Biotransformation of Nitrogen in Landfills
Kurian Joseph, Suneethi Sundar, S. Sri Shalini | 11 August 2016
A new and promising trend in solid waste management is to operate landfills as bioreactors in which moisture addition (often leachate recirculation) is used to create a solid waste environment capable of actively degrading the readily biodegradable organic fraction of the waste and produce bioenergy. Although the organic strength of leachate is significantly reduced in bioreactor landfills, ammonia-nitrogen (NH4 +-N) remains an issue, because there is no degradation pathway for ammonia-nitrogen in anaerobic systems. Ammonia-nitrogen removal methods often include complex sequences of physical, chemical, and/or biological processes, including chemical precipitation, nanofiltration, air stripping, and biological nitrification/denitrification via various reactor configurations. This chapter will present the facts about the ammonia nitrogen profile and nitrogen transformation pathways in bioreactor landfills including promising novel removal mechanisms (SHARON (Single reactor system for high activity ammonia removal over nitrite), ANAMMOX (Anaerobic Ammonium Oxidation), CANON (Complete Autotrophic Nitrogen removal Over Nitrite), OLAND (Oxygen Limited Autotrophic Nitrification and Denitrification) etc.) with the support of laboratory-scale and field-scale case studies. In a study on ex situ strategy for NH4 +-N removal by ANAMMOX applied using AnMBR (Anaerobic Membrane Bioreactors), NH4 +-N removal efficacy of 85.13 ± 9.67 per cent was achieved with an average nitrogen removal rate (NRR) of 5.54 ± 0.63 kg NH4 +-N/m3/day (d) at a nitrogen loading rate (NLR) of 6.51 ± 0.20 kg NH4 +-N/m3/d at a 1.5 d HRT. An in situ strategy for NH4 +-N removal by SHARON in a bioreactor landfill gave 85 per cent NH4 +-N removal efficacy with 98.5 per cent nitrite accumulation, while the ANAMMOX process gave 73 per cent of NH4 +-N removal efficacy with a specific ANAMMOX activity of 0.96 mg NH4 +-N/mg MLVSS (Volatile Suspended Solids)/d with an NLR of 1.2 kg N/d. Bioreactor landfills integrated with a combined SHARON-ANAMMOX processes provides promising results for nitrogen management (Total nitrogen removal—84 per cent and ammonia-nitrogen removal efficacy—71 per cent at NLR of 1.2 kg N/m3/d in 147 days). Further activities need to focus on full-scale demonstration of in situ ammonia-nitrogen removal in bioreactor landfills and assessing the effect of different environmental conditions affecting important operational parameters of the processes.