Highly efficient photodegradation of raw landfill leachate using cost-effective and optimized g-C3N4/SnO2/WO3 quantum dots under Vis-NIR light.

In this study, photodegradation of raw landfill leachate under Vis-NIR irradiation and sunlight has been investigated using optimized g-C3N4/SnO2/WO3 quantum dots as a novel nanocomposite. g-C3N4/SnO2/WO3 QDs was successfully synthesized and characterized using various analyses. The best mixing ratios of the nanocomposite components were obtained by response surface methodology (RSM). The morphology and the surface area characteristics of the photocatalyst were investigated by scanning and transmission electron microscopy (SEM and TEM) and Brunauer, Emmett and Teller (BET) analysis. Results of UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS) and photoluminescence (PL) spectrum revealed that the nanocomposite has a great light absorption capacity and improved separation of charge carriers. Using the optimized nanocomposite with the best mixing ratios of urea, SnO2, and WO3 QDs solution, obtained from the central composite design (CCD), the chemical oxygen demand (COD) of the leachate (4575 mg/L) was reduced by 74% and 47% in 4 h under visible-NIR and sunlight irradiations, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis also revealed that a significant reduction of aromatic compounds of the raw leachate occurred after the photodegradation process with g-C3N4/SnO2/WO3QDs nanocomposite. Moreover, the stability and recyclability of the photocatalyst were evaluated, and it was observed that after five experimental cycles of leachate degradation, no significant loss of nanocomposite performance could be seen. Financial analysis was also performed, and the feasibility of this process was investigated.

Surface modification of commercial reverse osmosis membranes using both hydrophilic polymer and graphene oxide to improve desalination efficiency.

Various methods have been applied to modify the surface of reverse osmosis (RO) membranes to modify the membrane performance to enhance the flux, rejection, and resistance to various factors of fouling. Hence, the main objective of the current study is to modify the surface of commercial RO membranes using the synergistic effect of the hydrophilic polymer and graphene oxide (GO). GO nanosheets were firstly synthesized by the modified hummer method, then characterized by FTIR, XRD, and SEM analyses. Then, the polyacrylic acid (PAA) was grafted on the membrane surface for membrane fabrication. Furthermore, effective factors of grafting such as monomer concentration, time, and temperature of polymerization were optimized. After that, different amounts of GO nanosheets were loaded in PAA optimized layer. Then, the effect of GO loading on the RO membrane structure and performance was investigated. The outcomes of membrane characterization demonstrated that modified RO membranes had a smoother surface, more negative surface charge, a little better hydrophilicity, and more thickness. Moreover, the results of PAA and GO optimization were shown that grafting 1.5 mM of PAA and loading 0.1 wt% of GO nanosheets give the best membrane performance. This membrane (GO 0.1@1.5M PAA/RO) between all modified membranes has the most water flux (37.1 L/m2h), the highest NaCl rejection (98%), and the best antifouling efficiency. Ultimately, it was concluded that the grafting of GO@PAA on the surface of a commercial RO membrane is an efficient approach for the enhancement of desalination and antifouling performance of this kind of membrane.

A feasibility study on production of concrete blocks using treated municipal solid waste leachate.

Increased water demand due to population growth and industrialization has led to increased water consumption. Hence, it is required to find an alternative to water in different industries. Concrete represents a remarkable water-consuming industry. The present study investigates whether the treated leachate of municipal landfills can be employed as a substitute for water in the concrete mixing scheme. For this purpose, concrete samples fabricated at different concentrations of treated leachates were compared to the control sample containing distilled water in terms of unconfined compressive strength (UCS) at the ages of 7 and 28 days. The experimental results revealed treated leachate accelerated the cement setting time by nearly 15 min and increased concrete slumping by 16%. The complete replacement of distilled water with treated leachate decreased UCS by 25% (from 50 to 38 MPa). The scanning electron microscope (SEM) and ultrasonic results showed that a rise in the treated leachate content of concrete increased porosity. Increased porosity would reduce UCS. Leaking of heavy metals existing in the leachate should be also investigated for the solidified matrices. The toxicity characteristic leaching procedure (TCLP) revealed that heavy metals leaching in all the samples are in the acceptable range. Results have shown that the use of leachate up to a concentration of 20% can be used in concrete, and the solidified product can also stabilize the pollutants, successfully. It is a valuable finding because using treated leachate as a practical additive in the concrete can prevent environmental contamination.

Characterization of oily sludge from a Tehran oil refinery.

In this study, oily sludge samples generated from a Tehran oil refinery (Pond I) were evaluated for their contamination levels and to propose an adequate remediation technique for the wastes. A simple, random, sampling method was used to collect the samples. The samples were analyzed to measure Total petroleum hydrocarbon (TPH), polyaromatic hydrocarbon (PAH) and heavy metal concentrations in the sludge. Statistical analysis showed that seven samples were adequate to assess the sludge with respect to TPH analyses. The mean concentration of TPHs in the samples was 265,600 mg kg⁻¹. A composite sample prepared from a mix of the seven samples was used to determine the sludge's additional characteristics. Composite sample analysis showed that there were no detectable amounts of PAHs in the sludge. In addition, mean concentrations of the selected heavy metals Ni, Pb, Cd and Zn were 2700, 850, 100, 6100 mg kg⁻¹, respectively. To assess the sludge contamination level, the results from the analysis above were compared with soil clean-up levels. Due to a lack of national standards for soil clean-up levels in Iran, sludge pollutant concentrations were compared with standards set in developed countries. According to these standards, the sludge was highly polluted with petroleum hydrocarbons. The results indicated that incineration, biological treatment and solidification/stabilization treatments would be the most appropriate methods for treatment of the sludges. In the case of solidification/stabilization, due to the high organic content of the sludge, it is recommended to use organophilic clays prior to treatment of the wastes.