Journal of Environmental Engineering

The distribution and migration characteristics of heavy metals; benzene, toluene, ethylbenzene, and xylene (BTEX); and polycyclic aromatic hydrocarbons (PAHs) in crude oil, regenerated oil products, and waste residues from four typically used mineral oil regeneration processes were analyzed. Results indicated that the majority of heavy metal and BTEX in crude oils entered into waste residues and regenerated oils, respectively, while PAHs contaminants would be transferred and accumulated in refined oil or waste residue basing on different regeneration process. These specific differences were primarily related to the actual operating conditions of selected regeneration process and the sources of particular contaminants in crude oil. Exogenous and newly generated heavy metal, BTEX, and PAHs were easily mixed in the regenerated products and subproducts during the regeneration process.

This study describes the formation, particle clustering, settling mechanism, and settling velocity ($V_s$) in a fluidized bed reactor using laboratory and field experiments based on its cohesivity, which is expressed as a sludge cohesion coefficient ($SCC$). At a constant upflow, solid loading leads to particle interactions that result in an increase in the floc size. The blanket thickens and reaches a steady state, at which point the blanket height remains static and $V_s$ reaches two to four times higher upflow velocity. During the steady state, $SCC$ increases with time ($0.6–0.8\mathrm{mm}/\mathrm{s}$) and $V_s$ decreases, whereas no significant variation in sludge volume ($SV$) is observed. Comparing the nondimensional parameter $V_s/SCC$ with the voidage ($1-SV$), the Reynolds number ($\mathsf{R}$) of the blanket is 3. At a high $\mathsf{R}$, hydrodynamic forces tend to overcome the adhesive forces. Turbulent conditions created by larger and faster settling clusters lead to their destruction, resulting in the formation of smaller subclusters. This increases the interstitial area between the clusters and reduces $V_s$. Blanket cohesivity increases due to the short-ranged cohesive forces between particles.

In this paper, behavior of clayey sand contaminated with gas oil was studied through a series of laboratory experiments, and the possibility of improving it for the treatment of physical and mechanical characteristics was studied by the addition of two kinds of clay nanoparticles in both hydrophilic and organophilic types of substances. Samples of natural soil, contaminated soil, and contaminated soil stabilized with nanoclay (NC) and organoclay (OC) were prepared. Tests of durability against the freeze-thaw (F-T) process and of Atterberg limits were performed. The results of the Atterberg limits test showed the return of plasticity properties and a reduction in hydrophobia of contaminated soil amended with a combination of nanoclay and organoclay. Durability tests indicated greater stability and durability in the stabilized contaminated samples at different cycles, including the freeze-thaw process in both types of clay nanoparticles. The initial strength of stabilized samples increased their stability and durability against temperature changes. In general, the possibility of using contaminated soil stabilized with absorbing nanoparticles as basic engineering materials is possible.

In the published literature, deflocculation of aerobic biological flocs under low dissolved oxygen (DO) ($<0.5\mathrm{mg}/\mathrm{L}$) conditions is typically reported as occurring as early as after 1 h of oxygen deficiency. However, results of this study involving aerobic sludge from three different sources repeatedly indicated a lack of deflocculation after 24 h of low DO conditions. This finding has led to the conclusion that low DO might not be a direct cause of deflocculation. In addition to the low DO conditions, the sludge samples were not re-fed throughout the experiment, but deflocculation was still not observed. An analysis of the soluble microbial products (SMP) and loosely and tightly bound extracellular polymeric substances (EPS) was performed to improve understanding of the sludge’s behavior in response to low DO conditions. Results indicated no increase in SMP content or change in the tightly bound EPS content upon extended periods of low DO. It was concluded that high proteins concentration in the bound EPS improved flocs stability, and so contributed to the maintenance of floc integrity during extended periods of low DO conditions.

Agriculture is the most extensive source of nitrate to water resources. A high concentration of nitrate contamination in drinking water is a significant risk to human health. The aim of this study was to select the appropriate combination of organic substrates and zero-valent iron (ZVI) to use as an electron donor for denitrification in a permeable reactive barrier. From the results, a nitrate-removal efficiency of more than 85% was achieved for all the tested organic substrates at ambient temperature ($25\pm 5°\mathrm{C}$), neutral pH, and under anaerobic conditions. The initial nitrate concentration of $150{\mathrm{mg}\mathrm{L}}^{-1}$ and the organic substrates ($50{g\mathrm{L}}^{-1}$ concentration) were tested in this study. Different dosages for ZVI (10, 30, 50, and $70{\mathrm{g}\mathrm{L}}^{-1}$) were also investigated. Using a mixture of rice husk and rice straw as an electron donor led to the highest nitrate-removal efficiency (93.3%). Using ZVI as an electron donor yielded a lower nitrate-removal efficiency than using the same amount of the organic substrate. However, the use of ZVI coupled with the organic mixture resulted in a higher nitrate-removal rate than when only the organic mixture was used. The nitrate-removal rate increased up to threefold when using ZVI wire, a type of waste from a lathe factory, mixed with the organic mixture as an electron donor.

Quantitative evaluation of soil quality is needed to investigate the sustainability of a particular land use and soil management in relation to plant production and environmental quality. The present study aims to detect the most suitable soil quality indicators and assess the influence of the five most predominant land-use and soil management types [dense forest (DF), bun cultivation (BC), pine forest (PF), shifting cultivation (SC), and abandoned land after shifting cultivation (AS)] on soil quality of two districts in Meghalaya, India. Ninety-three soil samples were assembled and analyzed for different soil quality indicators. For a selection of indicators, the collected soil samples were subjected to principal component analysis, followed by the varimax rotation algorithm. Subsequently, selected indicators were transformed and assigned a score based on the linear scoring function. Significant ($P<0.05$) variations in soil quality were found across different land uses. The overall soil quality index was found to follow the following order: $0.91(\mathrm{DF})>0.69(\mathrm{SC})>0.63(\mathrm{PF})>0.57(\mathrm{BC})>0.37(\mathrm{AS})$. Results denote that the quality degradation of the soils was due to anthropogenic activities. Soil organic carbon was observed to be a powerful soil indicator under prevailing land use. The method used in the present study proved to be sensitive to evaluate the soil quality and demonstrated that carbon management holds the key to improving the soil quality of the study area.

Biochar has recently emerged for the alleviation of various pollutants in urban runoff. However, the adsorption of arsenate (a frequently identified pollutant in urban runoff) with biochar is typically poor. In this study, an aluminum–impregnated biochar was investigated for adsorption of arsenate. Results with synthetic arsenic-polluted urban runoff show that As(V) was bound to amorphous aluminum hydroxide on biochar surface through irreversible inner-surface complexation. At pH 7.6, the adsorption kinetic data followed pseudo-second-order reaction models ($R^2\ge 0.96$), and the Langmuir and Frendulich models both fit well adsorption isotherm data ($R^2\ge 0.99$). The adsorption was little influenced by pH (4.5–8.5) and ionic strength (0–100 mM NaCl) in this study. Although phosphate and dissolved organic matter (DOM) have a potential to suppress As(V) adsorption, their inhibiting effects were insignificant under the study conditions [$0–200\mathrm{\mu g}/\mathrm{L}\mathrm{P}$, $0–40\mathrm{mg}/\mathrm{L}$ dissolved organic carbon, and $500\mathrm{\mu g}/\mathrm{L}$ As(V)]. However, it is likely that the suppression of phosphate or DOM on the As(V) adsorption becomes more significant with the increasing molar ratio of P or DOM to As in urban runoff during the realistic stormwater treatment. Besides As(V), the aluminum-impregnated biochar could effectively remove many other runoff pollutants (i.e., Pb, Zn, Cu, and ${\mathrm{P}\mathrm{O}}_4^3$) in a polluted real urban runoff. Exhausted aluminum-impregnated biochar passed the toxicity characteristic leaching procedure (TCLP) screening, suggesting that the spent adsorbent can be safely disposed of in municipal landfills. This study demonstrates that surface modification with aluminum enriches active surface sites of biochar for arsenate and expands biochar applications in stormwater treatment.

This paper compares two different carriers, polyurethane foam (PU) and polyurethane foam loaded with tourmaline (TPU), for the partial nitrification (PN) of supernatant from an anaerobic sludge digester using moving bed biofilm reactors (MBBRs). In parallel laboratory tests, the TPU reactor finished start-up in 51 days while the PU reactor took 67 days. In the TPU reactor, the ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$ removal efficiency, total nitrogen removal efficiency, and nitrite accumulation ratio were 83.8%, 55.6%, and 75.4%, respectively. In response to the hydraulic shocks, the recovery was observed in 20 days for the TPU reactor and 34 days for the PU reactor, respectively, showing that the TPU reactor had a good resistance to the hydraulic shock loading. The biofilm formed in the TPU and PU carriers was comprised of a network of spherical and bacillus communities, which were surrounded by the extracellular polymeric substances (EPS). The biofilm structure in the PU biofilm was less dense with cell-free voids compared to that in the TPU biofilm. The real-time polymerase chain reaction (RT-PCR) data showed a trend similar to the biomass results in that the TPU biofilm had a faster growing rate of bacteria concentration than the PU biofilm. Free ammonia (FA) and free nitrous acid (FNA) levels fell within the inhibition range for nitrite-oxidizing bacteria (NOB) during the whole operation. The inhibition mechanism of NOB might be due to the coexistence of FA and FNA. This study revealed the potential of a partial nitrification process to treat supernatant from an anaerobic sludge digester by combining tourmaline and biofilm.

Crystalline scorodite (${\mathrm{FeAsO}}_4·2{\mathrm{H}}_2\mathrm{O}$) is a common arsenic-(As-)containing solid waste produced from nonferrous metallurgical processes. Its stability is the key factor to determine environmental risks. Scorodite is stable in the mildly acidic environment, while in a neutral to weakly alkaline environment, it can easily decompose and release As into solutions. In this work, scorodite was microencapsulated with an aluminum silicate gel for improving its stability. The effect of Si/As molar ratios on the stability of microencapsulated scorodite was investigated. A short-term stability environmental testing of 10 days indicated that a coating formed at a Si/As molar ratio of 0.2 inhibited As release at pH 4 and 6. A coating formed at a Si/As molar ratio of 1.5 was proportionately more successful at preventing As release at pH 6 and 8. The morphology and elemental composition were analyzed using a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), respectively. Raman spectroscopy and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) were employed for characterization of encapsulated scorodite (E-scor). The results showed that aluminum silicate was uniformly coated on the surface of scorodite and the coating still adhered to the surface of scorodite after short-term stability testing performed at pH 4, 6, and 8. These findings have significant implications for the stabilization of the arsenic-containing solid waste in the hydrometallurgical industry and reducing its environmental risks.

Nitrification of chloraminated water in distribution systems, particularly in summer time, is a serious problem for some utilities because nitrifying bacteria deplete residual chloramine, allowing the growth of other bacteria. Some water utilities have proposed adding chlorite (${\mathrm{ClO}}_2^{-}$) to inhibit the nitrifying bacteria responsible for this process. However, chlorite is suspected to degrade due to reaction with chloramine, and the reaction kinetics is poorly understood. In this study, we investigate parameters such as dissolved organic carbon, chloramine, pH, and temperature that might influence the decay of chlorite in synthetic and finished chloraminated water from Louisville Water Company. Our results showed that in the absence of chloramines, chlorite is stable under typical distribution system conditions (buffered water at pH of 7–9; temperature between 15°C and 35°C; and in the presence of natural organic matter, ammonia, nitrite, and nitrate). However, under these same conditions chlorite decays if chloramines are also present; chlorite and chloramines both degrade in the presence of the other, reducing the effective disinfectant residual in the system. An empirical model was developed to show the dependence of chlorite decay on chloramine concentrations and other environmental conditions. Utilities can use the model as a guide for the chlorite feed concentration and estimation of the chlorite decay in the distribution system.

Supercritical water oxidation (SCWO) has emerged as a promising technique to eliminate refractory aromatic compounds, which are difficult to remove by conventional wastewater-treatment processes. Decompositions and degradation mechanisms of pyridine and 3-cyanopyridine (3-CP) were investigated using SCWO in this work. It was found that total organic carbon (TOC) removal efficiencies of pyridine and 3-CP were significantly improved as the oxidant dose ratio rose from 0 to 5, temperatures increased from 350°C to 550°C, and reaction time extended from 0.5 to 6 min. Based on the experimental results, degradation kinetics constants of pyridine and 3-CP were evaluated, which were $0.2525–0.7097{\min }^{-1}$ for pyridine and $0.2739–0.9590{\min }^{-1}$ for 3-CP. It is obvious that the degradation kinetics constants of 3-CP were higher than those of pyridine in general. Based on density functional theory (DFT) method, Fukui indices based on OH radical attack (F(0)) of pyridine and 3-CP were calculated. The results showed the greatest F(0) value of carbon atom in 3-CP was higher than that in pyridine, which indicated 3-CP would be more easily attacked by OH radicals than pyridine. According to these results, the conceivable degradation pathways of pyridine and 3-CP were proposed, which include hydroxylation, ring cleavage, and mineralization.

Cryptosporidia are opportunistic pathogens, some of which infect humans when ingested in water or food. Filtration through granular media is the primary mechanism to remove them from water. Natural soils’ ability to filter the oocysts is expected to be affected by their physicochemical properties. This study used two undisturbed soil cores: an Oxisol, rich in clay minerals and iron oxides and an Ultisol, dominated by quartz minerals and limited in clay minerals and iron oxides, both dominant in the tropics and subtropics. To better evaluate the impact of macropores on the movement of Cryptosporidium parvum oocysts, the two cores were scanned using computed tomography. Local rainwater was used as the leaching solution, and fluorescent carboxylated microspheres (1.75 μm) served as surrogates for cryptosporidial oocysts. Results showed early appearance of microspheres compared with the conservative tracer, suggesting an enhanced velocity for the microspheres due to preferred flow-path structure. Higher recovery (10% versus 0.5%) of microspheres occurred in the ultisol compared with the Oxisol. This was due to the high content of quartz, the limited content of minerals, and negligible content of iron oxide in the Ultisol. The long tailing that occurred in the Oxisol suggested the release of previously attached microspheres and a possible source of groundwater contamination.