Journal of Environmental Engineering

Turbidity is an important water-quality indicator as it not only indicates the presence of suspended solids but also shows the possible presence of algae, microorganisms, organic matter, and microparticulates. Generally, turbidity is removed through two very important steps in a typical water treatment process: coagulation and flocculation. At lab scale the measurement of flocculation activity may often be difficult and imprecise because reproducible water samples need to be taken offline and inserted into a turbidity meter or spectrophotometer, while the standard jar test system is relatively imprecise and measurements discontinuous and/or subjective. To allow routine quantification, an online quantitative method for the analysis of flocculation activity was developed, which can measure sedimentation as a function of time. This method involved modification of a standard, commercial jar test apparatus by the addition of six turbidity meters coupled with a data-acquisition system operating with LabView software. This system has been tested using a standard reference turbid water suspension containing kaolin, with aluminium sulphate and ferric sulphate as coagulants.

The compound bioflocculant (CBF) was modified by graft copolymerization of acrylic amide and dimethyl diallyl ammonium chloride, and the novel copolymer was denoted as MCBF. The effect of MCBF used as coagulant aid with titanium tetrachloride (${\mathrm{TiCl}}_4$) was investigated for both high and low molecule weight natural organic matter (NOM) removal. Floc characteristics were studied using a laser diffraction particle-sizing device. Results indicated that the monomers were successfully grafted onto the CBF, and the molecule weight and zeta potential of CBF were greatly improved. The MCBF with ${\mathrm{TiCl}}_4$ exhibited synergistic effect by promoting NOM removal, especially at low ${\mathrm{TiCl}}_4$ doses. Additionally, using MCBF as a coagulant aid with ${\mathrm{TiCl}}_4$ can significantly increase the floc growth rate, size, strength, and broken-floc recoverability. The effect of MCBF on fractal dimension of flocs generated by ${\mathrm{TiCl}}_4$ depended on NOM properties. Both coagulation performance and floc properties were significantly affected by dosing sequence.

In the last several decades there has been a proliferation of structural best management practices (BMPs) for particulate matter (PM) sequestration. However, effective separation and continued retention of PM without washout throughout loading periods in which there is no maintenance remains challenging. In this study the physical modeling (in situ testing) of a volumetric clarifying filter (VCF) for separation and retention of PM was conducted for an urban source area ($\sim 500{\mathrm{m}}^2$) in north central Florida loaded by rainfall runoff. This paper examines the event-based response of a VCF unit for 25 events (384 mm of rainfall, $117{\mathrm{m}}^3$ of runoff over 13 months with no maintenance), differentiating the role of volumetric sedimentation ($2.3{\mathrm{m}}^3$ tank) and depth filtration ($106{\mathrm{m}}^2$ of cartridge surface area). Manual sampling was conducted with a PM mass balance over the monitoring campaign. Suspended sediment concentration (SSC), suspended and settleable PM fractions, and turbidity were measured. PM was further differentiated as particle size distributions (PSDs). A two-parameter (shape and scale) gamma distribution for PSDs was used to examine sedimentation and filtration. The VCF separated and retained 99% (median) of SSC, driven primarily by separation of sediment-size PM. Median values for settleable and suspended PM were 94 and 84%, with an 85% reduction for turbidity. The median mass-based $d_{50}$ of influent, primary effluent, and secondary effluent were 85, 10, and 3 μm. While the VCF was designed to provide separation and retention of suspended and settleable PM through filtration, the dominant mass-based mechanism for PM separation was gravitational sedimentation.

In this study, effects of aeration and wastewater composition were evaluated on the clogging process in four laboratory-scale wavy subsurface-flow and vertical-flow constructed wetlands (WSVFCWs) used for secondary and tertiary treatment. The relationship between the accumulated solid material and infiltration rate, the content and particle size distribution as well as the ratio of organic and inorganic matter of the accumulated material in the filter media were determined, and the mechanisms of clogging were elucidated. The clogging mainly occurred in the upper 0–40 cm layer, and the accumulated material decreased with filter depth (along the flow direction). The main particle size contributing to clogging was $\sim 40\mathrm{\mu m}$ in the WSVFCWs for secondary treatment and $>110\mathrm{\mu m}$ in those for tertiary treatment. The accumulated material had 30–40% of organic matter. The clogging mechanisms varied as the composition of influent and aeration conditions are different in WSVFCWs. Aeration promoted the growth of biofilm and mineralization of the accumulated material as well as provided shear force in the WSVFCWs. Aeration has a good effect in extending operational time in the tertiary WSVFCW but has a mild effect in the secondary WSVFCWs because of high organic loading rate there. Both the organic and suspended solids (SS) loading rate are important factors and should be controlled to mitigate the clogging problem in WSVFCWs.

This paper describes laboratory testing to investigate the suitability of recycled construction and demolition (C&D) materials as alternative subbase materials for permeable pavements. Permeable pavements are increasingly being used as urban stormwater management systems. Three commonly found recycled C&D waste materials, crushed brick (CB), recycled concrete aggregate (RCA), and reclaimed asphalt pavement (RAP), were investigated to assess their suitability as permeable pavement subbase materials. Geotextile was also used in this research to trap pollutants. The laboratory tests included basic physical characterization such as particle size distribution, specific gravity, water absorption, Los Angeles abrasion, California Bearing Ratio (CBR), and modified Proctor compaction tests. In addition, hydraulic conductivity tests were undertaken in a laboratory test setup with different influent suspension percentages and moisture contents. Temporal variations of effluent suspension percentages were investigated to assess clogging effects. It was found that the geotextile layer did not have any effect in terms of permeability of the C&D materials. The chemical assessment included organic content, pH value, trace element, and leachate concentration for a range of contaminant constituents and compared with maximum allowable limits in soil and natural water as well as with the environmental protection authorities’ requirements. In terms of geotechnical and chemical assessment for permeable pavement applications, RCA was found to be a suitable alternative construction material for permeable pavements, while CB was borderline and RAP did not meet some of the specified requirements.

Stormwater filter media (SFMs) play a vital role in decreasing flooding and preventing urban contaminants from polluting surface and ground waters. The infiltration rate of a SFM is a governing factor in the hydrological and environmental performance of the stormwater management systems. This paper describes the effect of a common deicing salt (sodium chloride) in reducing the infiltration capacity of two types of SFMs, which were prepared using a clayey silty sand, one with compost and another without compost. This paper also describes the effect of sodium chloride application in the release of zinc, calcium, nitrogen, magnesium, phosphorous, potassium, and sulfur from the SFM, and whether their release was accelerated or reduced from the SFM with compost. Laboratory constant-head infiltration tests were conducted using sodium chloride (as the deicing salt) at concentrations of 150 and $\mathrm{1,200}\mathrm{mg}/\mathrm{L}$. After conducting the tests for comparable cumulative pore volumes of infiltration, soil only SFM experienced significantly smaller reduction ($p=0.0045$) in flow rate than the soil with compost SFM. However, $\mathrm{1,200}\mathrm{mg}/\mathrm{L}$ salt concentration did not result in significantly higher reduction ($p=0.96$) of flow rate compared with the $150\mathrm{mg}/\mathrm{L}$ salt concentration. At $150\mathrm{mg}/\mathrm{L}$ salt application, a significant increase ($p<0.001$) of the sodium adsorption ratio (SAR) was observed due to salt application, compost addition, and the interaction of salt and compost. In general, sodium adsorption resulted in the reduction of cation exchange capacity, increased SAR, and leaching of organic matter, nutrients, other cations, and zinc, with these losses being greater for compost-amended media. These results suggest that piling snowmelt laden with deicing salts close to stormwater management systems may result in their poor performance or premature failure. Further research is needed to understand the effect of various salt concentrations, pore structure differences, and temperature on the infiltration rate.

There are a growing number of microcystin-degrading organisms that have been isolated; however, their ability to degrade these toxins in an immobilized state within water treatment plant media filters is yet to be explored in detail. Modified polymer coatings were applied to a polystyrene surface through plasma polymerization to determine if biofilm attachment of two previously characterized microcystin-degrading bacteria, LH21 and ACM-3962, were enhanced. Under the experimental conditions, LH21 formed a biofilm [as measured by the specific biofilm formation (SBF) index] on the uncoated polystyrene surface, and attachment was enhanced upon the three polymer coatings, acrylic acid, propionic acid, and allyl amine. Conversely, ACM-3962 was unable to form a biofilm on any surface. This study provides insights into methods that can be used to promote attachment of such organisms to treatment plant filter media, which can ultimately result in greater control and more predictable removal of microcystins. Finally, the methods can be used for screening organisms for their ability to attach to surfaces, a critical process for biofiltration within water treatment plant filters.