Simulation of dense non-aqueous phase liquid remediation through steam-enhanced extraction

Steam-enhanced extraction has been reviewed by many researchers as an innovative technology to remediate dense non-aqueous phase liquid (DNAPL) from subsurface. However, the application of steam-enhanced extraction to heterogeneous subsurface conditions is still obscurity and its implementation is limited due to steam flow sensitivity to site characterization. Two-dimensional (2-D) simulations were performed to assess the efficiency of steam-enhanced extraction in remediation of heterogeneous subsurface contaminated with tetrachloroethylene (PCE) spill. The simulation was performed with four different steam injection rates. The results shows that increased in steam injection rate will increase the PCE remediation time. The steam injection with the rate of 1.0 x 10-4 kg/s was successfully removing 100% of the PCE. There are significant impacts in the difference in remediation time with the increment approximately 20 min, 40 min and 70 min for every 2.0 x 10-5 kg/s increment. The dominant mechanisms of PCE removal is physical displacement through vaporization and co-boiling enhanced by steam distillation and steam stripping. The simulation results of steam-enhanced extraction for PCE removal was compared with surfactant-enhanced method implemented in existing experimental study. It was discovered that the time required to remove PCE using steam-enhanced extraction is four times faster than the time required to remove PCE using surfactant-enhanced method. This shows the capability of steam-enhanced extraction to recover contaminant more effectively. Steam-enhanced extraction has a greatest potential to decrease clean-up time which will offset greater capitol cost of the system

Performance of an up-flow anaerobic sludge bed (UASB) reactor treating landfill leachate containing heavy metals and formaldehyde

Municipal Solid Waste (MSW) landfill leachate is a serious environmental issue and treated using various methods, mostly involving biological treatment. In the present study, an up-flow anaerobic sludge bed (UASB) was used for the treatment of matured landfill leachate that contains heavy metals (As, Fe, Ni, and Cd) and Formaldehyde (FA). Accordingly, the OLR to the UASB reactor was gradually increased from 0.125 to 2.5 kg CODm-3d-1, to observe the process performance. The process performance of the reactor was characterized in terms of pH, Chemical Oxygen Demand (COD) removal, Total Volatile Acid (TVA) production, Mixed Liquor Suspended Solids (MLSS), Mixed Liquor Volatile Suspended Solids (MLVSS) washout, and Methane composition. Results showed that at a Hydraulic Retention Time (HRT) of 4 days and an OLR of 0.125 kg CODm-3d-1, up to 79.04% COD removal efficiency was observed. However, when the OLR was increased gradually from 0.375 to 2.5 kg CODm-3d-1, the COD removal efficiency decreased to 9.5%, suggesting that the high accumulation of heavy metals may have inhibited the methanogens. During this period, the heavy metal and formaldehyde concentration were 9.40, 0.43, 0.50, 12.80 and 8.60 mgL-1 respectively

Surfactant-alcohol experiments for dense non-aqueous phase liquid removal: a review

The aim of this paper is to review and to summarize the existing laboratory experiment studies from other researchers regarding surfactant alcohol experiment for dense non-aqueous phase liquid (DNAPL) removal, their approach, method of measurement, factor consideration and their findings together with result discussion. This review includes the selection of surfactant-alcohol, their important characteristics in the remediation of DNAPL, the laboratory experimental setup using 2-D laboratory model and enhanced remediation of DNAPL from recent laboratory studies. It has been shown in the laboratory experiment studies that solubilization is the dominant removal process of DNAPL. After surfactant concentration reached the critical micelle concentration, interfacial tension between DNAPL, water and soil decreased. This has resulted in increasing of solubility and removal rate of DNAPL. Mobilization also takes place in the removal process. However, most of the laboratory experiments did not consider other factor such as soil permeability, soil texture, and interfacial tension between soil and DNAPL. Further studies of surfactant-alcohol flushing shall be considered in the near future

Overview of urban heat island (UHI) phenomenon towards human thermal comfort

Urban Heat Island (UHI) is expected to be a disastrous challenge to human in the following decade as a result of continuous urbanization without appropriate planning and design. The impacts of UHI are even getting worse due to large population density with improper building design especially in dense metropolitan cities. A lot of research has been carried out for UHI phenomenon both in tropical and seasonal climates. There are many factors contributing to the formation of UHI phenomenon that includes increasing rate of urbanization and population density, uncontrollable factors and controllable factors. In a fundamental study, a prolonged exposure to heat impact will significantly contribute to human discomfort and health problems resulting in heat-related illness. The cases of heat related deaths, such as heat strokes, are due to the result of climate changes and further the problem of heat waves will increase year by year. Since the consequences of UHI are considered to be more significant, the severity of the problem should be critically examined and carefully reported. Many research efforts have been implemented for making conceptual design and also a wide range of literature is available for continuing the mitigation strategies. Therefore, this study is emphasized on the critical investigation of the features, factors and impacts of UHI towards evaluating human safety and thermal comfort. Future research direction should also be encompassed on the design and planning parameters as well as assessment of climate change risks and vulnerability for reducing the effects of urban heat island onto human health and safety

Effect of organic loading rate (OLR) on modified anaerobic baffled reactor (MABR) performance

The performance of a Modified Anaerobic Baffled Reactor (MABR) treating synthetic wastewater at different Organic Loading Rate (OLR) was investigated. The MABR was seeded with anaerobic sludge taken from a local municipal wastewater treatment plant and fed continuously with glucose at an OLR of 0.258, 0.787 and 2.471 kg COD m-3 d-1 at a Hydraulic Retention Time (HRT) of 4 days. Results showed that 99.7% Chemical Oxygen Demand (COD) removal was achieved during the OLR of 0.258 kg COD m-3 d-1. However, when the OLR was increased to 0.787 kg COD m-3 d- 1, a minor decrease in the COD removal efficiency (95%) was noted. Further increase of the OLR to 2.471 kg COD m-3 d-1 caused the reactor performance to deteriorate dramatically in a COD removal efficiency of 39.5%. Biogas yield was evaluated for the reactor system and followed similar decreasing trend (0.542, 0.524 and 0.214 l g-1CODdestroyed for the different OLRs respectively). There were no significant different in the pH profiles (6.71 – 7.01) during the first two OLRs (0.258 and 0.787 kg COD m-3 d-1). However, during the final OLR (2.471 kg COD m-3 d-1) the pH profile in MABR dropped to significantly as low as 4.01. Similar trend was also observed in the volatile acids (VA) profile where higher values (2880 mg/L) were found at highest OLR. The poor performance of the MABR at high OLR signifies that the microorganisms could not metabolise the organic substance and probably need more time for digestion

Methane optimization in multi-stage anaerobic reactor (Ms-Ar)

The biological conversion of biomass in Anaerobic Digestion (AD) into methane was studied by many researchers in recent years. In the present study, optimization of methane production during chemical oxygen demand (COD) removal was observed in a novel Multi-Stage Anaerobic Reactor (MS-AR). A synthetic glucose was used as a feed substrate and the reactor was operated at a hydraulic retention time (HRT) of 1 to 4 d. Two complementary test procedures for methane optimization were evaluated; the theoretical and experimental. The theoretical methane gas was recorded as 50.13, 50.02, 50.16, and 50.22 % for HRT of 4, 3, 2 and 1 day, respectively. The results signify well with the empirical formula at each HRTs studied in the reactor. However, the quantity of methane gas present in the real application is significantly lower than the theoretical. This is due to the microorganism activity in the reactor that may have interfere with the efficiency of the biogas production. Actual data showed a decrease in the methane gas production (35.4, 21.2, 19.8, and 18.4 %) in the reactor. Thus, theoretical formula together with the actual data provides alternative method for the evaluation of bioenergy potential in AD

Reliable multiclass cancer classification of microarray gene expression profiles using an improved wavelet neural network

Properly designing a wavelet neural network (WNN) is crucial for achieving the optimal generalization performance. In this paper, two different approaches were proposed for improving the predictive capability of WNNs. First, the types of activation functions used in the hidden layer of the WNN were varied. Second, the proposed enhanced fuzzy c-means clustering algorithm—specifically, the modified point symmetry-based fuzzy c-means (MSFCM) algorithm—was employed in selecting the locations of the translation vectors of the WNN. The modified WNN was then applied to heterogeneous cancer classification using four different microarray benchmark datasets. The comparative experimental results showed that the proposed methodology achieved an almost 100% classification accuracy in multiclass cancer prediction, leading to superior performance with respect to other clustering algorithms. Subsequently, performance comparisons with other classifiers were made. An assessment analysis showed that this proposed approach outperformed most of the other classifiers

Antibiotics in the environment: mini review

Knowledge of pharmaceuticals in the environment is merely minute. Pharmaceuticals can enter the aquatic environment through the sewage treatment systems when they are excreted by people, or if they are disposed in the home. They can also enter sewage treatment works or waterways as a result of discharges from pharmaceutical manufacturing plants or medical establishments. The emission routes of veterinary drugs and feed additives to surface water are more complex than those of human pharmaceuticals. Emission to the surface water can take place either directly, when the animals are kept on pasture or indirectly by run-off and leaching through the soil. From an environmental side, the major effect of antibiotics is the toxic effect that may be exerted on aquatic organisms and disruption of the ecological balance. In addition, the presence of antibiotics in natural systems leads to the development of multi-resistant strains of bacteria. This paper outlines the different anticipated exposure routes to the environment, present knowledge of occurrence, fate and effect of pharmaceuticals

Performance of an innovative multi-stage anaerobic reactor during start-up period

Start-up of an anaerobic reactor is a relatively delicate process and depends on various factors such as wastewater composition, available inoculum, operating conditions and reactor configuration. Accordingly, systematized operational procedures are important, mainly during the start-up of an anaerobic reactor. In this paper, the start-up performance of an innovative multi-stage anaerobic reactor using synthetic wastewater at various organic loading rates (OLRs) was investigated. In Phase 1 of the experimental study, the reactor was operated at hydraulic retention time (HRT) of 1 day with corresponding OLR of 1.07 kg COD.m-3.d-1. Thereafter, the reactor was operated at intermittent feeding (Phase 2), with HRT of 1.4 day and OLR of 0.82 to 2.45 kg COD.m-3.d-1. Results showed up to 71% COD reduction in the Phase 1 of the experimental study. However, in Phase 2, when the reactor was operated at intermittent feeding, the COD removal efficiency increased from 75 to 92%. It can be concluded that the multi-stage anaerobic reactor system performed better at intermittent feeding, indicating that the reactor required low loading rate and sufficient HRT for gradual acclimatization for reactor start-up. The reduction of the period necessary for the start-up and improved operational control are important factors to increase the efficiency the reactor system.Key words: Anaerobic reactor start-up, biomass, glucose wastewater, intermittent feeding, multi-stage anaerobic reactor

Treatment of Textile Wastewater Using a Novel Electrocoagulation Reactor Design

This study explored the best operating conditions for a novel electrocoagulation (EC) reactor with the rotating anode for textile wastewater treatment. The influence of operating parameters like interelectrode distance (IED), current density (CD), temperature, pH, operating time (RT) and rotation speed on the removal efficiency of the contaminant was studied. A comparative study was done using conventional model with static electrodes in two phases under same textile wastewater. The findings revealed that the optimal conditions for textile wastewater treatment were attained at RT = 10 min, CD = 4 mA/cm2, rotation speed = 150 rpm, temperature = 25°C, IED = 1 cm and pH = 4.57. The removal efficiencies of color, biological oxygen demand (BOD), turbidity, chemical oxygen demand (COD) and total suspended solid (TSS) were 98.50, 95.55, 96, 98 and 97.10%, respectively, within the first 10 min of the reaction. The results of the experiment reveal that the newly designed reactor incorporated with cathode rings and rotated anode impellers provide a superior treatment efficiency within a short reaction time. The novel EC reactor with a rotating anode significantly enhanced textile wastewater treatment compared to the conventional model. The values of adsorption and passivation resistance validated the pollutants removal rate