Concentration Of Mixed Liquor Research Articles

Evaluating the Impacts of Cold and Wet Weather Events on Biological Nutrient Removal in Water Resource Recovery Facilities Nutrients

Maintaining effective biological nutrient removal (BNR) capability during adverse weather events (AWEs) can be challenging for water resource recovery facilities (WRRF). Mitigation of the impact of these weather events on BNR requires focused strategies that are known to be effective. In this study, the researchers worked with 12 WRRFs that experience AWEs to identify critical challenges they face when attempting to maintain optimal BNR performance during these weather events. As part of this work, the project team has also compiled and evaluated strategies that are currently implemented by BNR facilities for mitigating these impacts. Results from these evaluations indicate that resistance to and recovery from AWEs is closely linked to plant ability to protect and maintain sufficient mixed liquor concentrations and solids retention times for biomass growth. Therefore, strategies that employ biomass storage and recirculation are effective for helping plants maintain BNR capacity during and after AWEs. This title belongs to WERF Research Report Series ISBN: 9781780406701 (eBook)

Removal of nitrate from groundwater using ZVI treatment system combined with continuous CO2 gas bubbling

A zero-valent iron (ZVI) treatment system combined with pH adjustment, aeration, sedimentation and microfiltration processes was developed for the robust removal of nitrate from groundwater. Powdered ZVI dosed at 10 g L− 1 removed nitrate by 166 mg L− 1, of which 80% were converted to ammonium ion for a given contact time of 125 h. By diffusing gaseous carbon dioxide (CO2) into the ZVI reactor, pH was desirably controlled in the range of 5.5–6.5, and concurrently < 0.5 mg L− 1 dissolved oxygen was consistently maintained during the longer-term of dissolved oxygen ZVI treatment system. The combination of ZVI treatment and CO2 gas bubbling reached up to 35% removal of nitrate and passivation on the surface of ZVI was prevented by diffusing CO2 gas. Soluble Fe (II) concentration of mixed liquor in the ZVI reactor ranged between 0.2 and 7.8 mg L− 1 and Fe (II) dissolved in the ZVI-treated water was almost completely removed by subsequent aeration. The overall result shows that the novel ZVI treatment system is significantly promising to remove nitrate in groundwater and therefore to meet the regulatory limit for drinking water.

Investigation of a MBR membrane fouling model based on time series analysis system identification methods

Flux stepping tests were carried out on a novel sidestream MBR pilot plant treating industrial wastewater, and a membrane filtration unit treating tertiary quality municipal effluent. This included offline tests measuring mixed liquor concentrations, as well as soluble microbial product (SMP) levels in the sludge water which is the main irreversible foulant on the membrane [1]. A basic phenomenological 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 TMP operation was extensively modified [2,3]. 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 SMP in the liquor; and, it could be used in a crossflow scenario by the addition of scouring terms in the mod...

Exploration of dual optimal conditions for COD and nitrogen removal in an MBR

AbstractMembrane bioreactors (MBRs) have been increasingly used for wastewater treatment in last decade. MBR process has several characteristics such as high sludge retention time, high mixed liquor concentration and accumulation of soluble microbial products. Although activated sludge models (ASMs) have been developed for conventional activated sludge process, applying the ASM model to MBR process seems to be proper. In this study, a model‐based systematic approach that can find optimal operational conditions for chemical oxygen demand (COD) and nitrogen removal was explored to a MBR process. To enhance the modeling performance of the ASM, the precise influent characterization for MBR process was performed by using a respirometry. The optimization results in MBR plant showed that the removal efficiencies of COD and nitrogen in the plant were greatly improved to 88.10 and 62.67%, respectively. Copyright © 2011 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Model-based energy optimisation of a small-scale decentralised membrane bioreactor for urban reuse

The energy consumption of a small-scale membrane bioreactor, treating high strength domestic wastewater for community level wastewater recycling, has been optimised using a dynamic model of the plant. ASM2d was chosen as biological process model to account for the presence of phosphate accumulating organisms. A tracer test was carried out to determine the hydraulic behaviour of the plant. To realistically simulate the aeration demand, a dedicated aeration model was used incorporating the dependency of the oxygen transfer on the mixed liquor concentration and allowing differentiation between coarse and fine bubble aeration, both typically present in MBRs. A steady state and dynamic calibration was performed, and the calibrated model was able to predict effluent nutrient concentrations and MLSS concentrations accurately. A scenario analysis (SCA) was carried out using the calibrated model to simulate the effect of varying SRT, recirculation ratio and DO set point on effluent quality, MLSS concentrations and aeration demand. Linking the model output with empirically derived correlations for energy consumption allowed an accurate prediction of the energy consumption. The SCA results showed that decreasing membrane aeration and SRT were most beneficial towards total energy consumption, while increasing the recirculation flow led to improved TN removal but at the same time also deterioration in TP removal. A validation of the model was performed by effectively applying better operational parameters to the plant. This resulted in a reduction in energy consumption by 23% without compromising effluent quality, as was accurately predicted by the model. This modelling approach thus allows the operating envelope to be reliably identified for meeting criteria based on energy demand and specific water quality determinants.

Comparison of Performance and Operation of Side-By-Side Integrated Fixed-Film and Conventional Activated Sludge Processes at Demonstration Scale

A full-scale demonstration of an integrated fixed-film activated sludge (IFFAS) process with floating carriers has been conducted in Ontario, Canada, since August 2003. In this study, data collected on-site from July 2005 to December 2006 are analyzed and compared with the performance of a conventional activated sludge train operated in parallel. Both trains received similar loadings and maintained comparable mixed liquor concentrations; however, the IFFAS had 50% more biomass when the attached growth was considered. In the winter, the conventional train operated at the critical solids retention time (SRT) and had fluctuating partial nitrification. The IFFAS nitrified more consistently and had a doubled average capacity. In the summer, the suspended SRT was less limiting, and the benefit of IFFAS for nitrification was marginal. The lessons learned from the operational requirements and challenges of the IFFAS process (air flow, carrier management, and seasonal foaming) are discussed, and design recommendations are proposed for whole plant retrofit.

Effect of Operational Parameters on the Removal of Particulate Chemical Oxygen Demand in the Activated Sludge Process

The removal of particulate material in the aeration basin of the activated sludge process is mainly attributed to bioflocculation and hydrolysis of particulate substrate. The bioflocculation process in the aeration tank of the activated sludge process occurs only under favorable conditions in the system, and several common operational parameters affect its performance. The principal objective of this research was to observe the effect of mixed liquor suspended solids, solids retention time (SRT), and extracellular polymer substances on the removal of particulate substrate by bioflocculation. A first-order particulate removal expression, based on flocculation, accurately described the removal rates for supernatant suspended solids and colloidal chemical oxygen demand. Based on the results presented in this investigation, a mixed liquor concentration of approximately 2200 mg/L, an SRT of at least 3 days, and a contact time of 30 minutes are needed for relatively complete removal of the particulate substrate in a plug-flow reactor.

Effect of mean cell residence time on the performance and microbial diversity of pre-denitrification submerged membrane bioreactors

The effect of mean cell residence time (MCRT) (5, 8.3, 16.7, and 33.3 d) on domestic wastewater treatment performance had been investigated using four bench-scale pre-denitrification submerged membrane bioreactors (MBR) operated in parallel. The 33.3-d MCRT MBR had the lowest microbial activities in terms of specific oxygen uptake rate, specific denitrification rate and observed sludge yield. Excellent COD removal efficiency (more than 95%) and nitrification (more than 97%) were observed in all the four MBRs investigated. Even though high nitrification can be achieved in all the MBRs, total nitrogen (TN) removal efficiency was found to be affected by MCRT with a maximum of 77% at 33.3-d MCRT. Better TN removal efficiency achieved in the 33.3-d MCRT MBR was due to the combined effect of high mixed liquor concentration and lower dissolved oxygen concentration in the recycled mixed liquor. A comparison of terminal-restriction fragment length polymorphisms (T-RFLP) fingerprints based on 16S rRNA and nirS gene revealed that the microbial communities of 5- and 8.3-d MCRT are grouped under the same branch while 16.7- and 33.3-d MCRT are grouped in another branch. T-RFLP based on amoA gene shows that members from the Nitrosomonas genus were more dominant under shorter MCRT operating environment. Clustering analysis did not show any correlation with the organic and nitrogen removal performance obtained in this study.

Shock Effects of Copper Ion on Activated Sludge Unacclimated and Its Recovery Technique

To study the effects of heavy metals on the pilot-scale activated sludge process, the uptake of heavy metals and the removal rate of COD Mn by activated sludge were investigated in various conditions. When 20 mg/L of copper ion was added to the sequence batch reactor (SBR) of the unacclimated activated sludge, copper ion was rapidly adsorbed by the activated sludge flocs at first and then released from them after aeration. The copper ion concentration of mixed liquor in the reactor increased until the removal rate of COD Mn became constant. When three kinds of the additives including special nutrients (as COD Mn 45 mg/L), powdered activated carbon (PAC, 50 mg/L) and condensed sludge (as MLSS less than 300 mg/L), which are possible candidates for the recovery techniques, were added to the activated sludge, different bio-kinetic constants were obtained, indicating different inhibition rates of treatment efficiency. In the case of special nutrients, the removal rate of COD Mn was the highest among all three additives, showing that they stimulated microorganisms in the activated sludge to absorb organic substances. Addition of PAC and condensed sludge also improved the removal rates of COD Mn and copper ion. Especially when the organic load was light, the addition of PAC could efficiently remove organic substances and copper ion from the mixed liquor. However, the addition of the condensed sludge increased the turbidity of the mixed liquor. And some long time aeration was found leading to the deflocculation of activated sludge.

Final Clarification by Integrated Filtration within the Activated Sludge Aeration Tank

A laboratory sequencing batch reactor (SBR), integrating a novel filtration system, was used to treat wastewater from a cheese factory. For an average influent CODtot of 1,000 mg l−1 and at an HRT of 8 d, the SBR-Filtration system yielded an overall efficiency of 94.5% in terms of COD removal, and an effluent suspended solids (SS) concentration close to 0 mg l−1. Throughput fluxes as high as 443 l m-2 h−1 could be reached. No permanent clogging or decrease in permeability of the filtration step was observed over the 12 d testing period. The effect of solids concentration on filtration was assessed by increasing, stepwise, the MLSS concentration in successive stages. The food to microorganism ratio (F/M) was maintained almost constant by increasing the influent load proportionately to the increase in biomass. This was done by adding powdered milk waste to the real wastewater. As a result of rapid increases in influent COD, changes in composition and loading rates, and a lack of nutrients during this phase of experiments, steady state conditions were interrupted. Consequently, the biomass would not flocculate well and the SVI increased. The decrease in filtration efficiency was thought to be due to the transient biological state of the biomass, rather than to the concentration increase itself. An attempt to corroborate this observation was made by systematically decreasing the mixed liquor concentration in the reactor by dilution with water. Flux rates remained constant, regardless of the variation of MLSS concentration.

Organic Stabilization and Nitrogen Removal in Membrane Separation Bioreactor for Domestic Wastewater Treatment

In this study, organic stabilization and nitrogen removal were investigated using a household type hollow fiber membrane separation bioreactor of 6 2 1 volume. The process employed direct solid-liquid separation by hollow fiber membrane inside an activated sludge aeration tank. By providing highly turbulent conditions within the separation zone in conjunction with Jet aerating installation inside the membrane module, sludge accumulation on the membrane surface and inside the module can be reduced. Permeate flux obtained after 330 days of operation was 0.2 m/d under intermittent suction. High degree of organic stabilization was obtained in the system by operation without sludge wastage except for sampling purposes. Continuous and intermittent aeration modes were investigated in the study. The average effluent COD concentration of 20.8 and 16.5 mg/l were observed during continuous and intermittent aerating application respectively. Degree of nitrification depended upon DO concentration of mixed liquor during aeration period. Introduction of intermittent aeration enhanced total nitrogen removal up to 80% or more by simultaneous nitrification and denitrification, resulting in average of 4.9 mg/l of total nitrogen in the effluent. Increase in DO in aeration period from 1.5–2 mg/l to 4–5 mg/l improved percentage of nitrogen removal to more than 90%. Rejection of 4–6 log virus concentration by gel layer formed on the membrane surface was also observed.

Population Dynamics of Phenol Degrading Microorganisms in Activated Sludge Process under the Stress of Phenolic Wastewater

The process to gain and lose phenol degrading activity of activated sludge under different stress of phenol was studied by three types of operations, i.e. continuous flow reactor, aerobic SBR, and anaerobic/aerobic SBR under two types of loads, i.e. elevating and constant loads. The higher activity and tolerance under the higher concentration of phenol was gained in activated sludge of aerobic SBR under the constant high load. The higher phenolic stress, i.e. mixed liquor concentration of phenol, at the beginning of batch cycles seemed to increase the activity. Constant and low phenolic stress in continuous flow reactors and elevating load in SBR, however, could not build up tolerance and the higher degrading activity under the higher concentration of phenol. SBR operations which are able to give appropriate phenolic stress on activated sludge, even under the same daily loading of phenol as continuous flow reactor, would be preferable to build up and maintain the activity and to ensure stable operation of wastewater treatment even under shock loading. The degrading activity of activated sludge may be gained mainly by the increase in the ability of bacteria to degrade and tolerate phenol and not by the increase in population.

Considerations in Modeling Activated Sludge Process

Mathematical modeling of the activated sludge process is examined both from a unit process viewpoint and as an integral component of plant-wide mass balance models. Two modeling approaches are reviewed. The first is a standard approach now commonly used in practice. The second is an alternative approach which represents a modification of the first to directly account for influent suspended solids to the activated sludge process. Considerations are presented as to the proper application of both models in the prediction of waste sludge production and mixed liquor concentration. The two approaches also are compared for utility in wastewater treatment plant design. The alternative approach may be more flexible in accounting for sludge handling recycle loads. In many instances it also provides a more conservative estimate of waste sludge production.

A further examination of mass flux theory as applied to activated sludge settlement

The use of mass flux analysis has become well established for the design of settlement tanks. Recent work has suggested how this type of analysis might be used for operational control. This paper proposes a generalised expression which would enable the hindered settling velocities of activated sludge to be calculated for specific settlement (SSVI) values and mixed liquor concentrations.