Abstract:
Animal production in Australia THE OPERATION OF THE TWO LAGOON SYSTEM FOR THE DISPOSAL OF DAIRY SHED EFFLUENT K.R. KING* A system of treatment and re-use of dairy shed effluent, using one anaerobic and one aerobic lagoon, has been developed in New Zealand (Anon. 1972). This paper reports the performance of this system in the Goulburn Valley, Victoria in terms of its practicability and reduction of major pollutants. An anaerobic lagoon (3.7 m deep, surface area 380 m2, capacity 0.85 ML) and an aerobic lagoon (0.9 m deep, surface area 1070 m2, capacity 0.90 ML) were constructed in August 1977 and their contents monitored during the next two years. In an adjacent dairy shed 139 and 148 cows were milked from August to May during the first and second years respectively. Raw effluent, comprising faeces, urine, yard and machine washings, and run-off, was pumped into the anaerobic lagoon. Treated effluent was periodically released from the anaerobic to the aerobic lagoon. The quantity and quality of raw effluent and of the effluent from the anaerobic lagoon were measured. Groundwater changes were also measured. Sixty-five litres of raw effluent/cow/day (17,300 L/cow/year) were pumped into the anaerobic lagoon. Of this, 8,000 L/cow/year of treated effluent were released into the aerobic lagoon, ,but all were lost through evaporation and seepage. A description of the raw effluent and effluent from the 0.2 m depth in the anaerobic lagoon is given in Table 1. Treatment of raw effluent in the anaerobic lagoon only, reduced the concentration of organic pollutants (viz. total suspended matter, volatile matter and biological oxygen demand) in the treated effluent by a factor of about 6. Also, the treated effluent had high levels of nitrogen and potassium. During treatment, on average, 92% of organic pollutants was removed in the anaerobic lagoon. TABLE 1 The pH and concentration (mg/L) of alkalinity (A), total suspended matter (TSM), volatile matter (VM), biological oxygen demands (BODg), and nutrients (N, P and K) of dairy shed effluent and of the effluent from the 0.2 m depth in an anaerobic lagoon Sludge occupied 27% of the anaerobic lagoon volume at the start of the third season, and it was estimated that the lagoon would fill with sludge in eight years. Groundwater adjacent to the anaerobic lagoon increased for three months after the initial filling, but returned to its previous level thereafter. To enable effluent to be re-used in the Goulbum Valley, the size of the aerobic lagoon would have to be reduced, or alternatively, treated effluent could be used directly from the anaerobic lagoon. The latter system allows re-use of about 8,000 litres of effluent/cow/year with a potantial fertiliser value of 3.2, 0.3 and 5.4 kg of N, P and K respectively, per cow per year. ANON. (1972). 'Lagoon treatment of farm wastes'. Section, Ministry of Works: New Zealand). (Public Health Engineering * Department of Agriculture, Animal and Irrigated Pastures Research Institute, Kyabram, Vic. 3620.