Hussein Znad

Algal remediation of CO2 and nutrient discharges: a review

The recent literature pertaining to the application of algal photobioreactors (PBRs) to both carbon dioxide mitigation and nutrient abatement is reviewed and the reported data analysed. The review appraises the influence of key system parameters on performance with reference to (a) the absorption and biological fixation of CO2 from gaseous effluent streams, and (b) the removal of nutrients from wastewaters. Key parameters appraised individually with reference to CO2 removal comprise algal speciation, light intensity, mass transfer, gas and hydraulic residence time, pollutant (CO2 and nutrient) loading, biochemical and chemical stoichiometry (including pH), and temperature. Nutrient removal has been assessed with reference to hydraulic residence time and reactor configuration, along with C:nutrient ratios and other factors affecting carbon fixation, and outcomes compared with those reported for classical biological nutrient removal (BNR). Outcomes of the review indicate there has been a disproportionate increase in algal PBR research outputs over the past 5-8 years, with a significant number of studies based on small, bench-scale systems. The quantitative impacts of light intensity and loading on CO2 uptake are highly dependent on the algal species, and also affected by solution chemical conditions such as temperature and pH. Calculations based on available data for biomass growth rates indicate that a reactor CO2 residence time of around 4 h is required for significant CO2 removal. Nutrient removal data indicate residence times of 2-5 days are required for significant nutrient removal, compared with <12 h for a BNR plant. Moreover, the shallow depth of the simplest PBR configuration (the high rate algal pond, HRAP) means that its footprint is at least two orders of magnitude greater than a classical BNR plant. It is concluded that the combined carbon capture/nutrient removal process relies on optimisation of a number of process parameters acting synergistically, principally microalgal strain, C:N:P load and balance, CO2 and liquid residence time, light intensity and quality, temperature, and reactor configuration. This imposes a significant challenge to the overall process control which has yet to be fully addressed.

Ta/TiO2-and Nb/TiO2-Mixed Oxides as Efficient Solar Photocatalysts: Preparation, Characterization, and Photocatalytic Activity

Ta/TiO2- and Nb/TiO2-mixed oxides photocatalysts were prepared by simple impregnation method at different TiO2u2009:u2009Nb or Ta mass ratios of 1u2009:u20090.1, 1u2009:u20090.5, and 1u2009:u20091, followed by calcination at 500∘C. The prepared powders have been characterized by XRD, XPS, UV-Vis spectra, and SEM. The photocatalytic activity was evaluated under natural solar light for decolorization and mineralization of azo dye Orange II solution. The results showed that Nb/TiO2- and Ta/TiO2-mixed oxides have higher activity than the untreated TiO2 under natural solar light. The maximum activity was observed for Nb/TiO2 sample (at mass ratio of 1u2009:u20090.1), which is characterized by the smallest crystalline size (17.79u2009nm). Comparing with the untreated TiO2, the solar decolorization and mineralization rates improved by about 140% and 237%, respectively, and the band gap reduced to 2.80u2009eV. The results suggest that the crystal lattices of TiO2 powder are locally distorted by incorporating Nb5

Synergistic effects and optimization of nitrogen and phosphorus concentrations on the growth and nutrient uptake of a freshwater Chlorella vulgaris.

ABSTRACT The synergistic effects and optimization of nitrogen (N) and phosphorus (P) concentrations on the growth of Chlorella vulgaris (CCAP 211/11B, CS-42) and nutrient removal have been investigated under different concentrations of N (0–56 mg/L) and P (0–19 mg/L). The study showed that N/P ratio has a crucial effect on the biomass growth and nutrient removal. When N/P=10, a complete P and N removal was achieved at the end of cultivation with specific growth rate (SGR) of 1 d−1 and biomass concentration of 1.58 g/L. It was also observed that when the N content <2.5 mg/L, the SGR significantly reduced from 1.04 to 0.23 d−1 and the maximum biomass produced was decreased more than three-fold to 0.5 g/L. The Box–Behnken experimental design and response surface method were used to study the effects of the initial concentrations (P, N and C) on P and N removal efficiencies. The optimized P, N and C concentrations supporting 100% removal of both P and N at an SGR of 0.95 were 7, 55 and 10 mg/L respectively, with desirability value of 0.94. The results and analysis obtained could be very useful when applying the microalgae for efficient wastewater treatment and nutrient removal.

Solar photocatalytic degradation of chlorophenols mixture (4-CP and 2,4-DCP): Mechanism and kinetic modelling

The solar-photocatalytic degradation mechanisms and kinetics of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) using TiO2 have been investigated both individually and combined. The individual solar-photocatalytic degradation of both phenolic compounds showed that the reaction rates follow pseudo–first-order reaction. During the individual photocatalytic degradation of both 4-CP and 2,4-DCP under the same condition of TiO2 (0.5 g L−1) and light intensities (1000 mW cm−2) different intermediates were detected, three compounds associated with 4-CP (hydroquinone (HQ), phenol (Ph) and 4-chlorocatechol (4-cCat)) and two compounds associated with 2,4-DCP (4-CP and Ph). The photocatalytic degradation of the combined mixture (4-CP and 2,4-DCP) was also investigated at the same conditions and different 2,4-DCP initial concentrations. The results showed that the degradation rate of 4-CP decreases when the 2,4-DCP concentration increases. Furthermore, the intermediates detected were similar to that found in the individual degradation but with high Ph concentration. Therefore, a possible reaction mechanism for degradation of this combined mixture was proposed. Moreover, a modified Langmuir–Hinshelwood (L-H) kinetic model considering all detected intermediates was developed. A good agreement between experimental and estimated results was achieved. This model can be useful for scaling-up purposes more accurately as its considering the intermediates formed, which has a significant effect on degrading the main pollutants (4-CP and 2,4-DCP).

Chicken drumstick bones as an efficient biosorbent for copper (II) removal from aqueous solution

AbstractThe biosorption of copper (II) from aqueous solution on chicken drumstick bones as an efficient biosorbent was investigated. Batch shaking experiments were performed to examine the effects of solution pH (2–7), agitation speed (100–250u2009rpm), contact time (10–180u2009min), temperature (25–40°C), biosorbent particle size (250–100u2009μm), initial metal (50–250u2009mg L−1) and biosorbent concentrations (2.5–20u2009g L−1). An agitation speed of 200u2009rpm was found to be the optimum while the optimum pH was found to occur between a pH of 4–5. The maximum biosorption capacity obtained was 19.08u2009mg Cu(II)/g adsorbent. Within the range of 25–40°C, the higher temperature was found to boost the biosorption. The results indicate that Langmuir model provides best correlation of experimental data. It is proposed that the copper-uptake process is controlled by surface chemisorption interactions at the earlier stages (0–20u2009min) and by intraparticle diffusion at the later stages (after 20u2009min).

Boron removal from seawater using date palm (Phoenix dactylifera) seed ash

AbstractThe feasibility of date seed ash, a low-cost agricultural by-product in Oman, for the removal of boron from aqueous solution was investigated. The aim of this study was to understand the mechanism that governs boron removal from seawater using date seed ash as an adsorbent in batch adsorption experiments. The effects of adsorbent dose, contact time, and temperature on boron removal were tested. A surface study of the date seed ash was investigated using scanning electron microscope, energy-dispersive X-ray spectroscopy, and Fourier transform infrared. Thermogravimetric-analysis, specific area using Brunauer, Emmett and Teller method, and particle density were also obtained. The maximum removal efficiency of boron was around 47% at neutral pH. The application of date seed ash is a promising adsorbent for boron removal where it can be used as pretreatment before reverse osmosis desalination process. This will increase the stability of membranes, minimize the membrane scaling, and ultimately reduce t...

Dairy farm wastewater treatment and lipid accumulation by Arthrospira platensis

Dairy cattle treated wastewaters are potential resources for production of microalgae biofuels. A study was conducted to evaluate the capability of Arthrospira platensis cultivated in dairy farm wastewater for biodiesel production. The biomass of Arthrospira platensis was found to be 4.98xa0gxa0L-1 and produced 30.23xa0wt% lipids to dry biomass cultivated in wastewater which was found nitrogen stressed in photo bioreactor. The extracted lipid displayed a suitable fatty acid profile for biodiesel, although the content of linolenic acid was found a little higher than the standard EN14214. It was found that nitrogen stressed medium increase the total lipid content but temperature and intensities of light were the most important factors to control the quantity of linolenic acid and hence the quality of biodiesel, while the optimum CO2 helped to achieve maximum biomass and triacylglycerols. The Arthrospira platensis offer a good option for the treatment of wastewater before final discharge.

Use of Ceramic Membrane Technology for Sustainable Management of Oil Production Water: A Review

The huge quantities of water produced along with oil make production of water one of the main challenges in the oil and gas industry. In the past, water produced in oil production was considered a tiresome by-product which represented a significant liability and cost to oil and gas production. Recently this attitude has changed and this water is now seen more as a resource than a by-product. By 2025, 2.8 billion people (from 48 countries) will be living in water-scarce and water-stressed countries. The Sultanate of Oman is considered a semi-arid country where the average annual rainfall is about 100 mm. Petroleum Development Oman (PDO) produces around 700,000 m3/day of water associated with hydrocarbon production. Currently under half of this amount is injected back into reservoirs as water for reservoir management. The production of excessive quantities of water is the reason behind abandoning oil and gas wells, leaving huge quantities of hydrocarbons behind. Upgrading of low quality water (i.e. oil production water) for greening the desert or growing biofuels is becoming a strategic enabler for the sustainable development of remote oil fields. Although opportunities exist for the beneficial use of oil production water, there may be situations where treatment may not be economically feasible. In addition to volume, water quality is the other key determinant of suitable management options. Due to the poor quality of oil production water which contains a complex mixture of organic and inorganic materials similar to those found in crude oil and natural gas, treatment might introduce potential economic, technological and environmental challenges. Another constraint for the management of oil production water is the regulatory framework which might cause restrictions to management options imposed by legislation. Economic constraints imposed by the costs associated with management options can influence the feasibility of particular management techniques. The application of ceramic membranes has shown great potential for oil in water separation and purification due to their superior mechanical, thermal and chemical stability and ease of generation after fouling. Very promising results were achieved by many researchers when using ceramic membranes for oily water treatment. In some studies the removal of oil, COD and TOC reach up to 99 %, 96 % and 94 %, respectively.

Role of ferric and ferrous ions in the enhancement of the heterogeneous solar photocatalytic degradation of combined mixture of chlorophenols.

The solar photocatalytic degradation of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) was investigated individually and combined in the presence of Fe2+ and Fe3+ ions. The results revealed that both Fe2+ and Fe3+ ions enhanced the heterogeneous photocatalytic degradation. Fe3+ ions rapidly converted to Fe2+ ions as soon as the irradiation started. The intermediates formed during the degradation of 4-CP/2,4-DCP were also monitored and identified. Three main intermediates were observed, hydroquinone, phenol, and 4-chlorocatechol with traces of benzoquinone. The results support a new trend of research by utilising other cheap iron ion sources in the photocatalytic degradation.

Removal of Dissolved Organic Carbon from Oily Produced Water by Adsorption onto Date Seeds: Equilibrium, Kinetic, and Thermodynamic Studies

The feasibility of date seeds as a new low-cost natural adsorbent for the removal of dissolved organic carbon (DOC) from oily produced water was investigated. The aim of this study was to elucidate the mechanism associated with the removal of DOC and to find the best equilibrium isotherms and kinetic models for DOC removal in batch adsorption experiments. The effect of various physicochemical parameters such as initial DOC concentration (18.5–93.5xa0mg/L), solution pH (4–9), temperature (25–45xa0°C), and date seeds dosages (0.5–2.0xa0g) was evaluated. The equilibrium stage was attained after a contact time of 120xa0min. The maximum DOC removal was 82xa0% for 93.5xa0mg/L of DOC concentration. The equilibrium data were well represented by the Langmuir isotherm. The maximum monolayer adsorption capacity of date seeds was found to be 74.62xa0mg/g. The separation factor, RL, from the Langmuir equation and the Freundlich constant, n, indicated a favorable adsorption. The kinetic studies indicated that the adsorption process follows the pseudo-second-order kinetics. The adsorption of DOC is governed by both surface and pore diffusion. The results revealed that the DOC uptake decreases when temperature and pH increases. The adsorption process has been found exothermic in nature, and the thermodynamic parameters were determined. The Langmuir isotherm model equation was adopted to design a single-stage batch absorber for DOC adsorption onto date seeds. The study demonstrated that date seeds can be considered as a promising low-cost adsorbent for the removal of DOC from oily produced water.