Acid-hydrolyzed agricultural residue: A potential adsorbent for the decontamination of naphthalene from water bodies

Valorization of food wastes with a sequential two-step process for microbial β-carotene production: A zero waste approach

Here, two consecutive β-carotene fermentation processes were carried out with Rhodotorula glutinis yeast in the growth media obtained from orange and grape wastes. Firstly, waste biomasses were subjected to hot water extraction. Effects of waste type, drying pretreatment, particle size and solid/liquid ratio on the total concentration and yield of sugars recovered were tested. The highest sugar concentration was obtained by the hot water extraction of fresh grape pomace as 61.2 g total reducing sugars (TRS)/L at a solid/liquid ratio of 100 g/L. In the first fermentation process, effect of solid/liquid ratio (initial TRS concentration) on β-carotene production pattern of R. glutinis was investigated in the media obtained directly by hot water extraction of the wastes. Microorganism and β-carotene concentrations increased with increasing solid/liquid ratio (range 10-100 g/L), and the microbial growth data fit the Monod model well for all cases. Maximum β-carotene concentration in the growth medium obtained from hot water extraction of 100 g/L of grape pomace was determined as 5988.6 mg/L. In the second fermentation process, β-carotene was produced in the acid hydrolysate of extraction residues. 10.1 g/L and 6.7 g/L of TRS was obtained after acid hydrolysis of orange and grape residues, respectively, and the highest β-carotene concentration of 370.0 mg/L was found in the medium of hydrolyzed orange peel extraction residue. Total β-carotene production increased to 1777.1 and 3279.6 mg/L (26% and 4.9% of increase) after the second fermentation step. 85.3% and 80.2% of reduction in orange and grape waste weights were observed at the end of the process, which was an indicator of efficient waste biomass disposal. Two sequential β-carotene fermentation steps offered significant advantages in terms of both efficiency and a zero waste approach.

Effect of Ca2+ ions on naphthalene adsorption/desorption onto calcium oxide nanoparticle: Adsorption isotherm, kinetics and regeneration studies

The adsorptive nature of calcium oxide nanoparticles in aqueous sample of naphthalene in presence of Ca²⁺ ions was estimated. Enhanced efficiency of calcium oxide regeneration (90%) with the aid of calcium chloride in the solution concentration of 0.002-0.1 M was depicted. The less degree of toxic naphthalene desorption merged with SEM, FTIR and XRD characterization data portrays the importance of naphthalene adsorption onto calcium oxide using calcium chloride for regeneration. Batch adsorption studies were performed to evaluate the operating parameters such as pH, naphthalene concentration, contact time and impact of Ca²⁺ on naphthalene study. The adsorption isotherm of naphthalene on calcium oxide nanoparticle was described by Langmuir, Freundlich, Temkin and Dubinin Radushkevich and theoretical maximum monolayer adsorption capacity was found to be 63.81 mg/g at 303 K. The adsorption kinetic best fitted with pseudo second order kinetic model. The positive influence of making the addition of Ca²⁺ ions into naphthalene solution for its rapid adsorption was elucidated which is leaded by a probable increase in sorption capacity for naphthalene molecules at lower concentrations. The stable nature of crystallinity of calcium oxide and a less degree of naphthalene molecules leaching during consecutive cycles of adsorptive process and nanoparticle regeneration was also scrutinized.

In Situ Modification of Activated Carbons by Oleic Acid under Microwave Heating to Improve Adsorptive Removal of Naphthalene in Aqueous Solutions

This study aimed to improve the adsorption capacity of activated carbon (AC) towards naphthalene (NAP) in aqueous solutions. Starch-based AC (SAC) and pulverized coal-based AC (PCAC) were prepared in a one-pot procedure by activation with oleic acid and KOH under microwave heating. Brunauer–Emmett–Teller (BET) specific surface areas reached 725.0 and 912.9 m2/g for in situ modified SAC (O-SAC1) and PCAC (O-PCAC1), respectively. π–π bond, H-bond, and hydrophobic effects were directly involved in the NAP adsorption process. Batch adsorption data were well fitted by pseudo-second order kinetics and the Freundlich isotherm model. As compared to ACs prepared with only KOH activation, NAP adsorption capacities of PCAC and SAC prepared by the one-pot method increased by 16.9% and 13.7%, respectively. Influences of varying factors were investigated in column adsorption of NAP using O-SAC1 and O-PCAC1. Based on breakthrough curves analysis, the larger column height (H), lower flow rate (Q0), and lower initial concentration (C0) resulted in the longer breakthrough and exhaustion times in both cases. Specifically, we concluded that O-PCAC1 exhibits better adsorption capacity than O-SAC1 in the given conditions. The optimized operating parameters were 1 cm (H), 1 mL/min (Q0) and 30 mg/L (C0). Finally, column adsorption data could be well fitted by the Thomas model.

Hydrothermal synthesis and microwave-assisted activation of starch-derived carbons as an effective adsorbent for naphthalene removal

In this work, starch-derived spherical carbon (HC) was prepared by hydrothermal carbonization and further activated with microwave assistance to obtain the target activated carbon (HMAC). The samples were characterized by methods of N2 adsorption-desorption, Brunauer-Emmett-Teller analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis and scanning electron microscopy. Moreover, HMAC has a high BET surface area of 616.8 m2 g-1. The effects of initial naphthalene concentration, contact time, temperature, and pH of the naphthalene adsorbed on HC and HMAC were investigated systematically. The HMAC exhibits higher capability for naphthalene removal than HC, and the equilibrium adsorption quantity of HMAC was 223.03 mg g-1 at 303 K. The kinetic data revealed that the equilibrium time for naphthalene adsorption on samples was achieved at 40 min. The adsorption process of HC and HMAC for naphthalene both followed the pseudo-second-order kinetic and Freundlich isotherm models. Additionally, H-bond and π-π interactions were proposed to be involved in the adsorption process. An increasing adsorption amount of naphthalene onto HC and HMAC was observed when the pH value varied from 2 to 10. The HMAC can be successfully regenerated and maintained sorption performance after three cycles. This study revealed that HMAC obtained by hydrothermal synthesis combined with microwave-assisted activation has a promising application in the field of naphthalene removal.