It is well known that anaerobic bacteria are sensitive to ammonia. As the ammonia concentration increases, so the performance of the bacteria decreases. There are a number of locations in an anaerobic digestion (AD) process where ammonia may be removed. The first location is from the influent, prior to, or after hydrolysis. The second is as a side-stream recirculation line, from within the digester itself. The third is from the effluent line. This latter possibility will not impact digester performance but may be necessary to meet discharge consent requirements. A four option is within the reactor itself, using biogas as the carrier medium.
This paper concerns thermal ammonia stripping, a technology developed for use in Hong Kong where there exists an essential requirement for high-concentration, high-rate, reliable ammonia removal. The lack of space for extensive biological lagoons and the availability of waste-heat, provided the conditions necessary for this technology to be developed and applied.
In the United Kingdom, ammonia removal around anaerobic digestion (AD) facilities is becoming more of an issue as biological processing to produce biogas has become an increasingly significant route for disposal of, and energy recovery from, organic waste streams. Contractual experience has been gained with protein-rich AD centrate. Laboratory work has been carried out on sewage sludge digesters. This paper looks at the role of ammonia in the performance of AD plant, explains the background to the technology, and explores potential applications.