Phytoremediation is often discussed as a means of extracting trace metals in excess in the soil, but to increase its efficiency a better understanding of the factors controlling plant uptake is required. The main objective of this study was to examine the effect of origin (anthropogenic vs. geogenic) and mobility of thallium (Tl) in the rhizosphere on Tl uptake. Two Tl-hyperaccumulating Brassicaceae species, kale (Brassica oleracea acephala L. cv. Winterbor F1) and candytuft (Iberis intermedia Guers.), were grown in a rhizobox system to investigate the dynamics of Tl in the rhizosphere soil. Four different soils were used. Two soils contained high Tl amounts due to anthropogenic sources (emissions from a cement plant and mining activities). High Tl content in the two other soils was due to a high rock content (geogenic origin). On completion of growth in the rhizoboxes, the depletion of Tl in seven different chemical fractions, determined by sequential extraction, was compared to the plant uptake. Most of the Tl taken up was derived from the so-called "easily accessible" fractions in both soils with geogenic Tl as well as in the soils polluted by mining activities. Due to the small amounts of easily accessible Tl in the geogenic soils, Tl uptake by Brassicaceae was low. On the other hand, for the air emission-polluted soil, a high depletion of Tl from "less accessible" fractions was observed in addition to depletion of the easily accessible fractions. Hence, the latter soil demonstrated the highest potential for effective soil decontamination by phytoextraction within an appropriate time frame.
This study characterized the physicochemical properties of sewage sludge collected from Gaza wastewater treatment plant. Sludge samples were collected from the drying beds, air-dried, sieved through 2 mm and stored in plastic bags at room temperature. Sludge density, particle size distribution, water holding capacity, void volume, pH, EC, total organic carbon and hydrophobicity were determined. Results showed the bulk density is about 1.18 g/cm 3 whereas the real density is 2.12 g/cm 3 and void volume is 50%; Particle size distribution showed that the major size of sludge is sand-like size (630-200 µm) and the minor size is silt-like size (200-20 µm) and clay-like size is less than 20 µm. Sludge has an acidic pH reaction (6.78 ± 0.02) with an electric conductivity equal to (2.49 ± 0.04) mS•cm −1. The hydrophobicity of sludge is very high, water drop penetration time (WDPT) is 114.77 ± 18.78 sec with a radius of 0.44 ± 0.08 cm. In the way around, oil drop penetration time (ODPT) of sludge is 5.05 ± 1.28 sec with a radius of 1.25 ± 0.14 cm. The WDPT/ODPM ration has very high value 22.73 indicating extreme hydrophobicity. High value of hydrophobicity may reduce water filtration in soil when sludge applied for agriculture. These results suggest that sludge application to soil may change the physicochemical properties of soil.
This paper determined cations and anions concentrations, Total Kjeldahl Nitrogen (TKN), and heavy metals content in sewage sludge collected from the drying beds of wastewater treatment plant in Gaza. The aim was to test the possibility of using this sewage sludge as an alternative source of mineral fertilizers. Many instruments were used in this work: flame photometry (K, Na), EDTA titration (Ca, Mg), the turbidity method ( )
A field experiment was carried out to determine the effect of different land use systems such as continuous grass and agricultural crops rotation on the bioavailability of heavy metals in soils contaminated by former excessive sewage sludge application. The results show that Cd and Zn concentrations increased to 2 and 3.5 folds within 3 cuts of grass, respectively. Even 10 years after the end of excessive sewage sludge application the concentration of Cd in winter and summer wheat is 3.4 and 2.5 folds higher than the control, respectively. Zn concentration increased by two folds for both crops. In conclusion, the uptake depends on plant species and the degree of soil contamination. The availability of heavy metals was not changed with time.
a b s t r ac tScarcity of water resources increases the pressure to develop methods for wastewater treatments. In this study, modifications of sand filter were made by installing vertical devices with different length to change the conditions inside the sand filter; consequently, the produced water may be suitable for reuse. We assessed the performance of modified sand filters cultivated with and without reed plant in changing the flow rate, removing biochemical oxygen demand (BOD 5 ), chemical oxygen demand (COD), removal of ammonia, total Kjeldahl nitrogen (TKN), removal of nitrate, total suspended solids (TSS), and fecal coliforms (FC). Two types of sand filters were used in this study: one sand filter was planted with reed bed and the second without reed bed. Results showed that modified sand filters had the ability to reduce the flow rate nearly 10 times lower than regular sand filter (horizontal flow). Moreover, removal of BOD 5 , COD, nitrogen compound, TSS, and FC was also significant. An interesting outcome of the study is that sand filter removed 52% of BOD 5 , 32% of COD, 39% of TKN, 35% of NH 4 as result of NH 3 conversion to NO 3 , 93% of FC, and 71% of TSS. It is evident that modified filters have higher efficiency in removing pollutants from wastewater. It can be concluded that application of sand filters will significantly improve the quality of treated wastewater. The study revalued that increasing retention time in the sand filters considerably increased the removal efficiency.
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