Passivation of Sponge Iron and GAC in Fe⁰/GAC Mixed-Potential Corrosion Reactor

The Fe⁰/GAC mixed-potential corrosion reactor was used to treat the complicated, toxic, and refractory ABS resin wastewater. In the 100 days continuous run, the effect of the packing particles passivation on the treatment efficiency of the Fe⁰/GAC mixed-potential corrosion reactor was investigated seriously. The formation mechanism of the compounds in passive film was investigated first by SEM, EDS, and X-ray dot-mapping, which was the precondition for the control of the passivation of packing particles. The results show that the passive film consisted of five kinds of compounds such as Fe₃(PO)₂·8H₂O, FePO₄ ·3H₂O, Fe₂O₃, Fe₃O₄, and FeS, which obstructed the formation of macroscopic galvanic cells between sponge iron (Fe⁰) and GAC and decreased the COD treatment efficiency of the Fe⁰/GAC mixed-potential corrosion reactor from 45 to 55% to 0%. The formation of passive film mainly resulted from the elements of S and P, which were from the SO₄^2– and PO₄^3– in ABS resin wastewater. Therefore, the inorganic ions in wastewater, especially for SO₄^2– and PO₄^3–, should be removed first before the treatment of the Fe⁰/GAC mixed-potential corrosion reactor

Investigation on evaluation criteria of backwashing effects for a pilot-scale BAF treating petrochemical wastewater

<p>Parameters for evaluation criteria of air–water backwashing effects of a pilot-scale biological aerated filter (BAF) treating petrochemical wastewater were investigated. The parameters included the suspended solids (SS) and specific oxygen uptake rate (SOUR) of the backwashing effluent, recovery of the BAF after backwashing, and the removal of the biomass/bioactivity attached on the filter media after backwashing. Results showed that the weight of the total sludge produced in the backwashing effluent increased with the increase in water-backwashing intensity, while the total SOUR of backwashing effluent rose notably with the increase of air-backwashing intensity. The optimal backwashing intensity of 14 L/(m²<b>_·</b>s) for air and 4 L/(m²<b>_·</b>s) for water were obtained. When the BAF was backwashed on this condition, the BAF recovered with high average removal of chemical oxygen demand (COD) and ammonia nitrogen of 14.3% and 50.3%, respectively. High amount of biomass removal at 15.8% and low level of bioactivity removal at 8.8% attached on the filter media were also found. Concentrations of the benzene, toluene, ethylbenzene and (<i>o</i>-, <i>m</i>-, <i>p</i>-) xylenes (BTEX) and phenol in the backwashed sludge were analyzed, showing that the backwashing was essential to remove some aromatic compounds adsorbed in the microorganisms.</p

Passivation process and the mechanism of packing particles in the Fe⁰/GAC system during the treatment of ABS resin wastewater

<div><p>This study provides mechanistic insights into the passivation of the packing particles during the treatment of acrylonitrile–butadiene–styrene (ABS) resin wastewater by the Fe⁰/GAC system. The granular-activated carbon (GAC) and iron chippings (Fe⁰) were mixed together with a volumetric ratio of 1:1. GAC has a mean particle size of approximately 3–5 mm, a specific surface of 748 m² g⁻¹, a total pore volume of 0.48 mL g⁻¹ and a bulk density of 0.49 g cm⁻³. The iron chippings have a compact and non-porous surface morphology. The results show that the packing particles in the Fe⁰/GAC system would lose their activity because the removal of TOC and for ABS resin wastewater could not carried out by the Fe⁰/GAC system after 40 days continuous running. Meanwhile, the availability of O₂ and intrinsic reactivity of Fe⁰ play a key role on the form of passive film with different iron oxidation states. The passive film on the surface of iron chippings was formed by two phases: (a) local corrosion phase (0–20 d) and (b) co-precipitation phase (20–40 d), while that of GAC was mainly formed by the co-precipitation of corrosion products with and because and would not easily reach the Fe⁰ surface. Therefore, in order to avoid the occurrence of filler passivation, high concentrations of and in wastewater should be removed before the treatment process of the Fe/GAC system.</p></div