - for a methane yield of 360 L/kg VS and an organic loading rate (OLR) of 1.06 g VS/L d. This parameter was slightly lower than the unit thus indicating that the micro-plant was close to attaining self-sufficiency regarding electrical energy use. The temperature increase of the feed to process conditions supposed a significant amount of thermal energy which highly compromised the efficiency when operating at low organic load, thus accounting for more than 80% of the total energy demand of the installation. When the energy assessment of the process was performed at higher OLR of 2.7 g VS/ L d, the resulting COP_el value was1.68, demonstrating the feasibility of this configuration for decentralised digestion.

Lignocellulosic crop residue composting by cellulolytic nitrogen-fixing bacteria: A novel tool for environmental sustainability

Lignocellulosic crop residue (LCCR) composting is a cost-effective and sustainable approach for addressing environmental pollution associated with open biomass burning and application of chemical fertilizers in agriculture. The value-added bio-product of the composting process contributes to the improvement of the soil properties and plant growth in an environment-friendly way. However, the conventional process employed for composting LCCRs is slow and becomes an impediment for farmers who plant two or three crops a year. This concern has led to the development of different techniques for rapid composting of LCCRs. The use of cellulolytic nitrogen-fixing microorganisms for composting has emerged as a promising method for enhancing LCCR composting and quality of the compost. Therefore, this review addresses the recent progress on the potential use of cellulolytic nitrogen-fixing bacteria (CNFB) for LCCR composting and discusses various applications of nutrient-rich compost for sustainable agriculture to increase crop yields in a nature-friendly way. This knowledge of bacteria with both cellulose-degrading and nitrogen-fixing activities is significant with respect to rapid composting, soil fertility, plant growth and sustainable management of the lignocellulosic agricultural waste and it provides a means for the development of new technology for sustainability.

Assessment of biowaste composting process for industrial support tool development through macro data approach

This study aims to assess composting efficiency and quality of compost through the study of the parameters of the Catalan Waste Agency (ARC) data-base by developing indicators useful for industrial sector. The study includes 17 composting plants for an 8-years period (2010-2017), the quantities of materials treated and generated in these plants: biowaste, yard trimmings, refuse and compost, as well as chemical characterization of compost: moisture, total organic matter, organic nitrogen, pH, electrical conductivity, self-heating test, pollutants and ammonium. Plant were sorted into 4 size classes depending on size capacity and into 4 technologies employed during thermophilic phase. Different indicators were developed related to improper fraction content, yard trimmings ratio, mass losses, compost production, refuse generation and plant saturation. The main average results indicate that improper fraction is 10%, process losses 68%, refuse generated 25% and saturation 79%. Differences were observed in size and technology; for instance, smaller plants presented lower improper content, refuse and saturation and higher losses while plants with turned windrows during decomposition presented higher improper, yard trimmings ratio and plants with vessel technology showed lower losses and higher saturation. Also, the compost quality is higher if the plant saturation and improper fraction are below 90% and 7%, respectively. The indicators were useful to assess the process and were related to the compost quality obtained.

Optimization of Food Waste and Biochar In-Vessel Co-Composting

As bulking agents (BA) affect the composting process, this work examined the impact of combinations of different organic components in order to obtain an efficient co-substrate for food waste (FW) in-vessel composting. To boost the occurrence of microorganisms inhabiting the compost, mature compost was firstly coupled with wheat straw, added to FW, and considered as a control (BC0). Then, two trials (BC10, BC20) including 10% and 20% of biochar were monitored. The results indicated that the temperature of the amended bioreactors was notably increased compared to the unamended one. Thermophilic temperatures were achieved at 14, 34, and 78 h after the experimental setup for BC20, BC10, and BC0, which lasted for 14, 17, and 12 days, respectively. When it came to an assessment of maturity and stability, the quality of the compost was evaluated against several indicators and compared with the compost quality standards of the UK, France, Canada, the USA, Poland, and Germany. BC10 illustrated a high-quality product in relation to the heavy metal concentration, a C:N ratio which reached 14.97, an AT4 which was lower than 6 (4.36 mg O2/g TS), and a nitrification index of 2.61 (<3). Consequently, the addition of 10% of biochar as a co-substrate showed an improvement of the process evolution and the characteristics of the biofertilizer produced.