Influence of the content in fats and proteins on the anaerobic biodegradability of dairy wastewaters

The relative amounts of fats, proteins and carbohydrates in wastewaters fro m dairy industries cause problems during their anaerobic treatment. The ana erobic biodegradability of two synthetic wastewaters, one rich in fats (che mical oxygen demand (COD) ratio; Fats/Proteins/Carbohydrates: 1.7/0.57/1) a nd the other with a low fat content (COD ratio; Fats/Proteins/Carbohydrates : 0.05/0.54/1) was studied in samples with total COD ranging from 0.4 to 20 g/l, There were no problems of sludge flotation and the maximum biodegrada bility and methanisation were obtained when operating with wastewaters in t he range of 3-5 gCOD/l. The intermediates of fat degradation (glycerol and long chain fatty acids) seemed not to reach concentrations high enough to a ffect the process. The anaerobic biodegradation of fat-rich wastes was slow er than carbohydrate-rich wastes due to the slower hydrolytic step of fat d egradation which prevented the accumulation of volatile fatty acids (VFAs) and favoured the overall process. Carbohydrate-rich wastewater degradation produced free ammonia (FA) at concentrations near to inhibitory levels (62. 2 mg FA/l), but in this case, ammonia production facilitated regulation of fall in pH caused by of the accumulation of VFA. (C) 2000 Elsevier Science Ltd. All rights reserved.