Application and effectiveness of Methylobacterium symbioticum as a biological inoculant in maize and strawberry crops

The effectiveness of Methylobacterium symbioticum in maize and strawberry plants was measured under different doses of nitrogen fertilisation. The biostimulant effect of the bacteria was observed in maize and strawberry plants treated with the biological inoculant under different doses of nitrogen fertiliser compared to untreated plants (control). It was found that bacteria allowed a 50 and 25% decrease in the amount of nitrogen applied in maize and strawberry crops, respectively, and the photosynthetic capacity increased compared with the control plant under all nutritional conditions. A decrease in nitrate reductase activity in inoculated maize plants indicated that the bacteria affects the metabolism of the plant. In addition, inoculated strawberry plants grown with a 25% reduction in nitrogen had a higher concentration of nitrogen in leaves than control plants under optimal nutritional conditions. Again, this indicates that Methylobacterium symbioticum provide an additional supply of nitrogen.

Development of a controlled release fertilizer by incorporating lauric acid into microalgal biomass: Dynamics on soil biological processes for efficient utilisation of waste resources

Utilisation of microalgae to extract nutrients from the effluent of anaerobic digestion of food waste is an emerging technology. A by-product of this process is the microalgal biomass which has potential to be used as an organic bio-fertilizer. However, microalgal biomass are rapidly mineralized when applied to soil which may result in N loss. One solution is to emulsify microalgal biomass with lauric acid (LA) to delay the release of mineral N. This study aimed to investigate whether combining LA with microalgae to develop a new fertilizer product with a controlled release function of mineral N when applied to soil, and any potential impacts the bacterial community structure and activity. The treatments were applied to soil emulsified with LA and were combined with either microalgae or urea at rates of 0%, 12.5%, 25% and 50% LA, untreated microalgae or urea and unamended control were incubated at 25 °C and 40% water holding capacity for 28 days. Quantification of soil chemistry (NH4+-N, NO3--N, pH and EC), microbial biomass carbon, CO2 production and bacterial diversity were characterised at 0, 1, 3, 7, 14 and 28 days. The NH4+-N and NO3--N concentration decreased with increasing rate of LA combined microalgae indicating that both N mineralization and nitrification were impacted. As a function of time, NH4+-N concentration increased up to 7 days for the microalgae at lower rates of LA, and then slowly decreased for 14 and 28 days, with an inverse relationship with soil NO3-N. Aligning with soil chemistry, an observed decrease in the predicted nitrification genes amoA·amoB and relative abundance of ammonia oxidizing bacteria (Nitrosomonadaceae) and nitrifying bacteria (Nitrospiraceae) with an increasing rate of LA with microalgae provides further support for possible inhibition of nitrification. The MBC and CO2 production was higher in the soil amended with increasing rates of LA combined microalgae and there was an increase in the relative abundance of fast-growing heterotrophs. Treating microalgae by emulsification with LA has the potential to control the release of N by increasing immobilization over nitrification and therefore it might be possible to engineer microalgae to match plant nutrient growth requirements whilst recovering waste from waste resources.

Techno-economic assessment of biorefinery scenarios based on mollusc and fish residuals

Biorefineries aim to maximise resource recovery from organic sources that have been traditionally considered wastes. In this respect, leftovers from mollusc and seafood processing industries can be a source of multiple bioproducts such as protein hydrolysates (PH), calcium carbonate and co-composted biochar (COMBI). This study aims to evaluate different scenarios of biorefineries fed by mollusc (MW) and fish wastes (FW) to understand which is the most convenient to maximise their profitability. Results showed that the FW-based biorefinery obtained the highest revenues with respect to the amounts of waste treated, i.e., 955.1 €·t^-1 and payback period (2.9 years). However, including MW in the biorefinery showed to increase total income as a higher amount of feedstock could be supplied to the system. The profitability of the biorefineries was mainly dependent on the selling price of hydrolysates (considered as 2 €·kg^-1 in this study). However, it also entailed the highest operating costs (72.5-83.8% of total OPEX). This highlights the importance of producing high-quality PH in economic and sustainable way to increase the feasibility of the biorefinery.

Environmental comparison of banana waste valorisation strategies under a biorefinery approach

Banana wastes can be valorised in bioethanol due to its high content in cellulose (more than 30% of total on a dry basis) and hemicelluloses (25% of total). Large amount of these wastes is generated during the banana cultivation and harvesting stage. This study proposes the use of, beside conventional acid sulphuric, different organic acids (tartaric, oxalic and citric) during acid pretreatment step, to suppress the unwanted compounds formation and improve bioethanol production. Instead, bioethanol production generates a solid waste flow that is managed in an anaerobic digestion plant, obtaining biogas, to be converted into energy, and digestate, considered as a potential biofertiliser. Life cycle assessment methodology is used to analyse the environmental profiles of four valorisation scenarios to produce bioethanol from banana peel waste. According to the results, reported per kilogram of bioethanol, the citric acid-based scenario has the worst environmental profile due to the background processes involved in the acid production (around 55% for most impact categories). Conversely, the oxalic acid-based scenario has the best environmental profile, with a decrease of around 20% and 35%, depending on the impact category, compared to the citric acid scenario. The energy requirements production (mostly thermal energy) is the main hotspot in numerous subsystems regardless of the scenario (ranging from 30% to 50% depending on the impact category). Therefore, the use of renewable energy sources to satisfy energy requirements combined with an energy optimisation of the valorisation strategies through the reuse of some internal steams, is proposed as improvement activities.

Study of pig manure digestate pre-treatment for subsequent valorisation by struvite

This work evaluates the release of phosphorus contained in the digestate from the anaerobic digestion of pig manure, through an acidification process. The objective of this acidification is to increase the amount of phosphorus available in the digestate liquid fraction and, subsequently, recover this element by chemical precipitation in the form of struvite or calcium phosphate. Two digestate samples (one fresh and one old) were studied and treated by adding various amounts of sulphuric acid to the different digestate fractions (raw digestate, solid fraction and liquid fraction). For the raw digestate, phosphorus releases higher than 95% were obtained for pH 4.0. In the last part of the experiment, the influence of acid pre-treatment on the reaction yield of phosphorus precipitation, in the form of struvite or calcium phosphate, was determined. Improvements in reaction yield were obtained up to 15% for struvite and 80% for calcium phosphate, increasing also in 7.5 times the amount of phosphorus available in the digestate liquid fraction, for both cases.

Fruit quality and volatile compound composition of processing tomato as affected by fertilisation practices and arbuscular mycorrhizal fungi application

The effects of different fertilisation treatments with arbuscular mycorrhizal fungi (AMF) inoculation on AMF root colonisation, fruit yield, nutrient and total phenol contents, volatile compound composition, and sensory attributes of tomato (Solanum lycopersicum L.) were investigated. Mineral, organic, and mineral + organic fertiliser application positively affected tomato yield (35%-50%) and phosphorus concentration (24%-29%) compared with controls. AMF application had a significant impact on the total nitrogen (+9%), manganese (+12%), and hydrophilic phenol (+8%) contents in the fruit. Volatile compounds were affected by the interactive effects of fertilisation and AMF application. The response of tomato fruit sensory quality indicators was relatively modest, with only a few sensory characteristics affected to a lesser extent. Although tomato showed susceptibility to field-native AMF, particular combinations of fertilisation and AMF inoculation were more effective at improving the quality parameters of tomatoes under field conditions applied in this study.

A review on the valorisation of food waste as a nutrient source and soil amendment

Valorisation of food waste offers an economical and environmental opportunity, which can reduce the problems of its conventional disposal. Food waste is commonly disposed of in landfills or incinerated, causing many environmental, social, and economic issues. Large amounts of food waste are produced in the food supply chain of agriculture: production, post-harvest, distribution (transport), processing, and consumption. Food waste can be valorised into a range of products, including biofertilisers, bioplastics, biofuels, chemicals, and nutraceuticals. Conversion of food waste into these products can reduce the demand of fossil-derived products, which have historically contributed to large amounts of pollution. The variety of food chain suppliers offers a wide range of feedstocks that can be physically, chemically, or biologically altered to form an array of biofertilisers and soil amendments. Composting and anaerobic digestion are the main large-scale conversion methods used today to valorise food waste products to biofertilisers and soil amendments. However, emerging conversion methods such as dehydration, biochar production, and chemical hydrolysis have promising characteristics, which can be utilised in agriculture as well as for soil remediation. Valorising food waste into biofertilisers and soil amendments has great potential to combat land degradation in agricultural areas. Biofertilisers are rich in nutrients that can reduce the dependability of using conventional mineral fertilisers. Food waste products, unlike mineral fertilisers, can also be used as soil amendments to improve productivity. These characteristics of food wastes assist in the remediation of contaminated soils. This paper reviews the volume of food waste within the food chain and types of food waste feedstocks that can be valorised into various products, including the conversion methods. Unintended consequences of the utilisation of food waste as biofertilisers and soil-amendment products resulting from their relatively low concentrations of trace element nutrients and presence of potentially toxic elements are also evaluated.

High-throughput sequence analysis of bacterial communities in commercial biofertiliser products marketed in South Africa: an independent snapshot quality assessment

The genetic and predicted functional diversity of bacterial communities in 12 commercial biofertiliser products were evaluated using high-throughput sequencing of the 16S rRNA gene. Proteobacteria, Firmicutes and Bacteroides dominated the bacterial communities, with the genera Pseudomonas, Lactobacillus, Bacillus, Bradyrhizobium and Rhizobium being prevalent. The manufacturer-specified species were detected in relatively high abundance in two of the products while a few or none of the specified species were detected in some products. A number of unspecified microbes were detected, including potential human and crop pathogens such as Alcaligenes, Clostridium, Escherichia-Shigella and Proteus. The functional prediction unravelled high prevalence of enzyme-coding genes such as nitrogenase, NifT, alkaline phosphatase and reductases of nitric oxide, nitrate and nitrite which contribute to nitrogen-fixation, phosphorus solubilisation and degradation of nitrates and nitrites. In addition, toxins such as leukocidin/hemolysin and colicin V protein that cause product quality damage were highly predicted in over 67% of the products. Overall, high-throughput sequence analysis of bacterial communities in biofertiliser products revealed that majority of the products were of poor quality. This result justifies the need for regular quality assessment and improvement in quality control systems during biofertiliser formulation.

Physical-chemical traits, phytotoxicity and pathogen detection in liquid anaerobic digestates

Anaerobic digestates, which are co-products from biogas production, have been recognised as potential biofertilisers for their benefits in nutrient recovery and recycling of different types of organic wastes. Due to the increasing number of different types of organic wastes being used to produce biogas, it is necessary to identify how different types of anaerobic digestates vary in their physical-chemical traits, and how these can impact upon their use as fertilisers. In addition, safe land spreading of anaerobic digestates must be within recommended limits for potentially toxic elements (PTEs) and pathogens. This study analysed physical-chemical traits, phytotoxicity, PTEs and indicator pathogens in a set of eleven different commercial liquid anaerobic digestates from Ireland and the UK, and compared them to the Irish draft standard for digestate. Liquid anaerobic digestates exhibited significant differences (P < 0.001) for most of the physical and chemical traits evaluated, with higher variability found for dry matter (DM) and K (CV = 17.2 and 16.8 respectively), and lower variation for pH and P (CV = 1.78 and 3.55 respectively). PTE concentrations were in general within recommended limits; nevertheless, some digestates showed higher concentrations than the recommended limits for Pb, Zn and Cu. Digestate from wastewater treatment feedstock was shown to be high in PTEs. Anaerobic digestates were found to negatively affect early stages of seed germination, but phytotoxicity effects were decreased by dilution in water. Levels of Salmonella spp. and E. coli were within recommended limits for most of the anaerobic digestates analysed.

Assessing the agricultural reuse of the digestate from microalgae anaerobic digestion and co-digestion with sewage sludge

Microalgae anaerobic digestion produces biogas along with a digestate that may be reused in agriculture. However, the properties of this digestate for agricultural reuse have yet to be determined. The aim of this study was to characterise digestates from different microalgae anaerobic digestion processes (i.e. digestion of untreated microalgae, thermally pretreated microalgae and thermally pretreated microalgae in co-digestion with primary sludge). The main parameters evaluated were organic matter, macronutrients and heavy metals content, hygenisation, potential phytotoxicity and organic matter stabilisation. According to the results, all microalgae digestates presented suitable organic matter and macronutrients, especially organic and ammonium nitrogen, for agricultural soils amendment. However, the thermally pretreated microalgae digestate was the least stabilised digestate in comparison with untreated microalgae and co-digestion digestates. In vivo bioassays demonstrated that the digestates did not show residual phytotoxicity when properly diluted, being the co-digestion digestate the one which presented less phytotoxicity. Heavy metals contents resulted far below the threshold established by the European legislation on sludge spreading. Moreover, low presence of E. coli was observed in all digestates. Therefore, agricultural reuse of thermally pretreated microalgae and primary sludge co-digestate through irrigation emerges a suitable strategy to recycle nutrients from wastewater.

Use of the effluent from biogas production for cultivation of Spirulina

The effluent from the biogas process was tested as a nutrient source during cultivation of the protein-rich and edible microalgae Spirulina (Arthrospira platensis) and compared with conventional Spirulina medium. Equal biomass production was observed until late exponential phase and no significant differences could be observed between the treatments in protein amount, amino acid composition, and total lipid concentration. The concentration of the pigment phycocyanin differed significantly between Spirulina medium and the effluent-based medium (63.3 ± 11.7 and 86.2 ± 1.9 mg g⁻¹, respectively). Slightly higher concentrations of saturated fatty acids, mainly palmitic acid, were observed in the biomass produced in Spirulina medium than in that produced in the effluent-based medium. In the biomass produced in the effluent-based medium, the cadmium concentration was 0.07 ± 0.05 mg kg⁻¹ of dry weight, whereas it was below the detection limit in the biomass produced in Spirulina medium. There is a need to identify new food and feed resources and a possible future scenario is to integrate Spirulina production into the biogas plant for protein production as it contains more than 60% of protein on dry weight basis. In that scenario, it is important to control heavy metal concentrations in the biogas slurry fed to Spirulina.