Maneerat Ongwandee

Optimizing electrocoagulation process for the treatment of biodiesel wastewater using response surface methodology.

The production of biodiesel through a transesterification method produces a large amount of wastewater that contains high levels of chemical oxygen demand (COD) and oil and grease (O&G). Currently, flotation is the conventional primary treatment for O&G removal prior to biological treatments. In this study, electrocoagulation (EC) was adopted to treat the biodiesel wastewater. The effects of initial pH, applied voltage, and reaction time on the EC process for the removal of COD, O&G, and suspended solids (SS) were investigated using one factor at a time experiment. Furthermore, the Box-Behnken design, an experimental design for response surface methodology (RSM), was used to create a set of 15 experimental runs needed for optimizing of the operating conditions. Quadratic regression models with estimated coefficients were developed to describe the pollutant removals. The experimental results show that EC could effectively reduce COD, O&G, and SS by 55.43%, 98.42%, and 96.59%, respectively, at the optimum conditions of pH 6.06, applied voltage 18.2 V, and reaction time 23.5 min. The experimental observations were in reasonable agreement with the modeled values.

Commuter exposure to BTEX in public transportation modes in Bangkok, Thailand

Measurements and monitoring of volatile organic compounds (VOCs) have been conducted in the metropolitan Bangkok. However, in-vehicle levels of VOCs are still lacking. This study investigated VOCs concentrations in four public transportation modes in Bangkok, Thailand during two rush hour periods (7:00-9:00 a.m. and 4:00-7:00 p.m.). The four modes included an air-conditioned bus (A/C bus), non-air-conditioned bus (non-A/C bus), electric sky train, and a passenger boat traveling along the canal. Comparison among three important bus routes was also studied. In-vehicle air samples were collected using charcoal sorbent tubes and then analyzed by a gas chromatography-mass spectrometer. Results showed that the transportation modes significantly influenced the abundance of in-vehicle benzene, toluene, ethylbenzene, and m,p-xylene (BTEX). Median concentrations of BTEX were 11.7, 103, 11.7, and 42.8 microg/m3 in A/C bus; 37.1, 174, 14.7, and 55.4 microg/m3 in non-A/C bus; 2.0, 36.9, 0.5, and 0.5 Cig/m3 in sky train; and 3.1, 58.5, 0.5, and 6.2 microg/m3 in boat, respectively. Wilcoxon rank sum test indicated that toluene and m,p-xylene in the sky trains were statistically lower than that in the other three modes at a p-value of 0.05. There were statistical differences in TEX concentrations among the bus routes in the non-A/C buses. In addition, the benzene to toluene ratios implied that tail-pipe emissions were important contributor to the abundance of in-vehicle VOCs.

Concentrations and Strengths of Formaldehyde and Acetaldehyde in Office Buildings in Bangkok, Thailand

Exposure to aldehydes can have adverse health effects. Formaldehyde, the most abundant airborne aldehyde, is also a human carcinogen. This study investigated concentrations and strengths of formaldehyde and acetaldehyde in 12 office buildings in Bangkok, Thailand. Sampling was conducted during March and April 2008. Air samples were collected at ∼0.7—0.9 L · min—1 using cartridges filled with dinitrophenylhydrazine coated silica gel. The cartridge incorporated an ozone scrubber to prevent aldehyde losses on the silica gel surface. Samples were then desorbed by acetonitrile and analyzed by high performance liquid chromatography. Air exchange rates were estimated from the difference between indoor and outdoor carbon dioxide levels. A one-compartment mass balance model was used to estimate indoor source strengths. Results showed that the mean indoor concentrations of formaldehyde and acetaldehyde were 35.5 and 17.1 μg · m–3 respectively, while the outdoor concentra- tions were 10.1 and 7.9 μg · m–3, respectively. The estimated mean indoor strengths of formaldehyde and acetaldehyde were 15.3 and 5.8 mg · h–1, respect- ively. Indoor–outdoor (I/O) relationships showed that the I/O ratios were 3.5 for formaldehyde and 5.7 for acetaldehyde, suggesting that indoor sources are more important contributors to the indoor levels than outdoor sources such as infiltration of vehicle exhaust.

Anaerobic baffled reactor treatment of biodiesel-processing wastewater with high strength of methanol and glycerol: reactor performance and biogas production

Biodiesel-processing factories employing the alkali-catalyzed transesterification process generate a large amount of wastewater containing high amount of methanol, glycerol, and oil. As such, wastewater has high potential to produce biogas using anaerobic treatment. The aim of this research was to investigate the performance of an anaerobic baffled reactor for organic removal and biogas production from biodiesel wastewater. The effect of different organic loading rates, varying from 0.5 kg m−3 d−1 to 3.0 kg m−3 d−1 of chemical oxygen demand, was determined using three 22 L reactors, each comprising five separate compartments. Wastewater was pretreated with chemical coagulants to partially remove oil prior to experimentation. Results show that the anaerobic baffled reactor operated at 1.5 kg m−3 d−1 of chemical oxygen demand and ten days of hydraulic retention time provided the best removal efficiencies of 99 % of chemical oxygen demand, 100 % of methanol, and 100 % of glycerol. Increasing the organic loading rate over 1.5 kg m−3 d−1 of chemical oxygen demand led to excessive accumulation of volatile fatty acids thereby making the pH drop to a value unfavorable for methanogenesis. The biogas production rate was 12 L d−1 and the methane composition accounted for 64–74 %. Phase-separated characteristics revealed that the highest chemical oxygen demand removal percentage was achieved in the first compartment and the removal efficiency gradually decreased longitudinally. A scanning electron microscopic study indicated that the most predominant group of microorganisms residing on the external surface of the granular sludge was Methanosarcina.

Development of environmental sustainability for the biodiesel industry in Thailand

The Thai Government has committed to promoting the production and use of biodiesel in place of petro-diesel oil, with the objective of reducing the countrys dependence on imported oil. However, biodiesel production generates large amounts of waste and wastewater. This research aspires to adopt industrial ecology measures to alleviate environmental problems encountered in the biodiesel industry in Thailand. The proposed implementation options included clean technology and waste exchange measures. Five biodiesel production factories were selected to analyse material flow and balance in the production processes. The results show that 1 m3 biodiesel production generated 8 kg of spent bleaching earth, 140 kg of glycerine and 0.50 m3 of wastewater with a chemical oxygen demand (COD) content of up to 170,000 mg/L. The postulated options, on the basis of clean technology, included methanol recovery from the methyl ester and glycerine mixture, substitution of the hydroxide catalyst by methoxide, and reuse of the final washing water used in the methyl ester purification step. These options are expected to reduce raw material and water use in the production processes. The wastes or by-products generated from the biodiesel production process can be utilised as raw material for other industries. Crude glycerine, which is produced in large quantities from the trans-esterification process, can be reused or recycled by a value-added conversion for other industries. In addition, the biodiesel wastewater mostly obtained from the methyl ester washing process can be treated in an anaerobic digestion system to produce biogas for electricity generation.

Evaluation of Portable Household and In-Car Air Cleaners for Air Cleaning Potential and Ozone-Initiated Pollutants

Portable air cleaners are designed to remove airborne pollutants, but some types of air cleaners can emit or induce pollutants. This research was aimed at evaluating the performance of portable air cleaners in terms of a clean air delivery rate (CADR) for removal of fine particles and to measure ozone emission. The study was extended to investigate ozone-initiated pollutants from the use of an in-car ion generator in the presence of synthetic and natural air fresheners. The tested air cleaners included four household brands and two in-car brands. The experiments were conducted in an 8 m3 chamber. The CADRs and ozone emission rates of the tested air cleaners were determined by fitting time-dependent concentrations to mass balance models using a least-squares method. The CADRs for the household air cleaners using the HEPA and electrostatic precipitator ranged from 14 to 62 m3 h−1, while the ozone generator and the in-car ion generators were found to have negligible CADRs. The ozone generator, ion generators, and electrostatic precipitator emitted ozone at the rates of 55.7, 1.94, and 0.92 mg h−1, respectively. The use of the lemon-scented air fresheners in the presence of the in-car ion generator resulted in the substantial increases of formaldehyde, acetaldehyde, acetone, and PM2.5, while screw pine leaves and camphor did not increase the pollutants.

Ability of artificial and live houseplants to capture indoor particulate matter

Two artificial and three live houseplants were assessed for their abilities to capture particulate matter smaller than 2.5 µm (PM2.5) generated by burning an incense stick. The test plants included polyester Boston fern, polyethylene Dieffenbachia, Golden Pothos (Epipremnum aureum), Painted nettle (Plectranthus scutellarioides) and Rainbow tree (Dracaena cincta Bak. ‘Tricolor’). Each plant was tested one at a time in a closed 8-m3 chamber, and the PM2.5 concentrations were continuously measured for 24 h. A loss rate constant for PM2.5 due to deposition onto leaf surface was determined by fitting measured concentrations to a mass balance model using nonlinear regression. The PM2.5 loss rates for the artificial Boston fern correlated well with its total leaf surface areas at the significant level of 0.5. All studied plants had PM2.5 loss rates ranging from 0.05 to 0.08 h−1 under the testing condition of similar total leaf surface areas, while a PM2.5 loss rate due to deposition onto the chamber surfaces was 0.03 h−1. Stereo microscope leaf images revealed the particle accumulation mostly on the midribs and veins rather than the flat blades, while the woven polyester fabric of the artificial plant acts as a filter for collecting the coarse particles.

Understanding interactions in the adsorption of gaseous organic compounds to indoor materials.

We studied adsorption of organic compounds to a wide range of indoor materials, including plastics, gypsum board, carpet, and many others, under various relative humidity conditions by applying a conceptual model of the free energy of interfacial interactions of both van der Waals and Lewis acid-base (e-donor/acceptor) types. Data used for the analyses were partitioning coefficients of adsorbates between surface and gas phase obtained from three sources: our sorption experiments and two other published studies. Target organic compounds included apolars, monopolars, and bipolars. We established correlations of partitioning coefficients of adsorbates for a considered surface with the corresponding hexadecane/air partitioning coefficients of the adsorbates which are used as representative of a van der Waals descriptor instead of vapor pressure. The logarithmic adsorption coefficients of the apolars and weak bases, e.g., aliphatics and aromatics, to indoor materials linearly correlates well with the logarithmic hexadecane/air partitioning coefficients regardless of the surface polarity. The surface polarity in terms of e-donor/acceptor interactions becomes important for adsorption of the strong bases and bipolars, e.g., amines, phenols, and alcohols, to unpainted gypsum board. Under dry or humid conditions, the adsorption to flat plastic materials still linearly correlates well with the van der Waals interactions of the adsorbates, but no correlations were observed for the adsorption to fleecy or plush materials, e.g., carpet. Adsorption of highly bipolar compounds, e.g., phenol and isopropanol, is strongly affected by humidity, attributed to Lewis acid-base interactions with modified surfaces.