Production and nutrient removal by periphyton grown under different loading rates of anaerobically digested flushed dairy manure

Growing algae to scrub nutrients from manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. The objective of this study was to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in the previous experiments. Algal turfs, with periphyton mainly composed of green algal species, were grown under two light regimes (270 and 390 mumol photons.m(-2). s(-1)) and anaerobically digested flushed dairy manure wastewater (ADFDMW) loading rates ranging from 0.8 to 3.7 g total N and 0.12 to 0.58 g total P.m(-2).d(-1). Filamentous cyanobacteria (Oscillatoria spp.) and diatoms (Navicula, Nitzschia, and Cyclotella sp.) partially replaced the filamentous green algae at relatively high ADFDMW loading rates and more prominently under low incident light. Mean algal production increased with loading rate and irradiance from 7.6+/-2.71 to 19.1+/-2.73 g dry weight. m(-2).d(-1). The N and P content of algal biomass generally increased with loading rate and ranged from 2.9%-7.3% and 0.5%-1.3% (by weight), respectively. Carbon content remained relatively constant at all loading rates (42%-47%). The maximum removal rates of N and P per unit algal biomass were 70 and 13 mg.g(-1) dry weight.m(-2).d(-1), respectively. Recovery of nutrients in harvested algal biomass accounted for about 31%-52% for N and 30%-59% for P. Recovery of P appeared to be uncoupled with N at higher loading rates, suggesting that algal potential for accumulation of P may have already been saturated. It appears that higher irradiance level enhancing algal growth was the overriding factor in controlling nitrification in the algal turf scrubber units.