Journal of Environmental Engineering

The Surface Water Treatment Rule (SWTR) specifies the $Ct$ ($\text{disinfectant}\text{concentration}\times \text{time}$) calculation as the means by which disinfection efficacy, and therefore compliance, is determined. Baffle factors are used to scale the theoretical residence time of the water in a vessel to obtain the amount of time used for the $Ct$ calculation. The baffle factor formulation has been left to guidance and has been a topic of discussion. In this work, an extended baffle factor formulation is developed using disinfection contact system performance models that incorporate the methods imposed by and built into the SWTR. The performance models are based on chemical reactor analyses that have been validated extensively in the literature. A comparison made between the extended baffle factor formulation and methods that use hydraulic considerations alone shows that failing to account for the entire residence time distribution and disinfection kinetics can lead to significant errors. The result of this work is a baffle factor formulation that is compliant with the SWTR and is useful for troubleshooting utilities experiencing disinfection inadequacy or high levels of disinfection byproducts.

A mechanistic isopercentile flocculent sedimentation model was derived from basic fractal behavior of colloidal particles in turbid water. The model showed the fractal nature of growing particles, which was in opposition to the most commonly used semiempirical models that assume growth of particles as compact spheres. The model development was based on particle size distribution (PSD) analysis results from settling batch column experiments. The experimental batches were conducted at initial concentrations ranging from 150 to $350\mathrm{mg}/\mathrm{L}$ and coagulant doses in the range of 10–$70\mathrm{mg}/\mathrm{L}$. From the collected PSD data, a fractal dimension $D$ ($L$), fractal settling velocity $a_v$ ($L{T}^{-1}$), and model-fit parameters affecting the shape of isopercentile removal trajectories were obtained. The resulting calibrated model performed better than previously proposed semiempirical models. Lower degrees of fitting error, represented by sum of squares error (SSE) = 0.44–0.90, were achieved using the new model, which was much lower than the SSE range of 3.10–9.44 from previous models fitted to the same data set. The improved fitness of the new model was attributed to its ability to capture the fractal growth property of settling particles, which resulted in incipient buoyancy and settling deceleration of the formed flocs–properties that were not represented in previous models.

An analytical model is developed for unidirectional-flow waterways in which the dissolved oxygen (DO) mass balance is dominated by reaeration and sediment oxygen demand (SOD) fluxes. To accurately represent the feedback between the two principal fluxes and the resulting spatial distribution of depth-averaged DO concentration ($C_{\mathrm{DO}}$) in the water column, formulations for the fluxes are implemented that are consistent with mass transfer theory rather than commonly used formulations (e.g., zeroth-order SOD) that neglect mass transfer physics. Water-side and sediment-side processes are incorporated into the SOD formulation; the sediment-side processes are simplified and parameterized empirically. The resulting DO mass conservation equation is expressed as a first-order linear ordinary differential equation. The model has similarities to the classic Streeter–Phelps model in the following respects: (1) it implements a Lagrangian control volume, (2) it expresses the competition between two flux or source/sink terms in the DO mass balance, and (3) it applies downstream of a flow or DO introduction location. The analytical solution yields a steady-state longitudinal $C_{\mathrm{DO}}$ profile that spatially evolves to an asymptotic condition whereby reaeration and SOD fluxes have equal values. The difference in $C_{\mathrm{DO}}$ evolution when implementing a zeroth-order SOD formulation versus the first-order SOD formulation is highlighted. The flow management implications are discussed and an example calculation is presented for the case of flow augmentation in Bubbly Creek in Chicago, Illinois.

Ammonia-based feedback aeration control could avoid an unnecessary air supply and, therefore, save energy. However, this control method could be impacted by many factors such as solids retention time (SRT), nitrite oxidation rate, dissolved oxygen (DO) variation, influent load, temperature, and regular low DO operation. This study indicated that, with an unlimited DO ($\mathrm{DO}\ge 2\mathrm{mg}/\mathrm{L}$), the minimal SRT required to achieve complete nitrification was between 5 and 10 days. If the SRT was $\le 20\mathrm{days}$, reducing the DO could result in accumulation of nitrite. Nitrite could also accumulate under a peak ammonia load with a SRT of less than 15 days. In contrast, ammonia-based feedback control resulted in regular low DO operation. Because low DO enriches nitrifiers and selects nitrite-oxidizing bacteria (NOB) with a greater oxygen affinity, the required SRT to avoid the accumulation of nitrite can be substantially reduced. The authors recommend using a minimal SRT of 20 days to start a system. When the system reaches a stable condition, the minimal SRT can be reduced to 15 days, if needed. A pilot-scale field experiment indicated that the adverse effect of a low temperature can be overcome by extending the SRT.

Performance of the novel sludge-bed anaerobic membrane bioreactor (SB-AnMBR) at a mesophilic (35°C) and a thermophilic (55°C) temperature was compared for the treatment of the prehydrolysis liquor (PHL) at organic loading rates (OLRs) ranging from 0.8 to $10\mathrm{kg}\text{-}\mathrm{COD}/{\mathrm{m}}^3\text{-}\mathrm{d}$. An average chemical oxygen demand (COD) removal of 91% and a specific yield of $0.36{\mathrm{m}}^3\text{-}{\mathrm{CH}}_4/\mathrm{kg}\text{-}{\mathrm{COD}}_{\text{removed}}/\mathrm{day}$ [% relative standard deviation (RSTD) $=4.6$] was observed at a mesophilic temperature irrespective of the increase in loading rate. The temperature of the mesophilic (35°C) SB-AnMBR reactor was increased in a single step to achieve a thermophilic temperature (55°C). The one-step increase in temperature exerted stress on the biomass during the first 60 days of the operation at thermophilic temperature leading to the presence of slow-degrading lignin in the effluent with an average removal efficiency of less than 56% and average total COD removals of less than 60%. Subsequently, the methane yield was found to increase to an average value of $0.38{\mathrm{m}}^3/\mathrm{kg}\text{-}{\mathrm{COD}}_{\text{removed}}/\mathrm{day}$, indicating adaptation of biomass in the reactor. Flat-sheet membranes, used in both the mesophilic and thermophilic SB-AnMBRs, showed only two fouling events at a sustained flux of $0.1{\mathrm{m}}^3/{\mathrm{m}}^2/\mathrm{d}$ during combined continuous operation period of approximately 800 days.

The characteristics of Pseudomonas fluorescens biofilms formed under three different linear flow velocities ($u=0.1$, 0.4, and $0.8\mathrm{m}/\mathrm{s}$; Reynolds numbers of 1,000, 4,000, and 8,000, respectively) were studied providing an extension to the studies of earlier researchers. A flow cell reactor system was used to form biofilms, and they were characterized in terms of thickness, morphological structure, mass, cell density, outer membrane protein expression, and matrix and total protein and polysaccharide content. The external mass transfer coefficients were also assessed. The biofilms developed at $u=0.4$ and $0.8\mathrm{m}/\mathrm{s}$ had similar characteristics but were significantly different from those developed at $0.1\mathrm{m}/\mathrm{s}$. High flow velocities formed thinner biofilms with higher cell densities and contents of matrix/extracellular proteins and polysaccharides. The increase of flow velocity from 0.4 to $0.8\mathrm{m}/\mathrm{s}$ caused a higher production of matrix proteins and polysaccharides. The external mass transfer coefficients suggest mass transfer limitations for the lowest velocity. Scanning electron microscopy images show cell–surface and cell–cell attachment structures appearing more frequently in biofilms formed at the two higher velocities. No major differences were found in the outer membrane protein expression of biofilm cells formed under the selected linear flow velocities. The overall results show the effect of the hydrodynamic conditions under which biofilms were formed on selected macromolecular characteristics, demonstrating that higher flow velocities can originate more complex and denser biofilms.

The associated adsorption of ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Zn}}^{2+}$ by a novel biosorbent extracted from waste-activated sludge (WAS) after short-time aerobic digestion is systematically investigated by using aqueous binary metal solutions. ${\mathrm{Zn}}^{2+}$ slightly inhibited ${\mathrm{Pb}}^{2+}$ adsorption onto the biosorbent, while ${\mathrm{Pb}}^{2+}$ markedly inhibited ${\mathrm{Zn}}^{2+}$ adsorption onto the biosorbent. When the total mass concentrations of metal ions in the disposed solutions were the same, the total adsorption capacity of the biosorbent for ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Zn}}^{2+}$ in the binary-metal solution was more than that for ${\mathrm{Pb}}^{2+}$ in a single-metal solution, but less than that for ${\mathrm{Zn}}^{2+}$ in a single-metal solution. Moreover, a rising proportion of ${\mathrm{Zn}}^{2+}$ concentration in the binary-metal solution was found to increase the total adsorption capacity of the biosorbent. Both the Langmuir model and Freundlich model commendably described the adsorption isotherms of ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Zn}}^{2+}$ in the associated adsorption system. The maximal adsorption capacity for each metal ion in the binary-metal solution was obviously clearly lower than that in the single-metal solution. The spectra of energy dispersive $X$-ray confirmed that the adsorbed metal ions lay in the precipitates of the adsorption reactions. The spectra of Fourier transform infrared spectroscopy revealed that complexation and ion exchange between the functional groups and the metal ions played an important role in the associated adsorption process.

Hydrogen peroxide is a potential dechlorinating agent that can preserve chlorinated drinking water samples for the determination of disinfection by-products (DBPs). The impact of hydrogen peroxide on the storage of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and adsorbable organic halides (AOX) generated by chlorination in a model of natural water was investigated and compared with parallel samples quenched by sodium sulfite and ammonium sulfate. Positive errors of up to $9\mathrm{\mu g}/\mathrm{L}$ for THMs, $19\mathrm{\mu g}/\mathrm{L}$ for HAAs, $1\mathrm{\mu g}/\mathrm{L}$ for HANs, and $22\mathrm{\mu g}\mathrm{Cl}/\mathrm{L}$ for AOX were found after adding ammonium and storing for 9 days at 4°C, primarily due to the continued formation of chloroform, bromodichloromethane, dichloro- and trichloro-acetic acids, and dichloroacetonitrile. Hydrogen peroxide and sulfite led to smaller errors in the determination of THMs, HAAs, and AOX, while HANs degraded in the presence of sulfite. Hydrogen peroxide was the most suitable dechlorinating agent of these three for preserving THM, HAA, HAN, and AOX samples, provided that the relatively slow chlorine quenching reaction time (e.g., 3–4 min) is acceptable.

An episode of microbiological contamination of the drinking water supply of the City of Östersund, Sweden (63°10′45″N; 14°38′09″E) prompted a study of fecal pollution in four storm drainage catchments discharging in the vicinity of the water treatment plant intake, with the overall aim of determining the presence and variation of standard fecal indicator bacteria strains and total suspended solids (TSS) in stormwater from urban catchments with specific land uses and sizes varying from 5 to 40 ha. Four bacteria strains used as indicators of fecal pollution in Sweden were studied: total coliforms, enterococci, Escherichia coli (E. coli) and Clostridium perfringens (C. perfringens). In dry weather, indicator bacteria concentrations in storm sewers conveying baseflow did not exceed $100\mathrm{c}\mathrm{o}\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{y}\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{g}\mathrm{u}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{s}(\mathrm{CFU})/100\mathrm{mL}$, but during wet weather, total coliform and enterococci concentrations increased ${10}^2$ to ${10}^3$ times, compared to those in baseflow, and considerably less in the case of E. coli and C. perfringens. Bacteria concentrations differed significantly among the sampling sites and in the majority of events observed in the four catchments; higher bacteria concentrations were observed during the early phases of runoff. Only in one catchment, positive correlations were observed between TSS and total coliforms, E. coli, and enterococci, suggesting similar sources; in the remaining catchments, no such correlations were observed. The collected indicator bacteria data represent a useful addition to the available data on indicator bacteria in stormwater in cold-climate regions.