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Under anoxic conditions, zerovalent iron (Fe0) reduces nitrate to ammonium and magnetite (Fe3O4) is produced at near‐neutral pH. Nitrate removal was most rapid at low pH (2–4); however, the formation of a black oxide film at pH 5 to 8 temporarily halted or slowed the reaction unless the system was augmented with Fe2+, Cu2+, or Al3+ Bathing the corroding Fe0 in a Fe2+ solution greatly enhanced nitrate reduction at near‐neutral pH and coincided with the formation of a black precipitate. X‐ray diffractometry and scanning electron microscopy confirmed that both the black precipitate and black oxide coating on the iron surface were magnetite. In this system, ferrous iron was determined to be a partial contributor to nitrate removal, but nitrate reduction was not observed in the absence of Fe0 Nitrate removal was also enhanced by augmenting the Fe0–H2O system with Fe3+, Cu2+, or Al3+ but not Ca2+, Mg2+, or Zn2+ Our research indicates that a magnetite coating is not a hindrance to nitrate reduction by Fe0, provided sufficient aqueous Fe2+ is present in the system.

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The buildup of phosphorus (P) in the soil is a major factor limiting the operating life of a wastewater land treatment system. In this study, we evaluated changes of chemical properties, P profiles, and adsorption isotherms in the soils of a Muskegon wastewater land treatment system, which has received wastewater for ∼30 years. It was found that the pH in the 15-cm topsoil increased from ∼5−6 in 1973 to ∼7.4−7.8 in 2003; a large amount of salt (e.g., Ca, Mg) in wastewater was adsorbed by the soil; the soil Al content (either exchangeable or oxalate extractable) decreased, while the oxalate-extractable Fe content remained at the same level. Ca-bound P accounted for ≥70% of the total P adsorbed in the soil. The soil P adsorption capacity increased and was positively correlated with the concentration of exchangeable Ca in the soil. A higher concentration of exchangeable Ca was found in the 15-cm topsoil, where a higher total organic carbon was present. More P was accumulated in the upper soil than in the deeper soil. The adsorption of Ca in wastewater by the soil may extend the life expectancy of the Muskegon land treatment system.