Water Journal : Current May 2017
executive summary sewage catchment www.awa.asn.au 114 T asWater operates the Ti-Tree Bend (TTB) wastewater treatment plant (WWTP), a continuous mixed activated sludge (CMAS) plant, in Launceston. A synergy of equations has been utilised to produce a term that quantifies the energy density (ED) of any given system flow rate using any given pump. The equations have been presented in a format intended to have the most relevance, that is, Kilowatt Hours per Mega Litre (kWh/ML). The city was one of the first in the southern hemisphere to have a sewer system, dating back to the 1860s. The WWTP was commissioned in 1974 and receives combined wastewater including stormwater, domestic and industrial waste. Sulphide in wastewater can cause significant odour issues through the generation of hydrogen sulphide gas (H2S) in sewers and WWTPs. Ferrous iron salts (FeCl2) are added in excess to enable the precipitation of iron sulphide, effectively removing H2S. THE COMPLEXITIES OF MANAGING TRADE WASTE INPUTS AND FINDING EFFECTUAL TREATMENTS. Odour control in a combined stormwater catchment J Barnett www.awa.asn.au 114 Flow-paced iron salts dosing started on August 31, 2015. The water pH is also an important factor controlling the formation of H2S. The optimum pH to reduce the formation of H2S is approximately 8. The purpose of this report was to determine the optimal iron salts dosing levels and the effect of the dosing on the operability of TTB sewage treatment plant. THE GOLDILOCKS ZONE Iron salts dosing showed a statistically significant decrease in the mean monthly H2S levels detected at the wet well before the plant – between 20% and 70%. The optimal dose rate was estimated relative to the residual H2S detected on site; however, with inline monitoring the dose rate could be optimised further. Although H2S was significantly reduced, olfactometry testing showed that there was minimal difference in the total odorous gas on site. There were significant H2S diurnal patterns identified at TTB, with spikes identified throughout the system. Tankered waste could be contributing to the H2S levels at the inlet, and there is considerable H2S generated on site within the treatment train. PRECIPITATING CHANGE Iron salts precipitate phosphate and a 30% reduction in effluent total phosphorus (TP) cuts the TP load discharged by approximately 11,000kg/y – a significant benefit for the receiving environment. Alkalinity in the AST can be lower than the recommended levels for effective biological treatment; yet the data indicated that iron salts dosing had no effect on the levels in the STP. However, there were significant reductions in the pH in both the AST and the effluent. The mean effluent pH after the start of dosing was 6.51. This will result in pH non-compliances for the effluent. Following commissioning of the iron dosing unit and a community engagement program, total odour complaints dropped from 18 in 2014-15 to 10 in 2015-16. Many complaints were associated with the dosing system being offline and/or maintenance work being carried out. Dr Jason Barnett BEnvSc, PhD (Chem), is a senior wastewater scientist in the sewerage system optimisation group with TasWater. To read the full article, visit the Water e-Journal at bit.ly/water_ejournal Tankered waste could be contributing to the H2S levels at the inlet, and there is considerable H2S generated on site within the treatment train.
Current Feb 2017
Current August 2017