Analysis and modelling of powdered activated carbon dosing for taste and odour removal

Comparison of four pre-oxidants coupled powdered activated carbon adsorption for odor compounds and algae removal: Kinetics, process optimization, and formation of disinfection byproducts

Pre-oxidation and powdered activate carbon (PAC) are usually used to remove algae and odorants in drinking waterworks. However, the influence of interaction between oxidants and PAC on the treatment performance are scarcely known. This study systematically investigated the combination schemes of four oxidants (KMnO4, NaClO, ClO2, and O3) and PAC on the inactivation of Microcystis aeruginosa cells and removal of four frequently detected odorants in raw water (diethyl disulfide (DEDS), 2,2'-oxybis(1chloropropane) (DCIP), 2-methylisoborneol (2-MIB) and geosmin (GSM)). O3 showed highest pseudo-first-order removal rate for all four compounds and NaClO exhibited highest inactivation rates for the cell viability and Chlorophyll a (Chl-a). The Freundlich model fitted well for the adsorption of DEDS and DCIP by PAC. When treated by combined oxidation/PAC, the removal ratio of algae cells and odorants were lower (at least 1.6 times) than the sum of removal ratios obtained in oxidation or PAC adsorption alone. Among these four oxidants, the highest synchronous control efficiency of odorants (52 %) and algae (66 %) was achieved by NaClO/PAC. Prolonging the dosage time interval promoted the removal rates. The pre-PAC/post-oxidation processes possessed comparable efficiency for the removal of odorants and algae cells comparing with pre-oxidation/post-PAC process, but significantly inhibited formation of disinfection byproducts (DBPs), especially for the formation of C-DBPs (for NaClO and ClO2), bromate (for O3) and chlorate/chlorite (for ClO2). This study could provide a better understanding of improving in-situ operation of the combined pre-treatments of oxidation and PAC for source water.

Synthesis of CoNi-layered double hydroxide on graphene oxide as adsorbent and construction of detection method for taste and odor compounds in smelling water

Taste and odor (T&O) compounds are important water pollutant, some of which are toxic. The relevant studies are all expand upon the well-known T&O compounds but for the unknown odors in smelling water. In this work, a method combining purge and trap with gas chromatograph-mass spectrometer (PT-GC/MS) and disperse solid-phase extraction with gas chromatograph (GC) was first proposed to detect T&O compounds in unknown odorous water accurately. Firstly, PT-GC/MS was used for a qualitative test on unknown odors in smelling water and determine the analytes. The hollow CoNi-layered double hydroxide (LDH) on graphene oxide (GO) was then used as a composite adsorbent to pretreat the water, in which the GO provided large specific surface, and the LDH worked as a confinement cavity to enhance capture and retention capacity for volatile organic compounds (VOCs). According to the properties of T&O compounds determined by PT-GC/MS in water, a corresponding GC method was established for accurately quantitative analysis. In this paper, five T&O compounds were detected simultaneously, including dimethyl sulfide, meistylene, N, N-dimethylbenzylamine, 2, 4-dimethylbenzaldehyde and 2, 4-di-tert-butylphenol. Extraction parameters were optimized, including ratio of desorption solvent, amount of adsorbent, pH value, etc. Under the optimal conditions, the detection limits for analysis were 1.14 μg/L to 3.07 mg/L. The satisfactory recoveries were 94-98%. Furthermore, two optimal determination outcomes of odor waters from different places support the practicability of the method, which is expected to be widely used in the detection of unknown odors in smelling water.

Properties Tuning of Palm Kernel Shell Biochar Granular Activated Carbon Using Response Surface Methodology for Removal of Methylene Blue

This study aimed to produce palm kernel shell granular activated carbon (PKSGAC) from slow vacuum pyrolysed PKS biochar (PKSB) via chemical activation using a horizontal tubular split zone furnace. The study also investigated the effects of varying parameters of the PKSGAC on its colour removal ability. The PKSB was activated through chemical activation using potassium hydroxide (KOH) at various parameters such as activation temperature (700oC to 850oC), KOH concentration (50 % w/v to 100 % w/v) and particle size of PKSB (0.4 mm to 2.5 mm). The novelty of this work lies in the study of chemical activation on various particle size ranges using response surface methodology (RSM) to model the relationships between various parameters. The PKSB was characterized to determine its thermal condition, and the PKSGAC was characterized to determine the iodine number, bulk density, ash content, moisture content, surface area and morphology structure. The parameters that were used for each sample were determined by using the RSM based on central composite design (CCD). In this study, design expert version 11.0 software was used and three parameters as independent variables were manipulated. Finally, three different PKSGAC samples of different particle sizes were used to test for the methylene blue (MB) dye removal with the concentration of 5 mg/l, 10 mg/l, 15 mg/l and 20 mg/l. Thermal analysis showed that the total weight loss of the PKSB sample was 58.30% and for PKSGAC the range of the product yield as shown from the RSM was from 33.23% to 96.33%. The RSM also showed that the values for moisture content were in a range from 0% - 39%, as for the ash content value from 2% - 12%, while for the bulk density ranged from 0.17 g/cm3 - 0.50 g/cm3. The highest iodine value achieved was 1320 mg/g at activation temperature of 850oC, KOH concentration of 50% w/v and particle size of 0.4 mm. From the RSM, an iodine number of 1100 mg/g could be obtained using an activation temperature of 850oC, the KOH concentration of 69.22% w/v and the particle size of 0.59 mm. From the BET analysis, the PKSGAC sample obtained 581 m2/g for SBET and 0.3173 cm3/g for the Vtot. The highest percentage dye removal of MB dye was 89.61% to 97.63% at 775oC activation temperature, 75% w/v KOH concentration and 0.4 mm particle size. This work produced RSM models to predict the relationships between the parameters and the response, as well as the performance on MB dye removal.

Performance of BAC for DBPs precursors' removal for one year with micro-polluted lake water in East-China

Effectiveness of biological activated carbon (BAC) filter in removing disinfection byproducts (DBPs) precursors of micro-polluted lake water for one year was conducted. The formation potential (FP) of DBPs (trihalomethanes (THMs), haloacetic acids (HAAs) and Nitrosamines (NAs)), dissolved organic carbon (DOC), molecular weight (MW) distribution and excitation emission matrix fluorescence (EEM) of dissolved organic material (DOM) in the influent and effluent of BAC were determined. The results indicated that the removal efficiency (RE) of DOC ranged from 42.9-28.3%. Neither virgin GAC nor long-term operated BAC could efficiently dispose of THMs and HAAs precursors (RE from 35.2-18.8%, from 42 to 8.4%, respectively), however, BAC still showed good ability in removal of NAs precursors after a year operation, of which RE just dropped from 81.7-69.6%. There was strong correlation between RE of NAs precursors and DOC with small MW (<0.5 kDa). The removal of HAAs precursors showed relatively close relation to aromatic protein-like components and soluble microbial pollutants (SMPs). Weak direct relationship was found between the water quality parameters and THMs precursors.

Occurrence and removal of 10 odorous compounds in drinking water by different treatment processes

This study investigated the prevalence of ten odorous compounds (2-methylisoborneol, trans-1,10-dimethyl-trans-9-decalol, isophorone, 2,4,6-trichloroanisole, 2,3,6-trichloroanisole, 2,3,4-trichloroanisole, β-cyclocitral, β-ionone, 2-isobutyl-3-methyoxypyrazine, and 2-isopropyl-3-methoxypyrazine) in raw drinking water, as well as their removal by traditional processes, advanced oxidation processes, ultrafiltration, and nanofiltration processes, with the use of an ultrahigh-resolution Orbitrap. The most abundant odorous compounds referred to 2-methylisoborneol and trans-1,10-dimethyl-trans-9-decalol with maximal concentrations of 1.6 ng/L and 0.09 ng/L after treatment by traditional processes respectively, and their maximal concentration was 2.05 ng/L and lower than the detection limit after treatment by advanced oxidation processes, while the raw drinking water of the mentioned two processes was different. The high concentration of isophorone in water treated by traditional process, advanced oxidation process, and membrane process was also ascertained. On the whole, the removal rate of membrane process is the maximal for all odorous compounds except for 2,3,6-trichloroanisole, followed by the advanced oxidation process as well as the traditional process. Eight odorous compounds identified in raw water were preserved after traditional treatment, while five compounds were preserved after the advanced oxidation treatment. The combined ultrafiltration and nanofiltration with pre-flocculation was more effective than either the advanced oxidation process or the traditional treating process in removing odorous compounds, and over 90% of all the odorous compounds were removed. Further investigation is required to facilitate the removal of odorous compounds from drinking water by the incorporation of ultrafiltration and nanofiltration units based on current drinking water treatments.

A novel method for textile odor removal using engineered water nanostructures

The malodor attached to textiles not only causes indoor environmental pollution but also endangers people's health even at low concentrations. Existing technologies cannot effectively eliminate the odor. Herein, an effective and environmentally friendly technology was proposed to address this challenging issue. This technology utilizes electrospraying process to produce Engineered Water Nanostructures (EWNS) in a controllable manner. Upon application of a high voltage to the Taylor cone, EWNS can be generated from the condensed vapor water through a Peltier element. Smoking, cooking and perspiration, considered the typical indoor malodorous gases emitted from human activities, were studied in this paper. A headspace SPME method in conjunction with GC-MS was employed for the extraction, detection and quantification of any odor residues. Results indicated that EWNS played a significant role in the deodorization process with removal efficiencies for the three odors were 95.3 ± 0.1%, 100.0 ± 0.0% and 43.7 ± 2.3%, respectively. The Reactive Oxygen Species (ROS) contained in the EWNS, mainly hydroxyl (OH˙) and superoxide radicals are the possible mechanisms for the odor removal. These ROS are strong oxidative and highly reactive and have the ability to convert odorous compounds to non-odorous compounds through various chemical reaction mechanisms. This study showed clearly the potential of the proposed method in the field of odor removal and can be applied in the battle against indoor air pollution.

Evaluation of the treatability of various odor compounds by powdered activated carbon

This study focused on evaluating the use of powdered activated carbon (PAC) adsorption for the treatability of various odor compounds with different structures. The adsorption performance of 14 odor compounds under various PAC dosages were fitted with two isotherm models (the Langmuir and Freundlich models) to evaluate the adsorption ability. The results indicated that the adsorption capacities estimated from isotherm model predictions were not suitable for the evaluation of treatability of the odor compound due to the neglection of odor threshold. A novel assessment method, through the comparison of the residual concentration at an inflection point (where the downward trend of the odor compound residual concentration and PAC dosage curve starts to flatten) and the corresponding threshold concentration, was employed. This assessment method considered the different thresholds of the various odor compounds and their absorbability by PAC as well as the cost. The results indicated that only the sulfur odor compounds, including dimethyl disulfide, diethyl disulfide and dimethyl trisulfide, were not suitable for PAC treatment. Other odor compounds could be treated by PAC with varying success. The correlations between the adsorption capacity and the treatability of various odor compounds and their properties, including the coefficient between octanol and water (LogK_w), solubility, molar refractivity (MR), dipole and volume, were also evaluated using the Pearson and Spearman correlation analysis. The results indicated that there were not significant correlations between the adsorption capacity and the properties of the odor compounds, while there were significant correlations between the treatability and LogK_w, MR and volume. The odor causing compound with a larger LogK_w, MR and volume was more suitable to be treated by PAC.

Performance evaluation of integrated adsorption-nanofiltration system for emerging compounds removal: Exemplified by caffeine, diclofenac and octylphenol

Emerging pollutants introduced into surface water pose potential hazards to the safety of drinking water. In this study, the removal performance of three emerging compounds (exemplified by caffeine, diclofenac and octylphenol, with different physico-chemical properties) from synthetic water and source water by combining activated carbon (AC) adsorption and nanofiltration (NF) membrane processes was evaluated and analyzed. Results from synthetic water showed that the adsorption isotherms modeled well with the Langmuir equation. The removal performance of target compounds by AC-NF system was more remarkable than that of NF-AC combination. In the source water system, the integrated AC-NF process with coagulation pretreatment (the alum dosage of 60 mg/L) achieved satisfactory performance (the removal efficiencies of three target compounds reached > 95%). Results showed the electrostatic interaction and pollutant hydrophobicity determined the behavior and the fate of selected PPCPs/EDCs during the sequential treatment process of coagulation, activated carbon adsorption, and NF membrane separation. Finally, the AC and NF membranes were analyzed by Fourier transform infrared spectroscopy and scanning electron microscopy to understand the mechanisms, i.e. electrostatic and hydrophobic effects on the total removal process. It suggests that the integrated AC-NF process with coagulation pretreatment should be a feasible approach for removing emerging compounds in waterworks.