Mohammed Saedi Jami 1Md. Zahangir Alam 1Masashi Iwata 4
Bioenvironmental Engineering Research Centre (BERC), Biotechnology Engineering Department, Faculty of Engineering, International Islamic University Malaysia (IIUM), Kuala Lumpur, Malaysia 1
Department of Chemical Engineering, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan 4
In order to evaluate the efficiency of sludge dewatering, specific parameters such as settling velocity (Vs) and sludge volume index (SVI) have to be measured. However, problems arise when these parameters are used for the evaluation of efficiency using M. oleifera as natural phytocoagulant or sludge conditioner. Using statistical optimization, it was found despite good results of Vs and SVI, the concentration of residual suspended solids in supernatant liquid or turbidity was very high. Thus, turbidity of supernatant liquid was selected as a criteria to evaluate the efficiency of dewatering process. In this research, two optimization steps were run under two factors for each optimization; i.e., mixing time and concentration of M. oleifera seeds extract with NaCl (1 M). The range of these factors was 100 – 1000 mg/L for M. oleifera seeds extract concentration, and 5 – 30 min for mixing time. In the first optimization, Vs and turbidity were used as responses. While in the second optimization SVI and turbidity were used as response parameters. Both optimization steps were run under pH = 7, mixing speed = 120 rpm for the first minute, and 40 rpm during the rest period of experiment. Through using Design-Expert software v9, for the first optimization of settling velocity, the optimum Vs is 1 cm/min and the turbidity of the supernatant is found to be 350.7 NTU. Whereas in the optimization of the sludge volume index (SVI), the optimum value is 24.7 mL/g, corresponding turbidity value of suspended solids in supernatant liquid was 341.5 NTU. Since the turbidity was very high, second optimization by redesigning the factors was coducted resulting in optimum values of dosage of 462.8 mg/L, mixing time of 13.4 min, turbidity of 67.2 NTU (further 80.2 % reduction compared to the 350.7 NTU of the first optimization) and settling velocity of 0.93 cm/min were obtained. For the optimization of SVI, dosage of 447.5 mg/L and mixing time of 8.3 min gave 33.5 mL/g of SVI with 67.2 NTU. These optimized dewatering parameters can be used to improve the efficiency of sludge dewatering.
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