Journal of Environmental Engineering

The objective of this review was to acquire knowledge concerning the ammonium ion exchange technique within the field of wastewater treatment. General concepts as well as details concerning the loading and the regeneration phases were included. Both chemical and biological regeneration processes were reviewed. Concerning ion exchangers, the study focused on different kinds of zeolites. The possibilities of employing the ion exchange technique for the recovery of nitrogen was also discussed. The study was carried out as a literature review. Conclusions from this study are that full-scale wastewater treatment plants that employ the ammonium ion exchange technique are scarce and few applications have been developed to recover ammonia nitrogen, for example, for agricultural purposes. Zeolites are somewhat heterogeneous because of natural variations of the minerals. Factors that influence the ammonium adsorption during the loading phase are well known. Biological regeneration has primarily been developed to decrease the brine consumption at regeneration or to improve the conventional nitrification-denitrification process. If the ion exchange technique is to be used to recover ammonium, both chemical and biological regeneration might be employed.

A simplified, quasi-steady-state model has been formulated for groundwater denitrification using immobilized cells. The model takes into account the diffusion-limited penetration of nitrate and nitrite into the immobilized-cell biocatalyst particle, uniform intraparticle cell density, equivalent slab geometry for the spherical particle, zero-order intrinsic reaction kinetics of the immobilized cells, sequential reduction of nitrate to nitrite and nitrite to dinitrogen within the particle, no inhibition of the sequential reactions by either nitrate or nitrite, and ideal plug flow conditions in the bioreactor. As a result, the reaction in the bulk fluid of the plug-flow bioreactor can be described by a half-order kinetics, and the process is characterized by the half-order reaction rate constants for nitrate and nitrite reduction. These constants incorporate the intrinsic reaction kinetics of the immobilized cells, the size and packing density of biocatalyst particles in the reactor, and the effective diffusion coefficients of nitrate and nitrite in the particle matrix.

Laboratory experiments were conducted to characterize the performance of an immobilized-cell denitrification process treating nitrate-contaminated groundwater and to provide supporting data for the validation of a quasi-steady state model based on half-order reaction kinetics. The treatment process consists of laboratory-scale, plug-flow reactors packed with biocatalyst particles. Pseudomonas denitrificans (American Type Culture Collection 13867), a heterotrophic denitrifier, was cultured and immobilized in calcium alginate particles. Ethanol was used as the source of organic carbon. Thirty concentration profiles were obtained at four levels of nitrate concentration and at three ranges of flow rate. An analysis of the nitrate and nitrite concentration profiles suggested that a half-order reaction rate model could be used to describe the reduction of both nitrate and nitrite. The half-order reaction rate constants for nitrate and nitrite reduction were dependent on the age of the biocatalyst particles and the nitrate loading history. The validity of the half-order denitrification model was satisfactorily tested with experimental data. As illustrated by preliminary calculations, the immobilized-cell denitrification process is feasible for practical applications, particularly for small drinking water systems.

This paper describes a standardized method to assess the inhibitory effect of a toxicant on nitrifying microorganisms. Nitrification activity is measured by means of pH-stat titration, which exploits the stoichiometric relationship between ammonium oxidation and acidity production. First, the maximum ammonium oxidizing capacity of a sample of nitrifying activated sludge is assessed in the presence of ammonium as substrate (activity of the blank). Subsequently, five increasing amounts of toxicant are spiked at regular intervals into the sludge sample while its nitrifying activity is continuously monitored. Finally, nitrification is fully inhibited by allylthiourea to detect the presence of interference. Experiments on three nitrification inhibitors (allylthiourea, aniline, and cyanoguanidine) demonstrated a good repeatability (coefficient of variation on EC₅₀ determinations of 11, 38, and 14%, respectively) and good correlation with literature values.

A continuous-flow intermittent aeration (IA) process has been studied for nitrogen removal from anaerobically digested swine wastewater with high ammonium content. High nitrogen removal efficiency of average 91% total Kjeldahl nitrogen and 92% NH₄-N was achieved in an IA system with an alteration of 1-h aeration and 1-h nonaeration. Nitrification and denitrification were found to be responsible for the nitrogen removal in the system. Nitrite and nitrate in the effluent were less than 1.0 mg/L and 8.0 mg/L, respectively. The specific nitrification and denitrification rates of the single-sludge IA culture were determined through batch experiments as 2.79–3.70 mgNO₃-N/g volatile suspended solids-h and 0.59–1.03 mgNO₃-N/g volatile suspended solids-h, respectively. In the IA process, the aeration period created favorable conditions for nitrifying bacteria (dissolved oxygen = 4–6 mg/L and oxidation-reduction potential = 80–100 mV), while the nonaeration period provided good environment for denitrifying bacteria (dissolved oxygen < 1 mg/L and oxidation-reduction potential as low as 0 mV). Ammonia volatilization in the IA process was negligible (<0.008%). Denitrification activity in the IA process prevented nitrate from accumulation and significant pH change in the system, which is critical for nitrogen removal from swine wastewater with high ammonium content.

Copper removal to residual parts-per-billion (ppb) levels was achieved in an activated sludge system by employing iron bioflocculation and biosolids storage conditioning. Low copper residuals correlated to an increase in extracellular polysaccharides that were produced by microorganisms within activated sludge. In batch bench-scale tests, supernatant copper levels between 15 and 35 ppb were achieved when employing a coagulant dosage of 15 mg/L (as Fe) and when allowing 18 to 26 h of biosolids storage conditioning to enhance the production of exopolymers. These copper levels were less than half as much as when neither coagulant nor biosolids storage conditioning was employed. Minimum copper residuals occurred in a pH range from 6.5 to 8.8, and when at least half of the biosolids had been stored for a day. Biosolids that were conditioned under a closed-to-oxygen environment yielded the lowest copper residuals among the bench-scale conditions that were tested, and it also produced the largest amounts of extracellular polysaccharides, as determined by a ruthenium red adsorption method and an india ink method.

Surfactant-enhanced sorbent zones have potential utility for contaminant plume management in the subsurface. Changes in the hydraulic properties associated with the formation of such zones were studied by measuring hydraulic conductivities of sandy-loam soil mixtures with different fine contents (6, 12, 18, and 24%) that were either untreated, or treated in batch systems with hexadecyltrimethylammonium (HDTMA). Experimental conditions included treatment to 0.1, 0.7, 1.0, and 2.3 times the cation exchange capacities (CEC), and effective stresses from 0 to 766 kPa. Achieved treatment levels and the kinetics of HDTMA adsorption were evaluated using ¹⁴C-labeled HDTMA. Soil suspension turbidity was used to infer the degree of clay dispersion or flocculation; clays were dispersed in 0, 0.1, and 2.3 CEC treated soils and flocculated in 0.7 and 1.0 CEC treated soils. Consistent with their flocculated clay structures, the 0.7 and 1.0 CEC treated soils showed equal or higher conductivities compared to 0, 0.1, and 2.3 CEC treated soils. The 0.7, 1.0, and 2.3 CEC treated soils also showed higher compressibility. HDTMA adsorption occurred rapidly at levels up to 1.0 CEC but was kinetically limited at the high treatment level (2.3 CEC). Creation of sorbent zones by ex situ batch treatment with cationic surfactants was deemed hydraulically feasible as evidenced by equal or higher conductivity of HDTMA-treated soils to 0.7 and 1.0 CEC treatment levels, as compared to untreated soil, under all loads.

For a multicomponent competitive adsorption process, a mathematical model was built to describe the mass transfer kinetics in a fixed-bed adsorber packed with activated carbon fibers (ACFs). The effects of competitive adsorption equilibrium constants, axial dispersion, external mass transfer, and intraparticle diffusion resistances on the breakthrough curves were analyzed for weakly adsorbed and strongly adsorbed components. Experiments were carried out to remove phenolic compounds from an aqueous solution. With the equilibrium data and the intraparticle (intrafiber) diffusivities obtained from separate experiments in a batch adsorber, the axial dispersion coefficient was evaluated by fitting the experimental data of breakthrough curves with the theoretical model. The results show that the effects of intrafiber and external mass transfer resistances on the breakthrough curves can be neglected for a fixed-bed adsorber packed with ACFs, and the axial dispersion is confirmed to be the main parameter that controls the adsorption kinetics. A simpler model, based solely on a liquid phase mass balance and incorporating local equilibrium with axial dispersion, provides a good description of the adsorption process for a fixed-bed adsorber packed with ACFs.

A pilot TiO₂/V₂O₅ based selective catalytic reduction (SCR) system was installed in a glass manufacturing factory. The effects of important operation parameters such as the reaction temperature, space velocity, and inlet NH₃/NO_x molar ratio on the NO removal were evaluated. It was observed that >1 mol of NO_x is reacted for every 1 mol of NH₃ injected. This observation is different from that reported in the literature for laboratory experiments. The key design parameter values of the reaction rate and the NH₃ adsorption rate were determined based on results of the pilot tests using a theoretical SCR model developed by the same research group. The SCR model is a simple analytical solution that accounts for the simultaneous mass transfer and chemical reaction of an SCR reactor. The model results were compared to field data of NO_x conversion efficiency and NH₃ slip, and they were in reasonable agreement. The required catalyst volume and the cost of catalysts were then determined with the assistance of the design model.

The photodegradation (at λ = 253.7 nm) of a typical anthraquinone disperse dye (DO11) in a solution containing acetone and triethylamine (TEA) has been investigated. Anthraquinone disperse dyes are known to have very low photodecay rates in the natural environment because of their low solubility. Acetone (ACE) acts not only as a solvent to increase the dye's solubility, but also as a photosensitizer to enhance the dye's photodecay rate. The photodegradation of DO11 follows pseudo first-order decay via photoreduction. In general, the decay quantum yield increases with the increase of ACE/H₂O ratios and pH levels, except at very high ACE/H₂O ratios or pH levels. Under these circumstances, photoreaction will be retarded because of light attenuation by excess acetone and formation of intramolecular hydrogen bonds within the dye molecules. Adding a low concentration of TEA to the aqueous acetone can further enhance the reaction because TEA can be used as an additional hydrogen source. However, an overdose of TEA will quench the reaction. The possible photoreduction mechanisms of anthraquinone disperse dye in aqueous acetone and TEA were proposed, and two models were derived that successfully described the reaction at both low and high [TEA], which made the process performance predictable.

The effects of naphthalene concentrations and soil constituents (sand, clay, organic matter) on biodegrading naphthalene-contaminated soils using an acclimated Flavobacterium sp. were examined in continuously stirred slurry bioreactors. Soils with and without organic matter (1%) and kaolinite clay (20%) were used. Studies showed that sorption of naphthalene can be represented by the Freundlich isotherm. Among the soils investigated, clayey soil retarded the biodegradation process the most due to its desorption characteristics. Increasing the naphthalene contamination level from 500 mg/kg to 25,000 mg/kg doubled the biodegradation time in the slurry reactor with a soil loading of 10 g/L. A pseudo first-order kinetic was observed for naphthalene biodegradation, and the biodegradation constant was determined to be 0.20 mg/L/h. A kinetic model was developed to simulate the biodegradation of naphthalene in a continuously stirred batch slurry reactor and to understand the role of solubilization (solid phase naphthalene), desorption, and biodegradation in the removal of naphthalene. Predictions using the numerical model agreed with the experimental data.

Organoclays, clays modified by cationic surfactants, for engineering applications have recently drawn great attention because of their high organic removal capacity. In this study, the potential use of organoclays with soil-bentonite admixtures as waste containment barriers is investigated by experimental tests such as batch equilibrium sorption studies, compaction tests, and hydraulic conductivity tests. Sorption isotherms of total organic carbon (TOC), a gross organic term, by five different types of soil admixtures are nonlinear. The soil specimen with more organoclays exhibits higher organic sorption capacity and a larger retardation factor. The specimens with 20% by dry weight of bentonite have higher optimum water content and plasticity. With the addition of bentonite in the soil material consisting of completely decomposed volcanic rock (CDV) (natural soils) and organoclays, the hydraulic conductivity to leachate decreases from about 10⁻⁷ to 10⁻⁸ cm/s. This indicates that the presence of bentonite in the admixtures is important in reducing hydraulic conductivity.

The effect of grass root exudates and glucose on the lag time associated with 2,4,6-trichlorophenol (TCP) degradation by an unacclimated microbial inoculant and an acclimated microbial inoculant was investigated. The experimental medium was a nutrient solution containing TCP spiked with radiolabeled TCP and amended with either glucose or root exudates collected from fescue grass. Treatments containing TCP as the sole organic carbon source served as biotic controls. The acclimated microbial inoculant was not provided with TCP for 4 weeks prior to the experiment. The presence of an alternate organic carbon source reduced lag time for both the acclimated microbial inoculant and the unacclimated microbial inoculant. For the latter, three ratios of alternate organic carbon content to inoculant biomass were tested. The lag time for acclimation depended on this ratio. A lag time in excess of 11 days was observed for the biotic controls. The shortest lag time with the addition of an alternate organic carbon source was between 2 and 4 days for glucose and between 5 and 9 days for root exudates. It is proposed that the presence of a readily available, alternate organic carbon source affected lag time through promotion of microbial population growth and provision of a preferred source of carbon and energy.