Importance of nutrient availability for soluble microbial products formation during a famine period of activated sludge: Evidence from multiple analyses

Much remains unknown about compositional variations in soluble microbial products(SMP)with the shift of the substrate condition from a feast to a famine phase in biological treatment systems.This study demonstrated that the formation of SMP could be suppressed by up to 75%during the famine phase with the addition of essential nutrients.In contrast,presence of electron acceptor did not play any significant role during the stress condition,showing the similar amounts of SMP(r=0.98,p0.05)formation bet.Aween the bioreactors supplied with air and N2.The SMP formed in the famine phase was more biorefractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition(R~20.95).The fluorescence excitation-emission matrix coupled with parallel factor analysis(EEM-PARAFAC)revealed the presence of four different fluorescent components,including two protein-like(C1 and C4),fulvic-like(C2),and humic-like(C3)components,in the SMP and bEPS formed at different conditions.Both C1 and C4 showed increasing trends(R~20.95)with the length of starvation in the bioreactors without essential nutrients.Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers.This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules(particularly proteins),which typically exert many environmental concerns to effluent organic matter quality.