Licence conditions for pollution studies and reduction program


  

Licence conditions for pollution studies and reduction programs

Summary
 
Licence number: 4435
Title: Pollution Reduction Program 17 - Upgrade the Sewage Treatment Plant
Start date: 01 Dec 2017
 
Licence Condition
Background Pollution Reduction Program (PRP) 12 required the licensee to complete a concept design to upgrade the sewage treatment plant (STP). This concept design and associated Review of Environmental Factors(REF) identified the following works that will be completed at the STP: · Decommissioning of redundant sludge lagoons; · Replacement of existing inlet works drum screen; · Altered flow monitoring, moved from the inlet works flume to electromagnetic flow meters installed on individual rising mains upstream of the inlet works; · Installation of new bunded chemical dosing area(s) for caustic and alum dosing within the STP or sewerage system, including storage tank(s), bulk storage container(s), and associated pumps and pipelines; · Installation of a new UV disinfection unit to replace the current UV system; · Installation of a new sludge treatment system comprising two aerobic digesters and one sludge holding tank; and · Converting an existing 3.9 ML tank to a “Wet Weather Storage / Out of Specification Effluent Storage Tank” to provide a higher treated effluent quality for all flows received at the STP. The licensee has advised that the upgraded plant will provide full biological treatment up to 4 times "Average Dry Weather Flow" (ADWF) (which is 82 L/s) and provide "Storm-cycle Treatment" for flows between this and 8.7 x ADWF (180 L/s).  This is better than the historic industry practice of full treatment of 3 x ADWF and "Storm-cycle Treatment" up to 7 x ADWF.  The REF notes that flows in excess of 180 L/s stored in the “Wet Weather Storage / Out of Specification Effluent Storage Tank” would be returned to the inlet works during periods of lower flows to receive treatment.  The licensee modelled this approach using actual data (when there were several very large storm events) and noted treating 4 x ADWF is predicted to treat approximately 99.8 % of all flows.  The licensee therefore has noted that this storage capacity will be more than adequate to store excess flows without a bypass of the biological process resulting in a higher level of treatment to all flows received compared to the existing design. The REF concluded "By limiting the flows at the inlet works to 180 L/s and providing emergency storage and subsequent treatment for flows in excess of 180 L/s, the Project would improve the quality of effluent being discharged to the environment. On this basis, the EPL requirement to provide full treatment to flows less than 294 L/s can be reduced to 82 L/s, with partial treatment for flows between 82 L/s and 180 L/s." (p10 of the REF).  The REF also stated "The partial treatment provided by the wet weather cycle represents the treatment provided to achieve the maximum 100th percentile discharge limits." (p.10 of the REF)
Effluent Criteria Design Standards The design detailed in the REF was based around the STP having capacity and capability up until 2040 while meeting the following limits: · Ammonia: 90th percentile limit of 3 mg/L and 100th percentile limit of 5 mg/L; · BOD: 90th percentile limit of 10 mg/L and 100th percentile limit of 20 mg/L; · Total suspended solids: 90th percentile limit of 15 mg/L and 100th percentile limit of 30 mg/L. · Total Nitrogen: 50th percentile limit of 10 mg/L; and · pH: 100th percentile limit of 6.5 – 8.5 The design must also meet the following limits immediately downstream of the UV treatment system: .  Faecal coliforms: 90th percentile limit of 200 cfu/100ml and 100th percentile limit of 600 cfu/100ml.
Deliverables The STP must be upgraded consistent with the "Background" and the "Effluent Criteria Design Standards" detailed above and in accordance with the information detailed in the document titled “Review of Environmental Factors – Tanilba Bay WWTW Upgrade” prepared by AECOM and dated 25 May 2018. The construction and commissioning of the upgraded STP must be completed by 31 December 2021. The licensee must provide a report to the EPA upon construction and commissioning of the upgraded STP detailing all works completed.
Upon upgrade of the STP and completion of this PRP it is the intention of the EPA to vary the licence in the following manner: Vary condition P1.2 for Point 2 to reflect the new arrangement for measuring inflows to the STP, that is a new location description of “Inlet works to the STP with flows measured by addition of flows from all electromagnetic flow meters installed on individual rising mains upstream of the inlet works”. Vary the concentration limits at condition L3 to those detailed above, including a note that the limits will apply for all flows up to 180 L/s as the REF stated at page 10 "The partial treatment provided by the wet weather cycle represents the treatment provided to achieve the maximum 100th percentile discharge limits".  The REF notes the wet weather cycle at the STP will operate between flows of 82 L/s to 180 L/s. Vary the volume limit at condition L4 for Point 1 based on the treatment capacity of the upgraded plant, being 180 L/s, which equates to 15,500 kL/d. Vary condition O4.2 such that it reads “All sewage inflows up to 82 L/s must receive screening, biological treatment, clarification within the IDEA reactor, buffering within the “catch pond” and UV disinfection prior to discharge to Point 1.”                                                                                                                    . Vary condition O4.3 such that it reads “All sewage inflows between 82 L/s and 180 L/s must receive screening, partial biological treatment, clarification within the IDEA reactor, and buffering within the “catch pond” prior to discharge to Point 1.”   Add a new condition O4.4 that reads “All sewage inflows greater than 180 L/s must be diverted to the “Wet Weather Storage / Out of Specification Effluent Storage tank” for later treatment”. Add a new condition O4.5 that reads “Surplus capacity within the “Wet Weather Storage / Out of Specification Effluent Storage Tank” and buffering capacity the “Catch Pond” must be utilised such that the maximum volume of fully treated effluent passes through the UV disinfection system. Add a new condition O4.6 that reads “All flows from the treatment train at the plant up to 82 L/s (4 x ADWF at predicted flows in the year 2040) must pass through the UV disinfection system.” Add a new condition O4.7 that reads “The licensee must advise the EPA in writing within 24 hours of any situation where effluent flows by-pass the UV disinfection system. This notification must include details as to the capacities (per cent full) of the “Wet Weather Storage / Out of Specification Effluent Storage Tank” and the “Catch Pond” at the time of the by-pass and if both are not at 100 % capacity why they have not been utilised to the maximum extent possible to prevent undisinfected effluent being discharged."   Add a new condition O4.8 that reads “Once the “Wet Weather Storage / Out of Specification Effluent Storage Tank” has reached capacity additional flows greater than 180 L/s may travel direct to the Effluent Distribution Channel for discharge to the exfiltration ponds.” Vary condition M7.1 to reflect the new arrangement for measuring inflows to the STP, that is “Flow meters and continuous logger.”