SLIP SLIDING AWAY IN A ZINC CLARIFIER

SLIP SLIDING AWAY IN A ZINC CLARIFIER

About thirty years ago, after extensive lab scale testing and trials, Dorr-Oliver (India), my erstwhile employer of great merit,  designed, fabricated, supplied and erected a 30 metre diameter clarifier/ thickener to Indian Rayons Ltd ( Now called Aditya Birla Nuvo)., to remove Zinc from the industry’s wastewater.  From an initial concentration level of 50-60 mg/L, the plant had to achieve treated water Zinc level of less than 1 mg/L by the classic heavy metals precipitation route at a pH of 9.0-10.0, using slaked lime.

If you wish to see pictures of large clarifiers/ thickeners, visit :

http://www.flsmidth.com/~/media/PDF%20Files/Liquid-Solid%20Separation/Sedimentation/FLSmidthThickenersClarifiers_brochure.ashx

The massive factory was located in the town of Veraval, in Junagadh District, at the southern tip of the jawlike peninsular stub of Gujarat.  Aside from the factory, there was little else of note in Veraval, except for its fishing and boat building industry. Only the Somnath Temple a few miles out of Veraval was the star attraction of this town.  History books tell of the razing of this hapless temple at different times by such illustrious Moslem marauders as Mahmud Ghazni, Allauddin Khilji, and our very own Mughal emperor Aurangazeb, among others.

Zinc Sulfate is used as an adjunct in the spinning bath in the manufacture of Viscose Filament yarn (Rayon).  Zinc is not consumed in the Rayon making process, but goes out with the washwaters as industrial waste.  Years later American Enka would develop a two stage precipitation procedure to recover the Zinc from the waste sludge, fit enough to recycle back in the production process.

The Clarifier at Veraval was erected, and commissioning trials had begun.  As a sub-junior marketing engineer, it was not my business to preside over commissioning of treatment plants.  That activity was under the purview of the specialist Technology team in Dorr-Oliver.  However, using the good offices of an obliging colleague, I convinced Natarajan, my boss to let me make the trip to Veraval.

Keshod, a nondescript little hamlet with a patchy little airstrip was the aerodrome serving Veraval.  Indian Airlines ran a thrice weekly limited seater turboprop service from Bombay to Keshod.  From Keshod one had to hire a taxi to travel to Veraval, a distance of about 50 KM, and check in at the well appointed Guest House of Indian Rayons.

The commissioning trials were progressing well, and Zinc levels in treated water well below 1.0 mg/L were achieved.  A planned shut down of the clarifier was taken, and the tank was emptied to check the condition of the floor blades of the rake and the squeegees. Also of interest would be to get a sample of the settled sludge on the floor of the clarifier to run a Zinc assay. Anil Kini ( The above referred obliging colleague, and stalwart from Technology) and I wended our way to the clarifier, using a bridle path, cutting across thick underbrush.

Having gained the clarifier, full of youthful vigour, zest and enthusiasm, and an equal measure of ignorance,  I clambered down the central pier of the clarifier, and proceeded to walk along the rake arms ( these are sturdy structural members mind you) trying to reach  a point a little away from the centre of the clarifier.

I got off the arms of the clarifier and stepped on to the floor of the tank :  Little could I imagine  the nightmarish ordeal that was to follow !!

Immediately I stepped on the floor, my feet gave way under me, slipping and sliding on the slick, slimy, layer of Zinc sludge covering the floor of the clarifier.  I fell headlong, coming down heavily on all fours, the force propelling me a little distance away from the rake arms of the clarifier. The force of the fall stunned me for a while.  After brief moments of total blackout, (depicted in old comic books with stars and other choice punctuation marks over the victim’s head), I came to, shaking  off the stars, taking deep breaths to compose myself.

I pondered over my condition, lying there in the middle of a Zinc clarifier in Veraval, thinking of a hundred different places I would rather be.  Then I put my thoughts to the immediate and more pressing task of finding a way out of the mess I had fallen into.  I tried getting up from the floor, but that was an impossibility : even the little action of my trying to get off all fours, caused a violent reaction, and the momentum would  slide me back further.  After a few brave attempts, I gave up this course of action as a bad job.

I then tried swivelling around on all fours, trying in the first instance to point my nose in the direction of the rake arms, whence, I could safely crawl to the safety of the waiting arms. This strategy was even more disastrous than I had imagined : swivel, I did, but could not stop at will, and I kept spinning round and round, losing all traction.  Finally, I gave up all hope, and looked up to the heavens for deliverance.

That was when I spied  the Joker, Anil Kini on the bridge of the clarifier, doubling over with laughter, clapping his hands, stomping his feet, in gleeful merriment at the spectacle below.

The pleading in my eyes, and croaking appeals moved the uncouth lout to come to my rescue : He walked over to the  Push Button Starter on the bridge, switched the motor ON.  The rake arm inched slowly towards me, and the nightmare ended.

Dr. Ananth S Kodavasal                                                                          June 15, 2011

P.S :  Later in the evening, at Keshod Aerodrome, the experience was more pleasant.

I was on the waitlist for the flight to Bombay, with little hope of getting on the small aircraft. The spectre of being stranded in Keshod/ Veraval was a daunting prospect.  The amiable looking Station Manager with the big bold Iyengar Namam took one look at me, then at my ticket and said: “Son !  I am from Kodavasal too.  I will put you on that Bird, come hell or high water.”

Talk about filial and caste affiliations.