Journal of Environmental Engineering

The objective of this research was to investigate the effectiveness of aerobic thermophilic treatment in enhancing conventional anaerobic mesophilic digestion in terms of pathogen reduction. vector attraction reduction, volatile solids (VS) reduction, gas production, and product sludge dewaterability. Lab-scale two-stage experiments were conducted with the aerobic thermophilic stage as pretreatment (AerTAnM) or as posttreatment (AnMAerT) to mesophilic anaerobic digestion. The lab-scale AerTAnM and AnMAerT systems were operated at system sludge residence times (SRTs) of 15 and 15.5 days, thermophilic reactor temperature = 62°C, and mesophilic reactor temperature = 37°C. The control anaerobic digester was operated at a system SRT of 15 and 15.5 days and temperature = 37°C. The AerTAnM and AnMAerT systems and control anaerobic digester operated at a system SRT of 15 days were able to achieve VS reductions of >38% (Class A sludge vector attraction reduction requirement). The VS reductions by the AerTAnM and AnMAerT systems (∼65%) were higher than the VS reduction in the control (∼51%) by 14%. The AerTAnM and AnMAerT systems reduced fecal coliform density in the feed sludge from 10⁸ most probable number (MPN) per gram of total solids (TS) to <10³ MPN/g TS (Class A sludge fecal coliform density limit), whereas the control reduced the same feed sludge fecal coliform density to about 10⁶ MPN/g TS. The AerTAnM and AnMAerT systems and control can reduce Salmonella density in the feed sludge from 5 to 12 MPN/4 g TS to <1 MPN/4 g TS. Average methane gas production by the AerTAnM system anaerobic mesophilic digester (0.61 m³/kg VS destroyed) was higher than those of the AnMAerT system (0.50 m³/kg VS destroyed) and control (0.52 m³/kg VS destroyed) anaerobic mesophilic digesters. Average H₂S content of the AerTAnM [133 ppm volume-to-volume ratio (v/v)] system anaerobic thermophilic digester gas was significantly lower than those in gas from the AnMAerT system (249 ppm v/v) and control (269 ppm v/v) anaerobic mesophilic digesters. The dewaterabilities of the product sludge (measured as time-to-filter, s) from the AerTAnM system (237 s) and AnMAerT system (203 s) were significantly better than that of the product sludge from the control (346 s).

Conventional anaerobic mesophilic (AnM) digestion coupled with anaerobic thermophilic (AnT) pretreatment (AnTAnM system) and anaerobic thermophilic posttreatment (AnMAnT system) of mixed sludge (thickened waste activated sludge and primary sludge) was investigated. The main objectives were to investigate the ability of AnTAnM and AnMAnT systems to produce a product sludge that can meet Class A sludge requirements and to enhance sludge treatment in terms of volatile solids (VS) destruction, gas production, sludge supernatant chemical oxygen demand (COD) reduction, and sludge dewaterability. Lab-scale AnTAnM and AnMAnT systems were operated at a system sludge residence time of 15 days and temperature of 62°C in AnTAnM and AnMAnT thermophilic reactors. A lab-scale control anaerobic digester was operated at a system sludge residence time of 15 days and temperature of 37°C. The AnTAnM and AnMAnT systems and control achieved VS reductions of >38% (Class A sludge vector attraction reduction requirement). Average VS reductions by the AnTAnM (61%) and AnMAnT (63%) systems were significantly higher than VS reduction by the control (50%). The fecal coliform densities in the AnTAnM and AnMAnT system product sludges were below 1,000 most probable number (MPN) per gram total solids (TS) (Class A sludge fecal coliform density limit) compared to 10⁶ MPN/g TS in the control product sludge. The product sludge from the AnTAnM and AnMAnT systems and the control anaerobic digester met the Class A sludge Salmonella density limit (<3 MPN/4 g TS) when fed with feed sludge containing 2–12 MPN/g TS. Average methane production by the AnTAnM mesophilic digester (0.66 ± 0.10 m³/kg VS destroyed) was higher than those of the AnMAnT (0.51 ± 0.06 m³/kg VS destroyed) and the control anaerobic mesophilic digesters (0.52 ± 0.03 m³/kg VS destroyed). The average supernatant CODs in the AnTAnM system product sludge (10,500 ± 200 mg/L) and AnMAnT system product sludge (10,200 ± 150 mg/L) were approximately the same and were significantly lower than the supernatant COD in the control anaerobic digester (14,100 ± 350 mg/L). All three systems were fed with feed sludge containing an average supernatant COD of 22,500 mg/L. Dewaterability of the product sludges, measured as time to filter, was 244 and 207 s for AnTAnM and AnMAnT systems, respectively, whereas it was 364 s for the control anaerobic digester product sludge.

Theoretical and experimental investigations have been conducted on the adsorption characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) by macroreticular resins. A theoretical model is proposed for describing the BTEX breakthrough curves of the adsorption column. The column adsorption model contains two model parameters, τ and K, that are conveniently estimated using the observed breakthrough data. The model was tested for benzene adsorption with a flow rate between 12 and 30 mL/min, inlet concentration between 200 and 500 mg/L, and temperature between 30 and 60°C. Excellent fit of the model to the measured data was obtained. The proposed model hence offers a convenient means for accurate predictions of the adsorption capacity and breakthrough point of a column BTEX adsorption process. Also developed are the mass balance equations representing countercurrent multistage adsorption process. The countercurrent multistage adsorption process has been shown to save a significant amount of adsorption resin in achieving the same BTEX removal as the single-stage process. Experimental tests for a two-stage example verify that up to 60% of the Ambersorb resin can be saved over a single-stage process.

Metal working (MW) fluids are used to control friction and temperature, improve workpiece surface quality, and reduce tool wear. The batch-life of the MW fluid investigated was controlled primarily by the concentration of metallic soaps (complexes between the oil emulsifier and Al/Mg. Ethylenediaminetetraacetic acid, a strong metal chelator, was added to the MW fluid to break the oil-Al/Mg complexes. The aqueous-phase ethylenediaminetetraacetic acid-Al/Mg complexes were then separated from the oil phase by ultrafiltration (UF). Al levels were reduced between 39 and 49%, and Mg levels were reduced between 67 and 77%. Al transfer from the oil phase to the aqueous phase was slow and increased during UF concentration. Rinsing the concentrated MW fluid with deionized water decreased the ash content but had a lesser impact on Al/Mg removal. Al mass balances produced errors of 2.8% for run 3 and 6.2% for run 4. The UF system (0.11-μm ceramic membrane) effectively separated the oil and aqueous phases. Permeate turbidity was generally <1 nephelometric turbidity unit and permeate flux ranged from 390 to 220 L/m²-h (230 to 130 gal./ft²-day) depending on the degree of concentration.

Although biological treatment has been applied successfully to treat waste gases using conventional organic packing media such as compost, there is currently a need for further research on ways to optimize the medium selected. Use of a superior filter-bed medium could overcome or minimize many of the problems encountered in conventional biofilter operation (e.g., medium clogging, difficulty in control of moisture content, and nutrient limitation). In research described herein, polyurethane foam was manufactured and characterized to determine its suitability as a solid support medium for use in gas-phase biofilters. Part I of this paper describes studies conducted to determine the medium's porosity, pore size, head loss characteristics, density, sorption capacity, and chemical resistance. Results are presented that characterize the polyurethane foam medium's properties and suggest how it can be used effectively in treating gas-phase volatile organic compound contaminants. Part II of this paper describes studies conducted to determine the medium's ability to support an active biofilm and to study feasibility of a novel nutrient addition and biomass wasting strategy.

A polyurethane foam medium with characteristics described in Part I of this paper was tested in a toluene degrading biofilter to demonstrate its ability to support an active biofilm and to study feasibility of a novel nutrient addition and biomass wasting strategy. A laboratory-scale biofilter was fed a model waste stream containing toluene for more than 300 days using empty bed residence times ranging from 1 to 4 min and toluene concentrations ranging from 50 to 200 parts per million by volume. Results reported herein demonstrate that a polyurethane foam medium with high porosity, suitable pore size, low density, and an ability to sorb water was able to remove over 99% of the influent toluene after implementation of a nutrient addition and biomass removal strategy. The strategy, made possible by use of the foam medium, overcame problems such as clogging, high head loss, moisture content control, and nutrient limitation that are often associated with conventional biofilter operation.

Migration of non-aqueous-phase liquids (NAPLs) such as trichloroethylene or gasoline can be controlled by barrier systems. The research presented in this paper aims to form a horizontal layer by injecting gelling liquids and to test the ability of horizontal barriers to isolate the downward migration of NAPLs in subsurface environments. We developed a methodology in the laboratory to form a contiguous horizontal barrier by injecting gelling liquids through horizontal and vertical wells. A series of batch, column, and 2D sandbox experiments were conducted to investigate the gel development and horizontal barrier formation. Prior to 2D barrier formation experiments, two different methods were employed to measure pre- and postinjection hydraulic conductivity in 1D columns to quantify hydraulic conductivity reductions. After an impervious grout formed, the durability of the grouted porous media in the presence of two NAPL contaminants was investigated. The hydraulic conductivity of filter sand treated with colloidal silica was reduced by 100% in 1D column experiments. In 2D experiments, a contiguous horizontal layer was formed by horizontal or vertical injection of the gelling liquid. The grouted material in 1D columns worked well in controlling the downward migration of contaminants. Although some penetration of the gelled layer by the contaminant was observed, the integrity of the horizontal layer was preserved. Finally, based on scaled capillary pressure versus saturation relationships, it was determined that capillary pressures can reduce as much as 50% with gelling of the colloidal silica solutions.

A new method for predicting upward solute movement in unsaturated sand soil due to evaporation is developed and tested. Laboratory experiments were conducted in an unsaturated uniformly packed sand column with a cross section of 1.20 × 0.50 m² and a constant shallow ground-water table. Evaporation was measured by a new ventilated chamber system. Solute movement from the ground water upward was monitored. Water and solute movement could be accurately reproduced by numerically solving Richards' equation and the convection-dispersion equation in one-dimension. The experimentally measured dispersivity for the unsaturated homogeneous sand agreed closely with the values which are available in the literature. This paper offers a new approach for investigating dispersion phenomena in unsaturated porous media exposed to evaporation.

An innovative system was developed to enhance electrokinetic extraction of heavy metals from contaminated soils. The system consists of a layer that was continuously flushed with nitric acid at pH 3 near the cathodic region and two reservoirs with 0.4 M NaOAc at pH 3.8 and acetic acid at pH 4 flushing the anode and cathode, respectively. Both pure kaolinite and carbonate-rich illitic soils were tested. With traditional electrokinetic systems, approximately 60% of lead was transported to the cathode for kaolinite, whereas there was little removal for carbonate-rich illitic soil. This result indicates that clay minerals have an important effect on the desorption process. The integrated electrokinetic system maximized contaminant extraction and minimized precipitation in the cathodic region. Over 80% of the lead was removed from carbonate-rich illitic soil, with 5,000-mg/kg initial lead contaminated concentration, and leached out through the flushing layer. The system operated successfully in laboratory bench tests with carbonate-rich illitic soil.

A combined electrocoagulation and electroflotation process was applied to restaurant wastewater treatment. The effects of operational variables on performance were examined. The electrocoagulation and electroflotation charge loadings are the most important variables. In wide ranges, initial pH and conductivity have no remarkable effects on pollutant removal. However, when pH is <4, suspended solids removal decreases sharply. The proposed technique has two significant advantages: shorter retention time and lower water content in the sludge produced. The power requirement is only 0.5 kW⋅h/m³ under a set of typical operating conditions. The amount of dried sludge is 0.20–0.37 kg/kg chemical oxygen demand removed.

Adsorption capacities of adsorbents are necessary for selecting and designing adsorption systems for separation and removal processes, such as air quality control devices, because they are indicators of service life. This paper describes the use of the Dubinin-Radushkevich (DR) equation and the quantitative structure-activated relationship to predict the equilibrium adsorption of select organic vapor by activated carbon fiber (ACF) adsorbents. The DR isotherm parameter, k, depends on the adsorbate as well as the adsorbent, and the prediction for k can be obtained indirectly from the affinity coefficient. A correlation is developed to compute the affinity coefficient from the modified, first-order, valence molecular connectivity index. This method provides an improved way to predict equilibrium adsorption capacities for select volatile organic compound adsorbates and activated carbon fiber adsorbents.

The removal of As(III), As(V), Hg(II), and Pb(II) by virgin and Fe(III) impregnated activated carbons (FeAC) was investigated. Iron-oxide impregnation increased the pH_zpc of the carbon from 7.5 to about 8.2–8.7 but did not alter the surface area or the pore volume. The amount of acid or base needed to reach a given pH increased following impregnation, indicating that the FeAC was more active than its non-impregnated counterpart. Metal removal was a function of pH with removal increasing with pH for Hg(II) and Pb(II) and decreasing with pH for As(V). As(III) removal was not a strong function of pH below pH = 5, increased to a maximum at pH ≈ 7, then decreased with increasing pH. As(III) and As(V) removals were about one and two orders of magnitude higher, respectively, for the FeAC compared with the non-impregnated carbon, while Hg(II) and Pb(II) removals were only slightly higher. Fe-impregnation appears to be most effective for the anionic contaminants.