Reactor 1 Research Articles

Influence of the employment of adsorption and coprecipitation agents for the removal of PPCPs in conventional activated sludge (CAS) systems

Three activated sludge reactors were operated to improve the removal of organic micropollutants such as Pharmaceutical and Personal Care Products (PPCPs). Reactor 1 (R1) was operated as a Conventional Activated Sludge reactor (CAS), Reactor 2 (R2) consisted of a CAS unit that was continuously fed with FeCl3 whereas granular activated carbon (GAC) was fed directly into the mixed liquor of Reactor 3 (R3) in order to attain concentrations in the range 100-1,000 mg/L. PPCPs removal rates varied depending on the compound present in each reactor during the entire 220 days of operation. Some substances showed the same behaviour in all reactors, such as the acidic pharmaceuticals naproxen and ibuprofen, which were almost completely removed (> 90%). More hydrophobic organic substances, like musk fragrances, were about 90% removed after 40 days of operation in all of the reactors. The main difference between the three reactors was obtained in R3 when the GAC concentrations in the aeration tank were around 500-1,000 mg/L. Under these conditions, the more recalcitrant compounds like diazepam and carbamazepine could be removed by up to 40%, and diclofenac up to 85%. Adsorption isotherms for PPCPs were obtained with activated carbon, and the results were successfully fitted to the Freundlinch equation. The more recalcitrant compounds (carbamazepine, diazepam and diclofenac) had the highest adsorption capacities onto GAC, which is consistent with the behaviour observed in R3 and helps to identify the removal mechanism (adsorption for these compounds, whereas absorption for fragrances).

Enhanced aerobic granulation with extracellular polymeric substances (EPS)-free pellets

Extracellular polymeric substances (EPSs) were secreted by cells after they agglomerated into a compact aggregate. This study shows that the EPS initially embedded in seed sludge before granulation may sterically slow subsequent microbe–microbe contact, thereby delaying aerobic granulation. Three identical bioreactors were used in this study using glucose as the sole carbon and energy source. Reactor 1 (R1) was seeded with EPS-free pellets and operated in sequencing batch reactor (SBR) mode. Reactor 2 (R2) was seeded with the original sludge flocs and operated in SBR mode. Reactor 3 (R3) was seeded with EPS-free pellets and operated in continuously stirred tank reactor (CSTR) mode. Granulation occurred in R1 earlier than in R2; the granules that formed in R1 were larger and more compact than those in R2 at the same cultivation time. The few mature granules in R3 suggest that aerobic granulation can occur in a CSTR when a reactor is seeded with EPS-free pellets.

Biological treatment of a high strength nitrogenous wastewater

Bench‐scale studies were conducted to investigate nitrification of low and high strength nitrogenous wastewater. Two parallel completely mixed activated sludge reactors were operated over a wide range of mean cell residence times (MCRT) ranging from approximately 2.2 days to 21.0 days. Synthetic wastewater consisting of bactopeptone nutrient broth and ammonium sulfate was fed to the bench‐scale reactors. The feed to Reactor 1 (R‐1) was maintained at a COD:TKN ratio of 6.07:1 whereas feed to R‐2 was maintained at a C0D:TKN ratio of 0.65:1. Observed specific nitrification rates in R‐l ranged 0.037–0.11 mg N/mg MLSS‐day at 20°C, whereas in R‐2, observed specific nitrification rates ranged from 0.13 ‐ 0.38 mg N/mg MLSS‐day at 20°C. Nitrification and carbon removal were both inhibited at MCRTs of 7.9 days or greater in R‐2.