A modified septic system to effectively manage dairy farm milk house wastewater.

摘要

In 2001, the Quebec Ministry of Environment modified its waste management regulation and obliged dairy farms to treat their milk house wastewaters to prevent contamination of water courses. For small dairy farms with fewer than 60 cows, conventional technologies implied an investment of at least {dollar}15 000 to comply with the new regulation.; The objective of this master's project was therefore to develop a low cost and sustainable technology for the treatment and disposal of milk house wastewaters that would permit on-farm recycling of nutrients and water. With the help of the research results of Urgel Delisle and Ass., the new system was done by modifying existing septic tank systems on two dairy farms with 40-50 cows by installing a sediment and milk fat trap before the septic tank, and building a drained 0.45ha seepage field in a pasture or cropped field, after the septic tank.; The modified septic tank system on each farm was monitored during a three year period, which involved checking the system 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 water quality in drainage from the seepage field to that of a nearby control field.; The milk house wastewaters produced by the farms led to an average nutrient load of 60kg TN/ha/y, 50kg TP/ha/y and 80 kg TK/ha/y. The average volume of wastewater applied to the seepage field, between 16 and 19mm/month, did not saturate the soil as no sign of gleying (reduction of iron oxides) was observed when excavating the sewer pipes. In general, soil pH decreased when milk house wastewater entered the seepage field, while the NH4-N, K and Ca concentrations increased. However, soil salinity was low (4 dS m -1) on these farms. The soil P concentration was unchanged on one farm, but there was rapid and significant accumulation of P in the 20-60 cm depth of the soil profile on the second farm. 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. The milk fat was then flowed into the septic tank harming the correct operation of the system. Drainage water quality was similar from the seepage field of the modified septic tank system as an adjacent control field.; The low cost of system modification, about {dollar}4 400 Can., and the treatment efficiency achieved meant that the concept is feasible and offers a suitable solution for small dairy farms.