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Phosphorus Renovation of Wastewater by Overland Flow Land Application¹

ABSTRACT

An operating overland flow wastewater system was studied. Three treatments were imposed on the Reed canarygrass (Phalaris arundinacea L.) cover: cut four times per year and harvest residue (treatment 1); cut four times per year and leave residue (treatment 2); and cut one time per year and leave residue (treatment 3). Effluent was sampled at 6, 12, 18, and 37 m from the point of application as well as from final collection weirs and spray nozzles. Samples were collected at the beginning and the end of four continuous application periods, which were followed by rest periods of 4 to 6 weeks. Hydraulic loadings were 14 to 20 cm week^–1 (0.035 m³ m^–1 h^–1) of effluent containing 1.6 mg P L^–1. The removal rates for total P for three periods ranged from 62 to 72%, but there was no net total P removal during the first period (July). The removal rate for dissolved P was significantly greater at the end than at the beginning of the application period in three out of four cases. Following the season's final cutting in the fall, treatment 1 was significantly more efficient than treatment 3 for the removal of mass ortho-P. Plant uptake accounted for 45% of the total P annually removed by the system. It was suggested that more intensive cutting and harvesting might further improve P removal rates. On several occasions, dissolved P concentration was greater on the 6-m flow distance than in the influent as applied. The dispersed condition of the surface soil/thatch apparently affected P removal processes. In general, the extended periods of continuous application did not appear to reduce the system's capacity for P removal and offered some management flexibility.

Key Words: Runoff • Phosphorus removal • Cover crops • Application scheduling

¹ Contribution of the Agronomy Dep. and the Water Resources Research Center, Univ. of Maryland, College Park, MD 20742. Financed in part by the U.S. Dep. of the Interior, Office of Water Policy, as authorized by the Water Research and Development Act of 1978 (P.L. 95-467).

² Graduate research assistant and associate professor, respectively, Dep. of Agronomy, Univ. of Maryland, College Park, MD 20742. Present address of first author: Office of Environmental Programs, Maryland State Health Dep., Baltimore, MD 21201.

Received for publication November 20, 1986.