1. Introduction
The effective treatment of agricultural wastewaters, especially
those originating from animal husbandry such as liquid hog waste,
has posed a serious challenge to the wastewater treatment industry.
These wastewaters have very high organic loads as well as high
concentrations of suspended solids, nitrogen and phosphorus, and
pathogens.
Land application of raw or partially separated hog waste as
a biofertilizer often results in the emissions of greenhouse gas,
ammonia and odor, and potential nutrient contamination of surface
and groundwater due to excess concentrations of nitrogen
and phosphorus that exceed the soil-crop assimilation capacity. The
treatment of liquid hog waste is particularly important in Canada
and Quebec since hundreds of lakes and rivers have been contaminated
with blue-green algae as a result of excessive discharge of
nitrogen and phosphorus. The discharge of untreated or undertreated
wastewaters of agriculture industry with high nutrient
contents has been largely blamed for the increased concentration of
nitrogen and phosphorus in surface waters. In Quebec, the volume
of generated hog waste has drastically increased due to increased
pig production that has almost tripled during the last twenty
years.