Effect of Lime Dose on Thickener Sludge Settling and Supernatant Quality: East Sadra Case Study

کد مقاله : 1134-IWWA

نویسندگان

مریم کریمی *، مجید حبیب آگهی، بهار هوشداران، محمد رضا زحمتکش آب و فاضلاب شیراز

چکیده مقاله

Effective sludge thickening reduces sludge volume requiring subsequent handling and improves solid–liquid separation. This study evaluated the effect of calcium hydroxide (lime) on thickener sludge settling and supernatant quality at the East Sadra Wastewater Treatment Plant, Iran. Sludge samples were collected daily over three months and evaluated using jar tests. Seven lime doses (0, 33, 100, 200, 333, 466, and 666 mg/L) were tested in triplicate using 1000 mL sludge samples. Following rapid mixing (120 rpm, 2 min), slow mixing (40 rpm, 20 min), and 30 min settling, sludge volume after 30 min (SV30), supernatant pH, turbidity, and chemical oxygen demand (COD) were measured. One-way ANOVA followed by Tukey’s test was used to compare treatments. Lime dose significantly affected all measured parameters (P < 0.001). The 200 mg/L dose produced the most favorable overall response. SV30 decreased from 560 ± 20.00 to 300 ± 20.00 mL/L, representing a 46.4% reduction relative to the control. Turbidity decreased from 10.00 ± 0.20 to 6.53 ± 0.31 NTU, and COD decreased from 111.67 ± 3.06 to 94.33 ± 4.51 mg O₂/L. Supernatant pH increased from 7.43 ± 0.015 to 7.75 ± 0.025. Doses above 200 mg/L provided no further improvement and were associated with increases in SV30, turbidity, COD, and pH. Thus, 200 mg/L was the most favorable dose within the tested range. The findings indicate improved settling and supernatant quality, although direct sludge dewatering performance was not assessed because solids and dewaterability indices were not measured.

کلیدواژه ها

Keywords: sludge thickening, lime conditioning, SV30, supernatant quality, turbidity, COD

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