Membrane fouling due to algal attachment in water treatment processes | |
| Author | Babel, Sandhya |
| Call Number | AIT Diss. no.EV-99-6 |
| Subject(s) | Water--Purification--Membrane filtration Algae |
| Note | A dissertation submitted in partial fulfilment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Worsening eutrophication problems in lakes and reservoirs used as sources of drinking water have provoked growing concerns among water treatment engineers. Algal blooms create severe problems in conventional water treatment systems. Membrane technologies are clean technologies and can achieve complete removal of algae. The present research was undertaken to study the seasonal variation in algal characteristics affecting membrane filtration resistance and the membrane fouling phenomena and its control while treating the algae-laden water by membrane filtration. Batch filtration experiments in dead-end mode were conducted in the laboratory with Chlorella-laden water using cellulose ester and polyvinylidene fluoride (PVDF) membranes. Investigations were carried out to identify the causes of seasonal variation in membrane filtration resistance by Chlorella deposition. The influence of environmental and algal growth-limiting conditions on filtration resistance was examined. Experiments were also carried out to investigate the membrane fouling phenomenon due to algal deposition and to analyse the effectiveness of pre-treatment techniques (alum, chlorine and ozone) to control membrane fouling. Experiments were conducted to identify efficient and effective physical and chemical methods for cleaning the membrane. These experiments were conducted with dispersed and chemically-conditioned Chlorella algae and also with the natural water contaminated with mixture of algae. It was observed that the membrane filtration resistance under identical treatment conditions by the Chlorella algae cultured in open ponds varied significantly, from 1012 to 1013 perm during the study period. The filtration resistance was found to be function of environmental conditions such as temperature, radiation, rainfall, etc., which affect the release of extracellular organic matter (EOM). The presence of bacteria in the harvested algal cells did not play any imgo1tant role in the observed variation in resistance. The cake resistance was in the order of 10 2 per m when the algal growth rate was optimum in the favourable range of temperature (28 to 35°C). The algal growth was inhibited and the cake resistance increased for both higher and lower temperatures than the suitable temperature range. The cake resistance varied linearly with the amount of the EOM extracted by O.lN NaOH when culture conditions were the same. Experiments conducted with Chlorella grown in an open environment indicated that temperatures above 40°C and solar radiation greater than 50 klux inhibited the growth of algae, leading to higher resistance in the order of 1013 perm. The cake resistance increased drastically after actively growing cells were stored in nutrient-free water under dark condition due to light, nutrient and temperature limitations. The amount and characteristics of extractable EOM change depending on culture and growth-limiting conditions. Dispersed Chlorella algae can cause significant fouling of the cellulose ester and PVDF membranes. The effect of algal concentration on cake resistance was found to be similar for both the membranes. Initially when the deposition was less, the flux was high and the resistance was very low or negligible. As the deposition increased, the resistance increased iii exponentially. With fu1ther increase in deposition, the resistance increased linearly at a constant rate. Experiments canied out to study the effect of transmembrane pressure (TMP) on cake resistance showed that the cake deposited on the membrane was compressible in nature with a compressibility index of 0.439. Among the three pre-treatment techniques studied, coagulation with alum and ozonation were effective in controlling the fouling of membrane. Chlorine pretreatment was not effective in reducing the algal cake resistance because it brought about an extensive cell lysis. Photographs taken by Scanning Electron Microscope (SEM) showed damage to the cell surface architecture and release of organic matters to the medium after chlorination. Ozone disintegrated the extracelluar organic matters (EOM) without causing cell lysis, thus bringing down the algal cake resistance. Cleaning experiments after algal filtration without pre-treatment showed that physical cleaning was less effective than chemical cleaning. All four chemicals tested for membrane cleaning could reduce the cake resistance by more than 99%. For chemically conditioned Ch/ore/la algae, the cake resistance with algal deposition showed a sigmoidal curve. All the three pre-treatment techniques were found effective in controlling the membrane fouling by the chemically conditioned samples in contrast to the dispersed Chiarella algae where chlorination was not effective. Experiments conducted with natural water indicated linear increase in resistance with the feed concentration. Ozone and alum as pre-treatment technique were found effective whereas chlorine was ineffective in controlling membrane fouling by the natural water. |
| Year | 1999 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Preeda Parkpian; |
| Examination Committee(s) | Takizawa, Satoshi ;Ozaki, Hiroaki ;Traenkler, Josef ;Rakshit, Sudip K.; |
| Scholarship Donor(s) | Government of Japan ; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1999 |