Optimal biofilter depth for the treatment of cow manure from exercise pens - A laboratory study

• Published in: Canadian biosystems engineering 2023-12, Vol.65 (1), p.6-6.14
• Main Authors: Ruiz-González, Alexis, Bouchard, Alexandre, Álvarez-Chávez, Elizabeth, Godbout, Stéphane, Fournel, Sébastien
• Format: Article
• Language: English
• ISSN: 1492-9058; 1492-9066
• DOI: 10.7451/CBE.2023.65.6.1

Starting in 2027, Canadian regulations will require regular exercise for tie-stall dairy cows. Producers commonly use pasture-like outdoor pens, but these might not meet environmental regulations as leachate can carry nutrient-loaded runoff. Alternative methods using improved filtering media are needed. This study evaluated the removal capacity of different depths of materials (gravel, woodchips, sphagnum peat moss, and biochar) as a strategy for manure treatment in outdoor exercise pens used to provide movement opportunities to dairy cows. A laboratory experiment was performed using 15 PVC columns (n = 3), with a diameter of 5 cm and a length of 50 cm, filled with different combinations of products for 3 weeks. The increasing depth (10 to 40 cm) of a mix of sphagnum peat moss, wood chips, and biochar in the columns linearly increased the removal efficiency of chemical oxygen demand (50 to 74%), total nitrogen (60 to 97%), phosphates (34 to 59%), and suspended solids (14 to 61%). However, this removal efficiency was time-dependent, as a greater removal rate was observed during the first week (+30% relative to weeks 2 and 3). The filter media with a 300 mm depth of a mix composed of sphagnum peat moss (70%), woodchips (20%) and biochar (10%) was more effective in removing nutrients. However, the treated effluent still surpassed the allowable post-filtration limit. This emphasizes the need for supplementary filtration measures to ensure the safe discharge of effluent into the environment.