INFRASTRUCTURE & OPERATION

Transcription

1 SECTION C: INFRASTRUCTURE & OPERATION Advice on completing this section is provided in the accompanying Guidance Note. C.1 Operational Information Requirements Provide a description of the plant, process and design capacity for the areas of the waste water works where discharges occur, to include a copy of such plans, drawings or maps, (site plans and location maps, process flow diagrams), and such other particulars, reports and supporting documentation as are necessary to describe all aspects of the area of the waste water works discharging to the aquatic environment. Maps and drawings must be no larger than A3 size. C.1.1 Storm Water Overflows For each storm water overflow within the waste water works the following information shall be submitted: An assessment to determine compliance with the criteria for storm water overflows, as set out in the DoEHLG Procedures and Criteria in Relation to Storm Water Overflows, 1995 and any other guidance as may be specified by the Agency, and Identify whether any of the storm water overflows are to be decommissioned, and identify a date by which these overflows will cease, if applicable. C.1.2 Pumping Stations For each pump station operating within the waste water works, provide details of the following: Number of duty and standby pumps at each pump station; The measures taken in the event of power failure; Details of storage capacity at each pump station; Frequency and duration of activation of emergency overflow to receiving waters. Clarify the location where such discharges enter the receiving waters. Attachment C.1 should contain supporting documentation with regard to the plant and process capacity, systems, storm water overflows, emergency overflows, etc., including flow diagrams of each with any relevant additional information. These drawings / maps should also be provided as geo-referenced digital drawing files (e.g. ESRI Shapefile, MapInfo Tab, AutoCAD or other upon agreement) in Irish National Grid Projection. This data should be provided to the Agency on a separate CD-Rom containing sections B.1, B.2, B.3, B.4, B.5, D.2, E.3 and F.2. Attachment included Yes No MDW0350RP AO3

2 Attachment C.1 - Operational Information Requirements

3 ATTACHMENT C.1: Infrastructure & Operation The sewer collection system in Blessington consists of 4,557.0m of foul sewer ranging in diameter from 255 to 750 and 2,612.0m of surface water ranging in diameter from 300 to 600mm as shown on Drawing No. MDW0350DG/C.1. There are no foul sewer overflows and pumping stations, so all foul sewer flow by gravity directly to Blessington Waste Water Treatment Plant. The wastewater treatment facility has recently been upgraded and only came into full service in 2007 with capacity of 6,000PE. The hydraulic load conditions are presented in Table C.1 below. Final effluent from Blessington Waste Water Treatment Plant is discharged to Golden Falls Lake approximately 5.5km on the south of the Blessington Town, as shown on Drawing No. MDW0350DG/C.1.2. Table C.1: Blessington WWTP Hydraulic Load Conditions Hydraulic Load Unit Load Conditions Dry Weather Flow (DWF) Storm Flow - Plant capacity for continuous in line treatment - Plant capacity, utilising stormwater balancing tank, without spilling to stormwater lagoon m 3 /day m 3 /h m 3 /h m 3 /h 1,350 (16l/s) 1,800 (500 l/s) 173 (48l/s) 346 (96l/s) Hydraulic loading (DWF) is taken as 1,350m 3 /d (16l/s). The treatment facility has capacity for on-line treatment of 48l/s. A stormwater balancing tank is provided as part of the inlet works to ensure that the plant can cater for 95l/s (6 times DWF) without spilling to the stormwater lagoon. TableC.1.2: Blessington WWTP Influent Quality Loads Parameter Average Daily Load BOD kg/d Suspended Solids 440kg/d Total Nitrogen 100kg/d Ammonia (N) 60kg/d Total Phosphorus (P) 15kg/d 1 Five Day Biochemical Oxygen Demand. MDW0350RP AO3

4 A Flow diagram is presented on Drawing No. MDW0350DG/C.1.3, attached. Plant and process Operation description The wastewater arrives in the treatment plant through a gravity sewer from the Blessington catchment area into the receptor chamber. Under normal circumstances (flows to a maximum of 3 DWF), all sewage flow to the inlet works where the sewage is screened via duty/standby 6mm.screens. In the exceptional case that the screens are both blocked or otherwise not working, a manually raked bypass screen was provided guaranteeing a continuous flow of raw sewage to the aeration tanks. After screening the wastewater flow to the aerated grit/fat trap for grit and fat removal. Settled grit is removed from the bottom of the grit tank by a grit pump. The grit is classified and transported into a mini bin for off-site disposal. The fat is removed manually on a regular basis from the surface. After the grit trap the screened and degritted wastewater is sampled and monitored for ph, temperature and COD. After sampling etc. the sewage gravitates to the splitter box of the aeration tanks. Flows in excess of 3DWF are diverted from the inlet chamber to the storm tank, via a 6mm storm screen. The storm tank has a capacity of 337m 3 (i.e. 3DWF for 2 hours), and includes a jet aerator which keeps any solids in the storm tank in suspension, which prevents settling. This storm tank is sufficiently sized to catch the "first flush" of storm flows to the WWTP. If flows exceed the capacity of this storm tank, they overflow to the storm lagoon. The storm lagoon is 60m by 65m in plan area, and is approximately 1.5m deep, providing a capacity of over 5,500m 3. There is no storm overflow to the adjacent stream at the Blessington WWTP. When influent flows have reduced to less than 1.5 DWF, the flows to the storm tank and the lagoon will be pumped back to the inlet works, from where they will be passed on for full treatment. When the influent flow has reduced to less then 1.5 DWF, the storm water holding tank will be emptied by the storm water return pump in the storm water holding tank. Flow pumped back to the inlet works will be measured with flow meter. Flow from the inlet works to the splitter box is measured with an electronic flow meter. The measured flow will control the penstock between the reception chamber and the screens. The wastewater enters the flow splitter chamber where the flow is directed to one or two of the aeration tanks. The Return Activated Sludge (RAS) is pumped separately from each clarifier into the splitter chamber. The wastewater flowing into the aeration tank contains organic matter (BOD) as a food supply. Microbes metabolise the waste solids, producing new growth while taking in dissolved oxygen and releasing carbon dioxide. Some of the new microbes die releasing cell contents to solution wastewater removes organic matter from solution by synthesis into microbial cells. Mixed liquor is continuously transferred to the clarifiers for gravity separation of the biological flocs. Settled flocs are returned to the aeration tank for mixing with entering raw sewage from the inlet works. Oxygen for utilisation by the micro-organisms is transferred into the mixed liquor by means of an aeration system. The rate of Dissolved Oxygen (DO) utilisation is basically a function of the Feed to Biomass (F/M) ratio and temperature. The aeration system is designed to suit the configuration of the tanks and to maintain the sludge in suspension. A dissolved oxygen probe controls the oxygen input by the aeration system. After treatment in the aeration tanks, the wastewater flows to the secondary clarifiers. In the clarifiers, the treated water is separated from the sludge. The water enters in the centre of the tank and flows horizontally to the bottom of the tank. In this quiescent flow, the sludge or bacteria will settle to the bottom of the tank and when the water reaches the overflow weir of the clarifier, the water is ready for discharge to the outfall. The settled sludge is pumped form the bottom MDW0350RP AO3

5 of the clarifiers to the splitter box by the RAS pumps or by the WAS pumps to the Picket Fence Thickener (PFT). Coagulant (Aluminium Sulphate) is dosed in the outlet of the aeration tank. The coagulant forms a metal salt with phosphorous. The salt precipitates with the activated sludge in the secondary clarifier and thus reduces the effluent phosphorous amount to the required concentration. The final effluent from the secondary clarifier flows onto the final effluent sump. In the final effluent sump the effluent is sampled and measured for COD, ph and Temperature. The final effluent is pumped by two duty/standby pumps via a circa 250mm outfall pipe to the Golden Falls Lake outfall. In the pipeline the final effluent flow is measured. When the sludge concentration in the aeration tanks is elevated above the required set point for the loading of the plant, sludge has to be removed from the treatment system. The Waste Activated Sludge is pumped to the picket fence thickener. Import of liquid sludge from Knockieran and Hollywood takes place via a tanker connection from where the tanker, pumps sludge over the fine screen after which the sludge is pumped into the picket fence thickener. The level in front of the screen controls the flow to the screen, which is measured by an electronic flow meter and controlled with a valve. The screenings are washed, compacted and dropped into a mini bun for disposal off-site. Both the imported sludge and the Waste Activated Sludge flows into the picket fence thickener. In the picket fence thickener, the sludge has time to settle to the bottom of the tank resulting in a concentrated sludge in the bottom and clear liquid at the top. The liquid (Supernatant) overflows from the thickener to the return liquor sump from where it is pumped into the splitter box in front of the aeration tanks. The thickened sludge at the bottom of the PFT is pumped to the mixing chamber of the belt press. Polymers are added to the thickened sludge for dewatering. The sludge is dewatered in the belt press to a dry solids concentration greater then 15%. Depending on the off site disposal route, lime may be added to the dewatered sludge to produce a class B sludge. After that, the sludge is forwarded to the sludge skip before disposal off-site. When the sludge drying installation in Wicklow is available, the sludge will be transported there. The following is an extract from the Final Design Report for Blessington, Volume 1 Mechanical & Process Design prepared by DBO Contractor Veolia Water Ireland. MDW0350RP AO3

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17 C.2 Outfall Design and Construction Provide details on the primary discharge point & secondary discharge points and storm overflows to include reference, location, design criteria and construction detail. Attachment C.2 should contain any supporting documentation on the design and construction of any and all discharge outfalls, including stormwater overflows, from the waste water works. Attachment included Yes No MDW0350RP AO3 EPA Export :01:23:46

18 Attachment C.2 - Outfall Design and Construction EPA Export :01:23:46

19 ATTACHMENT C.2: Outfall Design and Construction The Outfall is located at Golden Falls Lake approximately 5.5 km from Blessington Waste Water Treatment Plant as shown on Drawing No. MDW0350/DG C.2 attached. Attachment C.2 also contains Longitudinal Section of the final effluent pressure Main as shown on Drawing Nos.: MDW0350/DG C.2.1, MDW0350/DG C.2.2 and MDW0350/DG C.2.3 attached. The Outfall was constructed as part of the original WWTP contract in 1980, but was sized for 6,000 PE. The average flow in the final effluent pressure main is 11.7 l/s, which is based on average daily discharge volume from Blessington WWTP 1, m 3 /24hrs. MDW0350RP AO3 EPA Export :01:23:46

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