Carbon Footprint Analyses of Wastewater Treatment Systems in Puducherry

Carbon footprint analysis is a method to quantify the life cycle Greenhouse Gases (GHGs) emissions and identify the measure to reduce climate change impacts. The Intergovernmental Panel on Climate Change (IPCC) has identified that the global warming and climate change which is one of the most important issues in the domain of environment are caused by the excessive emission of Greenhouse Gases (GHG) mainly constituting Carbon dioxide (CO₂), Methane (CH₄) and Nitrous oxide (N₂O). The municipal wastewater treatment plant receives wastewater for treatment and finally discharges the treated effluent. The emissions of GHG during the treatment of wastewater as well as during the treatment process of sludge and also for energy generation are known to be on-site GHG emissions. Off-site GHG emissions are generated due to transportation and disposal of sludge, off-site energy and chemical production.

In Puducherry, the municipal wastewater is being treated using oxidation ponds, Upflow Anaerobic Sludge Blanket (UASB) and Sequencing Batch Reactor (SBR). Wastewater treatment using Sequencing Batch Reactor (SBR) technology is one of the state-of-the-art wastewater management systems. In this technology equalization, biological treatment and secondary clarification are performed in a single reactor in a time control sequence.

In this paper, the emissions of GHG from the UASB, oxidation ponds and SBR in Puducherry were estimated. The emissions of CO₂, CH₄ and N₂O from all these treatment plants were also estimated based on the guidelines of IPCC and RTI-USEPA and the total equivalent CO₂ was computed and analyzed. The impact of biomass yield coefficient on the emissions of GHG was also examined and their variations were also studied. The total emissions of equivalent CO₂ from the SBR of 17 Mld capacity were less than 20% of the total CO₂ emissions of CO₂ from the UASB and oxidation ponds of 17.5 Mld capacity. Further study revealed that by modifying the treatment process of the sludge from the SBR, by altering the waste sludge flow rate and the MLSS, the total emissions of equivalent CO₂, could be reduced and it is possible to achieve a reduction of about 40% of total equivalent CO₂ emissions. The study also established that the emissions of CO₂ from the SBR are the least and that the SBR performs well and more efficient in terms of reduction of GHG emissions when compared to that of the UASB and oxidation ponds.

Article by G. Vijayan, et al, from Puducherry, India.

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