- ASpect’s Client: Beca Hunter H2O
- Head Client: Shoalhaven City Council
- Plant Configuration: IDEA
- Plant Size: 28,000 EP, 10,500 EP, 16,000 EP and 8,000 EP
- Project Value: $200k (ASpect Fee $80k)
- Project Duration: November 2022 to June 2023
Southern Shoalhaven STP Process Review, with Beca Hunter H2O for Shoalhaven City Council (NSW).
Sholahaven City Council (SCC) own and operate a number of STPs in the Shoalhaven region of NSW. This region is a popular, coastal holiday destination with high growth. During holidays, especially those in summer, the population and sewage load increases suddenly and dramatically. This places unique stresses on the STPs and their operation. SCC required a process review of four of their STPs in the southern Shoalhaven, namely Ulladulla STP, Culburra Beach STP, St Georges Basin STP and Sussex Inlet STP. The scope included a review of performance, asset condition and capacity. The high holiday influx made the current sewage loads difficult to determine. The first step was to sample and analyse flows and concentrations during the two weeks following Christmas and compare these to the baseline loadings from history. The holiday loads were found to be between 30% and 80% greater than the baseline loads. Furthermore, the sewage concentrations increased during the peak loading periods, especially TN. Whole plant models of each STP were produced and used to assess the capacity of each process unit during both baseline and peak loading periods and under dry and wet weather conditions. Ulladulla STP was found to be grossly overloaded, mainly due to poor process design. The other STPs were found to be within capacity during baseline loading, but overloaded during peak loading, especially under wet weather conditions. Aeration capacity was especially lacking. The suggested interim solutions were different for each STP. The detail devoted to capacity assessment uncovered an anomaly at St Georges Basin and Sussex Inlet STPs. The decanter travel distance was found to be significantly less than the design intent. A novel solution to the aeration capacity shortfalls was to increase the weir rest level of the decanters, increasing the fill time and aeration period each cycle. That, combined with modifications to overflow weir heights, allowed the capacity to be increased with almost no capital expenditure. Nevertheless, amplifications to all the STPs were found to be required in the medium term. Preliminary options for these amplification were provided to SCC including budget estimates.
