Improved nitrogen removal was reported by Van
Oostrum and Russell (1994) when nitrified slaughterhouse
wastewater was fed to a surface-flow
constructed wetland, provided that sufficient carbon
was available in either the influent and/or from
decaying plant litter. Nitrogen removal rates of up to
9.5 gN/m2/day were obtained, largely due to microbial
denitrification.
No reports of phosphorus removal from a slaughterhouse
wastewater have been published. This will
largely be dependent on the soil/stratum.
Activated sludge systems
Numerous activated-sludge plants were put into
slaughterhouse and rendering-plant wastewater
treatment systems in the US in the late 1970s/early
1980s to achieve BOD removal and the conversion
of ammonia by biological nitrification to nitrate,
typically with better than 95% ammonia removal
(Green et al., 1981; Witmayer et al., 1985), providedthat the dissolved oxygen concentration was above
2"0 mg/1 and the temperature above 10°C (Weber &
Hull, 1979). Since the requirement for nitrification
increases aeration costs by 50% over that for COD
removal only, a better strategy is to retrofit these
plants to achieve full nitrogen removal. In this way,
substantial reduction in aeration requirement is
obtained -- a safe estimate is that aeration costs of
such plants are only 10% higher than for COD
removal only (Randall et al., 1992). These systems
are discussed further in the next sectio