Alkalinity, and Not the Oxidation State of the Organic Substrate, Is the Key Factor in Domestic Wastewater Treatment by Mixed Cultures of Purple Phototrophic Bacteria

Abstract

Domestic wastewater treatment by purple phototrophic bacteria (PPB) is based on the assimilative uptake of organics and nutrients into the bacterial biomass. Thereby, it strongly depends on the carbon/nutrients ratio of the wastewater. The physiological COD/N/P ratio for PPB growth in domestic wastewater makes the addition of an external organic carbon source necessary in order to allow for an efficient process. However, PPB need a source of alkalinity (as CO2) to grow on reduced organics that serves as an electron acceptor since biohydrogen production (an alternative electron sink) is inhibited by ammonium. A preliminary experiment showed that high nutrients-loading wastewater was limited by CO2 imbalance, leading to poor removal efficiencies. Subsequently, the effect of the oxidation state of the organics added as external organic carbon sources to PPB reactors treating low nutrients-loading domestic wastewater has been analyzed. Three organics were used as additives to PPB development in four consecutive batches: acetate (more oxidized), ethanol and butyrate (more reduced). The PPB population was settled and the general performance under the three situations, in terms of organics, N and P assimilation, and growth kinetics was not significantly different irrespective of the external organic carbon source. The reactors were dominated by PPB, though reduced organics allowed for dominance of Rhodopseudomonas palustris, whereas oxidized organics caused co-dominance of R. palustris and Rhodobacter capsulatus. Thereby, alkalinity (as bicarbonate), and not the oxidation state of the organics, is the key parameter for the efficient treatment of domestic wastewater by PPB.

Achieving Discharge Limits in Single-Stage Domestic Wastewater Treatment by Combining Urban Waste Sources and Phototrophic Mixed Cultures

“…In contrast, the 100:7 ratio test started with the lowest SCOD (1010 ± 60 mgSCOD/L), and therefore, it achieved the lowest concentration by the end of the experiment (180 mgCOD/L). It is well-known that the assimilation of SCOD is directly related to the concentration of nutrients in the medium [ 40 ]. Thus, the N and P limitation at low COD/N ratios avoided reaching the 125 mgCOD/L COD discharge limits.…”

Direct Method to Design Solar Photovoltaics to Reduce Energy Consumption of Aeration Tanks in Wastewater Treatment Plants

“…In the oxidation tanks, to activate the reactions of biological substances, the presence of dissolved oxygens (DOs) is necessary; thus, its continuous creation to equilibrate the consumption of the carbon-oxidant bacteria respiration is also necessary [2,9,27]. DO is a parameter that allows the control of the biological process in relation to the energy reduction [6,28]; also, the biological oxidation processes are correlated to the temperature, T.…”

“…For this, the key design parameters are the air and wastewater temperatures and their correlations. Some parameters that consider the bacteria respiration have also been accounted for in accordance with innovative projects [2,3].…”