Effect of Pyrite Pretreatment, Particle Size, Dose, and Biomass Concentration on Particulate Pyrite Autotrophic Denitrification of Nitrified Domestic Wastewater

Nitrate (NO3-) loads from domestic and industrial wastewater contribute to surface and groundwater pollution and can have detrimental effects on human health and the environment. In this study, a particulate pyrite autotrophic denitrification (PPAD) process was compared with sulfur-oxidizing denitrification (SOD) in batch microcosms using a domestic wastewater seed. During a 65-day acclimation period, denitrification rates for PPAD reached 3.19mg/(Ld), but were slower than the maximum rate for SOD (approximate to 5mg/[Ld]). Lower sulfate (SO42-) production (5.66mg SO42-/mg NO3--N) and alkalinity consumption (1.70mg CaCO3/mg NO3--N) were observed with PPAD than with SOD (7.54mg SO42-/mg NO3--N and 4.57mg CaCO3/mg NO3--N). Acetone pretreatment of pyrite particles initially resulted in a transient increase in the denitrification rate; however, the rate of denitrification was similar to untreated pyrite in subsequent cycles. Box-Behnken design and response surface methodology were used to optimize biomass concentration, pyrite dose, and particle size. Denitrification rates were highest at a volatile suspended solids concentration of 1,250mg/L, a pyrite dose of 125g/L, and a particle size of 0.815-1.015mm. The PPAD process is a promising technology for the treatment of NO3--contaminated water and wastewater due to low biomass and sulfur by-product production, low alkalinity consumption and low carry-over of organic carbon to the effluent.