Straw Waste Research Articles

Steam Explosion-Based Method for the Extraction of Cellulose and Lignin from Rice Straw Waste

This paper focuses on the optimisation of an efficient extraction process for cellulose and lignin from rice straw waste from the Albufera of Valencia using the steam explosion method. This method is particularly pertinent given the environmental and economic challenges posed by the current disposal practices of agricultural waste. The technique comprises a high-temperature cooking stage followed by instantaneous decompression, effectively altering the biomass’s physical and chemical properties to enhance its surface area and porosity. Our adaptation of the steam explosion technique specifically addresses the challenges of rice straw waste, marking a significant departure from previous applications. This innovation is crucial in addressing the urgent need for more sustainable waste management practices, as it effectively deconstructs the lignocellulosic matrix of rice straw. This facilitates the selective extraction of cellulose at a 70% efficiency, with a 20% yield and the subsequent recovery of lignin. The results of this study are significant for sustainable biomaterial production, offering novel insights into optimising these crucial biomass components. By refining the process and focusing on critical parameters, our work advances the application of steam explosion methods for agricultural waste, enhancing efficiency and sustainability. By utilising rice straw biowaste, this research not only proposes a solution to a pressing environmental issue but also demonstrates the potential to create new market opportunities, increase the economic value for rice producers, and significantly reduce the environmental footprint of existing waste disposal methods. The holistic and ecological approach of this study underscores the vital need for innovative strategies in agricultural waste management, positioning the valorisation of rice straw waste as a key component in the pursuit of environmental sustainability.

Multifunctional coatings fabricated from Chinese hemp–derived superhydrophobic micro–nanocellulose

Ecologically feasible strategies for constructing superhydrophobic surfaces offer versatile applications in waterproofing, self–cleaning, selective absorption, and corrosion protection. Herein, we prepared low–surface–energy branched–chain–enriched micronanorod (F@SiO2@MNC) by hydrolyzing silane coupling agent and modifying fluoropolymer using micro–nanocellulose extracted from waste straw (Chinese hemp). These rods were sprayed and adhered to various substrates precoated with a binder, resulting in superhydrophobic surfaces. F@SiO2@MNC addition allowed for the formation of stable spherical liquid droplets when in contact with different types of aqueous liquids. Furthermore, these surfaces demonstrated excellent self–cleaning, robustness, abrasion resistance, UV resistance, cycling stability, and other multifunctionalities. They significantly enhanced the mechanical properties of filter paper, effectively separated oil water mixtures, and improved the corrosion resistance of metals. Our proposed strategy represents a novel approach for developing multifunctional coatings assembled from micronanocellulose.

Assisting role of carbonaceous skeleton in sludge thermal hydrolysis and press filtration

As a key step in disposal and reutilization, sludge dewatering is very difficult, since extracellular polymers substances (EPS) binds the water, and compressible organic matter deforms and causes water filtration channels to collapse. Sludge dewaterability was demonstrated to enhance by carbonaceous skeleton (CSkel)-assisted thermal hydrolysis in our previously study. This work further investigated the assisting role of different types of CSkel in EPS decomposition during sludge thermal hydrolysis stage and channels reformation during press filtration stage. Two major types of CSkel, lignocellulosic waste (waste sawdust, waste straw, processing by-product) and protein-rich waste (shrimp shells, jatropha oil cake), were selected. The experimental results showed that in the thermal hydrolysis stage, the decomposition of lignocellulosic waste would increase fatty acids production by 28%, resulting in an acidic environment that reduced the total amount of three hydrophilic amino acids, i.e., glycine, serine and threonine. These promoted the release of water from the sludge. In the press filtration stage, average pore size of sludge was reduced by approximately 87% and nanoscale holes began to appear and increase. Assisting of CSkel rebuilt the filtration channels which brought good connectivity between the pores in sludge cake. Lignocellulosic waste proved significantly more effective than protein-rich waste in achieving a water removal rate of 88.63% under 1 MPa. This study provided a basis for selecting suitable CSkel to optimize sludge dewatering for subsequent utilization.

Bifunctional electrocatalytic reduction performance of nitrogen containing biomass based nanoreactors loaded with Ni nanoparticles for oxygen and carbon dioxide

In the face of increasing energy demand, the approach of transformation that combines energy restructuring and environmental governance has become a popular research direction. As an important part of electrocatalytic reactions for gas molecules, reduction reactions of oxygen (ORR) and carbon dioxide (CO2RR) are very indispensable in the field of energy conversion and storage. However, the non-interchangeability and irreversibility of electrode materials have always been a challenge in electrocatalysis. Hereon, nickel and nitrogen decorated biomass carbon-based materials (Ni/N-BC) has been prepared by high temperature pyrolysis using agricultural waste straw as raw material. Surprisingly, it possesses abundant active sites and specific surface area as a bifunctional electrocatalyst for ORR and CO2RR. The three-dimensional porous cavity structure for the framework of biomass could not only provide a strong anchoring foundation for the active site, but also facilitate the transport and enrichment of reactants around the site. In addition, temperature modulation during the preparation process also optimizes the composition and structure of biomass carbon and nitrogen. Benefit from above structure and morphology advantages, Ni/N-BC-800 exhibits the superior electrocatalytic activity for both ORR and CO2RR simultaneously. More specifically, Ni/N-BC-800 exhibits satisfactory ORR activity in terms of initial potential and half wave potential, while also enables the production of CO under high selective. The research results provide ideas for the development and design of electrode materials and green electrocatalysts, and also expand new applications of agricultural waste in fields such as energy conversion, environmental protection, and resource utilization.

Evaluation on thermal pyrolysis of biomass straw waste: Focusing aspects of products yields, syngas emissions and solid products characterization

AbstractIn this study, a systematic and quantitative investigation of the pyrolysis characteristics of biomass was conducted in a fixed‐bed tubular reactor, and the influence of pyrolysis temperature on product yields, gas emission characteristics, and syngas compositions as well as physicochemical characterization of resulting solids (i.e., char/ash morphologies, mineral transformations, and elemental compositions) was explored in detail. The pyrolysis experiments were performed under N2, and the resulting solid characterization was detected by XRD, SEM, and EDX. The results indicated that with increasing the pyrolysis temperature from 400 to 800°C, the gaseous product yields increased from 54.9% to 66.7%, while the solid product yield showed a reverse trend, varying within 27.7%–40.5%. Meanwhile, the volume fraction of H2 in syngas increased from 7% to 33%, while the CO2 presented an opposite trend, suggesting that high temperature favored H2 formation and inhibited CO2 formation. On the whole, the CO and CO2 emissions were prior to CH4, H2, and CnHm in sequence. A large amount of sylvite (KCl), quartz (SiO2), dolomite (CaMg(CO3)2), and pyroxene (CaMgSi2O6) in the resulting solids were identified in crystal phases. Higher pyrolysis temperature had a significant influence on solid microstructures, resulting in a relatively higher slagging tendency due to low melting eutectics containing K‐rich and Ca‐rich minerals.

One-step synthesis of ferrous disulfide and iron nitride modified hydrochar for enhanced adsorption and reduction of hexavalent chromium in Bacillus LD513 by promoting electron transfer and microbial metabolism

Microbial immobilization technology is effective in improving bioremediation efficiency and heavy metal pollution. Herein, Bacillus LD513 with hexavalent chromium (Cr(VI)) tolerance was isolated and immobilized on a novel ferrous disulfide (FeS2)/iron nitride (FeN) modified hydrochar (Fe3-SNHC) prepared from waste straws. The prepared Fe3-SNHC-based LD513 (FeLD) significantly improves Cr(VI) adsorption and reduction by 31.4 % and 15.7 %, respectively, compared to LD513 alone. Furthermore, the FeLD composite system demonstrates efficient Cr(VI) removal efficiency and good environmental adaptability under different culture conditions. Microbial metabolism and electrochemical analysis indicate that Fe3-SNHC is an ideal carrier for protecting LD513 activity, promoting extracellular polymer secretion, and reducing oxidative stress. Additionally, the carrier serves as an electron shuttle that accelerates electron transfer and promotes Cr(VI) reduction. Overall, FeLD is an environmentally friendly biocomposite that shows good promise for reducing Cr(VI) contamination in wastewater treatment.

Evaluation of physical quality, pH, fresh weight reduction and fungal percentage in citronella (Cymbopogon nardus) straw waste amofer

Research on citronella waste using Amofer technology (ammoniated fermentation) treatment was carried out to increase its nutritional content so that it becomes a quality alternative feed. Analysis of physical quality, pH, fresh weight and percentage of fungi in citronella waste used a completely randomized design divided into four treatments based on different fermentation times, namely P0 = day P1 = 7 days, P2 = 14 days and P3 = 21 days. The results showed that amofer treatment with different curing times affected the physical quality of citronella straw waste, P2 and P3 showed significant differences (P<0.05). Amofer treatment with curing for 21 days is able to degrade the essential aroma which is a limiting factor in the palatability level of livestock for feed.

Characteristics of Compost from Straw and Fisheries Waste: A Comparative Analysis of Different Decomposers

The objective of this research was to assess the efficacy of three different decomposers in producing compost of high quality that meets the compost maturity standards (SNI 19-7030-2004). The experimental study was conducted with three treatments, each replicated five times, resulting in a total of fifteen composting holes. The research was conducted in South Batu Kuta Village, Narmada District, West Lombok Regency, from October to December 2019. The treatments included D1 (EM4 decomposer), D2 (Promi decomposer), and D3 (Phosphate Solubilizing Bacteria (PSB) decomposer). Various parameters, such as color, smell, temperature, pH, C-Organic, Total N, and C:N ratio, were assessed. The findings demonstrated that all three decomposers effectively decomposed the compost, yielding a high-quality product suitable for various plant applications. The compost produced by EM4, Promi, and PSB decomposers exhibited characteristics such as a blackish color, soil-like smell, a temperature ranging from 29.2°C to 29.8°C, a pH ranging from 6.83 to 6.87, organic carbon content ranging from 12.87% to 14.73%, total nitrogen content ranging from 0.83% to 0.87%, and a C/N ratio ranging from 14.35% to 14.60%. These results align with the compost maturity standards specified in SNI 19-7030-2004.

Green Development of Natural Fibre-Based Paper Mulch from Recyclable Cow Dung and Flax Straw Waste

Livestock dung, discarded crop straws, and residual plastic film are the primary agricultural non-point sources of pollution. For livestock dung and discarded crop straw, the general treatment focuses on compost, animal fodder, industrial raw material, and new energy. The development of degradable mulch film is the main way to solve pollution from residual plastic film. However, an effective way to solve the above three types of pollution simultaneously and use them for ecological circular agriculture has been less studied. In this study, using cow dung and flax straw wastes as raw materials, we prepared natural, fibre-based paper mulch using the rapid-Kothen method and analysed the film-forming mechanism. Based on the Van Soest method, the cow dung and flax straw waste contain abundant cellulose fibres: 36.75% and 54.69%, respectively. The tensile strength and tear strength of fibre paper mulch are 1.87 kN/m and 19.91 N/mm, respectively. To enhance the adaptability of the fibre paper mulch in humid environments, the surface of the mulch was treated with alkyl ketene dimer (AKD). The AKD-coated fibre paper mulch displays hydrophobic properties, indicated by a contact angle of 128° ± 2°. It has a wet tensile strength of 0.64 kN/m and a wet tear strength of 8.23 N/mm. Additionally, it exhibits a dry tensile strength and a tear strength of 2.13 kN/m and 16.43 N/mm, respectively. Notably, the dry tensile strength is increased by 16.31%. In this way, the livestock dung and discarded crop straw can be reused, reducing dung pollution and straw burning in livestock farms, and the final products can alleviate the residual film pollution simultaneously.

Cellulose extraction from rice straw waste for biodegradable ethyl cellulose films preparation using green chemical technology

A green process was devised to effectively extract cellulose from recycled rice straw waste, subsequently ethylating and modifying it into ethyl cellulose (EC), and ultimately blending the EC with ethanol to obtain biodegradable films. The optimal process conditions at each stage were investigated. An assessment was conducted on the crystallinity and thermal stability of rice straw cellulose (RSC), the degree of substitution of EC, and the biodegradability and mechanical properties of EC-ethanol films. The results demonstrated the following: The optimal process conditions resulted in a 95.73 % yield of extracted RSC, a type I crystalline structure, a 31.20 % increase in relative crystallinity, and thermal stability with a main weight loss peak at 340 °C. Under ideal ethylation conditions, the EC production reached 79.60 %, while the degree of substitution ranged from 2.0 to 2.5. After being landfilled in soil for 100 days, the EC-ethanol films degraded at rates of 6.77 %, 4.78 %, and 3.13 % (film concentrations were 0.02, 0.04, and 0.06 g/mL (w/v, EC/ethanol), respectively). Based on the analysis of the films' FT-IR and SEM images, it was concluded that the EC-ethanol films exhibit favorable biodegradability. Moreover, the tensile strength of 0.04 g/mL film reaches up to 44.60 MPa. Hence, the EC-ethanol films in this research could be an environmentally friendly and sustainable alternative to plastic films.

Safety of Chinese Cabbage Waste and Rice Straw Mixed Silage and Its Effect on Growth and Health Performance of Hu Sheep

Improper disposal of vegetable waste can cause serious environmental pollution, but because they contain huge water content and organic matter, they are not suitable for disposal by methods such as incineration and landfill. However, vegetable waste contains a large amount of nutrients and have some complementary effects with rice straw in terms of physical structure, nutrients, and moisture. In this experiment, the plant feed (corn husk, peanut shells and sorghum shells) was used as the control group (CON group), and the mixed silage of Chinese cabbage waste and rice straw (mixed silage) was used as the experiment group (TRE group), and its safety performance was evaluated by testing its toxin content, pesticide residues, vitamin contents and feeding experiment of Hu sheep. In the animal experiment, 16 healthy Hu sheep (5.5 months, 39.11 ± 4.16 kg) were randomly divided into two groups of 8 each. The results of the safety performance evaluation showed that the content of mycotoxins, heavy metals, and nitrites as well as pesticide residues in the crude feeds of both groups were within the range of Chinese feed hygiene standards. In addition, the levels of deoxynivalenol (DON) and aflatoxin (AFT) in the CON group were lower, while the content of ochratoxin (OTA) and zearalenone were higher than those in the TRE group (p &lt; 0.05). The levels of plumbum(Pb), chromium (Cr), cadmium (Cd), and nitrite in the CON group were lower than the mixed silage, while the levels of As were higher than the mixed silage (p &lt; 0.05). It is worth noticing that the content of vitamin B2 (VB2) and vitamin C (VC) in the TRE group was higher than the CON group (p &lt; 0.05). The results of the feeding experiment showed that the mixed silage did not affect the growth performance, nutrient digestibility, organ index, and intestinal index of Hu sheep (p &gt; 0.05). In addition, the mixed silage reduced the weight of omasum, the proportion of omasum to live weight before slaughter, the amount of compound stomach, and the proportion of compound stomach to live weight before slaughter, which were higher than those in the TRE group (p &lt; 0.05). The thickness of the basal layer of the rumen abdominal sac, the red blood cell count, the content of IL-10, and TNF-α in the blood, and TNF-α content in the rumen of the Hu sheep in the TRE group were higher than the CON group (p &lt; 0.05). In conclusion, the feed safety index content of the mixed silage did not exceed the Chinese feed hygiene and safety standards and did not cause adverse effects on the growth performance of the Hu sheep, and it improved the immune performance of the body and digestive tract of the sheep to a certain extent and promoted the healthy development of the sheep.

Показатели белкового обмена у жвачных животных при кормлении отходами соевого производства

The article presents the results of a zootechnical analysis of soybean waste (straw and forage waste), used as the main diet for sheep during the active feeding period. It was concluded on the basis of clinical and biochemical parameters of blood that there was an increase in the level of protein metabolism in experimental animals.

Assessment of agronomic crops-based residues for growth and nutritional profile of Pleurotus eryngii.

Among edible mushrooms, Pleurotus eryngii is unique due to its flavor, admirable medicinal and nutritional profiling. Pakistan is an agricultural country diverse in various crops. However, the residues of the horticultural and agronomic crops are wasted without utilization in the food chain. Hence, a study was performed to assess the performance of relatively low-cost, easily available crops residues i.e. cotton, rice, wheat, mustard and water chestnut for yield and nutrition enhancement of Pleurotus eryngii strains P9 (China) and P10 (PSU-USA). The results revealed that morphological attributes i.e. mycelium run, fruit development, yield and biological efficiency were significantly higher by using cotton waste as compared to other substrates. Regarding biochemical attributes i.e. total soluble solids (12.67 °Brix), phenolics (259.6 mg/100g), moisture (92.3%) and ascorbic acid contents (2.9 mg/100ml) were also significantly higher by using cotton waste. Whereas, acidity (0.30%), reducing sugar (7.67%), non-reducing (4.33%) and total sugars contents (12%) were found highest by using mustard straw. Nutrient analysis of substrates showed that nutrient levels were increased after harvesting of crop as compared to before harvesting levels. Overall results revealed that cotton waste and mustard straw are promising substrates for Pleurotus eryngii better growth and have potential in yield and nutrition enhancement. Moreover, P10 strain performed better as compared to P9.

Characterization of biodegradable plastic from jackfruit seed waste with the addition of rice straw cellulose

Biodegradable plastic is an environmentally friendly plastic; most of the components come from renewable raw materials. Biodegradable plastic can be made from starch derived from waste such as jackfruit seeds. Biodegradable plastics made only from starch have poor physical and mechanical properties, so adding reinforcement such as cellulose is necessary. One of the wastes that contain cellulose is rice straw waste. This study aimed to obtain the best ratio of jackfruit seed starch and rice straw cellulose to biodegradable plastic’s physical and mechanical properties. This research was carried out experimentally using a Completely Randomized Design (CRD) with five treatments, namely the ratio of starch and cellulose PS1 (1:0,3), PS2 (1:0,4), PS3 (1:0,5) PS4 (1:0,6), and PS5 (1:0,7) with three repetitions, 15 experimental units were obtained. The data obtained was analyzed statistically using analysis of variance (ANOVA). If Fcount ≥ Ftable data is obtained, it will be continued with Duncan’s Multiple Range Test (DMRT) at the 5% level. The selected treatment was PS5 (starch ratio 1:0,7 cellulose) with had water absorption rate of 34,82%, water vapor transfer rate of 19,12 g/m2hour, tensile strength of 20,21 MPa, elongation of 5,33%, and biodegradation for 6 days. The results showed that the addition of rice straw cellulose had a significant effect on the value of water absorption, water vapor transfer rate, tensile strength, elongation and biodegradation of the resulting biodegradable plastic.

Training on Making Fermented Rice Straw for Animal Feed in Nepo Village, Wonomulyo District, Polewali Mandar Regency

Training on making fermented rice straw for animal feed in Desa Nepo Kecamatan Wonomulyo Kabupaten Polewali Mandar aims to provide understanding to the community about making fermented rice straw for animal feed. The methods used include providing education regarding fermentation technology for rice straw waste, then discussions with participants regarding the problem that occur and obstacles in handling agricultural waste, and finally direct training in making fermented rice straw. The result of this community service activity is that participants know how to make fermented rice straw for animal feed. The conclusion of the community service activities in Desa Nepo is that the participants were able to learn about fermentation technology that can be used to process rice straw waste into highly nutritious animal feed.

Organic Mulch Innovation from Straw Waste in the Context of Realizing Climate Smart Agriculture as an Acceleration of Green Economy Achievement

Purpose: The general aim of this research is to encourage sustainable agricultural practices through innovative practices of organic mulch materials. Theoretical Framework: The theoretical framework of sustainable agriculture provides a conceptual basis for understanding and implementing agricultural practices that seek to balance environmental, social, and economic dimensions. At its core, sustainable agriculture is guided by the principles of ecological integrity, economic viability, and social equity. Ecological integrity emphasizes the importance of maintaining and enhancing the health of ecosystems, recognizing the interconnectedness of soil health, biodiversity, and water resources. Method: This research method consists of three stages. The first step is identifying the characteristics of straw, the initial stage of organic mulch production. The second stage is testing the characteristics of mulch, organic mulch innovation, testing the effectiveness and efficiency of organic mulch. The third stage is a business feasibility study analysis, mass mulch production, promotion and marketing analysis. Results: The results showed that identifying the characteristics of straw and organic mulch production is an important step in sustainable farming practices. This initial stage involves determining the type of straw that will be used as organic mulch and preparing the mulch. During this entire process, it is important to consider the type of crop being planted, local climatic conditions, and available resources in order to choose the right straw and manage organic mulch effectively. This practice can help improve soil health, reduce soil erosion, and increase agricultural productivity in a sustainable way. Conclusions: Identification of straw characteristics and production of organic mulch are important steps in sustainable agricultural practices. This initial stage involves determining the type of straw that will be used as organic mulch and preparing the mulch. During this entire process, it is important to consider the type of crop being planted, local climate conditions, and available resources to select the right straw and manage organic mulch effectively.

Effect of different organic loads on the performance and microbial community mechanism of dry anaerobic digestion

In this study, the vertical continuous push-flow dry anaerobic digestion (AD) reactor was developed independently. Typical agricultural organic waste straw and cow dung were used as raw materials in this paper to carry out long-term continuous mixed dry AD experiments on a controlled laboratory scale. The experimental results showed that the system was in low-stress operation at an organic load rate (OLR) of 3 g VS L-1 d-1, the VS methane production rate was located at 225 ∼ 272 mL CH4 g VS-1, and the volumetric methane production rate was located at 0.95 ± 0.08 L (L·d)-1, and the combination of the volumetric methane production rate, VS methane production rate, methane content of the gas, and the VS removal rate showed that the system's operational performance in this stage was in the best condition in the whole set of experiments. When the OLR reached 25 g VS L-1 d-1, the content of VFAs all began to climb rapidly above 8000 mg/L, with the content of acetic acid increasing most significantly due to the fact that the activity of acetic acid-type methanogenic bacteria was the first to be inhibited. Eventually, because of the kinetic differences between the hydrolytic acidifying bacteria and the methanogenic archaea, the final acidification destabilisation of the anaerobic digestion reactor occurred and the system was irreversibly destabilised. The system performance at this stage was in the best condition in the whole set of experiments. The study of microbial community succession and metabolic mechanisms showed that Methanoculleus and Methanobacterium play a key role in sustaining methane production, and the increased abundance and dominance of hydrogen methanogens implies that methane is produced via the hydrogen methanogenic pathway under high organic loading conditions.

Waste Management Towards Community Welfare and a Sustainable Environment

Effective and sustainable waste management is a crucial issue to maintain the welfare of society and the environment. A comprehensive approach to waste management involves three main pillars such as waste sorting, recycling and technology-based waste management. Waste management aims to maximize the value of waste by converting it into recyclable materials. The waste that is the focus of this activity is household waste and agricultural straw waste. The forms of community service carried out include socializing waste processing, forming work teams and assisting with the waste management process. The results of this activity are increased public knowledge regarding waste management, the formation of a team responsible for waste management, and waste processing products that can be utilized, namely compost and biodegradable pots. The benefit of the activity is reducing the impact of environmental waste into recycled goods to create a cleaner and healthier environment. The next suggestion is to increase cooperation between the village government and the Environmental Service to maximize the program.

Effects of organic loading rate on hydrogen and methane production in a novel two-stage reactor system: performance, enzyme activity and microbial structure

Two-stage anaerobic digestion (AD) system is an efficient technology; however, organic loading rate (OLR), a critical design and process parameter, influences the performance and capacity of digesters. This study investigates the impact of various OLRs on biogas production during co-digestion of food waste, chicken manure and corn straw in an innovatively designed two-stage reactor system, including variations in the enzyme and electron transfer system (ETS) activities and microbial community. The production of hydrogen and methane increased gradually with increasing OLR, with maximum production at 8 g VS/L d (690 mLH2/L d and 690 mLCH4/L d), which is 30–97 % higher than OLR of 1.5 to 6 g VS/L d. However, the maximum methane yield of 535 mL/g VSadded was attained at OLR of 4 g VS/L d consistent with the highest coenzyme F420 activity. Although no substantial ETS activity was seen during the acidogenic stage, the ETS activity decreased with increasing OLR in the methanogenesis stage, indicating that high substrate loading results in low syntrophic methanogenesis. Microbial analysis revealed a more diverse enrichment of acidogens and acetogens at high OLR with a wider range of substrate consumption, resulting in balanced acetoclastic and hydrogenotrophic methanogens (Methanosarcina and Methanothermobacter) in the biomethane process. These findings suggest the strengthening of syntrophic methanogenesis in high substrate-loading AD systems.

Efficient utilization of monosaccharides from agri-food byproducts supports Chlorella vulgaris biomass production under mixotrophic conditions

Microalgae are promising resources for the sustainable production of biofuels, feed, and high-value chemicals. Several strains can grow heterotrophically or mixotrophically on multiple organic substrates even if the high cost associated to their use can hinder scalability and economical sustainability of the overall process. The use of agri-food waste biomass hydrolysates might make the cultivation procedure more sustainable, while at the same time valorising underutilized by-products. In this study, Chlorella vulgaris biomass production and sugar utilization was investigated during mixotrophic cultivation on hydrolysates of two inexpensive and widely available recalcitrant agri-food waste biomasses: barley straw (BS) and citrus processing waste (CPW). CPW hydrolysate supported enhanced biomass production, compared to BS digestate, likely because of the presence, besides glucose, of significant amounts of galactose, which is rapidly metabolized by the algae. Notably, when pure monosaccharides were provided as sole organic carbon, growth stopped before complete sugar consumption. Arrested growth in presence of pure monosaccharides correlated with a drastic drop in extracellular pH, which appears to depend on both carbon and nitrogen sources. Our results show that mixotrophic cultivation of C. vulgaris on BS or CPW hydrolysates results in more efficient conversion of organic carbon into biomass, compared to growth on pure sugars, indicating that these agri-food by-products can be utilized as valid feedstocks for sustainable algal biomass production.