Optimal bulking agent particle size and usage for heat retention and disinfection in domestic wastewater sludge composting

Abstract

Composting of two types of sludge produced in wastewater treatment plants, raw sludge (RS) and anaerobically digested sludge (ADS), has been systematically studied by means of the experimental design technique. The results have been analyzed using a full factorial experimental design in order to determine the optimal conditions for composting such sludges in terms of bulking agent particle size and bulking agent:sludge volumetric ratio, two of the key parameters to ensure an optimal performance of the composting process. The objective function selected was a simulated death kinetics of Salmonella, which was chosen as a model pathogen microorganism to represent the disinfection of the material. For both types of sludge, optimal values were found at 5mm bulking agent particle size and 1:1 bulking agent:sludge volumetric ratio when a Gaussian function was fitted to the experimental data. Pilot scale experiments using optimal values obtained were successfully undertaken and confirmed a full disinfection of the sludge by means of the composting process. A mathematical model to simulate the disinfection performance of a composting material is presented. The model can be applied to simulate the disinfection performance of a given pathogen.

Influence of bulking agents on CH4, N2O, and NH3 emissions during rapid composting of pig manure from the Chinese Ganqinfen system

“…Michel et al (2004) and Hao et al (2004) found a lower decomposition of the compost substrate when using bulking materials rich in lignin (woodchip and sawdust) compared to composting with straw, which had a lower lignin content. In this study, the higher degradability of the sawdust may have been associated with its larger surface area-to-mass ratio, and also with the fact that the small bulking agent particles create a real porous structure and a homogeneous porous size distribution inside the material that acts as an efficient oxygen diffuser (Gea et al, 2007). However, an experiment with pig manure alone or pig manure with an inert bulking agent was not performed in this study, so it was not possible to evaluate the degradability of the bulking agents alone.…”

“…Therefore, the addition of a bulking agent is necessary to compost the separated solid fraction of pig manure (Nolan et al, 2011). A bulking agent is the material that adjusts the C/N ratio, provides optimum free air space (FAS), and regulates the water content of the waste to be composted (Gea et al, 2007;Kato and Miura, 2008;Iqbal et al, 2010;Jolanun and Towprayoon, 2010;Doublet et al, 2011), which are usually fibrous with carbonaceous material (Iqbal et al, 2010). The bulking agent represents a large proportion of the composting mixture as a source of carbon and energy for micro-organisms (Adhikari et al, 2009).…”

“…The bulking agent represents a large proportion of the composting mixture as a source of carbon and energy for micro-organisms (Adhikari et al, 2009). The composting processes are affected by the type of bulking agent used, its particle size, and the proportion of bulking agent in the composting mixture (Atkinson et al, 1996;Gea et al, 2007;Chang and Chen, 2010). The addition of biodegradable C fractions will balance the initial C/N ratio of the mixture and reduce the N losses during the composting process (Dias et al, 2010).…”

Effect of initial physical characteristics on sludge compost performance

“…Eftoda and McCartney (2004) studied BA requirements to optimize the free air space (FAS) value of sludge composted with wood chips. Gea et al (2007) are among the few who studied the individual effect of BA particle size distribution and mass ratio on sludge compost behaviour (O 2 uptake, consolidation, airflow patterns), but the interaction between MC and BA particle size distribution was not investigated. Therefore, the objective of this project was to study the impact and interaction of initial MC and BA particle size distribution on compost material biodegradability.…”

Chns analysis towards food waste in composting

“…Moreover, several studies also laid out the effect of adding bulking agents in which to adjust the MC, N-content, C/N ratio, and void spaces between particles in the past, since most waste materials such as sewage sludge, food waste and animal manure have too low C/N ratios and too high MC for efficient composting [6][7][8][9]. Generally, modification of physical properties of composting feed-stock may resulted from different bulking agents as well as change the biodegradation kinetics and composting performance [7,8,10].…”