Groundwater Replenishment System, Orange County, United States of America

The Groundwater Replenishment System (GWRS) has been operating since January 2008. Jointly developed by Orange County Water District (OCWD) and Orange County Sanitation District (OCSD), GWRS is the largest water purification project of its kind in the world. The state-of-the-art treatment plant has been in the planning phase since 1994 and construction began as late as 2003. The first phase of the plant cost $480m.

GWRS is now in the process of expansion. The proposed expansion work is expected to begin in the last quarter of 2011.In March 2011, the OCWD board of directors approved the first phase of expansion of GWRS. The expansion will increase the plant's treatment capacity by 30 million gallon per day (MGD). The project is scheduled for completion in September 2014. A $156.2m budget has been set aside for the project.

Groundwater replenishment system plant

The GWR System facility is located in Orange County, California and receives secondary treated sewer water for further treatment. The source water contains less than 15mg/L of biochemical oxygen demand (BOD), 5mg/L suspended solids (SS), 1,000mg/L total dissolved solids (TDS) and 11mg/L total organic carbon (TOC). Water produced after treatment contains 0.3mg/L TOC, about 100mg/L TDS, while TSS and BOD presence is negligible.

The plant is equipped with the Siemens MEMCOR submerged membrane system and is capable of supplying 86MGD of water. This membrane system is made up of 26 compact units which can treat water five times more than the formal purification system established in the same footprint. Each unit of the membrane system is fitted with 608 hollow fibre membrane modules which, in turn, are set up in racks. A filtration pump provided with each unit draws water from the membrane fibres.

Nearly half of the refined water is transferred to OCWD recharge facilities in Anaheim, California and any remaining water is injected into Orange County's seawater barrier for its expansion.

GWRS expansion

The GWRS expansion, second phase of development, is expected to cost about $156.27m. In April 2010, a bill was introduced to authorise $26m through federal funding for the expansion of the GWR System.

The expansion will involve Memcor CS membrane modules, ancillaries, control system upgrades and related electrical works. After expansion, the capacity of the existing MF membrane system will increase from 86MGD to 120MGD. The plant production capacity will increase from 70MGD to 100MGD.

Under a $16m pre-selection contract awarded in March 2010, Siemens will supply a hollow-fibre membrane treatment system. Commissioning of the expanded system and installation of membrane modules will be monitored by Siemens. The Siemens membrane system, at the time of its installation in the existing plant, was one of the largest in the world.

Design of the proposed expansion was taken up by Black & Veatch in July 2009. Staff assistance was offered by Separation Process.

In May 2011, a $128m construction management contract was awarded to Parsons. The scope of the contract includes a range of services from document control to commissioning oversight and operational start up services.

Purpose of the GWRS project

The existing plant generates enough water to supply 500,000 people. It is estimated that in the next 20 years the population of Orange County will increase from 2.3 million to 3 million. It is also projected that by 2020, water requirement for central and north Orange County will be 600,000 acre-feet.

To fulfil the future water demand for agricultural, industrial and indirect potable use, it was decided to expand the GWRS and the plant was constructed with scope for future expansion.

Water treatment

Water at the existing plant is treated using advanced techniques consisting of microfiltration, reverse osmosis (RO) and ultraviolet disinfection with hydrogen peroxide.

The source water, which is secondary treated sewer water, is first micro-filtered at a microfiltration unit. The microfiltration process removes small suspended particles, protozoa, bacteria and other harmful viruses from the water.

The water is then filtered through RO. This process removes salts, viruses, pesticides and most organic compounds by passing the forced water through thin plastic membranes. Water quality recovered after this step is near-distilled.

In the final stage, the water is treated with ultraviolet (UV) light and hydrogen peroxide as a precautionary measure.

Combining UV light and hydrogen peroxide produces advanced oxidation reaction and eliminates any remaining organic compounds.