Stabilisation of ammoniacal nitrogen from solid waste and leachate significantly improved by combining novel processes like SHARON (single reactor system for high activity ammonia removal over nitrite) and ANAMMOX (anaerobic ammonium oxidation) with advantages of lower carbon requirements, aeration and N2O emissions. This paper deals with establishing combined SHARON-ANAMMOX processes in situ pilot-scale landfill bioreactors (LFBR). Molecular analysis in LFBR with changes in nitrogen, hydrazine, hydroxylamine confirmed aerobic and anaerobic ammonium oxidising bacteria (AOB & ANAMMOX) as key players in SHARON-ANAMMOX processes. In situ SHARON-ANAMMOX process was established in LFBR with total nitrogen and ammoniacal nitrogen removal efficiency of 84% and 71%, respectively at NLR of 1.2 kgN/m(3)/d in 147 d, compared to ammoniacal nitrogen removal of 49% at NLR of 1.0 kgNH(4)-N/m(3)/d in 336 d feasible in Control LFBR. Nitrogen massbalance demonstrated in situ SHARON-ANAMMOX advantageous than control LFBR with higher nitrogen transformation to N-2 (50.8%) and lower residual nitrogen in solid waste (7.7%).