Journal of Environmental Engineering

A laboratory investigation explored treatment of wastewaters containing nitrobenzene, biphenyl, and polynuclear aromatic hydrocarbons (PAHs) by two aerobic reactors, with and without acidogenic pretreatment. A sequencing batch operation was adopted for both acidogenic-aerobic and aerobic systems. Results indicated that nitrobenzene, biphenyl, and PAHs such as naphthalene and anthracene could be effectively removed by the acidogenic-aerobic system with removal efficiencies of more than 98% for nitrobenzene, 97% for biphenyl, and 96% for the PAHs, with a hydraulic retention time of the acidogenic stage at as low as 8 h. The acidogenic-aerobic system was therefore found to be effective in treating wastewaters containing such complex organics. The relatively low hydraulic retention time required for the acidogenic stage makes the process a potentially cost-effective technology.

The performance of the conventional activated-sludge reactor (CASR) treating high-salinity, fish market wastewater (212–345 mg biochemical oxygen demand/L) can be enhanced by the addition of phototrophic bacteria (PTB). Under aerobic conditions, the PTB are not capable of synthesizing phototrophic pigments, and the decay rates of PTB in the light and dark follow first-order kinetics with rate constants of 0.187 and 0.229 day⁻¹, respectively. Statistical analyses of kinetic constants k, Y_T, a, and b indicate that the addition of PTB into the ASR (PASR) improves the treatment efficiency but it does not affect sludge production and the specific oxygen-utilization rate. From parametric sensitivity analyses, substrate effluent concentrations of the CASR and PASR are most sensitive to the parameters θ_c, k, and Y_T but least sensitive to the parameter k_d. According to model calculation, the predicted biochemical oxygen demand and chemical oxygen demand removal efficiencies of the CASR and PASR are in good agreement with the experimental data.

A concept of an energy spilling coefficient between anabolism and catabolism was developed. Based on this concept, two models were proposed to describe quantitatively the effect of a substrate on the coefficient for substrate-sufficient continuous and batch cultures. The models have been well verified using literature data obtained from the continuous cultures of Bacillus strains and the writers' own data obtained from both anoxic and aerobic batch cultures of activated sludge microorganisms. It has also been demonstrated that in both types of cultures, with an increasing residual substrate concentration or increasing initial food-to-microorganisms ratio, a decline of observed growth yield (Y_obs) was mainly due to energy spilling. The effect of the substrate on the energy spilling coefficient in the substrate-sufficient cultures can be expressed by a Monod type curve. In the continuous cultures, the maximum energy spilling coefficient was found to be 0.7 when the residual methanol concentrations were greater than 10 mmol/L. In the batch cultures, the efficiency of anoxic sludge reached 0.8 as the initial food-to-microorganisms ratio exceeded 10 mg chemical oxygen demand/mg mixed-liquor suspended solids, while that of aerobic sludge was only 60% with the same ratio. These findings reveal that anoxic activated sludge has a higher potential of energy spilling than does aerobic sludge.

The inocula requirements and other experimental conditions for the biodegradable dissolved organic carbon (BDOC) procedure have been investigated and optimized to facilitate its use as a routine parameter for characterizing treatment plant performance. Initial inocula of unfiltered secondary effluent, commercial biochemical oxygen demand seed, mixed-liquor suspended solids (MLSS), and incubation temperatures of 20 and 37°C were examined using standard solutions of known DOC, treatment plant effluents, and ozonated treatment plant effluents. Among all inocula tested, MLSS provides the fastest BDOC exertion rate. It is possible to measure BDOC within five days using a larger volume of MLSS inoculum. The results from this research may be used to support the development of a standard BDOC method for water quality assessment.

A laboratory investigation was performed to study the recovery of a biological tower (fixed-film biological wastewater treatment unit) after dosing the influent with copper or chromium. The pilot-scale biotower (1.83 m high) was shocked with copper at three different influent concentrations (3, 56, and 47 mg/L). A continuous 3 mg/L dose had no significant impact on soluble 5-day biochemical oxygen demand removal performance. After slug doses of 56 or 57 mg/L for 10 h, the biotower established a new steady-state condition, in terms of soluble 5-day biochemical oxygen demand in the effluent, within 14 h. Recoveries from shock loads of chromium were slower: Recovery from doses of 9 mg/L of chromium occurred after 12 h, but recovery from doses of 38 and 96 mg/L required approximately 250 h. The metals concentrations in both biofilm and effluent were described by a power function with a concentration equal to a constant multiplied by time to a power. Uptake of chromium was determined to be nearly independent of dose, at the doses tested.

Sulfate-reducing bacteria, under anaerobic conditions, reduce sulfate, ${\mathrm{SO}}_{\mathit{4}}^{\mathit{-}\mathit{2}}$, to sulfide, S⁻², which in turn can effectively precipitate heavy metals. In this research project, sulfate-reducing bacteria were grown in an upflow anaerobic fixed-film (UAFF) reactor using optimum growth conditions obtained in previous studies. These reactors were then fed with different heavy metals at increasing loading rates until complete failure occurred as metal removal reached zero and residual sulfide dropped to zero. The metal concentrations were measured as total, dissolved, and free ions both in the influent and in the effluent streams. The results of this research showed that 100% removal efficiencies could be obtained with individual concentrations up to 200 mg/L for Cu, 150 mg/L for Ni and Zn, 75 mg/L for Cr, 50 mg/L for Cd, and 40 mg/L for Pb. Also, the corresponding organic matter removal as total organic carbon was found to be about 50% of the influent total organic carbon. A set of mathematical equations were derived to express the mass balance inside the UAFF reactor, with respect to metal influent concentrations and sulfide production. These equations were corrected by incorporating a correction product, α⋅β, to represent the toxicity effect of the increasing metal concentrations.

An adsorption equilibrium model was developed for predicting the total organic carbon (TOC) removal by the International Space Station water processor's multifiltration beds. Ideal adsorbed solution theory is used to describe the competitive interactions between fictive components (FCs) that make up the TOC. The FC physical properties were based on several identified compounds to represent the distribution adsorbing compounds in the wastewaters. The TOC isotherms were performed using the wastewaters on three absorbents (a coconut-based granular activated carbon, a coal-based granular activated carbon, and a polymeric-based resin), which are contained in the multifiltration beds. The isotherms were used to validate the model for all three adsorbents. The FCs were determined in such a way that they can describe the TOC concentration for multiple beds in series.

The effect of temperature on equilibrium adsorption for pure gases has been investigated. A simple generalized equation already proposed by Khan and colleagues was modified to include temperature dependence for the equilibrium adsorption of pure gas. Eq. (5) was compared with similar published equations that included temperature effects. A statistical test was conducted by comparing the overall average percentage error and the correlation coefficient for the proposed equation with different reported expressions for the experimental gaseous adsorption published data. It was found that the proposed equation was the most accurate and simple to use.

Storm water from impervious urban areas can adversely impact water quality and quantity. The partial exfiltration trench (PET) is a control device designed to moderate both the quality and the quantity of urban runoff. This paper uses a 2D numerical model to evaluate variably saturated flow profiles and residence time distributions for a PET subject to storm water loading. Parameters estimated from laboratory experiments and hydrographs measured at a prototype PET are used to calibrate the numerical model. Simulation experiments show that flow through the PET is influenced strongly by the rate and duration of the hydraulic loading and by the type and properties of the surrounding soil. Unless the surrounding soil is nearly saturated or highly impermeable, propagation of the wetting front through an unlined PET occurs as 2D variably saturated flow. Variably saturated 2D flow through the PET is characterized by skewed residence time distributions, long mean travel times (relative to plug flow), high exfiltration losses to the surrounding soil, and low tracer mass recovery at the underdrain. These features of the PET performance are beneficial for storm-water treatment because the first flush of runoff often contains significantly higher pollutant concentrations than those present in later phases of the storm.

The problems created by sediment deposits in combined sewer systems (sanitary and storm) are internationally recognized. The loss in conveyance due to these deposits contributes to hydraulic overloading, leading to flooding and premature operation of combined sewer overflows. The washout of sediments through combined sewer overflows into urban water courses during times of storm and the associated pollution caused by this phenomenon may be a factor affecting many urban ecosystems. Based on field observations, coupled with sampling and analysis of combined sewer sediment deposits, it has been found that in the invert of pipes there is often coarse, loose, granular, predominantly mineral material overlain by a mobile, fine-grained deposit. The erosion of the latter type of deposit is considered to be the source of the “first foul flush” of pollution, which is observed in many sewerage systems in response to storm events. This paper describes an experimental laboratory investigation of the erosion and subsequent suspended sediment transport of an in-pipe, fine-grained, organic, cohesive-like sediment deposit analogous to those found in sewers. The development of the laboratory system, the test program, the results of the study, and the development of a new approach to model the erosion and transport of cohesive-like sediments in pipes are described. Conclusions regarding the importance of the structure of the bed and its erosional behavior under a wide range of time-varying hydraulic conditions are presented.

This paper describes laboratory research conducted to investigate the performance of partitioning tracers for the detection of nonaqueous-phase liquids (NAPLs) in vadose zones. Once evaluated, the tracers may be used for volume estimation of NAPLs and remediation performance assessment of vadose zones. These laboratory studies used glass chromatography columns packed with: (1) Ottawa sand; and then (2) in a separate experiment, soil extracted from the Chemical Waste Landfill at Sandia National Laboratories. The columns were prepared in a manner that resulted in a three-phase system of air, water, and NAPL in the columns. Conservative and partitioning gas tracers were injected into the columns, and their elution concentrations were analyzed. The method of moments was used to estimate partition coefficients between the air and NAPL phases for each of the tracers. The partition coefficients and retardation factors, also estimated during the study, are used to select appropriate tracers for NAPL detection. This research identified several suitable perfluorocarbon tracers and demonstrated the feasibility of using partitioning tracers as a tool for NAPL detection in the vadose zone.

In this study, a filter test system with clean new fabric bags was used to measure the pulse pressure and acceleration of the filter bag. Fabric acceleration and pulse pressure were used as an index of bag-cleaning intensity. The jet pump curves, which relate the flow rate through the venturi to the average developed pressure by the venturi, were determined by the similar system. The intersection of the jet pump curve and the bag operating line, which relates the pressure drop to flow rate across the bag during pulse-jet cleaning, is the system operating point that was used to predict the average pulse pressure in the bag during pulse-jet cleaning. Experimental results of this study show that a higher pulse pressure can be achieved without the venturi at the top of the bag for bag materials with low resistance coefficient. For bags with higher resistance coefficients, higher pulse pressure is obtained with a venturi installed at the top of the bag. The predicted pressure values are in good agreement with experimental data. Dimensional analysis for jet pump performance was developed to reduce the experimental data. The results show that the jet pump curves obtained under different operating conditions can be reduced to the same nondimensional curve, which can be used to facilitate the design and operation of a pulse-jet cleaning system.