الفهرس 
Acknowledgements
definition of sewage sludgeOnly 14 pages are availabe for public view
 |  | from | 143 |  |  |
| | | from | 143 | | |
Abstract
The EDTA- extractable Pb reached the maximum amount (53.14 mg/kg) with the application of 20% CKD treated sludge to the soil with an increase by 68.1 % compared to the control. Treating the soil with 10 and 20% silica gel amended sludge had the lowest effects on increasing EDTA-extractable Pb to be only 32.2 and 35.2%, respectively, compared with the control.2-4-2 Residual effect The EDAT-extractable Pb was extremely lower in the second season in all treatments including the control. EDTA-extractable Pb of the control treatment decreased from 31.62 mg/kg in the first season to 0.00 mg/kg in the second season (residual effect) In the soil amended with the untreated sludge, the high absorbance of Jew’s mallow plants significantly reduced EDTA- extractable Pb from 31.93 mg/kg in the first season to 1.84 mg/kg in the second season (residual effect). Generally, the application of sludge to the soil significantly increased EDTA- extractable Pb.
The application of stabilizers also increased EDTA- extractable Pb. Just like the first season, the most effective treatment on increasing EDTA-extractable Pb is sludge amended with 20% SG (9.52
mg/kg).
2-4-3 Reapplication effect
The EDTA-extractable Pb reached its minimum value (0.00 mg/kg) in the control treatment due to the high absorbance of Jew’s mallow plants.
The reapplication of sludge to the soil significantly increased soil content of EDTA-extractable Pb compared to the control.
The maximum value of EDTA-extractable Pb is found with the 20% FO treatment (9.32 mg/kg).
The comparison between the data of the first (direct effect) and the second (residual and reapplication effects) season show that the application of sludge always increases the EDTA-extractable Pb.
The increase of Pb in soil may be alleviated by some plant cultivars such as Jew’s mallow plants.
3- Vegetative properties of each harvest
3-1 Vegetative properties of onion plants (direct effect)
Compared with the control (the soil without any treatment), the untreated sludge decreased plant length for onion by (12.3%), shoot fresh weight (47.8%), bulb fresh weight (70.2%), shoot dry weight (33.3%) and bulbs dry weight (37.0 %).
The application of sludge treated with silica gel + iron oxide (SG+FO) and 20% silica gel (SG) significantly increased onion length from 30.50 cm for the control and from 26.75 cm for the untreated sludge to 37.88 cm and 35.75 cm, respectively.
The sludge treated with 20% silica gel was the best that increased the onion total length by (17.2%), shoot fresh weight (148.5%), bulb fresh weight (6.99%), shoot dry weight (127.8%) and bulb dry weight (159.2%) compared to the control.
The respective increases were 33.6, 376.4, 259.9, 241.8 and 311.8% compared to the untreated sludge treatment.
The application of sludge treated with iron oxide and cement kiln dust (FO+CKD) also significantly increased the plant length, shoot and bulb fresh weights by 22.4, 165.8 and 256.3%, respectively, compared to the untreated sludge.
3-2 Vegetative properties of Jew’s mallow plants (residual effects)
The residual effect of untreated sludge showed the same decrease trend that was indicated for onion plants (direct effect) with respect of the length, fresh and dry weights of Jew’s mallow plants compared to the control treatment.
The respective decreases were 10, 43.1 and 7.7% for the vegetative properties.
The residual effect of untreated sewage sludge also exhibited the same trend recorded for the direct untreated sewage application but with lower reduction effects on Jew’s mallow vegetative properties.
Treating the sludge with any of the investigated materials resulted in significant increases in the plant length, fresh and dry weights except the 20% FO amended sludge treatment. The plant length reached 32.25 cm using the sludge treated with 20% SG resulting in an increase of 222.5% compared to the control. 3 Vegetative properties of Jew’s mallow plants (reapplication effect) Generally, the reapplication of sewage sludge (untreated or treated sludge) resulted in increasing all discussed plant properties compared with the same properties in the residual experiment. The application of sludge treated with 20% FO had the best effect on all discussed plant properties followed by sludge treated with 20% SG.
Compared to the control, the 20% FO and 20% SG treated sludge increased the plant length from 16.0 cm to 76.0 and 54.0 cm, the fresh weight from 1.35 g/pot to111.53 and 26.81 g/pot and dry weight from 0.52 g/pot to 32.74 and 6.31 g/pot, respectively. The application of any of the treated sludge had improving effects on all discussed plant properties compared to the application of untreated sludge. 4- Ni content in plants 4-1 Direct effect (onion plants) In the first season (direct effect), the SG+FO treated sludge was the best treatment which reduced the Ni content in shoots and bulbs by 71.6% and 75.6% , respectively, compared to the control and by 87.0% and 68.7%, respectively, compared to the untreated sludge. In the second season, it was also one of the best treatments in reducing Ni content in Jew’s mallow plants by 60.7% compared to the control. In the first season, treating the sludge with 10 and 20% of FO significantly decreased the Ni content by 72.2 and 63.2%, respectively, for onion shoots and by 21.3 and 50.2%, respectively, for onion bulbs compared to the untreated sludge. 4-2 Residual effect (Jew’s mallow plants) In the second season, the SG+FO treated sludge was the best treatment which significantly reduced the Ni content in Jew’s mallow plants by 71.8 and 60.5% compared to the control and the untreated sludge, respectively Both of 20% FO and 10% SG treated sludge reduced the Ni content in Jew’s mallow plants by 56% compared to the control. The results also showed that Jew’s mallow plants could accumulate higher amounts of Ni in their tissues compared to onion plants. 4-3 Reapplication effect (Jew’s mallow plants) Compared to the control, the untreated sludge application resulted in a decrease of Ni content in Jew’s mallow plants from 119.45 mg/kg to 101.57 mg/kg. The reapplication of CKD treated sludge (at 10 and 20%) were the only treatments that significantly increased Ni contents in Jew’s mallow plants (338.80 mg/kg). The application of 20% CKD treated sludge resulted in the highest Ni content of Jew’s mallow plants. Whereas, the lowest Ni content was found with the application of 20% SG treated sludge (33.69 mg/kg). - Pb content in plants -1 Direct effect (onion plants)< Both onion bulbs and shoots contained high amounts of Pb (95.20 and 86.80 mg/kg, respectively) due to the pollution of the soil with Pb. In some cases the shoots contained larger amounts of Pb than the bulbs. The application of sludge significantly decreased Pb content in the shoots compared to the control. The most effective treatment that highly and significantly decreased Pb content (by 52.4%) in onion shoots is 10% SG (from 95.20 mg/kg to 45.34 mg/kg) The untreated sludge significantly increased the bulb content of Pb up to 96.25 mg/kg . Lead content in bulbs significantly decreased by 43.3% with the SG+CKD treatment compared to the untreated sludge (from 96.25 mg/kg with the untreated sludge to 54.60 mg/kg). The highest Pb content in onion bulbs is found with 10%CKD treatment. 5-2 Residual effect (Jew’s mallow plants) Jew’s mallow plants accumulates larger amounts of Pb compared to onion plants. The untreated sludge application reduced Jew’s mallow plants content of Pb by 28.8% compared to the control. All used materials increased Pb content in the Jew’s mallow plant shoots.
Lead content in Jew’s mallow plants reached its maximum value (562.18 mg/kg) with 20% SG treatment with an increase of 63.3% compared to the control.
5-3 Reapplication effect (Jew’s mallow plants) After the second application of untreated or treated sludge, Jew’s mallow plants followed the same trend of the residual effect experiment.
The application of untreated sludge decreased Pb content from 266.39 mg/ kg in the control to 212.43 mg/kg .
Lead content in Jew’s mallow plants reflected the EDTA-extractable Pb in th same treatments. The highest Pb content in Jew’s mallow plants is found with the 20% SG treatment (547.60 mg/kg) with an increase by 157.8% compared to the control. Conclusions: Treating sludge with stabilizer materials had different effects on the extractable Ni and Pb depending upon the type and the level of the stabilizing material, the application time and plant species. These results may need more analysis about the Ni , Pb forms and their contents of the soil and treated sludge . It seems that Jew’s mallow plants have the ability to secrete root exudates that may chelate nonexchangeable Ni, Pb and transform into an exchangeable forms. more researches should be done on Jew’s mallow plants and its ability to absorb and accumulate Ni and Pb.