Field analysis of PSA O2–ozone production process for water recycling

The use of an oxygen generator based on pressure swing adsorption technology (PSA) has been investigated as an alternative method for supplying oxygen for onsite ozone production. During the investigation period of 1040 h, the oxygen purity from the PSA process fluctuated within a range of 90.5–93 O₂% (v/v). Using the working ratio of 2.8 mol of O₂ to 1 m³ of raw water, the PSA process in series with a corona discharge ozone generator yielded an oxidation–reduction potential of ca. 200 mV and a concentration of 22.8 mg/L dissolved oxygen. The average efficiency of the raw water treatment was as follows: 47% chemical oxygen demand removal, 78% biological oxygen demand removal, 36% sulphide removal and 34% colour removal. The operating cost of the PSA O₂ generation was reduced 3 times compared with the cost of high‐pressure oxygen cylinders.     

Hydrogen recovery from the electrocoagulation treatment of dye-containing wastewater

In this paper, a technique of hydrogen recovery from an electrocoagulation process treating dye-containing wastewater is presented. The electrocoagulation system used consists of a continuous-mode electrocoagulator connected with a gas separation tank and two sedimenters. It is shown that a significant amount of hydrogen can be harvested using the gas separation tank whose configuration follows that of a conventional upflow anaerobic sludge bed. The experimental hydrogen yields obtained were comparable with those calculated from theory. The electrical energy demand of the electrocoagulation process for treating Reactive Blue 140 and Direct Red 23 was 1.42 and 0.69 kWh_e m⁻³, respectively, while the energy yield of harvested hydrogen was 0.2 kWh m⁻³. The quality of water treated by the electrocoagulation system was satisfactory, i.e., the color, COD and TS removal were 99%, 93% and 89%, respectively.