Investigation of Direct-Reduced Iron as a Filter Media for Phosphorus Removal in Wastewater Applications

• Main Author: Qin, Hongye
• Other Authors: Kinsley, Christopher
• Format: Others
• Language: en
• Published: Université d'Ottawa / University of Ottawa 2019
• Subjects: Phosphorus removal; Direct-reduced iron; Wastewaters; Filter; Media regeneration
• Online Access: http://hdl.handle.net/10393/39973; http://dx.doi.org/10.20381/ruor-24212

Passive reactive filters have the potential to provide effective phosphorus (P) removal from stormwater or agricultural drainage, or to act as an add-on P-removal technology for decentralized or small community wastewater treatment systems. Passive filters require minimal energy consumption and human maintenance. Direct-reduced iron (DRI), a steel-making intermediate, was investigated as a passive filter media for wastewaters phosphorus reduction. Phosphorus is a biologically active element that is in excess in many natural waterways due to intensive human activity. Eutrophication can occur when P concentrations exceed 0.02 mg/L in freshwater lakes and rivers. The harmful consequence of this phenomenon includes oxygen deprivation, fish death and cyanobacteria-produced toxins. There is a pressing need to limit phosphorus over-discharge into natural waterways. DRI is a novel media in the application of wastewater treatment and was characterized to have a porous structure with high metallic iron content. The phosphorus retaining mechanisms in batch and column studies suggest a combination of adsorption and surface crystal formation as the dominant removal mechanisms. Batch studies demonstrated increasing removal capacity with P concentration with a plateau observed at 21 mg P/g DRI relating to initial 3000 mg P/L. Media rejuvenation was investigated through chemical treatment with two iron solutions (Fe2(SO4)3, FeCl3) and two acidic solutions (H2SO4 and HCl) at varying molarity. P removal capacity could be fully recovered with 0.05 M Fe3+ or 0.4 N H+ (HCl/H2SO4), while a 37.6% P recovery was also achieved in an acidic solution at 1.2 N H+ (HCl/H2SO4). A column study utilizing three media sizes of DRI (3.5, 11, 19 mm) and one media size of activated alumina (AA) (7.5 mm) was conducted for 315 days using synthetic P solution varying from 2 to 10 mg/L and hydraulic retention times (HRTs) varying from 0.7 – 15 h. The results demonstrated that removal efficiency increased with HRT and decreased with increasing media size and concentration with minimum HRTs to maintain an 80% removal efficiency varying from 4.4 to 15 hrs for DRI and 3.9 hrs for AA for influent P concentrations of 10 mg/L and below. After 1 year of column operation, the DRI media had demonstrated a minimum removal capacity of 1.82 mg P/g DRI, which can be used as a conservative design parameter. A short duration column study (34 days) utilizing municipal lagoon effluent exhibited similar removal efficiencies to the synthetic column study under the same operational conditions. The 10 years lifespan DRI filter with 80% removal rate in the treatment of stormwater, municipal lagoon effluent, septic tank effluent and dairy wastewater application would have been estimated to have filter volumes of 0.24, 4.69, 15.3 and 36.2 m3, respectively.