The removal rate guarantee for ammonia was not driven directly by air quality concerns, but reflected reasonable performance expectations for the equipment to be supplied. Similarly, the removal rate requirements for hydrogen sulfide and methyl mercaptan do not reflect any specific air quality concern with the compounds. Hydrogen sulfide and methyl mercaptan were selected primarily because removal of these compounds has commonly been used as an indicator of odor control performance in wastewater treatment applications. As we shall see, the guaranteed removal rates for the two compounds proved problematic, but ultimately this choice has led to a better understanding of the degradation dynamics of reduced sulfur compounds. A mixture of raw primary and secondary and anaerobically digested biosolids are composted with ground wood residuals.
Ventilative air is fed into the building via makeup air units at either end of the building.
These ducts contain instrumentation to measure air flow, pressure and temperature. The makeup air units and exhaust fans have variable frequency drives to control their speeds in order to maintain preset air flow rates. The fans have the capacity to draw up to 50,000 cfm when only one unit is operating. The exhaust rate is set to exceed the makeup air rate to ensure that the building is maintained under negative pressure. The minimum temperature requirements for the biofilter are maintained by modulating heat from the makeup air units based on the temperature in the main exhaust ducts.