Photocatalysis hybrid system in removing organic matter from water

University of Technology, Sydney. Faculty of Engineering.Conventional processes used to treat water and wastewater mainly removes the suspended solids, pathogens and biodegradable organic matter. The majority of persistent organic pollutants are not generally removed by these processes. Persistent organic pollutants (POPs) constitute a class of anthropogenic substances (manmade) and can be found as trace quantity elsewhere in environment. They are toxic and bio-accumulate in humans, plants, animals, and have significant adverse impacts on human health and the environment, even at very low concentrations. They may cause cancer and disorders in the reproductive and immune systems as well as affecting the human developmental process. POPs do not readily break down in the environment with half-lives in soils in the order of years, although they may be transformed both physically and chemically over long periods of time. They exist in agricultural runoff, drainage to the sewerage system and industrial discharge. In this study, three organic pollutants were selected for investigation humic acid as natural organic matter (NOM), metsulfuron methyl herbicide as POP, and biological treated sewage effluent (BTSE). In the first part of the study, removal of humic substance representing NOM was investigated with various types of photocatalytic reactors. The percentage of dissolved organic carbon (DOC) removal with a batch reactor with titanium dioxide (TiO2) as the photocatalyst ranged from 20 to 60 %. When powdered activated carbon (PAC) was added together with TiO2 in the photo reactor, an improvement of more than twice DOC removal was noticed compared with the same amount of TiO2 used alone. From these results, the use of PAC - TiO2 demonstrated superior removal of humic substance within a shorter contact time and higher removal efficiencies compared with using TiO2 alone. Solid phase micro extraction coupled with Gas Chromatography and Flame ionisation detector (SPME/GC FID) equipped with DB-5 column was used to investigate the intermediate photo products during the photo-catalytic reaction. The manner in which intermediate photoproducts evolve and transform was demonstrated by the GC FID peak. The photo reaction can be summarised in the following way. The photo resistant by-products was adsorbed on the PAC-TiO2 surface as shown in GC peak results. From DOC measurements, it is estimated that less than 25 % of the initial material remained. It is noted that during the PAC-TiO2 batch process humic substance was removed immediately without forming a large amount of intermediate macromolecules of humic substance. In the photocatalysis continuous reactor, the humic substance removal efficiency was studied at different detention time (different flowrates). Better results were achieved at longer detention times as there was more contact time. When the PAC was added, the results also indicate that the photo-catalytic adsorption hybrid system removed a significant amount of humic substance (80% DOC removal) within a shorter contact time compared with using TiO2 alone. In a recirculated continuous plug flow reactors the factors for controlling removal rates in heterogeneous catalysis are mass transfer and surface reaction controls. These factors were improved when a high recirculation flow rate of 250 mL/min was used where flow is turbulent. When a small amount of PAC was added in addition to TiO2, DOC removal improved to 80% in a shorter operation time of less than 10 minutes. The results with various types of reactors indicate that recirculated continuous reactor gave the highest efficiency for removal of NOM (humic substance) in a shorter detention time. In the second part of the study, the removal efficiency of metsulfuron methyl representing persistent organic pollutants (POPs) was studied. Batch reactor experiments conducted with different doses of TiO2 and a small amount of PAC of 0.05 g/L revealed that the TOC removal efficiency can be significantly increased up to 80%. Further, the concentration profile and the rate constant showed superior photocatalysis performance in the presence of PAC. The PAC added during the photo-oxidation absorbed the intermediate compounds and thereby promoted the photocatalytic oxidation. The photooxidation with a detention time of 0.5 to 2 hours resulted in intermediate products of smaller molecular weight substances. In this study, a detailed analysis with SPME/GC (solid phase micro extraction/gas chromatography) was made to study on the photo oxidation intermediates. Following 10 min of residence time in the batch reactor the MM partitioned to smaller molecular weight compounds (or substrate) which occurred at different peak times during the GC (12.10, 14.25, 17.40, 19.63 and 20.18 minutes). After 5 hours of residence time in batch reactor, same substrate was found to be degraded. The photo oxidation was faster when activated carbon was used together with TiO2. The substrate that occurred at the peak times of 19.96 and 18.32 minutes during the GC had nearly disappeared, while the peak at time 14.27 minutes was lower. Some anionic by - photoproducts was investigated by using ion-chromatography. Nitrate and nitrite ions were formed as by-photoproducts. The formation of NO3- and NO2- anions occurred was faster when PAC was added to the photo-oxidation. Similarly, SO42- ions form during the photo-oxidation of MM. Where PAC is present in the reactor, the concentration of SO42- ions peaked earlier at approximately 50 min and thereafter reduces its (SO42-) concentration. The reduction in concentration of SO42- after 50 min may be due to a portion being adsorbed on the PAC-TiO2 surface and a portion being transformed to SO2. In this study, the increase in efficiency of MM degradation is similarly attributed to the adsorption of photo-products on the more surface available with TiO2 coupled with the PAC and active sites available to react with the pollutants. This reduces the competitive adsorption on active sites of PAC-TiO2 increasing efficiency of degradation of MM. However, complicated photo-oxidation and by-products occur during these processes, and it is difficult to determine the actual mechanism of photo-catalytic reaction on the PAC-TiO2 surface and the role of active sites because sophisticated instruments are required to do this. Experiments with recirculated continuous reactor were also conducted by using TiO2 and TiO2-PAC. The coupling of PAC with continuous heterogeneous TiO2 photocatalysis leads to a faster degradation of MM than the heterogeneous TiO2 photocatalysis alone. The incorporation of a small amount of PAC of 0.05 g/L with 1.5 g/L of TiO2 led to 78% removal even with a short residence time of 5.25 minutes. The granular activated carbon (GAC) filter was found to be very effective as a pretreatment for the removal of herbicide (MM). Fixed bed column experiments packed with GAC were conducted with different GAC bed heights (5, 10 and 15 cm) and different effluent velocities. The GAC photocatalytic hybrid system showed up to 90% removal with GAC bed depth of 10 and 15 cm. The 10 and 15 cm deep GAC columns showed a steady state of effluent concentration. The retention time of GAC followed by photoreaction was less than 10 minutes. Recirculated photocatalytic batch reactor experiments conducted with the biological treated sewage effluent showed effective DOC removal. After start up, with the recirculated flow of 60 mL/min the effluent DOC was reduced by 60% in a period of 180 min, and became relatively stable. There were no large differences between results obtained with various recirculation flow rates. About 70 to 75 % DOC removal was achieved using flow rates of 100 mL/min and 250 mL/min. However, with a recirculation flow of 250 mL/min, DOC removal decreased to 65% down from the 73% DOC removal obtained with that of 100 mL/min rate. This can be explained in terms of the characteristics of the plug flow reactor. The flow rates used in this study were large enough to keep the catalyst in suspension, and to promote good mass transfer between the reactants. When a small amount of PAC (0.05g/L) was added, a complete removal of DOC was observed after 250 and 300 min operation times. The addition of 0.05 g/L of PAC adsorbent to the recirculated continuous reactor facilitated better organic removal than titania photocatalyst alone. DOC removal was further increased to 75% within 30 min of operation. The membrane photocatalysis hybrid system was used to separate catalyst from the effluent. The membrane flux was very low and fouling was high when TiO2 was tried to be filtered through MF filter. To facilitated TiO2 separation, (i) pH adjustment and (ii) flocculation of TiO2 slurry were used. Although the use of pH adjustment achieved effective improvement to membrane operation, it was 15% less effective than applying a pre-treatment of flocculation of TiO2 slurry. Photocatalysis and flocculation pretreatment processes before MF/UF also resulted in high (over 90%) DOC removal, surpassing those achieved with mixed TiO2 and PAC photocatalyst

The degradtion of humic substance using continuous photocatalysis systems

Photocatalytic oxidation is an emerging technology in water and wastewater treatment. Photocatalysis often leads to complete degradation of organic pollutants without the need for chemicals. This study investigated the degradation of humic substances in water using photocatalysis systems coupled with physio-chemical processes such as adsorption and/or flocculation. Dissolved Organic Carbon (DOC) removal of PAC-TiO2 was improved by a factor of two to three times compared with TiO2 alone. Solid Phase Micro Extraction (SPME)/Gas Chromatograph (GC) flame ionisation detector (FID) was used to investigate intermediates of photocatalytic oxidation in a batch reactor with TiO2 alone and with powder activated carbon (PAC) with TiO2. GC peaks showed that PAC-TiO2 adsorbed some by-products which were photo-resistant and prevented the reverse reaction that occurred when TiO2 was used alone. The two other types of photocatalytic reactors used were the continuous photocatalytic reactor and recirculated photocatalytic reactor. The results show that the recirculated reactor had the highest efficiency in removing organic matter in a short photo-oxidation (detention) time of less than 10min. The use of PAC-TiO2 in recirculated continuous reactor resulted in 80% removal of organic matter even when it was operated for a short detention time and allowed the use of a smaller dose of TiO2

Submerged membrane system with biofilter as a treatment to rainwater

Rainwater has been used as drinking water in Thailand for centuries especially in the rural parts and is accepted as an important water resource. From past to present, the quality of rainwater has changed with the landuse of the landscape, and its water quality is influenced by a diverse range of conditions such as the management of pollutant sources, the catchment condition, wind and meteorological conditions, and the location of rainwater collection points. In this study, the quality of rainwater collected off roofs at several locations was examined. Granular activated carbon (GAC) filtration was used as a pretreatment to microfiltration (MF) to remove the dissolved organic matter (DOC). After an initial adsorption period, the biofilm that formed on the GAC (biofilter) was found to remove DOC by up to 40%, 35%, and 15% for bed filter depths of 15, 10, and 5 cm, respectively. Biofilters also removed nitrate and phosphate by more than 80% and 35%. The hollow fiber membrane microfiltration with pore size of 0.1 μm was used to treat the effluent from biofiltration to remove the microorganisms/pathogens in the rainwater. Although there was no significant additional removal of DOC by MF, the biofilter removed all microorganisms. The use of biofilters as pretreatment to MF/UF could remove a higher amount of DOC, remove microorganisms, increase the membrane treatment efficiency, and reduce membrane fouling. © Springer Science + Business Media B.V. 2009

Geographic information system applied to the water quality assessment of Ayutthaya Province, Thailand

Ayutthaya is a popular tourist destination located about 76 km north of Bangkok. The climate of the province is typical of Central Thailand, comprising three (cold, hot, and rainy) seasons, with relatively small changes in average temperatures but significantly varying rainfall patterns. In this study, we present a geographic information system (GIS) used for the assessment and monitoring of pollution in the watershed. The ArcInfo-based system combines geographical, meteorological and hydrological data for multiple uses. Water quality management is based on composite water quality index and corresponding water quality classes. The chief input parameters include temperature, pH, faecal bacteria count (FCB), dissolved oxygen (DO), nitrate (NO3), total phosphates (PO4), biochemical oxygen demand (BOD), suspended solids (SS), and total solids (TS), together with population density, rainfall and land-use. The initial results of years 2008 and 2009 show that water quality derogation is strongly related to high population density in the central (new City) districts that also affect the historical City. In addition, the increased runoff of the rainy season causes significant PO4, NO3, and BOD pollution of the Pa Sak River at the northern agricultural districts

The Potential of Using Rain Water in Thailand; Case study Bangsaiy Municipality, Ayutthaya

Rainwater has been widely use in developing countries including Thailand. In the study area, Ayutthaya, rainwater is not much in use due to the quality, abundance and low tariff of municipal water supply. However a survey of residents has shown that there is interest in using rainwater for drinking. The community purchases bottled water and treats water by boiling or by on-site purification devices. A high level of demand for rainwater use was found in this study and this is attributed to past practices and a local culture of using rainwater. It was found that more than 90% of respondents were interested in using rainwater if it was of good quality. Piped water tariffs are currently very low in the range of 4 to 5 THB per m3. Approximately 70% of households from a questionnaire survey were satisfied with the current tariff. However, it should be noted that the true cost of water should be 9-11 THB per m3. From the same survey, 63% of respondents who currently purchase bottled water are interested in using rainwater as drinking water subject to its acceptable quality. The estimation cost of pilot design is 50,000 to 80,000 THB or 1,200 to 2,500 US dollars

Integrated Design of a Small Wastewater Treatment Plant - A Case Study from Thailand

This study describes the development of an integrated design framework comprising technical, environmental, social, and economic modules to manage the design of communal wastewater treatment plant. It demonstrates a simple yet effective design management framework developed to tackle the challenges of incorporating Local Agenda 21 and the elements of triple bottom line reporting. The examined alternatives included stabilization pond, aerated lagoon, and biological contact oxidation treatment technologies with 1500 m3/day plant capacity. The integrated process facilitated comprehensive design and ensured the systemic and informed involvement of all relevant stakeholders. Environmental and technical criterion focused on reducing current impact on the aquatic environment in terms of nitrogen, ammonia, biochemical oxygen demand and suspended solids pollutants. Stabilization pond treatment was identified as the most appropriate solution to offer adequate treatment performance, simple and robust operability, and affordable user costs

Granular activated carbon (GAC) adsorptionphotocatalysis hybrid system in the removal of herbicide from water

The performance of the granular activated carbon (GAC) fixed bed adsorption, the continuous photocatalysis systems and a combination of the two were studied to evaluate their capabilities in removing the herbicide of metsulfuron-methyl (MM) from waste water. Columns packed with GAC at different bed depths were operated at different filtration rates over a period of several weeks. Removal of MM via adsorption using GAC fixed beds of 5, 10 and 15 cm depths (operated at meter per hour) achieved a removal of 35, 55 and 65% of MM respectively. In the continuous photocatalysis system, heterogeneous photocatalysis with TiO2 was used to degrade MM. The system achieved removal rates between 40 and 60%. GAC photocatalysis hybrid system is a coupling of GAC fixed bed adsorption and the continuous photocatalysis system where the effluent from the former was fed to the later. TiO2 and small amount of powder activated carbon (PAC) were used as the catalyst in the photocatalysis system. The system had a high removal rate of over 90%. The retention time of the photocatalysis system was less than 10 min. This system allows a greater degree of flexibility in the manner the system can be operated

A continuous photocatalysis system in the degradation of herbicide

The performance of both batch and continuous photo-catalytic reactors was studied to evaluate their capabilities in removing the sulfonyl urea herbicide of metsulfuron methyl (MM). It was found in a batch reactor that the addition of a small amount of powder activated carbon (PAC) significantly increased the rate of degradation of MM. The continuous photo-catalytic system resulted in 57% of MM removal. When a small dose of activated carbon was added in the photo-catalytic system, MM removal increased to 78-86% MM removal for retention times between of 5.25-21 min (corresponding to withdrawal rates of 10-40 mLmin-1). In this study, the pseudo first order rate constants of a continuous photo-catalytic system revealed that shorter retention times were associated with lower rate constants. Solid phase micro extraction/gas chromatography (SPME/GC) results showed that high concentrations of MM were broken down to small volatile organic compounds (VOCs) by photo-catalytic oxidation. PAC adsorbed the photo-products and increased the degradation of MM. © 2008 Springer

Photocatalytic degradation of organic pollutants from wastewater using aluminium doped titanium dioxide

© 2018 Elsevier Ltd The objective of this research was to study the performance of batch and continuous recirculating reactor to photo-degrade dye and synthetic wastewater. Here, Aluminium (Al) was used as the doped metal. The commercially available TiO2 P-25 and Al (NO3)3 was used as a Ti-precursor and doping agent, respectively, via the impregnation method. Various parameters such as the concentration of the doping agent, and calcination temperature were studied. The TiO2 nanocrystal doped with Al was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analyzer (TGA). The photocatalytic performance of Al-doped nanoparticle was quantified by the degradation of methylene blue (MB) solution under a visible light irradiation condition. Its performance was compared against undoped-nano-TiO2. The results showed that Al(NO3)3 solution with a concentration of 0.25% and volume of 100 cm/ml, and calcined at 300 ๐C for 4 h, was the optimum condition of Al-doped nano-TiO2. Furthermore, the highest pseudo-first-order kinetic rate was 0.096 where the doped Al(NO3)3 of 0.75 w/v was used in the batch reactor. The Al-doped nano-TiO2 that was obtained has the potential for use as a photocatalyst for degradation organics pollutant from wastewater under the visible light irradiation. The highest removal of organic pollutants from synthetic wastewater was 75% using TiO2 P-25 alone at 2 g/L dosage. In addition, the removal of organic pollutant by TiO2/doped with Al was 80% at a dosage of 0.5 g/L and was 85% at a dosage of 1 g/L