Biorefractory Organics Research Articles

Integration of continuous biological and chemical (ozone) treatment of domestic wastewater: 2. Ozonation followed by biological oxidation

A combined chemical-biological treatment, ozonation plus activated sludge, of domestic wastewater was studied and the results were compared with those shown in a previous study where the sequence of oxidation was reversed. Experimental results indicated wastewater preozonation to be an effective pretreatment step for domestic sewage. The goals of ozonation were the improvement in effluent biodegradability and the removal of certain biorefractory organics as aromatic and unsaturated compounds. The percentage of biodegradability was measured by the BOD/COD ratio (e.g. 0.69 was obtained for an ozonated effluent (D O3 =40 g/m 3 ) while a ratio of 0.57 was measured for raw sewage). Based on continuous experiments of a single activated sludge system (hydraulic retention time=5h; mixed liquor volatile suspended solids=1.6 g/dm 3 ) the combined oxidation leads to an improvement of BOD and COD percentage reductions (88% and 66% observed after the combined process for BOD and COD, respectively, compared with 80% and 47% obtained without preozonation). Preozonation also improves the total kjeldahl nitrogen (TKN) removal during subsequent single stage activated sludge treatment. The fraction of autotrophic biomass (f nit ) was more important when preozonation took place, so nitrification rates were enhanced in the combined process. The efficiency for the individual and combined process was computed and compared. Among the three processes studied, the sequence of ozonation plus biological oxidation resulted in the highest percentage COD, TKN and UV 254 reduction.

Electrochemical waste water treatment using high overvoltage anodes. Part I: Physical and electrochemical properties of SnO2 anodes

The electrochemical performance of SnO2 as an anode material with high oxygen gas-evolution overpotential was investigated in view of its application for electrochemical oxidation of bio-refractory organics in waste waters. The influence of the doping agent (Sb, F, Cl) and doping level on the oxygen-evolution reaction was studied in terms of Tafel slope, oxygen-overpotential and exchange current densities for the Ce3+→Ce4+ reaction. Tafel slopes of about 300 mV decade−1 were found and the oxygen evolution overpotential was 600mV higher than that of platinum. While the doping level had no significant influence on Tafel slopes and oxygen overpotentials the stability of the SnO2 electrode increased with charge carrier density. The oxidation of phenol was investigated as a test for the oxidizing power of the new anode material when compared to Pt or PbO2. The rate of phenol removal was much higher for SnO2 than for PbO2 or Pt.