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Nitrogen, Phosphorus, and Bacteria Removal in Laboratory-Scale Woodchip Bioreactors Amended with Drinking Water Treatment Residuals.

Zoski, E.D., Lapen, D.R., Gottschall, N., Murrell, R.S., and Schuba, B. (2013). "Nitrogen, Phosphorus, and Bacteria Removal in Laboratory-Scale Woodchip Bioreactors Amended with Drinking Water Treatment Residuals.", Transactions of the ASABE, 56(4), pp. 1339-1347. doi : 10.13031/trans.56.9836  Access to full text


A laboratory-scale bioreactor study was conducted to investigate the saturated hydraulic conductivity (Ksat) and removal efficiencies of N, P, and fecal indicator bacteria in bioreactors containing various mixtures of wood shavings and a P-immobilizing chemical containing reactive Al and Fe oxides (water treatment residual). The three laboratory-scale bioreactors used in this study consisted of an acrylonitrile butadiene styrene (ABS) pipe (0.15 m inner diameter and 3.25 m length) filled with wood shavings (reactor A), half water treatment residual (WTR) and half wood shavings (reactor B), and a homogenized mixture of wood shavings and WTR (60% wood shavings to 40% WTR by weight) (reactor C). Pumps at the inlet and a ball valve at the outlet were used to control flow rates and pressures in the reactors. Water amended with N, P, and E. coli concentrations of 58 mg L-1, 14 mg L-1, and 20,000 counts 100 mL-1, respectively, was passed through the bioreactors at flow rates of 1, 2, and 4 mL s-1. For reactor A, turbulent flow predominated. Reactor B had an average Ksat of 0.01 0. 004 cm s-1, and reactor C had an average Ksat of 0.04 0.033 cm s-1. Reactor A had the highest removal efficiency of NO3-N at all three flow rates, followed by reactor C and then reactor B. The same trend was seen for NH3-N and total N. Total nitrogen removal efficiencies decreased with increasing flow rates. Total Kjeldahl nitrogen increased in all three reactors at the lowest flow rate and also increased in reactor A for the two higher flow rates. Removal efficiencies were 81% and 27% for reactor B and 32% and 43% for reactor C for flow rates of 2 and 4 mL s-1, respectively. Total phosphorus and dissolved reactive phosphorus (DRP) were completely removed (>99% removal efficiency) in the two reactors containing WTR. The removal efficiency of total P and DRP for the bioreactor with wood shavings was <11% at each flow rate. Total coliforms increased in each reactor, while E. coli saw removal efficiencies >66% for all three reactors at all flow rates. Based on these observations, bioreactors containing wood shavings amended with WTR may be successful at removing significant quantities of P while reducing N and E. coli concentrations from tile drainage effluent. Recommendations for field implementation are based on water quality characteristics, land management, and hydrologic conditions of the site. If N is the main water quality issue, then bioreactors with wood shavings would be recommended. If N and P are both concerns, then bioreactors with a mixture of WTR and wood shavings would be recommended, with special considerations given for flow-through properties (i.e., retention times) and life span of the capacity for the WTR to treat P.

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