Enzyme activity as affected by surfactant APG in dairy manure compost in bioreactor

Using compost bioreactors with dairy manure and mushroom residues as feed-stocks, we studied microbial population and enzyme activity as affected by surfactant APG in a 28-day composting process under controlled aerobic condition. APG was added at rate of 100 mg·kg^-1 (amended treatment on dry-weight basis) with 0.00 APG (non-amended treatment) as CK. Results show that APG addition does not inhibit microbial population in terms of total bacteria, fungi and actinomycete (P>0.05). APG addition accelerates temperature increase, with prolonged periods of high temperatures. It, however, does not affect catalase activity at approximately 1.17 mmol·g^-1 for both treatments after 28 days of composting. Urease activity under APG addition and CK reaches its peaks of respectively 32.15 mg(NH₃-N)·g^-1·24h^-1 and 30.17 mg(NH₃-N)·g^-1·24h^-1 after 2 days. There is no significant difference between the 2 treatments and both treatments respectively hit the lowests of 0.81 mg(NH₃-N)·g^-1·24h^-1 and 0.38 mg(NH₃-N)·g^-1·24h^-1 on the 7th day. APG addition significantly enhances invertase and cellulase activity. Invertase activity peaks on day 3 at 18.15 mg(glucose)·g^-1·24h^-1 for APG treatment and 11.77 mg(glucose)·g^-1·24h^-1 for CK (P<0.05), and on day 21 at 24.09 mg(glucose)·g^-1·24h^-1 and 20.71 mg(glucose)·g^-1·24h^-1 for CK respectively (P<0.05). Cellulase activity reaches its peaks of 58.77 mg·min^-1 for APG treatment and 30.62 mg·min^-1 for CK (P<0.05) on day 3. The above results suggest that APG addition enhances organic matter decomposition and therefore potentially shortens decomposition time.