The Biotic and Abiotic Carbon Monoxide Formation During Aerobic Co-digestion of Dairy Cattle Manure With Green Waste and Sawdust

Abstract

Carbon monoxide (CO), an air pollutant and a toxic gas to humans, can be generated during aerobic digestion of organic waste. CO is produced due to thermochemical processes, and also produced or consumed by cohorts of methanogenic, acetogenic, or sulfate-reducing bacteria. The exact mechanisms of biotic and abiotic formation of CO in aerobic digestion (particularly the effects of process temperature) are still not known. This study aimed to determine the temporal variation in CO concentrations during the aerobic digestion as a function of process temperature and activity of microorganisms. All experiments were conducted in controlled temperature reactors using homogeneous materials. The lab-scale tests with sterilized and non-sterilized mix of green waste, dairy cattle manure, sawdust (1:1:1 mass ratio) were carried out for 1 week at 10, 25, 30, 37, 40, 50, 60, 70°C to elucidate the biotic vs. abiotic effect. Gas concentrations of CO, O2, and CO2 inside the reactor were measured every 12 h. The CO concentrations observed for up to 30°C did not exceed 100 ppm v/v. For 50 and 60°C, significantly (p < 0.05) higher CO concentrations, reaching almost 600 ppm v/v, were observed. The regression analyses showed in both cases (sterile and non-sterile) a statistically significant effect (p < 0.05) of temperature on CO concentration, confirming that the increase in temperature causes an increase in CO concentration. The remaining factors (time, O2, and CO2 content) were not statistically significant (p > 0.05). A new polynomial model describing the effect of temperature, O2, and CO2 concentration on CO production during aerobic digestion of organic waste was formulated. It has been found that the proposed model for sterile variant had a better fit (R2 = 0.86) compared with non-sterile (R2 = 0.71). The model predicts CO emissions and could be considered for composting process optimization. The developed model could be further developed and useful for ambient air quality and occupational exposure to CO.

The Fluctuation of Process Gasses Especially of Carbon Monoxide during Aerobic Biostabilization of an Organic Fraction of Municipal Solid Waste under Different Technological Regimes

“…CO is formed as a result of the biological decomposition of the OF together with other gases such as CO 2 , CH 4 , H 2 , nitrogen compounds, volatile organic compounds (VOCs), and H 2 S [15]. CO formation has been observed during composting of green waste [16], green waste with manure [17], organic waste [18,19], and municipal waste [20,21]. The discovery of CO formation during composting was unexpected.…”

Modeling of CO Accumulation in the Headspace of the Bioreactor during Organic Waste Composting

“…The kinetics data for CO production rates during composting of organic waste were also reported elsewhere [29]. [27], ** estimated using raw data in [29]. [27], ** estimated using raw data in [29].…”

Kinetics of Biotic and Abiotic CO Production during the Initial Phase of Biowaste Composting

“…Production of CO is a result of the biological decomposition of organic matter, which also generates CO 2 , CH 4 , H 2 , nitrogen compounds, VOC, and H 2 S [3]. CO emissions have been observed during the composting of green waste [4], green waste with manure [5], organic waste [2], and aerobic biostabilization of the municipal waste [6]. The detection of CO during the pioneering experiments was a surprise due to the widespread belief in its primary production by incomplete combustion [7].…”

“…In recent work [4], we have indicated that CO production during biowaste aerobic digestion can be biotic and abiotic in nature. The main observation was that CO concentrations varied throughout the process, with the temperature being the main influencing factor.…”

“…These results add to the small, yet growing evidence that biotic processes generate CO. What are the details of the kinetics of CO formation according to aerobic biowaste stabilization process parameters? Trying to answer this question requires reexamining the same dataset, i.e., CO, O 2 , and CO 2 concentrations reported in [4], with extensive statistical analysis to reveal the kinetics of CO formation.…”