Muskegon Wastewater Land Treatment System: Fate and Transport of Phosphorus in Soils and Life Expectancy of the System

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 (P max ) (based on 1-day isotherm tests) has been increased by ∼ 2-4 times since 1973; the actual P max of the Muskegon soils could be much higher than the 1-day P max . Therefore, the life expectancy of the Muskegon system has been extended significantly with the application of wastewater.

Phosphorus Sorption Capacity of Six Iowa Soils before and after Five Years of Use as Vegetative Treatment Areas

“…Although these results were unexpected, they aren't unprecedented. Similar increases in phosphorus sorption life were seen for the Muskegon wastewater treatment system (Hu et al, 2006).…”

Phosphorus Fate and Transport in Soil Columns Loaded Intermittently with Influent of High Phosphorus Concentrations

“…When the Muskegon plant was designed, the life expectancy of the system was estimated to be approximately 25 to 50 years ( Ellis et al, 1979 ). After approximately 30 years of operation, a large amount of calcium has been retained by the soil, resulting in an increase in the soil's phosphorus maximum adsorption capacity (P max ) and an extension of the life expectancy of the Muskegon's land by 2 to 4 times ( Hu et al, 2006 , 2005 ). However, these aforementioned estimates were based on the P max obtained from 1‐day batch isotherm tests, which may not mimic field conditions (e.g., the 1‐day P max does not provide phosphorus breakthrough information).…”

“…In neutral or calcareous soils, phosphorus would be adsorbed to surfaces of calcium carbonate (CaCO 3 ) and clay minerals and/or precipitate as secondary calcium phosphate minerals ( Sato et al, 2005 ). The reaction of inorganic phosphorus in soil is characterized by a fast reversible process ( Freeman and Rowell, 1981 ; Hu et al, 2006 ; Overman and Scholtz, 1999 ) and a slow, almost irreversible process that is mostly viewed as diffusion‐ or nucleation‐controlled precipitation reaction ( Christoffersen et al, 1989 ; Freeman and Rowell, 1981 ; Schoumans and Groenendijk, 2000 ). The adsorbed phosphorus might be in an amorphous form of calcium phosphate and would be slowly transformed into crystalline calcium phosphate ( Christoffersen et al, 1989 ; Freeman and Rowell, 1981 ), but the slow process can also cause a hysteresis effect of phosphorus sorption and desorption ( Barrow, 1983 ; Schoumans and Groenendijk, 2000 ).…”

“…A 1‐day batch test, at most, can simulate the process of phosphorus fast adsorption, as no slow transformation processes can occur within 1 day, but it can happen in land treatment systems after long‐term operation ( Beauchemin et al, 2003 ). Long‐term batch isotherm tests (i.e., reaction time of several weeks or months) may allow the slow transformation processes to occur with the batch reactors ( Hu et al, 2006 ; Overman and Scholtz, 1999 ). However, it is unknown how long the batch test needs to run and how many batch reactors are needed, because the P max increases with time ( Hu et al, 2005 , 2006 ; Van der Zee et al, 1987 ) and changes along the soil depth ( Hu et al, 2006 ).…”

“…Long‐term batch isotherm tests (i.e., reaction time of several weeks or months) may allow the slow transformation processes to occur with the batch reactors ( Hu et al, 2006 ; Overman and Scholtz, 1999 ). However, it is unknown how long the batch test needs to run and how many batch reactors are needed, because the P max increases with time ( Hu et al, 2005 , 2006 ; Van der Zee et al, 1987 ) and changes along the soil depth ( Hu et al, 2006 ). In addition, batch tests typically are conducted under well‐mixed conditions (e.g., in a rotator) with a high water‐to‐soil ratio (i.e., 10:1 to 100:1; Pierzynski, 2000 ), which does not occur in field conditions.…”