The effect of CKD on sludge stabilization compared with chemical stabilization with Lime is introduced in Table (3). Also comparison between different concentrations of sludge is introduced. Different dosages of CKD were examined and the dosage that achieves stabilization was 50% and 60% for thickened and diluted sludge respectively, while the required dosage of Lime was ranged between 22 and 29%. The required lime dosage complies with the results of EPA [4], Wang [18], Rahman [11] and Salah [12]. From table (2) it is clear that calcium oxide represents only 50% of the CKD composition, this explain why the required CKD dose was higher than twice that of Lime
Table (3) pH for treated sludge with CKD and Lime
Sludge type TS% CDK dosage (%TS) pH* T= 0 After 2 hr After 24 hr After 48 hr Dilluted 1 – 3 60 12.2 12.1 12.0 11.9 Thickened 4 – 6 50 12.4 12.3 12.1 11.9 Sludge type TS% Lime dosage (%TS) pH T= 0 After 2 hr After 24 hr After 48 hr Dilluted 1 – 3 29 12.4 12.3 12.3 12.2 Thickened 4 – 6 22 12.5 12.4 12.3 12 * Initial untreated sludge pH value were as table (1) 3.2 Zone Settling Rate Figure (2) shows sludge interface height change with settling time, from the curve it is clear that the CKD improved the thickening of sludge. …show more content…
At any operating time the sludge interface height for treated sludge is lower than that for untreated sludge. The Zone settling velocity is determined as the slope of the linear part, which in the calculations is defined as the steepest slope in the curve [16], Based on this criteria the zone settling velocity increased from 43.2(m/d) for untreated sludge to 98.4(m/d) for treated sludge, for factor of safety equal to 2 the hydraulic loading rate of gravity thickeners will be 21.06 (m/d), and 49.20 (m/d) for the untreated and treated sludge respectively. Figure (2) relation between sludge interface height and settling time The hydraulic loading rate for the untreated sludge complies with the hydraulic loading rate of the WEF [19,20] which ranged between 16 and 32 (m/d) for mixture of primary sludge and trickling filter hummus and also with the recommended design hydraulic loading values by Metcalf & Eddy [21] and Wang [18]. Regarding the extended settling test for the treated sludge no floating sludge occurs which implies that due to the use of CKD no biological action occurs, no gases formed and so good stabilization could be assumed, but in the other hand sludge floats in the untreated column. 3.3 Free Gravity Drainage Testing and specific resistance of filtration Figure 3(a, b) shows the relation between sludge solid content and filtrate time for the tested CKD concentration. Figure (3-a) shows that adding only 10% CKD reduced the filtrate time by a third, while from figure (3-b) shows that increasing the dosage to 50% improved the dewaterability by decreasing the filtrate time while increasing the dosage more than 50% had a reversible effect. SRF complies with the above results as the SRF of the untreated sludge was around 5.91(103 m/kg), while for CKD addition of (50%) the SRF decreased to be 0.676 (103 m/kg). from figure (4) it was found that the sludge SRF dramatically decreased with the increase of the CKD. When the CKD dosage exceeded 50%, the sludge SRF increased with the increase of CKD dosage. Therefore, the CKD was a good conditioner. These results comply with the …show more content…
Results of treated sludge complies with the results published by EPA [4] as they found that only two days are enough for treated sewage sludge with lime and some other conditioners to get sludge solid content varied between 20 and 30%.
Figure (6) shows the relation between drying time and sludge pH value, the results treated sludge shows that the pH value remains above 10.50 for the whole test which lasts for 5 days. This result complies with the results of Salah [12] who studied using CKD as stabilizer for thickened and dewatered sludge and found that using CKD with dosage more than 30% increased the pH value to be 11 for 7 days.
3.5 Additional Sludge
Table (3) pH for treated sludge with CKD and Lime
Sludge type TS% CDK dosage (%TS) pH* T= 0 After 2 hr After 24 hr After 48 hr Dilluted 1 – 3 60 12.2 12.1 12.0 11.9 Thickened 4 – 6 50 12.4 12.3 12.1 11.9 Sludge type TS% Lime dosage (%TS) pH T= 0 After 2 hr After 24 hr After 48 hr Dilluted 1 – 3 29 12.4 12.3 12.3 12.2 Thickened 4 – 6 22 12.5 12.4 12.3 12 * Initial untreated sludge pH value were as table (1) 3.2 Zone Settling Rate Figure (2) shows sludge interface height change with settling time, from the curve it is clear that the CKD improved the thickening of sludge. …show more content…
At any operating time the sludge interface height for treated sludge is lower than that for untreated sludge. The Zone settling velocity is determined as the slope of the linear part, which in the calculations is defined as the steepest slope in the curve [16], Based on this criteria the zone settling velocity increased from 43.2(m/d) for untreated sludge to 98.4(m/d) for treated sludge, for factor of safety equal to 2 the hydraulic loading rate of gravity thickeners will be 21.06 (m/d), and 49.20 (m/d) for the untreated and treated sludge respectively. Figure (2) relation between sludge interface height and settling time The hydraulic loading rate for the untreated sludge complies with the hydraulic loading rate of the WEF [19,20] which ranged between 16 and 32 (m/d) for mixture of primary sludge and trickling filter hummus and also with the recommended design hydraulic loading values by Metcalf & Eddy [21] and Wang [18]. Regarding the extended settling test for the treated sludge no floating sludge occurs which implies that due to the use of CKD no biological action occurs, no gases formed and so good stabilization could be assumed, but in the other hand sludge floats in the untreated column. 3.3 Free Gravity Drainage Testing and specific resistance of filtration Figure 3(a, b) shows the relation between sludge solid content and filtrate time for the tested CKD concentration. Figure (3-a) shows that adding only 10% CKD reduced the filtrate time by a third, while from figure (3-b) shows that increasing the dosage to 50% improved the dewaterability by decreasing the filtrate time while increasing the dosage more than 50% had a reversible effect. SRF complies with the above results as the SRF of the untreated sludge was around 5.91(103 m/kg), while for CKD addition of (50%) the SRF decreased to be 0.676 (103 m/kg). from figure (4) it was found that the sludge SRF dramatically decreased with the increase of the CKD. When the CKD dosage exceeded 50%, the sludge SRF increased with the increase of CKD dosage. Therefore, the CKD was a good conditioner. These results comply with the …show more content…
Results of treated sludge complies with the results published by EPA [4] as they found that only two days are enough for treated sewage sludge with lime and some other conditioners to get sludge solid content varied between 20 and 30%.
Figure (6) shows the relation between drying time and sludge pH value, the results treated sludge shows that the pH value remains above 10.50 for the whole test which lasts for 5 days. This result complies with the results of Salah [12] who studied using CKD as stabilizer for thickened and dewatered sludge and found that using CKD with dosage more than 30% increased the pH value to be 11 for 7 days.
3.5 Additional Sludge