Potential of biohydrogen production from effluents of citrus processing industry using anaerobic bacteria from sewage sludge

Biohydrogen Production from Waste Black Cumin (Nigella Sativa) Extract Liquid

Hydrogen creates water during combustion. Therefore, it is expected to be the most promising environmentally friendly energy alternative in the coming years. This study used extract liquid obtained from the waste nigella sativa generated by the black cumin oil industry. The performance of biological hydrogen manufacturing via dark fermentation was investigated in the fluidized bed reactor (FBR) and completely stirred tank reactor (CSTR) under the operation conditions of pH 5.0, 4.0, and 6.0 and a hydraulic retention time (HRT) of 36 and 24 h. The performance of hydrogen manufacturing was determined to be good under an organic loading ratio (OLR) of 6.66 g.nigella sativa extract/L and pH 4.0. According to these conditions, the maximum amount of hydrogen in CSTR and FBR was found to be 20.8 and 7.6 mL H2/day, respectively. The operating process of the reactors displayed that a reduction in HRT augmented biohydrogen manufacturing. The work that used mixed culture found that the dominant microbial population at pH 4.0 involved Hydrogenimonas thermophila, Sulfurospirillum carboxydovorans, Sulfurospirillum cavolei, Sulfurospirillum alkalitolerans, and Thiofractor thiocaminus. No research on waste black cumin extract was found in biohydrogen studies, and it was determined that this substrate source is applicable for biological hydrogen manufacturing.

Mixed culture biotechnology and its versatility in dark fermentative hydrogen production

Over the years, extensive research has gone into fermentative hydrogen production using pure and mixed cultures from waste biomass with promising results. However, for up-scaling of hydrogen production mixed cultures are more appropriate to overcome the operational difficulties such as a metabolic shift in response to environmental stress, and the need for a sterile environment. Mixed culture biotechnology (MCB) is a robust and stable alternative with efficient waste and wastewater treatment capacity along with co-generation of biohydrogen and platform chemicals. Mixed culture being a diverse group of bacteria with complex metabolic functions would offer a better response to the environmental variations encountered during biohydrogen production. The development of defined mixed cultures with desired functions would help to understand the microbial community dynamics and the keystone species for improved hydrogen production. This review aims to offer an overview of the application of MCB for biohydrogen production.

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

Citrus wastewaters (CWWs) are by-products of the citrus fruit transformation process. Currently, more than 700 million of m³ of CWWs per year are produced worldwide. Until nowadays, the management of CWWs is based on a take-make-use-dispose model. Indeed, after being produced within a citrus processing industry, CWWs are subjected to treatment and then discharged into the environment. Now, the European Union is pushing towards a take-make-use-reuse management model, which suggests to provide for the minimization of residual pollutants simultaneously with their exploitation through a biorefinery concept. Indeed, the recovery of energy nutrients and other value-added products held by CWWs may promote environmental sustainability and close the nutrient cycles in line with the circular bio-economy perspective. Unfortunately, knowledge about the benefits and disadvantages of available technologies for the management and valorisation of CWWs are very fragmentary, thus not providing to the scientific community and stakeholders an appropriate approach. Moreover, available studies focus on a specific treatment/valorisation pathway of CWWs and an overall vision is still missing. This review aims to provide an integrated approach for the sustainable management of CWWs to be proposed to company managers and other stakeholders within the legislative boundaries and in line with the circular bio-economy perspective. To this aim, firstly, a concise analysis of citrus wastewater characteristics and the main current regulations on CWWs are reported and discussed. Then, the main technologies with a general comparison of their pros and cons, and alternative pathways for CWWs utilization are presented and discussed. Finally, a focus was paid to the economic feasibility of the solutions proposed to date relating to the recovery of the CWWs for the production of both value-added compounds and agricultural reuse. Based on literature analysis an integrated approach for a sustainable CWWs management is proposed. Such an approach suggests that after chemicals recovery by biorefinery, wastewaters should be directly used for crop irrigation if allowed by regulations or addressed to treatment plant. The latter way should be preferred when CWWs cannot be directly applied to soil due to lack of concomitance between CWWs production and crop needs. In such a way, treated wastewater should be reused after tertiary treatments for crop irrigation, whereas produced sludges should be undergone to dewatering treatment before being reused as organic amendment to improve soil fertility. Finally, this review invite European institutions and each Member State to promote common and specific legislations to overcome the fragmentation of the regulatory framework regarding CWWs reuse.

Integrated biorefinery approach to valorize citrus waste: A sustainable solution for resource recovery and environmental management

Citrus fruits are extensively cultivated, consumed and major processed horticulture crops around the globe. High processing and consumption generate huge quantities of solid organic wastes. Citrus waste represents approximately 40-50% of total fruit weight, which consists of rag (membranes and cores), pulp, seeds, and peel (albedo and flavedo), which are a potential source of value-added products including essential oils, carotenoids, pectin, dietary fibers, and polyphenols biofuel, etc. However, waste produced is discarded as waste in the environment, which causes a serious threat due to the presence of bioactive compounds. Recent research strategies on the integrated biorefinery approach explore various ways to utilize the waste obtained from the citrus wastes for their subsequent recovery of value-added products. Moreover, the citrus waste can be turned into various bio-products, viz., enzymes, biofuels, and biopolymers using the integrated biorefinery approach, which can optimize the development of green waste for sustainability and economic benefits. Given the sustainable solution for resource recovery and environmental management, the article reviews the latest advances in the novel valorization approach and valuation of the existing state-of-the-art green technologies for citrus waste utilization to bring a sustainable solution for increasing demand for food, fuel, and energy security. To achieve the zero-waste approach and industrial viability, more efforts should be given to scale-up green recovery techniques along with diverse product profiling.

Hydrothermal pretreatment: An efficient process for improvement of biobutanol, biohydrogen, and biogas production from orange waste via a biorefinery approach

Orange waste (OW), an abundant and severe globally environmental treat, was used for biobutanol and biohydrogen production emploing acetone-butanol-ethanol (ABE) fermentation through a biorefinery process. The solvent yield from untreated OW was insufficient; thus, the substrate was subjected to hydrothermal pretreatment before hydrolysis. The pretreatment at 140 ℃ for 30 min resulted in the solid with the highest yield of hydrolysis and fermentation. Moreover, the anaerobic digestion of hydrolysis residue produced appreciable amounts of biomethane. However, the pretreatment liquor was not fermentable; thus, it was detoxified by overliming for 24 h at 30 ℃ and then fermented. Overall, this sustainable biorefinery, based on pretreatment without any additional chemical agent, hydrolysis of pretreated solids, detoxification of pretreatment liquor, ABE fermentation, and anaerobic digestion of residues, produced 42.3 g biobutanol, 33.1 g acetone, 13.4 g ethanol, 104.5 L biohydrogen, and 28.3 L biomethane per kg of OW that contained 4560 kJ energy.

Physico-chemical and multielemental traits of anaerobic digestate from Mediterranean agro-industrial wastes and assessment as fertiliser for citrus nurseries

Previous researches have demonstrated the bioenergetic potential of agri-food Mediterranean wastes showing that anaerobic co-digestion is a valuable solution for Mediterranean areas. This implies a great interest for anaerobic digestates use in agriculture to replace fertilizers. The present study aimed at: i) producing knowledge on continuous anaerobic co-digestion of feedstock mixture composed by different Mediterranean agri-food wastes in terms of multielemental characterization and ii) assessing the agronomic value of industrial anaerobic digestate (AD) based on the potential as fertiliser in nursery condition for the citrus seedlings. Results have demonstrated that agro-industrial biomasses have great potentiality to be converted by anaerobic digestion in biofertilizer to be used in citrus nurseries as sustainable alternative to mineral fertilisers. Multielemental traits of the tested AD were valuable in terms of nutritional supply for the growth and development of the plant. AD was useful to replace the mineral fertilizers in terms of total N content (10.81 ± 0.32 %TS) and organic matter (43.32 ± 0.80 %TS). The seedlings nutritive status showed that no need for supplemental of nutrients was requested. Volkamer lemon highly benefited from the administration of liquid digestate, increasing the total chlorophyll level (2.97 ± 0.31 mg g^-1 FW) presumably due to the higher ammonium content of the AD (59 ± 0.08 %TKN). Besides providing useful tools for citrus nurseries for conceiving new sustainable fertilization strategies, this study is a starting point for further in-depth works on physiological status and traits of citrus plants fertilized by using agro-industrial anaerobic digestate.

State-of-the-art technologies for continuous high-rate biohydrogen production

Dark fermentation is a technically feasible technology for achieving carbon dioxide-free hydrogen production. This review presents the current findings on continuous hydrogen production using dark fermentation. Several operational strategies and reactor configurations have been suggested. The formation of attached mixed-culture microorganisms is a typical prerequisite for achieving high production rate, hydrogen yield, and resilience. To date, fixed-bed reactors and dynamic membrane bioreactors yielded higher biohydrogen performance than other configurations. The symbiosis between H₂-producing bacteria and biofilm-forming bacteria was essential to avoid washout and maintain the high loading rates and hydrogenic metabolic flux. Recent research has initiated a more in-depth comparison of microbial community changes during dark fermentation, primarily with computational science techniques based on 16S rRNA gene sequencing investigations. Future techno-economic analysis of dark fermentative biohydrogen production and perspectives on unraveling mitigation mechanisms induced by attached microorganisms in dark fermentation processes are further discussed.

Biohythane production from food processing wastes - Challenges and perspectives

The food industry generates enormous quantity of food waste (FW) either directly or indirectly including the processing sector, which turned into biofuels for waste remediation. Six types of food processing wastes (FPW) such as oil, fruit and vegetable, dairy, brewery, livestock and finally agriculture based materials that get treated via dark fermentation/anaerobic digestion has been discussed. Production of both hydrogen and methane is daunting for oil, fruit and vegetable processing wastes because of the presence of polyphenols and essential oils. Moreover, acidic pH and high protein are the reasons for increased concentration of ammonia and accumulation of volatile fatty acids in FPW, especially in dairy, brewery, and livestock waste streams. Moreover, the review brought to forefront the enhancing methods, (pretreatment and co-digestion) operational, and environmental parameters that can influence the production of biohythane. Finally, the nature of feedstock's role in achieving successful circular bio economy is also highlighted.

Wastewater Management in Citrus Processing Industries: An Overview of Advantages and Limits

Citrus-processing industries produce large volumes of wastewater (CPWW). The large variability of these volumes coupled to physicochemical characteristics of CPWW determine severe constraints for their disposal due to both economic and environmental factors. To minimize the management costs and prevent the negative ecological impacts of CPWW, several systems have been proposed and adopted. However, all these treatment/valorization routes have many issues that are not yet thoroughly known by the scientific community and stakeholders of the citrus-processing chain. This paper reports an overview of the possible treatment/valorization opportunities for CPWW: intensive biological treatment, lagooning, direct land application, energy conversion, and biorefinery uses for the extraction of added-value compounds. Advantages and constraints are presented and discussed, and the following conclusions are achieved: (i) there is not a unique solution for CPWW treatment, since the best management system of CPWW must be chosen case by case, taking into account the quality/quantity of the effluent and the location of the transformation industry; (ii) the adoption of a biorefinery approach can increase the competitiveness and the further development of the whole citrus sector, but the cost of novel technologies (some of which have not been tested at real scale) still limits their development.

Making Virtue Out of Necessity: Managing the Citrus Waste Supply Chain for Bioeconomy Applications

The efficient use of agricultural wastes and by-products, which essentially transforms waste materials into value-added products, is considered as pivotal for an effective bioeconomy strategy for the rural development. Within this scope, citrus waste management represents a major issue for citrus processors. However, it also represents a potentially unexploited resource for rural sustainable development. This study focuses on analyzing the current management of citrus waste in South Italy, and on identifying the determinants and barriers that may affect an entrepreneur’s choice in the destination of citrus waste. This study investigates the preferences of citrus processors regarding the contract characteristics necessary to take part in a co-investment scheme. Both analyses are preliminary steps in designing an innovative and sustainable citrus by-product supply chain. Results show that the distance between the citrus processors and the citrus by-products plant is one of the main criteria for choosing alternative valorization pathways. Moreover, guaranteed capital, a short duration of the contract, and reduced risk are contract scheme characteristics that improve entrepreneurs’ willingness to co-invest in the development of a citrus waste multifunctional plant. The overall applied approach can be extended to other contexts for designing new and innovative by-product supply chains, thereby enhancing the implementation of bioeconomy strategies.

Valorisation of citrus processing waste: A review

This study analyses the quantitative and qualitative characteristics of citrus peel waste and discusses the systems for its valorisation. Citrus peel waste (CPW) is the main residue of the citrus processing industries and is characterised by a seasonal production (which often requires biomass storage) as well as high water content and concentration of essential oils. The disposal of CPW has considerable constraints due to both economic and environmental factors. Currently this residue is mainly used as food for animals, thanks to its nutritional capacity. If enough agricultural land is available close to the processing industries, the use of CPW as organic soil conditioner or as substrate for compost production is also possible, thus improving the organic matter content of the soil. Recently, the possibility of its valorisation for biomethane or bioethanol production has been evaluated by several studies, but currently more research is needed to overcome the toxic effects of the essential oils on the microbial community. Considering the high added value of the compounds that can be recovered from CPW, it has promising potential uses: in the food industry (for production of pectin, dietary fibres, etc.), and in the cosmetic and pharmaceutic industries (extraction of flavonoids, flavouring agents and citric acid). However, in many cases, these uses are still not economically sustainable.

Anaerobic co-digestion of sewage sludge and food waste for hydrogen and VFA production with microbial community analysis

In this study, the anaerobic co-digestion of food waste (FW) and sewage sludge (SS) was investigated for the production of hydrogen and volatile fatty acids (VFAs). The results showed that the anaerobic co-digestion of these materials enhanced the hydrogen content by 62.4% (v/v), 29.89% higher than that obtained by FW digestion alone, and the total VFA production reached at 281.84 mg/g volatile solid (VS), a 8.38% increase. This enhancement was primarily resulted from improvements in the multi-substrate characteristics, which were obtained by supplying a higher soluble chemical oxygen demand (23.78-32.14 g/L) and suitable a pH (6.12-6.51), decreasing total ammonia nitrogen by 18.67% and ensuring a proper carbon/nitrogen ratio (15.01-23.01). Furthermore, maximal hydrogen (62.39 mL/g VS) and total VFA production potential (294.63 mg/g VS) were estimated using response surface methodology optimization, which yielded FW percentages of 85.17% and 79.87%, respectively. Based on a pyrosequencing analysis, the dominant bacteria associated with VFA and hydrogen production were promoted under optimized condition, including members of genera Veillonella and Clostridium and the orders Bacteroidales and Lactobacillales.