Challenges and opportunities for citrus wastewater management and valorisation: A review

Advanced manufacture of polyphenols, essential oils and bacterial cellulose in a novel citrus processing wastewater biorefinery

Herein, a citrus processing wastewater-based biorefinery has been developed manufacturing essential oils, polyphenols and bacterial cellulose. Liquid-liquid extraction was evaluated for isolation of essential oils assessing different organic solvents, recovering 0.45 kg of essential oils per m3 of wastewater using n-heptane. Amberilte® XAD4, XAD16N and XAD7HP, PurSorb™ PAD900, biochar and activated biochar were compared as adsorbents for polyphenols recovery, demonstrating that the adsorption isotherms of the resins applied could be closely predicted using the Langmuir model. Adsorption and desorption density experiments exhibited that the phenolic content present in citrus processing wastewater could be efficiently recovered using PAD900, yielding 0.78 kg of polyphenols per m3 of wastewater. The sugar content remaining following polyphenols adsorption was applied for bacterial cellulose production employing Komagataeibacter sucrofermentans DSM 15973 determining the biopolymer's production efficiency as well as morphological and structural properties at different carbon to free amino nitrogen ratios. The higher content of the biomaterial was obtained employing 15.0 carbon to free amino nitrogen ratio, which yielded 4.4 kg of biopolymer per m3 of wastewater. The study has shown that by decreasing the carbon to free amino nitrogen ratio could enable enhancing the water-holding capacity of bacterial cellulose, exhibiting that the control of fermentation conditions could potentially enable tailoring the properties of the biomaterial for certain industrial applications. The bioactive, antioxidant and preservative properties of essential oils and polyphenols constitute the aforementioned products significant for a range of industrial applications within the pharmaceutical, cosmetics and food sectors.

Barriers to implementing circular citrus supply chains: A systematic literature review

Citrus is one of the world's most popular and widely cultivated fruits. The processing of citrus fruits for juice extraction generates solid and liquid biowaste, a valuable bio-resource that can be utilized in various sectors, including food and non-food industries. Incorporating Circular Economy (CE) principles into the citrus supply chain offers numerous opportunities but also presents certain barriers. The existing literature lacks a comprehensive study that explicitly explores the obstacles hindering the implementation of citrus waste valorization. Therefore, this study adopts a systematic literature review approach to answer three research questions related to defining the valorization processes and pathways of citrus processing waste to achieve net-zero waste and to explore, classify, and analyze the barriers to the implementation of Circular Citrus Supply Chains (CCSC). One hundred twenty-eight distinct barriers have been identified and classified into seven categories: economic, regulatory, technological, informational, market-related, managerial, and logistical. The most significant categories for CCSC were technological, economic, and informational barriers. This study provides practitioners and academics with a comprehensive understanding of the valorization opportunities and the various challenges faced during the adoption of circular models within the citrus processing supply chain. The findings thus provide a platform for the development of more competitive and sustainable strategies for CCSC. Additionally, future work was proposed regarding stakeholder engagement, barriers investigation, valorization processes' technical and economic feasibility, the interrelationship between barriers, and the effect of integrating emerging technologies to advance the CCSC field further.

Water reuse of treated domestic wastewater in agriculture: Effects on tomato plants, soil nutrient availability and microbial community structure

The reuse of treated wastewater (TWW) in agriculture for crop irrigation is desirable. Crop responses to irrigation with TWW depend on the characteristics of TWW and on intrinsic and extrinsic soil properties. The aim of this study was to assess the response of tomato (Solanum lycopersicum L.) cultivated in five different soils to irrigation with TWW, compared to tap water (TAP) and an inorganic NPK solution (IFW). In addition, since soil microbiota play many important roles in plant growth, a metataxonomic analysis was performed to reveal the prokaryotic community structures of TAP, TWW and IFW treated soil, respectively. A 56-days pot experiment was carried out. Plant biometric parameters, and chemical, biochemical and microbiological properties of different soils were investigated. Shoot and root dry and fresh weights, as well as plant height, were the highest in plants irrigated with IFW followed by those irrigated with TWW, and finally with TAP water. Plant biometric parameters were positively affected by soil total organic carbon (TOC) and nitrogen (TN). Electrical conductivity was increased by TWW and IFW, being such an increase proportional to clay and TOC. Soil available P was not affected by TWW, whereas mineral N increased following their application. Total microbial biomass, as well as, main microbial groups were positively affected by TOC and TN, and increased according to the following order: IFW > TWW > TAP. However, the fungi-to-bacteria ratio was lowered in soil irrigated with TWW because of its adverse effect on fungi. The germicidal effect of sodium hypochlorite on soil microorganisms was affected by soil pH. Nutrients supplied by TWW are not sufficient to meet the whole nutrients requirement of tomato, thus integration by fertilization is required. Bacteria were more stimulated than fungi by TWW, thus leading to a lower fungi-to-bacteria ratio. Interestingly, IFW and TWW treatment led to an increased abundance of Proteobacteria and Acidobacteria phyla and Balneimonas, Rubrobacter, and Steroidobacter genera. This soil microbiota structure modulation paralleled a general decrement of fungi versus bacteria abundance ratio, the increment of electrical conductivity and nitrogen content of soil and an improvement of tomato growth. Finally, the potential adverse effect of TWW added with sodium chloride on soil microorganisms depends on soil pH.

PHA and EPS production from industrial wastewater by conventional activated sludge, membrane bioreactor and aerobic granular sludge technologies: A comprehensive comparison

The present study has focused on the mainstream integration of polyhydroxyalkanoate (PHA) production with industrial wastewater treatment by exploiting three different technologies all operating in sequencing batch reactors (SBR): conventional activated sludge (AS-SBR), membrane bioreactor (AS-MBR) and aerobic granular sludge (AGS). A full aerobic feast/famine strategy was adopted to obtain enrichment of biomass with PHA-storing bacteria. All the systems were operated at different organic loading (OLR) rate equal to 1-2-3 kgCOD/m3∙d in three respective experimental periods. The AS-MBR showed the better and stable carbon removal performance, whereas the effluent quality of the AS-SBR and AGS deteriorated at high OLR. Biomass enrichment with PHA-storing bacteria was successfully obtained in all the systems. The AS-MBR improved the PHA productivity with increasing OLR (max 35% w/w), whereas the AS-SBR reduced the PHA content (max 20% w/w) above an OLR threshold of 2 kgCOD/m3∙d. In contrast, in the AGS the increase of OLR resulted in a significant decrease in PHA productivity (max 14% w/w) and a concomitant increase of extracellular polymers (EPS) production (max 75% w/w). Results demonstrated that organic carbon was mainly driven towards the intracellular storage pathway in the AS-SBR (max yield 51%) and MBR (max yield 61%), whereas additional stressors in AGS (e.g., hydraulic selection pressure, shear forces) induced bacteria to channel the COD into extracellular storage compounds (max yield 50%) necessary to maintain the granule's structure. The results of the present study indicated that full-aerobic feast/famine strategy was more suitable for flocculent sludge-based technologies, although biofilm-like systems could open new scenarios for other biopolymers recovery (e.g., EPS). Moreover, the AS-MBR resulted the most suitable technology for the integration of PHA production in a mainstream industrial wastewater treatment plant, considering the greater process stability and the potential reclamation of the treated wastewater.

Wastewater treatment in lagoons: A systematic review and a meta-analysis

This study has carried out a systematic review of 36 scientific papers (reporting 63 case studies) published in the last 15 years about the treatment of industrial, agri-food and municipal wastewater in lagoons. A concentration of studies from a few countries (Italy, Algeria and Iran) and about municipal wastewater (70% of papers) was revealed by the bibliographic analysis. Aeration was supplied in more than 50% of case studies; the storage capacity of lagoons (adopted as a measure of size) was extremely variable (over seven orders of magnitude), while their depth was generally lower than a few metres. The efficiency of lagoon treatments at removing COD was in a wide range (25-98%). Very few studies analysed the energy intensity of treatments in lagoons. The meta-analysis applied to a further selection of 10 papers with 29 case studies revealed significant differences in pH and dissolved oxygen concentration, due to aeration or type of treated wastewater. Treatment efficiency was higher in aerated lagoons compared to non-aerated systems, and did not depend on the type of treated wastewater. Based on the analysis of the reviewed papers, an urgent research need on this topic arises, mainly due to the oldness of most analysed studies. Practical suggestions are given to optimise the depuration performances of lagoons: (i) application of intermittent and night aeration; (ii) reduced air flow rates; (iii) adaptation of microbial biomass to high contents of inhibiting compounds in wastewater; (iv) construction of baffles to keep the planned hydraulic retention time avoiding short-circuit; (v) integration of lagoons with other treatments (e.g., constructed wetlands); (vi) ferti-irrigation of crops with lagoon effluents rather than disposal into water bodies.

Combined recovery of polyhydroxyalkanoates and reclaimed water in the mainstream of a WWTP for agro-food industrial wastewater valorisation by membrane bioreactor technology

The present study investigated the combined production of reclaimed water for reuse purposes and polyhydroxyalkanoates (PHA) from an agro-food industrial wastewater. A pilot plant implementing a two-stage process for PHA production was studied. It consisted of a mainstream sequencing batch membrane bioreactor (SBMBR) in which selection of PHA-accumulating organisms and wastewater treatment were carried out in, and a side-stream fed-batch reactor (FBR) where the excess sludge from the SBMBR was used for PHA accumulation. The performance of the SBMBR was compared with that of a conventional sequencing batch reactor (SBR) treating the same wastewater under different food to microorganisms' ratios (F/M) ranging between 0.125 and 0.650 kgCOD kgTSS-3 d-1. The SBMBR enabled to obtain very high-quality effluent in compliance with the relevant national (Italy) and European regulations (Italian DM 185/03 and EU, 2020/741) in the field of wastewater reclamation, whereas the performances in the SBR collapsed at F/M higher than 0.50 kgCOD kgTSS-1d-1. A maximum intracellular storage of 45% (w/w) and a production yield of 0.63 gPHA L-1h-1 were achieved when the SBMBR system was operated with a F/M ratio close to 0.50 kgCOD kgTSS-1d-1. This resulted approximately 35% higher than those observed in the SBR, since the ultrafiltration membrane avoided the washout of dispersed and filamentous bacteria capable of storing PHA. Furthermore, while maximizing PHA productivity in conventional SBR systems led to process dysfunctions, in the SBMBR system it helped mitigate these issues by reducing membrane fouling behaviour. The results of this study supported the possibility to achieve combined recovery of reclaimed water and high-value added bioproducts using membrane technology, leading the way for agro-food industrial wastewater valorization in the frame of a circular economy model.

Feeding Pellets Containing Agro-Industrial Waste Enhances Feed Utilization and Rumen Functions in Thai Beef Cattle

The objective of this research was to investigate the effects of citric waste fermented with yeast waste pellet (CWYWP) supplementation on feed intake, rumen characteristics, and blood metabolites in native Thai beef cattle that are fed a rice-straw-based diet. Four native male Thai beef cattle (1.0-1.5 years old) with an initial body weight (BW) of 116 ± 16 kg were held in a 4 × 4 Latin square design within 21-day periods. The animals were assigned to receive CWYWP supplementation at 0%, 2%, 4%, and 6% of the total dry matter (DM) intake per day. The results indicate that feeding beef cattle with CWYWP leads to a linear increase in the total intake as well was the intake of crude protein (CP) and the digestibility of CP, with the maximum levels observed at 6% CWYWP supplementation (p < 0.05). Rumen characteristics, including pH, blood urea-nitrogen concentration, and protozoal population, showed no significant alterations in response to the varying CWYWP dosages (p > 0.05). In addition, the CWYWP supplementation resulted in no significant changes in the concentration of ammonia-nitrogen, remaining within an average normal range of 10.19-10.38 mg/dL (p > 0.05). The inclusion of 6% CWYWP resulted in the highest population of ruminal bacteria (p < 0.05). Additionally, the CWYWP supplementation led to a statistically significant increase in the mean propionic acid concentration as compared to the group that did not receive the CWYWP supplementation (p < 0.05). In conclusion, this experiment demonstrates that supplementing Thai native beef cattle with CWYWP at either 4% or 6% DM per day can enhance their total CP intake as well as the CP digestibility and rumen bacterial population, and can increase propionate concentration.

The Chemistry and the Anti-Inflammatory Activity of Polymethoxyflavonoids from Citrus Genus

Polymethoxyflavonoids (PMFs) are a large group of compounds belonging to the more general class of flavonoids that possess a flavan carbon framework decorated with a variable number of methoxy groups. Hydroxylated polymethoxyflavonoids (HPMFs), instead, are characterized by the presence of both hydroxyl and methoxy groups in their structural unities. Some of these compounds are the aglycone part in a glycoside structure in which the glycosidic linkage can involve the -OH at various positions. These compounds are particular to Citrus genus plants, especially in fruits, and they are present mainly in the peel. A considerable number of PMFs and HPMFs have shown promising biological activities and they are considered to be important nutraceuticals, responsible for some of the known beneficial effects on health associated with a regular consumption of Citrus fruits. Among their several actions on human health, it is notable that the relevant contribution in controlling the intracellular redox imbalance is associated with the inflammation processes. In this work, we aim to describe the status concerning the chemical identification and the anti-inflammatory activity of both PMFs and HPMFs. In particular, all of the chemical entities unambiguously identified by isolation and complete NMR analysis, and for which a biochemical evaluation on the pure compound was performed, are included in this paper.