Nitrification potential of attached biofilms in dairy farm waste stabilisation ponds

Dairy farm waste stabilisation ponds are a major source of ammoniacal-N to surface waters in New Zealand. Ammoniacal-N is of particular concern in New Zealand where native aquatic invertebrates appear to be very sensitive to ammonia toxicity. This paper investigates improvement of ammoniacal-N nitri fication in dairy farm facultative ponds with mechanical aeration and provi sion of biofilm attachment surfaces. Biofilm was grown on surfaces at diffe rent depths (0.1 m, 0.2 m and 0.6 m) under three mechanical aeration regime s (no aeration, night-only aeration and continuous aeration). Nitrification potential of biofilm was determined as the rate of ammoniacal-N removal in bioassays with am moniacal-N spiked pond water or culture medium under con trolled conditions (20 degreesC, pH 7.0, constant stirring, DO 2-3 g m(-3), dark). The nitrification potentials (0.30 g N m(-2) biofilm d(-1) to 2.17 g N m(-2) biofilm d(-1)) of biofilm-coated surfaces were largely controlled by oxygen availability and consistency of supply in the pond. Nitrificatio n potentials were high where oxygen availability was high, such as close to the pond surface where atmospheric reaeration and algal photosynthesis wer e prevalent. Nitrification potentials of biofilms incubated at depth were e nhanced by mechanical aeration, with higher values achieved under the conti nuous aeration regime and at more turbulent sites closer to the aerator.