Water Journal : Water Journal November 2012-1
odour management refereed paper technical features 52 NOVEMBER 2012 water regeneration reaction. This free sulphur effectively puts a physical barrier between the hydrogen sulphide and rust, preventing further reaction. In order to reduce the sulphur barrier, reactors are periodically washed with service water. The removal is achieved through general attrition or promotion of further rusting causing flaking of the iron surface. Spent water containing sulphur is discharged back to the pump station. The length and frequency of washes is a function of the hydrogen sulphide load. In the case of the Sydney Street Pump Station a daily wash of no less than five minutes in duration is required due to the high load. The wash regeneration is responsible for iron loss over time, but is unavoidable if efficiency is to be maintained. Duty Cycling Some installations include standby units to allow duty cycling. This configuration provides a “rest” period, allowing rust to re-form. This resting period where fresh air is blown through the unit stems from iron filter’s original use, where the general gas had low to zero oxygen content. The reaction to re-form rust could not occur until the unit was taken off-line and “rested”. As the chemistry shows, such resting is not required in wastewater odour control operation, where the gas is essentially air with 21% oxygen content and comparatively very low contaminant concentrations. As such, multiple units to allow “resting” have not been integrated into the design of the Sydney Street Pump Station. The system design parameters as installed at Sydney Street Pump Station are shown in Table 2. Results Due to the simplicity of design and operation, the plant was commissioned in less than a day, with foul air introduced at the end of day one. Performance proving was carried out over the following three weeks. OdaLogs were placed on the RICF inlet, outlet and BTF outlet to monitor RICF hydrogen sulphide removal rate, BTF hydrogen sulphide removal rate and hydrogen sulphide load onto the activated carbon respectively. The results are shown in Figures 6, 7 and 8. The hydrogen sulphide inlet concentration average steadily increased over the test period, varying on a daily basis from 25 to 600ppm. The initial RICF hydrogen sulphide removal rate was measured at an average of 85%. This high removal rate was achieved by allowing the Figure 6. RICF hydrogen sulphide removal rate. Figure 7. BTF hydrogen sulphide removal rate. Figure 8. RCIF hydrogen sulphide removal capacity.
Water Journal December 2012
Water Journal September 2012-1