Induced rapid release and uptake of phosphate by microorganisms

Biological and chemical phosphorus fractionalization in swine manure under aeration

In this work, the dynamic responses of different phosphorous factions in swine manure to aeration treatment were investigated and profiled to provide insight on potential ways to improve the biological phosphorus removal process. Batch reactors fabricated from clear acrylic columns were filled with fresh swine manure containing a 4.6 % solids content, which was aerated continuously for 15 days at an airflow rate of 2 L/min. The results indicate that the treatment can reduce soluble phosphorus (P) by about 78 % after only one-day aeration due largely to chemical precipitations. At the end of the experiment, the average soluble inorganic P level was reduced by 12 % (from 91 down to 79 %), while the average soluble organic P was increased by 13 % (from 9 to 22 %). The biomass P (DNA/RNA/poly-P) was increased by 24 % in the first three days, but only by 14 % in the rest 12 days of aeration. Also increased by aeration was the lipid P (47 %) but not the protein P. The data reveal that the current aeration rate cannot maintain a stable oxygen level [represented by the oxidation-reduction potential (ORP)] in the treated manure, evidenced by the decrease in ORP from 250 mV at the beginning to almost zero at the conclusion of the experiment, which is considered the major factor hindering the growth of aerobes, including the phosphorus-accumulating organisms (PAOs). Therefore, it may be concluded that continuous aeration of swine manure at a constant rate will not guarantee the supply of sufficient oxygen to the growth of PAOs. On another front, it was observed that too much aeration might negatively impact the overall P removal by increasing the release of soluble organic P from dead cells.

Evidence for tin inhibition of enhanced biological phosphorus removal at a municipal wastewater treatment plant

Concentrations of 34 metals were determined in the concentrated waste activated sludge from a dissolved air flotation unit at an advanced municipal wastewater treatment plant (WWTP) with biological nutrient removal. Reduction in enhanced biological phosphorus removal (EBPR) efficiency was observed at total tin concentrations greater than 4 microg L(-1) in the solids fraction of the mixed liquor suspended solids. No influence on carbon or nitrogen removal efficiency was found by elevated tin concentrations. Other process control variables and metal concentrations were not correlated with reduced EBPR efficiency on dates with elevated tin levels. The known high contributions of organotin species toward total tin in activated sludges from other municipal WWTPs, and the high toxicity of these compounds, suggests elevated organotin levels may be responsible for the observed reduction in EBPR efficiency.

Seasonal variations in phosphorus species in the surface sediments of the Gulf of Riga, Baltic Sea

The redox-dependent variations in concentrations of phosphorus at two different accumulation bottom areas were investigated in the Gulf of Riga (Baltic Sea) between December 1993 and January 1995. The sediment samples from nine sampling occasions were analyzed for phosphorus forms and redox potential. The average concentrations of total phosphorus measured in 0-1 cm (65 and 89 micromol P g(-1) for sites G5 and T3, respectively) were among the highest reported from the entire Baltic Sea. Redox-dependent "mobile" phosphorus (MP) contributed more than 50% of total in the uppermost-oxidized centimeter, whereas in reduced layers it was 16-18% throughout the year. The significant differences (ANOVA, P<0.01) among months of inorganic phosphorus (IP) concentration at 0-1 cm were observed at site G5 due to temporary accumulation of mobile phosphorus mediated by redox-dependent bacteria activity during summer. On the contrary no accumulation was observed at T3 probably as a result of low redox potential caused by high accumulation rates and low bioturbation. Although the water column above sediments remained oxic throughout the investigation period, the redox potential at site T3 was close to the redoxcline (i.e., +230 mV) during summer. Further increase of eutrophication might lead to development of anoxic conditions at sediment-water interface and that in turn will result in rapid release of redox-dependent phosphorus stored in surface sediments. The availability of excess phosphorus will further enhance eutrophication in partly phosphorus-limited Gulf of Riga.

Effect of a hydrolytic/acidogenic pre-stage on the organic matter content of wastewater treated in a sequencing batch reactor for biological phosphorous removal

An increase of 52.7% in acetate concentration was observed when urban wastewater was used to feed a pilot-scale upflow-type, fixed-bed fermentor under a hydraulic retention time of 0.78 h. The fermentor influent and effluent were successively used to feed a laboratory-scale sequencing batch reactor (SBR) using similar operational variables of wastewater volume, sludge purging volume and retention times during the anaerobic and aerobic phase, giving a nominal 4 h hydraulic retention time. The fermentor effluent contained an organic substrate, with a volatile fatty acid content higher than 50mg L(-1), which was appropriate for the growth of the type of microorganisms characteristically found in biological phosphorous removal (BPR) systems, and showed the behaviour of an easily and rapidly biodegradable wastewater. The specific rate of phosphorous release at the anaerobic stage was found to be higher than 0.04mg Pr g VSS(-1) min(-1), when the fermentor effluent is used as feed of the SBR, which demonstrated its favourable conditions for an efficient processing in this type of systems.

Characterization of the bacterial population structure in an anaerobic-aerobic activated sludge system on the basis of respiratory quinone profiles

Bacterial respiratory quinones were used as biomarkers for studying the bacterial population structure, especially the content of Acinetobacter species, in a laboratory-scale anaerobic-aerobic activated sludge system and in the standard aerobic system. All tested sludges contained both ubiquinone and menaquinone, with a molar ratio of about 1:0.5. High-performance liquid chromatography showed that ubiquinone with eight isoprene units (Q-8) was present as the predominant ubiquinone, Q-10 was the second most common type, and Q-9 and other homologs were minor components in the anaerobic-aerobic sludge and the standard aerobic sludge. Bacteriological examination indicated that, in both sludge systems, Q-8-containing bacteria constituted a large proportion of the aerobic heterotrophic bacterial flora, but only a few strains with Q-9 were found. These findings demonstrate that the population of Acinetobacter species, which contain Q-9 as the major quinone, is negligible in those environments. The present results suggest that the introduction of anaerobic conditions into the aerobic batch process has little influence on the bacterial community structure.

Microbiological basis of phosphate removal in the activated sludge process for the treatment of wastewater

Several strains resembling members of theAcinetobacter-Moraxella-Mima group of bacteria were isolated from activated sludge-type sewage treatment plants designed for phosphate removal. The bacteria are obligate aerobes but utilize as carbon and energy sources low-molecular intermediates generated anaerobically, particularly acetate and ethanol. These bacteria can be shown to be responsible for the phosphate luxury uptake occurring in these treatment plants. The bacteria are physiologically unusual in that they perform luxury uptake of phosphates in a complete growth medium. Phosphate release occurs on addition of a carbon source to the carbon-starved bacteria, lowering pH or both. The bacteria persist in the system by virtue of their ability to form floc.