Organic matter and concentrated nitrogen removal by shortcut nitrification and denitrification from mature municipal landfill leachate

An UASB+Anoxic/Oxic(A/O)system was introduced to treat a mature landfill leachate with low carbon-to-nitrogen ratio andhigh ammonia concentration.To make the best use of the biodegradable COD in the leachate,the denitrification of Nox--N in therecirculation effuent from the clarifier was carried out in the UASB.The results showed that most biodegradable organic matters wereremoved by the denitrification in the UASB.The NH4+-N loading rate(ALR)of A/O reactor and operational temperature was 0.28-0.60 kg NH4+-N/(m3·d)and 17-29°C during experimental period,respectively.The short-cut nitrification with nitrite accumulationeffciency of 90%-99%was stabilized during the whole experiment.The NH4+-N removal effciency varied between 90%and 100%.When ALR was less than 0.45 kg NH4+-N/(m3·d),the NH4+-N removal effciency was more than 98%.With the influent NH4+-Nof 1200-1800 mg/L,the effuent NH4+-N was less than 15 mg/L.The shortcut nitrification and denitrification can save 40%carbonsource,with a highly effcient denitrification taking place in the UASB.When the ratio of the feed COD to feed NH4+-N was only 2-3,the total inorganic nitrogen(TIN)removal effciency attained 67%-80%.Besides,the sludge samples from A/O reactor were analyzedusing FISH.The FISH analysis revealed that ammonia oxidation bacteria(AOB)accounted for 4%of the total eubacterial population,whereas nitrite oxidation bacteria(NOB)accounted only for 0.2%of the total eubacterial population.