Civil Engineering

 

Date of this Version

2006

Comments

Published in Engineering in Life Sciences

Abstract

The build-up of phosphorus (P) in soil is a major factor limiting the operating life of a wastewater land treatment system. In this study, effects of long-term wastewater application on changes in chemical properties, P profiles, and P adsorption capacity were evaluated in soils of the Muskegon wastewater land treatment plant that has been treating wastewater for > 30 years. Results indicate that the major soil properties have been changed. In the 15 cm topsoil, the pH increased from &#;&#;5–6 in 1973 to &#;&#;7.4–7.8 in 2003; the soil’s total organic carbon (TOC) increased by 10–71 %; and the level of exchangeable Ca in 2003 is 8–9 times higher than that in 1973. The amount of Ca/Mg absorbed in the soil affects the P adsorption capability of the soil; Ca- and Mg-bound P accounts for > 70% of the total P adsorbed in the soil. The net P accumulated in the Rubicon soil increased from &#;&#;700 in 1993 to &#;&#;1345 kg/ha soil in 2001, but the plant available P varied between &#;&#;100–500 kg/ha soil during the same period, indicating a large amount of the applied P has become the fixed P that is unavailable to plants. P sorption in the soil consists of a fast adsorption and a slow transformation process. The soil’s maximum P sorption capacity (Pmax) (based on 1-day isotherm tests) has been increased by &#;&#;2–4 times since 1973; the actual Pmax of the Muskegon soils could be much higher than the 1-day Pmax. Therefore, the life expectancy of the Muskegon system has been extended significantly with the application of wastewater.

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