DOMESTIC WASTEWATER TREATMENT WITH A NATURAL COAGULANT, MORINGA OLEIFERA
A. A. ABU-BAKAR,
J. JAAFAR
M. AB-WAHID
Lecturer, Water Resources & Environmental System Division,
Faculty of Civil Engineering, Universiti Teknologi MARA Shah Alam
M. K. KHALIL
Engineer, Urban Drainage Division,
Department of Irrigation & Drainage Malaysia,
Jalan Sultan Salahuddin, Kuala Lumpur
INTRODUCTION
Wastewater treatment is a multi-stage process to renovate wastewater before it could reenters a body of water, applied to the land or reused. The goal is to reduce or remove organic matter, solids nutrients disease-causing organisms and other pollutants from wastewater. Each receiving body of water has limits to the amount of pollutants it can receive without degradation. Therefore, each wastewater treatment plant should have a proper treatment system to achieve the goal of wastewater treatment.
During biological treatment, wastewater is treated to remove turbidity, color and bacteria. The objective of coagulation (and subsequently flocculation) is to turn the small particles of color, turbidity and bacteria into larger flocs, either as precipitates or suspended particles. These flocs are then conditioned so that they will be readily removed in subsequent processes (Zeta Meter, 1993). Usage of synthetic polymers as coagulant to alleviate this problem is expensive and has to be imported with scarce foreign currency. Natural coagulants from vegetable and mineral origin have been in used in water and wastewater treatment before the advent of chemical salts. However, they are not as effective as the later due to the lacking of scientific research of their effectiveness and mechanism of action.
Recently however, it has been a resurgence of interest in natural coagulants such as Moringa oleifera for water and wastewater treatment in developing countries (Jahn, 1988) and also to reuse some of their by-products (Ndabigengesere et at, 1995). Natural coagulant like Moringa oleifera has several advantages over aluminum in that it is non-toxic and biodegradable. Significantly, it reduces the volume of sludge and gives less effect on the pH, conductivity and alkality of the water (Broin et al., 2002). Moreover, agro based material are annually renewable.
This study has been carried out to determine the optimum mixing condition for Moringa oleifera to be effective as coagulant in municipal wastewater treatmen and the optimum dosage of Moringa oleifera used as coagulant in turbidity removal of municipal wastewater.
METHODOLOGY
The preparation of the concentration of Moringa oleifera stock for the study was done as follows:
The wastewater used in this study was taken from the oxidation pond at Jalan Ilmu, Universiti Teknologi MARA, Shah Alam, Selangor. The wastewater sample was taken from the inlet of the oxidation pond. It was stored in plastic containers and transported back to the laboratory within one hour. The tests were done immediately after it reached the laboratory. The sample was taken everyday to minimize the changes in wastewater characteristics due to microbial activity and sedimentation. In this study, the wastewater was determined by its temperature, pH and turbidity. The turbidity of the wastewater sample was ranged from 80 to 100 NTU.
The jar test was done by using Phipps & Bird (PB-900) Programmable JarTester. The dimension of the pedal is 7.4 x 2.2 cm. In this study, the mixing condition determined are the mixing intensity (rpm) for rapid mixing, the duration for rapid mixing, the mixing intensity (rpm) for slow mixing and the duration for slow mixing. The settling time was constantly kept at 30 minutes and the experiments were run at room temperature which was about 25oC. No pH was controlled.
RESULTS AND DISCUSSION
Optimization of Rapid Mixing Intensity
The experiments to determine the optimum mixing intensity (rpm) for rapid mixing were done for 140 rpm, 120 rpm, 100 rpm and 80 rpm. For this varied rapid mixing rpm, the duration was set at 5 minutes. The slow mixing was constant at 30 rpm for 20 minutes.
At rapid mixing 140 rpm, the optimum dosage obtained was 20 mg/l. The turbidity decreased from 81.10 NTU to 2.50 NTU where the percentage removal was 96.9%. For rapid mixing 120 rpm, the turbidity removal was 97.8% where the decreased of turbidity was 93.80 NTU to 2.05 NTU. The optimum dosage was 41 mg/l. For rapid mixing 100 rpm, the turbidity decreased from 95.50 NTU to 2.00 NTU and the percentage removal was 97.91%. The optimum dosage for this rapid mixing was 25 mg/l. At rapid mixing 80 rpm, the optimum dosage obtained was 40 mg/l where the percentage removal was 97.69 %. That was turbidity removal from 92.79 NTU to 2.14 NTU. From the results obtained, the optimum rapid mixing was 100 rpm. The results are as shown in Figure 1.
Figure 1: Optimum Mixing Condition – Varies Mixing Intensity (rpm)
Optimization of Rapid Mixing Duration
The experiments to determine the optimum duration for rapid mixing were done for 8 min, 5 min, 3 min and 1 min. For this varied duration of rapid mixing, the rpm for rapid mixing was set as 100 rpm. The slow mixing was still fixed at 30 rpm for 20 minutes and settling time was fixed as 30 minutes.
At rapid mixing 100 rpm, the duration were varies from 8 min to 1 min. For the 8 min, the optimum dosage obtained was 40 mg/l. The results are shown in Figure 2. The turbidity decreased from 66.00 NTU to 3.06 NTU where the percentage removal was 95.36 %. When the duration for rapid mixing was 5 min, the turbidity decreased was 95.50 NTU to 2.00 NTU and the percentage removal was 97.91%. The optimum dosage for this rapid mixing was 25 mg/l. The duration for rapid mixing was shortening to 3 min and the optimum dosage was 40 mg/l. The turbidity decreased from 93.60 NTU to 2.22 NTU and the percentage removal was 97.63%. For rapid mixing duration of 1 min, the percentage removal was 96.59 % where the turbidity decreased from 80.00 NTU to 2.73 NTU. From the results obtained, the optimum duration for rapid mixing is 5 minutes.
Figure 2: Optimum Mixing Duration – Varies Mixing Duration
Optimization of Slow Mixing Intensity
The experiments to determine the optimum revolution per minutes (rpm) for slow mixing were done for 30 rpm, 20 rpm and 10 rpm. For this varied slow mixing rpm, the duration was set at 20 minutes. The rapid mixing was constant at 100 rpm for 5 minutes.
At slow mixing 30 rpm, the optimum dosage obtained was 22 mg/l. The turbidity decreased from 95.50 NTU to 2.00 NTU and the percentage removal was 97.91%. For slow mixing 20 rpm, the turbidity removal was 97.42 % where the turbidity decreased from 91.90 NTU to 2.37 NTU. The optimum dosage was 20 mg/l. For slow mixing 10 rpm, the turbidity decreased from 85.30 NTU to 2.74 NTU and the percentage removal was 96.79%. The optimum dosage for this rapid mixing was 40 mg/l. From the results obtained, the optimum slow mixing is 30 rpm. The results are shown in Figure 3.
Figure 3: Optimum Slow Mixing Intensity – Varies Mixing Intensity
Optimization of Slow Mixing Duration
The experiments to determine the optimum duration for slow mixing were done for 30 min, 20 min and 15 min. For this varied duration of slow mixing, the rpm for slow mixing was set as 30 rpm. The rapid mixing was constant at 100 rpm for 5 minutes and settling time was fixed as 30 minutes.
At slow mixing of 30 rpm, the duration were varies from 30 min to 15 min. The results for this condition are shown in Figure 4. For the 30 min, optimum dosage obtained was 20 mg/l. The turbidity decreased from 90.00 NTU to 2.65 NTU where the percentage removal was 97.06 %. When the duration for slow mixing was set as 20 min, the optimum dosage obtained was 22 mg/l. The turbidity decreased from 95.50 NTU to 2.00 NTU and the percentage removal was 97.91%. For 15 min and the optimum dosage was 20 mg/l. The turbidity decreased from 73.90 NTU to 3.31 NTU where the percentage removal was 95.52 %. From the results obtained, the optimum duration for slow mixing is 20 minutes.
Figure 4: Optimum Slow Mixing Duration – Varies Mixing Duration
The Optimum Mixing Condition
From all the experiments run, the optimum intensity for rapid mixing, duration for rapid mixing, intensity for slow mixing and duration for slow mixing results were obtained. The optimum mixing conditions for Moringa oleifera to be effective as coagulant in municipal wastewater treatment was the rapid mixing of 100 rpm for 5 minutes and the slow mixing that was done at 30 rpm for 20 minutes. These mixing conditions were suitable with settling time of 30 minutes. The optimum dosage was 20 mg/l and the turbidity decreased from 95.50 NTU to 1.80 NTU where the percentage removal was 98.0 %. The results are as shown in Figure 5.
Figure 5: Optimum Coagulant Dosage
CONCLUSION
Mixing condition that is the rapid mixing intensity, rapid mixing duration, slow mixing intensity and slow mixing duration when Moringa oleifera is used as coagulant has slight effects on the efficiency of the turbidity removal in wastewater treatment, depending on initial turbidity of wastewater samples.
The rapid mixing is 100 rpm for 5 minutes, slow mixing is 30 rpm for 20 minutes and settling time is 30 minutes. The optimum dosage when Moringa oleifera was applied as coagulant was 20 mg/l. The turbidity decreased from 95.50 NTU to 1.80 NTU where the percentage removal was 98.0.
ACKNOWLEDGEMENTS
The authors would like to express their gratitude to Assoc. Prof. Ir. Megat Johari Megat Mohd Noor form Department of Civil Engineering, UPM and Institut Penyelidikan, Pembangunan dan Pengkomersilan (IRDC), UiTM.