Concept: Activated carbon
A new desorption method was investigated, which does not require toxic organic solvents. Efficient desorption of organic solvents from activated carbon was achieved with an ananionic surfactant solution, focusing on its washing and emulsion action.
The potential of using anaerobic digestion for the treatment of poultry blood has been evaluated in batch assays at the laboratory scale and in a mesophilic semi-continuous reactor. The biodegradability test performed on residual poultry blood was carried out in spite of high inhibitory levels of acid intermediaries. The use of activated carbon as a way to prevent inhibitory conditions demonstrated the feasibility of attaining anaerobic digestion under extreme ammonium and acid conditions. Batch assays with higher carbon content presented higher methane production rates, although the difference in the final cumulative biogas production was not as sharp. The digestion of residual blood was also studied under semi-continuous operation using granular and powdered activated carbon. The average specific methane production was 216 ± 12 mL CH4/g VS. This result was obtained in spite of a strong volatile fatty acid (VFA) accumulation, reaching values around 6 g/L, along with high ammonium concentrations (in the range of 6-8 g/L). The use of powdered activated carbon resulted in a better assimilation of C3-C5 acid forms, indicating that an enhancement in syntrophic metabolism may have taken place. Thermal analysis and scanning electron microscopy (SEM) were applied as analytical tools for measuring the presence of organic material in the final digestate and evidencing modifications on the carbon surface. The addition of activated carbon for the digestion of residual blood highly improved the digestion process. The adsorption capacity of ammonium, the protection this carrier may offer by limiting mass transfer of toxic compounds, and its capacity to act as a conductive material may explain the successful digestion of residual blood as the sole substrate.
In ecotoxicology, it is continuously questioned whether (nano)particle exposure results in particle uptake and subsequent biodistribution or if particles adsorb to the epithelial layer only. To contribute to answering this question, we investigated different uptake routes in zebrafish embryos and how they affect particle uptake into organs and within whole organisms. This is addressed by exposing three different life stages of the zebrafish embryo in order to cover the following exposure routes: via chorion and dermal exposure; dermal exposure; oral and dermal exposure. How different nanoparticle sizes affect uptake routes was assessed by using polystyrene particles of 25, 50, 250 and 700nm. In our experimental study, we showed that particle uptake in biota is restricted to oral exposure, whereas the dermal route resulted in adsorption to the epidermis and gills only. Ingestion followed by biodistribution was observed for the tested particles of 25 and 50nm. The particles spread through the body and eventually accumulated in specific organs and tissues such as the eyes. Particles larger than 50nm were predominantly adsorbed onto the intestinal tract and outer epidermis of zebrafish embryos. Embryos exposed to particles via both epidermis and intestine showed highest uptake and eventually accumulated particles in the eye, whereas uptake of particles via the chorion and epidermis resulted in marginal uptake. Organ uptake and internal distribution should be monitored more closely to provide more in depth information of the toxicity of particles.
Here we show the efficacy of graphene oxide (GO) for rapid removal of some of the most toxic and radioactive long-lived human-made radionuclides from contaminated water, even from acidic solutions (pH < 2). The interaction of GO with actinides including Am(iii), Th(iv), Pu(iv), Np(v), U(vi) and typical fission products Sr(ii), Eu(iii) and Tc(vii) were studied, along with their sorption kinetics. Cation/GO coagulation occurs with the formation of nanoparticle aggregates of GO sheets, facilitating their removal. GO is far more effective in removal of transuranium elements from simulated nuclear waste solutions than other routinely used sorbents such as bentonite clays and activated carbon. These results point toward a simple methodology to mollify the severity of nuclear waste contamination, thereby leading to effective measures for environmental remediation.
A model of Langmuir monolayer liquid adsorption into effective pores was used to study the monolayer adsorption capacity by theory calculation. The activated carbon (AC) from rice husk with NaOH activation was selected as adsorbent to uptake phenol and methylene blue (MB). Materials were characterized by N(2) adsorption, infrared spectroscopy (IR), and ultraviolet spectrophotometer (UV). In adsorption kinetics, it was observed that the experimental data were well explained by the pseudo second-order equation. Moreover, the Langmuir isotherm was more suitable to explicate results than Freundlich isotherm, implying the monolayer adsorption. Basing on the molecule diameter of 0.72 nm and cross-sectional area of 0.414 nm(2) for phenol, the theoretical adsorption capacities were close to the actual values with small relative error (<7%). Due to the large molecule size of MB (0.98 nm, 0.749 nm(2)), the sample with wider pores activated at 900°C exhibited the higher adsorption capacity than AC at 700°C. And the capillary condensation increased the adsorption capacities, consistent with the order of average pore diameter for ACs. From the model, it indicated that the adsorbent was suitable for adsorption when its critical pore width was two times of adsorbate molecule diameter.
Naphthenic acids (NAs) are a complex group of alkyl-substituted acyclic, monocyclic and polycyclic carboxylic acids present in oil sands process waters, crude oil, refinery wastewater and petroleum products. Crude oil, desalter brine, influent, activated sludge mixed liquor and effluent refinery samples were received from six United States refineries. The total acid number (TAN) of the six crudes tested ranged from 0.12 to 1.5 mg KOH/g crude oil and correlated to the total NA concentration in the crudes. The total NA concentration in the desalter brine, influent, activated sludge mixed liquor and effluent samples ranged from 4.2 to 40.4, 4.5 to 16.6, 9.6 to 140.3 and 2.8 to 11.6 mg NA/L, respectively. The NAs in all wastewater streams accounted for less than 16% of the total COD, indicating that many other organic compounds are present and that NAs are a minor component in refinery wastewaters. Susceptibility tests showed that none of the activated sludge heterotrophic microcosms was completely inhibited by NAs up to 400 mg/L. Growth inhibition ranging from 10 to 59% was observed in all microcosms at and above 100 mg NA/L. NAs chronically-sorbed to activated sludge mixed liquor biomass and powdered activated carbon (PAC) were recalcitrant and persistent. More than 80% of the total NAs remained in the solid phase at the end of the 10-day desorption period (five successive desorption steps). Throughout a 90-day incubation period, the total NA concentration decreased by 33 and 51% in PAC-free and PAC-containing mixed liquor microcosms, respectively. The lower molecular weight fraction of NAs was preferentially degraded in both mixed liquors. The persistence of the residual, higher molecular weight NAs is likely a combination of molecular recalcitrance and decreased bioavailability when chronically-sorbed to the biomass and/or PAC.
Preparation of char from lotus seed biomass and the exploration of its dye removal capacity through batch and column adsorption studies.
- Environmental science and pollution research international
- Published about 6 years ago
Char was obtained from lotus seed biomass by a simple single-step acid treatment process. It was used as an adsorbent for the removal of malachite green dye (MG) from simulated dye bath effluent. The adsorbent was characterized for its surface morphology, surface functionalities, and zero point charge. Batch studies were carried out by varying the parameters such as initial aqueous pH, adsorbent dosage, adsorbent particle size, and initial adsorbate concentration. Langmuir and Freundlich isotherms were used to test the isotherm data and the Freundlich isotherm best fitted the data. Thermodynamic studies were carried out and the thermodynamic parameters such as ∆G, ∆H, and ∆S were evaluated. Adsorption kinetics was carried out and the data were tested with pseudofirst-order model, pseudosecond-order model, and intraparticle diffusion model. Adsorption of MG was not solely by intraparticle diffusion but film diffusion also played a major role. Continuous column experiments were also conducted using microcolumn and the spent adsorbent was regenerated using ethanol and was repeatedly used for three cycles in the column to determine the reusability of the regenerated adsorbent. The column data were modeled with the modeling equations such as Adam-Bohart model, Bed Depth Service Time (BDST) model, and Yoon-Nelson model for all the three cycles.
Activated carbon (AC) amendment is a recently developed sediment remediation method. The strong hydrophobic organic contaminant sorption efficiency of AC has been shown in several studies, but effects on benthic organisms require more investigation. The AC induced effects on egestion rate, growth and reproduction of Lumbriculus variegatus were studied by applying bituminous coal based AC in three different particle size fractions, namely <63 μm (90%, AC(p)), 63-200 μm (AC(m)) and 1000 μm (AC(g)), to natural uncontaminated (HS) and artificial sediment (AS). Egestion rate, growth and reproduction decreased with increasing AC concentration and finer AC particle fractions, effects being stronger on HS than on AS sediment. Lipid content in AS was reduced already at the lowest AC doses applied (AC(p) and AC(m) 0.05%, AC(g) 0.25%). In addition, hormesis-like response was observed in growth (AS) and reproduction (AS, HS) indicating that AC may disturb organisms even at very low doses. Potential ecological effects need to be further evaluated in an amendment- and site-specific manner.
Per- and poly fluorinated alkyl substances (PFASs), notably perfluorooctanoic acid (PFOA), contaminate many ground and surface waters and are environmentally persistent. The performance limitations of existing remediation methods motivate efforts to develop effective adsorbents. Here we report a β-cyclodextrin (β-CD)-based polymer network with higher affinity for PFOA compared to powdered activated carbon, along with comparable capacity and kinetics. The β-CD polymer reduces PFOA concentrations from 1 μg L(-1) to <10 ng L(-1), at least 7 times lower than the 2016 U.S. EPA advisory level (70 ng L(-1)), and was regenerated and reused multiple times by washing with MeOH. The performance of the polymer is unaffected by humic acid, a component of natural organic matter that fouls activated carbons. These results are promising for treating PFOA-contaminated water and demonstrate the versatility of β-CD-based adsorbents.
A cathode is a critical factor that limits the practical application of microbial fuel cells (MFCs) in terms of cost and power generation. To develop a cost-effective cathode, we investigate a cathode preparation technique using nickel foam as a current collector, activated carbon as a catalyst and PTFE as a binder. The effects of the type and loading of conductive carbon, the type and loading of activated carbon, and PTFE loading on cathode performance are systematically studied by linear sweep voltammetry (LSV). The nickel foam cathode MFC produces a power density of 1190±50 mW m(-2), comparable with 1320 mW m(-2) from a typical carbon cloth Pt cathode MFC. However, the cost of a nickel foam activated carbon cathode is 1/30 of that of carbon cloth Pt cathode. The results indicate that a nickel foam cathode could be used in scaling up the MFC system.