| Potassium ferrate was prepared by hypochlorite oxidation method. The influences of reaction time, reaction temperature, purification conditions on the purity and yield of product were investigated. The results show that, ice water bath and1hour of reaction time are the optimal preparation conditions. Using1mol/L KOH solution can effectively remove impurities in crude potassium ferrate. Under the condition of low temperature and strong mixing of15min, potassium ferrate crystal precipitated well. The sample was characterized by FT-IR and XRD, and it was proved that the product is potassium ferrate. The purity of the product was determinated by the oxidation of charomate. The purity and yield of potassium ferrate respectively were (72.34±1.14)%and (82.19±1.37)%, respectively, in the optimal preparation conditons.Different dosages of ferrate potassium were added to the excess activated sludge to investigate the effects of ferrate potassium oxidation on the sludge flocs characteristics and the dewatering property. Sludge flocs characteristics included particle sizes, the content of EPS, the content of proteins and polysaccharides in EPS. Dewatering indexes included sludge filtration (CST) and dewatering extent (solid extent of sludge cake after centrifugation). The results show that pretreatment by ferrate potassium can change the structure of the sludge flocs and improve sludge dewatering extent. But it also increases the content of EPS, which affects adversely the filtration rate of the sludge. Fe(OH)3derived from the decomposition of potassium ferrate can improve the sludge settleability. Statistical analysis suggests that capillary suction time (CST) is significantly correlated with the total content of EPS, m LB/m TB, PN and PS in LB-EPS and the content of LB-EPS. Meanwhile, CST is negatively correlated with the content of TB-EPS and PN in TB-EPS. There is no correlation between CST and PN/PS in EPS and PS in TB-EPS.After mixing ferrate potassium with excess activated sludge in different proportions, a sludge oxidative decomposition experiment was carried out. According to changes of soluble chemical oxygen demand (SCOD), total phosphorus (TP) and ammonia nitrogen (NH3-N) of the sludge supernatant, the effect of potassium ferrate on characteristics of the waste activated sludge was analyzed. The results show that potassium ferrate can disperse the sludge effectively. The content of sludge solid (SS) decreases as the dosages of potassium ferrate increases. The concentration of SCOD, NH3-N and TP respectively increases by (6±1.74) times,(7.4±1.72) times and (2.2±0.97) times, respectively, compared with the original sludge samples.After mixing0.81g/gSS potassium ferrate with excess activated sludge, an anaerobic digestion test was carried out. According to the changes of SCOD, VFA and TCOD removal rate, the effect of potassium ferrate on anaerobic digestion of the sludge was analyzed. The results show that the potassium ferrate pretreatment can effectively increase the concentration of SCOD and VFA of the sludge, compared with the untreated sludge. Potassium ferrate pretreatment can significantly improve the organic matter removal rate of the sludge. When digestion time is15d, the TCOD removal rate of untreated sludge is (1.72±0.03)%, however, the TCOD removal rate of treated sludge can reach (31.67±0.41)%. The TSS removal rate of the treated sludge is significantly higher than the TSS removal rate of untreated sludge. The TSS removal rate of untreated sludge is (9.88±0.17)%when the time is25d, but, the TSS removal rate of treated sludge can achieve (9.93±0.21)%when the digestion time is15d. |
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