Waste materials can broadly be categorized as industrial wastes such as cement kiln dust, wood lignins, bottom ash, fly ash, municipal domestic waste such as incinerator residue, scrap rubber, waste glass and roofing shingles. Waste cement dust or cement kiln dust is the by-product of the manufacture of Portland cement.
It is generated during the calcining process in the kiln. Lime (CaO) constitutes more than 60% of cement by-product dust composition (CBPD). Other compounds include SiO2, Al2O3, Fe2O3, K2O, Na2O, Cl2 etc. most of cement company generates high quantities of CBPD every year (Ahmed et al., 2006).
Waste material recycling into useful products has become a main solution to waste disposal problems. Major environmental problems arise from the disposal of kiln dust. This dust production is not only unpleasant for the workers but also creates equipment fractures, decrease efficiency and produce maintenance problems (Collins and Ciesielski, 1993).
The cement dust can be used in wastewater treatment. The first stage in the renovation of wastewater involves the removal of suspended solids and colloids by chemical coagulation flocculation and clarification. A substantial reduction in total phosphorus, organic nitrogen, microorganisms and heavy metals are also achieved.
The choice of chemical coagulation is a prime consideration, particularly in relation to be treated (Van-Vuuren et al., 1980; Amer, 1997; Ronen, 1978).
Wieehers et al. (1980), Grabow et al. (1978) and Kelppinger (1993) reported that lime treatment is often used as first process stage in the unit process trains designed for upgrading the quality of wastewater or reclamating wastewater for potable use. The reason for lime treatment's popularity is its ability to remove phosphates, organic matter, magnesium and carbonate hardness and heavy metals from wastewater. The World Health Organization guidelines (WHO, 2005) for microbiological quality of treated wastewater used for this purpose are as follows; (a) Restricted irrigation: ≤105 E. coli/100 mL and ≤1 human intestinal nematode egg L1 (reduced to ≤0.1 egg L1 if children under 15 are exposed), (b) unrestricted irrigation: ≤103 E. coli/100 mL and same egg numbers. The current study is performed to study the effect of using waste cement kiln dust or using straw rice as filter followed by cement kiln dust on wastewater treatment.
MATERIALS AND METHODS
Three experiments were carried out for the treatment of raw sewage form the 6th of October WWTP.
The first experiments, various doses of cement kiln dust (1, 1.5, 1.75, 2, 2.5 and 2.75) were used as a standard bench-scale (Jar test). Flash mixing is started at 180 rpm for 3-4 min during which by-pass cement kiln dust has been added with the pre-mentioned concentrations. Flocculation was carried out for 20 min at 40 rpm. Then it left for sedimentation for 1 h (Fig. 1).
The second experimental run was carried out using the effluent of the dose of 2 g L1 cement kiln dust followed through three stages of rice straw (as a filter). Each stage of rice straw was pressed in a plastic funnel with diameter and depth of 10 cm (Fig. 2).
The third experimental run the effluent from the three stages of rice straw filter (as a first step treatment) followed by treatment using 2 g L1 cement kiln dust. Coagulation sedimentation was carried out as in the first experimental run (Fig. 3).
All samples (influent and effluents from each treatment step) were collected and analysed for physico-chemical parameters (pH, TSS, COD and BOD) and bacteriological parameters (TBC, TC, FC. E. coli., FS, salmonellae and listeria). The analyses were carried out according to APHA 1998. Salmonellae and listeria detection were carried out according to El-Taweel et al. (2000).
chart of the first experimental run|
chart of the second experimental run|
chart of the third experimental run|
Table 1 summarizes the characteristics of wastewater and the treated effluent from each treatment step. The results showed that, the reduction of TSS, COD and BOD were 94.7, 90.6 and 92.4%, respectively with 2.75 g L1 cement kiln dust dose. On the other hand, the lowest reduction was recorded when using 1 g L1 cement kiln dust dose for TSS (50%), COD (46.6%) and BOD (51.9%).
pH value for wastewater treatment increased with increasing the dose of cement kiln dust which added to wastewater (Table 1). The residual value of COD, BOD and TSS after using 2 g L1 cement kiln dust was 98 mgO2 L1, 56 mgO2 L1 and 86 mg L1, respectively. While the recorded pH value was 9.9.
The results in Table 2 showed that, the reductions in TSS,
COD and BOD after filtration through rice straw were 50, 32.4 and 35.3%, respectively.
Also the reductions were 63.6% (TSS), 85.8% (COD) and 86.2% (BOD) using 2 g
L1cement kiln dust dose for treatment the effluent of filtration
through rice straw. pH value was 9.9 for the final effluent (Table
The reductions using 2 g L1 cement kiln dust dose were 79.5, 85.6 and 86.6% for TSS, COD and BOD. After filtration through rice straw, the reductions were 52.3, 53.1 and 50% for TSS, COD and BOD, respectively. The pH value was 9.6 for the final effluent (Table 3).
From Table 1 the results showed that salmonella were not detected in wastewater treated by cement kiln dust dose 2 g L1.
This dose of cement kiln dust dose, the pH value was 9.9 which affect the removal of classical bacterial indicator and pathogenic bacteria such as total bacterial counts (TBC) (7 log units), TC (6 log units), E. coli (6 log units), FS (6 log units) and listeria (4 log units).
Generally, the effect of additional cement kiln dust for wastewater treatment
on the removal rate of bacterial load which, increased by increasing the dose.
of wastewater and effluents using different dose of cement kiln dust|
of wastewater and treated effluent using rice straw followed by cement
of wastewater treated with cement kiln dust followed by rice straw|
The lowest reductions of bacterial load were 4 log units for salmonellae,
FS, E. coli and TC, 2 log units for listeria and 5 log units for
FC and TBC using 1 g L1 cement kiln dust dose.
On the other hand, the higher reductions of bacterial load were 9 log units
for TBC at 37°C, 8 log units for TBC at 22°C and TC and complete reduction
for salmonellae, listeria, FS, FC and E. coli using 2.75
g L1 cement kiln dust dose.
The results in Table 2 showed that, the reductions of bacterial load after filtration through rice straw were 2 log units for TC, FC, E. coli, salmonellae, listeria and TBC at 37°C 3 log units for TBC at 22°C and only one log unit for FS.
But the reductions using the dose 2 g L1 cement kiln dust were 6 log for TC and TBC. Complete reduction was achieved for FC, E. coli, salmonellae and listeria.
It can be noted from Table 3 that listeria, FC and E. coli were not detected in the final effluent after filtration with rice straw for the effluent resulting with treatment using 2 g L1 cement kiln dust. The reductions of other bacterial load in the final effluent were one log unit for TBC and FS at 22°C, 2 log units for both TBC at 37°C and TC.
The chemical treatment consists of separation of settleable, floatable and dissolved substances using chemicals. Chemical treatment depends on the nature and concentration of colloidal matters, type of chemical coagulant, dose and pH value (Gambrel et al., 1989).
Lime treatment reduces the number of microorganisms by fluctuation in sedimentation or flotation processes and at the same time, the hydroxide alkalinity has an antibacterial effect (Hansen, 1992; Wiechers et al., 1980; Gambrel et al., 1989; Mignotte-Cadiergues et al., 2001).
Generally, the increasing of pH value was proportional to the amount of cement
kiln dust added to wastewater. Ahmed et al. (2006) reported that, lime
(CaO) constitutes more than 60% of cement by-product dust composition and other
compounds 40% include SiO2, Al2O3, F2O3,
K2O, Na2O and Cl¯.
pH value is an important parameter
in wastewater treatment. High pH is known to excite molecular oxygen to the
ionic form which is toxic (Awuah et al., 2002). The cement kiln dust
is considered as a coagulant where lime reacts with bicarbonate alkalinity to
prehydroxy aptite. Magnesium hydroxide precipitates at high pH value level.
Good clarification usually requires the presence of some gelatinous Mg(OH)2 but this does make the sludge more difficult to dewater. The addition of cement
kiln dust will enhance coagulation by promoting the growth of large, rapid-settling
floc. Thus high pH value which promote the sedimentation (EcKenfelder, 1989).
The reduction of pathogenic bacteria and classical bacterial indicator may be attributed to sedimentation, elevated pH and toxic chemical. Aquatic organisms which play a role in treatment processes are sensitive to pH changes (Awuah et al., 2002; Hansen, 1992; Jepsen et al., 1997). Mignotte-Cadiergues et al. (1992) reported that high and fluctuating levels of pH and dissolved oxygen are detrimental to pathogens in wastewater. Additionally, elevated pH has been found to contribute significantly to FC removal (Amer, 1997).
Generally, using the dose 2 g L1 of cement kiln dust was active in the reduction of Salmonellae. The effluent of this dose contains E. coli densities 46/100 mL and FC density 3.1x102 100 mL1 which complied with WHO 2005.
The pH value with this dose was 9.9. Thus using rice straw in the filtration of this effluent removed E. coli, FC and listeria. This type of treatment enhances the quality of wastewater for reuse. Consequently, rice straw could be used as adsorbent agent for removing the pollutants from wastewater as concluded by Nicolaisen (2002).
Generally, the conventional wastewater treatment is inexpensive, simple and rapid technology and the effluent could be used for irrigation. Relatively simple wastewater treatment technologies can be designed to provide low-cost sanitation and environmental protection while, providing additional benefits from the reuse of water.