Reuse of Wastewater from Meat Processing Plants for Agricultural and Forestry Irrigation

Meat-processing wastewaters contain high concentrations of nitrogen, phosphorus and potassium (in this study 40-230 g m⁻³, 6-35 g m⁻³ and 20-130 g m⁻³ respectively), but only low concentrations of heavy metals and other toxic compounds. The nutrients can be recovered by agricultural or forestry irrigation schemes. Application of these wastes to land in excess of plant requirements results in elevated concentrations of organic nitrogen, nitrate, phosphorus, potassium and sodium in the plant material, with nitrate approaching levels toxic to ruminant animals. Excess phosphorus that is applied to the land is precipitated as metal phosphates, and excess nitrogen is partially denitrified, thereby reducing nitrate contamination of ground water. At an experimental pasture site, receiving nitrogen loadings of 1200 kg N ha⁻¹ y⁻¹, denitrification losses averaged about 4% of that applied. Denitrification losses at an experimental forestry site receiving 715 kg N ha⁻¹ y⁻¹ averaged about 27%. Similar losses were observed at a full-scale pasture and forestry irrigation site. Sodium concentrations in meat processing wastewaters could, on occasions, detrimentally affect soil structure and sodium concentrations should be closely monitored.