Articles
NEW METHODS FOR RAPID DETERMINATION OF COMPOST MATURITY (REFEREED)
Method 1 (respiration intensity, RImax): Composts were incubated by 38 °C in an oxygen-enriched atmosphere in pressure-tight pots.
CO2 released by the composts was caught with NaOH. Microbial oxygen consumption was measured by recording the pressure drop in the closed system and respiration intensity was calculated with the help of compost dry matter.
Method 2 (pH-drop after anaerobic incubation for 5 hours, pH5h): Composts were incubated in screwed up flasks at 40 °C after submergence with distilled water of the 6.25-fold quantity of compost dry matter. pH dropped depending on the quantity of available unstabilized C-compounds being microbiologically transformed into organic acids.
Maturity was determined of about 100 composts both from Bavarian praxis plants and from composting experiments.
The composts differed strongly in their proportion of biogenic household waste, turning interval, pile size and age.
With all methods progress in maturing during composting could be demonstrated well.
The methods also showed that great proportions of biogenic household waste, a large pile size and infrequent turning of piles retard the composting process.
The three methods were highly significantly correlated with each other.
Therefore – especially if quick evaluation of compost maturity is necessary – it would be possible to replace measurement of self-heating capacity, which lasts several days, by measurement of respiration intensity and pH drop requiring only 5 and 12 hours, respectively.
Composts can be referred to as mature, if Tmax < 30 °C, RImax < 0.2 mg O2/g dm/h or pH5h ≥ 7.5.