Response and Resilience of <i>Scenedesmus rubescens</i> Microalgae to ZnO Nanoparticles

Microalgae are microorganisms of great importance for aquatic ecosystems. The investigation of their interaction with potential environmental stressors like nanoparticles (NPs) is essential in order to assess their behavior and fate in aquatic ecosystems. The scope of this work is to investigate the response and potential toxic effects of the short-term exposure of Scenedesmus rubescens microalga to zinc oxide (ZnO) NPs with various initial nitrate concentrations in the culture medium. Scenedesmus rubescens was cultivated in four different compositions of modified BG-11 with a nitrate content varying from 0 to 300 mg/L, and it was exposed to four concentrations of ZnO NPs, ranging from 0.081 to 81 mg/L. S. rubescens was found to be resilient towards ZnO NP toxicity. The results also highlight the fact that the toxic effects of ZnO NPs on microalgae are highly dependent on the species tested. The nitrate content of the medium did not affect the toxicity of ZnO NPs but had a significant impact on cell concentration, as it was observed at an initial nitrate concentration of 300 mg/L. Further investigation should focus on studying the morphological and metabolic characteristics and mechanisms contributing to this species’ resilience

Screening of Raw and Modified Biochars from Food Processing Wastes for the Removal of Phosphates, Nitrates, and Ammonia from Water

The aim of this work was to compare the performance of biochar from various food processing wastes of different origin for the removal of different nutrients from water. Eggshells (EGS), rice husk (RH), and coffee biochars were pyrolyzed at 400 and 800 &deg;C and were examined for the removal of phosphates, nitrates, and ammonia nitrogen. The raw materials were also modified with magnesium chloride in order to investigate their sorption behavior. The highest sorption capacity (qmax) for phosphates and ammonium was observed with EGS pyrolyzed at 800 &deg;C and was 11.45 mg PO43&minus;-P/g and 11.59 mg NH3-N/g, while the highest nitrates sorption capacity was observed with the magnesium-modified RH pyrolyzed at 800 &deg;C (5.24 mg NO3&minus;-N). The modified EGS biochars pyrolyzed at 800 &deg;C had almost the half the sorption capacity for phosphates and nitrates compared to the unmodified materials. The modification of RH pyrolyzed at 800 &deg;C resulted in higher sorption capacity by 34 and 158% for phosphates and ammonium, respectively. The coffee raw and modified biochars were less efficient in nutrient removal compared to the other materials. The specific surface area values of the biochars examined is not a decisive factor for nutrient sorption. The reaction between magnesium and calcium (for the eggshell samples) ions with phosphates is responsible for the higher sorption efficiency. On the other hand, the presence of magnesium and calcium ions has a detrimental effect on the sorption of NH3-N

Screening of Raw and Modified Biochars from Food Processing Wastes for the Removal of Phosphates, Nitrates, and Ammonia from Water

The aim of this work was to compare the performance of biochar from various food processing wastes of different origin for the removal of different nutrients from water. Eggshells (EGS), rice husk (RH), and coffee biochars were pyrolyzed at 400 and 800 °C and were examined for the removal of phosphates, nitrates, and ammonia nitrogen. The raw materials were also modified with magnesium chloride in order to investigate their sorption behavior. The highest sorption capacity (qmax) for phosphates and ammonium was observed with EGS pyrolyzed at 800 °C and was 11.45 mg PO43−-P/g and 11.59 mg NH3-N/g, while the highest nitrates sorption capacity was observed with the magnesium-modified RH pyrolyzed at 800 °C (5.24 mg NO3−-N). The modified EGS biochars pyrolyzed at 800 °C had almost the half the sorption capacity for phosphates and nitrates compared to the unmodified materials. The modification of RH pyrolyzed at 800 °C resulted in higher sorption capacity by 34 and 158% for phosphates and ammonium, respectively. The coffee raw and modified biochars were less efficient in nutrient removal compared to the other materials. The specific surface area values of the biochars examined is not a decisive factor for nutrient sorption. The reaction between magnesium and calcium (for the eggshell samples) ions with phosphates is responsible for the higher sorption efficiency. On the other hand, the presence of magnesium and calcium ions has a detrimental effect on the sorption of NH3-N

A Novel Microalgae Harvesting Method Using Laser Micromachined Glass Fiber Reinforced Polymers

Microalgae are an ideal source for next-generation biofuels due to their high photosynthetic rate. However, a key process limitation in microalgal biofuel production is harvesting of biomass and extraction of lipids in a cost-effective manner. The harvesting of the algal biomass amounts to approximately 20 to 30% of the total cost of the cultivation; hence, developing an efficient and universal harvesting method will make the commercialization of microalgal bio-cultures sustainable. In this study, we developed, demonstrated, and evaluated a novel harvesting method based on Glass Reinforced Fiber Polymer (GFRP) panels, suitable for industrial-scale installations. The proposed method was based on previous observations of preferential micro-algae development on glass surfaces, as well as in the assumption that the microalgae cells would prefer to attach to and grow on substrates with a similar size as them. At first, we developed a laser micromachining protocol for removing the resin and revealing the glass fibers of the GFRP, available for algal adhesion, thus acting as a microalgae biomass harvesting center. Surface micromachining was realized using a ns pulsed ultraviolet laser emitting at 355 nm. This laser ensured high machining quality of the GFRP, because of its selective material ablation, precise energy deposition, and narrow heat affected zone. A specially built open pond system was used for the cultivation of the microalgae species Scenedesmus rubescens, which was suitable for biofuel production. The cultivation was used for the experimental evaluation of the proposed harvesting method. The cultivation duration was set to 16 days in order for the culture to operate at the exponential growth phase. The biomass maximum recovery due to microalgae attachment on the GFRP surface was 13.54 g/m2, a yield comparable to other studies in the literature. Furthermore, the GFRP surfaces could be upscaled to industrial dimensions and positioned in any geometry dictated by the photobioreactor design. In this study, the glass fiber reinforced polymer used was suitable for the adhesion of Scenedesmus rubescens due to its fiber thickness. Other microalgae species could be cultivated, adhere, and harvested using GFRP of different fiber sizes and/or with a modified laser treatment. These very encouraging results validated GFRPs&rsquo; harvesting capabilities as an attachment substrate for microalgae. Additional studies with more algae species will further strengthen the method

Activation of Persulfate by Biochars from Valorized Olive Stones for the Degradation of Sulfamethoxazole

Biochars from spent olive stones were tested for the degradation of sulfamethoxazole (SMX) in water matrices. Batch degradation experiments were performed using sodium persulfate (SPS) as the source of radicals in the range 250&#8722;1500 mg/L, with biochar as the SPS activator in the range 100&#8722;300 mg/L and SMX as the model micro-pollutant in the range 250&#8722;2000 &#956;g/L. Ultrapure water (UPW), bottled water (BW), and secondary treated wastewater (WW) were employed as the water matrix. Removal of SMX by adsorption only was moderate and favored at acidic conditions, while SPS alone did not practically oxidize SMX. At these conditions, biochar was capable of activating SPS and, consequently, of degrading SMX, with the pseudo-first order rate increasing with increasing biochar and oxidant concentration and decreasing SMX concentration. Experiments in BW or UPW spiked with various anions showed little or no effect on degradation. Similar experiments in WW resulted in a rate reduction of about 30%, and this was attributed to the competitive consumption of reactive radicals by non-target water constituents. Experiments with methanol and t-butanol at excessive concentrations resulted in partial but generally not complete inhibition of degradation; this indicates that, besides the liquid bulk, reactions may also occur close to or on the biochar surface