Phosphorus recovery from waste activated sludge by sponge iron seeded crystallization of vivianite and process optimization with response surface methodology.

As a novel phosphorus recovery product, vivianite (Fe3(PO4)2·8H2O) has attracted much attention due to its enormous recycling potential and foreseeable economic value. Taking sponge iron as seed material, the effect of different reaction conditions on the recovery of phosphorus in waste activated sludge by vivianite crystallization was studied. Through single factor tests, the optimal conditions for vivianite formation were in the pH range of 5.5-6.0 with Fe/P molar ratio of 1.5. Scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) were used to analyze the components of the crystals. The results showed that the vivianite produced by sponge iron as the seed crystal were larger and thicker (300-700 µm) than other seed (200-300 µm) and without seed (50-100 µm). Moreover, vivianite, which was synthesized with sponge iron as seed, was obviously magnetic and could be separated from the sludge by rubidium magnet. The Box-Behnken design of the response surface methodology was used to optimize the phosphorus-recovery process with sponge iron (maximum phosphorus recovery rate was 83.17%), and the interaction effect of parameters was also examined, pH had a significant effect on the formation of vivianite. In summary, this research verifies the feasibility of using sponge iron as the seed crystal to recover phosphorus in the form of vivianite from waste activated sludge, which is conducive to the subsequent separation and utilization of vivianite.

[Repair of urethral fistula resulting from correction of hypospadias: experience with 56 cases].

OBJECTIVE: To improve the success rate of one-stage urethral fistula repair by modifying the surgical procedures, suture material and application of urethral stent. METHODS: The clinical data of 56 cases of urethral fistula following correction of hypospadias were analyzed. The case group consisted of 38 cases with large fistula (over 3 mm in diameter) and 18 cases of small fistula (less than 3 mm). For the former cases, double skin flaps or pedicled skin flap from the scrotum were adopted for the repair; in the latter cases, transverse Y- or V-shaped skin flaps were used. Porous silica gel cannula was adopted for the stents. RESULT: A success rate of one-stage repair as high as 87.50% was achieved in these cases, with a rate for large fistula of 86.84%. CONCLUSION: Rich blood supply of the flaps, application of absorbable suture and urethral stent can improve the success rate of fistula repair.