Efficacy of drinking-water treatment residual in controlling off-site phosphorus losses: a field study in Florida.

Land application of drinking-water treatment residuals (WTR) has been shown to control excess soil soluble P and can reduce off-site P losses to surface and ground water. To our knowledge, no field study has directly evaluated the impacts of land application of WTRs on ground water quality. We monitored the effects of three organic sources of P (poultry manure, Boca Raton biosolids, Pompano biosolids) or triple superphosphate co-applied with an aluminum-based WTR (Al-WTR) on soil and ground water P and Al concentrations under natural field conditions for 20 mo in a soil with limited P sorption capacity. The P sources were applied at two rates (based on P or nitrogen [N] requirement of bahiagrass) with or without Al-WTR amendment and replicated three times. Without WTR application, applied P sources increased surface soil soluble P concentrations regardless of the P source or application rate. Co-applying the P sources with Al-WTR prevented increases in surface soil soluble P concentrations and reduced P losses to shallow ground water. Total dissolved P and orthophosphate concentrations of shallow well ground water of the N-based treatments were greater (>0.9 and 0.3 mg L(-1), respectively) in the absence than in the presence ( approximately 0.6 and 0.2 mg L(-1), respectively) of Al-WTR. The P-based application rate did not increase ground water P concentrations relative to background concentrations. Notwithstanding, Al-WTR amendment decreased ground water P concentrations from soil receiving treatments with P-based application rates. Ground water total dissolved Al concentrations were unaffected by soil Al-WTR application. We conclude that, at least for the study period, Al-WTR can be safely used to reduce P leaching into ground water without increasing the Al concentration of ground water.

Aging effects on reactivity of an aluminum-based drinking-water treatment residual as a soil amendment.

Several studies have shown that drinking-water treatment residuals (WTR) could be used to control mobility of excess phosphorus (P) and other oxyanions in poorly sorbing soils. Presently, only "aged" WTRs (those left, or manipulated, to dewater) are land applied. However, if demand for WTRs increase in the near future, freshly-generated WTRs could be considered for land application. To our knowledge, few studies have examined the reactivity and equilibration time of freshly-generated alum-based WTR (Al-WTR). A laboratory thermal incubation study was, therefore, conducted to determine various extractable Al forms in Al-WTR as a function of WTR "age", and the time required for freshly generated Al-WTR to stabilize. Freshly-generated Al-WTR samples were collected directly from the discharge pumps of a drinking-water treatment plant, and thermally incubated at 52 degrees C, either with or without moisture control, for < or = 24 wk. Additional dewatered Al-WTR samples of various ages (2 wk- to 2 y old) were also included in the study. Various methods of extracting Al [total-, oxalate (200 and 5 mM), and Mehlich 1 extractants] were utilized to assess Al extractability over time. Freshly-generated Al-WTR samples were potentially more reactive (as reflected in greater 5 mM oxalate extractable Al concentration) than dewatered Al-WTR samples stockpiled for > or = 6 mo. Aluminum reactivity of the freshly-generated Al-WTR decreased with time. At least 6 wk of thermal incubation (corresponding to > or = 6 mo of field drying) was required to stabilize the most reactive Al form (5mM oxalate extractable Al concentration) of the Al-WTR. Although no adverse Al-WTR effects have been reported on plants and grazing animals (apparently because of low availability of free Al(3+) in Al-WTR), land application of freshly-generated Al-WTRs (at least, those with similar physicochemical characteristics as the one utilized for the study) should be avoided.

Evaluating phosphorus loss from a Florida spodosol as affected by phosphorus-source application methods.

Incorporating applied phosphorus (P) sources can reduce P runoff losses and is a recommended best management practice. However, in soils with low P retention capacities, leaching can be a major mechanism for off-site P loss, and the P-source application method (surface or incorporation) may not significantly affect the total amount of off-site P loss. We utilized simulated rainfall protocols to investigate effects of P-source characteristics and application methods on the forms and amounts of P losses from six P sources, including five biosolids materials produced and/or marketed in Florida, and one inorganic fertilizer (triple superphosphate). A typical Florida Spodosol (Immokalee fine sand; sandy, siliceous, hyperthermic Arenic Alaquods) was used for the study, to which the P sources were each applied at a rate of 224 kg P ha(-1) (approximately the P rate associated with N-based biosolids applications). The P sources were either surface-applied to the soil or incorporated into the soil to a depth of 5 cm. Amended soils were subjected to three simulated rainfall events, at 1-d intervals. Runoff and leachate were collected after each rainfall event and analyzed for P losses in the form of soluble reactive P (SRP), total dissolved P (TDP), total P (TP), and bioavailable P (BAP) (in runoff only). Cumulative masses (runoff + leachate for the three rainfall events) of P losses from all the P sources were similar, whether the amendments were surface-applied or incorporated into the soil. The solubility of the amendment, rather than application method, largely determines the P loss potential in poorly P-sorbing Florida Spodosols.