Honghe Ma

Partial oxidation of municipal sludge with activited carbon catalyst in supercritical water

The partial oxidation (POX) characteristics of municipal sludge in supercritical water (SCW) were investigated by using batch reactor. Effects of reaction parameters such as oxidant equivalent ratio (OER), reaction time and temperature were investigated. Activated carbon (AC) could effectively improve the mole fraction of H(2) in gas product at low OER. However, high OER (greater than 0.3) not only led to the combustion reaction of CO and H(2), but also caused corrosion of reactor inner wall. Hydrogenation and polymerization of the intermediate products are possible reasons for the relative low COD removal rate in our tests. Metal oxide leached from the reactor inner wall and the main components of the granular sludge were deposited in the AC catalyst. Reaction time had more significant effect on BET surface area of AC than OER had. Long reaction time led to the methanation reaction following hydrolysis and oxidation reaction of AC in SCW in the presence of oxygen. Correspondingly, the possible reaction mechanisms were proposed.

Supercritical water oxidation of acrylic acid production wastewater

Supercritical water oxidation (SCWO) of wastewater from an acrylic acid manufacturing plant has been studied on a continuous flow experimental system, whose reactor was made of Hastelloy C-276. Experimental conditions included a reaction temperature (T) ranging from 673 to 773 K, a residence time (t) ranging from 72.7 to 339 s, a constant pressure (P) of 25 MPa and a fixed oxidation coefficient (α) of 2.0. Experimental results indicated that reaction temperature and residence time had significant influences on the oxidation reaction, and increasing the two operation parameters could improve both degradation of chemical oxygen demand (COD) and ammonia nitrogen (NH3‒N). The COD removal efficiency could reach up to 98.73% at 25 MPa, 773 K and 180.1 s, whereas the destruction efficiency of NH3‒N was only 43.71%. We further carried out a kinetic analysis considering the induction period through free radical chain mechanism. It confirms that the power-law rate equation for COD removal was 345 exp(−52200/RT)[COD]1.98[O2]0.17 and for NH3‒N removal was 500 exp(−64492.19/RT)[NH3‒N]1.87[O2]0.03. Moreover, the induction time formulations for COD and NH3‒N were suspected to be exp(38250/RT)/173 and exp(55690/RT)/15231, respectively. Correspondingly, induction time changed from 2.22 to 5.38 s for COD and 0.38 to 1.38 s for NH3‒N. Owing to the catalysis of reactor inner wall surface, more than 97% COD removal was achieved in all samples.