Selector basins- development of a cost effective design
TRUMPER, S.1, PHILP, R.1, SMYTH, M.2, LAVENDER, P.2 AND HORAN, N.J.3,
1SCOTTISH WATER SOLUTIONS, 2AQUA ENVIRO LTD, 3UNIVERSITY OF LEEDS
(free)
ABSTRACT
Since its design and construction in the early 1970’s, flow and organic loads to the Alva wastewater treatment plant, operated by Scottish Water have changed considerably. Currently the plant receives a high flow but with a reduced strength wastewater and this has led to the proliferation of filamentous organisms in particular Microthrix parvicella, which in turn has resulted in high SSVI values. Consequently this has put final effluent compliance at risk. A number of capital intensive remedies were considered to increase the asset life including: chemically aided final settlement, incorporation of conventional selector basins and possible extensive modifications to the primary treatment stages. However an innovative approach to selector design was evaluated which took account of the variable nature of the sewage and endeavoured to ensure an adequate floc loading under most flow and load conditions. As a result the selector has a retention time of just 7.5 minutes at average flow (including RAS) and this resulted in the SSVI values reducing progressively from 150 ml/g to less than 75 ml/g over a 2 month operating period. This illustrates how experience in selector design can be modified to increase plant asset life and significantly reduce capital spend.
Keywords:
Selector, bulking, activated sludge, asset life, M. parvicella
