Figure 4: Parameters monitored during condition 4, involving: (a) pH values measured as a function of applied sulfide concentration: (●) influent sulfide; (■) influent pH and (□) effluent pH; (b) concentrations of nitrogen compounds: (▲) influent NH4+-N; (Δ) effluent NH4+-N; (●) effluent NO3--N; (●) effluent NO2--N; (x) calculated N2-N.