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

Abstract 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 test, 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 with 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 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 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.

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Application of electrochemical peroxidation (ECP) process for waste-activated sludge stabilization and system optimization using response surface methodology (RSM)

Water Science & Technology ◽

10.2166/wst.2018.066 ◽

2018 ◽

Vol 77 (6) ◽

pp. 1765-1776 ◽

Cited By ~ 1

Author(s):

Gagik Badalians Gholikandi ◽

Khashayar Kazemirad

Keyword(s):

Response Surface Methodology ◽

Activated Sludge ◽

Response Surface ◽

Removal Efficiency ◽

Ph Value ◽

System Optimization ◽

Waste Activated Sludge ◽

Operational Conditions ◽

Sludge Stabilization ◽

Rsm Optimization

Abstract In this study, the performance of the electrochemical peroxidation (ECP) process for removing the volatile suspended solids (VSS) content of waste-activated sludge was evaluated. The Fe2+ ions required by the process were obtained directly from iron electrodes in the system. The performance of the ECP process was investigated in various operational conditions employing a laboratory-scale pilot setup and optimized by response surface methodology (RSM). According to the results, the ECP process showed its best performance when the pH value, current density, H2O2 concentration and the retention time were 3, 3.2 mA/cm2, 1,535 mg/L and 240 min, respectively. In these conditions, the introduced Fe2+ concentration was approximately 500 (mg/L) and the VSS removal efficiency about 74%. Moreover, the results of the microbial characteristics of the raw and the stabilized sludge demonstrated that the ECP process is able to remove close to 99.9% of the coliforms in the raw sludge during the stabilization process. The energy consumption evaluation showed that the required energy of the ECP reactor (about 1.8–2.5 kWh (kg VSS removed)−1) is considerably lower than for aerobic digestion, the conventional waste-activated sludge stabilization method (about 2–3 kWh (kg VSS removed)−1). The RSM optimization process showed that the best operational conditions of the ECP process comply with the experimental results, and the actual and the predicted results are in good conformity with each other. This feature makes it possible to predict the introduced Fe2+ concentrations into the system and the VSS removal efficiency of the process precisely.

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