Release of N-containing compounds during pyrolysis of milk/dairy processing sludge - Experimental results and comparison of measurement techniques

A dried dairy processing sludge (sludge from wastewater treatment of an effluent from a milk processing plant) was pyrolysed in a single -particle reactor at different temperatures from 400 C-degrees to 900 C-degrees. NH3 and HCN were measured online and offline by means of FTIR as well as by cumulative sampling in impinger bottles (in 0.05 H2SO4 and 1 M NaOH, respectively) and analysed by photometric method. NO and NO2 were measured online using a nitric oxide analyser while N2O was measured by FTIR. Nitrogen (N) in the sludge and in the remaining char, char -N, was determined. Moreover, tar content in pyrolysis gas was measured and tar -N was determined. The results with respect to N mass balance closure are discussed. The different measurements techniques are compared. For pyrolysis at 520(degrees)C and 700 C-degrees nitrogen in the gas phase was mainly contained as N-2 (36 % and 40 % respectively), followed by NH3 (15 % and 18 %), tar -N (10 % and 9 %), HCN (1 % and 3 %), NO (1 %) and NO2 (0.2 %). The dairy processing sludge has very specific properties with organic -N present predominantly proteins and a high content of inherent Ca. These characteristics affected the distribution of N. The amount of char -N was higher while the amount of tar -N lower than for sewage sludge from literature, at comparable pyrolysis temperature.