Autoheated thermophilic aerobic sludge digestion and metal bioleachingin a two-stage reactor system
Rohan Jain , Ashish Pathak , T. R. Sreekrishnan , M. G. Dastidar
DOI:
Received February 10, 2009,Revised May 15, 2009, Accepted , Available online
Volume 22,2010,Pages 230-236
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A two-stage process has been developed for stabilization of sludge and removal of heavy metals from the secondary activated sludge
with high rate of energy and time conservation. The first stage of the process involves autoheated thermophilic aerobic digestion at
55–60°C inoculated with less-acidophilic thermophilic sulfur-oxidizing microorganisms (ATAD). The results show that it is possible
to maintain the autoheated conditions (55–60°C) in the ATAD reactor up to 24 hr, leading to reduction of 21% total solids (TS), 27%
volatile solids (VS), 27% suspended solids (SS) and 33% volatile suspended solids (VSS) from the sludge. The sludge pH also decreased
from 7 to 4.6 due to the activity of less-acidophilic thermophilic microorganisms. In the second stage operation, the digested sludge
(pH 4.6, TS 31.6 g/L) from stage one was subjected to bioleaching in a continuous stirred tank reactor, operated at mean hydraulic
retention times (HRTs) of 12, 24 and 36 hr at 30°C. An HRT of 24 hr was found to be su cient for removal of 70% Cu, 70% Mn, 75%
Ni, and 80% Zn from the sludge. In all, 39% VSS, 76% Cu, 78.2% Mn, 79.5% Ni and 84.2% Zn were removed from the sludge in both
the stages
