wastewater treatment including municipal water treatment plants, sewerage treatment plants, trade waste and industrial treatment plants, ultrafiltration plants and pool treatment plants.
Their experience allows them to have a realistic understanding of problems affecting STPs, and enables them to recommend solutions that are practical, robust, cost effective and long-lasting. Simmond & Bristow's Manager of Engineering Services, Philippe de Greslan recommends the following five elements to assist small domestic treatment plants (operating for between 500 to 1000 equivalent persons) which have a nutrients removal process to ensure they are performing efficiently. • Sludge: The amount of sludge in an STP should be regularly checked as this gives an indication of the STP's operating situation. Most STPs have an activated sludge process in place, and the sludge waste is in many instances insufficient. The sludge concentration (mixed liquor) can be analysed. This amount should remain between 3 and 5 g/L to ensure the efficient operation of process. • Process: To maintain a sust ainable balance of nutrient removal bacteria, the STP needs to have both sequences with oxygen (aerobic) and without oxygen (or anoxic). The aeration equipment should be monitored to ensure a suitable time ratio between these sequences. The use of the switchboard is a good way to monitor the time ratios. Throughout the day, the aerobic period should represent 2A of the time and the anoxic 1A. • Flow: It's vitally important to ensure an STP is operating within its designated design capacity. A good way to do this is to measure the daily flow that comes into an STP. To do this, sites can measure the performance of the pumping station (number of pumping hours) to calculate the pumped flow, or with a flow met er. Sites can then compare what has been measured on site with the design hydraulic capacity for the STP (kl per day). 108 SEPTEMBER 2009
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• Load: It is also important to check the STP's biological load against the design capacity. Operators need to ensure there is adequate BOD (pollution) so that the biological load is operating efficiently. This can be measured over a 24 hour period with a composite sample of raw sewage which can then be sent off for analysis. In combination with the previous flow measurements, it will give a good indication of the organic load entering the STP that can be associated with overload troubleshooti ng. • People: Finally, the STP's operators need to be comprehensively trained and have a t horough understanding of what they're doing and why they're doing it. Some important elements to consider are reg ularly checking the performance of equipment, having correct procedures in place for cleaning, servicing and maintenance, and ensuring log books are kept up-todate. These five elements will assist small domestic STPs to ensure they are operating efficiently, and withi n safe environmental levels. For more information or to organise an audit of your STP, contact Simmonds & Bristow on 07 3710 9100 or visit www.simmondsbristow.com.au
CHRISTIES BEACH CATCHMENT STUDY lnfoWorks CS is being used to enable simulation of complex residential and commercial flows into the wastewater network serving Christies Beach wastewater catchment. Christies Beach is situated on the coast of South Australia around 15km south of the capit al city of Adelaide. The 105km 2 catchment is one of the three major metropolitan wastewater catchments in South Australia, the others being Bolivar and Glenelg. South Australian Water Corporation (SA Water) has initiated a project that represents the next step in developing its model expertise, based around Wallingford Software's lnfoWorks CS modelling platform. SA Water experienced considerable success in building models by importing data from its GIS system, but wanted to determine the best way to include pump stations, and wet and dry weather inflows within the model.
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The image shows, 'Christies Beach locality'.
SA Water req uired typical dry weather flow characteristics (diurnal pattern, typical daily loading rate per connection) and typical wet weather rainfall responses observed in sewers (percentage runoff contributing to inflow and infiltration characteristics). SA Water was interested in determining the flow characteristics for developments of varying age. Because the catchment was relatively new, SA Water wanted to confirm that there were no major groundwater infiltration issues, as had been assumed. SA Water has also undertaken an extensive "data cleansing" exercise on its GIS system to ensure that data is suitable to be directly imported for use in network modelling. The original network model of the Christies Beach area was built by SA Water to exclude all of the pump stations, which meant that the model comprised around 70 unconnected subnetworks. GHD was engaged initially to establish how the pump stations operated, then to carry out dry and wet weather calibrations, historical verification and undertake long-term time series analysis in preference to design storm analysis. The all-pipe model comprises around 1100km of pipes and 28,600 nodes across a 105km 2 catchment area. The system has no emergency relief structures. So far, 64 pump stations within t he network have been modelled some are extremely large trunk pump stations with inflows and pump capacities in excess of 400 1/s, controlled by variable speed drives which pose interesting modelling challenges.
Next steps GHD is currently undertaking wet weather flow calibrations, and is developing runoff parameters for this catchment. Because specific nonresidential areas have been monitored, an accurate understanding of t heir likely wet weather parameters including the