Microbiological parameters as indicators of compost maturity

TLDR

The study aimed to assess how microbial properties of pig manure change under different management and composting regimes, relate these changes to humification and temperature, and identify the best microbial indicators of compost maturity. The authors monitored six microbial parameters and humification metrics, together with temperature, throughout the composting of pig manure under varied turning and moisture regimes. Dehydrogenase activity emerged as the most reliable, rapid, and cost‑effective indicator of compost maturity, showing strong correlations with temperature and humification parameters and enabling prediction of a 56‑day maturation period under 60 % moisture and 4‑day turning.

Abstract

The objectives of this study were to determine the changes of microbial properties of pig manure collected from pens with different management strategies and composted using different turning and moisture regimes; relate their association with humification parameters and compost temperature; and identify the most suitable microbial indicators of compost maturity.Six different microbial parameters, including total bacterial count, oxygen consumption rate, ATP content, dehydrogenase activity, and microbial biomass C and N, along with humification parameters [humic acid (HA), fulvic acid (FA) and HA : FA ratio] and compost temperature were monitored during composting. Significant positive correlations were found between temperature and microbial properties, including O2 consumption rate, ATP content, dehydrogenase activity, and microbial biomass N. The humification parameters also showed significant correlations with microbial properties of the manure compost. For instance, HA contents of pig manures was positively correlated with total aerobic heterotrophs, and microbial biomass N and C; and negatively correlated with O2 consumption rate, ATP content, and dehydrogenase activity. Among the six microbial parameters examined, dehydrogenase activity was the most important factor affecting compost temperature and humification parameters. Composting strategies employed in this study affected the speed of composting and time of maturation. If the moisture content is maintained weekly at 60% with a 4-day turning frequency, the pig manure will reach maturity in 56 days.The composting process went through predictable changes in temperature, microbial properties and chemical components despite differences in the initial pig manure and composting strategies used. Among the six microbial parameters used, dehydrogenase activity is the most suitable indicator of compost maturity. Compared with respiration rate, ATP content and microbial biomass procedures, dehydrogenase activity is the simplest, quickest, and cheapest method that can be used to monitor the stability and maturity of composts.The results presented here show that microbial parameters can be used in revealing differences between composts and compost maturity. The statistical relationship established between humification parameters and microbial parameters, particularly dehydrogenase activity, demonstrates that it is possible to monitor the composting process more easily and rapidly by avoiding longer and more expensive analytical procedures.