A steady-state model for the evaluation of disk rotational speed influence on RBC kinetic: model presentation

Treatment of mustard tuber wastewater (MTWW) using a pilot-scale packed cage rotating biological contactor system: process modeling and optimization

The water quality range for wastewater treatment projects in the food processing industry changes constantly. To fully understand the threshold for pollutant removal with the lowest possible energy consumption, the relationship between pollutant removal and wastewater treatment conditions was established using response surface methodology (RSM). The optimum conditions for total COD, TN, and NH₃-N removal from saline mustard tuber wastewater (MTWW) with a packed cage rotating biological contactor (RBC) system were investigated by experiments based on a Box-Behnken design (BBD). The independent variables were organic load (ORL), rotational disk velocity (RDV), and immersion rate (IR). Parameters of COD, TN, and NH₃-N removal efficiency were selected as responses. The optimal conditions for the best COD, TN, and NH₃-N removal efficiency with the lowest energy consumption were found to be at an ORL of 26.71 kg/day, a RDV of 1.62 rpm (7.62 m/s), and an IR of 46%. After the optimization, the energy cost was evaluated by coupling energy performance indicators with organic pollution efficiencies to be the highest class of performance. This research demonstrates that the suggested models have a good predicting and fitting ability in interrelations between the pollutant removal and process parameters of the packed cage RBC system treating saline MTWW.

Novel micro/ultra/nanocentrifugation membrane process assessment for revalorization and reclamation of agricultural wastewater

The concentration and recovery of the high-added value phenolic fraction from two-phase olive mill wastewater and the simultaneous effluent treatment by a novel micro/ultra/nanocentrifugation membrane process assessment is addressed, permitting to gather information for a correct and effective screening procedure for the adequate membrane election (MF-UF-loose NF) for the target. Phenolic compounds are the major factor of phytotoxicity of these effluents, but on the other hand they present high antioxidant properties that makes them very relevant for food, cosmetic, pharmaceutical and biotechnological industries. The selection of a membrane MWCO between 100 kDa and 0.45 μm permitted the complete transfer of the phenolic fraction to the permeate, whereas below 3 kDa they would be transferred to the concentrate stream instead, with ∼60% COD reduction and EC lowered to 551-662 μS cm^-1 in the final treated stream ensured, sensibly improving the effluent quality. This would provide a purified effluent with good salinity standards according to the indications given by the FAO for irrigation reuse. This procedure could be quick and reliable for the assessment of the adequate membrane needed for a particular purification process, in contrast with long-term, time consuming common bench-scale procedures.

A new method to measure and model dynamic oxygen microdistributions in moving biofilms

Biofilms in natural environments offer a superior solution to mitigate water pollution. Artificially intensified biofilm reactors represented by rotating biological contactors (RBCs) are widely applied and studied. Understanding the oxygen transfer process in biofilms is an important aspect of these studies, and describing this process in moving biofilms (such as biofilms in RBCs) is a particular challenge. Oxygen transfer in RBCs behaves differently than in other biological reactors due to the special oxygen supply mode that results from alternate exposure of the biofilm to wastewater and air. The study of oxygen transfer in biofilms is indispensable for understanding biodegradation in RBCs. However, the mechanisms are still not well known due to a lack of effective tools to dynamically analyze oxygen diffusion, reaction, and microdistribution in biofilms. A new experimental device, the Oxygen Transfer Modeling Device (OTMD), was designed and manufactured for this purpose, and a mathematical model was developed to model oxygen transfer in biofilm produced by an RBC. This device allowed the simulation of the local environment around the biofilm during normal RBC operation, and oxygen concentrations varying with time and depth in biofilm were measured using an oxygen microelectrode. The experimental data conformed well to the model description, indicating that the OTMD and the model were stable and reliable. Moreover, the OTMD offered a flexible approach to study the impact of a single-factor on oxygen transfer in moving biofilms. In situ environment of biofilm in an RBC was simulated, and dynamic oxygen microdistributions in the biofilm were measured and well fitted to the built model description.

A new sponge tray bioreactor in primary treated sewage effluent treatment

The new attached growth sponge tray bioreactor (STB) was evaluated at different operating conditions for removing organics and nutrients from primary treated sewage effluent. This STB was also assessed when using as a pre-treatment prior to micro-filtration (MF) for reducing membrane fouling. At a short hydraulic retention time (HRT) of 40 min, the STB could remove up to 92% of DOC and 40-56% of T-N and T-P at an organic loading rate (OLR) of 2.4 kg COD/m(3) sponge day. This OLR is the best for the STB as compared to the OLRs of 0.6, 1.2 and 3.6 kg COD/m(3) sponge day. At 28 mL/min of flow velocity (FV), STB achieved the highest efficiencies with 92% of DOC, 87.4% of T-P, and 54.8% of T-N removal. Finally, at the optimal OLR and FV, the STB could remove almost 90% of organic and nutrient, significantly reduce membrane fouling with HRT of only 120 min.

The effect of disk rotational speed on oxygen transfer in rotating biological contactors

Lab-scale experiments using a synthetic wastewater were carried out to assess the influence of disk rotational speed on oxygen transfer rate in a RBC unit in the presence of biomass. The overall oxygen transfer coefficient (K(L)a) was computed. Five different disk rotational speeds were tested, in the typical RBC operating range (3-10 RPM). The soluble organic substrate was monitored through TOC analysis. Influent hydraulic organic loadings were in the range of 5.4-35.2 g TOC/m(2)d. The set of kinetic coefficients calculated fitting the experimental data by the selected model resulted in good agreement with the value reported in literature. A correlation for K(L)a as a function of disk rotational speed and disk diameter was obtained. Accordingly, a new expression of the enhancement factor of oxygen transfer was found, and compared to literature data.

Steady state model for evaluation of external and internal mass transfer effects in an immobilized biofilm

A steady model for the evaluation of external liquid film diffusion and internal pore diffusion effects in an immobilized biofilm system under continuous mode of operation was developed. The model takes into account, substrate diffusion through external liquid film and biofilm. Average rate of substrate consumption in the biofilm was considered. The overall efficiency of the biofilm was mathematically represented by considering the combined effects of substrate penetration and substrate utilization in the biofilm. The model was illustrated using a case study of pyridine biodegradation in a rotating biological contactor immobilized with pyridine degrading microbial film. The model is able to effectively predict both internal and external mass transfer effects in an immobilized biofilm system.

Electrochemical-assisted photodegradation of Allura Red and textile effluent using a half-exposed rotating TiO(2)/Ti disc electrode

In this work, a rotating photoelectrocatalytic (RPEC) reactor, using a half-exposed and half-immersed TiO(2)/Ti disc as photoanode was developed for the first time to degrade Allura Red (AR) and textile effluent. The TiO(2) film was characterised by X-ray reflection diffraction (XRD) spectra and field emission scanning electron microscope (FESEM). When AR solutions with concentrations ranging from 10 mg L(- 1) to 50 mg L(- 1)AR were treated by half-exposed disc PEC (EPEC) process for 1 hour, solution color and TOC were reduced by 36-54% and 19-33%, respectively, higher than reduction of 9-46% and 4-27% observed for the conventional PEC (CPEC) process with half TiO(2)/Ti disc immersed in solution. Similarly, solution color and TOC for textile effluent was reduced by 46% and 10% for EPEC process, respectively, higher than reduction of 26% and 2% for CPEC process. Effectiveness of the RPEC process was further demonstrated in the treatment of textile effluent and textile effluent containing 30 mgL(- 1) AR by determining change of solution color, total organic carbon (TOC), biochemical oxygen demand (BOD(5)), and chemical oxygen demand (COD). Furthermore, a long run experiment was carried out for the TiO(2)/Ti disc and almost stable photoactivity was found after 10 runs of RPEC oxidation of both AR and textile effluent. Our results indicate the proposed RPEC is effective in degrading textile wastewater, probably because the light can directly irradiate the exposed disc in air instead of through solution in the CPEC reactor.

TiO2/Ti rotating disk photoelectrocatalytic (PEC) reactor: a combination of highly effective thin-film PEC and conventional PEC processes on a single electrode

A TiO2/Ti rotating disk photoelectrocatalytic (PEC) reactor has been developed and successfully applied to degrade Rhodamine B (RB) and other dyes in textile effluents. The innovative concept behind the reactor design is to simultaneously perform two processes on one electrode. These two processes are (1) highly effective thin-film PEC, in which the upper half of the round disk photoanode was coated with a thin layer of wastewater and exposed to UV radiation in air; and (2) the conventional PEC, in which the other half of the disk was immersed in bulk wastewater and irradiated by the same light source. The average aqueous film thickness was about 75 microm. The disk electrode was kept rotating at 90 rpm to continuously refresh the thin aqueous film for the upper side of the electrode and to promote the mass transfer of the target pollutants and the degradation products on the lower part of the disk. Using 20-150 mg L(-1) RB solutions as a model system, thin-film PEC removed total color and total organic carbon (TOC) by 27-84% and 7-48%, respectively, within 1 h, much higher than 3-55% and 0-30% removal by conventional PEC under the same treatment conditions. Results also suggest that the thin-film process was especially superior for treating high concentration solutions. Application of the rotating disk PEC reactor in industrial textile effluents showed a satisfactory result. The recycle experiments demonstrated excellent stability and reliability of the rotating disk PEC electrode. This study proposed a new concept for designing a PEC reactor applicable to industrial wastewater treatment.