Impacts of Feedwater Quality Change on the Oldest Continuously Operated Brackish-Water Reverse Osmosis Desalination Plant in the United States

Brackish groundwater is abundant in many coastal zones of the world. The water can be economically treated with low-pressure reverse osmosis. A key issue is the stability of the feedwater pumped from groundwater systems. Commonly, groundwater solute-transport models are used to evaluate the long-term changes in salinity with time that impact brackish-water reverse osmosis (BWRO) desalination system process design. These models are run to assess changes over a 20- to 40-year period. The City of Cape Coral, Florida operates two regional BWRO facilities with the South Plant being the oldest continuously operated system in the world. This facility has a capacity of 68,182 m3/d and can treat raw water with a total dissolved solids (TDS) concentration up to 4000 mg/L. Two solute transport models were constructed to evaluate future salinity change in the groundwater source. The first model conducted in 1991 produced a range of probable changes with a high, most probable (mid), and low range. Actual data confirm the low range of the model produced an accurate result (within 15%) and that the 4000 mg/L threshold would not be exceeded until beyond 2031. The second modeling effort conducted in 2014 suggested that the 4000 mg/L TDS threshold would be reached in 2018, which did not happen. The use of real data and regression analyses for all wells suggests that the 4000 mg/L TDS concentration will not be exceeded until after 2060. Once the TDS threshold is reached, the plant would require a process change to allow treatment of higher TDS water. The current analysis shows that plant process design modification would not be required for up to 40 years into the future. The standard conceptual model assuming predominantly upward recharge during pumping was accurate with the addition of an enhanced zone of leakage caused by a fracture zone or a fault. A key issue that contributed to the success of the facility was the use of groundwater solute transport modeling prior to the final design of the membrane process during plant expansions.

Changes in Pumping-Induced Groundwater Quality Used to Supply a Large-Capacity Brackish-Water Desalination Facility, Collier County, Florida: A New Aquifer Conceptual Model

Brackish-water reverse osmosis (BWRO) desalination facilities are designed to treat feedwater within a fixed range in salinity. If the salinity and ion concentrations of the feedwater rises above the maximum design concentrations, then the plant may ultimately fail. BWRO plants typically use groundwater as a feedwater source. Prior to the process design, a detailed groundwater assessment is made to characterize the source aquifer system and to develop a solute-transport model that is used to project the changes in water quality over the expected useful life of the facility. Solute transport-modeling performed for the Collier County (Florida) South BWRO facility, which was designed to produce 30,303 m3/d with an expansion to 75,758 m3/d, used an aquifer system conceptual model that assumed upwards migration over time of brackish waters with higher salinities into the production zones. This conceptual model is typical of how most BWRO systems developed in the United States operate. The original solute transport model predicted a range of increases in dissolved chloride concentrations over a 20-year period from a low of 5 mg/L/yr, a mid-range of 35 mg/L/yr, and a high range of 85 mg/L/yr. Actual data collected over a 11- to 13.5-year period showed that the dissolved chloride concentration average of the feed water decreased by 16 mg/L/yr. The original conceptual model was found to be inaccurate in that it suggested an upwards recharging system, whereas downward leakage (or perhaps lateral migration) of fresher water appears to be occurring in the system. This is an example of a long-term solute-transport model audit, which is rarely performed, in which a new conceptual model was found to be applicable to an aquifer system used to feed a BWRO facility.

SOLUTE TRANSPORT MODELLING IN LOW-PERMEABILITY HOMOGENEOUS AND SATURATED SOIL MEDIA

Fickian and non-Fickian behaviors were often detected for contaminant transport activity owed to the preferential flow and heterogeneity of soil media. Therefore, using diverse methods to measure such composite solute transport in soil media has become an important research topic for solute transport modeling in soil media. In this article, the continuous-time random walk (CTRW) model was applied to illustrate the relative concentration of transport in low-permeability homogeneous and saturated soil media. The solute transport development was also demonstrated with the convection-dispersion equation (CDE) and Two Region Model (TRM) for comparison. CXTFIT 2.1 software was used for CDE and TRM, and CTRW Matlab Toolbox v.3.1 for the CTRW simulation of the breakthrough curve. It was found that higher values of determination coefficient (R2) and lower values of root mean square error (RMSE) concerning the best fits of CDE, TRM, and CTRW. It was found that in the comparison of CDE, TRM, and CTRW, we tend to use CTRW to describe the transport behavior well because there are prevailing Fickian and non-Fickian transport. The CTRW gives better fitting results to the breakthrough curves (BTCs) when β has an increasing pattern towards 2.00. In this study, the variation of parameters in three methods was investigated and results showed that the CTRW modeling approach is more effective to determine non-reactive contaminants concentration in low-permeability soil media at small depths.

Vulnerability assessment of the Trinity Aquifer in Texas due to sulfonamides antibiotics leaching to groundwater for

<p>Texas has the largest population of cattle farming and the highest production of poultry farming across the United States. In northeastern region, antibiotics have been widely used in Concentrated Animal Feeding Operations (CAFO) as veterinary pharmaceuticals (VP). Not fully metabolized and excreted antibiotics have caused soil pollution and resulted groundwater contamination. Sulfonamides’ high excretion rate from animals, low sorption to soils, and impact on nitrate-reducing bacteria for nitrate reduction capabilities, enhance leaching and secondary pollution from inherent nitrate-N contamination. However, there is a limited understanding of sulfonamides transport from the surface to groundwater. This research assessed the Trinity Aquifer vulnerability by incorporating major hydrogeological factors that affect and control the groundwater contamination using GIS-based DRASTIC along with major chemical factors using HYDRUS solute transport modeling. The study reclassified and refined subareas with different vulnerability potentials by overlaying various spatially referenced digital data layers. Additionally, sulfonamides transport was simulated for different vulnerable scenarios to estimate persistence of the antibiotic and potential concentrations reaching the aquifer, developing predicted methods to prevent, mitigate and remediate groundwater contamination caused by sulfonamides antibiotics.</p><p> </p>

PREDICTING USEFUL LIFE OF COCOPEAT IN A FILTER BED TREATING WASTEWATER WITH HEAVY METALS USING HYDRUS-1D

The effectiveness of cocopeat as an adsorbent for the treatment of wastewater containing heavy metals was reported in previous studies. In this study, cocopeat was used as an adsorbent in a filter bed system treating wastewater from a small scale gold mining (SSGM) ball mill facility. A total of 6,000 L of actual SSGM wastewater collected from a ball mill facility in Paracale, Camarines Norte were used in the experimental runs. The filter bed was evaluated by determining its heavy metal removal efficiencies for 50 days at a flow rate of 40 L/hr. After the experimental runs, HYDRUS1D was used to simulate the transport of lead (Pb) in the filter bed and predict the remaining useful life of cocopeat as a heavy metal adsorbent. Lead was selected for the solute transport modeling in HYDRUS-1D since Pb was the highest concentration in the wastewater and also exceeded the government effluent limit. Measured data from the experimental runs and water flow parameters of cocopeat were used as input values in the simulation with varying cocopeat thickness and initial concentration flux. Results showed that by increasing the thickness of the cocopeat layer, the useful life of cocopeat in the filter bed was extended. By using the actual concentration of Pb (0.0933 mg/L) in the wastewater, HYDRUS-1D was able to simulate Pb transport in the filter and predict that the useful life of cocopeat 50 cm thick treating an actual SSGM wastewater was 2.74 years.

Verification of Radiocarbon Transport Predicted by Numerical Modeling in the Porous Formation of NE Hungary Considering Paleo-Hydrogeology

ABSTRACTVerification of a groundwater flow model by radiocarbon (14C) data are presented taking into consideration the paleo-hydrogeological changes. Northeastern area of the Great Hungarian Plain was a deep-lying flat area, and its central part (Nyírség) has been uplifted in the last 15,000 years. These geological events have drastically changed the hydrogeological conditions of Nyírség. The groundwater flow system is composed of the Quaternary-Pliocene-Upper Pannonian clastic sediments. Groundwater flow modeling has been performed to define the main lateral and vertical flow directions and velocities controlling the propagation of the environmental radioactive tracer 14C. Solute-transport modeling was used to calculate the 14C activity. The recent steady-state groundwater flow velocity was reduced to a reasonable value characterizing the average flow velocity over the 15 ka simulation period using “trial and error” method. The best fit between the simulated and measured 14C data was achieved by assuming 0.4 flow velocity reduction factor. Results indicate that the present steady-state flow model with this flow velocity reduction factor is capable of reproducing the observed 14C data taking into account the effect of the significant uplift of the part of the land surface in the last 15 ka in NE Hungary.