Microbial oxygen uptake in sludge as influenced by compost physical parameters

Area of Science:

• Environmental Microbiology
• Waste Management Science
• Bioreactor Engineering

Background:

• Optimal physical parameters for compost mixtures vary widely, necessitating investigation into their interactive effects.
• Microbial oxygen uptake rate (OUR) is a key indicator of microbial activity and biodegradability during composting.

Purpose of the Study:

• To examine the microbial O(2) uptake rate (OUR) in various sludge waste recipes.
• To determine the influence of moisture content (MC), waste/bulking agent (W/BA) ratio, and bulking agent particle size on OUR.
• To develop a predictive model for cumulative O(2) consumption during sludge composting.

Main Methods:

• A central composite design was used to create 16 sludge waste recipes with varying MC, W/BA ratio, and BA particle size.
• Samples were incubated for 28 days under controlled temperature and aeration, with O(2) uptake measured using a respirometer.
• Multivariate regression analysis was employed to model cumulative O(2) consumption.

Main Results:

• Cumulative O(2) consumption after 14 and 28 days was significantly affected by MC, W/BA ratio, BA particle size, and their interaction (p<0.05).
• A predictive model for 28-day cumulative O(2) consumption achieved high accuracy (R(2)=0.84), driven by the MC and W/BA ratio interaction.
• High microbial O(2) uptake was achievable outside traditional MC ranges by adjusting the W/BA ratio to ensure adequate O(2) exchange.

Conclusions:

• The interaction between MC and W/BA ratio is critical for optimizing sludge composting and microbial O(2) uptake.
• Short-term respirometric indices, particularly peak OUR, strongly correlate with long-term biodegradability.
• Future studies can accurately predict overall O(2) consumption and biodegradability within 14 days by combining peak OUR and 14-day cumulative O(2) data.