The foaming inhibitor on Nocardia and alike (FIONA) process

Abstract

A new process to abate foam-causing micro-organisms of the genus of Nocardia sp. and alike was developed in the Sha Tin Sewage Treatment Works of Hong Kong in 2002 under an in-house research and development study. The new FIONA process relates to a process of inhibiting the growth of the foam-causing micro-organisms of genus Nocardia sp. and alike, which are commonly found in activated sludge sewage treatment process with nutrient removal. The Sha Tin Sewage Treatment Works is the largest secondary sewage treatment works in Hong Kong with nitrogen removal capability. It has been suffering from Nocardia foam since its commissioning in 1982, which had led to consistent non-compliant events. The new process has been put into full scale application since 2002 and its foaming abatement effect is very effective; resulting in resumption of full compliance with the discharge licence since November 2003. The FIONA Process basically comprises a chemical dosing system and a reaction zone with a mean hydraulic retention time of 1 hour. The dosing point of the Process can be at upstream sewage pumping stations as well as the inlet works of the sewage treatment works. The dosing chemicals are to create an anoxic environment in the sewage so as to boost up the removal of the readily biodegradable substrates, which are favourable substrates of the foam-causing micro-organisms, in the sewage prior to entering the bioreactors. In such way, it will help out-compete the foam-causing micro-organisms in the bioreactors. Full scale dosing results in the Sha Tin Sewage Treatment Works from 2002 to 2004 had demonstrated that the previous year-round appearance of the Nocardia foam in the bioreactors had been greatly abated to an extent from little to moderate appearance only from January to April with complete Nocardia foam disappearance from May to December. The dosing chemical being used is calcium nitrate at dosing rates from 15 to 50 mL of aqueous calcium nitrate at 50% concentration by weight (equivalently 50 to 150 mM of calcium nitrate) per m³ of sewage. For other metallic nitrate salts, the nitrate mass content must be equivalent to the nitrate mass of calcium nitrate at the above dosing range. For hydrogen peroxide, it is believed the same effect would occur, however, there is no practical data available. A theory for the FIONA Process based on the bio-selector effect is also proposed albeit further research is necessary for its substantiation.

Keywords:

• Activated sludge
• Nocardia foam
• FIONA process
• reaction zone
• sewer bio-selector effect
• biodegradable substrates.

Acknowledgments

The author wishes to express his gratitude to Miss Fiona Chung Hang Cheung for her great encouragement and valuable advice during the preparation of this paper. The FIONA Process is thereby named for her. Thanks are due to Mr. Warren Chi Wai Lo for his excellent proofreading.