Journal of Environmental Engineering

Input of active biomass into suspended-growth biological processes occurs when biological processes are in series, during bioaugmentation, and when input wastewaters contain active bacteria. This paper extends mathematical modeling to include steady-state processes that receive significant inputs of biomass active in degrading substrates present in the system. The equations for concentrations of substrate, active biomass, and inert biomass are of the same form as for the conventional solutions with no input of biomass. However, the true sludge age for the active biomass uses the net growth rate as its denominator. The true sludge age is greater than the conventionally computed sludge age when inputs of active biomass are significant. Several practical examples show that the input of active biomass can reduce effluent substrate concentrations, allow stable operation of systems otherwise in washout, and shift the competitive advantage to otherwise less-competitive species.

Wastewater containing high concentrations of cornstarch was treated in two 8.5-L upflow reactors: upflow anaerobic sludge blanket (UASB) and a modified anaerobic filter (AF). Both reactors were operated in parallel at 37°C and pH 6.8–7.9 over 510 d with increased loadings of chemical oxygen demand (COD). Results showed that, in spite of having different sludge concentration profiles, both reactors, with 12 h of hydraulic retention time, removed an average of 95.3% of COD from wastewater containing up to 45,000 mg-COD$\dot{s}$L ⁻¹ (loading rates up to 90 g-COD$\dot{s}$L ⁻¹ $\dot{s}$d ⁻¹ ). At loading rates up to 75 g-COD$\dot{s}$L ⁻¹ $\dot{s}$d ⁻¹ , only 0.42% and 0.80% of starch particulates remained unhydrolyzed and were washed out by the effluent from UASB and modified AF reactors, respectively. Of the COD removed, 85.9% was converted to methane and the rest was converted to biomass with a net sludge yield of 0.10 g-VSS$\dot{s}$g-COD ⁻¹ . Both reactors failed at loading rates higher than 90 g-COD$\dot{s}$L ⁻¹ $\dot{s}$d ⁻¹ , because of severe washout of solids. The sludge granules had a methanogenic activity of 1.90–1.92 g-methane-COD$\dot{s}$g-VSS ⁻¹ $\dot{s}$d ⁻¹ and consisted of various trophic bacteria in the order of 10 ⁸ –10 ⁹ m/L.

The resilience and operational control of a unique reactor design was studied in a series of transient experiments. The reactor design included an expanded-bed granular activated carbon (GAC) anaerobic reactor with a GAC adsorber located in the recycle line. The reactor was subjected to variable loadings, a shutdown period, and a step decrease in the hydraulic residence time (HRT). During the variable-loading experiment, the influent chemical oxygen demand (COD) loading was increased from 24 kg COD/m ³ -d to 71 kg COD/m ³ -d, three times. After extended operation at 71 kg COD/m ³ -d, severe biological inhibition was observed and reactor failure was imminent. Rapid recovery was facilitated by the replacement of GAC from the GAC adsorber. Adsorbed organics provided substrate during a 60 h shutdown, and removal efficiencies were not affected. A step decrease in the HRT from 1 d to 2.8 h did not affect biological removal efficiency and washout of attached biomass was negligible. When subjected to severe transient operation, the performance of this reactor system was robust, and operational control allowed for rapid recovery from severe inhibition.

Laboratory-scale experiments were conducted in contact flocculation filtration using a dual media filter operating in the upflow, saturated mode. The filter media was lighter than water; thus, the bed floated. Since coarse media remained at the bottom, the flow direction was upflow, which had the added advantage of the flow being in the direction of grain compression. Polypropylene and Polystyrene were the optimum combination of media, which due to their large density difference did not intermix even under severe agitation, thus eliminating the media intermixing problem common to dual media filters. The influent concentrations were kept constant and the flow velocity, and filter media size and shape were varied. The headloss variation along the filter, the influent quality of two filter layers, and the effluent quality were studied. Filter runs exceeding 40 h were achieved before reaching breakthrough at conventional rapid sand filtration rates. Floating media obtained turbidity removal per unit headloss in comparison to sand media, and floating media are proposed as a prefilter in surface-water filtration.

The understanding of the physical and chemical processes involved in the transport of heavy metals during municipal waste combustion is incomplete. As part of efforts to improve this understanding this research focuses on determining the composition, morphology, and distribution of lead-bearing phases in municipal solid-waste combustor fly ash. This research uses scanning electron microscopy coupled with energy dispersive spectrometry, an electron microprobe analyzer, and digital imaging software to automatically search, locate, and evaluate lead-bearing phases. Results indicate the presence of lead in several types of particles with various compositions and morphologies. Lead was observed in two forms including Pb-Cl rich inclusions that exhibit no specific crystal habit and in lower concentrations in K-Cl-Pb and Na-Cl-Pb inclusions that exhibit a cubic habit. Several elements including K, Na, S, Ca, Cl, and Zn were common to all lead-bearing phases. Although previous leaching studies have indicated lead to be predominant in the smaller-size ash particles, lead identified in this study was found to be reasonably well distributed throughout all size fractions studied. Results obtained in this study are a necessary part of engineering efforts to improve the process of municipal waste combustion including the control and transport of heavy metals.

Hydrogen sulfide and ammonia are two inorganic compounds that may cause severe odor problems. In this study, the effectiveness of applying dielectric barrier discharges (DBDs) to destroy and remove these two odor-causing compounds from gas streams via the generation of gas-phase radicals and high-energy electrons is experimentally evaluated with a bench-scale apparatus. Experimental results indicate that the removal efficiencies of both H ₂S and NH ₃ with DBD plasmas depend on the gas composition, gas residence time, and applied voltage. Electronegative gases, such as O ₂ and H ₂O _{( g)}, tend to increase the electron attachment and therefore decrease removal efficiencies. Simultaneous removal of H ₂S and NH ₃ from gas streams is accomplished with DBD technology. Results of this study indicate DBD is an effective technology for controlling inorganic odor-causing compounds.

Flushing of a Pb(II) synthetically contaminated sandy loam using 0.1 N HCl, 0.01 M EDTA, and 1 M CaCl ₂ was investigated in the continuous-flow (column) mode. Initial Pb soil concentrations ranged from 500 to 600 mg/kg. Pb-removal efficiencies (and final soil Pb concentrations) for HCl, EDTA, and CaCl ₂ were 85% (77 mg/kg Pb), 100% (≈0 mg/kg Pb), and 78% (135 mg/kg Pb), respectively. Given that HCl and CaCl ₂ could not reduce the soil Pb to background levels (≈25 mg/kg) for a synthetically contaminated soil brings into doubt their effectiveness in remediating actual contaminated soils where metal retention would be much stronger. While EDTA removed all lead (indigenous and “artificial”), its treatment and reuse and possible adverse health effects makes its use difficult. The final soil pH for HCl was near 1, raising the concern of increased contaminant mobility, decreased soil productivity, and adverse changes in the soil's chemical and physical structure due to mineral dissolution. Final soil pHs for EDTA and CaCl ₂ ranged between 4.85 and 5.2.

A heuristic approach for reliability-based design of water-distribution systems (WDSs) is presented. The reliability is expressed by reliability factors, estimated through extended-period simulation using node-flow analysis that predicts the availability of water at different nodes during deficient conditions. The approach is iterative, considers pump and pipe failures only, and is based on the trade-off between reliability and cost of the WDSs. An initial WDS is selected and the ratio of marginal increase in reliability to marginal increase in cost (MIRMIC ratio) for each pipe by changing its size to next higher one is evaluated. Pipes with large MIRMIC ratios are selected for change to next higher size and the iterative procedure is continued until a WDS of desired reliability is obtained. The approach can also be applied to reliability-based upgrading of existing WDSs.

Small on-site aerobic package plants are one alternative being explored to address situations in which septic-tank and leach-field systems are not appropriate or feasible. Such small aerobic systems use either mechanical-aeration or forced-air diffusers. However, the only information available in the literature on designing the aeration systems pertains to large-scale facilities. Oxygen-transfer characteristics of diffusers in shallow systems should be significantly different from those reported in the literature for deeper systems. This paper reports on a laboratory study conducted at the Environmental Technology Laboratory at the University of Alaska, Fairbanks, analyzing the oxygen-transfer characteristics of small diffusers. Data show that diffusers typically used in small on-site aerated wastewater-treatment systems provide lower overall oxygen transfer on a mass basis, but actually transfer oxygen at a faster rate than diffusers in deep tanks reported in the literature. The present research provides basic data of importance for the design of small wastewater-treatment systems using diffusers.

Advanced oxidation processes (AOPs) have great potential for the complete destruction of hazardous contaminants; however, the complex kinetics and mechanisms of the free-radical reactions involved often render process optimization difficult. In this paper, a kinetic model and associated rate expressions for AOPs are developed to facilitate evaluation and optimization of treatment performance. The kinetic model has been formulated based on key reactions known to occur in both illuminated and dark AOP systems in the aqueous phase. As a result of fast free-radical chain reactions, the hydroxyl radical (OH$\dot{s}$), which is mostly responsible for decontamination, is expected to be at low steady-state concentrations, depending on treatment conditions. Thus, the OH$\dot{s}$ concentration must be optimized with respect to treatment conditions to promote fast decontamination reactions and reduce wasteful scavenging reactions. A final rate expression is derived for the steady-state concentration of OH$\dot{s}$ as a function of light intensity, quantum yield, illuminated surface, reaction volume, total absorption coefficient of the water, extinction coefficients of O ₃ and H ₂ O ₂ , concentrations of oxidants (i.e., O ₃ and H ₂ O ₂ ) and OH$\dot{s}$ scavenger, and pH.

Explicit integration schemes used in many water-quality models often require small time steps to satisfy stability criteria. In this paper, we demonstrate an implicit scheme, which is unconditionally stable regardless of the time-step size, for a two-dimensional box model configuration. The scheme is used with an alternating direction implicit (ADI) solution technique, which integrates the box-model mass balance equations in the longitudinal direction over the first half time step, and in the vertical direction over the next half time step. It has been successfully applied to the Patuxent Estuary water quality model with significantly reduced computational effort.

Even in the present age of microcomputer technology, graphical approaches have certain intrinsic value in their own right. However, in some situations, graphical presentations of results need extra care with regard to nondimensionalization or normalization of involved parameters. In the present study, the influence of inappropriate parameterization on interpolated values has been identified with respect to design curves of biofilm processes. The interpolation error arising from inappropriate parameterization is illustrated and the associated ambiguity is analytically demonstrated. Subsequently, simplified design curves have been developed that are devoid of the limitation of inappropriate parameterization and minimize the need for computations and interpolation. Proposed design curves are concise and comparatively simple to use. Applicability of the developed curves has been demonstrated through an illustrative example. Although the issue of inappropriate parameterization has been conveyed through the design curves of biofilm processes, it is equally relevant to other areas as well. With this in view, the necessity of careful considerations for appropriate parameterization with graphical presentation of results is emphasized.

The present practice for the design of primary settling tanks is based on the overflow rate corresponding to the percentage removal using isoremoval plots. The design procedure would be more rational if it were based on the removal efficiency and the scour criterion of the deposited particles. This technical note presents closed-form equations for the removal efficiency and scour velocity of particles. The removal efficiency equation considers the size distribution of particles, and the scour velocity equation is based on the Rouse equation. The removal efficiency equation yields the minimum particle size completely removed by the sedimentation tank. Using these equations the design equations have been obtained for the length and width of the settling tank. Besides other parameters, the design equations involve the completely removed minimum particle size, the specific gravity of the sediment particles, and the kinematic viscosity of water. These equations will be useful for the design of grit chambers and settling basins undergoing class-I settling.

Site characterization on Johnston Island, Johnston Atoll, Pacific Ocean, has yielded preliminary data that seabird guano can be an interference in three common petroleum hydrocarbon quantification methods. Volatiles from seabird guano were measured on a hydrocarbon-specific handheld vapor meter (catalytic detector) in concentrations as high as 256 ppm by volume total hydrocarbon. Analysis of guano solids produced measurable concentrations of total petroleum hydrocarbon (TPH) as diesel using both an immunoassay test and the EPA 8015 Modified Method. The testing was conducted on one surface sample of guano collected from a seabird roosting and nesting area. Source species were not identified. Positive hydrocarbon test results for guano raise concerns regarding the effectiveness of standard methods of petroleum-contaminated site characterization for Johnston Island, other Pacific islands, and coastal areas with historic or contemporary seabird populations.