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The aim of this study was to investigate an electrochemical process for bulk disinfection of biologically treated sewage. The influence of operating conditions (current density and flow rate) on the electrochemical formation of free chlorine in the sewage was determined. Furthermore, the effect of wastewater-specific parameters on the inactivation of Escherichia coli was studied. The disinfection capacity is primarily influenced by the concentration of electrochemically produced free chlorine. The production rate of free chlorine is independent of the flow rate within the range of 25-125 L h À1 . The investigations have also shown that the electrochemical disinfection of E. coli in secondary effluents with BDD electrodes proceeds effectively at an electric charge input of 0.1-0.15 Ah L À1 corresponding to an energy expenditure of 2.0-2.6 kWh m À3 . The electrochemically generated concentration of free chlorine (c = 0.4-0.6 mg L À1 ) is sufficient for an E. coli reduction of four log levels under the following conditions: after-reaction time of 15-20 min, T > 6˚C, pH < 8.5 and DOC < 22 mg L À1 . The formation of organic by-products (AOX, THMs) was marginal to moderate. The inorganic by-products chlorate (1.2 mg L Àl ) and perchlorate (18 mg L À1 ) were produced in considerable concentrations.

Although UV irradiation represents an energy efficient disinfection method, bacterial regrowth in UV irradiated secondary effluents is a serious problem for their direct reuse (e.g., for domestic or irrigation purposes). The decrease of the lethal UV fluence caused by coverings (scaling and biofouling) on quartz sleeves of UV lamps and/or fluctuating specific water parameters (suspended solids, transmittance or turbidity) results in a reversible inactivation of faecal coliforms (Escherichia coli). The reactivation of E. coli is increased with rising light intensity (!470 Lux) and rising temperature (!20 W C). The supplementation of UV disinfection with an electrolysis compartment ensures a reliable, sustained bacterial reduction and prevents reactivation of E. coli in UV irradiated (H ¼ 138-140 J m À2 ) wastewater at a concentration of total oxidants of 0.5 mg L À1 . The electric charge input of 0.012 Ah L À1 was lowest on MOX (mixed oxide) electrodes compared to particle BDD (boron-doped diamond) and thin film BDD electrodes. The formation of organic by-products (adsorbable organically bound halogens, trihalomethanes) ranged from marginal to moderate. In contrast to BDD electrodes, no chlorite, chlorate and perchlorate were observed on MOX electrodes.The energy consumption of the UV/electrolysis hybrid reactor was 0.17 kWh m À3 .

Use of Diamond Electrodes for the Production of Service Water by Electrochemical Disinfection of Biologically Treated Waste WaterIn order to prevent infections due to pathogenic germs waste water needs to be disinfected prior to reuse. In addition to membrane filtration and treatment with UV radiation electrochemical disinfection can be a suitable alternative. The use of diamond electrodes for the disinfection of waste water was investigated depending on important operational conditions and characteristics of the waste water.