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#### Journal of Environmental Engineering

Archives Papers: 307
The American Society of Civil Engineers
Dewaterability of CAS and MBR Sludge: Effect of Biological Stability and EPS Composition
Abstracts:The dewaterability of sludge from two conventional activated sludge (CAS) and three membrane bioreactor (MBR)–based wastewater treatment plants is investigated prior to and after anaerobic digestion. The concentration and composition of extracellular polymeric substances (EPS) mostly affect the dewaterability of all raw sludge samples. Better sludge dewaterability is observed when the concentration of proteins, carbohydrates, uronic acids, and humic acids is below approximately 400, 250, 200, and $40 mg/L$, respectively. In contrast, the specific resistance to filtration (SRF) increases in the sludge samples with a higher EPS concentration. The MBR results in a lower EPS production and a uronic acid–dominating EPS composition. This especially affects the dewaterability of one MBR sludge, also characterized by high salinity and a smaller particle size. Anaerobic digestion results in a higher SRF for both CAS and MBR sludge, with the particle-size distribution having the preponderant effect on the digested sludge dewaterability.
Control Strategies for the Mitigation and Removal of Attached Manganese Biofilms
Abstracts:Biofilm formation and manganese oxidizing bacteria (MOBs) in water transmission and distribution systems can lead to a wide array of water quality issues, operational problems, and negative hydraulic impacts. To investigate possible methods to control biofilm formation, a study using chlorine dioxide ($ClO2$) and sodium hypochlorite (NaOCl) was performed with rotating annular reactors (ARs). Results showed that low ($0.5 mg/L$ as $ClO2$) and high ($1.0 mg/L$ as $ClO2$) doses of $ClO2$, and $2.0 mg/L$ as $Cl2$ of NaOCl, were effective at mitigating biofilm to different extents by oxidizing readily available dissolved manganese (Mn) and iron (Fe) and/or inactivating biofilm populations. The most effective biofilm control strategy tested was a $2.0 mg/L$ dose of NaOCl, which provided significant reductions of suspended bacteria (2.1 log reduction), established biofilm (2.5 log reduction), and new biofilm growth (3.2 log reduction). Results from this study suggest that the implementation of treatment strategies for the control of existing and future biofilms should consider both (1) the removal of readily available metals by oxidation, and (2) the direct inactivation of attached bacteria.
Field Testing of a Small-Scale Continuous-Flow Wastewater Electrodisinfection Unit Using Direct Current
Abstracts:This paper describes field testing of a small-scale, continuous-flow electrodisinfection reactor assembled with four $IrO2$-coated titanium plates and operated in bipolar mode using direct current, installed at the Marrero wastewater treatment plant in Marrero, Louisiana. The objective of this testing was to demonstrate the technical feasibility of replacing the current wastewater-effluent hypochlorination process with this new disinfection technology. Bacterial inactivation and chlorine production were the main parameters recorded. The experiments reported in this study demonstrate that the electrodisinfection process can meet and exceed 5-log coliform removal in a short contact time, thereby proving to be efficient enough to be considered as an alternative to chlorination in wastewater treatment facilities. Optimum operational conditions for fluid retention time, and volumetric current density and rate, were stablished from the experimental results. The following design recommendations summarize these findings: retention time of $5±0.3 min$, minimum volumetric current density of $1,000 A/m3$, and minimum volumetric current rate of $80 A·h/m3$. Implementation of these operational conditions in the field yielded excellent disinfection efficiencies and low chlorine residual production.
Monitoring and Maintenance of Phosphate Adsorbing Filters
Abstracts:Field installations of two iron-enhanced sand filters (IESFs), designed to remove phosphate and particulates from stormwater runoff, were monitored and maintained for 1–3 years. One application, a traditional IESF in an agricultural watershed, retained over 64% of the influent phosphate load, whereas the second, a pond perimeter IESF in a developing suburban watershed, retained 26%. The measured average effluent event mean concentration (EMC) for the traditional IESF was $56.1 μg/L$. All events exhibited positive removal of phosphate (i.e., effluent $loads loads). In contrast, the measured percent phosphate retained for the pond perimeter IESF in 2013, 2014, and 2015 was 18, 25, and 45%, respectively. In addition, the average effluent EMC for the 3 years was 64.1, 54.2, and $19.9 μg/L$, respectively. Half of the events (14 of 28) were found to have negative removal (i.e., effluent $loads>influent$ loads). Events with negative removal tended to be smaller events with low influent phosphate concentrations ($3.7–39.4 μg/L$). Nonroutine maintenance improved the hydraulic performance of the pond perimeter IESF and, after a rinsing event, also improved phosphate retention rates to an average of 45%. There are believed to be at least two reasons for this difference in performance between the two IESFs: First, the traditional IESF was treating agricultural tile drainage with a low particulate phosphorus concentration, while the pond-perimeter IESF had a degrading mat of filamentous algae transported onto the surface, creating a source of phosphate that was not quantified. Second, the pond-perimeter IESF had treated a relatively large volume of water for its size, resulting in substantial flow-through in the filter within 5 years of operation. This is greater than anticipated for an IESF, and may have partially caused the reduction in performance.
Inactivation of E. coli, Legionella, and Pseudomonas in Tap Water Using Electrochemical Disinfection
Abstracts:Disinfection of hot water systems is critical in reducing the incidence of disease outbreaks caused by pathogenic bacteria. Electrochemical disinfection (ED) has been identified as an economical, low-maintenance, and chemical-free alternative in the fight against waterborne pathogenic microorganisms. It also provides the residual disinfection needed to inactivate the planktonic bacteria released by the biofilm. The work presented here includes fundamental small-scale laboratory optimization experiments in a flask where platinum-coated electrodes were immersed in 3.5 L of tap water contaminated with Escherichia coli (NCT10418) with an initial population density between $3×105$ and $1.6×105$ colony forming $units/mL$ ($CFU/mL$) or Legionella pneumophila serogroup 1 (NCTC12821) ranging from 180 to $244 CFU/mL$. Voltage, electrode area, interelectrode distance, spiking time, volume of contaminated water, and mixer speed were varied to determine the optimal geometrical and operational requirements needed to kill bacteria. Experimental results indicate ED to be an effective control method, with a $>4$-log inactivation of E. coli and a $>5$-log inactivation of Legionella in 10 and 45 min, respectively, at a current density of $≈4 mA/cm2$. The findings of the flask experiments were translated into real-world conditions by evaluating the long-term performance of an optimized ED prototype device installed in the hot water recirculation system of a small-size healthcare center building. The results showed that ED is effective at minimizing pathogen contamination of the hot water distribution system from initial values, with total bacteria levels and Pseudomonas species being reduced in all of the samples over a 15-month period following activation of the ED device.
Scenario Analysis of the Impact on Drinking Water Intakes from Bromide in the Discharge of Treated Oil and Gas Wastewater
Abstracts:Elevated levels of bromide have been shown to contribute to increased formation of disinfection byproducts (DBPs). Both produced water from unconventional oil and gas wells, which are hydraulically fractured using high volumes of fluids, and produced water from conventional oil and gas wells, which are also typically hydraulically fractured but with lower volumes of fluids, can contain high levels of bromide. If these produced waters are treated in conventional commercial wastewater treatment plants, bromide may not be removed from the effluent and is discharged to receiving water bodies. Elevated bromide levels at drinking water plant intakes is a concern for public health reasons if elevated bromide levels cause elevated levels of DBPs. This study used data from commercial wastewater treatment plants and river flow data in western Pennsylvania to construct generic discharge scenarios that illustrate the potential impacts from disposal of five classes of water that were developed from flowback and produced water bromide concentrations. Months with the historical high and low flows in the Allegheny River (Pennsylvania) and Blacklick Creek (Pennsylvania) were chosen for simulation, and treatment plant discharge rates were set at 100, 50, 33, and 25% of the permitted value for the purpose of varying the mass loading. Steady-state simulation results showed the highest probably of impact, defined as concentrations above target levels of 0.02 and $0.10 mg/L$, for produced water in the creek at both high and low flows (100%), and produced water in the river at low flows ($>75%$). High probability of impact ($>50%$) occurred in the river at low flows and all flows in the creek with treated mixed/flowback water discharge. Modeled reduction in the effluent discharge rate reduced downstream impacts proportionally. Transient simulation showed that transient peak concentrations may exceed time-averaged concentration by up to a factor of four when mixing conditions are met.
Effects of Flow Rate and Gas Species on Microbubble and Nanobubble Transport in Porous Media
Abstracts:Transport of microbubbles and nanobubbles (MNBs) in porous media has drawn increasing attention as a promising technology for soil and groundwater remediation. Understanding the transport mechanisms of MNBs in soils is essential to optimize MNB-based remediation techniques. In this study, effects of flow rates and bubble gas species on transport characteristics of MNBs were investigated in columns packed with glass beads. Microbubbles and nanobubbles were created by either air or oxygen injection to the columns at different flow rates. All results showed marked entrapment of MNBs inside the columns and relatively higher retardation of MNBs with smaller bubble size. The entrapment was enhanced for air-based MNBs under lower flow rate. A convection-dispersion model including bubble attachment could well capture the obtained effluent curves for MNB transport at high flow conditions. For low flow conditions, a model including bubble attachment-detachment and straining terms best described the data. The fitted model parameters suggested that irreversible straining is an important deposition mechanism for MNB transport in porous media.
Framework for Enhanced Stormwater Management by Optimization of Sewer Pumping Stations
Abstracts:Control and reduction of pollution from stormwater overflow is a major concern to be addressed by municipalities in order to improve the quality of the receiving water bodies and the environment in general. In the European context, these actions are driven by the Water Directive 2000/60/CE. In this regard, assessment studies of the potential load from sewer networks recognize the need for adaptation and upgrade of existing networks with waterworks and management measures. In many cases this is done by building first-flush detention tanks that, however, present consistent practical and economical burdens. In this work, simple rules to manage existing pumping stations in combined sewer systems are proposed as a way to apply management rules that mitigate pollution load. Such rules can be easily implemented in real cases with minimal cost of activation and no need of additional infrastructures. The procedure is based on the previous knowledge of the precipitation forcing and of a quantity/quality model of the sewer network. The steps adopted are (1) use of a (long-term, high-resolution) sequence of rainfall events to compute a wide spectrum of flow conditions (hydrographs and pollutographs) to the pumping stations; (2) definitions of a pumping rule to apply to the whole sequence of events to filter the incoming flow toward the wastewater treatment plant, so to compute outflows; and (3) efficiency assessment of the pumping rule by cumulative frequency analysis of water volume, pollutant mass, and pollutant mean concentration. Rule optimization can be performed by iterating points (2) and (3). An example is proposed to show how two simple parameters (a discharge threshold on the inflow and a maximum pumping time) can control the management of water and pollutant fluxes. Numerical results show that a proper optimization allows one to reduce the pumped volumes (thus reducing energy requirements and increasing the treatment plant efficiency) without significant changes to the overall pollutant mass outflow. The new pumping rules can be implemented on real stations with minimal and economically sustainable interventions.
Abstracts:Ethylenediaminetetraacetic acid (EDTA) as traditional chelating agent and nitrilo triacetic acid (NTA) as biodegradable chelating agent were used to evaluate the efficiency of leaching in silty-clay-loam soil contaminated with Pb, Cd, and Zn. Three concentrations of NTA and EDTA, 0.1, 0.01, and 0.005 M, were used in column leaching and each was set up in triplicate. Results demonstrate that the highest efficiency of heavy metals extraction was obtained in treatments with a concentration of 0.1 M EDTA and NTA. The extraction efficiency in first, second, and third pore volumes of 0.1 M EDTA were 41.92, 70.35, and 81.63% of Pb, 19.26, 44.28, and 77.58% of Cd, and 41.24, 56.14, and 65.8% of Zn, respectively. Also the extraction yields in first, second, and third pore volumes of 0.1 M NTA were 6.44, 14.72, and 16.78% of Pb, 47.68, 59.4, and 66.85% of Cd, an 11.44, 15.45, and 18.84 8% of Zn, respectively. Statistical analysis showed that EDTA concentration and pore volume have significant ($p<0.05$) effects on heavy metal leaching efficiency. At a washing solution pH of 4.5, the Pb, Cd, and Zn extraction efficiencies at the fifth pore volume were 87.25, 81.23, and 70.05% for the 0.1 M EDTA and 79.7, 59.8, and 60.12% for the 0.1 M NTA, respectively, when multiple heavy metals were used. The Pb, Cd, and Zn extraction efficiency for reuse of EDTA from leached solution were 99.12, 99.71, and 99.33%, respectively, for $Na2S$ and 99.66, 99.74, and 98.59%, respectively, for $Na2S/Ca(OH)2$ treatment. The acidity of the environment has a significant impact on heavy metals removal for both chelating agents. The overall orders of metal extraction efficiency for EDTA and NTA that resulted from this study are $Pb>Cd>Zn$ and $Cd>Zn>Pb$, respectively.