Journal of Environmental Engineering

Wastewater treatment is an energy-intensive operation. Energy consumption is forecast to increase by 60% in the forthcoming decade due to tightened legislation surrounding the discharge of final effluent to watercourses. Treatment plants rely on the time-consuming and unreliable biochemical oxygen demand to assess the quality of final effluent, leading to process inefficiencies. Here, the authors show that fluorescence spectroscopy is a robust technique for real-time monitoring of changes in effluent quality. Three portable fluorimeters were installed for one month at the final effluent discharge point of a large municipal wastewater treatment plant. The authors show that organic matter composition of the wastewater varies diurnally depending on the flow rate and antecedent rainfall. High fluorescence intensity and ammonia are attributed to sewage sludge liquor, which is regularly discharged to the treatment plant. Moreover, elevated fluorescence intensities were recorded as a result of process failure following a power outage. The study shows that online fluorescence analysis is capable of detecting both minor changes in effluent quality and issues with treatment process performance.

Nutrient removal in two identical pilot-scale reactors is assessed at influent flow rates of 30, 45, and $60\mathrm{L}/\min$. The bacteria community structure of nitrifiers and denitrifiers and the protein:polysaccharide ratio (PN/PS) in extracellular polymeric substances (EPS) are monitored at each flow rate. Except for the chemical oxygen demand (COD), the reactor performance in terms of ammonia and phosphorous removal begins to deteriorate at the $45\mathrm{L}/\min$ influent flow rate. Nitrobacter are more dominant than are nitrite-oxidizing bacteria (NOB). The PN/PS ratio in sludge EPS significantly decreases as the solids retention time (SRT) decreases from 9.3 to 2.2 days. The PN/PS ratio temporarily increases in response to an increase in flow rate before normalizing to a steadier value.

The use of woven and nonwoven fibers and meshes in membrane bioreactors (MBRs) has enhanced the study of the development of dynamic membranes, which aid to a large extent in overcoming the traditional problem of fouling associated with MBRs. The present study reports the mixing characteristics and the gas–liquid mass transfer characteristics of a pneumatically agitated high-density polyethylene (HDPE) mesh–based bioreactor developed for wastewater treatment. The HDPE mesh is not a material traditionally used in MBRs. The pore size of the mesh used in the study, 2 mm, has not been reported on for the development of self-forming dynamic membranes. The reactor was configured in a novel way by integrating the mesh into the reactor. Aeration was provided at the bottom for meeting the oxygen requirements and obtaining maximum mixing. The mixing characteristics and the mass transfer coefficients were determined at various superficial air velocities. The reactor exhibited excellent mixing characteristics at a superficial air velocity of 3.79 cm/min and possessed the optimum gas–liquid mass transfer coefficient. The reactor was modeled to tanks-in-series and extended tanks-in-series models. The reactor was then used for nitrification of ammonia wastewater. The treatment efficiency was recorded to be around 98%.

Sediment basins provide quiescent conditions that enable settling of fine particles present in runoff, mitigating environmental effects created by excessive sediment discharges. Yet, settled particles are susceptible to undesired resuspension if, during dewatering of the basin, new flows are admitted that increase velocities, shear forces, and turbulence near the basin bottom. This study presents results from an investigation of the benefits of confinement cells as a lining strategy for the bottom of sediment basins. Characteristics of effluents in an experimental apparatus representing the bottom of sediment basins were studied for varying geometries of confinement cells and flow conditions. A significant decrease in effluent turbidity was reported with the use of cellular confinement cells, with smaller cell widths as a key parameter to reduce outflow turbidity. Computational fluid dynamics modeling was used to determine which geometries were more likely to succeed in decreasing turbulence and shear within confinement cells. A nondimensional resuspension parameter $R_P$ was proposed to correlated cell geometry and intracell flow velocity for the tested sediment.

Anaerobic biodegradability tests of algae biomass produced on a facultative sewage stabilization pond were conducted at 303 K for up to 24 days. The addition of urea and $\mathrm{K}{\mathrm{H}}_2{\mathrm{PO}}_4$ enabled the algae biomass to adjust its chemical oxygen $\text{demand}:\mathrm{N}:\mathrm{P}$ ratio to $350:5:1$. Comparison with the raw substrate showed that it contained sufficient amounts of N and P for bacteria metabolism. The addition of anaerobic sludge as inoculum did not affect the overall degradation efficiency but increased the initial biogas production rate, from 9.2 (without inoculum) up to $30.2\mathrm{mL}/\mathrm{days}$ with 10% volume/volume (v/v) inoculum. The codigestion of algae biomass and anaerobic sludge was evaluated in the range of 5–50% (v/v) of algae biomass, and specific methane production of substrate combination achieved values up to $60\mathrm{NmL}{\mathrm{CH}}_4/\mathrm{g}$ volatile solids, which is 10 times higher than the degradation of just raw sludge. Destruction of volatile solids also increased with the addition of algae biomass, varying from 20% degradation (with raw sludge) up to 42% when 50% (v/v) of algae biomass was added.

This study develops an ecofriendly and inexpensive biological treatment for high-salinity wastewater. The marine bacteria Bacillus sp. KGN1 and Vibrio sp. KGP1 show removal efficiencies of 75.3 and 65.4% for chemical oxygen demand by the dichromate method (${\mathrm{COD}}_{\mathrm{Cr}}$), 91.3 and 92.0% for ${\mathrm{NH}}_3─\mathrm{N}$ (ammoniacal nitrogen), and 90.6 and 84.6% for ${\mathrm{PO}}_4^{3-}─\mathrm{P}$ (phosphate), respectively, during batch mode for 12 h in 3.5% saline artificial wastewater. The lab-scale sequencing batch reactor (SBR) system with marine bacteria–supplemented aerobic granule sludge (AGS) is operated under the following conditions: 12 h hydraulic retention time (HRT), 20 days solid retention time (SRT), 6 h per cycle, $\mathrm{3,000}\mathrm{mg}{\mathrm{L}}^{-1}$ mixed liquid volatile suspended solid (MLVSS), and $80\mathrm{L}{\mathrm{d}}^{-1}$ treatment amount per day (Q). The system has an average ${\mathrm{COD}}_{\mathrm{Cr}}$ removal efficiency of 79.8%, a ${\mathrm{NH}}_3─\mathrm{N}$ removal efficiency of 91.5%, and a ${\mathrm{PO}}_4^{3-}─\mathrm{P}$ removal efficiency of 76.5% in 3.5% saline synthetic wastewater including 400 mg ${\mathrm{COD}}_{\mathrm{Cr}}$ ${\mathrm{L}}^{-1}$, 10 mg ${\mathrm{NH}}_3─\mathrm{N}$ ${\mathrm{L}}^{-1}$, and 5 mg ${\mathrm{PO}}_4^{3-}─\mathrm{P}$ ${\mathrm{L}}^{-1}$. The results indicate that the SBR biological system with AGS supplemented with high-efficiency marine bacteria is effective for treating saline wastewater containing a high concentration of salt.

Two activated carbons (ac) were prepared by achieving nitric acid oxidation (ox-ac) and iron chloride impregnation (Fe-ac) in order to remove uranium (VI) ions from aqueous solutions. The porosity of the adsorbents was evaluated using the Brunauer-Emmett-Teller (BET) technique, where Infrared (IR) spectroscopy and Boehm’s titration were applied to analyze the surface functional groups of the samples. The scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques were used to identify the structural characteristics of the tested materials. The uranium adsorption of the materials was evaluated in batch experiments. Influencing adsorption factors were investigated. According to this research’s results, it is found that iron-impregnated activated carbon (Fe-ac) presents an excellent adsorption capability for uranium removal compared to acid-treated activated carbon (ox-ac). The uptake capacity is enhanced by 300.32% for Fe-ac, whereas it is only 51.52% for ox-ac. It can be concluded that the uranium adsorption capacity is mainly related to the surface functional groups and the amount of oxygen at the surface of the adsorbents.

Sophorolipid biosurfactants have shown promise in remediation of oil-contaminated environments. This study investigated the potential application of sophorolipid biosurfactants for enhanced dispersion of weathered biodiesel, diesel, and light crude oil–contaminated water under salinities (0, 10, 20, and 30 ppt), temperatures (8, 22, and 35°C), and pH (6–8) using bench-scale experiments. Solutions of oil-artificial seawater-sophorolipid were prepared, shaken, solvent extracted, and analyzed. Sophorolipid biosurfactants reduced the surface tension of seawater (30 ppt) to $34\mathrm{mN}/\mathrm{m}$ with a critical micelle concentration of $38\mathrm{mg}/\mathrm{L}$. Results of dispersion experiments showed that oil dispersion significantly increased as the sophorolipid concentrations increased so that the biodiesel, diesel, and light crude oil dispersion in seawater was enhanced 27, 16, and 12%, respectively, by $80\mathrm{mg}/\mathrm{L}$ of sophorolipid. Salinity, mixing, and temperature influenced the oil dispersion, but pH had the least effect on the oil dispersion. Oil dispersion was because of the decreases in the surface and interfacial tensions and encapsulation of oil droplets in micelles. This study suggests that sophorolipid has the properties to enhance oil dispersion in seawater under the examined laboratory conditions.

Persulfate (PS) activated by zero-valent iron (ZVI) for the degradation of $p$-aminobenzoic acid (PABA) was investigated in this study. Compared with the removal of PABA, the degradation of ${\mathrm{PABA}}_{-\mathrm{CAP}}$ (in the presence of chloramphenicol) was not obviously affected in the ZVI/PS system. The removal of PABA (0.05 mM) and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ (0.05 mM) were nearly 100% after 50 min. Moreover, the effective degradation of PABA and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ were observed at a brand range of pH from 3.0 to 8.5, and the higher degradation efficiencies of PABA and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ were obtained under acidic and neutral conditions. With the increase of ${\mathrm{Cl}}^{-}$ and Suwannee River humic acid (SRHA) dosage, the degradation rate of PABA decreased continuously. However, the degradation of ${\mathrm{CAP}}_{-\mathrm{PABA}}$ (in the presence of PABA) was significantly inhibited by the addition of PABA in the ZVI/PS system. The results of scavenging tests suggested that the sulfate radical (${\mathrm{SO}}_4^{•-}$) predominated the PABA and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ degradation, while the hydroxyl radical (${\mathrm{HO}}^{•}$) contributing to the ${\mathrm{CAP}}_{-\mathrm{PABA}}$ removal approximated to ${\mathrm{SO}}_4^{•-}$ by the ZVI/PS system. Major intermediate products were identified during ${\mathrm{PABA}}_{-\mathrm{CAP}}$ and ${\mathrm{CAP}}_{-\mathrm{PABA}}$ degradation processes. A primary reaction pathway of ${\mathrm{PABA}}_{-\mathrm{CAP}}$ and ${\mathrm{CAP}}_{-\mathrm{PABA}}$ degradation was proposed in the ZVI/PS system.

Novel iron (Fe) cross-linked alginate (FCA) beads were used for phosphate removal from synthetic water, lake water, and wastewater. Batch experiments were conducted with the beads (0.118 g dry weight) using three different initial concentrations of phosphate ($C_0=5$, 50, and $100\mathrm{mg}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$) as well as environmentally relevant (eutrophic lakes) concentration of $100\mathrm{\mu g}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$. Approximately 97% of phosphate ($C_0=5\mathrm{mg}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$) was removed by the beads in 360 min from an aqueous solution. In 360 min, beads removed $\sim 76\%$ of phosphate from water with $C_0=50{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$ and $\sim 46\%$ from water with $C_0=100\mathrm{mg}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$. For $100\mathrm{\mu g}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$, 80% removal was achieved within 20 min. The second-order reaction fit well for all the concentrations with reaction rate constants (k) of 0.076 and $0.2027\mathrm{L}/\mathrm{mg}/\min$ ($C_0=5\mathrm{mg}$ and $100\mathrm{\mu g}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$, respectively). The maximum phosphate sorption capacity was found to be $\sim 79\mathrm{mg}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{g}$ of dry beads. No change in phosphate removal was observed in the presence of $\mathrm{C}{\mathrm{l}}^{-}$, $\mathrm{H}\mathrm{C}{\mathrm{O}}_3^{-}$, $\mathrm{S}{\mathrm{O}}_4^{2-}$, $\mathrm{N}{\mathrm{O}}_3^{-}$, and natural organic matter (NOM). To investigate the feasibility of using the FCA beads in a real-life situation (e.g., in eutrophic lakes), actual lake waters ($11–69\mathrm{\mu g}{\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}/\mathrm{L}$) were used and 81–100% phosphate removal was observed in 24 h. Results presented here demonstrate the potential for the use of the FCA beads for the reclamation of eutrophic lakes (removal of excess of phosphate).

Adsorption of fluoride on seawater-washed activated bauxite residue (SWABR) was studied by using fluoride ion analyzer (ion-selective electrode meter). Bauxite residue from the Bayer process is a waste of aluminium refinery, which is highly alkaline and generated in large quantities, which make its disposal a growing problem. The characterization of SWABR was done by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy with X-ray microanalysis (SEM/EDS), transmission electron microscope (TEM), and selected-area electron diffraction (SAED) techniques. The adsorption studies indicate the highest fluoride removal efficiency of 95.83% for a SWABR dosage of $50\mathrm{g}/\mathrm{L}$ at pH 5. The effect of pH, SWABR dosage, contact time, and initial fluoride concentration on the fluoride removal efficiency was studied and discussed. Adsorption isotherm experiments showed that fluoride adsorption on SWABR fits Freundlich adsorption isotherm ($R^2=0.998$) better than Langmuir adsorption isotherm ($R^2=0.983$). The field application of SWABR as an adsorbent for defluoridation of groundwater from Gadag District of Karnataka State, India, was also investigated.

Chemical technologies efficiently remove cyanide from wastewater, but only marginally degrade thiocyanate (${\mathrm{SCN}}^{-}$); they also produce ammonia nitrogen (${\mathrm{NH}}_3\text{-}\mathrm{N}$) and nitrates (${\mathrm{NO}}_3^{-}$), which require complementary treatment. Biological nitrification-denitrification is environmentally friendly and of low cost, but little is known about the treatment efficiency for highly contaminated gold mine effluents. This study assesses the performance of a nitrification-denitrification pilot-scale system using methanol as an energy source. A gold mine effluent is sampled at the inlet of an operating treatment plant. The effluent is alkaline (pH 7.5–8.4) and contains high concentrations of ${\mathrm{SCN}}^{-}$ ($435\pm 53\mathrm{mg}/\mathrm{L}$) and ${\mathrm{NH}}_3\text{-}\mathrm{N}$ ($41\pm 8\mathrm{mg}/\mathrm{L}$). Physicochemical characteristics of the effluent, both before and after the treatment, are evaluated over a 140-day period while varying the hydraulic retention time (HRT) and dilution factor. The results indicate the presence of biological activity. The low HRTs and dilution factors adversely influence the ${\mathrm{NH}}_3\text{-}\mathrm{N}$ removal. ${\mathrm{SCN}}^{-}$ and ${\mathrm{NO}}_3^{-}$ are efficiently removed ($>97$ and $>80\%$, respectively), demonstrating the satisfactory performance of the nitrification-denitrification approach and the effectiveness of methanol as an energy source.