Greenhouse gas emissions from sludge treatment reed beds

Sludge treatment reed bed systems (STRBs) are considered as an alternative technology for surplus sludge treatment. Organic matter is decomposed by various microbial reactions, resulting in gases such as CO₂and CH₄emitting into the atmosphere. The aim of this study is to investigate gas emission from STRBs. The static transparent chamber was adopted to measure gas emission; it allows sunlight to enter and plants to photosynthesise. The comparison of total solids and volatile solids showed STRBs have a higher efficiency in dewatering and mineralization than a conventional unplanted sludge drying bed (USDB). The CO₂emission ranged from 28.68 to 100.42 g CO₂m⁻² d(-1) in USDB, from 16.48 to 65.18 g CO₂m⁻² d⁻¹ in STRBs; CH₄emission ranged from 0.26 to 0.99 g CH₄ m⁻² d⁻¹ in USDB, from 0.43 to 1.95 g CH₄m⁻² d⁻¹ in STRBs. Both gas fluxes decreased towards the end of vegetation and reached the highest rates during the hot and dry summer. After the system was loaded by sludge, the fluxes of CO₂and CH₄significantly decreased in the USDB, whereas they increased in STRBs. In terms of CO₂equivalent, the global warming potential of CH₄was 13.13 g CO₂eq m⁻² d⁻¹ and 15.02 g CO₂eq m⁻² d⁻¹ in USDB and STRBs, respectively.