Muskegon wastewater land treatment system: fate and transport of phosphorus in soils and life expectancy of the system.

摘要

The build-up of phosphorus (P) in soil is a major factor limiting the operating life of a waste water land treatment system. In this study, the effects of long-term waste water application on changes in chemical properties, P profiles, and P adsorption capacity were evaluated in soils of the Muskegon waste water land treatment plant, in Michigan, USA, that has been treating waste water 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 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 waste water..