Impact of Temperature Variation on Urban Composting Efficiency: An Empirical Field Study

Thesis Abstract

Urban waste management in cities faces rising pressures to convert organic fractions into stable, reusable materials while minimizing greenhouse gas emissions. Temperature variation critically influences microbial activity, composting kinetics, and end-product quality, yet empirical evidence from urban contexts remains fragmented. This study addresses how diurnal and seasonal temperature fluctuations affect composting efficiency, process stability, and product suitability for urban soil applications. The aim is to quantify the relationship between ambient and pile temperatures and composting performance across real-world urban bins and windrow setups, with a view to informing optimized operational protocols for municipal programs. Specific objectives are (1) to evaluate the effect of temperature regimes on composting rate constants, volatile solids reduction, and mature compost yield; (2) to assess how temperature-driven microbial succession influences intrinsic respiration rates, enzymatic activity, and pathogen reduction; (3) to compare static pile versus turned windrow configurations under similar environmental conditions; (4) to determine thresholds of temperature beyond which efficiency gains plateau or decline; and (5) to develop actionable recommendations for temperature management and process monitoring in urban composting facilities. The study tests the hypotheses that higher sustained pile temperatures accelerate reduction of organic matter up to an optimum, after which efficiency declines, and that active aeration and turning regimes modulate the temperature–performance relationship. A mixed-methods approach is employed in urban field settings across three municipal composting sites in a metropolitan region. The population comprises municipal organic waste streams processed through static piles and windrow systems. A total of 180 composting cycles are monitored over 12 months, with 60 cycles per site, distributed evenly between configurations. Data collection combines quantitative measurements—temperature profiles captured with calibrated thermocouples at multiple depths, oxygen levels, moisture content, moisture reduction, carbon-to-nitrogen ratio, pH, electrical conductivity, pile volume, and mass loss—with qualitative observations of odor intensity and visual indicators of stability. Instrumentation includes data loggers recording at 15-minute intervals, gas probes for CO2 and CH4 concentrations, and laboratory analyses for C/N, NH4+, NO3-, microbial carbon mineralization rates, and pathogen indicators (Salmonella, E. coli) following standard methods. Ancillary meteorological data (ambient temperature, humidity, solar radiation, rainfall) are obtained from local weather stations. Analytical methods comprise time-series analysis and mixed-effects modeling to account for repeated measurements within cycles, with multivariate regression to identify independent predictors of process efficiency. Survival analysis techniques assess time-to-stability thresholds, while ANOVA and post hoc tests compare performance between configurations and temperature bands. Microbial community structure is inferred through 16S rRNA gene sequencing on selected samples (n=24) to link temperature regimes with functional guilds involved in lignocellulose degradation and ammonification. A conceptual framework combining the Thermophilic–Mesophilic Continuum and the Waste Stabilization Theory guides interpretation of thermal profiles and maturation indicators. Data triangulation integrates physicochemical parameters with microbial and process indicators to establish robust causal inferences. Expected findings indicate a clear positive association between elevated pile temperatures within the thermophilic range (55–65°C) and rapid reduction of volatile solids during the initial phase, accompanied by enhanced pathogen reduction. However, temperatures surpassing approximately 65°C show diminishing returns in overall efficiency, with increased energy input requirements and potential volatilization losses. Turned windrow systems are anticipated to exhibit more stable temperature control and faster maturation under equivalent feedstock compositions, compared with static piles. The study is expected to identify critical thresholds for turning frequency and aeration rate that optimize heat generation efficiency while maintaining microbial diversity essential for complete stabilization. The contribution to knowledge includes empirical quantification of temperature–performance relationships in urban composting, validation of an operational decision-support framework for temperature management, and evidence-based guidelines for scale-appropriate process monitoring. It informs policy directions for urban sustainability programs seeking to maximize resource recovery from organic waste while minimizing greenhouse gas emissions. Recommendations emphasize adaptive temperature control through targeted aeration, timed turning schedules, sensor-network-based process monitoring, and standardized performance metrics to facilitate comparability across urban facilities.