Environmental Engineering Science

A widely applicable hydraulic flocculator design model would facilitate increased adoption of this sustainable technology. To this end, the authors previously proposed rate equations for the removal of nonsettleable aggregates in hydraulic flocculators (Pennock et al.). This work continues the prior effort by developing two models for coupled flocculation/sedimentation performance. The first model describes settled effluent turbidity for flocculators where the relative velocities between particles are dominated by viscous forces (e.g., laminar flows). Similarly, the second model applies where inertial forces dominate. Predictions of these models were compared with laboratory-scale flocculation/sedimentation data obtained from both a laminar- and a turbulent-flow flocculator. The viscous equation fit data from the laminar flow flocculator well. For the turbulent flocculator, both models gave good fits of the data, but the inertial model performed slightly better. The similarity of the two models under the experimental constraints explains this result, and further study in different conditions is needed to delineate the applicability of the models in turbulent flocculation. Given the similarity between the models and that the product of the mean fluid velocity gradient applicable to laminar flow \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$( \overline G )$$ \end{document} and hydraulic residence time \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$( \theta )$$ \end{document} , \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$\overline G \theta$$ \end{document} , has historically been used in flocculator design, it is recommended that the viscous flocculation model introduced in this article be used. The new flocculation models have a single adjustable parameter and, in addition to being able to predict settled effluent turbidity from coagulant dose, also provide reasonable estimates of flocculator design parameters from first principles and dimensional analysis.

The number of biogas power plants increased significantly in the recent years. A lot of countries developed competitive national biogas markets after decades of intensive research and technology innovation. Biogas power plants make use of advanced anaerobic digestion processes to increase the production of biogas as a principal source of income. On the other hand, digestate is still considered a by-product and usually disposed of in landfills. This article proposes energy generation from digestate as a financially viable alternative. Before energy generation, digestate is separated into solid and liquid fractions and dried by thermal energy. Calorimetric measurements showed that the heating value of digestate is 13 MJ/kg, which favors its energy generation potential, especially if the excess heat from cogeneration is used for the drying. The digestate produced in biogas power plants can be used as a low-cost alternative fuel for electricity generation in biomass power plants. It is estimated that digestate-generated electricity could contribute with 4.2% of the total electricity generation in Croatia. The economic analysis revealed that the price of electricity generated from digestate, under the present feed-in tariff system in Croatia, is two to three times higher than the total cost of digestate.

Anaerobic ammonium oxidation (Anammox) is attracting significant attention for use in mainstream sewage treatment. However, its application is limited by sensitivity of anaerobic ammonia-oxidizing bacteria (AAOB) to environmental conditions. Use of nanoparticles (NPs) for sewage treatment has increased in recent years, but so has the risk of NPs entering into municipal sewage. In this study, three identical sequencing batch reactors were fed with CuO, ZnO, and TiO₂ NPs in different concentrations (0, 1, 5, 10, 20, and 50 mg/L) to study the short-term effects of the NPs on Anammox. Results showed that ZnO and CuO NPs had a similar effect on Anammox, that is, both NPs at low concentrations (1 mg/L) significantly suppressed nitrogen removal. Reactors also exhibited self-adaptation to ZnO NPs at concentrations in the range 5–20 mg/L and CuO NPs in the range 10–50 mg/L. ZnO and CuO NPs exerted different levels of inhibition on Anammox within the experimental range of concentrations (1–50 mg/L). TiO₂ NPs were beneficial for Anammox and improved nitrogen removal at low concentrations, but significantly suppressed AAOB bioactivity at high concentrations (>1 mg/L). However, they had no impact on Anammox at a concentration of 50 mg/L due to NP aggregation.

Treatment of styrene-contaminated air using a combined process of microelectrolysis and biotrickling filter was studied in this article for the first time. Removal of styrene was higher than 95% and kept rather stable after the process reached a stable state. The active substance produced by microelectrolysis with an appropriate electric current presenting the synergy effect for the combined process, resulted in an improvement in the styrene removal. There exists an optimum electric current for the combined process. At the residence time (RT) of 108 s and the styrene inlet load of 15 g/(m³·h), when the electric current increased from 50 to 150 mA, styrene removal increased from 92.6–94.4% to 98.5–99.1%. When the electric current further increased to 200 mA, however, styrene removal reduced to 92.9–95.5%. When RT was 216 or 108 s and the styrene inlet load was 7.5 or 15 g/(m³·h), varying the styrene inlet concentration did not affect the styrene removal. The influence of styrene inlet concentration on the styrene removal gradually emerged with decrease of RT. At a relative low styrene inlet load (≤30 g/[m³·h]), styrene removal load increased linearly with increasing styrene inlet load. In addition, we found that the optimum pH value was relatively low (5.2) when the electric current (100 mA) was applied to the biological process.

In this study, the high-reactive Co/Al₂O₃-EPM (prepared by electroless plating method) were used for catalytic ozonation. On account of the powerless degradation of small molecule acid by ozone alone, succinic acid (SA), a kind of small molecule acid, was selected as the simulated pollutant to evaluate the performance of Co/Al₂O₃-EPM in Co/Al₂O₃-EPM/O₃ system. First, several key preparation parameters of Co/Al₂O₃-EPM and operational parameters in Co/Al₂O₃-EPM/O₃ system for SA removal were optimized. The maximum SA removal (100%) and the total organic carbon (TOC) removal (66.9%) were obtained under the optimal conditions. Second, the superior performance of Co/Al₂O₃-EPM/O₃ system for SA removal was confirmed by four control experiments (i.e., Co/Al₂O₃-EPM alone, O₃ alone, Co/Al₂O₃-IM alone, and Co/Al₂O₃-IM/O₃ systems). The conversion and mineralization of SA were investigated by high-performance liquid chromatography and TOC analyzer, respectively. The stability of different systems was evaluated by cobalt leaching in the effluent. Besides, X-ray diffraction, Fourier transform infrared, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller were used to analyze the characteristics of Co/Al₂O₃-EPM and Co/Al₂O₃-IM (prepared via impregnation method). The results show that Co/Al₂O₃-EPM had a more uniform and dense cobalt film than Co/Al₂O₃-IM. In addition, in the Co/Al₂O₃-EPM/O₃ system, quenching experiments were conducted, and the dynamic concentration of HO^• in the bulk solution was detected. Finally, a possible reaction mechanism for SA degradation in Co/Al₂O₃-EPM/O₃ system was proposed. In brief, all results suggest that Co/Al₂O₃-EPM is a promising catalyst with high catalytic activity and strong stability for ozone decomposition.

Azo dyes represent the most important class of textile dyes and pose a serious environmental issue when released in wastewater. White rot fungi decolorize azo dyes efficiently; however, some difficulties arise when they are cultured as suspended pellets. This study analyzed decolorization performance of an azo dye by Trametes versicolor immobilized on polyurethane foam in a sequencing batch reactor (SBR). The SBR was operated for 27 days with nine cycles of 73.25 h each and dye decolorization of ∼96% ± 1.39%, irrespective of initial dye concentration and the number of cycles. In the SBR, free biomass barely accounted for 5% of total biomass, which did not significantly (p > 0.05) contribute to the decolorization process or biomass conglomerate formation. Along the SBR culture, laccase, manganese, and lignin peroxidase activities were produced with a sustained increase, related to the decolorization process, reaching maximal activities (15.9, 40.4, and 14.4 U/L, respectively) at the end of the culture. Changes observed in the absorption spectrum showed that dye decolorization was related to a change in dye chemical structure, attributed to the action of enzymatic activity. The kinetic study of decolorization and enzymatic activity, by means of a first-order model, suggested that decolorization rates could decrease at higher dye concentrations as well as by increasing the cycle's number in the SBR. On the other hand, higher dye concentration could produce an increase in the total enzyme production rate, probably as a physiological response of the immobilized fungus.

Dongdagou Ditch in Baiyin City was one of the key demonstration areas for remediation of heavy metal contamination in China. Solidification/stabilization (S/S) is an appropriate technology that has positive impact on both leaching and strength performance of the riverbed site. This field trial was designed to investigate the long-term S/S effects and mechanism of ordinary Portland cement (OPC) on Cd, Zn, and Pb co-contaminated soil in Dongdagou Ditch, and to evaluate the influence of groundwater and low temperature. Leaching tests showed that 8 wt.%-OPC could effectively stabilize Cd, Zn, and Pb by 99.9%, 99.4%, and 67.9%, respectively, higher compared with 5 wt.%-OPC treatment, and had long-term stability. The bearing capacities of the OPC-treated soil reached 0.75–0.92 Mpa and met the USEPA (United States Environmental Protection Agency) standard for landfill disposal. Cd, Zn, and Pb were chemically stabilized and physically encapsulated by OPC simultaneously, the unstable acid-extractable Cd and Zn in soil were transformed into residual fraction after OPC treatment, and insoluble sulfides such as PbS and ZnS were specially formed due to high groundwater table of the site. In this field trial, groundwater showed negative effects on both leaching and strength properties of the OPC-treated soil due to anaerobic conditions and structural damage of S/S products. The 5 wt.%-OPC S/S effects on Cd and Zn decreased to 72.3% and 63.4%, respectively, and the soil strength reduced by 0.08–0.11 MPa below groundwater table. On-site S/S remediation with OPC was insensitive to low temperature, so that it was suitable for application in the cold Northwest China.

Wastewater, especially anaerobic treatment effluent, contains high ammonia nitrogen (NH₄-N) and inorganic orthophosphate (PO₄-P), which necessitate additional treatment to meet stringent discharge regulations. Ion exchange regeneration is a process that can be adopted for not only removing but also recovering nutrients. However, recovering nutrients by ion exchange from nutrient-rich effluents that also contain micropollutants (which typically pass through anaerobic treatment as well) may result in subsequent problems, since micropollutants could end up in ion exchange effluent, regenerant, or recovered fertilizer products. Micropollutant removal by a nonselective adsorbent, such as biosolids-derived biochar, before nutrient recovery processes would mitigate potential risks. The objective of this research was to evaluate the capability of biosolids-derived biochar as a pretreatment step for separating micropollutants from nutrient-rich water before ion exchange for nutrient recovery. In the presence of ammonium and phosphate, both pristine and regenerated biosolids-derived biochar could effectively adsorb triclosan (TCS) and estradiol (E2), and to a lesser extent, sulfamethoxazole (SMX) in batch sorption experiments. On the other hand, nutrient ions were not effectively adsorbed by biosolids-derived biochar. A continuous flow-through system consisting of columns in series filled with biochar, LayneRT, and then clinoptilolite was operated to test selective removal of micropollutants and nutrients in a flow-through system. The biochar column achieved more than 80% removal of influent TCS and E2, thereby reducing the chances of micropollutants being adsorbed by ion exchangers. Sulfamethoxazole removal through the biochar column was only 50%, indicating that biosolids-derived biochar would have to be optimized in the future for hydrophilic micropollutant removal. Influent nutrients were not effectively removed by the biochar column, but were captured in their respective selective ion exchanger columns. This research revealed that biosolids-derived biochar could be employed before ion exchange resins for removal of micropollutants from nutrient-rich water.

Biochar (BC) continues to gain considerable interest for remediating metal-contaminated soils. A laboratory incubation study was conducted to evaluate the comparative efficiency of rapeseed residue and rice straw BCs pyrolyzed at 300°C and 550°C for lead (Pb) and copper (Cu) immobilization in naturally contaminated soil, which was not reported earlier. X-ray diffraction, scanning electron microscopy, and fourier-transform infrared (FT-IR) analysis were performed to study the nature of the BCs. Effectiveness of the amendments for Pb and Cu immobilization was assessed using a modified community bureau of reference extraction procedure, single extraction with CaCl₂, and the toxicity characteristic leaching procedure, respectively. Amending the soil with RS550 significantly decreased the acid-extractable portions of Pb and Cu by 63.30% and 66%, respectively, whereas the residual (stable) fractions of Pb and Cu were increased by 40.31% and 52.98%, respectively. Immobilized metals were mainly transformed to the reducible fractions. High reductions in the bioavailable phase of Pb (97.13%) and Cu (93.71%) were recorded, while Pb and Cu solubility were reduced by 92.62% and Cu 72.55%, respectively. Affinity of BCs toward Pb and Cu was enhanced due to the increased negativity with increasing pH, as described by zeta potential and cation exchange capacity, which is one of the mechanisms of Pb and Cu immobilization. BCs produced at high temperature efficiently immobilized Pb and Cu compared to low-temperature BCs. These findings suggested that rapeseed residue and rice straw BCs could be used as Pb and Cu stabilizers in contaminated agricultural soils.

The present research is based on the removal of safranin (cationic) dye, an emerging contaminant from wastewater by sodium bicarbonate modified Bambusa tulda (variety of bamboo and a bioadsorbent) using adsorption technology. Characterization study of sodium bicarbonate-treated bamboo was done through scanning electron microscope analysis and it was found that after treatment with sodium bicarbonate, pore structure of B. tulda gets widened increasing active pore cavity in the adsorbent resulting in larger surface area for higher adsorption. Energy dispersive X-ray analysis showed the presence of Na, Cl, etc., in safranin dye adsorbed adsorbent; in Fourier transform infrared spectroscopy analysis presence of Hydroxyl and Carboxyl group helps largely for adsorption of safranin dye. The batch study experiment gave optimum results for safranin dye at pH 7; rpm 200, temperature 298 K, with an initial concentration of 50 mg/L and a dose of 10 g/L with maximum adsorption capacity of 32.26 mg/g, followed by pseudo second order rate equation and a removal rate of 98.15% for 60 min of time duration. The activation energy was 17.376 kJ/mol. Two algorithms are used in artificial neural network (ANN), that is, Levenberg–Marquardt (LM) and Bayesian Regularization algorithm with different nodes. LM algorithm with three hidden nodes has higher R² value with the lesser value of statistical error. Time, dose, and initial concentration can be considered for t-test. Intensive research has been carried out on the modified B. tulda along with characteristic study and modeling analysis by ANN and regression analysis Model Study and Error analysis. Taking considerations of all experimental results and model analysis, it is concluded that sodium bicarbonate treated B. tulda is a good, low cost, and effective adsorbent in comparison to commercially activated carbon for the removal of safranin (cationic) dye from wastewater.

Biological treatment is insufficient for infield treatment of domestic wastewater that contains low amounts of carbon. This study proposes a pretreatment process for enhancing the nutrient removal efficiency by improving the biodegradability of organic matter using glow discharge nonthermal plasma (GDNTP), which generates several strongly oxidizing active species. A series of batch experiments was conducted at pH 5.0 and 9.0 to investigate removal of nitrogen based on either physiochemical effects or improvement of the biodegradability of organic matters by the GDNTP pretreatment. At pH 5.0, total nitrogen (TN) was not removed by chemical reactions with active species from the GDNTP generator, whereas more TN was removed by chemical reactions or air stripping with the gas discharged from GDNTP at pH 9.0. Part of nitrogen removal was not achieved by ammonia air stripping, but by the improvement of biodegradation due to the GDNTP pretreatment for each operational sequencing batch reactor cycle. Findings indicate that GDNTP pretreatment improves the denitrifying of nitrate rather than producing a better carbon/nitrogen (C/N) ratio.

Dredging efficacy in reducing polychlorinated biphenyl (PCB) sediment contamination in the Lower Fox River, Wisconsin, was assessed by comparing predredging and postdredging concentration profiles from portions of Operable Unit (OU) 3 and OU4. Sediment PCB concentrations (in 0.15 m depth intervals) from predredging and postdredging core locations were compared. Results show that dredging reduced PCB concentrations in the surface sediment layer (0 to 0.15 m) in 77% of the locations. At locations where surface layer PCB concentrations were lower than predredging sediments, concentrations were reduced by an average of 72%. Average PCB concentration in the surface layer of all postdredging cores was 1.86 ppm compared to 0.61 ppm in the second (0.15 to 0.30 m) layer. The difference (significant at the p = 0.006 level) suggests that residual sediments were present in the postdredging surface layer. Dredging reduced the maximum PCB concentration in sediment cores at all locations except the 2% where the maximum predredging PCB concentration in the sediment profile was less than 1.5 ppm. Dredging reduced the maximum PCB concentration in the sediment profile by 84% on average (significance level of p = 0.008).