A modified septic system for the treatment of dairy farm milk house wastewaters.

In 2001, the Quebec Ministry of Environment modified its livestock waste management regulations and required dairy farms to treat or land spread their milk house wastewaters because of the contamination load exerted when discharged into a water course without treatment. For small dairy farms with fewer than 60 cows, conventional technologies implied an investment of at least $15 000 Can. The objective of the project was, therefore, to develop a modified, low cost and sustainable septic tank - seepage field system for the treatment and disposal of milk house wastewaters while fully valorizing the nutrients and using the water for irrigation. On two dairy farms with 40 and 50 cows, a sediment and milk fat trap was installed before, and a drained 0.45 ha seepage field was built after, the existing septic tank. The project consisted of checking the two modified systems for clogging by digging out sections of sewer pipes after two years of operation; measuring and sampling milk house wastewaters to establish the annual nutrient load; and comparing the contamination load of the seepage field drainage waters to that of a control area. The milk house wastewaters produced by the farms lead to an average field TN, TP, and TK loading of 60, 50, and 80 kg ha-1 y-1, respectively. The average volume of wastewater generated, of 17.5 mm/month, did not saturate the soil as no sign of saturation was observed when excavating the sewer pipes. The accumulation of milk fat inside the sewer pipes on one farm resulted from the disposal of wasted milk into the septic system, the absence of a water softener, and the fact that this fat was not regularly removed from the trap as required. The modified septic system had no major impact on the quality of its drainage water. The low system modification cost of $4400 Can and the treatment efficiency achieved meant that the concept is a feasible solution for most small dairy farms [ABSTRACT FROM AUTHOR]