A study was carried out to evaluate a  method for treating the wastewater from pig pens (consisting of feces, urine and feed leftovers) by draining if to fish and subsequently water-hyacinth ponds and to determine the effect of the number of the pigs per unit of water surface on the water quality parameters:  dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), suspended solids (SS), total nitrogen, total phosphorus, total Coliforms and parasitic eggs.  Samples were taken from six pig houses of the farm  at two week intervals.

The quality of the wastewater in the water hyacinth pond met the government standards and reached type A (Vietnam Standard: TCVN 5945 ? 2005). The concentrations of COD, BOD5, SS, total nitrogen and total phosphorus were significantly reduced as compared with samples directly collected from the pens, except for Coliforms. Increasing fishpond water surface area from 105m² to 227m²/ pig improved water quality parameters. Water quality of the river surrounding the pig farm area nearly reached type A according to Vietnam Standard TCVN 5942 - 1995.

Key words: Biochemical parameters, pig manure, Vietnam standard, wastewater treatment