The removal of low concentration formaldehyde over sewage sludge char treated using various methods

Sewage sludge char was activated, using several different methods, to be used for the adsorption of formaldehyde. First, sewage sludge was pyrolyzed at 700 degrees C for one hour to produce char. The sewage sludge char was then activated with 20% steam gas. To produce a chemically activated char, KOH was used with the char at a weight ratio of KOH/char=0.5. To produce another kind of activated char containing nitrogen functional groups, the sewage sludge char was activated with ammonia at 350 degrees C. These activated chars were used for indoor low concentration formaldehyde adsorption experiments. All the chars tested in this study were shown to have better performance than activated carbon. In particular, the char activated with both ammonia and KOH showed the best formaldehyde adsorption performance. This result was attributed to the combination of surface basicity due to large amounts of metal components and generation of oxygen and nitrogen functional groups as a result of the KOH and ammonia treatments.