Performance of a batch-fed High Rate Algal Pond for animal waste treatment

Two 13.1 m(2) ponds at Auchincruive, Scotland, were used to treat the dilut ed liquid phase of separated piggery slurry, in order to identify the clima tic and pond operational parameters which influence biomass production and nutrient removal in these systems at a constant areal loading rate. The pon ds were operated from April to November at 0.12, 0.24 and 0.34 m depth as b atch-fed reactors. Average 5-day biochemical oxygen demand (BOD5) loading w as 6.24 g m(-2) d(-1) and the ponds were mixed at a mean surface velocity o f 0.20 m s(-1). Dry matter, chlorophyll, optical density (OD560), NO3, NO2, NH4, urea and total phosphorus were determined daily. Temperature, pH, dis solved oxygen and incident irradiance were monitored continuously. Correlat ion and multiple regression analyses were used to determine significant int eractions between environmental factors, biomass production and nutrient re moval. Both chlorophyll a and optical density were accurate predictors of d ry matter biomass, All measures of pond biomass were positively correlated with elapsed time, surface daily irradiance, daylength and pH, but negative ly correlated with pond depth. Significant correlations between pH and dail y irradiance, maximum dissolved oxygen and forms of nitrogen (nitrite or ni trate) suggested that the final pond pH represents an equilibrium between a lkalization by photosynthesis and acidification by nitrification. Total nit rogen removal was influenced by biomass, elapsed time, temperature and dail y irradiance, but not by either pH or depth. The concentration of ammonium nitrogen (NH4-N) was inversely correlated with temperature, biomass, depth, daily irradiance and daylength. Nitrification was found to occur with nitr ate concentration showing a strong negative correlation with daylength, ref lecting an increase in nitrifying activity by the pond biomass throughout t he season. Nitrate concentrations were positively correlated with elapsed t ime, but negatively correlated with biomass, temperature and daily irradian ce. Phosphorus removal was influenced by elapsed time and biomass concentra tion. Removal of biological and chemical oxygen demand (COD) at the complet ion of the batch runs was 96% and 78.6% respectively.