C and N turnover and lignocellulose degradation during composting of Miscanthus straw and liquid pig manure

To obtain a peat substitute for pot plants, Miscanthus straw and liquid pig manure were composted in two different systems (open box and closed reacto r) and examined for changes in pH, water content and chemical composition ( nitrogen, carbon, hemicellulose, cellulose and lignin). Temperature maxima of 65-70 degreesC were achieved within a few days in both systems. Composti ng and sampling were continued for 190 days in the box system and 150 days in the reactor. Major loss of nitrogen was found in a period of eight days after temperature maximum followed by stabilization. Accumulation of nitrat e was observed during final weeks of composting in both Systems. A marked d ecrease in content of hemicellulose was seen just after temperature maximum followed by slow, constant decrease throughout remaining composting period . The same pattern was observed for degradation of cellulose, though degrad ation was initiated later in the experiment. Degradation of hemicellulose w as nearly 100% in both systems, whereas the cellulose decrease was 64 and 7 0% in the box and reactor, respectively. Lignin was not degraded during the experiments. Though initial C / N ratio was different in the two systems ( 25 in box and 16 in reactor), final ratios were the same (C / N = 13). In s pite of the similarities, the more complicated closed system is preferred i f removal of ammonia from exit gas is considered.