Microbial community-based protein production from wastewater for animal feed applications

Characterization of cotton stalk as a lignocellulosic feedstock for single-cell protein production

Cotton stalk, an important by-product of cotton farming, is challenging in lignocellulosic feedstock application due to the limited understanding of their compositional and lignin structural characteristics. This study elucidates the composition of lignocellulose components and fundamental lignin structural features of cotton stalk. Lignocellulosic hydrolysates were prepared from various cotton stalk parts and used for single-cell protein production. As a proof of concept, cotton stalk hydrolysates were successfully converted into single-cell protein using the superior microbial host, Candida utilis ACCC20060, owing to its favorable sugar consumption efficiency and high protein quality. The highest SCP concentration of 5.74 g/L was obtained, yielding 0.23 g/g from the lignocellulose-derived sugars released from cotton stalk roots. This study provides valuable references for cotton stalk utilization toward lignocellulosic feedstock application and introduces a promising microbial host for single-cell protein production from such feedstocks.

Recycling potential of Cupriavidus necator for life support in space: Production of SCPs from volatile fatty acid and urea mixture

The International Space Station currently requires four annual replenishments for food supply, a practice that won't be feasible for deep space missions due to the greater distances. Based on the design of closed ecological life support systems, two waste streams were identified: urea from the crew urine, volatile fatty acids (VFAs) from a first stage of anaerobic digestion of waste. The objective of this study was to assess the ability of bacterium Cupriavidus necator to produce single cell protein on urea and VFAs. Thus, the effect of carbon sources (glucose vs VFAs) and the dilution rate on the biomass composition was determined in continuous cultures. Complete transformation of the carbon source into protein-rich biomass was achieved up to 78 % cell dry weight (CDW). For both carbon sources, the protein content increased from 55.0 %CDW to 78 %CDW with a decrease in the dilution rate. Conversely, the nucleic acid and polyhydroxyalkanoate contents decreased with the dilution rate from 8.8 %CDW to 4.8 %CDW and 9.8 %CDW to 0.6 %CDW respectively. Working at a low dilution rate seems to be a good way to maximize protein content while minimizing unwanted nucleic acids and polyhydroxyalkanoates.

Current trends and possibilities of typical microbial protein production approaches: a review

Global population growth and demographic restructuring are driving the food and agriculture sectors to provide greater quantities and varieties of food, of which protein resources are particularly important. Traditional animal-source proteins are becoming increasingly difficult to meet the demand of the current consumer market, and the search for alternative protein sources is urgent. Microbial proteins are biomass obtained from nonpathogenic single-celled organisms, such as bacteria, fungi, and microalgae. They contain large amounts of proteins and essential amino acids as well as a variety of other nutritive substances, which are considered to be promising sustainable alternatives to traditional proteins. In this review, typical approaches to microbial protein synthesis processes were highlighted and the characteristics and applications of different types of microbial proteins were described. Bacteria, fungi, and microalgae can be individually or co-cultured to obtain protein-rich biomass using starch-based raw materials, organic wastes, and one-carbon compounds as fermentation substrates. Microbial proteins have been gradually used in practical applications as foods, nutritional supplements, flavor modifiers, and animal feeds. However, further development and application of microbial proteins require more advanced biotechnological support, screening of good strains, and safety considerations. This review contributes to accelerating the practical application of microbial proteins as a promising alternative protein resource and provides a sustainable solution to the food crisis facing the world.

Creating Single-Cell Protein-Producing Bacillus subtilis Mutants Using Chemical Mutagen and Amino Acid Inhibitors

Due to population growth and climate changes, there is a rising need for alternative food and protein sources to reduce protein scarcity and the environmental impact of food industries. Single-cell proteins (SCPs) have the potential to partially or fully substitute plant- and animal-derived dietary proteins. Bacillus subtilis is an appealing bacterium for SCP production because of its fast growth and ability to obtain high protein and essential amino acid (AA) content in its biomass. It is also capable of utilizing a wide range of substrates. B. subtilis attractiveness and efficiency can be further enhanced using mutagenesis. In this study, a novel approach to creating mutant strains with enhanced protein and AA content was experimentally validated. The method is based on the application of AA inhibitors for selective pressure to ensure the growth of mutants with enhanced protein and/or AA synthesis capacity. For AA inhibitors, three herbicides were used: glufosinate-ammonium (GA), L-methionine sulfoximine (MSO), and S-(2-aminoethyl)-L-cysteine (AEC). Initially, AA inhibitor doses for the complete inhibition of wild-type (WT) B. subtilis strain were determined. Then, B. subtilis was treated with EMS chemical mutagen and created mutants were cultivated on a medium containing inhibitory dose of AA inhibitors. Growing samples were selected, analyzed, and compared. The optimal inhibitory concentrations of herbicides for mutant selection were 0.05-0.4 M for GA, 0.01-0.05 M for MSO, and 0.2 M for AEC. The best-performing mutants were selected when using GA-improvement of 7.1 times higher biomass content, 1.5 times higher protein concentration, 1.2 times higher AA content, and 1.2 times higher essential AA index was achieved in comparison with WT B. subtilis. Enhanced mutants were also successfully selected when using MSO and AEC. This study demonstrates the potential of using AA inhibitors for the selection of mutants with improved protein and AA profiles.

Evaluation of various carbon sources on ammonium assimilation and denitrifying phosphorus removal in a modified anaerobic-anoxic-oxic process from low-strength wastewater

A pilot-scale continuous-flow modified anaerobic-anoxic-oxic (MAAO) process examined the impact of external carbon sources (acetate, glucose, acetate/propionate) on ammonium assimilation, denitrifying phosphorus removal (DPR), and microbial community. Acetate exhibited superior efficacy in promoting the combined process of ammonia assimilation and DPR, enhancing both to 50.0 % and 60.0 %, respectively. Proteobacteria and Bacteroidota facilitated ammonium assimilation, while denitrifying phosphorus-accumulating organisms (DPAOs) played a key role in nitrogen (N) and phosphorus (P) removal. Denitrifying glycogen-accumulating organisms (DGAOs) aided N removal in the anoxic zone, ensuring stable N and P removal and recovery. Acetate/propionate significantly enhanced DPR (77.7 %) and endogenous denitrification (37.9 %). Glucose favored heterotrophic denitrification (29.6 %) but had minimal impact on ammonium assimilation. These findings provide valuable insights for wastewater treatment plants (WWTPs) seeking efficient N and P removal and recovery from low-strength wastewater.

A comprehensive report on valorization of waste to single cell protein: strategies, challenges, and future prospects

The food insecurity due to a vertical increase in the global population urgently demands substantial advancements in the agricultural sector and to identify sustainable affordable sources of nutrition, particularly proteins. Single-cell protein (SCP) has been revealed as the dried biomass of microorganisms such as algae, yeast, and bacteria cultivated in a controlled environment. Production of SCP is a promising alternative to conventional protein sources like soy and meat, due to quicker production, minimal land requirement, and flexibility to various climatic conditions. In addition to protein production, it also contributes to waste management by converting it into food and feed for both human and animal consumption. This article provides an overview of SCP production, including its benefits, safety, acceptability, and cost, as well as limitations that constrains its maximum use. Furthermore, this review criticizes the downstream processing of SCP, encompassing cell wall disruption, removal of nucleic acid, harvesting of biomass, drying, packaging, storage, and transportation. The potential applications of SCP, such as in food and feed as well as in the production of bioplastics, emulsifiers, and as flavoring agents for baked food, soup, and salad, are also discussed.

Review of the mechanisms involved in dissimilatory nitrate reduction to ammonium and the efficacies of these mechanisms in the environment

Dissimilatory nitrate reduction to ammonium (DNRA) is currently of great interest because it is an important method for recovering nitrogen from wastewater and offers many advantages, over other methods. A full understanding of DNRA requires the mechanisms, pathways, and functional microorganisms involved to be identified. The roles these pathways play and the effectiveness of DNRA in the environment are not well understood. The objectives of this review are to describe our current understanding of the molecular mechanisms and pathways involved in DNRA from the substrate transfer perspective and to summarize the effects of DNRA in the environment. First, the mechanisms and pathways involved in DNRA are described in detail. Second, our understanding of DNRA by actinomycetes is reviewed and gaps in our understanding are identified. Finally, the effects of DNRA in the environment are assessed. This review will help in the development of future research into DNRA to promote the use of DNRA to treat wastewater and recover nitrogen.

Integration of ammonium assimilation with denitrifying phosphorus removal for efficient nutrient management in wastewater treatment

Nutrient removal from sewage is transitioning to nutrient recovery. However, biological treatment technologies to remove and recover nutrients from domestic sewage are still under investigation. This study delved into the integration of ammonium assimilation with denitrifying phosphorus removal (DPR) as a method for efficient nutrient management in sewage treatment. Results indicated this approach eliminated over 80 % of the nitrogen in the influent, simultaneously recovering over 60 % of the nitrogen as the activated sludge through ammonia assimilation, and glycerol facilitated this process. The nitrification/denitrifying phosphorus removal ensured the stability of both nitrogen and phosphorus removal. The phosphorus removal rate exceeded 96 %, and the DPR rate reached over 90 %. Network analysis highlighted a stable community structure with Proteobacteria and Bacteroidota driving ammonium assimilation. The synergistic effect of fermentation bacteria, denitrifying glycogen-accumulating organisms, and denitrifying phosphorus-accumulating organisms contributed to the stability of nitrogen and phosphorus removal. This approach offers a promising method for sustainable nutrient management in sewage treatment.

Production of safe cyanobacterial biomass for animal feed using wastewater and drinking water treatment residuals

The growing interest in microalgae and cyanobacteria biomass as an alternative to traditional animal feed is hindered by high production costs. Using wastewater (WW) as a cultivation medium could offer a solution, but this approach risks introducing harmful substances into the biomass, leading to significant safety concerns. In this study, we addressed these challenges by selectively extracting nitrates and phosphates from WW using drinking water treatment residuals (DWTR) and chitosan. This method achieved peak adsorption capacities of 4.4 mg/g for nitrate and 6.1 mg/g for phosphate with a 2.5 wt% chitosan blend combined with DWTR-nitrogen. Subsequently, these extracted nutrients were employed to cultivate Spirulina platensis, yielding a biomass productivity rate of 0.15 g/L/d, which is comparable to rates achieved with commercial nutrients. By substituting commercial nutrients with nitrate and phosphate from WW, we can achieve a 18 % reduction in the culture medium cost. While the cultivated biomass was initially nitrogen-deficient due to low nitrate levels, it proved to be protein-rich, accounting for 50 % of its dry weight, and contained a high concentration of free amino acids (1260 mg/g), encompassing all essential amino acids. Both in vitro and in vivo toxicity tests affirmed the biomass's safety for use as an animal feed component. Future research should aim to enhance the economic feasibility of this alternative feed source by developing efficient adsorbents, utilizing cost-effective reagents, and implementing nutrient reuse strategies in spent mediums.

Microbial community-based protein from soybean-processing wastewater as a sustainable alternative fish feed ingredient

As the global demand for food increases, aquaculture plays a key role as the fastest growing animal protein sector. However, existing aquafeeds contain protein ingredients that are not sustainable under current production systems. We evaluated the use of microbial community-based single cell protein (SCP), produced from soybean processing wastewater, as a partial fishmeal protein substitute in juvenile Asian seabass (Lates calcarifer). A 24-day feeding trial was conducted with a control fishmeal diet and a 50% fishmeal replacement with microbial community-based SCP as an experimental group, in triplicate tanks containing 20 fish each. Both diets met the protein, essential amino acids (except for lysine), and fat requirements for juvenile Asian sea bass. The microbial composition of the SCP was dominated by the genera Acidipropionibacterium and Propioniciclava, which have potential as probiotics and producers of valuable metabolites. The growth performance in terms of percent weight gain, feed conversion ratio (FCR), specific growth rate (SGR), and survival were not significantly different between groups after 24 days. The experimental group had less variability in terms of weight gain and FCR than the control group. Overall, microbial community-based protein produced from soybean processing wastewater has potential as a value-added feed ingredient for sustainable aquaculture feeds.

Production of single cell protein rich in potassium by Nectaromyces rattus using biogas slurry and molasses

Single-cell protein (SCP) is a vital supplement for animal protein feed. This study utilized biogas slurry and sugarcane molasses to ferment Nectaromyces rattus for the production of SCP. The optimal batch fermentation conditions were obtained in a 5L jar with a tank pressure of 0.1 MPa, an initial speed of 300 rpm, and an inoculum volume of 30%. The highest cell dry weight concentrations of the fed-batch fermentation without reflux and the fed-batch fermentation with reflux were 46.33 g/L and 29.71 g/L, respectively. The nitrogen conversion rates (47.05% and 44.12%) and the cell yields of total organic carbon (1 g/g and 1.17 g/g) of both fermentation modes were compared. The SCP contained 42.32% amino acids. Its high concentrations of potassium (19859.96 mg/kg) and phosphorus (7310.44 mg/kg) present a novel approach for the extraction of these essential nutrients from biogas slurry. The enrichment of K was related to the H+ efflux and sugar transport.

Biofilm reactors for the treatment of used water in space:potential, challenges, and future perspectives

Water is not only essential to sustain life on Earth, but also is a crucial resource for long-duration deep space exploration and habitation. Current systems in space rely on the resupply of water from Earth, however, as missions get longer and move farther away from Earth, resupply will no longer be a sustainable option. Thus, the development of regenerative reclamation water systems through which useable water can be recovered from "waste streams" (i.e., used waters) is sorely needed to further close the loop in space life support systems. This review presents the origin and characteristics of different used waters generated in space and discusses the intrinsic challenges of developing suitable technologies to treat such streams given the unique constrains of space exploration and habitation (e.g., different gravity conditions, size and weight limitations, compatibility with other systems, etc.). In this review, we discuss the potential use of biological systems, particularly biofilms, as possible alternatives or additions to current technologies for water reclamation and waste treatment in space. The fundamentals of biofilm reactors, their advantages and disadvantages, as well as different reactor configurations and their potential for use and challenges to be incorporated in self-sustaining and regenerative life support systems in long-duration space missions are also discussed. Furthermore, we discuss the possibility to recover value-added products (e.g., biomass, nutrients, water) from used waters and the opportunity to recycle and reuse such products as resources in other life support subsystems (e.g., habitation, waste, air, etc.).

Resource recovery and valorization of food wastewater for sustainable development: An overview of current approaches

The food processing industry is one of the world's largest consumers of potable water. Agri-food wastewater systems consume about 70% of the world's fresh water and cause at least 80% of deforestation. Food wastewater is characterized by complex composition, a wide range of pollutants, and fluctuating water quality, which can cause huge environmental pollution problems if discharged directly. In recent years, food wastewater has attracted considerable attention as it is considered to have great prospects for resource recovery and reuse due to its rich residues of nutrients and low levels of harmful substances. This review explored and compared the sources and characteristics of different types of food wastewater and methods of wastewater treatment. Particular attention was paid to the different methods of resource recovery and reuse of food wastewater. The diversity of raw materials in the food industry leads to different compositional characteristics of wastewater, which determine the choice and efficiency of wastewater treatment methods. Physicochemical methods, and biological methods alone or in combination have been used for the efficient treatment of food wastewater. Current approaches for recycling and reuse of food wastewater include culture substrates, agricultural irrigation, and bio-organic fertilizers, recovery of high-value products such as proteins, lipids, biopolymers, and bioenergy to alleviate the energy crisis. Food wastewater is a promising substrate for resource recovery and reuse, and its valorization meets the current international policy requirements regarding food waste and environment protection, follows the development trend of the food industry, and is also conducive to energy conservation, emission reduction, and economic development. However, more innovative biotechnologies are necessary to advance the effectiveness of food wastewater treatment and the extent of resource recovery and valorization.

In-situ microbial protein production by using nitrogen extracted from multifunctional bio-electrochemical system

Upgrading of waste nitrogen sources is considered as an important approach to promote sustainable development. In this study, a multifunctional bio-electrochemical system with three chambers was established, innovatively achieving 2.02 g/L in-situ microbial protein (MP) production via hydrogen-oxidizing bacteria (HOB) in the protein chamber (middle chamber), along with over 2.9 L CO2/(L·d) consumption rate. Also, 69% chemical oxygen demand was degraded by electrogenic bacteria in the anode chamber, resulting in the 394.67 J/L electricity generation. Focusing on the NH4+-N migration in the system, the current intensity contributed 4%-9% in the anode and protein chamber, whereas, the negative effect of -6.69% on contribution was shown in the cathode chamber. On the view of kinetics, NH4+-N migration in anode and cathode chambers was fitted well with Levenberg-Marquardt equation (R2 > 0.92), along with the well-matched results of HOB growth in the protein chamber based on Gompertz model (R2 > 0.99). Further evaluating MPs produced by HOB, 0.45 g/L essential amino acids was detected, showing the better amino acid profile than fish and soybean. Multifunctional bio-electrochemical system revealed the economic potential of producing 6.69 €/m3 wastewater according to a simplified economic evaluation.

Microbial community-based production of single cell protein from soybean-processing wastewater of variable chemical composition

The use of food-processing wastewaters to produce microbial biomass-derived single cell protein (SCP) is a sustainable way to meet the global food demand. Microbial community-based approaches to SCP production have the potential benefits of lower costs and greater resource recovery compared to pure cultures, yet they have received scarce attention. Here, SCP production from soybean-processing wastewaters using their existent microbial communities was evaluated. Six sequencing batch reactors of 4.5-L working volume were operated at 30 °C for 34 d in cycles consisting of 3-h anaerobic and 9-h aerobic phases. Four reactors received no microbial inoculum and the remaining two were amended with 1.5 L of a mixed culture from a prior SCP production cycle. Reactors produced more SCP when fed with wastewaters of higher soluble total Kjeldahl nitrogen (sTKN) content. The protein yield in biomass ranged from 0.53 to 3.13 g protein/g sTKN, with a maximum protein content of 50 %. The average removal of soluble chemical oxygen demand (sCOD) and soluble total nitrogen (sTN) was 92 % and 73 %, respectively. Distinct microbial genera were enriched in all six bioreactors, with Azospirillum, Rhodobacter, Lactococcus, and Novosphingobium dominating. The study showed that constituents in soybean wastewater can be converted to SCP and demonstrated the effect of variable influent wastewater composition on SCP production.

Dissolution rate and growth performance reveal struvite as a sustainable nutrient source to produce a diverse set of microbial protein

To provide for the globally increasing demand for proteinaceous food, microbial protein (MP) has the potential to become an alternative food or feed source. Phosphorus (P), on the other hand, is a critical raw material whose global reserves are declining. Growing MP on recovered phosphorus, for instance, struvite obtained from wastewater treatment, is a promising MP production route that could supply protein-rich products while handling P scarcity. The aim of this study was to explore struvite dissolution kinetics in different MP media and characterize MP production with struvite as sole P-source. Different operational parameters, including pH, temperature, contact surface area, and ion concentrations were tested, and struvite dissolution rates were observed between 0.32 and 4.7 g P/L/d and a solubility between 0.23 and 2.22 g P-based struvite/L. Growth rates and protein production of the microalgae Chlorella vulgaris and Limnospira sp. (previously known as Arthrospira sp.), and the purple non‑sulfur bacterium Rhodopseudomonas palustris on struvite were equal to or higher than growth on conventional potassium phosphate. For aerobic heterotrophic bacteria, two slow-growing communities showed decreased growth on struvite, while the growth was increased for a third fast-growing one. Furthermore, MP protein content on struvite was always comparable to the one obtained when grown on standard media. Together with the low content in metals and micropollutants, these results demonstrate that struvite can be directly applied as an effective nutrient source to produce fast-growing MP, without any previous dissolution step. Combining a high purity recovered product with an efficient way of producing protein results in a strong environmental win-win.

High-yield production of single-cell protein from starch processing wastewater using co-cultivation of yeasts

Single-cell protein (SCP) from potato starch processing wastewater (PSPW) shows great potential against protein scarcity and unsustainable production of plant and animal proteins. In this study, five yeasts were selected to conduct a series of PSPW fermentation for obtaining high-value SCP by optimizing fermentation conditions. The yeast combination was optimized as Candida utilis, Geotrichum candidum and Candida tropicalis with the volume proportion of 9:5:1. The inoculum size, temperature, rotation speed and initial pH were optimized at 12 %, 24℃, 200 r·min^-1 and ∼ 4.13 (natural pH), respectively. At the optimal conditions, SCP yield of 3.06 g·L^-1 and water-soluble protein of 17.32 % were obtained with the chemical oxygen demand removal of 56.9 %. A resource-recycling process of PSPW was proposed by coupling yeast fermentation and up-flow anaerobic sludge blanket (UASB) treatment to achieve simultaneous high-level organic removal and SCP production, which could be a promising alternative technology for PSPW treatment.

Biowaste upcycling into second-generation microbial protein through mixed-culture fermentation

Securing a sustainable protein supply at the global level is among the greatest challenges currently faced by humanity. Alternative protein sources, such as second-generation microbial protein (MP), could give rise to innovative circular bioeconomy practices, synthesizing high-value bioproducts through the recovery and upcycling of resources from overabundant biowastes and residues. Within such a multi-feedstock biorefinery scenario, the wide range of microbial pathways and networks that characterize mixed microbial cultures, offers interesting and not yet fully explored advantages over conventional monoculture-based processes. In this review, we combine a comprehensive analysis of waste recovery platforms for second-generation MP production with a critical evaluation of the research gaps and potentials offered by mixed culture-based MP fermentation processes.

Toward the Transition of Agricultural Anaerobic Digesters into Multiproduct Biorefineries

Anaerobic digestion allows for the proper management of agro-waste, including manure. Currently, more than 18,000 anaerobic digestion plants are under operation in EU, 80% of which are employed in the rural context. Tariff schemes for power generation from biogas produced during anaerobic digestion of agricultural feedstocks in Germany, Italy and Austria are coming to an end and new approaches are needed to exploit the existing infrastructures. Digesters in the rural context can be implemented and modified to be transformed into sustainable multi-feedstock and multi-purpose biorefineries for the production of energy, nutrients, proteins, bio-chemicals such as carboxylic acids, polyesters and proteins. This paper describes how the transition of agricultural anaerobic digesters into multi-products biorefineries can be achieved and what are the potential benefits originating from the application of a pilot scale platform able to treat cow manure and other crop residues while producing volatile fatty acids, polyhydroxyalkanoates, microbial protein material, hydrogen, methane and a concentrated liquid stream rich in nitrogen, potassium and phosphorus.

Innovations and developments in single cell protein: Bibliometric review and patents analysis

Background

Global demand for food products derived from alternative proteins and produced through sustainable technological routes is increasing. Evaluation of research progress, main trends and developments in the field are valuable to identify evolutionary nuances.

Methods

In this study, a bibliometric analysis and search of patents on alternative proteins from fermentation processes was carried out using the Web of Science and Derwent World Patents Index^™ databases, using the keywords and Boolean operators "fermentation" AND "single cell protein" OR "single-cell protein." The dataset was processed and graphics generated using the bibliometric software VOSviewer and OriginPro 8.1.

Results

The analysis performed recovered a total of 360 articles, of which 271 were research articles, 49 literature review articles and 40 publications distributed in different categories, such as reprint, proceedings paper, meeting abstract among others. In addition, 397 patents related to the field were identified, with China being the country with the largest number of publications and patents deposits. While this topic is largely interdisciplinary, the majority of work is in the area of Biotechnology Applied Microbiology, which boasts the largest number of publications. The area with the most patent filings is the food sector, with particular emphasis on the fields of biochemistry, beverages, microbiology, enzymology and genetic engineering. Among these patents, 110 are active, with industries or companies being the largest depositors. Keyword analysis revealed that the area of study involving single cell protein has included investigation into types of microorganisms, fermentation, and substrates (showing a strong trend in the use of agro-industrial by-products) as well as optimization of production processes.

Conclusion

This bibliometric analysis provided important information, challenges, and trends on this relevant subject.

Intracellular and extracellular sources, transformation process and resource recovery value of proteins extracted from wastewater treatment sludge via alkaline thermal hydrolysis and enzymatic hydrolysis

Excess sludge contains a large amount of protein and can be recycled to prepare industrial foaming agents, foliar fertilizers and other high value-added products. The optimization and effects of sludge protein extraction using the common processes of alkaline thermal hydrolysis (ATH) and enzymatic hydrolysis (EH) have been widely studied. This study focused on the protein extraction mechanisms of ATH and EH by comparing the ratio of intracellular to extracellular proteins extracted and the transformation of protein during the hydrolysis process. The extracellular protein content was 82.6 ± 5.07 mg/g VSS, and the content of intracellular protein extracted using ATH and EH was 376.9 mg/g VSS and 127.9 mg/g VSS, respectively. The ratio of intracellular to extracellular proteins extracted by ATH and EH was 4.5 and 1.5, respectively, indicating that ATH had a much better wall-breaking effect that allowed it to extract abundant intracellular proteins. The protein content obtained from ATH continuously increased over time, and approximately 38 % of proteins were further hydrolyzed to polypeptides. In contrast, the relatively low protein content extracted by EH possibly limited subsequent polypeptide hydrolysis, but subsequent hydrolysis to amino acids was not noticeably affected and was linearly correlated with the amount of protein extracted. An analysis of the recycling convenience and value of extracted proteins showed that the sludge dewatering performance increased by 86.7 % and 45.5 % after ATH and EH treatment, respectively, which was conducive to the subsequent separation of the protein solution. The protein extracted by ATH, with a large amount of peptides, would be beneficial to prepare industrial foaming agents, while the protein extracted by EH was rich in free amino acids and could be used to prepare foliar fertilizer.

Nitrogen recovery from wastewater by microbial assimilation - A review

The increased nitrogen (N) input with low utilization rate in artificial N management has led to massive reactive N (Nr) flows, putting the Earth in a high-risk state. It is essential to recover and recycle Nr during or after Nr removal from wastewater to reduce N input while simultaneously mitigate Nr pollution in addressing the N stress. However, mechanisms for efficient Nr recovery during or after Nr removal remain unclear. Here, the occurrence of N risk and progress in wastewater treatment in recent years as well as challenges of the current technologies for N recovery from wastewater were reviewed. Through analyzing N conversion fluxes in biogeochemical N-cycling networks, microbial N assimilation through photosynthetic and heterotrophic microorganisms was highlighted as promising alternative for synergistic N removal and recovery in wastewater treatment. In addition, the prospects and gaps of Nr recovery from wastewater through microbial assimilation are discussed.

Effects of Solid-State Fermentation Pretreatment with Single or Dual Culture White Rot Fungi on White Tea Residue Nutrients and In Vitro Rumen Fermentation Parameters

Fermentation of agricultural by-products by white rot fungi is a research hotspot in the development of ruminant feed resources. The aim of this study was to investigate the potential of the nutritional value and rumen fermentation properties of white tea residue fermented at different times, using single and dual culture white rot fungal species. Phanerochaete chrysosporium, Pleurotus ostreatus, and Phanerochaete chrysosporium + Pleurotus ostreatus (dual culture) solid-state fermented white tea residue was used for 4 weeks, respectively. The crude protein content increased significantly in all treatment groups after 4 weeks. Total extractable tannin content was significantly decreased in all treatment groups (p < 0.01). P. chrysosporium and dual culture significantly reduced lignin content at 1 week. The content of NH3-N increased in each treatment group (p < 0.05). P. chrysosporium treatment can reduce the ratio of acetic to propionic and improve digestibility. Solid state fermentation of white tea residue for 1 week using P. chrysosporium was the most desirable.

Microalgae-bacteria consortium for wastewater treatment and biomass production

The diversity of microalgae and bacteria allows them to form a complementary consortium for efficient wastewater treatment and nutrient recovery. This review highlights the potential of wastewater-derived microalgal biomass as a renewable feedstock for producing animal feed, biofertilisers, biofuel, and many valuable biochemicals. Data corroborated from this review shows that microalgae and bacteria can thrive in many environments. Microalgae are especially effective at utilising nutrients from the water as they grow. This review also consolidates the current understanding of microalgae characteristics and their interactions with bacteria in a consortium system. Recent studies on the performance of only microalgae and microalgae-bacteria wastewater treatment are compared and discussed to establish a research roadmap for practical implementation of the consortium systems for various wastewaters (domestic, industrial, agro-industrial, and landfill leachate wastewater). In comparison to the pure microalgae system, the consortium system has a higher removal efficiency of up to 15% and shorter treatment time. Additionally, this review addresses a variety of possibilities for biomass application after wastewater treatment.

Biogranulation process facilitates cost-efficient resources recovery from microalgae-based wastewater treatment systems and the creation of a circular bioeconomy

Energy self-sufficient wastewater treatment designs can reduce net energy consumption and achieve resources recovery. Microalgae are regarded as a promising candidate for developing a circular bioeconomy in wastewater treatment plants (WWTPs) due to its potential for simultaneous wastewater remediation and high value-added materials production. Much effort has been made to overcome the high production costs for microalgae; however, biomass harvesting still remains as the bottleneck for its large-scale application. In this study, the novel biogranulation system facilitating easier and faster microalgae harvesting was firstly compared with the conventional suspended culture for energy-efficiency and sustainability assessment on microalgae (Ankistrodesmus falcatus var. acicularis) cultivation using the synthetic anaerobic digestion liquor. Results demonstrated that the biogranulation system enhanced volumetric biomass productivity (223.17 ± 11.82 g/m³/day) by about 4.4 times compared to that from the suspended system (41.57 ± 2.08 g/m³/day) under the same environmental conditions. It was noticed that lipids, carbohydrates and proteins were accumulated in microalgae cells along with nutrients remediation, and the microalgae granules with much higher proteins content (313.28 ± 26.67 mg/g-VSS) could be easily harvested through 2 min gravity sedimentation with little impact on the contents of carbohydrates and lipids. In the whole cultivation and harvesting process, the biomass mass-based electricity consumption and footprint demand by the biogranulation system were reduced by 58% and 76%, respectively. Results from this study provide a cost-effective and sustainable approach for microalgae in the treatment of nutrients rich digestion liquor with simultaneous production of valuable biomaterials.

Potential use of microbial engineering in single-cell protein production

Single-cell proteins (SCPs) have been widely used in human food and animal feed applications, still, there are challenges in their production and commercialization. Recently, advances in microbial synthetic biology, genomic engineering, and biofoundry technologies have offered capabilities to effectively and rapidly engineer microorganisms for improving the productivity, nutritional, and functional quality of SCPs. In this review, we discuss various synthetic biology, genomic engineering, and biofoundry tools that can be harnessed for SCP production and genetic modification. We also describe the current and potential applications of genetic modification in producing intermediate feedstocks, as well as biomass-based and multifunctional SCPs. Finally, we discuss the technological and policy-control related challenges encountered when deploying genetic modification in SCP production for animal feed and human food applications.

The removal of ammonia nitrogen via heterotrophic assimilation by a novel Paracoccus sp. FDN-02 under anoxic condition

A novel strain FDN-02 was isolated from a sequencing batch biofilm reactor. FDN-02 was identified as Paracoccus sp., and the Genbank Sequence_ID was MW652628. Comparing with the removal efficiency of ammonia nitrogen (NH₄⁺-N) by bacterium FDN-02 under different growth conditions, the optimal initial pH, carbon source, and C/N ratio were 7.0, sucrose, and 16, respectively. The maximum removal efficiency and rate of NH₄⁺-N were respectively 96.2% and 10.06 mg-N/L/h within 8 h under anoxic condition when the concentration of NH₄⁺-N was 44.87 mg/L. Specifically, 71.9% of NH₄⁺-N was utilized by strain FDN-02 through heterotrophic assimilation to synthetize organic nitrogen, and approximately 24.1% of NH₄⁺-N was lost in the form of gaseous nitrogen without the emission of nitrous oxide. Bacterium FDN-02 was also found to be a denitrifying organism, and nitrate nitrogen and nitrite nitrogen of lower concentrations were removed by denitrification after the enlargement of biomass. Further investigation showed that the biomass after the removal of NH₄⁺-N by strain FDN-02 had resource utilization potential, and the contents of proteins and amino acids were 635 and 192.97 mg/g, respectively, especially for the usage as an alternative nutrient source for livestock and organic fertilizers. This study provided a promising environmentally friendly biological treatment method for the removal of NH₄⁺-N in the wastewater.

Engineering microbial technologies for environmental sustainability: choices to make

Microbial technologies have provided solutions to key challenges in our daily lives for over a century. In the debate about the ongoing climate change and the need for planetary sustainability, microbial ecology and microbial technologies are rarely considered. Nonetheless, they can bring forward vital solutions to decrease and even prevent long-term effects of climate change. The key to the success of microbial technologies is an effective, target-oriented microbiome management. Here, we highlight how microbial technologies can play a key role in both natural, i.e. soils and aquatic ecosystems, and semi-natural or even entirely human-made, engineered ecosystems, e.g. (waste) water treatment and bodily systems. First, we set forward fundamental guidelines for effective soil microbial resource management, especially with respect to nutrient loss and greenhouse gas abatement. Next, we focus on closing the water circle, integrating resource recovery. We also address the essential interaction of the human and animal host with their respective microbiomes. Finally, we set forward some key future potentials, such as microbial protein and the need to overcome microphobia for microbial products and services. Overall, we conclude that by relying on the wisdom of the past, we can tackle the challenges of our current era through microbial technologies.

Waste-to-nutrition: a review of current and emerging conversion pathways

Residual biomass is acknowledged as a key sustainable feedstock for the transition towards circular and low fossil carbon economies to supply whether energy, chemical, material and food products or services. The latter is receiving increasing attention, in particular in the perspective of decoupling nutrition from arable land demand. In order to provide a comprehensive overview of the technical possibilities to convert residual biomasses into edible ingredients, we reviewed over 950 scientific and industrial records documenting existing and emerging waste-to-nutrition pathways, involving over 150 different feedstocks here grouped under 10 umbrella categories: (i) wood-related residual biomass, (ii) primary crop residues, (iii) manure, (iv) food waste, (v) sludge and wastewater, (vi) green residual biomass, (vii) slaughterhouse by-products, (viii) agrifood co-products, (ix) C₁ gases and (x) others. The review includes a detailed description of these pathways, as well as the processes they involve. As a result, we proposed four generic building blocks to systematize waste-to-nutrition conversion sequence patterns, namely enhancement, cracking, extraction and bioconversion. We further introduce a multidimensional representation of the biomasses suitability as potential as nutritional sources according to (i) their content in anti-nutritional compounds, (ii) their degree of structural complexity and (iii) their concentration of macro- and micronutrients. Finally, we suggest that the different pathways can be grouped into eight large families of approaches: (i) insect biorefinery, (ii) green biorefinery, (iii) lignocellulosic biorefinery, (iv) non-soluble protein recovery, (v) gas-intermediate biorefinery, (vi) liquid substrate alternative, (vii) solid-substrate fermentation and (viii) more-out-of-slaughterhouse by-products. The proposed framework aims to support future research in waste recovery and valorization within food systems, along with stimulating reflections on the improvement of resources' cascading use.