Journal of Environmental Engineering

A laboratory investigation evaluated the effect of backpulsing (BP) and continuous surface cleaning (CSC) on high-shear rotary membrane system (HSR-MS) flux performance while treating three surrogate naval shipboard wastewaters (i.e., bilgewater, blackwater, and thermal destruction quench water) while also seeking to better understand the HSR-MS permeate flux-rotation-diameter ($J\text{-}\omega \text{-}D$) relationship. $J$ increased with $\omega$, BP, and CSC. BP and CSC provided the most benefit at lower $\omega$. Incorporating BP and CSC improved the inner area $J$. A volumetric flow rate analysis conveyed the importance of disc diameter—the outer membrane area produced the majority of the total flow. Collectively, the results indicate that BP and CSC enhanced the standard HSR-MS flux performance at low $\omega$ by replacing the loss of or augmenting the rotationally induced shear. This conclusion supports HSR-MS operation at lower $\omega$, which allows the use of larger disc diameters, providing an increase in performance per disc and a reduction in the number of membrane discs required.

Floc blankets are fluidized, concentrated beds of particles utilized in some upflow sedimentation tank reactor configurations in water treatment. The presence of a floc blanket can significantly enhance removal of turbidity when coupled with lamellar sedimentation. Blanket dynamics have not been extensively studied, but are important for understanding blanket formation and operational control in full-scale water treatment plants. This research employed image analysis to reveal the temporal dynamics of floc blanket suspended solids concentration and floc-water interface height. Turbidity measurements were used to corroborate image analysis as a valid method for measuring solids concentration in the floc blanket and in the floc blanket supernatant. Observations from image analysis reveal relatively distinct stages in the creation of a floc blanket: thickening (increasing suspended solids concentration) in the absence of a floc-water interface, thickening with an interface, and steady state. Preliminary performance results suggest that turbidity removal is more significantly impacted by blanket concentration than blanket height. Two important factors were found to impact blanket dynamics during the interval when the height of the floc-water interface was increasing: (1) thickening, and (2) mass transfer between the supernatant above the floc-water interface and the floc blanket. Floc blanket thickening during formation has been confirmed to occur at both variable and constant interface upflow velocity. This observation suggests that floc properties (size and density) change during floc blanket formation.

Research has shown biological filtration to be a successful treatment for the removal of manganese (Mn) from groundwater and surface water. In this study, bench-scale direct biofiltration was used to remove Mn and dissolved organic carbon (DOC) from a pH 6 surface water source in Halifax, Nova Scotia, Canada. Three factors were examined for their effects on Mn and DOC removal: media type (granular activated carbon and anthracite), pH (6 and 9–11), and nutrient enhancement with phosphorus (P; 20 and $200\mathrm{\mu g}/\mathrm{L}$). pH was a significant factor in Mn removal ($\alpha =0.05$). The P-enhanced pH 6 biofilters for both media obtained an average 91% Mn removal; the P-enhanced pH 9–11 filters for both media achieved an average 70% Mn removal. An average of 23% DOC removal was achieved with P enhancement, compared to 12% DOC removal without P enhancement. Mn was likely removed by biological oxidation and biogenic oxide adsorption. These results show that direct biofiltration of raw surface water at pH 6 can remove Mn to below the $50\mathrm{\mu g}/\mathrm{L}$ guideline from an influent Mn concentration of over $1\mathrm{mg}/\mathrm{L}$.

A numerical turbidity limit that will affect highway construction sites to meet a standard turbidity value in the runoff was to be implemented in 2013. Although the limit appears to be deferred to future permits, this study addresses multiple turbidity issues that are relevant in implementations of numerical limits for construction storm water quality. Background turbidity maps are created to graphically present the natural turbidity background levels in the state of Texas, and those maps are compared with the proposed numerical limit; the median value map is interpreted as supportive of a regionally adjusted numerical limit. The water and solids color effect on turbidity measurement is evaluated, in addition to the use of sample dilution to extend instrument range. Substantial turbidity measurement differences between two different types of turbidimeters (field portable and bench) is explored, and a cause is postulated. Two construction sites were monitored to develop a reasonable protocol for self-reporting, should future permits require such activity. The results suggest that adjustable numerical limits should be used in future permits if such permits require monitoring; water and solids color effects are negligible for intended application; sample dilution can extend instrument range, but diluted samples under-report turbidity; and the selection of instrumentation is nontrivial.

The application of simultaneous adsorption and biodegradation processes in the same reactor was known to be effective in the removal of both biodegradable and nonbiodegradable contaminants in various kinds of wastewater. The objective of this study was to evaluate the efficacy of the two processes under sequencing batch reactor (SBR) operation in treating lead- and cadmium-containing synthetic wastewater with activated rice husk (ARH) as the adsorbent. The SBR systems were operated with FILL, REACT, SETTLE, DRAW, and IDLE periods in the ratio of $1.0:19.0:3.0:0.5:0.5$ for a cycle time of 24 h. Cadmium (II) was found to exert a more pronounced inhibitory effect on the bioactivity of the microorganisms compared with Pb (II). The addition of ARH into the SBR reduced the toxicity of Cd(II) on microorganisms by Cd(II)-ARH adsorption and hence enhanced the biooxidation. It was observed that the combined presence of Cd(II) and Pb(II) did not exert synergistic effects on the microorganisms.

Storm water management is becoming increasingly important as communities seek to mitigate the problems of accelerated storm water runoff. Using rain barrels to capture roof runoff is one strategy being advocated, but to be effective, this requires a beneficial use for the captured water such as garden irrigation. A previous analysis of this strategy based on the meteorological conditions of Cleveland, Ohio indicated that this would only yield a modest runoff reduction. The results presented here extend analysis to the wide range of meteorological conditions experienced across the continental United States. Theoretical rain barrel performance at seventy locations was evaluated using 2000–2009 daily precipitation records and local growing season durations. Simulations indicated that rain barrel performance would have been highly variable. The use of 235 L (64 gal.) rain barrels would have achieved total roof service area runoff reductions of 3 to 44%. The largest reductions would have occurred in southwestern states. The smallest would have occurred in southeastern states. While accomplishing these reductions, the rain barrels would have satisfied 5 to 73% of the irrigation demand of $13.9{\mathrm{m}}^2$ ($150{\mathrm{ft}}^2$) gardens. The assessment method and results presented should help communities evaluate the potential effectiveness of rain barrels and help establish storm water management program priorities.

In this study, the chemical and microbiological characteristics of bridge deck runoff were evaluated at four bridge locations in the state of Nebraska. These bridges represent a range of annual average daily traffic (AADT) and receiving stream characteristics. In addition to runoff sampling, dry weather water quality and sediment quality was evaluated to determine if bridges influence dry weather water quality. Bridge deck runoff was determined to be not toxic using a 48-h acute toxicity assay with fathead minnows (Pimephales promelas). The results determined no significant differences in water and sediment quality upstream and downstream of the bridge at each of the four locations, indicating that bridges do not influence the receiving water quality or sediment during dry weather. The bridge deck runoff was found to contain a number of chemical constituents, and metals and nutrients were detected most frequently. The quality of bridge deck runoff was determined to be similar to that of roadway runoff, and no relationship between the contaminant concentrations and AADT or antecedent dry period (ADP) could be determined in this study.