Simulation of temperature variation during aerobic composting of dairy cattle manure using a biologically based mathematical model

Date

2011

Degree

Bachelor of Science in Agricultural Engineering

College

College of Engineering and Agro-Industrial Technology (CEAT)

Adviser/Committee Chair

Ronaldo B. Saludes

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Abstract

A biologically based mathematical model was used in simulating the temperature during composting of dairy cattle manure. The simulation was done using a macro-enabled spreadsheet. Substrate concentration was calculated and used in simulating temperature distribution during composting. The model was also used to simulate different composting scenarios by varying the initial moisture content, free air space, aeration rate, and substrate concentration. The rate of increase in predicted temperature is faster during the mesophilic stage compared to the actual experimental data. The maximum temperature was predicted accurately, with an error of 3.79°C after day 3. The predicted thermophilic stage was longer and ended only after the moisture level reached 40%. Generated contour maps of the temperature distribution within the reactor showed that the top layer has a higher temperature than the bottom layer. Simulating the different composting scenarios showed that moisture content is a limiting factor for the rise in compost temperature. For very low moisture content such as 30% heat production was reduced. Decrease i n temperature was associated with low moisture content. Free air space did not show any significant changes in the temperature of the compost. The decrease in substrate concentration reduced the peak temperature. A substrate concentration of 29.33kg/m³ was predicted to reach a peak temperature of 67.63°C . Aeration rate affected the rate of moisture and heat removal, which in turn,influenced the thermophilic stage of composting. An increase in aeration rate of 10kg/h-m³ resulted into a shorter thermophilic stage. Substrate degradation was suppressed at lower air flow rates.

Language

English

LC Subject

Mathematical models Computer simulation

Location

UPLB College of Engineering and Agro-Industrial Technology (CEAT)

Call Number

LG 993.5 2011 A2 J37

Document Type

Thesis

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