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Performance of a combined system up-flow anaerobic sludge blanket (UASB) followed by aerobic treatment activated sludge (AS) for removal of carbonaceous and nitrogenous contaminants at an average temperature of 25°C was investigated. The combined system was fed with high strength synthetic sewage having chemical oxygen demand (COD) of 2500 mg L−1. The organic loading rate (OLR) of the UASB reactor was increased gradually from 1.1 to 3.8 gCOD Lr−1d−1. At steady state condition, the UASB reactor achieved removal efficiency up to 83.5% of total COD (CODtot), 74.0% of volatile fatty acid (VFA) and 94.0% of protein. The combined system performed an excellent organic removal pushing the overall removal efficiency of CODtot, VFA and protein to 91.0%, 99.9% and 98.2%, respectively. When the OLR of the UASB increased to 4.4 g COD Lr−1d−1, the UASB was overloaded and; thus, its effluent quality deteriorated. In respect to nitrogen removal, both partial nitrification and complete nitrification took place in aerobic post-treatment. When the dissolved oxygen (DO) concentration was >2.0 mg L−1, complete nitrification (period B) occurred with an average nitrification efficiency of 96.2%. The partial nitrification occurred due to high OLR to AS during the overloading event (period A) and when DO concentration was <2.0 mg L−1(period C). The maximum accumulated nitrite concentration in periods A, B and C were 90.0, 0.9 and 75.8 mg NO−2-N L−1, respectively. The nitrogen balance results of periods A and C indicated that there was a discrepancy between the amount of ammonium nitrogen removed and the amount of oxidized nitrogen formed. This suggests the occurrence of simultaneous nitrification/denitrification (SND) in aerobic post-treatment. [ABSTRACT FROM AUTHOR]

Anaerobic bioreactors that can support simultaneous microbial processes of denitrification and methanogenesis are of interest to nutrient nitrogen removal. However, an important concern is the potential toxicity of nitrate (NO3 -) and nitrite (NO2-) to methanogenesis. The methanogenic toxicity of the NOx - compounds to anaerobic granular biofilms and municipal anaerobic digested sludge with two types of substrates, acetate and hydrogen, was studied. The inhibition was the severest when the NOx - compounds were still present in the media (exposure period). During this period, 95% or greater inhibition of methanogenesis was evident at the lowest concentrations of added NO2 - tested (7.6- 10.2 mg NO2 --N l-1) or 8.3-121 mg NO3 --N l-1 of added NO3 3, depending on substrate and inoculum source. The inhibition imparted by NO3 - was not due directly to NO3 - itself, but instead due to reduced intermediates (e.g., NO2 -) formed during the denitrification process. The toxicity of NOx - was found to be reversible after the exposure period. The recovery of activity was nearly complete at low added NOx - concentrations; whereas the recovery was only partial at high added NOx - concentrations. The recovery is attributed to the metabolism of the NOx - compounds. The assay substrate had a large impact on the rate of NO2 - metabolism. Hydrogen reduced NO2 - slowly such that NO2 - accumulated more and as a result, the toxicity was greater compared to acetate as a substrate. The final methane yield was inversely proportional to the amount of NOx - compounds added indicating that they were the preferred acceptors compared to methanogenesis. [ABSTRACT FROM AUTHOR]

Large quantities of polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in clothing and plastic products since the 1970s. A small fraction of the PBDEs in manufactured products subsequently enters municipal wastewater. Nevertheless, the resistance of these compounds to chemical and biochemical transformations provides opportunities for accumulation in sediments that are in contact with wastewater effluent and agricultural soils that are amended with biosolids derived from wastewater treatment. Balances developed for PBDE congeners indicate that conventional wastewater treatment processes and soil infiltration of treated wastewater in recharge operations do not discriminate significantly among the major congeners in commercially available PBDE products. Accumulation of PBDEs at near part-per-million levels was measured in the surface sediments at the Sweetwater Recharge Facility in Tucson, Arizona, during 10–15 years of operation. Half-lives for loss of major PBDE congeners from sediments were decades or longer. Local agricultural soils amended with biosolids over a 20-year period showed similar accumulation of PBDEs. The widespread use of PBDEs in commercial products, compound persistence, and toxicity indicate that additional effort is warranted to better understand fate-determining processes for PBDEs in the environment. [ABSTRACT FROM AUTHOR]