Use of fermentation processes for improving the dissolution of phosphorus and its recovery from waste activated sludge.

Recycling phosphorus from waste activated sludge has attracted a lot of interest to tackle the problem of phosphorus stocks depletion and the increase in food demand. In this study, the use of fermentation processes was investigated to enhance phosphorus dissolution from waste activated sludge to improve its recycling. Two fermentation processes, bioacidification and dark fermentation, were used on two different sludges fermented with wheat starch syrup in continuous operating conditions. Hydrogen yield from the co-substrate fermentation with waste activated sludge reached 3.9 mmolH2.gCODcosubstrate-1 yield during dark fermentation process and was negligible during bioacidification. Dissolved phosphorus in the waste activated sludge increased by 68% during bioacidification and by 43% during dark fermentation. In both processes, phosphorus dissolution was accompanied by iron, calcium and magnesium dissolution. Results show that fermentation enhances phosphorus dissolution in waste activated sludge to improve its recovery along with hydrogen and organic acids.

Technical and economical assessment of formic acid to recycle phosphorus from pig slurry by a combined acidification-precipitation process.

Dissolution by acidification followed by a liquid/solid separation and precipitation of phosphorus from the liquid phase is one possibility to recycle phosphorus from livestock effluents. To avoid increase of effluent salinity by using mineral acids in the recycling process, the efficiency of two organic acids, formic and acetic acid, in dissolving the mineral phosphorus from piggery wastewater was compared. The amount of formic acid needed to dissolve the phosphorus was reduced three fold, compared to acetic acid. The amount of magnesium oxide needed for further precipitation was decreased by two with formic acid. Neither the carbon load nor the effluent salinity was significantly increased by using formic acid. An economical comparison was performed for the chemical recycling process (mineral fertilizer) vs. centrifugation (organic fertilizer) considering the centrifugation and the mineral fertilizers sold in the market. After optimisation of the process, the product could be economically competitive with mineral fertilizer as superphosphate in less than 10 years.

The efficiency of biological aerobic treatment of piggery wastewater to control nitrogen, phosphorus, pathogen and gas emissions.

Due to the water pollution and in order to reduce the nitrogen load applied on soils, biological nitrogen removal treatment of piggery wastewaters was developed in Brittany (France), with 250-300 units running. Four types of treatment processes were built including a biological reactor allowing to remove about 60-70% of the nitrogen content as gas by nitrification/denitrification. The addition of different mechanical separators (screw-press, centrifuge decanter ...) led to concentration of phosphorus in an exportable solid phase, allowing a reduction up to 80% of the phosphorus applied locally on soils. Moreover, a reduction of the gaseous emissions was observed using this management process as compared to conventional management (storage + land spreading) including ammonia (up to 68%) and greenhouse gases (55%). Finally, the level of enteric and pathogenic bacteria was also decreased with the treatment process as compared to conventional management systems. However, in spite of these results, the significant cost of the treatment must be underlined and alternative systems including anaerobic digestion will have to be studied.

Modelling of biological processes during aerobic treatment of piggery wastewater aiming at process optimisation.

A dynamic mathematical model was developed for the simulation of the aerobic treatment of piggery wastewater. This model includes the carbon oxidation, the nitrification and the denitrification. According to the experimental results obtained during this study, a modified version of the activated sludge model No. 1 has been developed. The model includes (1) nitrite as intermediate of nitrification and denitrification, (2) the distinction between the anoxic heterotrophic yield and the aerobic heterotrophic yield, respectively equal to 0.53 and 0.6 and (3) the first-order hydrolysis of the slowly biodegradable fraction. The calibration and the validation of the model was performed using experimental data from three experiments with two piggery wastewaters. A set of kinetic and stoichiometric parameters emerged from these tests. Except the kinetic of hydrolysis of the slowly biodegradable organic matter varying from 6 to 25 gCOD(gCODday)(-1), all other parameters were similar for all experiments. The dissolved oxygen concentration was identified as the main variable influencing the nitrite accumulation during nitrification. In the calibrated model, the oxygen half-saturation coefficient of the ammonium oxidisers (0.3g O(2)m(-3)) was lower than for the nitrite oxidisers (1.1 gO(2)m(-3)), leading to nitrite accumulation when the dissolved oxygen concentration was low. Simulations with the proposed model could be very useful for improved design and management of biological treatment of piggery wastewaters, particularly in case of partial nitrification to nitrite directly followed by denitrification.

Fate of phosphorus from biological aerobic treatment of pig slurry. By-products characterization and recovery.

The fate of phosphorus distribution in the products obtained from biological aerobic treatment of pig slurry, e.g. separated solids, liquid effluent and sludge, was monitored in three different farm-scale units. Samples of raw slurry, solid products, aerated slurry, liquid effluent and sludge were characterised and analysed for their concentration in total phosphorus, nitrogen content and heavy metals (Cu and Zn). At each treatment stage, nitrogen, phosphorus and heavy metals mass balance between input and output was established. Moreover, liquid products were characterised and analysed both for their total and dissolved ortho-phosphate content. Separated solids, sludge and liquid effluent represented 5%, 15-40% and 75-83% of the mass of the raw slurry, respectively. A mechanical separation step prior to aeration allowed the export of 25-30% of total phosphorus for further use as organic fertiliser. A large amount of total phosphorus (e.g. 60-70%) was located in sludge while phosphorus remaining in liquid effluent was about 15-25%. Raw slurry separation and sufficient aeration allowed phosphorus to concentrate in the sludge. Insufficient aeration resulted in the release of phosphorus as dissolved ortho-phosphate within the liquid effluent. Finally, relevance of the agronomic use of the products was discussed and improvements of biological aerobic treatment to enhance phosphorus removal and/or recovery were considered.

[Effects of human recombinant basic Fibroblast Growth factor on endothelial wound healing in organ culture of human cornea]. / Effet du basic Fibroblast Growth Factor (bFGF) recombinant humain sur la cicatrisation endothéliale en organoculture de cornée humaine.

PURPOSE: The effects of human recombinant bFGF has been evaluated on 9 paired human donor corneas (age 75 +/- 8 years), preserved in organ culture medium. MATERIAL AND METHODS: The endothelium of corneas were mechanically wounded (area of 7.53 +/- 2.05 mm2) and placed in culture medium during 14 days. For each pair, one cornea was tested with bFGF (50 ng/ml), delivered in two times (day 0, day 7), according to the stockage of the bFGF on the basal membranes (low affinity receptor), while the ipsilateral cornea served as control. Endothelium was assessed by trypan staining at day 0, day 7, and day 14. At this term of fourteenth day, alizarine red and trypan blue staining permitted morphometric data. RESULTS: The bFGF factor increases significantly cell density in the wound area (p < 0.05), and in the transitional area (p < 0.01), compared to the control group. In the transitional area, cells depletion was only 15% (392 +/- 55 cells/mm2) in the treated group compared to the 28% (716 +/- 0.1 cells/mm2) in the untreated group. In the wound area, the mean cell area was averaged 2581 microns2 in the control group and 2161 microns2 in the bFGF treated group (p < 0.05); in the transitional area the mean cell size was 549 microns2, and 479 microns2 in the control and the bFGF treated group (p < 0.05) respectively. The bFGF group do not affect the shape factor. CONCLUSION: This assay demonstrates that human bFGF greatly facilitates wound closure in endothelium of human cornea. The cellular migration from the transitional zone seems the dominant healing mechanism.