Comparison of Five Organic Wastes regarding Their Behaviour during 1 Composting : Part 2 , Nitrogen Dynamic

1 This paper aimed to compare household waste, separated pig solids, food waste, pig slaughterhouse sludge 2 and green algae regarding processes ruling nitrogen dynamic during composting. For each waste, three 3 composting simulations were performed in parallel in three similar reactors (300L), each one under a constant 4 aeration rate. The aeration flows applied were comprised between 100 and 1100 L/h. The initial waste and the 5 compost were characterized through the measurements of their contents in dry matter, total carbon, Kjeldahl and 6 total ammoniacal nitrogen, nitrite and nitrate. Kjeldahl and total ammoniacal nitrogen and nitrite and nitrate 7 were measured in leachates and in condensates too. Ammonia and nitrous oxide emissions were monitored in 8 continue. The cumulated emissions in ammonia and in nitrous oxide were given for each waste and at each 9 aeration rate. The paper focused on process of ammonification and on transformations and transfer of total 10 ammoniacal nitrogen. The parameters of nitrous oxide emissions were not investigated. The removal rate of 11 total Kjeldahl nitrogen was shown being closely tied to the ammonification rate. Ammonification was modelled 12 thanks to the calculation of the ratio of biodegradable carbon to organic nitrogen content of the biodegradable 13 fraction. The wastes were shown to differ significantly regarding their ammonification ability. Nitrogen 14 balances were calculated by subtracting nitrogen losses from nitrogen removed from material. Defaults in 15 nitrogen balances were assumed to correspond to conversion of nitrate even nitrite into molecular nitrogen and 16 then to the previous conversion by nitrification of total ammoniacal nitrogen. The pool of total ammoniacal 17 nitrogen, i.e. total ammoniacal nitrogen initially contained in waste plus total ammoniacal nitrogen released by 18 ammonification, was calculated for each experiment. Then, this pool was used as the referring amount in the 19 calculation of the rates of accumulation, stripping and nitrification of total ammoniacal nitrogen. Separated pig 20 solids were characterised by a high ability to accumulate total ammoniacal nitrogen. Whatever the waste, the 21 striping rate depended mostly on the aeration rate and on the pool concentration in biofilm. The nitrification rate 22 was observed as all the higher as the concentration in total ammoniacal nitrogen in the initial waste was low. 23 Thus, household waste and green algae exhibited the highest nitrification rates. This result could mean that in 24 case of low concentrations in total ammoniacal nitrogen, a …