Differential Membrane Lipid Profiles and Vibrational Spectra of Three Edaphic Algae and One Cyanobacterium.

The membrane glycerolipids of four phototrophs that were isolated from an edaphic assemblage were determined by UPLC-MS after cultivation in a laboratory growth chamber. Identification was carried out by 18S and 16S rDNA sequencing. The algal species were Klebsormidium flaccidum (Charophyta), Oocystis sp. (Chlorophyta), and Haslea spicula (Bacillariophyta), and the cyanobacterium was Microcoleus vaginatus (Cyanobacteria). The glycerolipid profile of Oocystis sp. was dominated by monogalactosyldiacylglycerol (MGDG) species, with MGDG(18:3/16:4) accounting for 68.6%, whereas MGDG(18:3/16:3) was the most abundant glycerolipid in K. flaccidum (50.1%). A ratio of digalactosyldiacylglycerol (DGDG) species to MGDG species (DGDG/MGDG) was shown to be higher in K. flaccidum (0.26) than in Oocystis sp. (0.14). This ratio increased under high light (HL) as compared to low light (LL) in all the organisms, with its highest value being shown in cyanobacterium (0.38-0.58, LL-HL). High contents of eicosapentaenoic acid (EPA, C20:5) and hexadecenoic acid were observed in the glycerolipids of H. spicula. Similar Fourier transform infrared (FTIR) and Raman spectra were found for K. flaccidum and Oocystis sp. Specific bands at 1629.06 and 1582.78 cm-1 were shown by M. vaginatus in the Raman spectra. Conversely, specific bands in the FTIR spectrum were observed for H. spicula at 1143 and 1744 cm-1. The results of this study point out differences in the membrane lipid composition between species, which likely reflects their different morphology and evolutionary patterns.

Application of Vibrating Reverse Osmosis Technology for Nutrient Recovery from Pig Slurry in a Circular Economy Model.

The rapid growth of the livestock sector in some areas of Europe has caused an imbalance between the generation of livestock manure and the availability of agricultural soil for its direct application as a fertilizer. Since the transport of pig slurry to other areas with nutrient-deficient soils is costly from an economic point of view due to its high water content, the application of new technologies for the concentration of this waste is considered key for reducing management costs. Consequently, the main objective of this study was to demonstrate the potential of vibratory shear enhanced processing (VSEP) operated with reverse osmosis membranes to recover nutrients from the liquid fractions of pig slurry (LF-pig slurry) and digestate (LF-digestate) and obtain concentrated fertilizing products. Use of the VSEP unit permitted reductions in the water contents of the LF-pig slurry and LF-digestate, around 77% and 67%, respectively. Both VSEP concentrates were characterized by their significant nutrient contents and showed a nitrogen fertilizer replacement value similar to that of mineral fertilizer as demonstrated in a barley crop pot-test, although the salinity of the digestate concentrate was identified as a key limitation, negatively impacting the agronomic yield of the test crop.

Application of olive mill waste-based biochars in agriculture: Impact on soil properties, enzymatic activities and tomato growth.

The olive oil industry is an important economic sector in Mediterranean countries. However, oil production is unfortunately accompanied by the generation of huge amounts of olive mill solid wastes (OMSW) and olive mill wastewater (OMWW). In the present study, a strategy is proposed for converting these olive mill wastes into biochar through pyrolysis, for their later use as an organic amendment in agriculture. Specifically, two biochars were prepared from the pyrolysis of OMSW at 500 °C, either alone or impregnated with OMWW (OMSW-B and I-OMSW-B). The characterization of the OMSW and I-OMSW samples and their derived biochars showed that the fixed carbon and ash contents in the feedstocks increased by 38% and 11% respectively for OMSW-B, and by 37% and 12% respectively for I-OMSW-B. Interestingly, the impregnation process significantly increased Na, P, K, Ca and Fe contents in the produced biochars. The effect of OMSW-B and I-OMSW-B amendments at different application dose (1%, 2.5% and 5% wt/wt) on the enzymatic activity of an agricultural soil was performed at laboratory scale with a pot test. The experimental results showed that phosphatase and urease activity increased with biochar application rate; amendment with I-OMSW-B at 1%, 2.5% and 5% enhanced the phosphatase activity by 63%, 142% and 285% and urease activity by 50%, 116% and 149%, respectively. On the other hand, dehydrogenase and protease activities were higher for the application rate of 2.5% biochar. Biochar amendment promoted tomatoes seedling growth after 10 weeks, which was highest in the application rates of 2.5% and 5% for both OMSW-B and I-OSMW-B. Thus, the produced biochars had great potential to be used as biofertilizers in agriculture.

The biostimulating effects of viable microalgal cells applied to a calcareous soil: Increases in bacterial biomass, phosphorus scavenging, and precipitation of carbonates.

Microalgae used in wastewater treatment may be applied to soil as a biofertilizer - this is a novel strategy for recycling of nutrients in the circular economy. There is little information about how the application of large concentrations of unicellular algae to soil will affect soil biochemistry, particularly when they are living algal cells with the potential to form a soil biofilm, whereas soil biofilms are expected to influence plant-microbe interactions. Chlorophyte unicellular algae of the Chlorella genera are widely employed in algae-based water treatment systems, and Chlorella sorokiniana has proven to be highly adaptable for this purpose. We applied three filtrates of a Chlorella sorokiniana culture to soil microcosms, separating the microalgae from other microorganisms, as well as a sterile control filtrate without biological activity. Bacterial biomass in soils receiving the non-filtered (NF) slurry with viable algal cells was increased by 25% in the soil surface (0-8mm), and heterotrophic activity in those treatments increased as measured by CO2-C evolution. Total soil carbon concentrations were increased in the treatment with living algal cells (NF) by 0.4%, but no differences in organic carbon were measured; instead, it was found that inorganic carbon (CaCO3) concentrations increased by 0.6% in the NF treatment only. Soil phosphorus availability was also reduced in the surface of the NF treatment, indicating an increased biological demand. The results show that, when applied to soil, microalgae and associated biofilms will have relevant direct and indirect effects on soil quality and nutrients of agricultural importance.

Application of a microalgal slurry to soil stimulates heterotrophic activity and promotes bacterial growth.

Active microalgae biomass from wastewater treatment may be given added value as a biofertilizer, but little is known about how this may affect soil nutrient dynamics and biology. If the goal is to recycle waste nutrients and matter, live algae applied in a liquid slurry to soil may add both organic carbon and nutrients while providing other benefits such as biological carbon fixation. However, the potential persistence of unicellular green algae after such an application is not known, nor the influence of their photosynthetic activity on soil organic carbon - the aim of the present study was to probe these basic questions. In a controlled laboratory microcosm experiment, suspensions of Chlorella sp. microalga culture and sterile filtrates were applied to an agricultural soil and incubated for 42days, whereas the effect of darkness was also tested to understand the importance of photosynthetic activity of the algae. Autotrophic microorganism development was 3.5 times higher in treatments with algae application as measured by chlorophyll pigment concentration. Against expectations that increased photosynthetic activity would decrease the CO2-C flux, the algal suspension with a photoperiod significantly increased soil respiration compared to culture filtrates without algal cells, with accumulated quantities of 1.8 and 0.7gCO2-Cm-2, respectively. Also, phospholipid fatty acid (PLFA) analyses showed that the suspension accelerated the development of a stable community of eukaryotic and prokaryotic microorganisms in the soil surface, whereas bacterial PLFA biomarkers were significantly associated with eukaryote biomarkers on the study level.