Predictions of Diurnal Fluctuations in an Algal Bacterial Clay Wastewater Treatment System

Abstract

Carberry's proposed algal bacterial clay treatment (ABCT) process would generate an algal biomass, useful as a food source. This study examined the diurnal fluctuations resulting from alternating light-dark periods and the magnitude of resulting O2, CO2, and pH oscillations. The magnitude of these oscillations was studied under controlled conditions, in order to determine acceptable limits of these fluctuations. The effects of progressive drifts for these parameter values under uncontrolled conditions was also studied in order to determine the rate of decreasing wastewater bacterial biodegradation efficiency and rate of deterioration of algal biomass viability. Experiments were conducted in which algae, bacteria, and substrate were combined at various concentrations in a biostat. Dissolved gas concentrations and pH were continuously recorded; biomass and substrate concentrations were determined over time by periodic sampling. A 12-hour light/dark cycle simulated the natural diurnal light variation. Based on results from these runs, two computer programs were developed to predict the changes in these parameters over a 24-hour period. One model, incorporating redox potential, appeared to be more sensitive to changes in the aqueous environment than the model based on COD. pH values of less that 5 were found to cause system failure due to a continuing decrease in algal concentration. No critical levels were found for either O2 or CO2 although the duration of time spent at a dissolved oxygen concentration of zero depended on initial algal concentration.