A non-biological surrogate for sequential disinfection processes

An evaluation of Fluorescent YG-microspheres (Polysciences Inc.) was performed to simulate Cryptosporidium parvum (C. parvum) oocysts inactivation in treatment systems that utilize multiple disinfectants. Experiments were conducted in batch reactors that included an ozone primary stage and a secondary free chlorine treatment stage. A flow cytometer was used to track changes in the fluorescence intensity distribution due to exposure to the chemical disinfectant. Microsphere 'survival ratios' (N/No) were calibrated by selecting an appropriate fluorescence intensity threshold to replicate the inactivation of different C. parvum oocysts strains. Results showed that fluorescent microspheres displayed synergistic effects in the presence of two sequential disinfectants. In addition, microsphere structural tests showed that the polystyrene surface was damaged due to exposure to ozone. This polystyrene damage enhanced the diffusion of the secondary disinfectant into the microsphere, where dye was degraded in the opened polymer layer. As a result, YG-fluorescent microspheres is a promising non-biological technique that is capable of producing similar synergistic behavior as with C. parvum oocysts exposed to ozone followed by chlorine.     

Inorganic carbon limitations on nitrification: experimental assessment and modelling

Nitrification is a two-step process that involves two different biomass populations: ammonia oxidising biomass (AOB) and nitrite oxidising biomass (NOB). Both populations are autotrophic (i.e. their carbon source is inorganic). Therefore, a deficit of this substrate should result in a decrease of the process rate. Recent technology advances such as the SHARON process have brought new scenarios in biological nitrogen removal where these limitations should be considered. Hence, this work examines the inorganic carbon limitation using respirometric and titrimetric techniques. For this aim, the nitrification rate was measured at different total inorganic carbon (TIC) concentrations. The experimental results obtained show that AOB was limited at TIC concentrations lower than 3mmol CL(-1). At the same time, no carbon source limitation for NOB was observed in spite of the low TIC concentrations attained (lower than 0.1mmol CL(-1)). The AOB limitation could be successfully modelled using Monod, Tessier and sigmoidal kinetics. The best fit was obtained with sigmoidal kinetics. However, unexpected biomass activity (oxygen consumption) was observed despite a very low TIC concentration (lower than 0.1mmol CL(-1)).     

Respirometric calibration and validation of a biological nitrite oxidation model including biomass growth and substrate inhibition

The modelling of the nitrification process of high-strength ammonium wastewater must be designed to consider it as a two-step reaction with substrate inhibition. Consequently, kinetic and stoichiometric parameters of both steps are required. In this work, the second step in the nitrification process was studied: a biological nitrite oxidation model was formulated, calibrated and validated using only oxygen uptake rate (OUR) measurements. The model included biomass growth and substrate inhibition. First, the biomass yield coefficient for nitrite-oxidising biomass was determined. Then, a respirometric experiment with one nitrite pulse of 500 mg N-NO₂⁻ L⁻¹ was performed to estimate the rest of the model parameters. The practical identifiability study showed that the parameters were strongly correlated. Hence, a new experimental design consisting of two consecutive pulses and a delayed third one was designed to improve the parameter identifiability. Both experimental designs were compared using contour plots of the objective function and optimal experimental design criteria for parameter estimation. It was concluded that the parameter identifiability was improved with the new experimental design. Finally, the estimated parameters were validated and the pH effect on the inhibition coefficient was evaluated.     

Output Characteristics of an Optical Fibre Ring Resonator Using a Planar or Nonplanar 3 × 3 Fibre Coupler: A Comparison

Abstract

A comparison is made between the output characteristics of type 1 optical fibre ring resonators with a different type of 3 × 3 fibre coupler, that is a planar or a nonplanar coupler. Three different nonplanar couplers are formed when the central fibre 1 of a loosely coupled planar 3 × 3 fibre coupler is displaced normally from the common plane. Such a 3 × 3 fibre coupler can be identified by the value of its relative coupling ratio m ₃. The dependence of the output intensities of the ring resonator on the coupling length kd and the relative coupling ratio m ₃ of the 3 × 3 fibre coupler is investigated. The former dependence can be used as a guide to obtain suitable output characteristics of a fibre ring resonator for a specific application, while the latter can be used to choose the right type of 3 × 3 fibre coupler to build a fibre ring resonator. It is found that the output characteristics of a fibre ring resonator with a 3 × 3 planar (m ₃ = 0) or an equilateral triangular (m ₃ = 1) fibre coupler are usually better than those of the others.     

An improved hybrid classifier

Abstract. A new hybrid classifier is proposed which utilizes the advantages of the maximum likelihood classifier and the parallelepiped classifier. The new hybrid classifier reduces the processing time more substantially than the conventional one by introducing a lower boundary for each class. The rate of misclassification is comparable to that of maximum likelihood classifier. Performance of the conventional and the new method are compared by an example.     

Understanding the detrimental effect of nitrate presence on EBPR systems: effect of the plant configuration

The interaction between enhanced biological phosphorus removal (EPBR) and biological nitrogen removal may result in EBPR failure in full‐scale wastewater treatment plants (WWTPs). This work studies one of the common causes of this failure: the presence of nitrate in the anaerobic phase, which may act as an inhibitor for polyphosphate accumulating organisms (PAO) activity or may activate the competition between PAO and denitrifying bacteria for the carbon source. Several batch experiments were performed with different carbon sources (acetic acid, propionic acid and sucrose) at different nitrate concentrations using PAO‐enriched sludge from two different pilot plants: an anaerobic/aerobic sequential batch reactor (SBR) and an anaerobic/anoxic/aerobic (A²/O) continuous plant. The results imply that the operational conditions of the A²/O pilot plant selected a PAO population capable of i) coexisting with nitrate without an inhibitory effect and ii) outcompeting denitrifying bacteria for the carbon source, in contrast to the SBR pilot plant where nitrate had an inhibitory effect on EBPR. Copyright © 2012 Society of Chemical Industry