Laboratory Scale Continuous-flow System Research Articles

Performance of nanoscale zero-valent iron in nitrate reduction from water using a laboratory-scale continuous-flow system

Nanoscale zero-valent iron (nZVI) is a versatile treatment reagent that should be utilized in an effective application for nitrate remediation in water. For this purpose, a laboratory-scale continuous-flow system (LSCFS) was developed to evaluate nZVI performance in removal of nitrate in different contaminated-water bodies. The equipment design (reactor, settler, and polisher) and operational parameters of the LSCFS were determined based on nZVI characterization and nitrate reduction kinetics. Ten experimental runs were conducted at different dosages (6, 10 and 20 g) of nZVI-based reagents (nZVI, bimetallic nZVI-Cu, CuCl2-added nZVI). Effluent concentrations of nitrogen and iron compounds were measured, and pH and ORP values were monitored. The major role exhibited by the recirculation process of unreacted nZVI from the settler to the reactor succeeded in achieving overall nitrate removal efficiency (RE) of >90%. The similar performance of both nZVI and copper-ions-modified nZVI in contaminated distilled water was an indication of LSCFS reliability in completely utilizing iron nanoparticles. In case of treating contaminated river water and simulated groundwater, the nitrate reduction process was sensitive towards the presence of interfering substances that dropped the overall RE drastically. However, the addition of copper ions during the treatment counteracted the retardation effect and greatly enhanced the nitrate RE.

Design and operation of an inexpensive, laboratory-scale, continuous hydrothermal liquefaction reactor for the conversion of microalgae produced during wastewater treatment

Recently, much research has been published on the hydrothermal liquefaction (HTL) of microalgae to form bio-crude, which can be further upgraded into sustainable 3rd generation biofuels. However, most of these studies have been conducted in batch reactors, which are not fully applicable to large-scale industrial production. In this investigation an inexpensive laboratory scale continuous flow system was designed and tested for the liquefaction of microalgae produced during wastewater treatment. The system was operated at a range of temperatures (300°C–340°C) and flow rates (3–7mLmin−1), with the feed being delivered using high pressure N2 rather than a mechanical pump. The design incorporated the in-situ collection of solids through a double tube design. The algae was processed at 5wt% and the results were compared to those from a batch reactor operated at equivalent conditions. By combining high heating rates with extended reaction times, the continuous system was able to yield significantly enhanced bio-crude yields compared to the batch system. This demonstrates the need for inexpensive continuous processing in the lab, to aid in scale up decision making.

Microbial removal of selected volatile organic compounds from the model landfill gas

Abstract Landfills of municipal waste are an important source of BTEXs in the atmosphere. Biodegrability of these compounds implies that biological methods, such as oxidation in landfill covers, may be an effective way to mitigate emission of these gases. The aim of the study was to evaluate the efficiency of BTEXs removal from landfill gas by biofiltration method and to analyze the influence of methane on BTEXs oxidation rate. The experiments were carried out at laboratory scale continuous flow system (microcosms) and in batch tests. A mixture of municipal waste compost and expanded clay pellets (1:1 of volume) was used as a filter bed material. The model landfill gas (50% vol. of CH4 and 50% vol. of CO2) purged through the microcosms was enriched with toluene (series 1) and all the BTEXs (series 2). The results of 7-month continuous flow experiment showed that removal efficiency of BTEXs in experimental columns ranged from 91 to 100% when the individual trace gases loading rates in model gas were in the range of 0.1-0.2 g m−2d−1. The rate of toluene removal, which followed the first order kinetics, depended on the presence of methane in treated gas. About 2-fold higher values of rate constant and 2.5-fold higher values of initial toluene removal rates were observed when no methane was present in the headspaces inside the vials used in the batch tests.

Effect of Dissolved Oxygen on Biological Nutrient Removal by Denitrifying Phosphorus‐Accumulating Organisms in a Continuous‐Flow System

A laboratory-scale continuous-flow system with an anaerobic/anoxic/aerobic configuration was set up to study the effect of oxygen in the internal recycle stream; of particular interest was its performance of denitrifying phosphorus-accumulating organisms (DPAOs). It was found that, by using a degas device, the dissolved oxygen in the nitrate recycle stream was effectively decreased from 0.1 +/- 0.02 to 0.01 +/- 0.01 mg/L. This provided a favorable condition for DPAOs to grow under an anoxic condition and thus be sustained successfully in the system. When the degas device was removed from the system, the dissolved oxygen concentration in the anoxic reactor increased to 0.1 +/- 0.02 mg/L. The proliferation of the denitrifying glycogen-accumulating organisms (DGAOs) population and deterioration of DPAOs performance was observed. The increased population of DGAO/GAOs, which competed for the carbon source with DPAO/ PAOs, resulted in a poor performance of biological phosphorus removal.

Supercritical water gasification of industrial organic wastes

Supercritical Water Gasification (SCWG), in which supercritical water is not only a solvent for organic materials but also a reactant, is one of the applications for producing fuel from organic resources. In this way, besides the destruction of wastewaters, it is aimed to harness their energy potential by burning the gas effluent generated in the process, which contains a high level of heating power due to its high content in hydrogen and light hydrocarbons. In the work described here, SCWG has been tested on a laboratory scale continuous-flow system with two different industrial wastewaters that contain a high concentration of organics, with both wastes having a high energy potential: cutting oil wastes, oleaginous wastewater from metalworking industries, and vinasses, alcohol distillery wastewater. Reports on SCWG processes on these types of wastewaters have not previously been published in the literature. The influence of the temperature, amount of oxidant and catalyst addition on the yield and composition of the gas phase generated were studied. Experiments were carried out in the temperature range 450–550 °C, the amount of oxidant ranged from the absence of oxygen (oxygen coefficient, n = 0) to 20% of stoichiometric oxygen ( n = 0.2), and 250 bar of pressure in all cases. A maximum of 0.19 mol H 2 per initial COD m (COD m is given as mol O 2 consumed for total oxidation) was obtained in the gas phase under the best conditions.

The effect of applied direct current on biological phosphorus uptake

An increase in metabolic activity of bacteria capable of accumulating excess phosphorus may also improve the phosphorus removal efficiency of the biological phosphorus removal system. It has been observed that the amount of intracellular biochemical energy (ATP) in bacterial cells has increased when they were exposed to pH or electrical stress. The utilization of the surplus intracellular energy generated by the stress may be utilized to stimulate the metabolic activity of bacterial cells. It was hypothesized that the introduction of direct current into mixed liquor might also increase the metabolic activity of bacteria capable of accumulating excess phosphorus. A direct current with 6 V and 200 mA was applied intermittently for one minute in every five. The direct current was introduced at the anaerobic step of a Phoredox type laboratory scale continuous flow system. Graphite electrodes were used to introduce the current. To separate the effect of the electric current from that caused by other environmental factors a control system was run in parallel using the same operational parameters. Synthetic wastewater with the same composition was used as feed for both systems. As a result of the intermittent application of direct current, the rate of phosphorus accumulation in activated sludge increased by 30% during the start-up period of the biological system and by 11 % during steady state conditions. The applied direct current changed the movement and concentration of potassium ions. The pH of the mixed liquor in the anaerobic reactor dropped to 4 as soon as the direct current was introduced and returned to the initial pH 6 value when the current flow ceased. The number of viable cells in the activated sludge decreased by a factor of 2–5 as a result of the electrification. The reduction observed in viable cell count did not influence the overall organic carbon removal efficiency or the nitrification-denitrification processes. A hypothetical model was developed which combines known biological reactions with results observed during the research. The model summarizes the effects of direct current on biological phosphorus uptake. This work provides insight into a method of enhancing the biological removal of phosphorus from a wastewater stream without adding chemicals. It has many practical applications where electric power is available but chemical addition is unacceptable (water reuse), the cost is prohibitive or the appropriate chemicals are locally unavailable.