A farm plant for pig slurry treatment

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The slurry from about 200 fattening pigs was treated over a period of 56 weeks in a treatment system with separation, high-rate filtration and sludge de-watering stages. The overall output of the system consisted of separated solids (19% of slurry input) and de-watered sludge (52% of slurry input) which were stored on the farm midden and were relatively smell-free and easy to handle. When evaporative losses were low in winter there was some filtrate from the de-watering stage for disposal as liquid effluent. When evaporative losses were high in summer water was added to maintain the plant liquid level. A total of 28,9501 of water were added and 25,1901 of filtrate removed giving a net 37601 water input in addition to an estimated 20,160 1 of rainwater which entered the plant. If rainwater were excluded it is likely that there would be no liquid effluent from the plant even when evaporative losses were lower than those prevailing during the trial period which included the hot dry summer of 1975. There was good agreement between the evaporative losses calculated from the experimental results and those predicted from weather data. About 38% of total N and 77% of NH 4N were lost during treatment but there was no loss of P and K. The sludge was conditioned prior to de-watering with aluminium chlorohydrate or ferric sulphate which was the cheaper at £2·64 pig place per year. Laboratory trials showed that a number of polyelrolytes were ineffective and none was as cheap as ferric sulphate. The complete system was easily operated by farm staff, and apart from the separator, which was a very early prototype machine, was robust and reliable enough for farm conditions.