Dairy waste treatment by high-rate trickling filtration, with particular reference to nitrogen : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Biotechnology
The effective disposal of dairy factory waste is becoming increasingly important in New Zealand. Treatment by high-rate trickling filtration is a successful method in use overseas. For New Zealand conditions, a 'roughing' treatment removing 60 - 90% of the BOD of the waste should be adequate. One objective of this research was the development of a filter capable of providing this treatment. Another objective was the resolution of the controversies between the theoretical and empirical performance-prediction relationships available for trickling filtration. Because nitrogen is receiving a greater emphasis as a pollutant, a third objective was the study of nitrogen removal in dairy waste trickling filtration. The experimental work primarily involved the use of a pilot-scale trickling filter. This was designed using conventional parameters. The filter column was an 18" diameter, 8' long concrete pipe, filled with river stone. An artificial waste compounded from whey and water was fed to the plant at a controlled rate, being diluted with flow from a 25 gallon recirculation tank prior to application to the column. The treated waste overflowed from the recirculation tank and was discharged. The plant was operated at the high organic loading intensities of 1.3 - 2.7 lb BOD/yd 3
day, and at the high recirculation ratios of 20 - 55 : 1. The levels of BOD and organic, ammoniacal, nitrite and nitrate nitrogen were measured in the feed and settled effluent at different recirculation ratios. Aqueous suspensions of biomass collected from the plant were incubated under aerobic and anaerobic conditions, in the presence of a variety of carbonaceous and nitrogenous additives. The nitrogen balance of these suspensions was studied. The plant fulfilled its design function of providing a 'roughing' treatment, as it removed 60 - 85% of the feed BOD. The experimental data did not support the available performance- prediction relationships, and hence the controversies between these relationships were not resolved. The pilot plant performance could be described by the equation Y = 17.778 + 3.079X - 0.0342 X2 where Y = % removal of applied BOD X = recirculation ratio This equation, specific to the pilot plant, predicts an optimum recirculation ratio of 45 : 1, which is considerably higher than the 10 : 1 ratio commonly used. Successful operation of the plant was achieved at BOD : nitrogen ratios in the feed of 21 - 27 : 1, which are higher than the 20 : 1 maximum generally recommended. Despite this high ratio, typically 30% of the feed organic nitrogen was present in the effluent. There was no evidence of nitrification. The nitrogen balance experiments provided evidence of net nitrogen loss from the suspensions, under aerobic conditions. Denitrification under anaerobic conditions followed normal routes.