Journal of Environmental Engineering

Biofilm density, porosity, and thickness are biofilm architecture properties that are important but often difficult to measure. In this study, wet and dry biofilm densities and biofilm porosity in shredded tire biofilters were measured using a volumetric displacement method and a new porosity equation. Methods for determining the surface area and mean thickness of biofilms attached to shredded tires were developed on the basis of the box- and ellipsoid-shape models with the data of (1) the volume calculated from the measured weight of the filter medium ($V_{\mathrm{MW}}$) or (2) the three longest lines of the filter medium measured with a digital caliper. As a benchmark, the surface area of the shredded tire particles were calculated from X-ray computed tomography (CT) scanning and compared to, and linearly correlated with, the results from the models. The ellipsoid-shape model with the modified length-width-depth data and $V_{\mathrm{MW}}$ was determined to be the best model to compute the surface area and biofilm thickness. The method of biofilm thickness measurement may be applicable in attached growth systems packed with other irregular-shaped media.

The perception of the maintenance demands of low impact development (LID) systems represents a significant barrier to the acceptance of LID technologies. Despite the increasing use of LID over the past two decades, stormwater managers still have minimal documentation in regard to the frequency, intensity, and costs associated with LID operations and maintenance. Due to increasing requirements for more effective treatment of runoff and the proliferation of total maximum daily load (TMDL) requirements, there is a greater need for more documented maintenance information for planning and implementation of stormwater control measures (SCMs). This study examined seven different types of SCMs for the first 2–4 years of operations and studied maintenance demands in the context of personnel hours, costs, and system pollutant removal. The systems were located at a field facility designed to distribute stormwater in parallel in order to normalize watershed characteristics including pollutant loading, sizing, and rainfall. System maintenance demand was tracked for each system and included materials, labor, activities, maintenance type, and complexity. Annualized maintenance costs ranged from $\$\mathrm{2,280}/\mathrm{ha}/\mathrm{year}$ for a vegetated swale to $\$\mathrm{7,830}/\mathrm{ha}/\mathrm{year}$ for a wet pond. In terms of mass pollutant load reductions, marginal maintenance costs ranged from $\$4–\$8/\mathrm{kg}/\mathrm{year}$ TSS removed for porous asphalt, a vegetated swale, bioretention, and a subsurface gravel wetland, to $\$11–\$21/\mathrm{kg}/\mathrm{year}$ TSS removed for a wet pond, a dry pond, and a sand filter system. When nutrients such as nitrogen and phosphorus were considered, maintenance costs per gper year removed ranged from reasonable to cost-prohibitive, especially for systems with minimal to no nutrient removal. As such, SCMs designed for targeting these pollutants should be selected carefully. The results of this study indicate that generally, LID systems, as compared to conventional systems, have lower marginal maintenance burdens (as measured by cost and personnel hours) and higher water quality treatment capabilities as a function of pollutant removal performance. Cumulative amortized system maintenance expenditures equal the SCM capital construction costs (in constant dollars) in 5.2 years for wet ponds and in 24.6 years for the porous asphalt system. In general, SCMs with higher percentages of periodic and predictive or proactive maintenance activities have lower maintenance burdens than SCMs with incidences of reactive maintenance.

Infrastructure for water treatment faces numerous challenges around the world, including the high failure rate of digital, electronic, pneumatic, and mechanical control systems due to their large number of components and their dependency on proprietary parts for repair. The development of more efficient, reliable, easily repaired water treatment controls that rely on simple fluidics rather than on complex systems has the potential to significantly improve the reliability of drinking water treatment plants, particularly for cities and towns in developing countries. A stacked rapid sand filter (SRSF) has been proposed as a more robust and sustainable alternative to conventional rapid sand filters because each filter can backwash at the same flow rate used for filtration without requiring pumps or storage tanks. While the concept of this filter has been demonstrated in previous studies, this paper presents a novel control system for the SRSF based on fluidics that eliminates the need for mechanized controls. The water level in the filter is regulated by a siphon pipe, which conveys flow during backwash and which contains an air trap to block flow during filtration. The state of the siphon pipe and the ensuing state of the filter are controlled by one small-diameter air valve. This fluidic control system was tested in pilot-scale experiments, which demonstrated its ability to set the mode of operation of the filter and served as the basis for the derivation of design equations. In addition, the first full-size SRSF was built at a municipal water plant in Honduras using this fluidic control system, which provided a full-scale demonstration of its effectiveness. This simple and robust control system shows promise as part of a sustainable rapid sand filtration process.

Water has a considerable role in all aspects of human life. Thus, evaluation of water characteristics in general and water quality in particular are necessary to enhance the health of humans and ecosystems. Data-driven models are computing methods that are capable of extracting different system states without using complex relationships. Prediction and simulation are two branches of data-driven modeling that use previous and previous-current data sets to fill gaps in time series. This paper investigates the capability of an adaptive neural fuzzy inference system (ANFIS) and genetic programming (GP) as two data-driven models to predict and simulate water quality parameters (e.g., sodium, potassium, magnesium, sulfates, chloride, pH, electrical conductivity, and total dissolved solids) at the Astane station in Sefidrood River, Iran. The writers considered six combinations of data sets, including the previously noted water quality parameters and river discharge in the previous and previous-current months, as input data. Implementation of the ANFIS and GP models in this paper illustrates the flexibility of GP in time series modeling relative to ANFIS, especially in the testing data set. Accordingly, the writers calculated the coefficient of variation of root mean squared error as the error criterion in different ANFIS and GP models (for assigning achievement probability to an appropriate solution) for each quality parameter. The average of the previously noted values for the six combinations of data sets improved (decreased) 80.51 and 80.89%, respectively, in the training and testing data sets with GP relative to ANFIS. These results indicate that the writers’ proposed modeling, based on GP, is an effective tool for determining water quality parameters.

To evaluate granular activated carbon (GAC) adsorption using low-cost–high-performance materials for removal of pesticides and organic matter in potable water production, a pilot-scale upgrade of the conventional treatment process was studied in the Cam Giang Water Treatment Plant, Hai Duong Province, Vietnam. The pilot system was designed to test various process schemes consisting of a series of processes, such as coagulation/flocculation, horizontal sedimentation, rapid sand filtration, and adsorption, using three types of GAC (activated carbon from bituminous coal, from bamboo, and from coconut shell). The treatment efficiencies of the individual processes and the overall treatment trains were evaluated by studying several parameters, such as turbidity, chemical oxygen dissolved, and pesticides (chlorpyrifos, diazinon, carbofuran). Results show that the two locally produced adsorbents have a similar efficiency to commercial activated carbon for adsorption. The removal efficiency was somewhat lower for both materials, but in the same order of magnitude. The removal of pesticides and organic matter with a column filled with activated carbon derived from bamboo was found the best among the two locally produced materials, approximately 30 and 23% higher than those observed for the column filled with activated carbon from coconut shells. It is concluded that bamboo-derived activated carbon can be employed on a larger scale as a low-cost–high-performance adsorbent and an alternative to commercial activated carbon in drinking water treatment.

This study investigated the feasibility of nanoscale zero-valent iron(nZVI) as the source of catalytic ferrous iron for Fenton and photo-Fenton oxidation of petroleum aromatic hydrocarbons. The oxidation processes were able to degrade more than 99% of benzene, toluene, ethylbenzene, and xylene (BTEX) within 15 min at pH 3.0, which the initial concentrations of BTEX, nZVI, and ${\mathrm{H}}_2{\mathrm{O}}_2$ were $\mathrm{4,000}\mathrm{\mu g}/\mathrm{L}$, 9 mM, and $150\mathrm{mg}/\mathrm{L}$, respectively. The average pseudo-first-order constants for BTEX degradation were 0.309 and $0.368{\min }^{-1}$ at pH 3.0 for Fenton and photo-Fenton processes, respectively. Experiments revealed that by increasing pH, solubility of nZVI decreased significantly, while ultraviolet (UV) irradiation improved nZVI solubility and subsequently BTEX degradation. Cations and anions were found to reduce oxidation efficiencies of BTEX; among anions, ${\mathrm{SO}}_4^{2-}$ and ${\mathrm{CO}}_3^{2-}$ had the most negative effect on the removal efficiencies. On the other hand, ${\mathrm{Mg}}^{2+}$ and ${\mathrm{Ca}}^{2+}$ played a considerable inhibitor role among cations. The removal efficiencies of both systems declined when treating real polluted groundwater collected from the city of Tehran, Iran.

To treat wastewater containing paraquat, the interaction of the herbicide with unmodified and modified (i.e., chemically treated) proprietary silicas is explored using liquid chromatography—mass spectrometry and ultraviolet-visible spectrometry. Strong adsorption and rapid exchange kinetics (i.e., more than 80% within 30 s) of the contaminant onto both unmodified and modified silica surfaces indicate that paraquat adsorption is inherent to the unmodified silica. Although activated carbon sequesters paraquat more effectively than silica at long times (i.e., after 2 h), considering both constant mass and constant area approaches in loading the adsorbents, the best performance in the short-term (i.e., at least up to 150 s) interaction was achieved by using unmodified silicas. Comparison of data fitting to a competitive binding model with or without consideration of homogeneous solid diffusion indicates that, at least for times relevant to water-treatment applications, the competitive binding model is an appropriate mathematical tool to explain experimental adsorption data. Addition of ${\mathrm{H}}_2{\mathrm{O}}_2$ is also attempted to initiate paraquat decomposition; however, silica is not an effective catalyst for peroxide decomposition paraquat.

This paper presents the results of an experimental study of the effects of porosity on the flow rate and Escherichia coli (E. coli) filtration characteristics of porous ceramic water filters (CWFs) prepared without a coating of silver. Clay-based CWFs were fabricated by sintering composites of redart clay and fine woodchips (sawdust) in three different proportions by volume, viz: $50:50$, $65:35$, and $75:25$. Sintering the greenware below 1,000°C produced reddish colored pot of three different degrees of porosity and micro- and nanoscale pores, which are the key to efficient filtration. The porosities and pore size distribution frequencies of the sintered clay ceramics were characterized using mercury intrusion porosimetry (MIP). The porosity of the CWFs ranged from $\sim 36\%$ to $\sim 47\%$ and increased with increasing sawdust content in a linear fashion, and the pore size varied from $\sim 10\mathrm{nm}$ to $\sim 100\mathrm{\mu m}$. The volume flow rates of water through the CWFs were investigated by measuring the cumulative amount of water flow as a function of time. The flow rate was found to increase with increasing porosity of the CWFs. The effective intrinsic permeabilities of the CWFs were then obtained from Darcy fits to the flow rate data. These were compared with values obtained using the Katz-Thompson method. Both approaches gave comparable results of permeability between $\sim 1\mathrm{millidarcy}$ to $\sim 50\mathrm{millidarcy}$. The tortuosity of the CWFs was found from Hager’s equation to range from $\sim 10$ to $\sim 60$. In general, while the permeability of the CWFs decreased with increasing clay content, tortuosity increased with increasing clay content. The CWFs removed E. coli from aqueous suspension very efficiently with average log reduction values between 5.7–6.4. The implications and limitations of the results are discussed for the effective filtration of water in the developing world.

This paper proposes a new method of removing fluoride from drinking water. It presents the results of an experimental study on the effects of the temperature and mixture ratio on the adsorption characteristics of fluoride on clay-hydroxyapatite (C-HA) composites. The writers fabricated the C-HA materials from composites of hydroxyapatite (HA), redart clay, and fine wood chips (sawdust) in well-controlled proportions. Five different ratios of clay to HA at five different temperatures (500, 600, 700, 800, and 900°C) were sintered. The results of the adsorption tests demonstrated that the defluoridation capacity of the adsorbent that contains only HA decreases with increasing sintering temperature. The adsorption capacities of the C-HA adsorbents also increase with increasing HA volume fraction. The adsorption capacity of the porous C-HA mixtures and HA are well modeled by the Freundlich equation. The changes in the free energy reveal the spontaneous nature of the adsorption process. A particle and intraparticle (pore) model was also used to characterize the batch kinetics. The potential implications of the results are then discussed for the development of future point-of-use water filtration devices for the removal of fluoride and microbial pathogens from C-HA filters.

In the present study, restaurant wastewater containing high concentrations of chemical oxygen demand (COD), total suspended solids (TSS), and oil and grease (OG) was treated by the combined electrocoagulation-electroflotation (EC-EF) process on a pilot scale. A central composite design was applied to the experiment design and the response surface methodology was adopted to build the response surface models of effluent COD, TSS, and OG. The sequential quadratic programming method was utilized to optimize the operating conditions of the treatment process. The analysis of variance of the experimental data shows that the coefficients of determination of the response surface models of effluent COD, TSS, and OG were 0.98, 0.982, and 0.989, respectively. The validity of these models was tested by confirmation experiments with satisfactory results. Zero trade effluent surcharges were achieved under optimized operating conditions. In spite of the operating cost calculated with respects to energy, electrode, and chemical consumptions, up to Hong Kong Dollar $1.3/{\mathrm{m}}^3$ water or 52% of the concession in trade effluent surcharge can be saved, revealing the cost-effectiveness of the combined EC-EF technique and its potential for full-scale implementation.

This research attempts to evaluate a previously developed model for predicting influent concentrations of prescription pharmaceuticals and understand why some drugs are more accurately predicted than others. It also investigates the impact of demographics on influent drug concentrations in municipal wastewater treatment plants (WWTPs). Samples from two WWTPs in the southeastern United States indicate that the model generates concentration estimates that are accurate to within at least one order of magnitude for a diverse set of drug compounds. Additionally, strategically timed sampling at college-town WWTPs, wherein 19–25% of the population comprises students ages 18–22, reveals that the influent concentrations of several drugs (atorvastatin, simvastatin, rosuvastatin, and metformin) generally prescribed to older-than-average persons increase while students are absent on holiday, whereas the influent concentration of one drug ($17\alpha$-ethynyl estradiol) prescribed to younger-than-average persons decreases. These observations reveal the impacts of demographics on prescription drug concentrations in WWTP influents, offering some explanation for the wide variability among previously measured influent drug concentrations. It was also observed that hospital size is generally correlated with increased influent drug concentrations.