2003-063 - Laserfiche WebLink

Home Browse Search

ODOR CONTROL STUDY solutions have a higher oxidizing power at near neutral pH (--7 ) than at a high pH (� 12 ) . The sampling data indicates that approximately 10 % of the total reduced sulfides entering the scrubber are organic sulfides . Removal efficiencies for the existing scrubbers are approximately 50 % for total reduced sulfides and 35 to 40 % for organic sulfides . Because of the high volume of air that flows through the scrubber, the sulfur mass emission rate is quite high . The H2S and organic sulfide removal efficiency of the existing scrubbers can be increased by: • Operating the scrubbers in series , as a two-stage system . • Adding hypochlorite solution to both scrubbers . • Installing oxidation-reduction potential (ORP ) monitors on both scrubbers . • Adding a chlorine monitor to the last scrubber to ensure adequate chlorine addition . • Operating the first scrubber with mostly caustic soda . Based on our experience , the pH would be set at approximately 10 and the ORP would beset at approximately +600 mV . This stage would remove most of the H2S and some of the organic sulfides . • Operating the second scrubber with mostly -hypochlorite solution . The pH would be set at approximately 8 and the chlorine monitor would be used to pace the addition of chlorine solution . This stage would remove most of the remaining H2S and organic sulfides . The chlorine monitor measures residual gas phase chlorine . A small amount of chlorine in the gas phase indicates that almost all of the liquid phase sulfides have been oxidized . The existing ductwork would allow the system to be operated in two stages . In addition , the existing fan appears capable of overcoming the additional pressure drop required . The County may want to consider a two-speed motor or variable frequency drive (VFD ) for this fan , so that it would operate more efficiently when one stage is off-line for maintenance or when the dewatering facilities are not operating . Based on cursory analysis of the existing sodium hypochlorite feed system , it is believed that the exiting hypochlorite generation facilities can be used to provide hypochlorite solution to the existing RSF scrubbers . This will need to be confirmed by further detailed analysis during design . However, automatic control of hypochlorite addition is essential to successful operation of the scrubbers . It is recommended that ORP sensors be installed adjacent to the existing pH sensors . ORP is an indication of the oxidizing power of the chemical solution . For scrubbers intended to remove organic sulfides , it is recommended that the ORP be maintained at approximately + 700 to + 800 mV and the pH be maintained at approximately 7 to 8 . Of course these values are generic and site-specific operations will dictate the exact values . Ma19 Indian River County, Central Wastewater Treatment Facility 111 PBSW #071230, February 2003