In order to design a future large-scale lignocellulose ethanol plant it is of
crucial importance to monitor and minimize the discharge from the factory to
the environment. The Ethanol Pilot Plant in Örnsköldsvik, which is being
operated near industrial conditions, is an excellent tool to study these
effects. In the present study, the liquid and gas process streams have been
analysed in order to close the mass balances of the studied chemical
compounds. Of special interest was to close the mass balance on sulphur from
H2SO4 or SO2 used for hydrolysis catalysts. Sulphur containing compounds have
unpleasant smells and are often highly toxic to animals and human. High
sulphur concentration in effluent wastewater leads to formation of high
concentration of sulphide that upset the anaerobic biological organisms of
wastewater. The existing gas treatment unit, wet scrubbers were also studied
for their removal efficiency of TOC. The removal of TOC is very important
because in air organic compounds along with oxides increase the level of
ozone in the atmosphere. Wastewater samples obtained during continuous
operation were investigated for COD, TOC, pH, total sulphur and TS as well as
SS. The waste waters were sampled individually from the membrane filter
press, the scrubbers, the condensate from the evaporation unit and the
stillage.
Mass balance estimation of sulphur indicates a lost of sulphur in the
reactors, evaporators as well as the fermentation unit. The estimations
further indicate that most sulphur emissions end up in the stillage.
In the gas stream after the H2O scrubber, the largest sulphur emission
release (43 mg/m3) into atmosphere was registered when SO2 was used as a
catalyst in the hydrolysis. The use of H2SO4 as a catalyst however release
small amount of sulphur (4 mg/m3) into air, which is advantageous for
environment. The TOC discharged into air on all occasions were in the range
(9-17mg/m3). The removal efficiency of TOC is found to be a function of TOC
loading, the gas flow rate and the liquid hold up. Results indicate that high
liquid hold up as well as high inlet TOC concentration results in higher TOC
absorption efficiency whereas a higher inlet gas flow rate decrease the
absorption efficiency. The removal efficiency of the SO2 scrubber shows that
almost 85-97% removal efficiency could be achieved. H2O scrubber shows 2-97%
removal efficiency.
Wastewater parameters investigated indicate high strength wastewater
effluent asit contains high residual COD and TOC. The TOC and COD levels in
the wastewater were however not dependent on the acid catalyst used in the
hydrolysis process. The total effluent wastewater has a pH level th...
