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SULFIDE AND GREENHOUSE GAS EMISIONS FROM MEDITERRANEAN SEWERS

Final Report Summary - SGHGEMS (SULFIDE AND GREENHOUSE GAS EMISIONS FROM MEDITERRANEAN SEWERS)

The SGHGEMS research project studied the production of sulfide (H2S) and greenhouse gas emissions from sewers exposed to Mediterranean climate conditions. Production and build-up of sulfide and methane (CH4) in wastewater collections systems causes several detriment al effects. Sulfide accumulation in sewers causes: i) odour nuisance in sewer surrounding areas, ii) health hazards due to its toxicity, and iii) corrosion of pipes and inlet structures of sewage treatment plants. On the other hand, methane is a potent greenhouse gas significantly contributing to global warming. Despite these important impacts, sewer-produced sulfide and methane are yet to be considered in the management of Mediterranean Urban Water Systems. The project methodology combined extensive experimental work on real sewers with advanced mathematical modelling to provide effective applicable control measures.

The project successfully monitored and simulated the detrimental emissions of 2 catchments on the Costa Brava area: l’Escala sewer system and Sant Pere Pescador sewer system. In both cases, the methodology applied was able to establish the optimal functioning-strategy of the sewer system in order to completely reduce the emissions of H2S and CH4. In addition to the environmental impacts obtained (nearly zero emissions in hotspots of the sewer) the guidelines generated in the project helped reduce the occupational hazards at the entrance of the pump stations and wastewater treatment plant of the area. For instance, the time of “safe conditions related to H2S concentration” at the inlet of the wastewater treatment plant of l’Escala has increased from 15% to 99% of the time, thus making the work-environment for sewer operators much safer. Moreover this was achieved at the same time that the operational cost of the chemical dosage in sewers were significantly reduced (by 50% and 90% respectively) thus ensuring an important economic benefit for the water utilities. Overall the project combined these important environmental, social and economic benefits to the water utilities and wastewater treatment systems managers. The knowledge acquired and the methodology can now be applied in other sewer systems with similar problems.

During the SGHGEMS project, new research topics related to sewer systems were identified and thus incorporated to the research plan. Those included the
i) Development of tools for the online monitoring of dissolved CH4 in sewers. CH4 production in sewers is a concern recently discovered and there are still gaps in the methodologies used to monitor and properly characterize this compound. So far, the detection of methane was carried out by manual grab sampling on site, a valuable but limited method as involves extensive monitoring campaigns, the use manpower and limited results. To overcome this limitations, a prototype of system of automatic CH4 online detection has been designed and constructed within SGHGEMS.
ii) Development of tools for the Combined Sewer Overflow (CSO) spills from sewer systems. During periods of heavy rainfall the wastewater volume in a sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other water bodies. There are also several limitations with the current methods used to monitor CSOs. Within SGHGEMS, the CSO functioning have been studied and a new method for its monitoring was proposed. The method is based in low-cost temperature sensors and has led to a patent (reference number ES2490065A1) a research paper and presentations in international specialized conferences.
iii) Investigation of the fate of pharmaceutical compounds in sewers systems. Sewers are infrastructures of significant changes in water composition and its dissolved compounds. Amongst those pharmaceutical compounds have been recently detected, reported and are gaining attraction in an emerging field of research called “sewage epidemiology.” Sewage epidemiology tracks wastewater content to establish population habits in catchments. Within SGHGEMS, the fate of pharmaceutical compounds in the system of Sant Pere Pescador was monitored.
Studies performed under SGHGEMS provided new insights on those topics including a new tools for advanced monitoring of those (including a patent on CSO detection) and several related publications.