Side-stream Configuration Research Articles

Energy saving design and control of side-streams reactive distillation configuration for diphenyl carbonate production process

Diphenyl carbonate (DPC), a phosgene-free precursor for polycarbonate production, has traditionally undergone industrial production through a well-established two-step transesterification process by a reactive distillation (RD) and a distillation column. Thermal enhancement techniques in RD, such as thermally coupled (TCRD) and hybrid heat-integrated (HIRD) methods, have consistently demonstrated significant improvements in energy efficiency, eliminating remixing effect and reducing total annual cost (TAC) during DPC synthesis. However, the combination of TCRD or HIRD with a side-stream configuration (SS) remains relatively underexplored, particularly in the context of DPC production. This study aims to address this gap by proposing a novel combination of TCRD/HIRD, incorporating both a one side-stream (SS1-TCRD and SS1-HIRD) and a two side-streams configuration (SS2-TCRD and SS2-HIRD). Employing a sequential iterative procedure for optimization, the study sought to minimize TAC. Results unveiled SS2-HIRD as the optimal configuration, showcasing a remarkable 47.27% reduction in energy consumption and a 31.46% decrease in TAC. Moreover, four proposed control structures (CS1∼CS4) were implemented for SS2-HIRD to ensure both product quality and process safety. Among all structures, CS4 exhibited remarkable efficacy in managing disturbances in feed and composition throughput, demonstrating the smallest integral of the absolute error (IAE) value.

A dynamic control structure of liquid-only transfer stream distillation column

The intention of this fundamental work is to explore the manipulation of a mixture of benzene, toluene and o-xylene separated from liquid-only transfer divided-wall column (LTS-DWC). First, two control structures are clearly proposed, including seven component control loops (CS1) and seven temperature control loops (CS2). However, two control structures can handle ±10% feed disturbances rather than larger feed disturbances. Subsequently, an equivalent four-column model by introducing withdraw ratio is developed to discuss the effect of two liquid-only side-stream on the overall reboiler duty. It is indicated that the second liquid-only side-stream withdraw ratio strongly affects the overall energy consumption. Hence, six-component control loops within the fixed second liquid-only side-stream withdraw ratio (CS3) is proposed and the purity of products returns to set value even as facing ±20% feed disturbances. Finally, based on the above results, it is established a temperature control structure (CS4) for controlling fixed second liquid-only side-stream withdraw ratio, which can cope with ±15% disturbances. Inspired by these findings, an insight into the dynamic control of LTS-DWC promotes the industrial implementation of DWC through new liquid-only side-stream configurations.

Are process-intensified extractive distillation always energetically more efficient?

The thermally coupled, dividing wall column, and side-stream configurations are some of the energy-intensified techniques widely applied to the extractive distillation for improving the energy efficiency. Today, several heuristics are available for analysing the energy-saving efficiency of these intensified techniques for ideal distillation system but there is no heuristic available for analysing the complex distillations system. Therefore, it has not yet been established what variables affect the energy-savings and under what particular conditions the intensified processes for these complex distillation systems present energy-savings. In this work, we aim to provide insights and preliminary conclusions that open a field of study for a more detailed and in-depth analysis for future researches through three different case studies where their corresponding intensified configurations do not provide any energy-saving relative to the conventional extractive distillation (CED). Based on our preliminary analysis, we attributed this to the poor values of interconnecting flowrate or composition and high column internal vapour flowrate. Our results also revealed the possibility of extending several heuristics, previously developed for evaluating the energy-saving efficiency in ideal distillation system, for complex distillation. Lastly, several recommendations are given that were derived from our simulation results and the analyses we carried out on existing publications.

Concentration of Municipal MBBR Effluent by FO for Resource Recovery: Batch Experiments in Side-Stream Configuration.

A novel approach for resource recovery includes forward osmosis (FO) as a concentration step in municipal wastewater treatment. The current study investigates different pre-treatment strategies including biological treatment with a moving-bed bioreactor (MBBR) at different loading rates and particle removal by filtration and sedimentation. Membrane performance and recovery potential for energy and nutrients were investigated in laboratory-scale FO experiments in batch mode using pre-treated municipal wastewater as feed and 35 g/L NaCl as a draw solution. Initial water fluxes were in the range of 6.3 to 8.0 L/(m2·h). The baseline fluxes were modelled to account for flux decline due to concentration effects and to enable the prediction of flux decline due to membrane fouling. Fouling-related flux decline varied from 0 to 31%. Both organic fouling and precipitation of CaCO3 and CaHPO4 were identified by using SEM–EDS. High-rate flushing resulted in complete flux recovery under most conditions. Scaling could be avoided by lowering the pH. Two operation strategies were tested to achieve this: (1) applying a bioreactor with a low organic loading rate to achieve high nitrification, and (2) adding a strong acid. A low organic loading rate and the use of additional particle removal were efficient measures that reduced organic/particulate fouling. The recovery potentials for COD and phosphorous in FO concentrate were close to 100%.

High-solids thermophilic anaerobic digestion of sewage sludge: effect of ammonia concentration

High-solids thermophilic anaerobic digestion fed with sewage sludge of 7–8% and 9–10% total solids was investigated at the hydraulic retention time of 20 days in this lab-scale study. The anaerobic digester fed with 7–8% sewage sludge was successfully operated, resulting in volatile solids (VS) destruction of 57.8% and methane production of 0.327 L/gVS (at standard temperature and pressure). When fed with 9–10% sewage sludge, the control digester was upset after about 80 days of operation. Total ammonia nitrogen (TAN) of 2500 mgN/L or more caused inhibition to anaerobic microorganisms. Another digester combined with weekly batch ammonia stripping of digested sludge in a side-stream configuration (80 °C, 2 h, initial pH of 9 with NaOH and return ratio of 70%), was maintained at the average TAN of 1720 mgN/L, and was able to continue without ammonia inhibition. TAN was a better indicator on inhibition of ammonia than free ammonia nitrogen (FAN). Microbial analysis revealed poor microbial diversity of digested sludge, that is, Class Clostridia for Bacteria and Geneus Methanothermobacter and Methanosarcina for Archaea were predominated. In conclusion, high-solids thermophilic anaerobic digestion can accommodate the influent sewage sludge up to 10%, as far as TAN is properly controlled in digester.

Accurate real-time FENO expirograms using complementary optical sensors

The fraction of exhaled nitric oxide (FENO) is an important biomarker for the diagnosis and management of asthma and other pulmonary diseases associated with airway inflammation. In this study we report on a novel method for accurate, highly time-resolved, real time detection of FENO at the mouth. The experimental arrangement is based on a combination of optical sensors for the determination of the temporal profile of exhaled NO and CO2 concentrations. Breath CO2 and exhalation flow are measured at the mouth using diode laser absorption spectroscopy (at 2 μm) and differential pressure sensing, respectively. NO is determined in a sidestream configuration using a quantum cascade laser based, cavity-enhanced absorption cell (at 5.2 μm) which simultaneously measures sidestream CO2. The at-mouth and sidestream CO2 measurements are used to enable the deconvolution of the sidestream NO measurement back to the at-mouth location. All measurements have a time resolution of 0.1 s, limited by the requirement of a reasonable limit of detection for the NO measurement, which on this timescale is 4.7 ppb (2 σ). Using this methodology, NO expirograms (FENOgrams) were measured and compared for eight healthy volunteers. The FENOgrams appear to differ qualitatively between individuals and the hope is that the dynamic information encoded in these FENOgrams will provide valuable additional insight into the location of the inflammation in the airways and potentially predict a response to therapy. A validation of the measurements at low-time resolution is provided by checking that results from previous studies that used a two-compartment model of NO production can be reproduced using our technology.

Low-pressure submerged membrane filtration for potential reuse of detergent and water from laundry wastewater

Membrane filtration is an attractive for laundry wastewater treatment especially when aiming for detergent and water reuse. However, its performance is largely restricted by membrane fouling, especially when it is run under high and trans-membrane pressure (△P) and in the sidestream configuration. The conventional treatment systems typically consist of multi-processes for removal of pollutants -including detergent- to meet the water discharge or reuse specification. This study assesses performance of a submerged membrane filtration under low △P for treatment of real laundry wastewater, obtained from local laundry shop, aiming for detergent and water reuse. Results show that low △P of as low as 0.05 bar offers the highest permeability of 297 ± 15.3 Lm−2 h−1 bar−1 without significant membrane fouling. Increasing the △P leads to decreasing trend in the permeability especially in the early stages of filtration. Aeration was found to be effective in enhancing hydraulic performance by 60 % at rates >1 Lmin−1, below which offers ineffective foulant scouring impact. The membrane effectively removes chemical oxygen demand, total nitrogen, total phosphorus and turbidity of 52 %, 13 %, 65 % and 97 % respectively, and the system offers recovery of detergent from the spent laundry wastewater by 78 %. Implementation of the concept in a laundry set-up can be done by treating wastewater from the washing cycle and reusing back the permeate for the following cycle. Our overall results suggest that the system is suitable to be applied for detergent and water reuse from wash cycle of industrial laundry.

Eliminating the vapor split in dividing wall columns through controllable double liquid-only side-stream distillation configuration

The liquid-only transfer streams are sometimes preferred to replace the thermal coupling stream in distillation at similar energy efficiency for easier controllability. However, the dynamic controllability and practical control structures for such distillation configurations with liquid-only side-stream are still lacking. In search of a solution, this work investigates the dynamic performance of a double liquid-only side-stream process, which has the most complex structure but the lowest energy consumption among all possible liquid-only type ternary distillation configurations. With the aid of composition measurements, the control performances are generally well in case of adding feedforward controllers. Besides, the structure with only temperature controllers is also tested. On the occurrence of ±10% throughput and feed composition disturbances, the process is well-controlled with tiny product purity deviations. However, when the disturbances increase to ±20%, large offsets appear in some cases. To improve the effectiveness of the inferential control scheme, a modified structure with one internal composition controller is finally proposed to handle ±20% step changes. Overall, this work verifies well the easy controlling nature of the liquid transfer stream. The result of the work encourages the promotion of liquid-only side-stream configurations, as a competitive substitute of the well-known Petlyuk column or dividing wall column, for both academic and industrial purposes.

Anaerobic membrane reactor: Biomethane from chicken manure and high-quality effluent

Chicken manure was treated in a pilot scale reactor anaerobic membrane bioreactor constituted by a completely mixed reactor combined with an ultrafiltration tube-shaped membrane in a side-stream configuration. The process operated under mesophilic condition and the inhibition of high concentration of ammonia was avoided using an ammonia stripping system. The experimental plan included a preliminary evaluation, where organic loading rates between 1.0 and 7.6 kgVS/m3/day were tested. The organic load higher than 4 kgVS/m3/d caused the accumulation of volatile fatty acids and process instability. Application of the ammonia stripping was also evaluated. The best performances were achieved using a retention time of 21 days, an organic load between 1.4 and 2.0 kgVS/m3/d, and the recirculation of stripped permeate. Reduction of the ammonia permeate content by 90% through stripping and utilization of a mixture of chicken manure/water/permeate in a ratio of 0.22/0.72/0.72 w/w led to a specific biogas production of 0.59 m3biogas/kgVS and methane content of 66–69%. The ammonia thus removed can be recovered by sulphuric acid treatment as ammonium sulphate, which can be used as a fertilizer. The proposed configuration allowed satisfactory biogas production with appropriate methane percentages, recovery of ammonium sulphate, and a high-quality effluent.

Microbial desalination fuel cell using membrane bioreactor as a sludge supplier: comparison between immersed and side-stream configurations

Microbial desalination fuel cell using membrane bioreactor as a sludge supplier: comparison between immersed and side-stream configurations

New prospects for immersed hollow-fiber membranes in fruit juices microfiltration: Case of grapefruit juice

Side-stream tubular membranes are largely used to perform cross-flow microfiltration of fruit juices. However, this configuration presents well-known drawbacks (e.g. energy consumption). Immersed membranes configurations have been developed in many fields to overcome these disadvantages. This paper investigates for the first time the possibility of using immersed configuration for fruit juices microfiltration. Firstly, a lab-scale methodology was adopted to characterize the fouling propensity of the juice, while studying the impact of transmembrane pressure, membrane material and the role of large particles on the juice fouling behavior. Secondly, pilot-scale experiments were performed to identify the optimal operating conditions for both configurations. Both lab-scale and pilot-scale experiments suggested that the operating conditions of immersed configuration (no removal of large particles, low pressure and organic membranes) could be suitable to perform juice microfiltration. The optimal permeate flux of immersed configuration was in accordance with the ones reported in other fields. A productivity similar to the one related to side-stream configuration might be obtained through an increase of the filtration surface, made possible by the great packing density and low membrane cost related to immersed configuration. These findings offer new application for immersed membrane configuration in the microfiltration of delicate fruit juices.

Submerged or sidestream? The influence of module configuration on fouling and salinity in osmotic membrane bioreactors

The role of submerged and sidestream forward osmosis (FO) membrane module configuration in osmotic membrane bioreactors (OMBRs) was investigated. Experiments were performed under identical conditions (solids retention time, bioreactor volume, feed solution, draw solute, and draw solution concentration) to isolate the effect of FO module configuration and associated hydrodynamics on water flux, reverse salt flux, and membrane fouling. Steady-state water flux of fouled membranes was the same for submerged and sidestream configurations and two draw solution concentrations, leading to the concept of a homeostatic flux in OMBRs similar to the critical flux in conventional membrane bioreactors. For the 35g/L NaCl draw solution, specific reverse salt flux (SRSF) was 1.61 ± 0.01 and 0.59 ± 0.07g/L for submerged and sidestream configurations, respectively and for the 100g/L NaCl draw solution, SRSF was 2.22 ± 0.25 and 1.05 ± 0.35g/L for submerged and sidestream configurations, respectively. Despite a significant increase in driving force, fouled membranes did not have higher steady-state water flux; instead, the 100g/L draw solution resulted in greater membrane fouling; foulant cake layers were 2 to 4 times thicker, likely due to higher initial water flux that resulted in more foulants being transported to the membrane surface. Experimental results were used as model inputs to predict results for a larger scale system. Model results predicted lower steady-state bioreactor salinities in the sidestream configuration, particularly when longer solids retention times were used.

Osmotic Membrane Bioreactor for Oily Wastewater Treatment using External & Internal Configurations

The present work aims to study the treatment of oily wastewater by means of forward osmosis membrane bioreactor process. Side stream (external) configuration and submerged (internal) configuration of osmotic membrane bioreactor were performed and investigated. The experimental work for each configuration was carried out continuously over 21 days. The flux behavior of forward osmosis membrane in an osmotic membrane bioreactor (OMBR) was investigated, using NaCl as the draw solution and CTA as FO membrane. The effect of mixed liquor suspended solids (MLSS) concentration and TDS accumulation of bioreactor on water flux and membrane fouling behaviors was detected. The accumulation and rejection of nutrients in the bioreactor (Nitrate, COD, and Phosphate) were investigated over the days of the experiment. Water flux and membrane fouling were not significantly affected by MLSS concentration at low level and this effect increase with increasing MLSS concentration (4000–10000 mg/L). Besides, water flux was severely affected by elevated salinity of the aeration tank. OMBR showed high removal of COD (96%) and FO membrane revealed high retention of phosphate (97%) but retention for nitrate was relatively low (72%). The sparingly soluble salts in the influent, bioreactor, draw solution, and RO effluent were detected through the experiment. The results showed flux decline with time to about 47% from the initial flux and two osmotic backwashing were applied at day 7 and 14 during the operation and the flux restored approximately 30% of its loss. Side stream and submerged configurations revealed nearly similar response over the experiments while side stream module showed better water flux (7.0 LMH) than submerged (6.1 LMH). The results showed that the concentration of inorganic ions is below the limits that may cause severe scaling.

Mainstream Deammonification

The objective of this research was to investigate the feasibility of applying the deammonification concept, which is already highly successful and proven in sidestream configurations, in the mainstream treatment process. The deammonification process for nitrogen removal provides a more efficient biological pathway compared to traditional nitrification/denitrification. The demonstrated advantages of applying deammonification to mainstream treatment include energy-neutral or even energy-positive wastewater treatment, reduction of aeration energy, and reduction in external carbon and alkalinity demands. Implementation of mainstream deammonification is compatible with existing wastewater infrastructure, often with minimal modifications. The successful application of full-plant deammonification could save wastewater utilities operations costs for aeration and external carbon costs in the life cycle. Through demonstration and conceptual application at collaborating utilities, this research develops an evaluation framework for implementing full-plant deammonification.Deammonification is a two-step biological process where ammonia-oxidizing bacteria (AOB) aerobically convert half of the ammonia present in the wastewater to nitrite. In the second step, anammox bacteria oxidize the ammonia using nitrite to produce nitrogen gas without the organic carbon substrate required for conventional heterotrophic denitrification. Deammonification requires significantly less oxygen and so less energy is needed for nitrogen removal. Deammonification requires no external carbon addition, eliminating chemical purchases such as methanol. Process configurations using mainstream deammonification maximize energy recovery by diverting more particulate organic carbon away from the nitrogen removal process and directing it toward anaerobic treatment from which methane can be captured. The implications of deammonification for sustainable, cost effective and energy positive wastewater treatment are extraordinary.The report discusses application of short-cut nitrogen removal which includes nitritation-denitritation, in which ammonia oxidation ends at the intermediate nitrite, with the mainstream deammonification pathway. Both short-cut nitrogen removal pathways result in savings in energy, carbon and alkalinity over conventional nitrification-denitrification. To be successful, short-cut nitrogen removal strategies require maximizing AOB activity, while preventing the establishment of the nitrite oxidizing bacteria (NOB) that oxidize nitrite to nitrate and this report introduces and develops concepts for NOB out-selection.To progress from nitritation-denitritation to deammonification, the AOB activity must be controlled to oxidize only half of the influent ammonia to nitrite, and a method of retaining the slow-growing anammox bacteria must be implemented. The report presents a progressive pathway from conventional nitrification-denitrification to short-cut nitrogen removal and discusses a framework of conditions and drivers for implementation.The research concludes that mainstream deammonification can be achieved. It is possible for wastewater treatment plants to retrofit to short-cut nitrogen removal utilizing existing infrastructure, often with minor modifications. The research revealed key site-specific drivers for applying short-cut nitrogen removal technology.This title belongs to WERF Research Report SeriesISBN: 9781780407852 (eBook)

Start-up and operation of an AnMBR for winery wastewater treatment

A sidestream anaerobic membrane bioreactor (AnMBR) was started up and operated under organic load oscillations in order to determine its feasibility for winery wastewater treatment. The stable operation was assured by keeping a ratio between intermediate alkalinity and total alkalinity below 0.4 and the specific organic loading rate below the methanogenic activity (0.3kgCODkgMLSS−1d−1) achieving a 96.7±2.7% chemical oxygen demand (COD) removal efficiency. The maximum organic loading rate (OLR) achieved was 3.4kgCODm−3d−1. The biogas production varied according with the OLR that was on average 0.50±0.17m3biogasm−3digesterd−1 with an 87.1±3.0% of methane. The external membrane module reached a flux of 20.2±8.5LMH operating at a mixed liquor suspended solids concentration of 4.78±1.9gL−1 and a crossflow velocity of 0.64ms−1. The crossflow velocity helped to remove the cake layer attached on the membrane that was the main contribution (>80%) to flux decline. The energy balance of the AnMBR revealed that a sidestream configuration would be a feasible option during vintage season.

Development and testing of a fully adaptable membrane bioreactor fouling model for a sidestream configuration system.

A dead-end filtration model that includes the three main fouling mechanisms mentioned in Hermia (i.e., cake build-up, complete pore blocking, and pore constriction) and that was based on a constant trans-membrane pressure (TMP) operation was extensively modified so it could be used for a sidestream configuration membrane bioreactor (MBR) situation. Modifications and add-ons to this basic model included: alteration so that it could be used for varying flux and varying TMP operations; inclusion of a backwash mode; it described pore constriction (i.e., irreversible fouling) in relation to the concentration of soluble microbial products (SMP) in the liquor; and, it could be used in a cross flow scenario by the addition of scouring terms in the model formulation. The additional terms in this modified model were checked against an already published model to see if they made sense, physically speaking. Next this modified model was calibrated and validated in Matlab© using data collected by carrying out flux stepping tests on both a pilot sidestream MBR plant, and then a pilot membrane filtration unit. The model fit proved good, especially for the pilot filtration unit data. In conclusion, this model formulation is of the right level of complexity to be used for most practical MBR situations.

Upgrading of submerged membrane bioreactor operation with regard to soluble microbial products and mathematical modeling for optimisation of critical flux

Abstract Recent studies have shown that the colloidal and soluble fraction of the sludge (sludge water) correlates well with Membranes Bioreactor (MBR) fouling. Soluble microbial products (SMP) are the main constituent of MBR sludge water. However, it is not clear how to predict the foulant concentrations, how foulants are deposited onto the membrane, and how to predict the impact of deposited foulants on membrane permeability. The goal of this paper was therefore to characterize the foulants in MBRs and to develop a mathematical model to predict both membrane fouling and effluent quality. The focus of this study is the interaction between the MBR biology, membrane fouling and the optimum critical flux for the treatment of a municipal wastewater was determined. A lab-scale MBR reactor was constructed for biological nutrient removal, equipped with a tubular membrane in side-stream configuration. Laboratory scale tests were performed at two sludge retention time conditions: 15 and 40 d, respectively, while ...

Modelling the energy demands of aerobic and anaerobic membrane bioreactors for wastewater treatment

A modelling study has been developed in which the energy requirements of aerobic and anaerobic membrane bioreactors (MBRs) are assessed in order to compare these two wastewater treatment technologies. The model took into consideration the aeration required for biological oxidation in aerobic MBRs (AeMBRs), the energy recovery from methane production in anaerobic MBRs (AnMBRs) and the energy demands of operating submerged and sidestream membrane configurations. Aeration and membrane energy demands were estimated based on previously developed modelling studies populated with operational data from the literature. Given the difference in sludge production between aerobic and anaerobic systems, the model was benchmarked by assuming high sludge retention times or complete retention of solids in both AeMBRs and AnMBRs. Analysis of biogas production in AnMBRs revealed that the heat required to achieve mesophilic temperatures (35°C) in the reactor was only possible with influent wastewater strengths above 4–5 g COD L−1. The general trend of the submerged configuration, which is less energy intensive than the sidestream configuration in aerobic systems, was not observed in AnMBRs, mainly due to the wide variation in gas demand utilized in anaerobic systems. Compared to AeMBRs, for which the energy requirements were estimated to approach 2 kWh m−3 (influent up to 1 g COD L−1), the energy demands associated with fouling control in AnMBRs were lower (0.80 kWh m−3 for influent of 1.14 g COD L−1), although due to the low fluxes reported in the literature capital costs associated with membrane material would be three times higher than this.

Development of an integrated shipboard wastewater treatment system using biofilm-MBR

An integrated shipboard wastewater treatment system using a biofilm-MBR process is developed, where the objective is to include the bilge water effluent with the treatment of black/grey wastewater for enhanced treatment and potential reuse of all wastewater streams on ships. The KeraNor flat sheet ceramic membrane modules were developed and applied in the biofilm-MBR process with recycle side-stream configuration. The operating parameters, such as hydraulic retention time, influent oil concentration, organic shock load, influent salinity were investigated. It is found that the biofilm reactor combined with membrane filtration is a suitable process for shipboard wastewater treatment. The treatment capacity of the biofilm-MBR can be increased up to 160 mg/L influent fuel oil concentration and even higher (400 mg/L influent oil in shock load test) in HRT 8 h. Results indicate that serious membrane fouling always correlates with high FCOD and SMPs values in the concentrate solution around the membrane for biofilm-MBR process.

Development of a biofilm-MBR for shipboard wastewater treatment: The effect of process configuration

The direct discharge of wastewater from ships is prohibited by the International Maritime Organization, especially discharge of oily bilge water. This study aims to develop a compact onboard integrated wastewater treatment system for all the wastewater streams on ships, including grey water, black water and bilge water, using biofilm-MBR technology. Both dead-end side-stream and recycle side-stream configurations of a biofilm-MBR concept have been investigated. Flat sheet ceramic membranes from KeraNor AS were applied in the membrane filtration unit. A good membrane permeate quality was achieved in each process configuration, with oil concentrations < 5 mg/L. However, the membrane was seriously fouled when the dead-end side-stream configuration was operated with a high filtration unit recovery (93%). A significantly improved membrane performance, and better permeate quality, was achieved by recycling the concentrate solution back to the biofilm reactor due to better bio-flocculation and biodegradation of oil compounds in the process. The effect of process configuration was investigated by comparing oil concentration, SMP, TSS, FCOD, TCOD, PSD of the concentrate solutions around the membrane in filtration unit. The membrane fouling rate was found to be directly related to oil concentration and oily biomass characteristics in the membrane filtration unit.