Groundwater Treatment Plant
Introduction
The main part of the Orica Botany Groundwater Cleanup Plan is hydraulic containment along the three containment lines and treatment of extracted groundwater in the Groundwater Treatment Plant (GTP). The GTP treats the extracted groundwater by removing the dissolved chlorinated hydrocarbon (CHC) (Fact sheet:  37kb) contamination.
Orica built a $167 million GTP to treat contaminated groundwater and produce high quality water for re-use. The GTP has a capacity to treat up to 15 ML/day and has been designed to operate for 30 years. It took two years to design and build the plant. Commissioning commenced in late 2005 and groundwater was first introduced to the plant in January 2006. In March 2007, the GTP entered its fully operational phase and treats groundwater at an average rate in excess of 5 ML/day. The actual daily treated volume is lower than the plant's design capacity as the Botany area's average groundwater flow rates were later found to be lower than what was initially used in the design model. At times of high rainfall the GTP treats up to 7 ML/day. By pumping at an average rate of over 5 ML/day from the containment areas, Orica achieves hydraulic containment of the contaminated groundwater.
Night shot of the Groundwater Treatment Plant:
Air Stripping Unit (left) and Quench Tower & Stack (right)
The GTP was constructed using proven process technology from around the world.
The plant has successfully achieved containment of the contaminated groundwater, protecting Botany Bay and the local environment, and is currently supplying six local factories with high quality treated water, replacing up to 7 ML/day of demand on Sydney's potable water supply.
GTP and Botany Groundwater Cleanup Project
The GTP plays an essential role in Orica's Botany Groundwater Treatment Project. As shown in the diagram below, the groundwater extracted from wells along the three containment lines is pumped and transferred through pipelines to the GTP for treatment. Treated water is then reused by local factories. Excess treated water is discharged to Botany Bay via a local stormwater canal.
GTP Layout and Key Units
GTP layout
The principal unit processes employed in the GTP are:
How the GTP Cleans the Groundwater
Extraction of Groundwater
The contaminated groundwater is extracted from the three containment areas (primary, secondary and BIP), which are equipped with multiple extraction wells to pump water from the shallow, intermediate and deep aquifers.
Treatment Process
Simplified diagram of process flow
Extracted groundwater is pumped through the containment pipelines and enters the GTP Feed Tank where it is blended and dosed with hydrochloric acid (to minimise mineral scaling in the air strippers). It is then pumped through the Air Stripping Units, where the volatile CHCs are removed. The Air Stripping Units remove contaminants from the groundwater by blowing air through a falling column of groundwater in a closed structure called a stripping column. This process results in an air stream containing gaseous CHCs, and stripped water with negligible concentration of volatile CHCs.
The removed CHCs are blown through a Thermal Oxidiser at a temperature around 900ºC*, and are destroyed. The combustion gases are principally carbon dioxide, water vapour and hydrogen chloride. The hot gas passes through a waste heat boiler and energy recovery heat exchanger before passing through a quench tower (to rapidly drop the gas temperature to avoid dioxin formation), hydrochloric acid absorber and caustic scrubber (to remove acid gases). Prior to the release of air from the stack, the cleaned gas is mixed with a hot air steam to improve dispersion and reduce plume visibility. For more information on the thermal oxidiser, view Fact Sheet No 12 Thermal Oxidiser (31kb).
*In order to optimise GTP operation and reduce the amount of greenhouse gas produced in the operation, Orica successfully conducted trials to reduce the temperature from 1000ºC to 875-900ºC in September 2007. The Department of Environment and Climate Change (now the Deparment of Environment, Climate Change and Water) has consequently amended the Environment Protection Licence in November 2007 with a new lowest operating temperature limit of 875ºC.
Groundwater 'stripped' of volatile CHCs (stripped groundwater) is treated further at the Stripped Groundwater Treatment Plant in the GTP to remove iron, aluminium, residual organics, organic acids and ammonia through various sets of filters. First, the stripped groundwater is pumped to an Actiflo® unit where sodium hydroxide and flocculating agents are dosed, and iron and aluminium are removed by precipitation and flocculation. Then, the water passes through multimedia filters (sand and cartridge filtration) and then through Granular Activated Carbon (GAC) to remove non-volatile compounds, such as phenol and chlorinated phenols, as well as Biological Aerated Filters (BAFs) to remove readily biodegradable organic matter. The water is dosed with chloramine to suppress biological fouling before passing through a second bank of multimedia filters. At the final stage, the water is pumped through two sets of Reverse Osmosis (RO) Units to remove salt and other impurities to yield high quality recycled water suitable for industrial re-use. The salty reject stream from the RO units is discharged to sewer.
The final treated water gets either reused by neighbouring industries (Treated Water Recycling Project), or discharged to a stormwater canal, which then flows into Botany Bay. The excess discharged treated water is dosed with sodium metabisulphite to chemically remove chloramine from the water before discharging.
Although chloramine is a common disinfectant found in drinking water that has no health risks to humans, it may be toxic to aquatic life.
What Does Orica Do with the Treated Water?
Treated Water Recycling
The GTP currently treats an average in excess of 5 ML of contaminated groundwater per day. This amounts to about 0.5% of total water consumption in Sydney. Orica was required to maximise use of the treated water (by conditions outlined in our Environment Protection Licence) and is delighted to be providing high quality water for the following uses:
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water supply for cooling towers
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water supply for demineralisation plants (for use at other facilities, e.g. boiler)
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industrial process water
Orica is committed to expanding water recycling opportunities at Botany and beyond, and has created a separate environmental project solely for this purposes (Treated Water Recycling Program).
Excess Treated Water
The excess treated water that is not being used by neighbouring industries is discharged to Botany Bay (Brotherson Dock) through a stormwater canal at Perry Street, Matraville.
Why Doesn't Orica Return Treated Water to the Underground Aquifer?
The treated water is a valuable resource that can be used to displace consumption of Sydney's limited portable water supplies. Hence, Orica is endeavouring to maximise the reuse of treated water. In any case, it is not feasible to return treated groundwater into the underground aquifer. Since the groundwater is anaerobic (free of oxygen) returning the treated water (which is fully aerated) to the aquifer may cause significant disruption due to biological fouling in the vicinity of the injection points.
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