Phosphorus Removal from Natural Waters Using Controlled Algal Production

Abstract

A series of experiments designed to demonstrate the potential of using managed, attached algal production to permanently remove excess phosphorus from agricultural run‐off is described. The experiments were carried out on a secondary canal in the New Hope South region of the Florida Everglades Agricultural Area from October, 1991, to May, 1992. Natural algal populations of periphyton, including species of the genera Cladophora, Spirogyra, Enteromorpha, Stigeoclonium, and a variety of filamentous diatoms such as Eunotia and Melosira, were grown on plastic screens in raceways, under a wave surge regime. Considerable biomass production of algae occurred, and the resulting algal canopy also trapped plankton and organic particulates from the water column. A seven‐ to eight‐day harvest interval was determined to be optimal, and both hand harvesting and vacuum harvesting were employed. The vacuum device is applicable to large scale‐up. In source water having total phosphorus concentrations of 0.012–0.148 ppm, mean macro‐recovery dry biomass production levels of 15–27 g/m2/day were achieved. The lower rates occurred in the winter, the higher rates in the late spring. Two techniques were employed to reduce losses of fine material at harvest during the March to May period. Gravity sieving increased mean dry production levels to 33–39 g/m2/day. The mean phosphorus content of harvested biomass ranged from 0.34% to 0.43%. Total phosphorus removal rates during the spring period of average solar intensity and low nutrient supply, by methods demonstrated in this study, ranged from 104 to 139 mgTP/m2/day (380–507 kgP/ha/year). Over the incoming nutrient range studied, phosphorus removal was independent of concentration and was 16.3% of total phosphorus for 15 m of raceway. Up‐stream‐downstream studies of overflowing water chemistry (total P, total dissolved ‐P, orthophosphate ‐P) showed highly ‐significant reductions of all phosphorus species. Total phosphorus reduction closely correlated with phosphorus yield from biomass removal. Yearly, minimum phosphorus removal rates are predicted that are 100–250 times that achieved both experimentally and in long‐term, large‐area wetland systems. Engineering scale‐up to systems of hundreds of acres is being studied.

Ecological Water Treatment System for Removal of Phosphorus and Nitrogen from Polluted Water

“…Using hand and vacuum harvesting of the periphyton, they achieved P removal rates ranging from 104 to 139 mg TP·m Ϫ2 ·d Ϫ1 . Nutrient removal rates were lower in our study compared to removal rates found by Adey et al (1993). In Experiment 1 the presence of the fish resulted in an increase in movement of P and N from the water to the sediment sink, and significant masses of P were also incorporated into their tissue as the fish grew.…”

“…Vymazal (1988) found that a trough system containing screens with periphyton removed both P and N. Adey et al (1993) examined nutrient removal from agricultural runoff by natural algal populations in raceways. Using hand and vacuum harvesting of the periphyton, they achieved P removal rates ranging from 104 to 139 mg TP·m Ϫ2 ·d Ϫ1 .…”

“…Such separation has been accomplished by mechanically harvesting periphyton using rotating discs (Hemens and Stander 1970), hand tools, and vacuuming (Adey et al 1993). Although periphyton is consumed by many types of organisms including fish and invertebrates, few studies have addressed whether algal-consuming organisms can be used to enhance nutrient removal using a periphyton-based system.…”

“…Conventional tertiary treatment using chemical precipitation is effective at P removal, but this process is costly and generates extra sludge for disposal. Manuscript received 22 September 1995;revised 14 April 1996;accepted 20 May 1996. Treatment systems utilizing controlled periphyton production have been suggested as an alternative to conventional nutrient removal methods (Sladeckova et al 1983, Vymazal 1988, Davis et al 1990, Adey et al 1993, Sladeckova 1994. Periphyton has the potential to uptake both P and N from nutrient-enriched water at very high rates (up to 160 mg P·m Ϫ2 ·d Ϫ1 and 1900 mg N·m Ϫ2 ·d Ϫ1 ) (Davis et al 1990).…”

Recovery of dairy manure nutrients by benthic freshwater algae

“…Small-scale algal growth chambers are used in aquaria, in a variety of mesocosms, and for the commercial production of coral reef organisms (Adey and Loveland, 1998). Large-scale ATS units are in commercial use for treating wastewater generated by tilapia aquaculture operations (Adey and Loveland, 1998), agricultural runoff (Adey et al, 1993), and for N and P removal in tertiary treatment of municipal wastewater (Craggs et al, 1996a,b).…”