Journal of Environmental Engineering

Mass reduction rates of particles and metals were simulated for a two-compartment settling tank composed of a storage compartment and a continuous flow compartment. Particle-size distribution, rainfall, and flow data from 16 storm events measured at three highway sites were used. The volume ratio (i.e., ratio of surface areas for a given depth) between storage and continuous flow compartment was optimized for a given design storm size to maximize total mass reduction rates of particles and heavy metals. Measured settling velocity profiles of runoff samples were used in the simulation. Simulation results showed that in a given total design storm, larger storage compartment fractions $(>0.95)$ enhanced the removal of smaller particles $(2–104\mu \mathrm{m})$ and particulate phase metals, and even a small fraction $(<0.05)$ of continuous flow compartment effectively removed larger particles $(104–\mathrm{1,000}\mu \mathrm{m})$ . A volume fraction of 0.75 for the storage compartment is suggested to optimize annual reductions of particles and associated heavy metals.

Whether the concentration of selected genetic biomarkers could be correlated to the rate of trichloroethylene (TCE) reductive dechlorination was investigated. Samples from a pilot-scale aquifer that had been bioaugmented with a halorespiring mixed culture to promote bioremediation of a chlorinated solvent source zone were used for this purpose. Dechlorination rates were determined in batch microcosms, and real-time quantitative polymerase chain reaction (qPCR) analyses were used to estimate the concentration of phylogenetic 16S rRNA for total Bacteria and for Dehalococcoides spp., and the catabolic gene tceA and its expressed mRNA. The first-order dechlorination rate coefficient $\left(k^{\prime }\right)$ obtained from the mixed culture used to bioaugment the pilot scale aquifer ranged from $0.033\text{to}0.662{\mathrm{h}}^{-1}$ . Samples collected from the source zone showed the highest $k^{\prime }$ value ( $0.03{\mathrm{h}}^{-1}\pm 0.011$ ; $n=6$ ) as well as the highest concentration of the biomarkers tested: $2.2\pm 0.5\times {10}^7\text{genes}∕\mu \mathrm{L}$ for total Bacteria, $1.97\pm 0.1\times {10}^7\text{genes}∕\mu \mathrm{L}$ for Dehalococcoides spp.; $9.6\pm 1.2\times {10}^5\text{genes}∕\mu \mathrm{L}$ for tceA; and $1.44\pm 0.2\times {10}^4\text{genes}∕\mu \mathrm{L}$ for the tceA mRNA. Apparently, the inoculated halorespirers thrived near the dense nonaqueous phase liquid, which is important to enhance source zone remediation. Surprisingly, the strongest biomarker correlation $(r^2=0.86)$ with TCE dechlorination rate coefficients $\left(k^{\prime }\right)$ was obtained with the universal biomarker for total Bacteria. No significant correlations $(p>0.05)$ were obtained between $k^{\prime }$ and the concentration of specific biomarkers for Dehalococcoides 16S rRNA $(r^2=0.02)$ , the tceA gene $(r^2=0.40)$ , or its transcriptome (mRNA) $(r^2=0.11)$ . Therefore, although qPCR is an important tool to verify the presence and distribution of halorespirers, its use to estimate dechlorination rates based on the tested biomarker concentrations was unreliable.

A 3D computational fluid dynamics model for describing the water flow and suspended solids (SS) concentration distribution in a rectangular sedimentation tank is presented. The interfacial momentum transfer, buoyant forces, and the effect of sediment-induced density currents are considered. A convection-diffusion equation, which is extended to incorporate the sedimentation of activated sludge in the field of gravity, governed the mass transfer in the clarifier. The double-exponential law is used to describe the dependence of the settling velocity on the concentration. The results show that during the dynamic settling process of the sludge, the mud surface rose slowly, and a period of time later, the mud surface kept stability and reached dynamic equilibrium in the tank. The distribution of velocity along the $z$ axis in the rectangular tank is not uniform, and the surface return flow is found. The turbulent kinetic energy is larger and dropped drastically in the inlet zone, while in the settling zone the turbulent kinetic energy is relatively small. Density current is formed, and the clear water zone, flocculation zone, lamella zone, and compression zone are found. Furthermore, under certain operational conditions, the influence of inlet baffle length on SS settling in the rectangular sedimentation tank is discussed. The prediction by the present model for liquid flow and SS concentration is confirmed by the experimental measurement in a rectangular sedimentation tank in Sweden reported by Larsen in 1977.

Hydrodynamic separation is a preliminary unit operation frequently utilized in wastewater and more recently in storm water for separation of coarse particulate matter (PM) and gross solids. In order to examine the behavior and separation mechanisms of a screened hydrodynamic separator (HS) not influenced by scour, this study examined the event-based performance of an empty-bed (clean sump and volute) HS for PM fractions transported in eight runoff events from a $\mathrm{1,088}{\mathrm{m}}^2$ paved source area urban watershed. Influent particle-size distributions (PSDs) { $d_{50}\mathrm{m}$ from $270\text{to}\mathrm{2,202}\mu \mathrm{m}$ } and HS particle separation efficiency (PSE) (from 38 to 70% of mass) exhibited variations influenced by hydrology and previous loadings. When examined as PM size fractions, results demonstrate separation of the sediment fraction $(>75\mu \mathrm{m})$ ranging from 76 to 94% while for settleable and suspended $(1–25\mu \mathrm{m})$ fractions, the PSE was variable and significantly lower; from 3 to 57% and 2 to 43%, respectively. Results demonstrate a correlation between higher influent PM concentration and coarser PSDs, illustrating why higher PM concentrations promote higher PSEs; and why HS performance must be specified at a PM concentration, PSD, and flow rate. Results demonstrate that HS behavior is influenced by influent PSDs coupled with flow rate. Hydrodynamic separation is effective for high-rate gross solids control. However, current HS designs require incorporation of hydrologic control, methods of frequent sludge zone management before scour, and stored runoff management to control interevent redox conditions.

A new process using a sequencing batch reactor (SBR) and two smaller sludge hoppers is proposed for the simultaneous removal of phosphorus and nitrogen from wastewater. In the double sludge switching sequencing batch reactor, denitrifying phosphate accumulating bacteria (DPB) sludge and nitrification sludge are transferred to the SBR at different phases instead of flowing wastewater through different reactors. The process was operated with a cycle time of $10.5\mathrm{h}$ , consisting of DPB sludge filling phase $\left(0.5\mathrm{h}\right)$ , anaerobic phase I $\left(2.0\mathrm{h}\right)$ , settling and changing DPB sludge phase $\left(0.5\mathrm{h}\right)$ , anaerobic phase II $\left(0.5\mathrm{h}\right)$ , aerobic phase $\left(4.0\mathrm{h}\right)$ , settling and changing nitrifying sludge phase $\left(0.5\mathrm{h}\right)$ , and anoxic phase $\left(3.0\mathrm{h}\right)$ . Results of stable operation showed that the process was very efficient over a range of temperatures varied from $10\text{to}28°\mathrm{C}$ . The average effluent concentrations and removal efficiencies were as follows: ${\mathrm{COD}}_{\mathrm{Cr}}$ $28.0\mathrm{mg}∕\mathrm{L}$ , 92.1%; ${\mathrm{BOD}}_5$ $7.0\mathrm{mg}∕\mathrm{L}$ , 95.1%; $\mathrm{N}{\mathrm{H}}_3–\mathrm{N}$ $0.8\mathrm{mg}∕\mathrm{L}$ , 98.0%; TN $9.8\mathrm{mg}∕\mathrm{L}$ , 76.7%; and TP $0.5\mathrm{mg}∕\mathrm{L}$ , 92.3%.

Many separate storm-water systems in China suffer functional problems of discharge of dry-weather pollutants or non-storm-water materials into storm-water systems via pipes or other direct connections, which plays as a main contributor to receiving water pollution. The general methods of identifying and locating illicit connections are not really suitable for pump drainage systems with severe problems on the decision-making level. This note presents an efficient methodology for diagnosing the systems and quantifying the flow rate of non-storm-water inflow with a hydraulic model. In this methodology, complicated hydraulic connections were simplified to virtual equivalent pipes, and then hydraulic parameters of the equivalent pipes were calibrated and verified with the hydraulic model that was built based on fieldwork. The method was successfully applied to the North Beixinjing storm-water system along the Suzhou Creek, Shanghai, China to quantify dry-weather flow from illicit connections and inflow of receiving body into the storm-water systems.

Influent and effluent samples originating from two wastewater treatment plants (WWTPs) (treating hospital wastewater and domestic wastewater, Belgium) have been analyzed in order to estimate their steroid hormone content. The natural estrogens estrone (E1), $17\beta$ -estradiol (E2), and the synthetic $17\alpha$ -ethinylestradiol (EE2) together with other steroid hormones progesterone (P) and testosterone (T) metabolites were detected in these samples. The hormone concentrations in both the hospital and the domestic WWTP samples were not significantly different and ranged from $<0.2\mathrm{ng}$ EE2/L to $114\mathrm{ng}$ EE2/L, from $<0.2\mathrm{ng}$ E1/L to $58\mathrm{ng}$ E1/L and from $<0.2\mathrm{ng}$ P/L to $>100\mathrm{ng}$ P/L. E2 was detected once at a concentration of $17\mathrm{ng}∕\mathrm{L}$ . In the domestic WWTP which comprises a conventional activated sludge treatment in parallel with a membrane bioreactor, no differences in estrogen removal efficiency could be observed for both treatments. In comparison to chemical analysis data, the Yeast Estrogen Screen (YES) appears to underestimate the influent estrogen concentrations, probably due to influent toxicity for the YES. Effluent estrogen concentrations, on the other hand, were overestimated by the YES test, probably due to the presence of other estrogenic compounds in the effluent.