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In this study, natural zeolite with maximum adsorption capacity of 3.59 mg g -1 was used for the simultaneous removal of ammonium nitrogen (NH 4 + -N), dissolved chemical oxygen demand (d-COD) and color from raw sanitary landfill leachate (SLL). Saturation, desorption and regeneration tests of zeolite were performed. Optimum adsorption conditions were found for particle size 0.930 µm, stirring rate of 1.18 m s -1 , zeolite dosage of 133 g L -1 and pH 8. NH 4 + -N removal efficiency reached 51.63 ± 0.80% within 2.5 min of contact. NH 4 + -N adsorption follows mostly the linear pseudo-second order model, with intra-particle diffusion. NH 4 + -N desorption follows the linear pseudo-second order model. Adsorption data fitted to the Temkin Isotherm in linear and nonlinear forms. Saturation tests showed that zeolite can be efficiently used in three successive adsorption cycles. NH 4 + -N release from the saturated zeolite was not completely reversible, suggesting that the zeolite may be used as slow ΝΗ 4 + -Ν releasing fertilizer and an attractive low cost material for the treatment of SLL. NH 4 + -N removal with the regenerated zeolite exceeded 40% of the initial concentration in the fluid within 2.5 min. SEM analysis showed significant changes through saturation and regeneration. XPS revealed that adsorption of ΝΗ 4 + -Ν to the zeolite was accompanied by ion exchange., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In the present study, indigenous microorganisms from industrial sludge were used to reduce the activity of Cr(VI). Molasses, a by-product of sugar processing, was selected as the carbon source (instead of sugar used in a previous work) as it is a low-cost energy source for bioprocesses. Initially, experiments were carried out in suspended growth batch reactors for Cr(VI) concentrations of 1.5-110 mg/L. The time required for complete Cr(VI) reduction increased with initial Cr(VI) concentration. Initial molasses concentration was also found to influence the Cr(VI) reduction rate. The optimal concentration for all initial Cr(VI) concentrations tested was 0.8 gC/L. Experiments were also carried out in packed-bed reactors. Three different operating modes were used to investigate the optimal performance and efficiency of the filter, i.e. batch, continuous and SBR with recirculation. The latter mode with a recirculation rate of 0.5L/min lead to significantly high Cr(VI) reduction rates (up to 135 g/m(2)d). The results of this work were compared with those of a similar work using sugar as the carbon source and indicate that molasses could prove a feasible technological solution to a serious environmental problem., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The present work was conducted to study integrated chromium removal from aqueous solutions in horizontal subsurface (HSF) constructed wetlands. Two pilot-scale HSF constructed wetlands (CWs) units were built and operated. One unit was planted with common reeds (Phragmites australis) and one was kept unplanted. Influent concentrations of Cr(VI) ranged from 0.5 to 10mg/L. The effect of temperature and hydraulic residence time (8-0.5 days) on Cr(VI) removal were studied. Temperature was proved to affect Cr(VI) removal in both units. In the planted unit maximum Cr(VI) removal efficiencies of 100% were recorded at HRT's of 1 day with Cr(VI) concentrations of 5, 2.5 and 1mg/L, while a significantly lower removal rate was recorded in the unplanted unit. Harvested reed biomass from the CWs was co-composted with olive mill wastes. The final product had excellent physicochemical characteristics (C/N: 14.1-14.7, germination index (GI): 145-157%, Cr: 8-10mg/kg dry mass), fulfills EU requirements and can be used as a fertilizer in organic farming., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Several approaches of hydrogenotrophic denitrification of potable water as well as technical data and mathematical models that were developed for the process are reviewed. Most of the applications that were tested for hydrogenotrophic process achieved great efficiency, high denitrification rates, and operational simplicity. Moreover, this paper reviews the variety of reactor configurations that have been used for hydrogen gas generation and efficient hydrogen delivery. Microbial communities and species that participate in the denitrification process are also reported. The variation of nitrate concentration, pH, temperature, alkalinity, carbon and microbial acclimation was found to affect the denitrification rates. The main results regarding research progress on hydrogenotrophic denitrification are evaluated. Finally, the commonly used models and simulation approaches are discussed., (Copyright 2010 Elsevier B.V. All rights reserved.)

The aim of this work was to study hydrogenotrophic denitrification in packed-bed reactors under draw-fill and continuous operation. Three bench-scale packed-bed reactors with gravel in different sizes (mean diameter 1.75, 2.41 and 4.03 mm) as support media were used, in order to study the effect of particle size on reactors performance. The maximum denitrification rate achieved under draw-fill operation was 4.4 g NO(3)(-)-N/ld for the filter with gravel of 2.41 mm. This gravel size was chosen to perform experiments under continuous operation. Feed NO(3)(-)-N concentrations and hydraulic loadings (HL) ranged between 20-200mg/l and 5.7-22.8m(3)/m(2)d, respectively. A comparison between the two operating modes showed that, for low HL the draw-fill operation achieved higher denitrification rates, while for high HL and intermediate feed concentrations (40-60 mg NO(3)(-)-N/l) the continuous operation achieved higher denitrification rates (4.67-5.65 g/ld). Finally, experiments with three filters in series (with gravels of 4.03, 2.41 and 1.75 mm mean diameter) were also performed under continuous operation. The maximum denitrification rate achieved was 6.2 g NO(3)(-)-N/ld for feed concentration of 340 mg/l and HL of 11.5m(3)/m(2)d. A model, which describes denitrification in packed-bed reactors, was also developed. The model predicts the concentration profiles of NO(3)(-)-N along filter height, in draw-fill as well as in continuous operation, satisfactorily.

Two pilot-scale trickling filters were used in order to estimate Cr(VI) reduction through biological mechanisms in biofilm reactors operated in SBR mode with recirculation using different filter media types, i.e. plastic media and calcitic gravel. The feed concentrations of Cr(VI) examined were about 5, 10, 20, 30, 50 and 100mg/l, while the concentration of the organic carbon was constant at 400mg/l, in order to avoid carbon limitations in the bulk liquid. Maximum reduction rates of 4.8 and 4.7gCr(VI)/d were observed for feed Cr(VI) concentration of about 5mgCr(VI)/l, for the filters with the plastic support material and the gravel media, respectively. The reduction rates were significantly affected by the feed Cr(VI) concentration in both bioreactors. A dual-enzyme kinetic model was used in order to describe Cr(VI) reduction by aerobically grown mixed cultures. Model predictions were found to correspond very closely to experimental quantitative observations of Cr(VI) reduction at both pilot-scale trickling filters used.

A pilot-scale trickling filter was constructed and tested for biological chromium(VI) removal from industrial wastewater. Indigenous bacteria from industrial sludge were enriched and used as inoculum for the filter. Sodium acetate was used as carbon source and it was found to inhibit chromate reduction at high concentrations. Three different operating modes were used to investigate the optimal performance and efficiency of the filter, i.e. batch, continuous and SBR with recirculation. The latter one was found to achieve removal rates up to 530 g Cr(VI)/m2 d, while aeration was taking place naturally without the use of any external mechanical means. The low operating cost combined with the high hexavalent chromium reduction rates indicates that this technology may offer a feasible solution to a very serious environmental problem.