Hydraulic assessment of waste stabilization ponds : Comparison of computational fluid dynamics simulations against tracer data
The overall performance of a wastewater treatment plant is in addition to the effectiveness of the biokinetic processes controlled by the flow dynamics. A wide used technique to characterize the water flow dynamics is the use of tracers. At full-scale tracer experiments in wastewater treatment plants provide insufficient information to completely grasp the flow dynamics. Additionally results are often biased by uncontrolled external factors. As alternative, computational fluid dynamic (CFD) models for performance analysis of existing and the design of new wastewater treatment plants have been increasingly used over the last decade. The paper presents the results of a tracer experiment against the output of a CFD model with application to a 7 ha large maturation pond. The tracer study was conducted with the fluorescence dye Rhodamine WT using the stimulus response technique. The three dimensional CFD model was built considering a variable density distribution of spatial grids based on the specific characteristics of the system. For the unsteady flow simulations the turbulence model k- was adopted. Residence time distribution (RTD) generated by both approaches were compared and showed fairly good agreement. The velocity and turbulence profiles of the CFD model were compared with experimental data confirming, although the high computational demand, the robustness of the used CFD model.
Study of the internal hydrodynamics in three facultative ponds of two municipal WSPS in Spain
Abstract The hydraulic performances of three facultative ponds, two of the Cieza and one of the Lorqui–Ceuti joint municipal wastewater stabilization ponds systems, were studied. The ponds of Cieza have a maximum capacity of 16,500 m 3 (F.1) and 32,000 m 3 (F.2), and both have a maximum depth of 1.6 m. The pond of Lorqui–Ceuti have a maximum capacity of 27,000 m 3 and a maximum depth of 1.8 m. A dye tracer, sulforhodamine B, was injected with the feed flow of each one facultative ponds. In the course of time, samples from within and at the outlet of every system were taken. The data obtained prove that the hydrodynamic behavior of the ponds is similar to a perfectly mixed tank reactor. The average real residence times were also determined. When these were compared to ponds, considered ideal perfectly mixed tank reactors, a high level of coincidence was noted. It was also observed that the hydrodynamics of the ponds presented virtually no flow anomalies.
Synthesis and chemical recycling of novel poly(ester-urethane)s using an enzyme.
A series of enzymatically recyclable poly(ester-urethane)s consisting of a biodegradable diurethane moiety as a hard segment and an ester moiety as an enzymatically cleavable linkage was chemo-enzymatically prepared by two routes. The poly(ester-urethane) was prepared by a) the ring-opening polymerization of a cyclic ester-urethane monomer synthesized via the transesterification reaction of biodegradable diurethanediol and dicarboxylate ester using lipase and b) the direct polycondensation of a diurethanediol and a dicarboxylate ester. A significantly higher molecular-weight poly(ester-urethane) having the highest molecular weight (Mw) of 101,000 was produced by the ring-opening polymerization of the cyclic ester-urethane monomer when compared with that produced by the polycondensation of the dicarboxylate ester with diurethanediol. The poly(ester-urethane) was readily degraded by lipase into the corresponding cyclic oligomers; the oligomers were readily repolymerized by the ring-opening polymerization using lipase for chemical recycling.