Investigation of potential pathways and multi-cycle bioregeneration of ion-exchange resin laden with perchlorate

Ion-exchange (IX) is possibly the most feasible technology for perchlorate removal and perchlorate-selective and non-selective IX resins are commercially available for this purpose. The use of both resins has shortcomings. Selective resins are incinerated after one time use, and non-selective resins produce a regenerant waste stream that contains high concentration of perchlorate. A process involving directly contacting of spent IX resin containing perchlorate with perchlorate-reducing bacteria (PRB) to bioregenerate the resin has been developed and proven recently. In this process PRB biodegrade perchlorate ions which are attached to the functional groups of the resin. Although its feasibility has been proven, there are two issues related to resin bioregeneration technology that deserve attention and were addressed in this research. The first issue relates to the investigation of the mechanisms responsible for resin bioregeneration. It was envisioned that the bioregeneration process involves four steps. First, resin-attached perchlorate (RAP) ions are desorbed from their original functional groups by chloride ion. Second, perchlorate ions are diffused through the pores of the resin. It was expected that this diffusion is affected by both resin bead size and structure. Third, perchlorate ions are transferred through the liquid film surrounding the resin to the bulk liquid. Forth, perchlorate ions are utilized by the PRB present in the bulk liquid. The results of the bioregeneration experiments suggested that chloride, the waste product of perchlorate biodegradation, is more likely the desorbing agent of RAP, and increasing the concentration of chloride enhances the bioregeneration process. For commercially available resins, both film and pore diffusion were found to affect the rate of mass transfer. In addition, macroporous resins were found to be more effective than gel-type resins in the bioregeneration process. Bioregeneration rates were faster for resins of smaller bead diameter. The outcome of this study implies that in resin bioregeneration, the use of macroporous resin with relatively smaller bead size in presence of chloride would be preferred. Chloride concentration, however, should be kept below the inhibitory level for PRB microbial activities. The second issue of bioregeneration process is the possibility of multi-cycle bioregeneration of IX resin. The results of the experiments revealed that capacity loss, which is the main concern in multi-cycle bioregeneration process, stabilized after a few cycles of bioregeneration indicating that the number of loading and bioregeneration cycles that can be performed is likely greater than the five cycles tested. The results further indicated that as bioregeneration progresses, clogging of the resin pores results in the decrease in mass transfer flux from the inner portion of the resin to the bulk microbial culture contributing to stronger mass transfer limitation in the bioregeneration process. Perchlorate buildup, resulting from un-degraded perchlorate accumulation in the inner portion of the resin, after each bioregeneration cycle is a major drawback that limits the number of bioregeneration cycles that can be performed

Effects of Hydrological and Climatic Variables on Cyanobacterial Blooms in Four Large Shallow Lakes Fed by the Yangtze River

Shallow lakes, one of the most widespread water bodies in the world, are easily shifted to a new trophic state due to external interferences. Shifting hydrologic conditions and climate change can cause cyanobacterial harmful algal blooms (CyanoHABs) in shallow lakes, which pose serious threats to ecological integrity and human health. This study analyzed the effects of hydrologic and meteorological variables on cyanobacterial blooms in Yangtze-connected lakes (Lake Dongting and Poyang) and isolated lakes (Lake Chao and Tai). The results show that (i) chlorophyll-a (Chl-a) concentration tends to decrease exponentially with increasing relative lake level fluctuations (RLLF) and precipitation, but to increase linearly with increasing wind speed and air temperature; (ii) Chl-a concentrations in lakes were significantly higher when RLLF \u3c 100, precipitation \u3c 2.6 mm, wind speed \u3e 2.6 m s−1, or air temperature \u3e 17.8 °C; (iii) the Chl-a concentration of Yangtze-isolated lakes was more significantly affected by water level amplitude, precipitation, wind speed and air temperature than the Yangtze-connected lakes; (iv) the RLLF and the ratio of wind speed to mean water depth could be innovative coupling factors to examine variation characteristics of Chl-a in shallow lakes with greater correlation than single factors

Multi-cycle bioregeneration of spent perchlorate-containing macroporous selective anion-exchange resin

Ion exchange using perchlorate-selective resin is possibly the most feasible technology for perchlorate removal from water. However, in current water treatment applications, selective resins are used once and then incinerated, making the ion-exchange process economically and environmentally unsustainable. A new concept has been developed involving the biological regeneration of resin-containing perchlorate. This concept involves directly contacting perchlorate-containing resins with a perchlorate-reducing microbial culture. In this research, the feasibility of multi-cycle loading and bioregeneration of a macroporous perchlorate-selective resin was investigated. Loading and bioregeneration cycles were performed, using a bench-scale fermenter and a fluidized bed reactor followed by fouling removal and disinfection of the resin. The results revealed that selective macroporous resin can be employed successfully in a consecutive loading-bioregeneration ion-exchange process. Loss of resin capacity stabilized after a few cycles of bioregeneration, indicating that the number of loading and bioregeneration cycles that can be performed is likely greater than the five cycles tested. The results also revealed that most of the capacity loss in the resin is due to perchlorate buildup from previous regeneration cycles. The results further indicated that as the bioregeneration progresses, clogging of the resin pores results in strong mass transfer limitation in the bioregeneration process

Performance of Pumice Stone as a Packing in Fixed-bed Aerobic Bioreactor

In this research, the performance of pumice stone as a fixed bed support in the biological treatment of the synthetic wastewater of sugar beet factory was evaluated. Pumice is a volcanic rock having high porosity and specific surface. and in comparison with other supports, pumice has a very low price. The experiments were done on an up-flow biofilm reactor, the effective volume of which was 14.2 L, with pumice fixed bed supports. After the starting period, the reactor was operated in steady-state mode, which lasted 222 days, at hydraulic retention time of 12, 16 and 24 hours and influent COD concentration of 750, 1500 and 2250 mg/L. During the operation, the contamination removal efficiencies from 89 to 97 percent were achieved in 9 experimental runs. The results demonstrate that in organic loading rate from 750 to 4500 gr.COD/m3/day in the mentioned status the reactor's efficiency is satisfactory. In addition, some kinetic prevalent models were tested with the experimental data. Results show that according to the regression coefficients, Grau second order kinetic model and modified Stover-Kincannon model are appropriate for predicting similar reactors situations and designing new reactors, and the related equations were derived

Bioregeneration of Perchlorate-Laden Gel-Type Anion-Exchange Resin in a Fluidized Bed Reactor

Selective ion-exchange resins are very effective to remove perchlorate from contaminated waters. However, these resins are currently incinerated after one time use, making the ion-exchange process incomplete and unsustainable for perchlorate removal. Resin bioregeneration is a new concept that combines ion-exchange with biological reduction by directly contacting perchlorate-laden resins with a perchlorate-reducing bacterial culture. In this research, feasibility of the bioregeneration of perchlorate-laden gel-type anion-exchange resin was investigated. Bench-scale bioregeneration experiments, using a fluidized bed reactor and a bioreactor, were performed to evaluate the feasibility of the process and to gain insight into potential mechanisms that control the process. The results of the bioregeneration tests suggested that the initial phase of the bioregeneration process might be controlled by kinetics, while the later phase seems to be controlled by diffusion. Feasibility study showed that direct bioregeneration of gel-type resin was effective in a fluidized-bed reactor, and that the resin could be defouled, reused, and repeatedly regenerated using the method applied in this research

Engineered Biochar Production and Its Potential Benefits in a Closed-Loop Water-Reuse Agriculture System

Biochar’s potential to remove various contaminants from aqueous solutions has been widely discussed. The rapid development of engineered biochar produced using different feedstock materials via various methods for wastewater treatment in recent years urges an up-to-date review on this topic. This article centers on summarizing state-of-the-art methods for engineered biochar production and discussing the multidimensional benefits of applying biochar for water reuse and soil amendment in a closed-loop agriculture system. Based on numerous recent articles (<5 years) published in journals indexed in the Web of Science, engineered biochar’s production methods, modification techniques, physicochemical properties, and performance in removing inorganic, organic, and emerging contaminants from wastewater are reviewed in this study. It is concluded that biochar-based technologies have great potential to be used for treating both point-source and diffuse-source wastewater in agricultural systems, thus decreasing water demand while improving crop yields. As biochar can be produced using crop residues and other biomass wastes, its on-farm production and subsequent applications in a closed-loop agriculture system will not only eliminate expensive transportation costs, but also create a circular flow of materials and energy that promotes additional environmental and economic benefits

Impact of Ammonia-Based Aeration Control (ABAC) on Energy Consumption

An Ammonia-Based Aeration Control (ABAC) system is installed in the primary aeration basins of a regional wastewater treatment facility. The energy consumption of the system of air blowers, measured in kilowatts per hour by an existing meter, is analyzed for seven months after the installation of the ABAC system and compared to system performance prior to commissioning of the ABAC system. Processed data, including volume flow rate, ammonia loading, and treatment equipment efficiency, are evaluated for periods before and after the ABAC system installation. Ammonia mass loading and air transfer ratio in the aeration basins are determined to be the leading factors affecting the performance of the ABAC system and thus impacting the metered energy consumption. The metered energy consumption data are normalized by the two calculated ratios, which reflect the change in ammonia loading and air transfer ratio. The normalized and metered energy consumption data are compared, and the results show a reduction in energy consumption since the installation of the ABAC system. A yearly savings of approximately 9 ± 1% in energy costs is estimated with the installation of the ABAC system. The savings in energy consumption calculated as well as the improvements in nitrification efficiency confirm the benefit of an ABAC system in reducing operation costs and enhancing process control