PERFORMANCE OF ARSENIC REMOVAL PLANT FOR TREATING GROUND WATER WITH COMMUNITY PARTICIPATION
On principle both the techniques are technically sound and flawless if properly used. Both the systems are known for many years and are used in many countries all over the world. The scientists of these two institutes (AIIHPH & BE College) made a novel attempt to adopt it to arsenic affected villages for removal of arsenic from groundwater considering local need and difficulties.
School of Environmental Studies suggested Chandranath Basu Seva Sangha to install 4 AIIHPH and 4 BE College's units in Betai. 7 units, 4 from BE College and 3 from AIIHPH were installed in Betai during last one year. One unit of AIIHPH was recommended for installation in a very highly arsenic affected area in Bangaon, North 24-Parganas.
School of Environmental Studies is monitoring the arsenic concentration in raw and filtered water fortnightly and also bacteriological suitability of the water was checked once in a month. Dr. Chakraborti visited the plants several times. Collections of samples with preservative for arsenic analysis and for bacteriological analysis in sterilized bottle were done. Samples were analyzed as soon as possible after collection. Kept refrigerated until analysed.
Table-1 shows the arsenic concentration in finished water of the 7 units during about last nine months. Out of these seven units, except one unit (No.-2), all others units time and again showed some problems including high arsenic in finished water. Our results of microbiological analysis showed unsuitability of the water (total plate count above permissible limit) once or twice to all the units (except unit no-02). Even villagers observed small worms in finished water and that only happened after the instruments were not in working condition for couple of days and immediately after regeneration.
Each unit except one (no.2) has some problems. The write up below describes merits and demerits of the individual unit.
The unit remains inactive at least a couple of days during every month. Reasons are many: tubewell head broken; leakage from valve; washer not functioning; water is not coming on pumping from underground etc. Arsenic in finished water found twice higher than maximum permissible limit (0.05 µg/L) during our study. Time and again it has been observed that the finished water turns brown after sometime [i.e. precipitation Fe(OH)3]. This indicates that the Al2O3 bed was not washed properly. People do not understand the importance of back washing the Al203 column. This is the unit where about 500 families use the plant for water. It appears that the Al2O3 bed is getting exhausted. Still we do not know the money to be required for regeneration and also for replacement of Al2O3 in final stage. From the solder joint water leaks time to time. We do not know how long the structure will stand. Too much pressure is on the instrument.