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Coastal wetlands and estuaries are impacted by nutrient loads from a variety of sources including infrequently occupied hunting and fishing camps. The marshland upwelling system (MUS) was designed to treat wastewater in the coastal environment where traditional septic systems or centralized wastewater collection and treatment are not viable. A laboratory macrocosm study was designed to simulate field conditions in which domestic wastewater is treated via injection into a marsh subsurface. Treatment of wastewater nitrogen (N) utilizing the MUS was examined under high (∼20 ppt) and low (∼2 ppt) salinity conditions. Two N wastewater solutions were used, one treatment consisted of 100 mg NH

The sulfate release from solidified/stabilized fluorogypsum was measured to develop the effective diffusion coefficients (De) as a parameter to assess the dissolution potential in aquatic a...

The presence of bulk water and the resistant cell walls significantly limit the efficiency of lipid extraction from microalgal biomass paste. Current methods to rupture the cell walls (i.e. grinding after freeze-drying, osmotic shock, sonication) are energy intensive and time consuming. Due to their high surface energy concentration and high surface to volume ratio, silver nanoparticles can enhanced the cell wall rupture to increase the extraction efficiency of cell components. In this study, silver nanofibers were added as enhancers for the Folch’s extraction method and microwave assisted extraction of lipids from wet biomass paste (water content of 80.9%). Nanofibers concentrations of 0–1000 μg g−1 were tested. Two solvent:biomass ratios were tested in the Folch’s extraction method. Two temperatures (70 and 90 °C) and three treatment times (2, 5 and 10 min) were compared in the microwave assisted extraction. The results showed that the extraction efficiency increased with increased concentration of the nanofibers in the range tested. At concentrations of 1000 μg g−1 silver nanofibers (w/w based on the solvent and biomass solution) the efficiency of lipid extraction increased by ∼30% and 50% for the Folch’s and microwave assisted lipid extraction respectively. Treatment with AgNO3 in the same concentration as the nanofibers did not improve the extraction compared with no silver or nanofibers addition. The extraction method affected the lipid fatty acids profile. The Folch’s extraction with no silver nanofibers resulted in proportionally higher short chain saturated fatty acids, but lower lipid extraction. The microwave assisted lipid extraction provides the best results considering fatty acid profile, treatment time, solvent use and lipid extraction efficiency.

Enterococci concentrations in seawater samples collected in 2010 at a Gulf Coast beach in the afternoon were significantly lower (12 MPN/100 mL) compared with morning samples (172 MPN/100 mL). The factors affecting temporal differences of enterococci concentration in beach waters were studied through five laboratory experiments analyzing beach sands, solar radiation, salinity, and turbidity. Enterococci were found in beach sands at a geometric mean of 43 MPN per 100 g of sand, demonstrated the ability to persist for extended periods of time, and increased when incubated (geometric mean of 54 MPN per 100 g sand). Solar radiation inactivated large enterococci concentrations (≥24,196 MPN/100 mL) in as little as four hours in salinities ranging from 0 to 25 parts per thousand (ppt). Increased turbidity (70 and 140 NTU) hindered the effect of solar radiation, suggesting that near-shore turbidity may promote higher enterococci concentrations. The results indicate that enterococci replenishment alo...

The effect of salinity, dissolved oxygen and NO3-N concentration on the denitrification of recirculating aquaculture water using polyhydroxybutyrate (PHB) was evaluated. Four PHB media with different molecular weights and configurations were tested. The results show that at higher nitrate concentrations in the influent water, the consumed PHB:NO3-N ratio decreased. An average of 2.9 g of PHB:1 g NO3-N removed at temperatures of 20.8 ± 1.1 °C was measured. Although the molecular weight showed an apparent correlation with the denitrification rates, the correlation was not statistically significant. A moderately biofouled granular media displays a heterogeneity of microenvironments that allow some denitrification to occur in the presence of bulk dissolved oxygen levels approaching 5 mg L−1. As a practical approach, the inhibitory effects of oxygen can be mitigated either by design of the denitrification media bed and/or by control or reduction of the influent dissolved oxygen levels. The high plastic consumption needed for oxygen removal indicates that the second approach is more cost efficient. At a flux of 60 m3 m−2 d−1 the denitrification rate decreases at a constant rate in the first 30 cm of the PHB bed. Below this depth, the denitrification rate decreases very slowly and stays above 1 kg-NO3-N m−3 d−1. In a pragmatic sense, denitrification abilities can be expected to be similar in all salinities. Volumetric nitrate removal rates in the order of 2.5 kg-NO3-N m−3 media d−1 should be broadly obtained in fresh and marine water systems. In the range of up to 250 mg NO3-N L−1, the PHB can be used as a base for a passive denitrification unit that requires little management. The availability of an economic source of PHB such as production waste and the development of the bioplastic industry is determinant for the adoption of this material as a carbon source for denitrification processes.

Aerobic biodegradation of polyhydroxybutyrate (PHB) was investigated. Mass loss experiments were performed to determine degradation kinetics. Tributyl citrate was blended with some test samples to determine the impact of a natural plasticizer on biodegradation. Effects of biodegradation in the physical, chemical, thermal, and mechanical properties of the materials tested were determined. Plates of different thicknesses (0.24, 1.2, 3.5, and 5.0 mm) were degraded to determine the effect of initial mass:initial surface area ratio on degradation rates. The mass:initial surface area is proportional to the plate thickness. PHB biodegradation rates obtained are dependent on the mass:surface area ratio. Temperature affects the relation of degradation rate to initial mass:initial surface area. PHB in plates up to a thickness of 3.5 mm can degrade completely in compost. Plates with an initial mass:initial surface area ratio of

Anaerobic biodegradation in sewage sludge of polyhydroxybutyrate (PHB) was investigated. Evolved gaseous carbon was measured to assess biodegradability according to ASTM D5210. Mass-loss experiments were performed to determine degradation kinetics. Changes in the polymer properties were investigated. The impact of a natural plasticizer [tributyl citrate (TBC)] on biodegradation was determined. Polylactic acid was also biodegraded for comparison. Melt-pressed plates of PHB (with thicknesses of 0.24, 0.5, 1.2, 3.5, and 5.0 mm) were biodegraded to investigate the relationship between initial mass:initial surface area ratios and decay rates. Scanning electron microscopy micrographs of degraded specimens were recorded for visual illustration of the degradation process. A relationship between initial mass:initial surface area and degradation rates indicates that the thickness and surface area of the material affect its degradation. The degradation rates were impacted by the sewage sludge activity. TBC additive hindered PHB's rate of degradation. Thermal properties, molecular bonding, and molecular weight measured by differential scanning calorimetry, Fourier transform infrared, and size exclusion chromatography, respectively, were only slightly affected by biodegradation, indicating that recycling PHB will not affect its performance.

The marshland upwelling system (MUS) was developed as an onsite wastewater treatment approach for coastal dwellings. The MUS removes fecal bacteria in injected wastewater by utilizing the processes of filtration, straining, adsorption, predation, and die-off through saturated subsurface sediments. The objective of this research was to evaluate the long-term sustainability of the MUS by evaluating removal efficiency of fecal bacteria from raw wastewater and assessing the system background recovery after the MUS stopped operation. Based on 32-month monitoring on an MUS site located in Bayou Segnette Canal Waterway, Louisiana, we found that the MUS compared well with other constructed wetland systems. The MUS showed an enhanced efficacy of fecal bacteria removal after long-time operation due to the deposition of solid particles from primary wastewater and the growth of biofilm in subsurface over time. Moreover, the background recovery study indicates that the subsurface environment has recovered com...

This research investigated the sorption and transport of MS-2 in saturated sand under a wide range of salinities using one-dimensional column experiments. The salinity varied from 0 ppt (fresh water) to 30 ppt. The MS-2 in the fresh water showed very weak adsorption due to having the same negative charge as the sand. Increasing the salinity concentrations dramatically enhanced MS-2 adsorption. The MS-2 breakthrough revealed the existence of reversible and irreversible sorption sites in the sand. Salinity increased MS-2 attachment by compressing the double layers of MS-2 and reversible sorption sites. The salinity also changed some reversible sorption sites into irreversible sorption sites by reversing to positive surface charges of silica powder. An advection-dispersion-sorption model with a two-site reversible-irreversible kinetic sorption was developed to describe MS-2 breakthrough under different salinity conditions. The sorption parameters were estimated and their independence was evaluated by minimizing the total squared error of the MS-2 data. The proposed model showed good agreement with the experimental data for a wide range of salinity levels from fresh water to near seawater. The strong sorption shown in the MS-2 breakthrough at high salinity levels above 8 ppt was able to distinguish the proposed model from other sorption models. This study promotes the understanding of the viral sorption with salinity and provides a useful model for coastal management of viral migration in saline coastal groundwater.

A continuous microwave system to treat ballast water inoculated with Artemia salina cysts as a model invasive spore was tested for its efficacy in inactivating the cysts present. The system was tested at two different flow rates (1 and 2 L x min(-1)) and two different power levels (2.5 and 4.5 kW). Temperature profiles indicate that the system could deliver heating loads in excess of 100 degrees C in a uniform and near-instantaneous manner when using a heat recovery system. Except for a power and flow rate combination of 2.5 kW and 2 L x min(-1), complete inactivation of the cysts was observed at all combinations at holding times below 100 s. The microwave treatment was better or equal to the control treatment in inactivating the cysts. Use of heat exchangers increased the power conversion efficiency and the overall efficiency of the treatment system. Cost economics analysis indicates that in the present form of development microwave treatment costs are higher than the existing ballast water treatment methods. Overall, tests results indicated that microwave treatment of ballast water is a promising method that can be used in conjunction with other methods to form an efficient treatment system that can prevent introduction of potentially invasive spore forming species in non-native waters.

A continuous microwave system to treat ballast water inoculated with different invasive species was designed and installed atthe Louisiana State University Agricultural Center. The effectiveness of the system to deliver the required heating loads to inactivate the organisms present was studied. The targeted organisms were microalgae (Nannochloropsis oculata), zooplankton at two different growth stages (newly hatched brine shrimp-Artemia nauplii and adult Artemia), and oyster larvae (Crassosstrea virginica). The system was tested at two different flow rates (1 and 2 liters per min) and power levels (2.5 and 4.5 kW). Temperature profiles indicate that, depending on the species present and the growth stage, the maximum temperature increase will vary from 11.8 to 64.9 degrees C. The continuous microwave heating system delivered uniform and near-instantaneous heating at the outlet proving its effectiveness. The power absorbed and power efficiency varied for the species present. More than 80% power utilization efficiency was obtained at all flow rate and microwave power combinations for microalgae, Artemia nauplii and adults. Test results indicated that microwave treatment can be an effective tool for ballast water treatment, and current high treatment costs notwithstanding, this technique can be added as supplemental technology to the palette of existing treatment methods.

The marshland upwelling system (MUS) is an alternative onsite wastewater treatment system developed for coastal communities. The phosphorus treatment efficiency of the MUS operated under high background salinity conditions (∼32 ppt) was examined over the course of a one-year field study. Five individual studies were investigated by intermittently injecting wastewater at a depth of 3.8 m using flow rates/injection frequency regimes of 1.9 L∕min (30 min∕3 h) , 5.5 L∕min (30 min∕3 h) , 2.8 L∕min (30 min∕3 h) , and 2.8 L∕min (15 min∕h) . There were two studies conducted within the 2.8 L∕min (30 min∕3 h) flow regime: (1) with normal influent and (2) with high strength synthetic wastewater. Over the course of the study, no signs of phosphorus saturation were observed. The overall system efficiency for the entire study was estimated to be >98% . Removal rate coefficients ranged from 0.73– 1.25 m−1 and 0.66– 1.08 m−1 for total phosphorus and orthophosphate, respectively. Upon completion of the final 2.8 L∕min (15...

The effectiveness of the marshland upwelling system (MUS) installed in a low-background salinity area was investigated for the removal of fecal bacteria from domestic wastewater. It was hypothesized that travel distance required to meet the treatment objectives would be greater under low-salinity conditions. A suite of three injection regime (flow rate/frequency; 18.9 L/min-15 min/h; 0.95 L/min-15 min/h; and 1.9 L/min-15 min/h) studies was performed over a 1.25-year period to investigate the impact of injection flow rate on the removal of fecal coliforms and Escherichia coli from domestic wastewater injected into the MUS system. Each injection regime resulted in removal efficiencies greater than 99.9% for fecal coliforms and E. coli. The 18.9 L/min study (10 times design flow rate) tested the upper hydraulic loading limit of the system and resulted in eventual system channelization. First-order removal rate constants were estimated as 2.5–2.6 and 1.5–1.7 m–1 for the 0.95 and 1.9 L/min studies, respectivel...

The marshland upwelling system (MUS) was installed on private camps in the Grand Bay National Estuarine Research Reserve, Moss Point, Mississippi. The system was evaluated for its effectiveness in removing fecal coliforms from settled, raw wastewater. A suite of studies was performed at flow rates of 1.9, 2.8, and 5.5 L/min and an injection frequency of 30 min every 3 h to investigate fecal coliform removal. An additional study was performed at a flow rate of 2.8 L/min and an injection frequency of 15 min every hour. Overall, the MUS consistently maintained fecal concentrations below effluent regulatory standards for shellfish harvesting waters (14 most probable number of colonies per 100 mL). Mean influent concentrations of 55,269±2,218,016 colony forming units (CFU)/100 mL were reduced to effluent counts of 2.7±14.07 CFU/100 mL (observed in the 1.5 m wells). Three- to four-log reductions in influent counts were observed over the initial 1.4 vector m from the injection well. The overall removal followed a first-order decay relationship with respect to vector distance, resulting in removal rate constants ranging from 5.6 to 6.6/m and predicted surface concentrations approaching 0 CFU/100 mL. The 2.8 L/min for 30 min every 3 h treatment provided the best effluent quality.

The construction of mixture designs and the methods of response surface analysis of mixture data are discussed and applied for determining the optimum ingredients for stabilized phosphogypsum (PG) composites conducive to marine application. Of particular importance is the ability of the composites to maintain physical integrity when submerged. Therefore, potential indicators for the survivability of the stabilized PG composites were also screened. The triangular coordinate system was used to present the three ingredient components of the PG composites as well as their dependent variables. The augmented simplex centroid design with pseudocomponents was used in determining mixture ingredient composition. A quadratic model with two process variables was used to analyze the experimental results and predict the optimum ingredient composition. The model predicts that a series of PG: class C fly ash:portland type II cement ingredients, such as 62%:35%:3% PG:class C fly ash:portland type II cement and 65%:31%:4% ...

The Marshland Upwelling System (MUS), a decentralized wastewater treatment strategy for coastal dwellings, was examined to assess its ability to remove Escherichia coli from raw sewage as a step towards total treatment. Wastewater was intermittently injected down a 4.6-m injection well into the surrounding salt marsh at 0.9, 1.9, and 3.8 lpm over the 13-month evaluation period. Optimal E. coli removal and hydraulic performance was achieved at the 1.9-lpm flow rate with influent concentrations of 260,000±370,000 E. coli/100 mL reduced to a mean effluent count of 0.4±10.6 E. coli/100 mL. Escherichia coli concentrations declined exponentially with only 0.9-m travel distance needed to reduce influent concentrations by 1 order of magnitude. Predicted surface concentrations were less than 1 E. coli/100 mL. The probability of effluent counts exceeding the U.S. Environmental Protection Agency standard of 126 E. coli/100 mL for recreational waters was 5.5×10-12%. Increasing flows to 3.8 lpm initiated localized hyd...

Phosphogypsum (PG, CaSO4 x H20), a byproduct of phosphoric acid manufacturing, contains low levels of Ra226. PG can be stabilized with portland type II cement and class C fly ash for use in marine environments, thus eliminating the airborne vector of transmission for radon gas. An augmented simplex centroid design with pseudocomponents was used to select 10 PG:class C fly ash:portland type II cement compositions. The 43 cm3 blocks were fabricated and subjected to a 1.5-yr field submergence test and a 28-d saltwater dynamic leaching study. All field composites survived with no signs of degradation. Dynamic leaching resulted in effective calcium diffusion coefficients ranging from 0.21 to 7.5 x 10(-14)m2 s(-1). Effective diffusion depths, calculated for t=1 and 30 yr, ranged from 0.4 to 2.2 mm and from 2.0 to 11.9 mm, respectively. Scanning electron microscopy and wavelength dispersive microprobe and X-ray diffraction analyses of the leached composites identified a 40-60-microm calcite layer that was absent in the control composites. This suggests that a reaction between the composites and the saltwater results in the precipitation of calcite onto the block surface, encapsulating the composites and protecting them from saltwater attack and dissolution.

Phosphogypsum (PG), a solid waste byproduct of phosphoric acid production, was stabilized with lime and cement to produce composites for aquatic applications. Fifteen PG:cement:lime compositions were fabricated and subjected to a 28 day dynamic leaching test (salinity = 20‰) to determine calcium diffusion coefficients used to estimate the composites' long-term dissolution potentials. A one-dimensional diffusion model was used to calculate diffusion coefficients, which were then regressed against PG, cement, and lime percentages to determine the optimal composition for saltwater applications. The diffusion coefficients of the composites ranged from 10-4 to 10-7 (cm2·day-1). Both cement and lime contribute negatively to the diffusion coefficient; however, the interactions between cement and PG and between lime and PG contribute positively. Scanning electron microscope (SEM) observations of the composites used in the dynamic leaching test showed that ruptures developed in all combinations except the 70%:30%:...

Polarized optical microscopy, scanning electron microscopy, and X-ray microprobe analysis were used to investigate the effect of sea water on phosphogypsum (PG):cement composites. Thin surface sections were taken from 85%: 15% PG:cement composites that had been submerged under natural seawater conditions for 1 month and 70%:30% PG:cement composites that had been submerged under natural seawater conditions for 1 year. The optical microscopy results revealed a crystalline layer of carbonates on the surface of the 70%:30% composites, which was absent on the 85%:15% composites. Microprobe analyses indicated that the carbonates, in the form of CaCO3, were formed from Ca2+ and CO32− contained in the seawater, not from the composites. This CaCO3 coating may act as a physical barrier to seawater intrusion into the composites, preventing block degradation. The polarized optical and scanning electron microscopy images of the 85%:15% composites showed surface disruption, which is hypothesized to be caused b...

The objective of this research was to study the sorption and transport of bacteriophage MS-2 (a bacterial virus) in saturated sediments under the effect of salinity and soluble organic matter (SOM). One-dimensional column experiments were conducted on washed high-purity silica sand and sandy soil. In sand column tests, increasing salinity showed distinct effect on enhancing MS-2 sorption. However, SOM decreased MS-2 sorption. Using a two-site reversible-irreversible sorption model and the double layer theory, we explained that pore-water salinity potentially compressed the theoretical thickness of double layers of MS-2 and sand, and thus increased sorption on reversible sorption sites. On irreversible sorption sites, increasing salinity reversed charges of some sand particles from negative to positive, and thus converted reversible sorption sites into irreversible sites and enhanced sorption of MS-2. SOM was able to expand the double layer thickness on reversible sites and competed with MS-2 for the same binding place on irreversible sites. In sandy soil column tests, the bonded and dissolved (natural) soil organic matters suppressed the effects of pore-water salinity and added SOM and significantly reduced MS-2 adsorption. This was explained that the bonded soil organic matter occupied a great portion of sorption sites and significantly reduced sorption sites for MS-2. In addition, the dissolved soil organic matter potentially expanded the double layer thickness of MS-2 and sandy soil on reversible sorption sites and competed with MS-2 for the same binding place.

In this research, the sorption and transport of MS-2 in saturated sediments under the impacts of salinity and soluble organic matter (SOM) are studied through one-dimensional column experiments. The experiments are conducted with the prepared fine sand (d 50 =0.13mm) from industry and the mixture of the sand and field soil (d 50 =0.16mm) obtained from Bayou Segnette State Park, Louisiana. The controlled conditions in all experiments include constant flow rates (0.2 mm/s), neutral condition (pH=7.0±0.5), and constant temperature (25±0.2°C). Bromide is adopted as the conservative tracer to evaluate the retardation factors of MS-2 in the column. In the sorption and transport experiment with MS-2 mixing with nanopure water, the MS-2 showed slight adsorption effect onto sediments. When SOM was added, no attenuating effect on MS-2 adsorption was observed because of MS-2's already weak adsorption in nanopure water. The MS-2 with salinity experiment showed dramatically enhanced adsorption effect in the sand column. It can be explained that the salinity compressed double layers, thereby increasing attachment rates. However, no effect was observed in the sand/soil mixture column, counteraction by organic matter from the soil is the main reason.

Polyhydroxybutyrates (PHB; a bacterially produced biodegradable plastic) was used as a carbon source for biological denitrification of water. The use of a solid, nonwater soluble bioplastic in the denitrification process reduces the need for monitoring and dosing of the carbon source. Denitrification rates at four different salt concentrations (0, 5, 15 and 30 ppt) using synthetic salt water were determined. The mean denitrification rates varied from 2.4 to 3.2 kg-NO3N/m 3 -day, with the highest rate in water with a salinity of 15 ppt. While differences in denitrification rates were observed, they were not statistically significant. Additionally, denitrification rates were higher at higher nitrate concentrations. The denitrification rates had no significant differences with PHA of different molecular weights. Hydrogen sulfide production was not observed in any of the studies, even 45 days after the depletion of nitrates. The mean bioplastic consumption was 2.92 ± 2.70 mg/mg of NO3-N reduced.

A one-dimensional diffusion model based on Fick's second law with a non-zero surface concentration at the solid-solution interface was developed to calculate effective calcium and sulfate diffusion coefficients of composites placed in saltwater. A regression method was used to identify the leaching kinetics. The regression method decomposes the stabilized PG leaching processes into diffusion, surface wash-off, and immediate and long-term precipitation. The immediate surface precipitation of both calcium and sulfate ions occurred only in three of the PG composite combinations. The effective diffusion coefficients of calcium (2.58-4.68 x 10(-13) m2 s(-1)) and sulfate (2.77-5.02 x 10(-13) m2 s(-1)) obtained from the regression method are similar to those obtained from methods of cumulative flux and daily flux associated with the simple diffusion model, provided that the leaching processes do not deviate significantly from that of the diffusion. The ratio (1.13) of effective sulfate to calcium diffusion coefficients obtained using the regression analysis is statistically consistent with the theoretical value (1.31), which further justifies the regression method. The research also implies that the leaching processes of calcium and sulfate ions stop after a certain period of time (300-900 d for calcium and 80-170 d for sulfate) and that the precipitations of calcium and sulfate affect the leaching processes. The regression method can be used to identify the leaching mechanisms and to predict the long-term stability of the stabilized wastes.

Phosphogypsum (PG, CaSO4·H2O), a solid byproduct of phosphoric acid manufacturing, contains low levels of radium ( 266 Ra ), resulting in stackpiling as the only currently allowable disposal/storage method. PG can be stabilized with class C fly ash and lime for potential use in marine environments. An augmented simplex centroid design with pseudo-components was used to select 10 PG:class C fly ash:lime compositions. The 43 cm3 blocks were fabricated and subjected to a field submergence test and 28 days saltwater dynamic leaching study. The dynamic leaching study yielded effective calcium diffusion coefficients (De) ranging from 1.15×10−13 to 3.14×10−13 m2 s−1 and effective diffusion depths (Xc) ranging from 14.7 to 4.3 mm for 30 years life. The control composites exhibited diametrical expansions ranging from 2.3 to 17.1%, providing evidence of the extent of the rupture development due to ettringite formation. Scanning electron microscopy (SEM), microprobe analysis showed that the formation of a CaCO3 on the composite surface could not protect the composites from saltwater intrusion because the ruptures developed throughout the composites were too great. When the PG:class C fly ash:lime composites were submerged, saltwater was able to intrude throughout the entire composite and dissolve the PG. The dissolution of the PG increased the concentration of sulfate ions that could react with calcium aluminum oxides in class C fly ash forming additional ettringite that accelerated rupture development. Effective diffusion coefficients and effective diffusion depths alone are not necessarily good indicators of the long-term survivability of PG:class C fly ash:lime composites. Development of the ruptures in the composites must be considered when the composites are used for aquatic applications.

The Marshland Upwelling System (MUS), a potential alternative wastewater treatment strategy for coastal dwellings, was examined to assess its ability to remove fecal coliforms (FC) from domestic wastewater as a step towards total treatment. Wastewater was intermittently injected down a 4.6-m injection well into the surrounding salt marsh. Optimal performance was achieved at an injection flowrate of 1.9 L/min and injection frequency of 30 minutes every 3 hours. Average influent concentrations of 930000 ± 650 000 colonies / 100 mL were reduced to effluent counts of 4.6 colonies / 100 mL . Coliform removal followed exponential decay versus vector distance traveled with predicted surface concentrations less than or equal to 0.1 colony / 100 mL. Hydraulic performance was acceptable with no significant reductions in permeability observed. Increasing flows to 3.8 L/min produced localized hydraulic dysfunction as indicated by sudden increases in effluent bacterial counts and injection pressures. Although fecal coliform removal typically decreased with increasing injection flowrates and isolated instances of abnormally high effluent counts were observed the MUS never experienced a catastrophic failure during the 13-month evaluation period.