MLSS Concentration Research Articles

A comparative study on the chronic responses of titanium dioxide nanoparticles on aerobic granular sludge and algal-bacterial granular sludge processes.

The chronic effects of titanium dioxide nanoparticles (TiO2 NPs) on aerobic granular sludge (AGS) and algal-bacterial granular sludge (ABGS) was examined in this study. Sequencing batch bioreactors (SBRs) and photo sequencing batch bioreactors (PSBRs) were operated with synthetic wastewater containing 0, 1, 5, 10, 20, 30, and 50mg L-1 TiO2 NPs for 10days. Nanoparticles at concentrations of 1 and 5mg L-1 did not impact nutrient removal but led to an increase in extracellular polymeric substances (EPSs), primarily in protein (PN). With increasing nanoparticle concentration, the negative effect became more pronounced, mainly in the AGS SBRs. At 50mg L-1 TiO2, chemical oxygen demand (COD), ammonia-nitrogen (NH3-N), and phosphorus (PO43-) removal decreased by 20.9%, 12.2%, and 35.1% in AGS, respectively, while in ABGS, they reached only 13.4%, 5.7%, and 14.2%. ABGS exhibited steady-state nutrient removal at 30 and 50mg L-1 TiO2 NPs after around 5days. The higher microbial activity and EPS content in the sludge, coupled with the symbiotic relationship between algae and bacteria, contributed to the higher tolerance of ABGS to nanoparticles. Finally, although nanoparticles reduced biomass in both types of bioreactors, the accumulation of TiO2 NPs in the sludge, confirmed by Energy-dispersive X-ray spectroscopy analysis, and the absence of detectable titanium concentrations in the effluent wastewater, measured by Inductively-coupled plasma mass spectrometry, may be attributed to the specific operational conditions of this study, including the relatively short operation period (10days) and high initial MLSS concentration (6g L-1).

Critical flux-based fouling control method for forward osmosis during simultaneous thickening and digestion of waste activated sludge

The use of forward osmosis (FO) membranes for simultaneous thickening and digestion of waste activated sludge (WAS) (FO-MSTD) has recently garnered significant interest. However, a major challenge hindering the widespread adoption of the FO-MSTD process is severe membrane fouling, which results from increasing sludge concentrations and deteriorating sludge properties. In response, this study proposes a novel FO membrane fouling control strategy based on the critical flux concept, involving a variable draw solution (DS) operating mode. Two operating modes were examined based on the critical flux behavior of the FO membrane: a constant DS concentration mode (with a fixed DS concentration of 1.5 M, referred to as Constant DS1.5) and a variable DS concentration mode (with varying DS concentrations at different operational stages, referred to as Variable DS1.5-1.0 and Variable DS1.5-0.75). Over 21 days of operation, the MLSS concentrations of WAS in the Constant DS1.5, Variable DS1.5-1.0, and Variable DS1.5-0.75 reactors increased from initial values of 3.46, 3.88, and 4.20 g/L to 35.2, 31.5, and 29.2 g/L, respectively. Concurrently, the cumulative digestion rates of MLVSS in the three FO-MSTD processes reached 29.3 %, 29.0 %, and 36.3 %, respectively. After adjusting the DS concentration, the FO membrane flux decay rates for Constant DS1.5, Variable DS1.5-1.0, and Variable DS1.5-0.75 were 57.7 %, 49.4 %, and 13.8 %, respectively. In addition to experiencing a lower flux decline, the Variable DS1.5–0.75 mode achieved a significantly higher flux recovery rate of 98.5 % compared to the other two modes. Moreover, the biovolume of proteins and microorganisms in the membrane fouling layer decreased by 85.2 % and 72.7 %, respectively, in the Variable DS1.5–0.75 mode compared to the Constant DS1.5 mode. These findings indicate that operating with a DS below the critical concentration can significantly improve the reversibility of membrane fouling and reduce the presence of organic and biological foulants in the fouling layer, thereby mitigating membrane fouling in the FO-MSTD reactor.

Modeling of the Full-Scale Secondary Sedimentation Basin Using the GPS-X Model

The secondary sedimentation basin is being modeled in this study for the first time using the GPS-X model instead of the computational fluid dynamics (CFD) model. This study was conducted in the extended-aeration Al-Hur treatment plant that struggles with unstable sedimentation in its sedimentation tank. After collecting and entering the data into the GPS-X model, the model was calibrated and validated, and the results were statistically examined based on R and RMSE. To determine the efficiency of the sedimentation tank, the following scenarios were investigated: 1) testing the efficiency in removing pollutants; 2) conducting state point analysis (SPA); and 3) measuring the concentration of sludge in the layers of the sedimentation basin. Six factors were considered during the sensitivity analysis, namely sludge volume index (SIV), surface area, underflow rate (RAS), pumped flow (WAS), maximum settling velocity, and liquid temperature. The calibration and validation results were within the specified limits, and the secondary sedimentation basin demonstrated high efficiency in removing pollutants, with the analysis point (SPA) obtaining the highest MLSS concentration of 3000 mg/L. The sludge concentrations in the lower layers were 7000 mg/L, while those in the upper layer were 18 mg/L. These results suggest that a lower (100 ml/g) sludge volume index corresponds to a better sedimentation basin efficiency. Increasing the surface area of sedimentation basins can positively affect their efficiency, while increasing waste-activated sludge, maximum settling velocity, and liquid temperature may reduce pollutants and improve the sedimentation process. The GPS-X model is demonstrated as an excellent tool for understanding and predicting the work behavior of sedimentation basins, making this model particularly valuable for the management of sewage treatment plants. Doi: 10.28991/CEJ-2024-010-09-017 Full Text: PDF

Study on the effect and regularity of plating parts cleaning wastewater by enhanced aerobic process with high-density bacterial flora

In this research, we established an enhanced aerobic biological method utilizing a high-density bacterial flora for the treatment of low-biochemical plating parts washing wastewater. The elucidation of pollutant removal mechanisms was achieved through a comprehensive analysis of changes in sludge characteristics and bacterial community structure. The results demonstrated that throughout the operational period, the organic load remained stable within the range of 0.01–0.02 kgCOD/kgMLSS·d, the BOD5/COD ratio increased from 0.004 mg/L to 0.33 mg/L, and the average removal rates for key pollutants, including COD, NH4+-N, and TN, reached 98.13%, 99.86%, and 98.09%. MLSS concentration remained at 7627 mg/L, indicating a high-density flora. Notably, Proteobacteria, Bacteroidota, and Acidobacteriota, which have the ability to degrade large organic molecules, had been found in the system. This study affirms the efficacy of the intensive aerobic biological method for treating low-biochemical plating washing wastewater while ensuring system stability.

Dynamic α-factor models for fine-bubble- and surface aeration – impact of settleability and implications on N2O emission

In water resource recovery facilities (WRRF), aeration efficiency and N2O greenhouse gas emission are affected by the variability of the α-factor. Dynamic calibration of α using sensor data represents a significant knowledge gap this contribution aims to address. To assess factors influencing oxygen and N2O gas mass-transfer, a continuous flow laboratory-scale reactor system was operated to encourage the proliferation of filamentous bacteria. Gas mass-transfer was assessed using fine-bubble and surface aeration. Significant impacts of solid settling velocity on the α-factor – relative to that by MLSS concentration – is obtained. The feasibility of using solid settling velocity and concentration, as α-factor predictors, is tested. The theoretical approach of using relative diffusivity to dissolved oxygen – as an effective predictor of N2O liquid–gas mass-transfer stripping – is experimentally validated, for the first time. Plant-wide WRRF simulations show that surface aeration is inferior to fine-bubble aeration in terms of greenhouse gas emission and treated water quality.

Modification and Performance of a Rotating Biological Contactor for the Rectification of Synthetic Auramine O dye Wastewater

The disposal of domestic and industrial wastewater into the drainage/atmosphere without treatment is a major source of pollution that endangers the health of the population and needs to be controlled. Despite long been used as a secondary treatment strategy for wastewater, conventional rotating biological contactor (RBC) suffers from the drawbacks of limited surface area for the growth of biofilms. There are persistent problems of less oxygenation capacity, and inefficient mixing resulting in inadequate mass transfer. To address these issues conventional RBC has been modified in the present study by replacing a bank of discs using a rotating drum. The use of a rotating drum in RBC enhanced the biofilm attachment surface area up to 2.29 m2 (?108.2% higher than conventional RBC), thereby improving the working performance. To prevent the dissolved oxygen as a limiting factor, four small aerators were placed as supplement aeration system in the wastewater collection tank of modified RBC. To prevent the influence of atmospheric temperature on biological process, a blast-proof aquarium glass heater was placed in the tank. For experimental work, a 700 ppm pretreated synthetic solution of Auramine-O dye as wastewater was utilized. A constant level of percentage variation in biological oxygen demand (BOD) removal efficiency was observed after 15 days of the experiment. After day-15, the MLSS concentration increased to 2960 mg/L, and the BOD concentration reduced to 12.85 mg/L, resulting in a reduction of 89.86% in BOD, indicating the meeting of effluent discharge standards.

Exploring the application of the hybrid nano-bioreactor technology based on the developed polyethersulfone mixed-matrix membrane for industrial effluent treatment

Due to the high concentration of various contaminants in the paper mill effluent, it must undergo an efficient treatment process before being discharged to the environment or being reused in the production cycle. In the present study, the submerged membrane adsorption bioreactor (SMABR) system was used for the treatment of the paper mill effluent. The modified polyethersulfone PES/MoS2 membrane was fabricated by incorporating exfoliated MoS2 nanosheets prepared in the laboratory, into the PES matrix. This membrane along with the powdered activated carbon (PAC) were utilized in the SMABR system for the paper mill effluent treatment. After the acclimation of the sludge with the target effluent, the optimum values of food to microorganism (F/M), hydraulic retention time (HRT), and adsorbent dosage were determined separately to be 0.451, 18 h, and 3 g/L by considering the maximum values of chemical oxygen demand (COD) removal and mixed liquor suspended solid MLSS concentration in each stage. In the final stage, the MBR and SMABR systems (using the pristine and modified membranes, separately) were prepared to separately investigate the effect of the presence of the PAC adsorbent and modified membrane, on the output parameters. In all systems, the values of pH and dissolved oxygen (DO) were maintained in the normal range (pH: 6.2–6.7, DO>2) to provide favorable conditions for the growth of microorganisms. Most importantly, best performance in this study was related to the SMABR system consisting the PES/MoS2 membrane and PAC adsorbent, with the highest values of COD removal (96%), MLSS concentration (15620 mg/L), and membrane permeation flux (110 L/m2.h). It is worth mentioning that the functionalized membrane exhibited better hydrophilicity compared with the pristine membrane, resulting in high water permeation flux, which is in accordance with the performance results.

Mechanistic assessment reveals the significance of HRT and MLSS concentration in balancing carbon diversion and removal in the A-stage process

Nowadays, the shift toward energy and resource-efficient wastewater treatment plants (WWTPs) has become a necessity rather than a choice. For this purpose, there has been a restored interest in replacing the typical energy and resource-extensive activated sludge process with the two-stage Adsorption/bio-oxidation (A/B) configuration. In the A/B configuration, the role of the A-stage process is to maximize organics diversion to the solids stream and control the following B-stage's influent to allow for the attainment of tangible energy savings. Operating at very short retention times and high loading rates, the influence of the operational conditions on the A-stage process become more tangible than typical activated sludge. Nonetheless, there is very limited understanding of the influence of operational parameters on the A-stage process. Moreover, no studies in the literature have explored the influence of any operational/design parameters on the Alternating Activated Adsorption (AAA) technology which is a novel A-stage variant. Hence, this article mechanistically investigates the independent effect of different operational parameters on the AAA technology. It was inferred that solids retention time (SRT) shall remain below 1 day to allow for energy savings up to 45% and redirecting up to 46% of the influent's COD to the recovery streams. In the meantime, the hydraulic retention time (HRT) can be increased up to 4 h to remove up to 75% of the influent's COD with only 19% decline of the system's COD redirection ability. Moreover, it was observed that the high biomass concentration (above 3000 mg/L) amplified the effect of the sludge poor settleability either due to pin floc settling or high SVI30 which resulted in COD removal below 60%. Meanwhile, the concentration of the extracellular polymeric substances (EPS) was not found to be influenced or to influence process performance. The findings of this study can be employed to formulate an integrative operational approach in which different operational parameters are incorporated to better control the A-stage process and achieve complex objectives.

High-rate activated sludge at very short SRT: Key factors for process stability and performance of COD fractions removal

In high-rate activated sludge (HRAS) processes, reducing the solid retention time (SRT) minimizes COD oxidation and allows to obtain the maximum energy recovery. The aim of this research was to operate a pilot plant with an automatic control strategy to assure the HRAS process stability and high COD fractions removal at very low SRT. This study combines simulation and experimental tools (pilot plant 35 m3·d − 1) operating at SRT (0.2 d), HRT (0.6 h) and DO (0.5 mg·L − 1) treating high-strength raw wastewater, at 18–26°C, at variable flow. The research includes the effects of temperature, influent concentration and MLSS reactor concentration over the sCOD, cCOD and pCOD removal.The study points out that the best parameter to control the HRAS at a low SRT is not strictly the SRT but rather the reactor MLSS concentration: operating at 2,000±200mg·L − 1 assured a stable process despite the large influents variation. Low SVI values of 50–70ml·g − 1 indicated the good settling properties of the biomass. With only a 6.9% COD oxidation, a high organic matter removal (57±9% for COD and 56±10% for BOD5), was reached. The high removal efficiencies for pCOD (74%) compared to the (29%) for sCOD and (12%) for cCOD also confirmed the importance of settling efficiency and stability in the HRAS. The direct correlation between COD influent and COD removal makes advisable to use the HRAS as a replacement of the primary clarifier. The HRAS acted efficiently as a filter for COD and pCOD peak loads and, in a lesser extent, for BOD5, while sCOD peaks were not buffered. The adopted model presented a good fit for COD fractions except for pCOD when the temperature exceeds 23 °C.

Treatment of Dairy Wastewater with Pretreatment Techniques and Sequencing Batch Reactor for the Removal of Pollutants: Kinetics and Optimization

In order to remove pollutants like BOD, COD, TKN, TP, TSS, sulphates, chlorides, oil and grease effectively, this study outlines the treatment of dairy effluent by employing the advanced oxidation process (AOP) as pretreatment method with a sequencing batch reactor. It also describes the impact of aeration time and bacterial mass concentration (MLSS) in the sequencing batch reactor for pollutant removal. The high percentage of nutrient contents can be removed by the sequencing batch reactor (SBR), which only needs a single tank for the entire treatment procedure. The pretreatment technique of a combination of ozone and AOP was introduced into the dairy effluent to increase the removal efficiency of pollutants. In this research, the optimal conditions for ozone were a pH of 10, a reaction time of 5 minutes, and an amount of H2O2 of 10 mL/L. The experiments were conducted in the 4 L Plexiglas reactor and the analysis was carried out for different aeration times of 4, 6, 8, 12, 16 and 24 h at the different MLSS concentrations of 2100, 2400, 2900, 3200, 3700 and 4200 mg/L after the addition of ozone and hydrogen peroxide. In this analysis, the higher percent removal of BOD, COD, TKN, TP, TSS, sulphates, chlorides, oil and grease was obtained for the MLSS of 2100 mg/L at the aeration time of 16 h. The percent removal of above pollutants for the above MLSS concentration was in the order of 99.8%, 99.6%, 76.7%, 99%, 99.3%, 34%, 46% and BDL, respectively. The GC-MS analysis was carried out to find the level of contaminants present in the raw and treated water. Further, the sludge analysis was done for the wasted sludge to find its characteristics and its uses. This study suggests that at low MLSS concentrations, a large percentage of pollutants can be removed.

Enrichment of anammox sludge by using an Internal Circulation Reactor innoculated with anaerobic granular sludge and old landfill leachate

In recent years, anammox has not only economic benefits but also potential for wastewater treatment containing ammonium and low organic carbon. Along with breakthroughs ammonium treatment in the world, anammox process in internal circulation reactor (IC) is a new technology being researched and developed in high-load ammonium treatment. There In this study, an laboratory scale IC was used to enrich anammox sludge by seeding anaerobic granular sludge and feeding old leachate from the Go Cat municipal solid waste landfill. The seed sludge, which was anaerobic granular sludge taken from an UASB reactor of an industrial wastewater treatment plant was innoculated to IC at MLSS and MLVSS concentrations of 55.1 g.L-1 and 45 g.L-1, respectively, equivalent to the MLVSS:MLSS ratio of 0.82. Since 80 days of operation, the sludge in the IC was divided into two separate zones: a granular zone at the IC bottom part and the floc zone in the upper part. The average total nitrogen (TN) removal efficiency was 45% at nitrogen loading rate 0.4 – 0.6 kg N. m-3.day. The SAA of floc sludge and granular sludge on day 61, increased 6 and 8 times compared to thosed on day 27. The study illustrated that the enrichment of anammox sludge took a long time and granulation in the IC reactor was an important operating factor for anammox growth.

Improving nitrogen and phosphorus removal and sludge reduction in new integrated sewage treatment facility by adjusting biomass concentration

Aiming at the practical problem of rural wastewater and excess sludge treatment difficulties, micro-pressure swirl reactor (MPSR) was employed to carry out the experiment on the treatment of sewage under five different biomass concentration (MLSS concentration) conditions (4.14, 6.05, 7.98, 11.45, 14.46 g/L). The results showed that the nitrogen removal and phosphorus removal and sludge reduction performance of the system showed an increase and then a decrease with increasing MLSS concentration, and 7.98–11.45 g/L was the optimal MLSS concentration range. In addition, parameters related to in situ sludge reduction were further examined, and the extracellular polymeric substance content and sludge dehydrogenase activity were negatively and positively correlated with sludge reduction, respectively. According to the microbial analysis, at suitable MLSS concentration, beneficial microorganisms (Tetrasphaera, Aeromonas, Candidatus_Competibacter) were enriched in the MPSR to facilitate the nitrogen and phosphorus removal and sludge reduction of the system. In addition, the potential gene(nirK, norB, nosZ) functions of the microorganisms were positively regulated. The increase in the expression abundance ratio of dissimilatory and anabolic nitrate reduction genes played a positive role in denitrification and sludge reduction of the system.

UV/iodide advanced reduction process and biological treatments to ofloxacin photo-degradation and mineralization: influence parameters, kinetic, degradation pathway, energy consumption and toxicology

ABSTRACT The degradation of ofloxacin (OFL) by ultraviolet (UV) radiation in the presence of iodide was studied as an advanced reduction process (ARP), and followed resulting effluents were biodegraded for further mineralisation in the biological treatment. About 100% degradation of OFL was obtained under the selected condition (OFL: Iodide molar ratio of 2:1 and pH 9.0) after 20 min reaction time. In UV/Iodide ARP, the obtained range for reaction rate constant (k obs) and reaction rate (r obs) were from 0.311 to 0.039 min−1, and from 15.55 to 7.94 mg/L.min, respectively. The calculation of the energy consumption (using kinetic model) indicated with increasing OFL concentration from 50 to 200 mg L−1, the amount of energy consumption increases from 0.905 to 7.09 kW per cubic metre of treatment (also it was observed increase from 0.91 to 6.29 kW per cubic metre of treatment using IUPAC model). Intermediate (I) products and possible photodegradation pathways of OFL in the UV/Iodide ARP effluent were analysed after 30 min using GC-MS. Investigations showed after 30 min, most of the intermediates were converted to simple linear compounds such as acrylic acid (I6: C3H4O2), formic acid (I9: CH2O2) and acrylaldehyde (I10: C3H4O), that finally mineralised to CO2, H2O, NH4+ and NH3. Modified Kirby-Bauer disc diffusion test (applied to investigation of bacterial inhibition) was reduced from 33 mm (in initial concentration of OFL without treatment) to 9 mm (after 30 min of reaction). The UV/Iodide effluent reduced the COD by 40.9% after 30 min of reaction. When the biological reactor as post-treatment was operated at a concentration of MLSS 1000 mg L−1, the COD removal efficiency reached to 65.28% (121 to 42 mg L−1) within 11 h. However, by increasing the amount of MLSS to 3000 mg L−1, the COD removal efficiency reached to 84.09% (from 176 to 28 mg L−1) and at the 5000 mg L−1 of MLSS, the COD removal efficiency was 91.52% (from 236 to 20 mg L−1). It can be concluded from this study, although, the UV/Iodide ARP was very effective in breaking down OFL molecules, but it is not cost-effective due to the high time and cost of mineralisation. Therefore, application of the biological reactors as a post-treatment method after UV/Iodide ARP, due to cost-effective, environmentally friendly and the ability to degrade the intermediates produced can be useful.

MBR반응조내의 수리학적 거동이 막여과에 미치는 영향

The purpose of this study is to investigate the effects of hydraulic behavior on membrane fouling and filtration in an aerobic membrane bioreactor (MBR). Aeration as hydraulic behavior parameter is required in an aerobic MBRs for providing dissolved oxygen (DO) to microbes, making the sludge flocs in a suspended state and mitigating membrane fouling. Membrane stirring-cell (effective volume of 500 mL) was used as an aerobic MBR which was filled with real mixed liquor suspended solid (MLSS, <7000 mg/L) taken from real activated sludge tank. When applying stirring rate (<600 rpm) for MBR, a high stirring rate and low MLSS concentration have achieved a relative low TMP build-up. Permeate flux of membrane decreased with the increase of MLSS concentration, whereas it increased with the increase of stirring rate. This indicates that a high hydraulic shear force on the surface of membrane due to rapid stirring rate results in the mitigation of membrane fouling due to detachment of particulate and dissolved organic matter generated from sludge. The above results indicate that a suitable hydraulic shear force and MLSS level in an aerobic MBR should be considered to be cost-effective operation of an aerobic MBR due to the mitigation of membrane fouling.

Dynamic modeling of a full-scale membrane bioreactor performance for landfill leachate treatment.

Leachate treatment is crucial in landfill management. As landfill ages, inert constituents and ammonia nitrogen concentration in leachate increases, which results in a decrease in biological treatability. In this study, a full-scale MBR treating leachate was dynamically modeled using ASM1. The investigated landfill has been serving for more than 25years; thus, a decrease in biodegradable organic content and an increase in nitrogen content of the leachate is expected in the years ahead. The calibrated model predicted MLSS, effluent COD, and effluent TN concentrations with high accuracy. Following the calibration study, it was found that soluble inert COD and soluble inert organic nitrogen fractions were the primary reasons ofhigh COD and TKN concentrations in the effluent, respectively. The validated model of the full-scale MBR system treating leachate can be a useful tool to understand the limitations of the system. Soluble inert constituents of the leachatethat pass through the membranenecessiate additional treatment processesfor discharge into surface water bodies.

A COMPARATIVE STUDY ON TREATMENT OF CETP WASTEWATER USING SBR AND SBR-IFAS PROCESS

The wastewater generated from industries needs to be treated before discharge but ETPs are not affordable and hence the common effluent treatment plant was provided for collectively treating wastewater from various industries. The existing treatment methods used for such wastewater are costly and hence the present study focusses on using biological method for treating pre-treated mixed industrial wastewater from CETP using a sequencing batch reactor (SBR) with suspended biomass and an SBR-IFAS, a combined suspended and attached growth process at an HRT of 10 hours. After treatment with SBR technology, the maximum COD removal efficiency obtained was 68.69% at an MLSS concentration of 2756 mg/L. Similarly, for the SBR-IFAS reactor, the COD removal efficiency reached 75.51% at an MLSS concentration of 2846 mg/L. MLVSS obtained was 1395.00 mg/L in SBR and 1433.00 mg/L in SBR-IFAS. Chromium removal reached 62.85% and 66.67% in SBR and SBR-IFAS reactors, respectively. The study revealed that the attached growth media and suspended growth media combinedly resulted in a higher reduction in industrial wastewater treatment and can ultimately help reduce the volume of the secondary treatment at CETP by increasing the footprint of the treatment plant.

Simultaneous shortcut nitrification and denitrification in a hybrid membrane aerated biofilms reactor (H-MBfR) for nitrogen removal from low COD/N wastewater

The residues of nitrogen contaminants due to insufficient organic carbon sources in sewage has always been the main problem faced by wastewater treatment plants in the process of nitrogen removal. In this study, simultaneous shortcut nitrification and denitrification (SND) was achieved in the hybrid membrane aerated biofilm reactor (H-MBfR) for treating low COD/N ratio (∼x223C 4: 1) wastewater. The effects of the aeration pressure and the influent COD/N ratio in H-MBfR were investigated and further optimized by the response surface methodology (RSM). By controlling the dissolved oxygen to achieve SND, the removal efficiencies of NH4+-N, COD and TN of low COD/N ratio wastewater reached maximum values of 95.52%, 96.61% and 72.23%, respectively. Microbial community analysis showed that the influent COD/N ratio had an obvious influence on the microbial community structure. In particular, ammonia oxidizing bacteria (AOB) and denitrifying bacteria had a good commensalism when the COD/N ratio was 4.3. Compared to control reactor, the analysis of membrane bio-fouling showed that H-MBfR has a lower amount of extracellular polymeric substance (EPS) on membrane and a low concentration of MLSS in bulk liquid, which is helpful for the longer-term operation of H-MBfR.

Determination of kinetic coefficients for treating synthetic oily wastewater in suspended growth batch fed reactor.

Discharge of oily wastewater imparts serious threat to the environment because of high level concentration of chemical oxygen demand (COD), biochemical oxygen demand (BOD) as well as oil and grease and it is difficult to treat such wastewater due to its inherent toxic and inhibitory property. A treatability study of oily wastewater (carrying petroleum) has been performed in the present work using a batch suspended growth reactor. The experiment was conducted using acclimatized suspended biomass in laboratory environment and the kinetic coefficients were determined which are immensely important for the design of such reactor. The oil removal efficiency was observed to be in the range of 62.84-85.45% corresponding to average MLSS concentration range of 1,797-3,668 mg/L. Haldane kinetic model was found to be the best fitted for the biodegradation of oily wastewater with acclimatised microorganisms in the present investigation. The kinetic co-efficients including Ks, Y, kd, k and ki were calculated from the experimental data and the values were compared with published results cited by various scientists. The derived kinetic coefficients values are to be useful for understanding the dynamics of substrate utilisation with production of biomass and efficient design of biological systems and also for pilot plant investigation with real life wastewater of similar nature.

Influence of substrates concentrations on the dynamics of oxygen demand and aeration performance in ideal bioreactors

The effect of bioreactor configurations on the dynamics of aeration modelling was investigated by incorporating three different correlations from the literature to estimate α-factors into the aeration model. Estimated air flow rates using the three correlations were then validated against experimental data obtained from pilot sequencing batch reactors (SBRs). Two identical SBRs were operated in parallel; one received raw wastewater and the other received primary treated wastewater. The validated aeration model was then used to evaluate aeration dynamics in different bioreactor configurations, both for nitrification only and nitrification/denitrification, with the three different correlations. The current study is the first to investigate the validity of the aforementioned correlations using various bioreactor configurations and to establish that the bioreactor configuration not only impacts spatial and temporal biological oxygen demands as currently understood but also oxygen transfer efficiency. The first correlation based on the real-time bioreactor soluble chemical oxygen demand (sCOD) was able to predict the temporal measured air flow rate in the pilot SBRs. The second correlation based on the influent COD overestimated the air flow rates as it considered the impact of the influent loading rates on the α-factor and overlooked the improvement in α-factor due to biodegradation. The third correlation based on MLSS concentrations underestimated the air flow rates at the beginning of the aeration cycle as it ignored the impact of influent loading rates on the α-factor and considered only the insignificant change in MLSS during the aeration cycle. In terms of bioreactor configuration, the model-based analysis showed that the first correlation is suitable for designing SBR, plug flow reactor (PFR), step-feed PFR, and completely mixed stirred reactor (CSTR) systems, and the third correlation is suitable for designing CSTRs and membrane bioreactors (MBRs), while the second correlation was not accurate in any of the reactors modelled. When nitrification was targeted, the CSTR reduced aeration energy by 44 %–49 % compared to the PFR, and 41 %–43 % when both nitrification and denitrification were targeted. Compared to the plug-flow reactor, the step-feed PFR reduced aeration energy by 9% when nitrification only was targeted. However, when pre-denitrification was added, both systems showed the same aeration energy consumption. Pre-denitrification reduced organic loadings to aeration tanks and decreased aeration energy by 22 %, 11 %, 15 %, and 14 % in PFR, CSTR, PFR step feed and MBR systems, respectively.

Effect of Current Density and Contact Time of Electro-Coagulation on the Characteristics of Activated Sludge and Membrane Filtration

Objectives : The effect of current density and contact time of electro-coagulation on membrane fouling was investigated. In order to elucidate the reason why the membrane fouling was reduced by electro-coagulation, the changes in the characteristics of activated sludge were examined before and after electro-coagulation.Methods : A series of electro-coagulation of activated sludge suspensions was carried out with current density of 2.5, 6, 12, 24 A/m2 for 0, 2, 6, 12 hours. After membrane filtrations of the activated sludge suspensions, the membrane fouling was compared before and after the electro-coagulation. Characteristic changes in the activated sludge were also analyzed quantitatively.Results and Discussion : Total fouling resistances (Rt) of the electro-coagulated activated sludge decreased as current density and contact time increased. For example, Rt decreased 15%, 63% and 86% under the condition of current density of 24 A/m2 and 2, 6, 12 hours of contact time. Particularly, three activated sludge suspensions having very different initial MLSS concentrations showed a similar reduction of Rt, indicating that the membrane fouling was reduced not dominantly by particulates but by soluble foulants. The MLSS increased as current density increased, but MLVSS had not changed accordingly, which means that inorganic solids such as Al(OH)3 and AlPO4 produced during electro-coagulation were the main reasons for the increased MLSS concentration. These solids could play a key role in the reduction of membrane fouling by means of a dynamic membrane. As current density increased, the EPS (extracellular polymeric substances) and soluble COD concentration were reduced, which led to the reduction of membrane fouling. Soluble TN and TP were not significantly changed after electro-coagulation.Conclusions : The fouling materials, particularly, EPS and soluble COD decreased as current density and contact time increased, which played a key role in the reduction of membrane fouling. In addition, the insoluble solids produced during the electro-coagulation would act as a dynamic membrane, which led to fouling reduction.