Thermal ammonia stripping as a means of ammoniacal nitrogen control: PAPER & POSTER
Eden, R.1, Richardson, K.1 and Thomas, T.2, 1Organics Ltd, UK, 2University of Warwick, UK
(free)
The removal of ammonia from leachate, and wastewater in general, can be accomplished by means of biological processes or physicochemical process technologies. This paper is concerned with thermal ammonia stripping, a technology developed for use in Hong Kong where the demand for highconcentration ammonia removal, combined with a lack of space and the plentiful availability of wasteheat, provided the right conditions for this technology to be applied. High-strength ammonia removal is now becoming more of an issue globally, both with landfill sites and anaerobic digesters. This paper explains the background to the technology developed in Hong Kong, explores the basis of improvements in thermal efficiency and reviews novel developments to capture and recover ammonia for re-use.
Introduction
Given its high population density, coupled with the demanding environmental standards enforced by the Environmental Protection Department, it is not surprising that Hong Kong has been the incubator for a world leading technology. The removal of ammonia from wastewater is a permanent challenge for wastewater engineers. In Hong Kong this is accomplished with low operating costs, to high standards, in a small footprint, by means of a novel thermal ammonia stripping technology.
Since 1997, the technology has been applied to both leachate from landfill sites, as well as the sidestream effluent from an anaerobic digester (AD). Whilst highly focused on the needs of Hong Kong, the technology is gaining momentum in other countries, where environmental compliance is a serious issue to address. It is also moving from leachate clean-up applications into AD.
To many engineers not involved with AD, the problems caused by ammonia may come as a surprise. It is well known that ammonia is toxic to fish and humans (sniff that floor cleaner if in doubt), so it should not be unexpected that many bacteria are similarly distressed.
Although ammonia is an important source of nutrient for bacterial growth during AD, its inhibitory effect at high concentrations can be lethally toxic to bacteria that have thrived on its presence at lower concentrations.
According to the UK’s National Non-Food Crops Centre (NFCC), there are now 486 operational AD plants in the UK, with a further 343 under development. AD is established as a commercially viable form of renewable energy generation. The AD process produces biogas, consisting of methane and carbon dioxide, as well as various traces gases. Biogas can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane. The nutrient-rich digestate produced can be used as fertiliser.
Keywords: Ammonia, ammonium salt, anhydrous ammonia, digestate, leachate, thermal air-stripping
