Shallow aeration of piggery waste treatment lagoons. II. Odour control

Abstract

The effect of shallow aeration on odours from anaerobic lagoons treating piggery wastes was determined in the laboratory under conditions of approximately constant temperature (20°C). The loading rate to the simulated lagoon profiles was approximately 50 g BOD 5 m −3 day −1 and the average retention time was 128 days. The removal of organic pollutants and bacteria in this system has been discussed elsewhere. Shallow surface aeration to depths ranging from 8 to 40 cm reduced odours from piggery waste treatments. Chemical and organoleptic estimates consistently indicated that odour levels from all aerated treatments were similar and markedly better than those from the unaerated treatment. The average volatile sulphides levels in the aerated treatments were less than 5% of the levels found in the space above the unaerated treatment. The levels in the aerated treatments of less than 0.07 ppm were below the odour threshold limit of 0.1 ppm compared with 1.45 ppm in the unaerated column. Odour threshold dilution (OTD), and more particularly odour offensiveness, were also reduced by shallow surface aeration. The mean OTD values (log 10) of all lagoon treatments (unaerated 2.9 and <2.6 for aerated treatments) were less than that of the untreated waste (3.3) or from wastes stored anaerobically in underslat pits (4.2). Once perceived however, the offensiveness rating of odours from the unaerated treatment was greater (9.4) than from the aerated systems (<1.7). Volatile fatty acid (VFA) levels in the effluents from all treatments were negligible (< 0.01 g l −1). Total VFA levels in the untreated waste were 2.1 g l −1, of which approximately 57, 20 and 11% were acetic, propionic and n-butyric, respectively. Sludge VFA levels were about 0.2 g l −1, of which 75% was acetic acid.