Cytotoxic-Ag-Modified Eggshell Membrane Nanocomposites as Bactericides in Concrete Mortar.

Against the backdrop of escalating infrastructure budgets worldwide, a notable portion-up to 45%-is allocated to maintenance endeavors rather than innovative infrastructure development. A substantial fraction of this maintenance commitment involves combatting concrete degradation due to microbial attacks. In response, this study endeavors to propose a remedial strategy employing nano metals and repurposed materials within cement mortar. The methodology entails the adsorption onto eggshell membranes (ESM) of silver nitrate (ESM/AgNO3) or silver nanoparticles (ESM/AgNPs) yielding silver-eggshell membrane composites. Subsequently, the resulting silver-eggshell membrane composites were introduced in different proportions to replace cement, resulting in the formulation of ten distinct mortar compositions. A thorough analysis encompassing a range of techniques, such as spectrophotometry, scanning electron microscopy, thermogravimetric analysis, X-ray fluorescence analysis, X-ray diffraction (XRD), and MTT assay, was performed on these composite blends. Additionally, evaluations of both compressive and tensile strengths were carried out. The mortar blends 3, 5, and 6, characterized by 2% ESM/AgNO3, 1% ESM/AgNPs, and 2% ESM/AgNPs cement replacement, respectively, exhibited remarkable antimicrobial efficacy, manifesting in substantial reduction in microbial cell viability (up to 50%) of typical waste activated sludge. Concurrently, a marginal reduction of approximately 10% in compressive strength was noted, juxtaposed with an insignificant change in tensile strength. This investigation sheds light on a promising avenue for addressing concrete deterioration while navigating the balance between material performance and structural integrity.

Synthesis and Assessment of Antimicrobial Composites of Ag Nanoparticles or AgNO3 and Egg Shell Membranes.

Engineering research has been expanded by the advent of material fusion, which has led to the development of composites that are more reliable and cost-effective. This investigation aims to utilise this concept to promote a circular economy by maximizing the adsorption of silver nanoparticles and silver nitrate onto recycled chicken eggshell membranes, resulting in optimized antimicrobial silver/eggshell membrane composites. The pH, time, concentration, and adsorption temperatures were optimized. It was confirmed that these composites were excellent candidates for use in antimicrobial applications. The silver nanoparticles were produced through chemical synthesis using sodium borohydride as a reducing agent and through adsorption/surface reduction of silver nitrate on eggshell membranes. The composites were thoroughly characterized by various techniques, including spectrophotometry, atomic absorption spectrometry, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, as well as agar well diffusion and MTT assay. The results indicate that silver/eggshell membrane composites with excellent antimicrobial properties were produced using both silver nanoparticles and silver nitrate at a pH of 6, 25 °C, and after 48 h of agitation. These materials exhibited remarkable antimicrobial activity against Pseudomonas aeruginosa and Bacillus subtilis, resulting in 27.77% and 15.34% cell death, respectively.

Online Control of Lemna minor L. Phytoremediation: Using pH to Minimize the Nitrogen Outlet Concentration.

Phytoremediation technologies are employed worldwide to remove nutrient pollutants from agricultural and industrial wastewater. Unlike in algae-based nutrient removal, control methodologies for plant-based remediation have not been standardized. Control systems that guarantee consistently low outlet concentrations of nitrogen and phosphorous often use expensive analytical instruments and are therefore rarely viable. In this study, pH measurement was used as the sole input to control the nitrate outlet concentration in a continuously operated Lemna minor (lesser duckweed) phytoremediation tank. When grown in 20 L batches of modified Hoagland's solution, it was found that a constant ratio exists between the amount of nitrate removed and the amount of acid dosed (required for pH control), which was equal to 1.25 mol N·(mol H+)-1. The nitrate uptake rates were determined by standard spetrophotometric method. At critically low nitrate concentrations, this ratio reduced slightly to 1.08 mol N·(mol H+)-1. Assuming a constant nitrogen content, the biomass growth rate could be predicted based on the acid dosing rate. A proportional-integral controller was used to maintain pH on 6.5 in a semi-continuously operated tank covered by L. minor. A nitrogen control strategy was developed which exploited this relationship between nitrate uptake and dosing and successfully removed upwards of 80% of the fed nitrogen from synthetic wastewater while a constant biomass layer was maintained. This study presents a clear illustration of how advanced chemical engineering control principles can be applied in phytoremediation processes.

Optimal Growth Conditions for Azolla pinnata R. Brown: Impacts of Light Intensity, Nitrogen Addition, pH Control, and Humidity.

Nitrogen pollution from agriculture is a major challenge facing our society today. Biological nitrogen fixation is key to combat the damage that is caused by synthetic nitrogen. Azolla spp. are ideal candidates for fast nitrogen fixation. This study aimed to investigate the optimal growth conditions for Azolla pinnata R. Brown. The growth conditions that were investigated included the growth medium type and strength, light intensity, the presence/absence of nitrogen in the medium, pH control, and humidity. Higher light intensities increased plant growth by 32%, on average. The highest humidity (90%) yielded higher growth rate values than lower humidity values (60% and 75%). The presence of nitrogen in the medium had no significant effect on the growth rate of the plants. pH control was critical under the fast growth conditions of high light intensity and high humidity, and it reduced algal growth (from visual observation). The optimal growth rate that was achieved was 0.321 day-1, with a doubling time of 2.16 days. This was achieved by using a 15% strength of the Hoagland solution, high light intensity (20,000 lx), nitrogen present in the medium, and pH control at 90% humidity. These optimised conditions could offer an improvement to the existing phytoremediation systems of Azolla pinnata and aid in the fight against synthetic nitrogen pollution.

Effective Adsorption of Congo Red from Aqueous Solution Using Fe/Al Di-Metal Nanostructured Composite Synthesised from Fe(III) and Al(III) Recovered from Real Acid Mine Drainage.

This study presents the first known exploration of Congo red dye (CR) adsorption by a polycationic Fe/Al Di-metal nanostructured composite (PDFe/Al) synthesised using Fe(III) and Al(III) recovered from authentic acid mine drainage (AMD). The PDFe/Al successfully removed CR from the aqueous solution. The mineralogical, microstructural, and chemical properties of the synthesised PDFe/Al adsorbent (before and after adsorption) were studied using state-of-the-art analytical instruments. The optimum conditions were observed to be 100 mg·L-1 CR, 1 g of the PDFe/Al in 500 mL adsorbate solution, 20 min of shaking, pH = 3-8, and a temperature of 35 °C. At optimised conditions, the PDFe/Al showed ≥99% removal efficacy for CR dye and an exceptionally high Langmuir adsorption capacity of 411 mg·g-1. Furthermore, a diffusion-limited adsorption mechanism was observed, with two distinct surfaces involved in the adsorption of CR from an aqueous solution. It was determined that the adsorption of CR induced internal strain and deformation within the matrices and interlayers of the PDFe/Al which resulted in a marked increase in the adsorbent pore surface area and pore volume. The remarkably high adsorption capacity could be attributed to the high surface area. A regeneration study showed that the adsorbent could be reused more than four times for the adsorption of CR. The findings from this study demonstrated the feasibility of recovering valuable minerals from toxic and hazardous AMD and demonstrated their potential for the treatment of industrial wastewaters.

Effect of shear on morphology, viability and metabolic activity of succinic acid-producing Actinobacillus succinogenes biofilms.

Two custom-designed bioreactors were used to evaluate the effect of shear on biofilms of a succinic acid producer, Actinobacillus succinogenes. The first bioreactor allowed for in situ removal of small biofilm samples used for microscopic imaging. The second bioreactor allowed for complete removal of all biofilm and was used to analyse biofilm composition and productivity. The smooth, low porosity biofilms obtained under high shear conditions had an average cell viability of 79% compared to 57% at the lowest shear used. The maximum cell-based succinic acid productivity for high shear biofilm was 2.4 g g-1DCW h-1 compared to the 0.8 g g-1DCW h-1 of the low shear biofilm. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays confirmed higher cell metabolic activities for high shear developed biofilm compared to biofilm developed at low shear conditions. Results clearly indicated that high shear biofilm cultivation has beneficial morphological, viability, and cell-based productivity characteristics.

Impact of metabolite accumulation on the structure, viability and development of succinic acid-producing biofilms of Actinobacillus succinogenes.

Biofilms of Actinobacillus succinogenes have demonstrated exceptional capabilities as biocatalysts for high productivity, titre and yield production of succinic acid (SA). The paper presents a microscopic analysis of A. succinogenes biofilms developed under varied fermenter conditions. The concentration of excretion metabolites is controlled by operating the fermenter in a continuous mode where the liquid throughput is adjusted. It is clearly illustrated how the accumulation of excreted metabolites (concomitant with the sodium build-up due to base dosing) has a severe effect on the biofilm structure and physiology. Under high accumulation (HA) conditions, some cells exhibit severe elongation while maintaining a cross-sectional diameter like the rod/cocci-shaped cells predominantly found in low accumulation (LA) conditions. The elongated cells formed at high accumulation conditions were found to be more viable than the clusters of rod/cocci-shaped cells and appear to form connections between the clusters. The global microscopic structure of the HA biofilms also differed significantly from the LA biofilms. Although both exhibited shedding after 4 days of growth, the LA biofilms were more homogenous (less patchy), thicker and with high viability throughout the biofilm depth. The viability of the HA biofilms was threefold lower than the corresponding LA biofilms towards the end of the fermentation. Visual observations were supported by quantitative analysis of multiple biofilm samples and strengthened the main observations. The work presents valuable insights on the effect of metabolite accumulation on biofilm structure and growth.

Succinic acid production with Actinobacillus succinogenes: rate and yield analysis of chemostat and biofilm cultures.

BACKGROUND: Succinic acid is well established as bio-based platform chemical with production quantities expecting to increase exponentially within the next decade. Actinobacillus succinogenes is by far the most studied wild organism for producing succinic acid and is known for high yield and titre during production on various sugars in batch culture. At low shear conditions continuous fermentation with A. succinogenes results in biofilm formation. In this study, a novel shear controlled fermenter was developed that enabled: 1) chemostat operation where self-immobilisation was opposed by high shear rates and, 2) in-situ removal of biofilm by increasing shear rates and subsequent analysis thereof. RESULTS: The volumetric productivity of the biofilm fermentations were an order of magnitude more than the chemostat runs. In addition the biofilm runs obtained substantially higher yields. Succinic acid to acetic acid ratios for chemostat runs were 1.28±0.2 g.g(-1), while the ratios for biofilm runs started at 2.4 g.g(-1) and increased up to 3.3 g.g(-1) as glucose consumption increased. This corresponded to an overall yield on glucose of 0.48±0.05 g.g(-1) for chemostat runs, while the yields varied between 0.63 g.g(-1) and 0.74 g.g(-1) for biofilm runs. Specific growth rates (µ) were shown to be severely inhibited by the formation of organic acids, with µ only 12% of µ(max) at a succinic acid titre of 7 g.L(-1). Maintenance production of succinic acid was shown to be dominant for the biofilm runs with cell based production rates (extracellular polymeric substance removed) decreasing as SA titre increases. CONCLUSIONS: The novel fermenter allowed for an in-depth bioreaction analysis of A. succinogenes. Biofilm cells achieve higher SA yields than suspended cells and allow for operation at higher succinic acid titre. Both growth and maintenance rates were shown to drastically decrease with succinic acid titre. The A. succinogenes biofilm process has vast potential, where self-induced high cell densities result in higher succinic acid productivity and yield.

The influence of shear on the metabolite yield of Lactobacillus rhamnosus biofilms.

A tubular recycle bioreactor was employed to ensure homogeneous shear conditions on the biofilm surface. Superficial liquid velocities of 0.19 ms(-1), 0.37 ms(-1), 0.55 ms(-1) and 3.65 ms(-1) were used. The highest velocity resulted in negligible cell attachment (chemostat) while the ratio of attached-to-total cell mass escalated as the superficial velocity decreased. The lactic acid yield on glucose increased from 0.75 g g(-1) to 0.90 g g(-1) with declining shear while the corresponding acetoin yield on glucose decreased from 0.074 g g(-1) to 0.017 g g(-1). Redox analysis of the catabolites revealed a net consumption of NADH in the anabolism, while the extent of NADH consumption decreased when shear was reduced. This was attributed to the formation of more extracellular polymeric substance (EPS) at low shear conditions. A simplified metabolic flux model was used to estimate the EPS content of the biomass as a function of the shear velocity. Rate data supported the notion of increased EPS at lower shear.