TREATING CLARIFIER AND BACKWASH WASTEWATER WITH ULTRAFILTRATION MEMBRANES
THE PILOT TRIAL RESULTS OF A GROUNDWATER CLEAN-UP PROJECT AT THE BOTANY GROUNDWATER TREATMENT PLANT IN SYDNEY
P El Jbeily, F Barendregt, K Clark, F Akkawi
Publication Date (Web): 12 February 2016
The Botany Groundwater Treatment Plant (GTP), located in Sydney, NSW, forms a major component of the Groundwater Cleanup Project being undertaken by Orica and Chemicals Division (now Ixom Operations) to clean up contaminated groundwater arising from former chemical industry operations at Botany Bay.
The GTP generates wastewater at 32 kL/h from clarifier underflow and backwashing media and biological filters. The wastewater is pumped to a sludge thickener to remove iron and biological flocs, and the thickener underflow pumped to sewer. The original plant design included recovery of the thickener overflow, but the biological activity from the dissolved organic carbon in the groundwater required more frequent backwashing of filters and consequential overloading of the thickener. Attempts to recover the overflow overloaded the media filters, so the overflow was diverted to the sewer.
In order to reduce trade waste costs, Orica and the Chemicals Division investigated the use of membranes to recover some of the waste discharged to the sewer and trialled DOW outside-in polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes in 2013. The trial assessed the suitability of the DOW membrane format and configuration and enabled optimisation of system design parameters.
The feedwater quality to the UF system was particularly challenging as the water was highly biologically active, with suspended solids up to 45 mg/L, including iron as high as 10 mg/L and volatile suspended solids up to 30 mg/L.
The pilot trial conducted prior to the construction and supply of the fullscale plant was able to validate the suitability of the DOW UF membrane and module format for the required application. The trial demonstrated that the membranes were able to treat and recover this industrial wastewater characterised by high suspended solids, turbidity and iron, to meet GTP treated water quality criteria. It also enabled process engineers to optimise process set-points to maximise water recovery and cleaning effectiveness.
The project objective of bringing the UF plant into operation as quickly as possible to realise savings was made possible through Chemicals’ execution methodology and the selection of a standardised DOW IntegraPac UF module skid.
Maximisation of off-site works, early engagement of stakeholders to expedite site works, and ongoing technical support through the start-up and operations phases were crucial to meeting this objective.
The plant has been in operation since October 2014. The UF system has been producing filtrate with total iron less than 0.5 mg/L and turbidity less than 1 NTU, which has allowed the water to be recovered back into the process. Selection of a membrane material with good tolerance to oxidant exposure has allowed slug dosing of chlorine to resolve biofouling issues. While further work is required to resolve operating constraints and achieve the full benefit of the UF system, the plant is estimated to be delivering a net saving of $1500 per day under current operating protocols.
The successful operation of the Orica Botany GTP project demonstrates that ultrafiltration can be coupled with existing conventional processes to reduce waste volumes and trade waste costs.
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