A study of a thin-film algae-bacteria wastewater treatment system

A thin algae-bacteria biofilm system was developed as a potential wastewater treatment process, which would provide reasonable organic stabilization and a simple surface to assist in harvesting the microbial biomass for application on land as an organic fertilizer. The purpose of this study was to evaluate the removal of both organic and nutrient in a laboratory, thin film system using algae-bacteria symbiosis and to examine some of the fundamental biological and biochemical interactions in photosynthetic biofilms.; The laboratory reactor consisted of an inclined acrylic plastic plate, 4 in. wide by 67.5 in. long, on which the algae-bacteria biofilm was grown. The wastewaters were applied to the reactor at flow rates ranging from 2.5 L/d to 20 L/d. Fluorescent lights over the length of the reactor provided continuous luminescence at an intensity of 700 foot-candles at the microbial surfaces. The microbial growths were harvested in 12 to 13 equal segments on a daily basis to maintain a reasonable thickness of biofilm for suitable wastewater treatment. Four pure organic compounds: sodium butyrate, monosodium. glutamate, glucose and sodium benzoate, were examined as sole carbon sources to permit evaluation of their different characteristics with respect to metabolic pathways and cell energy/synthesis relationships. Lawrence municipal wastewaters were examined to determine the treatability characteristics of complex mixtures of organic compounds, as well as to demonstrate the efficiency of this system in processing municipal wastewaters.; The results obtained during this study showed that the overall energy/synthesis relationships observed during the metabolism of soluble, pure organic compounds tended to follow those observed in batch-fed systems rather than those observed in continuously fed, complete mixing systems. It was also noted that the algae metabolism was primarily related to the carbon dioxide released during the energy reactions for bacteria and fungi synthesis. The removal of COD ranged from a low of 53% for sodium butyrate to a high of 79% for glucose. While the COD removal rates were less than those obtained in activated sludge systems, they were close to those obtained in trickling filter systems. The overall growth of biomass varied from 0.54 mg VSS/mg COD removed for sodium butyrate to 0.86 mg VSS/mg COD removal. As more COD was oxidized, more bacteria and more algae were produced. The COD removal rates were essentially the same, 38%, for the septic, raw municipal wastewaters. The suspended solids harvested from the reactor ranged from 1.0 mg VSS/mg COD removed at the 20 L/d flow rate to 2.8 mg VSS/mg COD removed at the 5 L/d flow rate. There was greater algae growth at the lower flow rates and in the municipal wastewaters than in the pure organic compounds.; This initial study of the thin film, algae-bacteria reactor demonstrated the ability of bacteria, fungi, algae, and protozoa to produce a simple wastewater treatment system. It was shown that the thin film bioreactor was quite different from the completely mixed activated algae previously studied. Further research will be needed to determine if the thin film algae-bacteria bioreactor has practical value in treating municipal and industrial wastewaters in developing countries where simple wastewater treatment systems and nutrient recovery are essential.