Journal of Environmental Engineering

A combination of rice straw and Bacillus subtilis (B. subtilis) was used to remove methylene blue (MB) from wastewater at varied operational conditions. Virtually identical reductions in MB of 58.4, 61.8, 64.6, and 64.6 mg from 1 L solution were achieved for different initial MB concentrations (100, 200, 300, and $400\mathrm{mg}/\mathrm{L}$) when rice straw was used alone, which were increased to 91.6, 184.6, 275.3, and 368.1 mg after the rice straw was inoculated with B. subtilis. The amounts of total removed MB in the treatment groups were almost 1.5, 3, 4.5, and 6 times of that in the control group without B. subtilis. These results demonstrated that the combination of rice straw and B. subtilis was effective for the removal of MB from aqueous solutions. In the four treatment groups, of the total removed MB, 52.5%, 58.7%, 66.4%, and 76.3% were adsorbed by rice straw and bacterial biomass, respectively, and the rest were removed by microbial biodegradation. The significant improvement in MB removal was mainly because the B. subtilis increased the specific surface area of the straw and produced more functional groups on it. Additionally, microbial biodegradation was another reason for the improvement in MB removal. Furthermore, inoculation of rice straw with B. subtilis represented an efficient means of removing MB from wastewater in an actual project in Minkang Printing and Dyeing Co., Ltd., Sichuan, China. After 4 days of treatment by 2.5 g of rice straw (per liter of wastewater) inoculated with B. subtilis, a 94.5% decolorization rate was achieved, which was higher than that of the currently used biological filter with activated carbon as a filter bed (78.3%).

Hydroxide precipitation is the most widely used heavy metal wastewater treatment method. However, the metal hydroxide sludge produced must be treated concurrently. In this paper, an integrated treatment procedure, which modifies hydroxide precipitation with oxidation treatment and sulfide precipitation, is proposed to sequentially precipitate Fe, Cu, and Zn from wastewater for metal recovery. An industrial wastewater specimen containing Cu ($290\pm 6.25\mathrm{mg}/\mathrm{L}$), Fe ($\mathrm{2,092}\pm 12.3\mathrm{mg}/\mathrm{L}$), and Zn ($\mathrm{4,648}\pm 15.4\mathrm{mg}/\mathrm{L}$) was used. First, hydroxide precipitation using lime was applied to study the precipitation characteristics of Cu, Fe, and Zn, following which ${\mathrm{H}}_2{\mathrm{O}}_2$ oxidation treatment and NaHS sulfide precipitation were conducted and integrated with hydroxide precipitation to selectively precipitate Cu, Fe, and Zn from the wastewater specimen. The Fe, Cu, and Zn were sequentially removed from the wastewater by introducing 0.1% (v/v) ${\mathrm{H}}_2{\mathrm{O}}_2$, altering the pH of the wastewater to pH 3.5–4.0 using lime, adding $1\mathrm{g}/\mathrm{L}$ NaHS, and subsequently altering the pH to 9.0. The Fe, Cu, and Zn were subsequently separated as individual precipitates with recoveries of $99.8\pm 0.1$, $94.0\pm 0.3$, and $96.1\pm 0.7\%$, respectively, which can facilitate metal recovery and render sludge disposal unnecessary.

Carbon monoxide oxidation reaction was carried out over Cu-doped ${\mathrm{CeO}}_2$, prepared by a simple and cost-effective route without the aid of any stabilizing agents or solvents. A low-percentage incorporation of Cu of 2% by weight with Ce was sufficient for 100% conversion of CO at a reaction temperature of 300°C. The efficiency of the catalyst remained as such for a sustained period of 5 h. The activity was also tested in the treatment of diesel engine exhaust gas at a very high flow rate of $\mathrm{3,600}\mathrm{mL}/\min$. Complete oxidation of CO and high conversion of hydrocarbons (90%) were achieved at the reasonably moderate temperature of 300°C. In the catalysts, ${\mathrm{CeO}}_2$ is found to exist in its fluorite structure as revealed from X-ray diffraction (XRD) patterns. Raman spectral analysis indicated lattice expansion and oxygen vacancies upon incorporation of Cu, whereas X-ray photoelectron spectroscopic analysis pointed out the existence of Cu in the forms of CuO and ${\mathrm{Cu}}_2\mathrm{O}$ as well as the presence of Ce in its $+4$ oxidation state, all of which could facilitate oxidation reactions. The ${\mathrm{CeO}}_2$ nanoparticles were found to be irregular in shape, with size varying from 10 to 20 nm, as evident from the transmission electron microscopic images and crystallite size determination from XRD patterns, confirming the efficiency of present preparation method in the formation of ${\mathrm{CeO}}_2$ nanoparticles. Catalyst characterization studies and catalytic oxidation results indicated the formation of lattice-expanded ${\mathrm{CeO}}_2$ solid solution as well as highly dispersed copper oxides as the active centers of the catalyst.

Rejection of tetracycline resistant bacteria (TRB) and tetracycline resistance genes (TRGs) in the secondary effluent of a lab-scale anaerobic/anoxic/oxic (lab-AAO) system and real-scale AAO by forward osmosis (FO) membranes was investigated. Changes in the bacteria diversity in the FO membrane process were also studied. High-throughput sequencing and the real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) were used for identifying diversity changes in the microorganisms of the FO process and the abundances of eight TRGs (namely, tetA, tetB, tetC, tetE, tetM, tetO, tetS, and tetX), respectively. Results revealed that both TRB and TRGs could be effectively removed by different FO membranes in the active layer facing the feed solution or the draw solution, which were defined as AL-FS and AL-DS. Three genera, consisting of Proteobacteria, Bacteroidetes, and Actinobacteria, were identified as potential TRB at the phylum level. This study reveals that an FO membrane can be a good process for reducing the health risks caused by TRB and TRGs in reclaimed water.

An electrode, stainless steel supported on graphite, was used for the degradation of hazardous organic compounds, azo dye Orange G (OG), using the photoelectro- Fenton (PEF) process. Results showed that the applied current controlled the electrogeneration rate of both ferrous ion and hydrogen peroxide, which in turn affected the dye degradation kinetics. At an applied current density of $45\mathrm{\mu A}{\mathrm{cm}}^{-2}$, the SS-graphite electrode yielded a molar $[{\mathrm{H}}_2{\mathrm{O}}_2]/[{\mathrm{Fe}}^{2+}]$ ratio of 3.6, which was optimal for dye degradation. Under otherwise identical conditions, UV irradiation significantly enhanced OG degradation, i.e., PEF is more effective than electro-Fenton (EF) process. At the optimal applied current density of $45\mathrm{\mu A}{\mathrm{cm}}^{-2}$, or optimal molar $[{\mathrm{H}}_2{\mathrm{O}}_2]/[{\mathrm{Fe}}^{2+}]$ of 3.6, OG decolorization and total organic carbon removal were 83% (in 3 h) and 55% (in 7 h), versus 75% (in 3 h) and 20% (in 7 h) by PEF and EF, respectively. OG degradation by both PEF and EF processes followed the pseudo first-order kinetics, which suggested the major role of OH radical in OG decolorization.

Groundwater contamination is expensive to remediate, primarily because of the treatment time required. Increased treatment time can be caused by several contributing factors, such as sequestration in low-permeability regions of an aquifer, which can cause tailing and rebound phenomena. One such region consists of dead-end pores. Once a contaminant enters the dead-end pores, it remains in an eddy and only moves back into well-connected pores, from which it can be advected away, by molecular diffusion. A previous study with computational fluid dynamics suggested that rapidly pulsed flow demonstrated the potential to accelerate contaminant removal from dead-end pores. Here, we tested the recovery of a dissolved contaminant under steady and rapidly pulsed flow from a porous media column with crushed glass, which should have naturally formed dead-end pores. This test simulated the fluid dynamics in a flow constrained by a column without sorption; therefore, this tested the dynamics in the dead-end pores but did not include the complete dynamics of a remediation scheme. The results showed accelerated removal under rapidly pulsed flow, which is consistent with results from the computational model; however, there may be additional or alternative sources of the sequestered contaminant.