In this study the removal of Chromium (III) and Chromium (VI) ions are investigated via polymer enhanced ultrafiltration under important process parameters. This study proposes the use of unmodified starch as a novel polymer in the ultrafiltration process and its performance on the removal of chromium ions was compared with a commonly used polymer, polyethylene glycol.
In this study, a twin-chamber upflow bio-electrochemical reactor packed with palm shell granular activated carbon as biocarrier and third electrode was used for sequential nitrification and denitrification of nitrogen-rich wastewater under different operating conditions. The experiments were performed at a constant pH value for the denitrification compartment. The effect of variables, namely, electric current (I) and hydraulic retention time (HRT), on the pH was considered in the nitrification chamber. The response surface methodology was used based on three levels to develop empirical models for the study on the effects of HRT and current values as independent operating variables on NH(4)(+)-N removal. The results showed that ammonium was reduced within the function of an extensive operational range of electric intensity (20-50 mA) and HRT (6-24h). The optimum condition for ammonium oxidation (90%) was determined with an I of 32 mA and HRT of 19.2h.
In this study, a novel continuous reactor has been developed to produce high quality methyl esters (biodiesel) from palm oil. A microporous TiO2/Al2O3 membrane was packed with potassium hydroxide catalyst supported on palm shell activated carbon. The central composite design (CCD) of response surface methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst amount and cross flow circulation velocity on the production of biodiesel in the packed bed membrane reactor. The highest conversion of palm oil to biodiesel in the reactor was obtained at 70 °C employing 157.04 g catalyst per unit volume of the reactor and 0.21 cm/s cross flow circulation velocity. The physical and chemical properties of the produced biodiesel were determined and compared with the standard specifications. High quality palm oil biodiesel was produced by combination of heterogeneous alkali transesterification and separation processes in the packed bed membrane reactor.
Removal of Cr(VI) ions from aqueous solution was investigated using modified palm shell activated carbon. Low Molecular Weight Polyethyleneimine (LMW PEI) was used for impregnation purpose. The maximum amount of LMW PEI adsorbed on activated carbon was determined to be approximately 228.2mg/g carbon. The adsorption experiments were carried out in a batch system using potassium dichromate K(2)Cr(2)O(7) as the source of Cr(VI) in the synthetic waste water and modified palm shell activated carbon as the adsorbent. The effects of pH, concentration of Cr(VI) and PEI loaded on activated carbon were studied. The adsorption data were found to fit well with the Freundlich isotherm model. This modified Palm shell activated carbon showed high adsorption capacity for chromium ions.
In this study the kinetics of autohydrogenotrophic denitrification was studied under optimum solution pH and bicarbonate concentration. The optimal pH and bicarbonate concentration were firstly obtained using a design of experiment (DOE) methodology. For this purpose a total of 11 experiments were carried out. Sodium bicarbonate concentrations ranging of 20-2000 mg/L and pH values from 6.5 to 8.5 were used in the optimization runs. It was found that the pH has a more pronounced effect on the denitrification process as compared to the bicarbonate dose. The developed quadratic model predicted the optimum conditions at pH 8 and 1100 mg NaHCO(3)/L. Using these optimal conditions, the kinetics of denitrification for nitrate and nitrite degradation were investigated in separate experiments. Both processes were found to follow a zero order kinetic model. The ultimate specific degradation rates for nitrate and nitrite remediation were 29.60 mg NO(3)(-)-N/g MLVSS/L and 34.85 mg NO(3)(-)-N/g MLVSS/L respectively, when hydrogen was supplied every 0.5h.
The effects of polyethyleneimine (PEI) impregnation on the Pb(2+) adsorption kinetics of palm shell-activated carbon and pH profile of bulk solution were investigated. Adsorption data were fitted to four established adsorption kinetics models, namely, pseudo-first-order, pseudo-second-order, Elovich equation and intraparticle diffusion. It was found that PEI impregnation at 16.68 and 29.82 wt% PEI/AC increased the Pb(2+) uptake rate while the opposite was observed for PEI impregnation at 4.76 and 8.41 wt% PEI/AC. The increased uptake rates were due to higher concentration of PEI molecules on the surface of clogged pores as well as varying pore volumes. The adsorption kinetics data fitted the pseudo-second-order model better than the pseudo-first-order model, implying chemisorption was the rate-controlling step. The bulk solution pH generally showed an increasing trend from the use of virgin to PEI-impregnated activated carbon.
Acclimation of autohydrogenotrophic denitrifying bacteria using inorganic carbon source (CO(2) and bicarbonate) and hydrogen gas as electron donor was performed in this study. In this regard, activated sludge was used as the seed source and sequencing batch reactor (SBR) technique was applied for accomplishing the acclimatization. Three distinct strategies in feeding of carbon sources were applied: (I) continuous sparging of CO(2), (II) bicarbonate plus continuous sparging of CO(2), and (III) only bicarbonate. The pH-reducing nature of CO(2) showed an unfavorable impact on denitrification rate; however bicarbonate resulted in a buffered environment in the mixed liquor and provided a suitable mean to maintain the pH in the desirable range of 7-8.2. As a result, bicarbonate as the only carbon source showed a faster adaptation, while carbon dioxide as the only carbon source as well as a complementary carbon source added to bicarbonate resulted in longer acclimation period. Adapted hydrogenotrophic denitrifying bacteria, using bicarbonate and hydrogen gas in the aforementioned pH range, caused denitrification at a rate of 13.33 mg NO(3)(-)-N/g MLVSS/h for degrading 20 and 30 mg NO(3)(-)-N/L and 9.09 mg NO(3)(-)-N/g MLVSS/h for degrading 50mg NO(3)(-)-N/L.
Accumulation of nitrite intermediate in autohydrogenotrophic denitrification process has been a challenging difficulty to tackle. This study showed that further growth of "true denitrifying" bacteria and adaptation to nitrite led to a faster reduction of nitrite than nitrate as a solution to circumvent nitrite accumulation. Moreover, two effective parameters namely pH and bicarbonate dose were optimized in order to achieve a better reduction rate. Sodium bicarbonate dose ranging from 20 to 2000 mg/L and pH in the range of 6.5-8.5 was selected to be examined employing 0.2 g MLVSS/L of reacclimatized denitrifying bacteria. Eleven runs of experiments were designed considering the interactive effect of these two operative parameters. A fairly close reduction time less than 4.5 h (>22.22 mg NO2(-)-N/g MLVSS/h) was gained for the pH range between 7 and 8. The highest specific nitrite reduction rate at 25 mg NO2(-)-N/g MLVSS/h was achieved applying 1000 mg NaHCO3/L at pH 7.5 and 8. The pH was found to be the leading parameter and bicarbonate as the less effective parameter on nitrite reduction removal. Central composite design (CCD) and response surface design (RSM) were employed to develop a model as well as define the optimum condition. Using the experimental data, the developed quadratic model predicted optimum condition at pH 7.8 and sodium bicarbonate dose 1070 mg/L upon which denitrifiers managed to accomplish reduction within 3.5 h and attained the specific degradation rate of 28.57 mg NO2(-)-N/g MLVSS/h.
In this study, the kinetics of adsorption of Pb(II) from aqueous solution onto palm shell-based activated carbon (PSAC) were investigated by employing ion selective electrode (ISE) for real-time Pb(II) and pH monitoring. Usage of ISE was very appropriate for real-time adsorption kinetics data collection as it facilitated recording of adsorption data at very specific and short time intervals as well as provided consistent kinetics data. Parameters studied were initial Pb(II) concentration and agitation speed. It was found that increases in initial Pb(II) concentration and agitation speed resulted in higher initial rate of adsorption. Pseudo first-order, pseudo second-order, Elovich, intraparticle diffusion and liquid film diffusion models were used to fit the adsorption kinetics data. It was suggested that chemisorption was the rate-controlling step for adsorption of Pb(II) onto PSAC since the adsorption kinetics data fitted both the pseudo second-order and Elovich models well.
Nitrates in different water and wastewater streams raised concerns due to severe impacts on human and animal health. Diverse methods are reported to remove nitrate from water streams which almost fail to entirely treat nitrate, except biological denitrification which is capable of reducing inorganic nitrate compounds to harmless nitrogen gas. Review of numerous studies in biological denitrification of nitrate containing water resources, aquaculture wastewaters and industrial wastewater confirmed the potential of this method and its flexibility towards the remediation of different concentrations of nitrate. The denitrifiers could be fed with organic and inorganic substrates which have different performances and subsequent advantages or disadvantages. Review of heterotrophic and autotrophic denitrifications with different food and energy sources concluded that autotrophic denitrifiers are more effective in denitrification. Autotrophs utilize carbon dioxide and hydrogen as the source of carbon substrate and electron donors, respectively. The application of this method in bio-electro reactors (BERs) has many advantages and is promising. However, this method is not so well established and documented. BERs provide proper environment for simultaneous hydrogen production on cathodes and appropriate consumption by immobilized autotrophs on these cathodes. This survey covers various designs and aspects of BERs and their performances.
The continuous adsorption of lead ions from aqueous solution on commercial, granular, unpretreated palm shell activated carbon (PSAC) was studied. Effect of pH, flow rates and presence of complexing agents (malonic and boric acids) were examined. The breakthrough period was longer at pH 5 indicating higher adsorption capacity of lead ions at higher pH. Increase of the flow rate, expectedly, resulted in the faster saturation of the carbon bed. Presence of complexing agents did not improve adsorption uptake of lead ions. However, presence of malonic acid resulted in smoother pH stabilization of solution compared to single lead and lead with boric acid systems. The results on continuous adsorption of lead were applied to the model proposed by Wang et al. [Y.-H. Wang, S.-H. Lin, R.-S. Juang, Removal of heavy metals ions from aqueous solutions using various low-cost adsorbents, J. Hazard. Mater. B 102 (2003) 291-302]. The agreement between experimental and modelled breakthrough curves was satisfactory at both pHs.
This study deals with the removal of chromium species from aqueous dilute solutions using polymer-enhanced ultrafiltration (PEUF) process. Three water soluble polymers, namely chitosan, polyethyleneimine (PEI) and pectin were selected for this study. The ultrafiltration studies were carried out using a laboratory scale ultrafiltration system equipped with 500,000 MWCO polysulfone hollow fiber membrane. The effects of pH and polymer composition on rejection coefficient and permeate flux at constant pressure have been investigated. For Cr(III), high rejections approaching 100% were obtained at pH higher than 7 for the three tested polymers. With chitosan and pectin, Cr(VI) retention showed a slight increase with solution pH and did not exceed a value of 50%. An interesting result was obtained with PEI. The retention of Cr(VI) approached 100% at low pH and decreased when the pH was increased. This behavior is opposite to what one can expect in the polymer-enhanced ultrafiltration of heavy metals. Furthermore, the concentration of polymer was found to have little effect on rejection. Permeate flux remained almost constant around 25% of pure water flux.
Palm shell was used to prepare activated carbon using potassium carbonate (K2CO3) as activating agent. The influence of carbonization temperatures (600-1000 degrees C) and impregnation ratios (0.5-2.0) of the prepared activated carbon on the pore development and yield were investigated. Results showed that in all cases, increasing the carbonization temperature and impregnation ratio, the yield decreased, while the adsorption of CO2 increased, progressively. Specific surface area of activated carbon was maximum about 1170 m2/g at 800 degrees C with activation duration of 2 h and at an impregnation ratio of 1.0.
Palm shell activated carbon was modified via surface impregnation with polyethyleneimine (PEI) to enhance removal of Cu(2+) from aqueous solution in this study. The effect of PEI modification on batch adsorption of Cu(2+) as well as the equilibrium behavior of adsorption of metal ions on activated carbon were investigated. PEI modification clearly increased the Cu(2+) adsorption capacities by 68% and 75.86% for initial solution pH of 3 and 5 respectively. The adsorption data of Cu(2+) on both virgin and PEI-modified AC for both initial solution pH of 3 and 5 fitted the Langmuir and Redlich-Peterson isotherms considerably better than the Freundlich isotherm.
The performance of a commercially available palm shell based activated carbon to remove lead ions from aqueous solutions by adsorption was evaluated. The adsorption experiments were carried out at pH 3.0 and 5.0. The effect of malonic and boric acid presence on the adsorption of lead ions was also studied. Palm shell activated carbon showed high adsorption capacity for lead ions, especially at pH 5 with an ultimate uptake of 95.2mg/g. This high uptake showed palm shell activated carbon as amongst the best adsorbents for lead ions. Boric acid presence did not affect significantly lead uptake, whereas malonic acid decreased it. The diffuse layer surface complexation model was applied to predict the extent of adsorption. The model prediction was found to be in concordance with the experimental values.