‘Bug hotels’ are being investigated by research engineers as a novel way to treat the noxious liquids that seep from landfill sites.
As artificial havens for nitrogen-hungry bacteria, bug hotels will be created by providing bacteria with a comfortable habitat, warmth and food. The landfill leachate can then be pumped through these ‘hotels’ where microbes remove ammonia, the main pollutant, turning it into harmless nitrogen gas.
Ammonia is very soluble in water and can be toxic to invertebrates at relatively low concentrations.
To prevent it from contaminating the environment the leachate is either diverted into a municipal sewerage system if it large enough, or it goes for on-site treatment.
The Loughborough researchers are attempting to harness specific populations of bacteria to detoxify ammonia.
Two groups of bacteria, Nitrobacter and Nitromonas, can oxidise ammonia into nitrate which can then be passed to another group of bacteria, Pseudomonas, which converts it into nitrogen.
The researchers are attempting to identify the most favourable conditions for the bacteria to thrive. Once established, the work will be scaled up using a series of four bioreactors based at a landfill site.
To immobilise bacteria a variety of surfaces within the bioreactor are being tested to see which are the ‘stickiest’.
Once the bacteria have been secured into position their environment will be made as conducive as possible for healthy growth.
The pH of the incoming effluent stream can be adjusted by subtle blending of recycled components to enhance bacterial growth. The vessel will be warmed to optimum temperature, the heat coming potentially from the burning of methane produced by the landfill.
The eventual aim is to treat the leachate in the reactor vessels sequentially – first removing anything likely to inhibit the growth of sensitive bacteria, followed by the microbial oxidation of the ammonia to nitrate. The nitrate would then be de-oxidised into nitrogen, with a ‘clean’ leachate emerging in the process.