Paul R. Anderson

Influence of selector technology on heavy metal removal by activated sludge: Secondary effects of selector technology

Abstract The purpose of this research is to compare the ability of metal removal between an aerobic selector activated sludge system and a conventional CSTR system. Metal biosorption by sludge harvested from experimental systems was determined by a series of batch experiments. Heavy metals studied in this research were zinc, cadmium and nickel. Results of experimental data revealed that metal biosorption by activated sludge was rapid; about 70% of the soluble metals in solution was removed during the first 30 min. The sorption isotherm showed that at metal equilibrium concentrations greater than 0.05 mg/l, the selector sludge had significantly higher sorption capacity than did the CSTR sludge. Metal biosorption behavior closely followed a Freudlich isotherm model for equilibrium concentrations above 0.05 mg/l. Results of the Freundlich model suggested that the adsorption capacity of sludge from the aerobic selector was significantly higher than that of the CSTR system.

Kinetics of cadmium hydroxide precipitation

Abstract The kinetics of cadmium hydroxide precipitation in the presence and in the absence of citrate was investigated. Precipitation experiments were conducted in a continuous stirred tank reactor. Experiments were performed with initial cadmium concentrations ranging from 2.0 to 4.0 × 10−4 M; a range commonly occurring in electroplating rinsewater. A population balance model was used to compute the nucleation and particle growth rates and relate these to the supersaturation ratio. Particle growth rates found in the presence of citrate were much lower than that in the absence of citrate. The examination of growth inhibition suggested that the mechanism was surface reaction controlled.

Predicting influent biochemical oxygen demand: Balancing energy demand and risk management

Ready access to comprehensive influent information can help water reclamation plant (WRP) operators implement better real-time process controls, provide operational reliability and reduce energy consumption. The five-day biochemical oxygen demand (BOD5), a critical parameter for WRP process control, is expensive and difficult to measure using hard-sensors. An alternative approach based on a soft-sensor methodology shows promise, but can be problematic when used to predict high BOD5 values. Underestimating high BOD5 concentrations for process control could result in an insufficient amount of aeration, increasing the risk of an effluent violation. To address this issue, we tested a hierarchical hybrid soft-sensor approach involving multiple linear regression, artificial neural networks (ANN), and compromise programming. While this hybrid approach results in a slight decrease in overall prediction accuracy relative to the approach based on ANN only, the underestimation percentage is substantially lower (37% vs. 61%) for predictions of carbonaceous BOD5 (CBOD5) concentrations higher than the long-term average value. The hybrid approach is also flexible and can be adjusted depending on the relative importance between energy savings and managing the risk of an effluent violation.

Exploring aeration-associated energy savings at a conventional water reclamation plant

Aeration accounts for a large fraction of energy consumption at conventional water reclamation plants (WRPs). Older plants were designed when control techniques were relatively primitive and energy consumption was less of a concern. As a result, although process operations at older WRPs can satisfy effluent permit requirements, they can operate with excess aeration. In this study, we developed a wastewater process model to evaluate possible aeration savings at the Metropolitan Water Reclamation District of Greater Chicago Calumet WRP, one of the oldest plants in Chicago. Based on subsets of influent characteristics, we identified eight steady-state scenarios. We also identified transient scenarios that included high probability perturbations and more challenging but lower probability conditions. Results indicate that the Calumet WRP frequently operates with excess aeration. Effluent dissolved oxygen is the limiting parameter with respect to aeration saving and permit requirements. In a typical storm event, aeration could be reduced by up to 50%; even under low probability challenging perturbations, aeration can be decreased by 35% from current average levels and all permit requirements can be satisfied. Annual cost savings from cutting the aeration by 35% could be more than

SA-MAC: Self-Stabilizing Adaptive MAC Protocol for Wireless Sensor Networks

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Effect of silicon on the crystallization and adsorption properties of ferric oxides.

A common method of prolonging the lifetime of wireless sensor networks is to use low power duty cycling protocol. Existing protocols consist of two categories: sender-initiated, and receiver-initiated. In this paper, we present SA-MAC, a Self-stabilizing Adaptive MAC protocol for wireless sensor networks. SA-MAC dynamically adjusts the transmission time-slot, waking up time-slot, and packet detection patten according to current network working condition, such as packet length and wake-up patterns of neighboring nodes. In the long run, every sensor node will find its own transmission phase so that the network will enter a stable stage when the network load and qualities are static. We conduct extensive experiments to evaluate the energy consumption, packet reception rate of SA-MAC in real sensor networking systems. Our results indicate that SA-MAC outperforms other existing protocols.