Monroe L. Weber-Shirk

Bacterivory by a chrysophyte in slow sand filters

Bacterivory previously was shown to be responsible for significant removal of bacteria in slow sand filters. This research was designed to identify the responsible bacterivores and to evaluate their ability to remove a significant fraction of bacteria. A small (3-μm diameter) chrysophyte was isolated from slow sand filter effluent. The ability of a pure culture of the chrysophyte to rapidly ripen a slow sand filter was demonstrated.

An Affordable Open-Source Turbidimeter

Turbidity is an internationally recognized criterion for assessing drinking water quality, because the colloidal particles in turbid water may harbor pathogens, chemically reduce oxidizing disinfectants, and hinder attempts to disinfect water with ultraviolet radiation. A turbidimeter is an electronic/optical instrument that assesses turbidity by measuring the scattering of light passing through a water sample containing such colloidal particles. Commercial turbidimeters cost hundreds or thousands of dollars, putting them beyond the reach of low-resource communities around the world. An affordable open-source turbidimeter based on a single light-to-frequency sensor was designed and constructed, and evaluated against a portable commercial turbidimeter. The final product, which builds on extensive published research, is intended to catalyze further developments in affordable water and sanitation monitoring.

Fluid shear influences on the performance of hydraulic flocculation systems.

Gravity driven hydraulic flocculators that operate in the absence of reliable electric power are better suited to meet the water treatment needs of green communities, resource-poor communities, and developing countries than conventional mechanical flocculators. However, current understanding regarding the proper design and operation of hydraulic flocculation systems is insufficient. Of particular interest is the optimal fluid shear level needed to produce low turbidity water. A hydraulic tube flocculator was used to study how fluid shear levels affect the settling properties of a flocculated alum-kaolin suspension. A Flocculation Residual Turbidity Analyzer (FReTA) was used to quantitatively compare the sedimentation velocity distributions and the post-sedimentation residual turbidities of the flocculated suspensions to see how they were affected by varying fluid shear, G, and hydraulic residence time, θ, while holding collision potential, Gθ, constant. Results show that floc breakup occurred at all velocity gradients evaluated. High floc settling velocities were correlated with low residual turbidities, both of which were optimized at low fluid shear levels and long fluid residence times. This study shows that, for hydraulic flocculation systems under the conditions described in this paper, low turbidity water is produced when fluid shear is kept at a minimum. Use of the product Gθ for design of laminar flow tube flocculators is insufficient if residual turbidity is used as the metric for performance. At any Gθ within the range tested in this study, best performance is obtained when G is small and θ is long.

Enhancing slow sand filter performance with an acid-soluble seston extract.

An acid-soluble extract was obtained from Cayuga Lake (Ithaca, NY) seston and applied to slow sand filters at different application rates. Biological activity in the filters was inhibited with 3mM sodium azide. The filters were challenged with a synthetic raw water containing Escherichia coli. The Cayuga Lake seston extract (CLSE) fed filters removed up to 99.9999% of the influent coliforms while the control filter (no CLSE) removed 50%. Filter performance was correlated with the amount of CLSE applied to the filters.

Method for quantitative analysis of flocculation performance

The sedimentation rate and the post-sedimentation residual turbidity of flocculated suspensions are properties central to the design and operation of unit processes following flocculation in a water treatment plant. A method for comparing flocculation performance based on these two properties is described. The flocculation residual turbidity analyzer (FReTA) records the turbidity of flocculent suspensions undergoing quiescent settling. The fixed distance across which flocs must travel to clear the measurement volume allows sedimentation velocity distributions of the flocculent suspension to be calculated from the raw turbidity data. By fitting the transformed turbidity data with a modified gamma distribution, the mean and variance of sedimentation velocity can be obtained along with the residual turbidity after a period of settling. This new analysis method can be used to quantitatively compare how differences in flocculator operating conditions affect the sedimentation velocity distribution of flocs as well as the post-sedimentation residual turbidity.

Flocculation model and collision potential for reactors with flows characterized by high Peclet numbers

A mechanistically-based model is developed to characterize flocculation in the context of flow regimes with high Peclet numbers such as would occur in serpentine flow reactors. These flow conditions are obtained in gravity-driven hydraulic flocculators without mechanical agitation that are an important component of sustainable water treatment systems where energy efficiency and cost are receiving increasing emphasis. The model incorporates a fractal description of flocs, estimates of floc separation distances, estimates of relative velocities of floc particles dependent on the relevant flow regime, and provides an overall prediction of the required reaction time for formation of settleable flocs based on influent turbidity, alum dose, and energy dissipation rate. Viscosity is shown to be significant for the early stage of flocculation and turbulent eddies are shown to be significant for the final stage of flocculation. The collision potential defined as the product of the hydraulic residence time (θ) and the cube root of the energy dissipation rate (ɛ), i.e., ɛ(1/3)θ, is shown to be a better predictor of flocculator performance than the conventional product of θ and the velocity gradient (G), i.e., Gθ.

Apparatus for Observation and Analysis of Floc Blanket Formation and Performance

AbstractFloc blankets are fluidized beds of aggregated suspended particles utilized in some upflow sedimentation tanks for drinking water treatment. Floc blankets can significantly enhance particle removal and may reduce operation and maintenance costs. An experimental apparatus was built with the goal of developing an understanding of floc blanket physics and to establish a mechanistic basis for optimizing floc blanket performance. Visual insights into floc blanket mechanics are obtained by analyzing transmitted light intensity through a 1.3-cm-thick section of a floc blanket. Floc blankets were formed under simulated raw water conditions of 100 nephelometric turbidity units (NTU), an alum coagulant dose of 45  mg/L (4.1  mg/L as Al), and at sedimentation tank upflow velocities ranging from 0.4 to 1.8  mm/s. This study presents nondestructive methods for measuring floc blanket concentration and position of the floc-water interface, steady-state performance data from the experimental apparatus, and the ef...

Enhanced Particle Capture through Aluminum Hydroxide Addition to Pores in Sand Media

In this study, precipitation of AlðOHÞ3ðamÞ was used to modify a sand filter medium by fluidized-bed pretreatment. A mixture of alum, sodium hydroxide, and tap water was applied to the filter bed in the last stage of the backwash cycle. The placement of AlðOHÞ3ðamÞ in the filter pores was evaluated for both alum-treated raw water (contact filtration) and untreated raw water. The filter pretreated with AlðOHÞ3ðamÞ achieved better than 99.98% removal of an untreated clay suspension, with a filter effluent turbidity below the detection limit of 0.01 NTU. AlðOHÞ3ðamÞ-pretreated filters that were challenged with clay and humic acid achieved ≥ 99:8% turbidity removal efficiency for 14 h of operation in the contact filtration mode. Pretreatment with AlðOHÞ3ðamÞ also enhanced turbidity removal efficiency (up to 99.8%) when the filter was challenged with clay and humic acid, even when the raw water was not coagulated. The aluminum concentration in the filter effluent of an AlðOHÞ3ðamÞ-pretreated filter was below the EPA secondary drinking water maximum contaminant level (200 μg= Lf or aluminum) when the raw water pH was between 6 and 7; the pretreated filter had the best performance at pH 6. DOI: 10.1061/(ASCE)EE .1943-7870.0000370.

Stacked Filters: Novel Approach to Rapid Sand Filtration

AbstractRapid sand filters are a familiar and mature technology, but the mechanical sophistication they incorporate in industrialized nations limits their sustainable application in developing countries. Conventional rapid sand filters require pumps, elevated tanks, or multiple filter units to generate high flow rates for backwashing. Stacked rapid sand filtration is introduced here as a more robust and sustainable alternative. A stacked rapid sand filter can backwash itself with no additional flow, which eliminates the need for pumps or other expensive equipment. This study presents laboratory and field proof-of-concept demonstrations of this novel technology. The multilayer configuration of stacked rapid sand filters allowed a laboratory unit to be loaded at 1.4–1.83  mm/s (120–160  m/day) per layer and backwashed at 10–11  mm/s (860–950  m/day) with the same or similar total flow rate. The filtered effluent met U.S. Environmental Protection Agency drinking water standards. The backwash cycle was also d...

Postsedimentation Application of Polyaluminum Chloride to Enhance Dual Media Filter Performance

The postsedimentation addition of polyaluminum chloride (PACl) was investigated as a means to enhance particle removal effi- ciency in dual media filtration. The process modification was evaluated in laboratory studies and at the Cornell Water Filtration Plant (CWFP). The PACl was continuously metered into CWFP filter influent to increase concentrations by 0.06-4.2 mg=L (as aluminum) during the filter-to-waste stage of the filter operation cycle to accelerate filter ripening. Lower influent PACl concentrations ranging from 0.056-0.43 mgAl=L were also continuously applied during filtration. In comparison to a control filter that received no PACl addition, the ripening time required decreased with PACl dose, and the incremental improvement in particle removal during filtration increased with PACl dose. The addition of 0.056 mgAl=L of PACl (the lowest concentration tested) significantly reduced initial filter ripening time at the CWFP from 10-1.4 h, and effluent turbidity in the test filter over the 77 h filter run was lower than the control filter by an average of 17%. Incremental head loss increase caused by the PACl feed was dose dependent and was negligible for the lowest dosage tested. DOI: 10.1061/ (ASCE)EE.1943-7870.0000659.