Phosphorus removal from wastewater using an algal turf scrubber

Algal turf scrubbing is a novel technology for the treatment of agricultural runoff and eutrophic lake water and may have application for wastewater treatment. The algal turf scrubber (ATS)^TM consists of a natural, mixed assemblage of attached periphyton, microalgae and bacteria which colonise an inclined floway over which wastewater flows in a series of pulses. A large-scale ATS (152.4 m long 6.5 m wide) was constructed in Patterson, California and tested in conjunction with UV disinfection over one year for its ability to treat secondary effluent from an evaporation pond. The hydraulic loading rate of the wastewater was varied between 436 and 1226 m³ per day and various operational parameters were tested. The biomass was mechanically harvested from the floway at one or two week intervals depending upon the season. This paper will present the results for phosphorus removal and productivity of the algal turf. Phosphorus removal from the secondary wastewater was measured twice a week during four, 8 week quarters corresponding to the solar seasons. The phosphorus content of the harvested solids was also measured during these periods. Based on the mean percentage of P (2.1 %) in the harvested solids and the mean productivity (35 g m⁻² d⁻¹), the yearly mean removal of phosphorus was 0.73 ± 0.28 g m⁻² d⁻¹. An inverse relationship was found between reduction in hydraulic loading rate and increase in pH, phosphorus removal and hardness reduction by the ATS. This indicated that pH mediated precipitation probably accounts for much of the phosphorus removal by the ATS and for the high mean phosphorus content of the harvested solids. Measurement of nutrient concentrations in influent and effluent of the ATS over 24 hours showed that at night phosphorus removal declined. These results indicate the potential of the ATS for phosphorus removal from wastewaters and suggest that removal may be easily controlled by altering the hydraulic loading rate.