The removal of nitrogen compounds from farming wastewater - The effect of different carbon substrates and different microbial activators

•Biological optimisation of nitrogen removal from leachate of manure is proposed.•Five different variants of carbon source for microbial activity are studied.•The fastest nitrate removal is observed after applying the coal/straw mix.•Genus Pseudomonas dominates among denitrifiers isolated from two working barriers.•Microbiota from working barriers stimulate both denitrification and nitrification.

The present study describes an extensive investigation on the optimal carbon source and the role of microbial activators to reduce nitrogen compounds within a leachate of manure landfill. In the first stage, the genetic and biochemical properties of culturable denitrifying bacteria isolated from working denitrifying barriers was done. Then, twelve strains of predominating Pseudomonas genus were selected for a preparation of the first variant of microbial activator. Furthermore, the second variant of activator, comprised a complete microbiota obtained from deposits of two working denitrifying barriers was proposed. Experimental, field bioreactors were filled with various carbon substrates: brown coal, pine sawdust, flax harl, barley straw or coal/straw mix together with the microbial activators. They were supplied with wastewater chemically imitating liquid manure. The fastest and most effective nitrate removal was observed after applying the coal/straw mix (reduction from 488.18 NO3− mg/l to 0.08 NO3− mg/l). Adding the microbiota from the deposits resulted in the most efficient removal of ammonium ions (reduction from 259.49 NH4+ mg/l to 38.05 NH4+ mg/l). Hence, the use of coal/straw mix as a substrate in bioreactors appears to maintain microbial activity at a high level and sustain it for a longer time than other carbon substrates studied. Inoculating the bioreactor deposit with an additional pool of microorganisms taken from another active nitrogen barrier may increase the efficiency of the deposit and stimulates both denitrification and nitrification process. The proposed application of the selected mix of carbon substrate and the microbiological inoculation of the deposit would be a good solution to increase an effective work of barriers removing nitrogen compounds from farming areas, and would improve the quality of groundwater discharged from agriculture.