Journal of Environmental Engineering

This study investigated the removal of fluoride from water using a calcium-modified dairy manure–derived biochar (Ca-DM500). The Ca-DM500 showed a $3.82-8.86\mathrm{times}$ higher removal of fluoride from water than the original (uncoated) manure-derived biochar (DM500). This is primarily attributed to strong precipitation/complexation between fluoride and calcium. The Freundlich and Redlich–Peterson sorption isotherm models better described the experimental data than the Langmuir model. Additionally, the removal kinetics were well described by the intraparticle diffusion model. The Ca-DM500 showed high reactivity per unit surface area [0.0001, 0.03, 0.16 mg F per ${\mathrm{m}}^2$ for Douglas fir–derived biochar (DF-BC), DM500. and Ca-DM500, respectively] for retention of fluoride reflecting the importance of surface complexation. The copresence of anions reduced removal by Ca-DM500 in the order ${\mathrm{SO}}_4^{2-}\approx {\mathrm{PO}}_4^{3-}>{\mathrm{NO}}_3^{-}$. The sorption behavior of fluoride in a continuous fixed-bed column was consistent with the Thomas model. Column studies demonstrated that the Ca-DM500 shows a strong affinity for fluoride, a low release potential, and a stable (unreduced) removal capacity through regeneration and reuse cycles.

In the application of ultraviolet (UV light), it is necessary to obtain reliable information on UV effectiveness, i.e., one should know the fluence reached by microorganisms or the dose absorbed by chemicals. For this reason, a collimated beam apparatus (CBA) is widely used. International Ultraviolet Association (IUVA) recommends a protocol on CBA in which the beams are assumed to be collimated. In this work, focusing on the fact that so-called collimated beams are not really collimated, a mathematical model for CBA is established, and the influencing factors and specifications of CBA are rigorously analyzed. The aperture type not only has high measurement accuracy, but its specific characteristics are also suitable for the calibration of radiometers in chemical actinometers. The suitable conditions for the calibration are also investigated.

Thermal hydrolysis processes (THP) play an important role in sewage sludge treatment. In this study, both low-temperature (60°C–90°C) and high-temperature (120°C–170°C) thermal hydrolysis experiments were performed on the initial sludge (at a total solid of a 7.03% and 6.45% by weight). The results have shown that the release of organic matter is logarithmic with the duration during low-temperature thermal hydrolysis (LTHP). For high-temperature thermal hydrolysis (HTHP), the release of organic matter is linear with a treated temperature. Good linear relationships were obtained between the release of a soluble chemical oxygen demand (rSCOD) and soluble proteins/polysaccharides. The pH decreased with the increase of the treatment temperature. The apparent viscosity of the sludge decreased after the thermal hydrolysis, especially at a high temperature. The yield stress of the sludge disappeared, and the thixotropy increased. Moreover, the flow behavior index increased, and the consistency coefficient $K$ decreased with the increase of the thermal hydrolyzed temperature. Meanwhile, we found a linear relationship between the rSCOD and increasing infinite viscosity. It demonstrated that the rheological measurement could be used as an indicator to evaluate the extent of organic matter solubilization in THP.

Excess phosphorous in waterways is known to be a cause of harmful algal blooms. This research evaluated if baking water treatment residuals (WTRs) would increase the number of adsorption sites, thereby increasing the WTRs ability to adsorb phosphorous. Initial $24\text{-}\mathrm{h}$ sorption studies determined optimal baking temperatures of 175°C for alum based-WTR (Al-WTR) and 150°C for Al-WTR amended with power activated carbon (PAC) (PAC-WTR). Adsorption-desorption isotherm studies for baked Al-WTR (175°C) and PAC-WTR (150°C) found that there was a net desorption of phosphorous when distilled water was used as the background solution. When surface water was used, baked Al-WTR adsorbed more phosphorous at $5°\mathrm{C}$ while baked PAC-WTR adsorbed more at $20°\mathrm{C}$. Continuous flow column tests were also conducted and found a sorption capacity of $7.91{\mathrm{mg}\mathrm{PO}}_4{\mathrm{g}}^{-1}$ WTR for baked Al-WTR that was less than as-is and $16.21{\mathrm{mg}\mathrm{PO}}_4$ per kg-WTR, which was 83% better than its as-is counterpart. An analysis of all experiments found that as-is WTR performed better ($p<0.05$) than baked WTR and would be the recommended reuse of the water treatment plant’s WTR for the adsorption of phosphorous.

The consumption of veterinary drugs has grown over the past decades as a consequence of the increasing global demand for food. However, the nonmetabolized fraction of these drugs ends up in the environment through animal excretion, with substantial adverse effects on the environment. Therefore, novel and effective water and wastewater treatment techniques capable of eliminating these pollutants are urgently needed. To this end, advanced oxidation processes (AOPs) are promising alternatives for this purpose. Fenton reactions are among the most studied AOPs, although they present some practical restrictions due to iron low solubility at environmental pH. Thus, the use of irradiated Fe(III)-carboxylates emerges as a possible solution to overcome this drawback. The aim of this study is to investigate the possibility of using UVA-irradiated Fe(III)-tartrate complex as a source of Fe(II) in a photo-Fenton-like reaction, for degrading the veterinary drug enrofloxacin (ENR). ENR removal was studied for different Fe(III) to tartrate proportions and pH, which were varied according to a Doehlert experimental design. Results indicate that higher tartrate concentrations enable the pH extension up to neutral, which potentiates the application of the studied process in real water matrices. Moreover, antimicrobial assays with Vibrio fischeri and Lacto bacillus, performed with untreated and treated ENR solutions, showed that antibiotic removal does not necessarily lead to toxicity removal. Further investigation is thus required to correlate the toxicity results to ENR degradation products.

Wastewater stabilization ponds (WSPs) are a popular and economical method to treat wastewater. In the current study, algae-treated effluent from WSPs was used to compare microalgal biomass harvesting methods (aluminum sulfate coagulation and chitosan flocculation) and microalgal biomass drying methods (sun drying, oven drying, and freeze drying). The physicochemical characteristics of the supernatants resulting from microalgal biomass harvesting were determined and the microbial composition of the harvested microalgal biomass was investigated using next-generation sequencing. The optimal chitosan and alum concentrations to harvest microalgal biomass were 0.368 and $9.96\mathrm{g}/\mathrm{L}$, respectively. The calculated optimal exposure period was 2 h. The harvest microalgal biomass with alum caused a decrease in the sulfate concentration ($68.44\mathrm{mg}/\mathrm{L}$) and nitrogen (below detection limit), while the orthophosphate ($14.93\mathrm{mg}/\mathrm{L}$), iron ($0.12\mathrm{mg}/\mathrm{L}$), and total carbon concentration ($327.78\mathrm{mg}/\mathrm{L}$) increased in comparison to the positive control. Furthermore, harvesting the microalgal biomass with chitosan resulted in a decreased sodium ($155.17\mathrm{mg}/\mathrm{L}$) and magnesium concentration ($12.40\mathrm{mg}/\mathrm{L}$), while an increase in ammonia ($27.57\mathrm{mg}/\mathrm{L}$), total carbon ($182.04\mathrm{mg}/\mathrm{L}$), and iron concentration ($0.16\mathrm{mg}/\mathrm{L}$) was observed. The dominant microbial phyla in the positive control were Bacteroidetes (0.242) and Proteobacteria (0.340). Cyanobacteria (0.725) was dominant in the alum-harvested microalgal biomass and Proteobacteria (0.504) was dominant in the chitosan-harvested microalgal biomass. Drying the microalgal biomass to 0.1 NTU using the sun- and oven-drying methods would require 9 days and 25 h, respectively. The freeze-drying method was not able to dehydrate the microalgal biomass to 0.1 NTU. Depending on the application of the dried microalgal biomass, in this case as potential animal feed or soil fertilizer, the sun-drying method may be the superior method because higher-quality nutrients of the microalgal biomass would be retained, while the oven-drying method would require less time but could potentially destroy most of the nutrients.

A three-dimensional bioelectrochemical reactor (3D-BER) system combining heterotrophic and autotrophic denitrification processes was developed, which possesses the effects of pH on nitrate or nitrite removal and simultaneously elimination of antibiotic sulfamethoxazole (SMX) from simulated municipal wastewater. The experimental results demonstrated that the variation of microbial communities was examined with electric current from 0 to $90\mathrm{mA}$ at pH $6.50\pm 0.12$ to $7.9\pm 0.04$. When the current increased from 0 to $90\mathrm{mA}$, the nitrate removal efficiency increased from 59.05% to 99.21%, and SMX removal efficiency of 43.9%–93.9% was achieved. The optimum pH of this reactor was $7.0\pm 0.20$ to $7.50\pm 0.31$, and a lower or higher pH condition may effect autotrophic and heterotrophic denitrification processes. Simultaneously, the denitrification mechanism in this system was analyzed through pH variation in the effluent. The ${\mathrm{CO}}_2$ produced from the anode acted as a good pH buffer, automatically controlling pH in the reaction zone. A low current intensity does not effect the degradation by-products but increases the SMX removal efficacy. Bacterial community analysis revealed substantial changes in microbial communities at the phylum, class, and genus levels after SMX acclimatization. Thauera, a well-known aromatic-degrading bacteria, was the most dominant genus present in acclimatized conditions at $60\mathrm{mA}$. In summary, this study shows that high currents changed the microbial structure, and the acclimatized sludge can play a vital role in the biodegradation of SMX, and removal of ${\mathrm{NO}}_3^{-}─\mathrm{N}$ from simulated municipal wastewater by a novel 3D-BER.

Hydrogen sulfide (${\mathrm{H}}_2\mathrm{S}$) is the primary cause of odor and corrosion in sewer systems. When wastewater breaks up into small droplets in drop structures, the emission of ${\mathrm{H}}_2\mathrm{S}$ is expected to be significantly enhanced relative to that of the continuously falling sewage. However, limited studies have been conducted on the mass transfer coefficient, $K_L$, of dissolved gas in falling water droplet emissions into air. In this study, laboratory experiments of falling liquid droplets in air were conducted with two gases: ${\mathrm{H}}_2\mathrm{S}$ and carbon dioxide (${\mathrm{CO}}_2$). In the droplet diameter ($3.02–4.68\mathrm{mm}$) and free-falling height ($0.1–1.5\mathrm{m}$) testing ranges, the $K_L$ value at 20°C was found to be $0.9–4.5\times {10}^{-4}\mathrm{m}/\mathrm{s}$, which increased with the falling height (or velocity) and decreased with the droplet size. Existing prediction equations show a great range (up to 10 times) for $K_L$ and cannot accurately predict the experimental results. Therefore, a modified equation was proposed to better predict $K_L$. In addition, ${\mathrm{CO}}_2$ was found to be a suitable surrogate for ${\mathrm{H}}_2\mathrm{S}$ in mass transfer due to the toxicity of ${\mathrm{H}}_2\mathrm{S}$. Finally, the research results were applied in large and small sewage drop structures. More than 70% of ${\mathrm{H}}_2\mathrm{S}$ emission to equilibrium could be achieved after falling $15\mathrm{m}$ in large drop structures depending on droplet sizes. In small drop structures, the results of free-falling water droplets were found to approximately model the complex ${\mathrm{H}}_2\mathrm{S}$ emission process. This study provides new insights into the physical process and modeling of ${\mathrm{H}}_2\mathrm{S}$ release in sewage drop structures, which are useful for odor and corrosion control in municipal drainage systems.

Erosion of sediment deposition in storm sewers is dominated by the bed shear stress and the deposition characteristics. A laboratory study investigated the critical shear stress and erosion processes for different types of deposition in storm sewers. The critical shear stress increased from 0.19 to $0.41\mathrm{N}/{\mathrm{m}}^2$ for the $0.4\text{-}\mathrm{mm}$ sand when the weight content of silt-clay changed from 0% to 20%, whereas the critical shear stress increased from 0.98 to $1.98\mathrm{N}/{\mathrm{m}}^2$ for the $1.8\text{-}\mathrm{mm}$ sand deposition. A prediction method for the critical shear stress was developed based on the particle size and silt-clay content. The erosion patterns can be classified as ripple surface, dune surface, flat surface, and rugged surface, mainly determined by the cohesive effect, particle size, and bed shear stress. The erosion rate is a function of the sediment transport rate per unit width and particle transport distance. A field sampling program was conducted to obtain sediment deposition characteristics in a storm trunk sewer. Based on the sediment characteristics and estimated flow rate, the predicted deposition profile using the method developed in this study compared well with the field measurements.

This study investigates a solar thermal water heating system that is effective in drying and disinfecting fecal sludge (FS) and recovering nutrients and water resources that happen to have fertility values for agricultural use. The fertilization value of the dried sludge and condensate was tested in a laboratory-scale plantation using three types of plants used as fodder for animals. Results showed average sludge temperatures reached during sludge drying and disinfection were 39.5°C and 33.9°C in dry and wet seasons, respectively. The sludge’s water content decreased from 99.32% to 5.3% and 81.57% to 5.5% in 40 and 54 days of dry and wet seasons, respectively. Pathogen reduction in the dry season was 100% for 13 days compared to 42 days in the wet season. The evaporation rate was higher in the dry season at $9.099\times {10}^{-4}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/{\mathrm{m}}^2·\mathrm{d}$, compared to $6.4514\times {10}^{-4}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/{\mathrm{m}}^2·\mathrm{d}$ in the wet season, whereas condensation rate was higher in the wet season at $5.59\times {10}^{-5}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/\mathrm{day}$ compared to $4.94\times {10}^{-5}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/\mathrm{day}$ in the dry season. Dried sludge increased the soil porosity by 9.39% compared to 8.41% for raw FS. Also, it increased the soil permeability from $0.06302\times {10}^{-6}$ to $5.773\times {10}^{-6}\mathrm{cm}/\mathrm{s}$, whereas raw FS decreased the soil permeability to $0.02163\times {10}^{-6}\mathrm{cm}/\mathrm{s}$. Moreover, dried sludge improved soil pH values between 7.04 and 7.39. Statistical analysis results at a 95% confidence level revealed that plants in the soil treated with dried sludge had significantly better growth characteristics than others.

An automated nonintrusive image analysis method is used to measure the settling velocity of particles and characterize their geometric properties using a fractal approach. A range of suspension characteristics is represented by particles collected from four field sites and one laboratory sample of a montmorillonite clay suspension. The field sites are Lake Ontario, Lake Erie, Lake LaSalle (a small lake in Buffalo, New York), and the Buffalo River (also in Buffalo, New York). In fractal descriptions of aggregates, particle areas do not scale with diameter squared, and settling rates vary with size, shape, and porosity. Measured settling rates are found to be less than values estimated by Stokes’ law, which is consistent with other studies of natural floc settling and indicates the flocs are not solid and spherical, as assumed for that law. They also are less than settling predicted with relationships developed for spheres at higher Reynolds number than the range associated with Stokes’ law. A dimensional analysis is performed to determine the relationship of settling rate with size, which is also correlated with other geometric and physical quantities that can be described using fractal geometry. The relationship determined using this approach provides a very good description of the observed settling rates for each of the five samples, and suggests settling velocity varies with particle size, expressed as area equivalent diameter raised to a power of approximately 1.4. Furthermore, a 2- to 7-fold overestimation of the settling velocity of larger aggregates can occur when Stokes’ law is applied. These results are useful for better prediction of particle fate and particle-bound contaminant transport, particularly in estimating contaminant residence time, fate, and overall surface water quality.

Municipal solid waste landfills are a source of major greenhouse gases such as methane (${\mathrm{CH}}_4$) and carbon dioxide (${\mathrm{CO}}_2$) and emit a trace amount of hydrogen sulfide (${\mathrm{H}}_2\mathrm{S}$). Recently, steel slag has extensively been used for mineral ${\mathrm{CO}}_2$ sequestration to minimize the ${\mathrm{CO}}_2$ releases to the atmosphere. This study explores the potential of basic oxygen furnace (BOF) steel slag to simultaneously remove ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ from landfill gas (LFG). Various batch and column tests were conducted to evaluate the ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ removal potential of the BOF slag under various conditions such as moisture content and particle size of the BOF slag. The three different particle sizes of BOF slag (coarse, as-is, and fine) were exposed to continuous flow of a synthetic LFG [50% ${\mathrm{CO}}_2$, 48.25% ${\mathrm{CH}}_4$, and 1.75% ${\mathrm{H}}_2\mathrm{S}$ by volume ($\mathrm{v}/\mathrm{v}$)] in a column reactor to evaluate the effect of particle size on ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ removal capacity of the slag. Similarly, the BOF slag was exposed to synthetic LFG as well as 20% ($\mathrm{v}/\mathrm{v}$) of ${\mathrm{H}}_2\mathrm{S}$ alone in batch reactors at varying moisture contents (10%–30% by weight) to evaluate the effect of moisture content on the ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ removal capacity of the slag. A significant ${\mathrm{H}}_2\mathrm{S}$ removal of $27\mathrm{g}{\mathrm{H}}_2\mathrm{S}{\mathrm{kg}}^{-1}$ BOF slag and ${\mathrm{CO}}_2$ removal of 76 g ${\mathrm{CO}}_2{\mathrm{kg}}^{-1}$ BOF slag were obtained in the batch reactor. The fine BOF slag ($<0.106\mathrm{mm}$) showed the maximum ${\mathrm{CO}}_2$ removal (300 g ${\mathrm{CO}}_2{\mathrm{kg}}^{-1}$ BOF slag) and ${\mathrm{H}}_2\mathrm{S}$ removal (38 g ${\mathrm{H}}_2\mathrm{S}{\mathrm{kg}}^{-1}$ BOF slag) upon exposure to continuous synthetic LFG flow in the column reactor. The quantitative X-ray diffraction (QXRD) analysis showed the highest increase in carbon ($77.5\mathrm{g}\mathrm{C}{\mathrm{kg}}^{-1}$ BOF slag) and sulfur ($28\mathrm{g}\mathrm{S}{\mathrm{kg}}^{-1}$ BOF slag) contents in the fine BOF slag, which was consistent with the mass balance of carbon and sulfur from ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ uptake in column tests. The major reaction product with ${\mathrm{H}}_2\mathrm{S}$ was elemental sulfur depicted by the significant increase in the sulfur content in the X-ray fluorescence analysis. The key minerals involved in carbonation reactions were lime, portlandite, and larnite, as these minerals showed significant reduction in weight percentage (100%, 82%, and 80%, respectively) in the QXRD analysis. Overall, BOF slag showed promising results in mitigating ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{S}$ from LFG.

Computational fluid dynamics (CFD) have been applied to predict the performance of chemical water treatment disinfection systems in recent decades. However, computation times remain sufficiently long and prevent their use in optimal design. As an alternative, the use of an artificial neural network (ANN) metamodel to simulate CFD results was assessed. The ANN metamodel was trained by a series of CFD simulations of peracetic acid (PAA) disinfection characteristics in a chemical treatment reactor in the wastewater treatment process. The design space was sampled by applying a quasi-random sampling technique. A total of 40 CFD cases with 11 variables were obtained and used as input to the training process of the metamodel development. Metamodels were developed to predict disinfectant residual concentration and a microbial inactivation rate on full-scale reactors. The performance of the ANN-based metamodel is evaluated by comparison to CFD simulation results and pilot-scale experimental measurements. As a mathematical approximation method to a high dimensional nonlinear system, the ANN-based metamodel shows its ability to provide an efficient yet accurate solution to the wastewater disinfection process with PAA.

The chemisorption of sulfur(IV) oxide (${\mathrm{SO}}_2$) from air by natural aqueous media containing iron (Fe) ions is a current area of research interest. At the same time, studies of ${\mathrm{SO}}_2$ absorption from gases with higher concentrations of ${\mathrm{SO}}_2$ and at high temperature by solutions containing Fe compounds are not enough to predict the purification process of industrial waste sulfur-containing gases. This study investigated ${\mathrm{SO}}_2$ absorption from a gas-air mixture by solutions containing Fe compounds under near-industrial conditions, viz., froth mode of bubbling, ${\mathrm{SO}}_2$ concentrations in the gas-air mixture about $0.21{–4.05\mathrm{g}/\mathrm{m}}^3$, and temperatures of $22°\mathrm{C}–80°\mathrm{C}$. The experimental results showed that a rise in process temperature, ${\mathrm{SO}}_2$ concentration in the gas phase, the Fe species, and the initial pH of the absorbing solutions lead to an increase in the rate and efficiency of ${\mathrm{SO}}_2$ removal. It was determined that ${\mathrm{SO}}_2$ absorption by an Fe(II)- and Fe(III)-containing solution (initial $\mathrm{pH}=7.85$) consists of three stages: (1) induction, (2) increase in absorption rate, and (3) decrease in absorption rate. Absorption of ${\mathrm{SO}}_2$ occurred efficiently only in the presence of $\mathrm{Fe}(\mathrm{OH}{)}_2$ in the solution (the maximum rate of ${\mathrm{SO}}_2$ absorption reached 100%). Replacing $\mathrm{Fe}(\mathrm{OH}{)}_2$ with $\mathrm{Fe}(\mathrm{OH}{)}_3$ led to a decrease in the absorption rate by more than four times. This was caused by heterogeneous catalytic oxidation on the surface of ${\mathrm{Fe}(\mathrm{OH})}_2$ accompanied by the formation of peroxide compounds. The proposed mechanism of heterogeneous catalytic oxidation is discussed in reference to the available information in the literature.