Simulated acid mine drainage treatment in iron oxidizing ceramic membrane bioreactor with subsequent co-precipitation of iron and arsenic

Acid mine drainage (AMD), generated in the active and abandoned mine sites, is characterized by low pH and high metal concentrations. One AMD treatment possibility is biologically oxidizing Fe²⁺ followed by precipitation through pH control. As compared to autotrophic iron oxidizing microbial community, a microbial community enriched in the presence of organic nutrients was hypothesized to yield higher biomass during commissioning the bioreactor. In this study, the treatment of Fe, Cu, Co, Mn, Zn, Ni, and As containing simulated AMD was studied using an iron-oxidizing ceramic membrane bioreactor (CMBR) at varying hydraulic retention times (HRTs) (6-24 h) and two different feed Fe²⁺ concentrations (250 and 750 mg/L). The impact of tryptone soya broth (TSB) on the CMBR performance was also investigated. Almost complete Fe²⁺ oxidation and sustainable flux at around 5.0 L/(m².h) were obtained in the CMBR with the Alicyclobacillus tolerans and Acidiphilium cryptum dominated enrichment culture. The Fe²⁺ oxidation rate, as assessed in batch operation cycles of CMBR, increased significantly with increasing Fe²⁺ loading to the bioreactor. The iron oxidation rate decreased by the elimination of organic matter from the feed. The increase of the CMBR permeate pH to 3.5-4.0 resulted in selective co-precipitation of As and Fe (over 99%) with the generation of biogenic schwertmannite.

Key process parameters involved in the treatment of olive mill wastewater by membrane bioreactor

The Olive Mill Wastewater (OMWW) biodegradation in an external ceramic membrane bioreactor (MBR) was investigated with a starting acclimation step with a Ultrafiltration (UF) membrane (150 kDa) and no sludge discharge in order to develop a specific biomass adapted to OMWW biodegradation. After acclimation step, UF was replaced by an Microfiltration (MF) membrane (0.1 µm). Sludge Retention Time (SRT) was set around 25 days and Food to Microorganisms ratio (F/M) was fixed at 0.2 kg_COD kg_MLVSS^-1 d^-1. At stable state, removal of the main phenolic compounds (hydroxytyrosol and tyrosol) and Chemical Oxygen Demand (COD) were successfully reached (95% both). Considered as a predominant fouling factor, but never quantified in MBR treated OMWW, Soluble Microbial Products (SMP) proteins, polysaccharides and humic substances concentrations were determined (80, 110 and 360 mg L^-1 respectively). At the same time, fouling was easily managed due to favourable hydraulic conditions of external ceramic MBR. Therefore, OMWW could be efficiently and durably treated by an MF MBR process under adapted operating parameters.

Chemical cleaning-associated generation of dissolved organic matter and halogenated byproducts in ceramic MBR: Ozone versus hypochlorite

This study characterized the dissolved organic matter (DOM) and byproducts generated after the exposure of activated sludge to ozone and NaClO in ceramic MBR. It was found that NaClO triggered more significant release of DOM than ozone. Proteins with the molecular weight greater than 20 kDa and humic acid like-substances were the principal components of DOM generated by NaClO, while ozone was found to effectively degrade larger biopolymers to low molecular weight substances. The results showed that more than 80% of DOM generated by NaClO and ozone could pass through the 0.2-μm ceramic membrane. Furthermore, total organic chlorine (TOCl) was determined to be the principal species of halogenated byproducts in both cases, while the generation of TOCl by NaClO was much more significant than that by ozone. Only a small fraction of TOCl was removed by the 0.2-μm ceramic membrane. More importantly, the toxic bioassays further revealed that the supernatant of sludge suspension and permeate in the MBR with NaClO cleaning exhibited higher developmental toxicity to the polychaete embryos than those by ozone. The results clearly showed that on-line chemical cleaning with ozone should be a more eco-friendly and safer approach for sustaining long-term membrane permeability in ceramic MBR.