Analysis of the Spatial and Temporal Distribution of Process Gases within Municipal Biowaste Compost

Abstract

Composting processes reduce the weight and volume of biowaste and produce products that can be used in agriculture (e.g., as fertilizer). Despite the benefits of composting, there are also problems such as odors and the emission of pollutants into the atmosphere. This research aimed to investigate the phenomenon of process gas (CO, CO2, NO, O2) evolution within a large-scale municipal composter. The effects of turning frequency and pile location (outdoor vs. indoors) on process gas and temperature spatial and temporal evolution were studied in six piles (37‒81 tons of initial weight) over a six-month period. The biowaste consisted of green waste and municipal sewage sludge. The chemical composition and temperature of process gases within four cross sections with seven sampling locations were analyzed weekly for ~7–8 weeks (a total of 1375 cross sections). The aeration degree, temperature, CO, CO2, and NO concentration and their spatial and temporal distribution were analyzed. Final weight varied from 66% reduction to 7% weight gain. Only 8.2% of locations developed the desired chimney effect (utilizing natural buoyancy to facilitate passive aeration). Only 31.1% of locations reached thermophilic conditions (necessary to inactivate pathogens). Lower O2 levels corresponded with elevated CO2 concentrations. CO production increased in the initial composting phase. Winter piles were characterized by the lowest CO content. The most varied was the NO distribution in all conditions. The O2 concentration was lowest in the central part of the pile, and aeration conditions were good regardless of the technological regime used. Turning once a week was sufficient overall. Based on the results, the most favorable recommended procedure is turning twice a week for the first two weeks, followed by weekly turning for the next two weeks. After that, turning can be stopped unless additional removal of moisture is needed. In this case, weekly turning should continue until the process is completed. The size of the pile should follow the surface-to-volume ratio: <2.5 and <2 for cooler ambient conditions.

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

“…Much of the microbial activity occurs in tropical regions where temperatures are consistently high (>30°C) and damp enough to support thriving microcosm (Liu et al, 2018). CO is also generated during municipal biowaste composting, which was confirmed in our earlier study (Stegenta et al, 2018, 2019a,b), but the biotic and abiotic factors causing it are still not well-understood. Measured CO concentrations were high, thus raising concerns about occupational safety for workers and local air quality.…”

“…However, the precise knowledge of chemical pathways influenced by thermal degradation in natural systems remains elusive due to the numerous interacting processes and conditions observed in composting organic materials, such as microbial activity and the heterogeneous availability of O 2 (Cowan et al, 2018). However, our previous studies (Stegenta et al, 2018, 2019b) shown that the concentrations of CO in an aerobic composting pile are significant (>1,000 ppm). Additionally, there is an immediate need to drastically reduce emissions in order to limit climate change (Liew et al, 2016).…”

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.…”

“…The authors recommend deleting this data, for statistical calculations, due to unknown real values. The procedure of calibration of the Kigaz 300 analyzer was as described in our previous study [18]. Each time the analyzer was started, it performed a 2 min autocalibration.…”

“…As the experiment was done at a technical scale under normal operation (B1) with some technological modifications (A1, A2, B2, C1, C2), there is no variant zero (control), but all data should be compared to pile B1, which describes the standard AB procedure implemented in that installation. Detailed information about the methodology of process and temperature measurements is provided in our previous study [18].…”