Characterization of dissolved organic carbon leached from a woodchip bioreactor

Abstract

Woodchip bioreactors are increasingly being applied to remove nitrate from agricultural subsurface drainage. However, dissolved organic carbon (DOC) released from woodchips may negatively affect the aquatic ecosystems and drinking water supplies. The objective of this study was to evaluate the leaching characteristics, disinfection byproduct (DBP) formation potentials, and treatability of DOC derived from a laboratory woodchip bioreactor. Initial flush of woodchips resulted in the release of high organic content from woodchips. The DOC concentration in the bioreactor effluent decreased rapidly from 71.8 to 20.7 mg/L during the first week of operation, and then gradually decreased to 3.0 mg/L after 240 days of operation under a hydraulic retention time of 24 h. A recycled steel chip filter removed an average of 44.2% of the DOC in the bioreactor effluent. Hydrophobic carbons and organic compounds with molecular weight of 10–100 KDa were the most abundant organic fractions in the DOC released from woodchips. These two DOC fractions were also the most important precursors to the formation of total organic halogen (TOX) during chlorination and chloramination. The TOX yields of woodchip DOC were similar to those of Suwannee River Fulvic Acid, suggesting that organic compounds released from woodchips have great potentials for DBP formation. Alum and polyaluminium chloride were more effective at removing woodchip DOC than ferric chloride during coagulation. Drinking water treatment plants may need to adjust coagulant types and doses in order to remove woodchip DOC in the source water to reduce the DBP formation potential.