BEENYUP ADVANCED WATER RECYCLING PLANT: THE PERTH, AUSTRALIA GROUNDWATER REPLENISHMENT SCHEME. Introduction

Transcription

1 BEENYUP ADVANCED WATER RECYCLING PLANT: THE PERTH, AUSTRALIA GROUNDWATER REPLENISHMENT SCHEME James C. Lozier, CH2M, 1501 W. Fountainhead Parkway, Suite 401, Tempe, AZ Ph: (480) Kevin Guppy and Stacey Hamilton, Water Corporation of Western Australia, Leederville, Perth, Western Australia Introduction The Water Corporation of Western Australia (Water Corporation) is the principal supplier of water, wastewater and drainage services in Western Australia (WA), with projects and activities spanning over one million square miles. Water Corporation is headquartered in Perth, the capital and largest city in Western Australia with a greater metropolitan population of approximately two million. Water supply for Perth has historically come from surface water (through dams) and groundwater. Climate change has resulted in a significant reduction in rainfall in southwest WA since the 1970s. Average dam inflow decreased from 90 billion gallons per year between 1935 and 1974 to 47 billion gallons per year from 1980 to 2000 with a further decline to 19 billion gallons per year between 2000 and 2010, with 2010 experiencing the lowest inflow to Water Corporation dams on record, equal to only 13 summer day s demand. In response to this dramatic decline and predictions that rainfall will decline further over the next 50 years, Water Corporation developed a 50-year water supply strategy Water Forever: Toward Climate Resilience that included water conservation, construction of seawater desalination plants (SDPs) and the advanced treatment and recycling of wastewater through groundwater replenishment. Water Corporation commissioned their first SDP in 2006 and their second in 2011, which was expanded in These plants provide nearly 40 billion gallons per year of drought-proof water supply. The groundwater replenishment scheme is a key component of the Water Corporation s 10-year water supply strategy called Water Forever: Whatever the Weather and is the subject of this paper. The scheme, depicted in Figure 1, was initiated in 2008 with the design and construction of the Groundwater Replenishment Trial. Groundwater Replenishment Trial The Groundwater Replenishment Trial or GWRT, involved the construction and operation of an Advanced Water Recycling Plant (AWRP) that treated secondary effluent from the Beenyup wastewater treatment plant (WWTP) using ultrafiltration (UF), reverse osmosis (RO) and ultraviolet (UV) disinfection to produce water (product water) that met Australian Drinking Water Guidelines. A simplified process schematic for the AWRP is shown in Figure 2. Once produced, AWRP product water was then recharged into a confined aquifer (Leederville) at a depth of ~400 to ~700 feet. Water quality was monitored throughout the treatment process and via an extensive network of 22 groundwater monitoring wells at the site of the wastewater treatment plant and AWRP. The Trial, overseen by the Department of Health (DoH), Department

2 of Water (DoW) and Department of Environment and Conservation (DEC), as well as technical consultants; had three principal objectives: To provide a context for the three regulatory agencies to develop health and environmental regulation and water allocation policy for groundwater replenishment. To demonstrate the technical feasibility of the treatment process and aquifer response to reliably meet health and environmental water quality regulations. To raise awareness and encourage community discussion about groundwater replenishment and its potential as a future water source. The trial and AWRP operation lasted from November 2010 to December Figure 1. Water Corporation s Groundwater Replenishment Scheme

3 Compliance with Recycled Water Quality Requirements The recycled water produced by the AWRP was required to comply with 254 water quality guidelines (which required the analysis of 292 recycled water quality parameters (RWQPs)) and a subset of 18 RWQ indicators (RWQIs) defined by the DOH and DEC at the point of recharge. The RWQIs are listed in Table 1. The extensive sampling program, which consisted of 4,104 separate compliance samples carried out during the GWRT, demonstrated that the product water met all water quality guidelines. Figure 2. GWRT process schematic Table 1. GWRT Recycled Water Quality Indicators and Associated Groups Represented Indicator (Surrogate) Group Represented Boron Metals and Metalloids Nitrate Inorganic anions NDMA N-nitrosamine DBPs Chlorate DPB anions 1,4-dioxane Miscellaneous organics EDTA Organic chemicals Chloroform DBPs

4 1,4-dichlorobenzene Fluorene 2,4,6-trichlorophenol Carbamazepine Estrone Diclofenac Trifluralin Octadioxin MS2 phage Alpha particle activity Beta particle activity Volatile organics Polycyclic aromatic compounds Phenols Persistent pharmaceuticals Hormones Acidic pharmaceuticals Pesticides Dioxins, furans and dioxin-like PCBs Microbial pathogens including viruses Radioisotopes Radioisotopes Critical Control Points To ensure that both the WWTP and the AWRP were reliably and consistently operated in a manner that would ensure compliance with recycled water quality guidelines as well as to protect human health and environmental values of the recharged aquifer, the Water Corporation identified appropriate surrogates of treatment process operational performance and critical limits for performance, termed critical control points (CCPs). Where a CCP was breached, the AWRP was required to divert water from the treatment process. A diagram showing the thirteen CCPs established for the GWRT are shown in Figure 3. Quantitative values were established for each CCP which were then used to determine compliance or breach. The treatment process operated within the CCPs 99.93% of the time. Figure 3. Critical Control Points for GWRT AWRP

5 Full-Scale Advanced Water Recycling Plant Following completion of the GWRT, DoH, DEC and DoW determined that groundwater replenishment is a safe and sustainable water source option. In August 2013, the Western Australian State Government announced that groundwater replenishment would become the next climate independent water source for Perth. Water Corporation then proceeded to prepare and issue request for proposals for engineering, procurement, construction services and commissioning for a full-scale AWRP through a competitive alliance. In November 2013, Water Corporation selected two teams to develop a preliminary design and total outturn cost (TOC) for three separate stages of the full-scale AWRP: 7, 14 and 28 gigalitres/year (5, 10 and 20 mgd). In July 2014, Water Corporation then selected the Joint Venture of CH2M HILL and Thiess Constructors (known as the CHTJV) to perform detailed design, construction and commissioning of the a 14-gigalitre/year (10 mgd) AWRP to be constructed in the vicinity of the Beenyup WWTP and called the Beenyup AWRP. The Beenyup AWRP treatment process, as shown in Figure 4, is very similar to the process used in the GWRT. In addition to UF, RO and UV, the process includes both coarse and fine screens (the latter to protect the UF membranes); dosing of pre-formed chloramines prior to the fine screens to prevent biofouling in the downstream unit processes; dosing of antiscalant and acid to the RO feed to prevent precipitation of sparingly soluble salts, most notably calcium carbonate, calcium phosphate and barium sulfate; degasification (full or partial) of the RO permeate to remove excess carbon dioxide; and caustic dosing to the UV effluent. Microbial Log Reduction In addition to the RWQIs discussed previous, a key DoH requirement for the plant to ensure the protection of public health is providing minimum log reductions for the three categories of pathogens- bacteria, viruses and protozoa. The established requirements are 8.5, 9.5 and 8 logs for bacteria, viruses and protozoa, respectively. To achieve this, DoH has assigned log reduction credits for UF, RO and UV as shown in Table 2, provided each process is operated in compliance with established CCP values. Based on the assigned log reduction credits, the combined Beenyup WWTP and AWRP treatment processes achieve log reductions well in excess of the DoH requirements, with excess credits providing a comfortable safety margin. Design Criteria Design criteria for the UF, RO and UV systems are presented in Table 3. All products were selected by the CHTJV using a competitive procurement process and specifications that incorporated technical performance requirements as stipulated by Water Corporation in their Basis for Design and Construction document. The ability of the UF module (and system) to achieve the assigned 3-log virus reduction was a key performance criterion. This was demonstrated for the selected UF product by third-party testing conducted by the National Sanitation Foundation (NSF) through their ETV program. For RO, 3-log pathogen reduction will be demonstrated though module-by-module vacuum testing and train testing using both Rhodamine WT dye and sulfate. Dye and sulfate testing was performed during the GWRT on the selected RO element. The UV reactor has been validated through third-party testing in the U.S.

6 Table 2. Microbial Log Reduction Credits and Requirements Equivalent Log Reduction Credits (ELRC) Bacteria Virus Protozoa Wastewater Treatment Plant (WWTP) Advanced Water Recycling Plant (AWRP) UF with chloramination >1.5 mg/l Reverse Osmosis UV Disinfection at >186 mj/cm Total ELRC - AWRP Total ELRC (WWTP and AWRP) DoH Requirement Excess Credits (safety factor) Table 3. Design Criteria for Major AWRP Treatment Processes Criterion Value Ultrafiltration Filtrate Flow, mgd 17.3 Module Type Dow SFD-2880 No. of skids/modules per skid 7 duty + 1 standby Flux, gfd 29.5 (max instantaneous) Recovery, % 92 Reverse Osmosis Permeate Flow, mgd 13 Element Type Hydranautics ESPA2-LD No. of skids 4 duty Skid array 70:35 Membrane Flux, gfd 11.3 Recovery, % 75 initial; 80 final Energy recovery device FEDCO turbocharger UV Disinfection Flow, mgd 12.7

7 Reactor type Calgon Sentinel 9L24 medium pressure No. of units 2 duty MS-2 phage RED, mj/cm Transmittance (at 254-nm), % 94 Project Schedule The schedule for design, construction and commissioning, including critical validation and verification requirements, in which the ability of the plant to meet DoH requirements must be demonstrated, is shown in Table 4. As of the date of this paper s preparation, construction is nearing completion and the functional testing of equipment in underway. Table 4. Project Schedule for BAWRP Phases 1 and 2 Milestone Date Project Award July 2014 Start of Design Aug 2014 Design Completion Feb 2015 UV/RO/UV Systems Delivery June 2015 Construction Completion Mar 2016 Validation and Verification Completion Nov 2016 Summary The Water Corporation is proactively addressing the impacts of global climate and the significant reduction in rainfall that the Perth region has experienced over the last several decades by implementing a water supply strategy that includes water conservation, increased use of secure (deep) groundwater and seawater desalination. A key part of this strategy is the construction and operation of the Beenyup Advanced Water Recycling Plant, which will transform wastewater effluent into recycled water meeting all drinking water related standards and guidelines. When the BAWRP is operational at full planned capacity in 2022, the water supply for the greater Perth area will be provided in whole by the climate-independent sources of desalinated seawater and secure deep groundwater, allowing Water Corporation to have achieved their Water Forever: Whatever the Weather strategy.

8 STAGES 1 AND 2 FROM COARSE SCREENS P PRE-FORMED CHLORAMINES PRE-FORMED CHLORAMINES ANTISCALANT SULFURIC ACID P REVERSE OSMOSIS P SODIUM HYDROXIDE P TO LEEDERVILLE TO LEEDERVILLE AQUIFER AND YARRAGADEE AQUIFERS AWRP BALANCE TANK FINE SCREEN ULTRA- FILTRATION RO FEED TANK DEGASSER UV TREATED WATER STORAGE TANK ALK = 8.4 MG/L PH = 7.5 NAOH = 11 MG/L BACKWASH TO RETURN WORKS CONCENTRATE TO OCEAN OUTFALL Figure 3. Process Flow Diagram for Beenyup Full-Scale Advanced Water Recycling Plant