Impact of influent characteristics on a partial nitritation SBR treating high nitrogen loaded wastewater

The Anammox process allows a sustainable treatment of wastewater with high nitrogen content. Partial oxidation of ammonium to nitrite is a previous and crucial step. Given the variability on wastewater composition, the operation of sequencing batch reactors (SBR) for partial nitritation (PN) is very challenging. This work assessed the combined influence of influent characteristics and process loading rate. Simulation results showed that wastewater composition - Total nitrogen as ammonia (TNH) and total inorganic carbon (TIC) - as well as nitrogen loading rate (NLR) govern the outcomes of the reactor. A suitable effluent can be produced when treating wastewater with different ammonia levels, as long as the TIC:TNH influent molar ratio is around 1:1 and extreme NLR are avoided. The influent pH has a key impact on nitrite conversion by governing the CO -bicarbonate-carbonate equilibrium. Finally, results showed that oxidation of biodegradable organic matter produces CO , which acidifies the media and limits process conversion

Sulfide and methane production in sewer sediments

Recent studies have demonstrated significant sulfide and methane production by sewer biofilms, particularly in rising mains. Sewer sediments in gravity sewers are also biologically active; however, their contribution to biological transformations in sewers is poorly understood at present. In this study, sediments collected from a gravity sewer were cultivated in a laboratory reactor fed with real wastewater for more than one year to obtain intact sediments. Batch test results show significant sulfide production with an average rate of 9.20 +/- 0.39 g S/m(2).d from the sediments, which is significantly higher than the areal rate of sewer biofilms. In contrast, the average methane production rate is 1.56 +/- 0.14 g CH4/m(2).d at 20 degrees C, which is comparable to the areal rate of sewer biofilms. These results clearly show that the contributions of sewer sediments to sulfide and methane production cannot be ignored when evaluating sewer emissions. Microsensor and pore water measurements of sulfide, sulfate and methane in the sediments, microbial profiling along the depth of the sediments and mathematical modelling reveal that sulfide production takes place near the sediment surface due to the limited penetration of sulfate. In comparison, methane production occurs in a much deeper zone below the surface likely due to the better penetration of soluble organic carbon. Modelling results illustrate the dependency of sulfide and methane productions on the bulk sulfate and soluble organic carbon concentrations can be well described with half-order kinetics. (C) 2014 Elsevier Ltd. All rights reserved

Thermophysical properties of the Lipari lavas (Southern Tyrrhenian Sea)

Results of thermophysical investigations into the lavas of the island of Lipari (Southern Tyrrhenian Sea) are presented. Samples selected for laboratory measurements belong to four main magmatic cycles, which produced basaltic-andesitic, andesitic and rhyolitic lavas. The wet-bulk density and the thermal conductivity measured on 69 specimens range from 1900 to 2760 kg m-3 and from 1.02 to 2.88 W m-1 K-1, respectively. Porosity is never negligible and its influence on density is maximum in rhyolites of the third cycle. The thermal conductivity is also influenced by the amount of glass. Rhyolitic obsidians show values lower than other rhyolites, although the latter rocks have a larger average porosity. The radioactive heat production determined on 36 specimens varies with the rock type, depending on the amount of U, Th and K. In basic lavas of the first cycle its value is 0.95°± 0.30 mW m-3, while in rhyolites of the fourth cycle it attains 6.68°±0.61 mW m-3. A comparison between results of g-ray spectrometry and X-ray fluorescence points out that the assumption of equilibrium in the decay series of the isotopic elements seems fulfilled. The information obtained is useful not only for the interpretation of geophysical surveys but also for the understanding of the geochemical characteristics of lavas

Effect of temperature on AOB activity of a partial nitritation SBR treating landfill leachate with extremely high nitrogen concentration

This study investigates the effects of temperature on ammonia oxidizing bacteria activity in a partial nitritation (PN) sequencing batch reactor. Stable PN was achieved in a 250\ua0L SBR with a minimum operating volume of 111\ua0L treating mature landfill leachate containing an ammonium concentration of around 6000\ua0mg N-NH\ua0L at both 25 and 35\ua0°C. A suitable influent to feed an anammox reactor was achieved in both cases. A kinetic model was applied to study the influence of free ammonia (FA), the free nitrous acid (FNA) inhibition, and the inorganic carbon (IC) limitation. NH and NO concentrations were similar at 25 and 35\ua0°C experiments (about 2500\ua0mg N-NH\ua0L and 3500\ua0mg N-NO\ua0L), FA and FNA concentrations differed due to the strong temperature dependence. FNA was the main source of inhibition at 25\ua0°C, while at 35\ua0°C combined FA and FNA inhibition occurred. DGGE results demonstrated that PN-SBR sludge was enriched on the same AOB phylotypes in both experiments

Simultaneous use of caustic and oxygen for efficient sulfide control in sewers

Periodic caustic shock-loading is a commonly used method for sulfide control in sewers. Caustic shock-loading relies on the elevation of the sewage pH to ≥ 10.5 for several hours, thereby removing sewer pipe biofilms as well as deactivating SRB activity in the remaining biofilm. Although a widely used method, SRB activity is often not completely inhibited, and as such sulfide is still being generated. Here, we propose and experimentally demonstrate an innovative approach which combines caustic with oxygen, another commonly used method, as a dosing strategy for overcoming the drawbacks of caustic shock-loading. Six laboratory-scale rising main reactors were subjected to three dosing schemes over a period of three months, namely (i) simultaneous caustic and oxygen addition, (ii) caustic addition and (iii) no chemical addition. Our results showed that the combination of caustic and oxygen achieved efficient sulfide control, leading to a prolonged biofilm recovery period in between caustic shocks. In addition, methane emissions were reduced to a negligible level compared to caustic treatment only. To translate the findings to real-life application, the key parameters obtained during the long-term lab-scale experiments were subjected to extensive simulation studies using the SeweX model under a wide range of conditions commonly found in sewers. Overall, this study highlights the potential of periodic shock-loading and intermittent oxygen injection as combined dosing strategy for efficient sulfide control in sewers