**3.4 Effect of different concentration of HBSH on sludge solid reduction**

The settleability i.e. settling rate expressed as TSS was measured by collecting samples with time in 1000 cm3 (sampling point) of the settling column. The same amount of raw and the treated sludge with (0.8, 1.6 and 2.4 g/L) HBSH was used to conduct to evaluate the settling performance as compared to untreated sludge. The settling rate as TSS concentration was measured with settling time is illustrated in **Figures 2**–**4**. The observed results showed that the 0.8 treated sample, at the first

**Figure 3.** *Variation in TSS concentrations along raw and treated sewage at 1.6gL−1.*

*Perspective Chapter: Removal of Heavy Metals and Salmonella Pathogens from Sewage Sludge… DOI: http://dx.doi.org/10.5772/intechopen.109224*

**Figure 4.** *Variation in TSS concentrations along raw and treated sewage at 2.4gL−1.*

part of the curve (up to 12 min) displayed a slightly higher settlement of TSS than that recorded by the raw sludge. However the settleability was doubled after that time and the overall TSS decreased to about half that in the untreated sludge at the end of 30 min period. The settlement rate was enhanced upon further addition of HBSH (1.6 g/L), the TSS decreased quickly and exceeded the TSS value recorded at 30 min by the untreated sludge within only about 17 min. The figure also shows a sharp reduction of TSS recorded after 10 min of settling then gradual decrease in TSS takes places to reach 230 g/L at 30 min. The faster settling rate was recorded by the 2.4 g/L treated sample. It was noticed that the TSS concentration decreased quickly and within less than 5 min reached the TSS concentration recorded by the raw sludge in 30 min. After such very sharp a decrease in the TSS concentration gradually continued to reach the lowest TSS value (150 g/L) recorded by the samples under experiment. The highest percentage of solids settlement (58.38%) was recorded by the 2.4 g/L HSBH treated sample after about 6 min of settling operation [55].

### **3.5 HMs binding capacity of HBSH at different concentration**

**Figures 5**–**7** shows the heavy metals (HMs) distribution in the liquid sludge phase before and after treating with the HBSH ligand at three different concentrations (0.8, 1.6 and 2.4 g/L). It was found that heavy metal concentrations were very high in the raw sludge. On the other hand, the heavy metal concentration showed a remarked decrease upon treating with the ligand (HBSH); this finding could be assigned to the ability of the HBSH to chelate the heavy metals ions. The results show that among all the HBSH concentrations used, Cd extraction efficiencies are noticeably the highest. The concentration of the chelator is inversely correlated with the general trend of HMs removal. As the concentration of HBSH raised from 0.8 to 2.4 g/L, removal

**Figure 5.**

*Variation in heavy metals concentrations along raw and treated sewage at 0.8 gL−1 dose.*

**Figure 6.**

*Variation in heavy metals concentrations along raw and treated sewage at 1.6 gL−1 dose.*

of lead, cadmium, copper, zinc and chromium showed a continuous progress. This behavior is not the same in case of iron and nickel removal which firstly improved significantly by increasing the addition of HBSH from 0.8 to 1.6 g/L, while there is almost no change occurs upon raising the concentration from 1.6 to 2.4 g/L [56].

*Perspective Chapter: Removal of Heavy Metals and Salmonella Pathogens from Sewage Sludge… DOI: http://dx.doi.org/10.5772/intechopen.109224*

**Figure 7.** *Variation in heavy metals concentrations along raw and treated sewage at 2.4 gL−1 dose.*

**Figure 8** depicted the percentage of HMs removal upon addition of varying concentration of the HBSH. At 0.8 g/L, the ligand showed the highest removal potential toward cadmium with percentage 81.25% followed by nickel (66.3%). On the other hand, the lowest removal percentage was recorded for cupper. For other metal species (Pb, Fe, Zn and Cr) the removal percentages was around 50%. Upon further addition of HBSH (1.6 g/L), the removal percentages of all metal species have been enhanced to reach over than: 80% for iron and nickel, 70% for lead and chromium, and 60% for copper and zinc. However there is almost no change in removal percentage of cadmium (1.5%). Finally, further addition of HBSH (2.4 g/L) resumes its ability

to remove cadmium content of the sludge to reach 93.75%. Removal of other metal species was elevated to: over than 80% of cupper, iron, nickel and lead and more than 85% for zinc and chromium [57].

The results suggest also a higher HBSH lead to more effective extraction of heavy metals, this could be explained on basis that increasing dose of chelating ligand would facilitate the complexing reaction between metal ion and the chelating ligand leading to the formation of a chelate. Enhancing of the removal efficiency could be also related to the reason that there are many substances presented in the sludge beside the studied metal species such as: Ca, and Mg which consequently compete with the targeted metal species to bind the ligand and hence participate in the consumption of HBSH and according a large excess of ligand is required to solubilize the target metal due to the co-solubilization of Ca and Fe. Nowack et al. [29].

### **3.6 Removal of salmonella pathogens**

Specific tests for the presence of Salmonella sp. were carried out, in both raw and dry sludge, we identified the presence of Salmonella spp. Confirmation of Salmonella was carried out using the API E20 Enterobacteriaceae test system and RISA molecular profiling. The data demonstrated that the total count of Salmonella sp. have been markedly lowered upon contacting with Schiff base for 30 min (**Figure 9**). The total counts for salmonella in the raw sludge recorded an averages of 2.8 × 103 and 1.7 × 104 MPN index/100 ml in the liquid and dray raw sludge respectively. These values have drastically decreased to only (25–28) MPN index/100 ml with successful removing of salmonella by about 99% upon treating with different concentration of Schiff base. From the results, it is clear the Salmonella sp. present in the effluent were in fact successfully being removed or inactivated upon treating with the Schiff base. The removal

### **Figure 9.**

*MPN index/100 ml of salmonella count in solid, liquid raw sludge as well as treated with varying concentrations (0.8, 1.6, 2.4 g/L) of Schiff base (HBSH).*
