Thermally processed sewage sludge for methylene blue uptake

Abstract

Sewage sludge, with zero recycling rate, poses landfill problems as Semakau island, the dumping site, is rapidly occupied in within a short period of time. Dried sewage sludge was heated at different temperatures ranging from 200 °C to 700 °C over various heating times of 2–5 h. The heated dried sludge (DS) was equilibrated with methylene blue (MB) solutions at different concentration to determine the optimum adsorption time, effect of different heating temperatures of sludge, effect of pH and effect of adsorbent concentration on the percentage of MB adsorbed. The results were compared to a commercial activated carbon (AC) in adsorbing the same MB concentration. The higher heating temperatures the more the DS was able to adsorb MB. DS, which was heated at 700 °C, showed the highest percentage of MB adsorbed of 95%, compared to that of AC, which were 91.20% (Grade 17) and 97.99% (Grade 19), when adsorbing the same initial MB concentration of 10 μmol l−1. However, DS heated at 200 °C for 5 h (DS-200-5) was found to have a ratio of MB adsorbed per power consumption of 21.568 (μmol l−1 kW), the highest ratio among the other sludge samples, making it the most cost effective type of sludge. Overall, DS was able to adsorb MB between 90% and 98% at a wide pH range of 3 < pH < 12, showing the potentiality of DS to remove contaminant from industrial discharge. In addition the reuse of sludge for other environmental application can help to prolong the lifespan of landfill dumping site.