Assessing the impact of biomass on gaseous emissions from traditional brick kilns

Abstract

The traditional brick making process remains essential to Uganda's construction sector and primarily depends on the burning of biomass fuels, such as hardwood in clamp kilns, which are temporary and unregulated. However, the environmental implications of this process, particularly pollutant emissions during firing, remain underexplored. This study, therefore, addresses this gap by assessing the impact of biomass on gaseous emissions from traditional brick kilns in the Ugandan construction sector. The study employed a cross-sectional design that involved fieldbased emission measurement to obtain CO2, CO, NO and NOx; and laboratory tests to obtain the calorific value and moisture content of hardwood samples. Emissions were measured for approximately 2 hours per kiln using a flue gas analyzer across 63 traditional kilns in the Greater Kampala Metropolitan Area (GKMA). The results demonstrate that hardwood biomass, mainly species like eucalyptus and mugavu, is dominating owing to its availability and energy content. Nonetheless, poor combustion technology, together with the increasing moisture content of certain biomass varieties, result in increased emissions. Fuel moisture content varied from 11-18%, with calorific values ranging from 11-27 MJ/Kg. Fuel quantities used were between 2.3 to 12.65 tonnes. Higher moisture content was negatively associated with calorific value and fuel quantity used, suggesting potential precombustion preparation issues impacting kiln efficiency and emissions. Emissions analysis revealed significant CO (273-3,899 ppm) and CO2 (4,716-91,786 ppm) concentrations, indicative of inefficient combustion. NOx was negligible due to low nitrogen in the fuel. Fuel-based emission factors were 18.81 ± 9.84 g/kg for CO and 500.82 ± 313.85 g/kg for CO2. Moisture content and calorific value significantly influenced CO emissions, while only calorific value impacted CO2. This research addresses a critical knowledge deficiency in Uganda's emissions inventory and advocates for the advancement of cleaner biomass alternatives and enhanced kiln designs. The findings serve as a significant reference for environmental regulators, architects, and quantity surveyors aiming to integrate sustainability indicators into building procurement and materials planning.