Pilot-scale evaluation of the application of low pH-inducible polyphosphate accumulation to the biological removal of phosphate from wastewaters.

To investigate the possible biotechnological application of the phenomenon of low pH-inducible phosphate uptake and polyphosphate accumulation, previously reported using pure microbial cultures and under laboratory conditions, a 2000 L activated sludge pilot plant was constructed at a municipal sewage treatment works. When operated as a single-stage reactor this removed more than 60% of influent phosphate from primary settled sewage at a pH of 6.0, as opposed to approximately 30% at the typical operational pH for the works of 7.0-7.3-yet without any deleterious effect on other treatment parameters. At these pH values the phosphorus content of the sludge was, respectively, 4.2% and 2.0%. At pH 6.0 some 33.9% of sludge microbial cells were observed to contain polyphosphate inclusions; the corresponding value at pH 7.0 was 18.7%. Such a process may serve as a prototype for the development of alternative biological and chemical options for phosphate removal from wastewaters.

Stimulation of phosphate uptake and polyphosphate accumulation by activated sludge microorganisms in response to sulfite addition

Enhanced phosphate removal from wastewaters is dependent on the synthesis and intracellular accumulation of polyphosphate by sludge microorganisms. However the role played by polyphosphate in microbial metabolism and the factors that trigger its formation remain poorly-understood. Many examples of the accumulation of the biopolymer by environmental microorganisms are documented; these include a recent report of the presence of large polyphosphate inclusions in sulfur-oxidizing marine bacteria. To investigate whether any link might exist outside the marine environment between the presence of reduced sulfur compounds and enhanced levels of microbial phosphate uptake and polyphosphate accumulation, activated sludge cultures were grown under laboratory conditions in media that contained sulfite, thiosulfate, hydrosulfite or tetrathionate. Only in the presence of sulfite was there any evidence of a stimulatory effect; in medium that contained 0.5 mM sodium sulfite some 17% more phosphate was removed by the sludge, whilst there was an almost two-fold increase in intracellular polyphosphate levels. No indications of sulfite toxicity were observed.

Biological phosphorus removal during high-rate, low-temperature, anaerobic digestion of wastewater.

We report, for the first time, extensive biologically-mediated phosphate removal from wastewater during high-rate anaerobic digestion (AD). A hybrid sludge bed/fixed-film (packed pumice stone) reactor was employed for low-temperature (12°C) anaerobic treatment of synthetic sewage wastewater. Successful phosphate removal from the wastewater (up to 78% of influent phosphate) was observed, mediated by biofilms in the reactor. Scanning electron microscopy and energy dispersive X-ray analysis revealed the accumulation of elemental phosphorus (~2%) within the sludge bed and fixed-film biofilms. 4’, 6-diamidino-2-phenylindole (DAPI) staining indicated phosphorus accumulation was biological in nature and mediated through the formation of intracellular inorganic polyphosphate (polyP) granules within these biofilms. DAPI staining further indicated that polyP accumulation was rarely associated with free cells. Efficient and consistent chemical oxygen demand (COD) removal was recorded, throughout the 732-day trial, at applied organic loading rates between 0.4-1.5 kg COD m-3 d-1 and hydraulic retention times of 8-24 hours, while phosphate removal efficiency ranged from 28-78% on average per phase. Analysis of protein hydrolysis kinetics and the methanogenic activity profiles of the biomass revealed the development, at 12˚C, of active hydrolytic and methanogenic populations. Temporal microbial changes were monitored using Illumina Miseq analysis of bacterial and archaeal 16S rRNA gene sequences. The dominant bacterial phyla present in the biomass at the conclusion of the trial were the Proteobacteria and Firmicutes and the dominant archaeal genus was Methanosaeta. Trichococcus and Flavobacterium populations, previously associated with low temperature protein degradation, developed in the reactor biomass. The presence of previously characterised polyphosphate accumulating organisms (PAOs) such as Rhodocyclus, Chromatiales, Actinobacter and Acinetobacter was recorded at low numbers. However, it is unknown as yet if these were responsible for the luxury polyP uptake observed in this system. The possibility of efficient phosphate removal and recovery from wastewater during AD would represent a major advance in the scope for widespread application of anaerobic wastewater treatment technologies.

Arsenic removal from soil with high iron content using a natural surfactant and phosphate

An environment friendly arsenic removal technique from contaminated soil with high iron content has been studied. A natural surfactant extracted from soapnut fruit, phosphate solution and their mixture was used separately as extractants. The mixture was most effective in desorbing arsenic, attaining above 70 % efficiency in the pH range of 4–5. Desorption kinetics followed Elovich model. Micellar solubilization by soapnut and arsenic exchange mechanism by phosphate are the probable mechanisms behind arsenic desorption. Sequential extraction reveals that the mixed soapnut–phosphate system is effective in desorbing arsenic associated with amphoteric–Fe-oxide forms. No chemical change to the wash solutions was observed by Fourier transform-infrared spectra. Soil:solution ratio, surfactant and phosphate concentrations were found to affect the arsenic desorption process. Addition of phosphate boosted the performance of soapnut solution considerably. Response surface methodology approach predicted up to 80 % desorption of arsenic from soil when treated with a mixture of ≈1.5 % soapnut, ≈100 mM phosphate at a soil:solution ratio of 1:30.

Removal of ortho-phosphate from aqueous solution by adsorption onto dolomite

An experimental study on the adsorption of phosphate onto cost effective fine dolomite powder is presented. The effect of solution pH, solution ionic strength and adsorption isotherm were examined. The adsorption of phosphate was pH dependent and phosphate adsorption favoured acidic conditions. The adsorption was significantly influenced by solution ionic strength indicating outer-sphere complexation reactions. The experimental data further indicated that the removal of phosphate increased with increase in the ionic strength of solution. The experimental data were modelled with different isotherms: Langmuir, Freundlich and Redlich–Peterson isotherms. It was found that the Redlich–Peterson isotherm depicted the equilibrium data most accurately. The overall kinetic data fitted very well the pseudo-first-order rate model.

Microbial phylogenetic and functional responses within acidified wastewater communities exhibiting enhanced phosphate uptake

Acid stimulated accumulation of insoluble phosphorus within microbial cells is highly beneficial to wastewater treatment but remains largely unexplored. Using single cell analyses and next generation sequencing, the response of active polyphosphate accumulating microbial communities under conditions of enhanced phosphorus uptake under both acidic and aerobic conditions was characterised. Phosphorus accumulation activities were highest under acidic conditions (pH 5.5 > 8.5), where a significant positive effect on bioaccumulation was observed at pH 5.5 when compared to pH 8.5. In contrast to the Betaproteobacteria and Actinobacteria dominated enhanced biological phosphorus removal process, the functionally active polyP accumulators at pH 5.5 belonged to the Gammaproteobacteria, with key accumulators identified as members of the families Aeromonadaceae and Enterobacteriaceae. This study demonstrated a significant enrichment of key polyphosphate kinase and exopolyphosphatase genes within the community metagenome after acidification, concomitant with an increase in P accumulation kinetics.