PROJECT DESCRIPTION
BACKGROUND
A 2012 study by the Joint Research Centre study found that many wastewater treatment plants use versions of mechanical and biological treatment technology that dates from the 1970s. Plants built more than 20 years ago may struggle to deal with higher loading rates, especially in areas with a large seasonal increase in population (e.g. due to tourism). In many cases, space restrictions mean that it is not possible to install a primary clarifier to tackle the problem in plants that use an extended aeration activated sludge process.
The treatment and disposal of sewage sludge is expensive, environmentally-sensitive and a growing problem for wastewater treatment plants. The main sludge management options are reuse in agriculture, burning for energy or disposal to landfill. Energy contained in sludge can be used to power wastewater treatment plants and reduce their running costs.
DEYAR is a municipal enterprise that operates a wastewater treatment plant serving the Rethymno area of Crete. The plant, which applies an extended aeration activated sludge process, has an average daily flow of 13 000 to 15 000 m3. Its peak flow capacity is some 17 000 m3/day. DEYAR is expanding the capacity of the plant with an aeration and sedimentation tank (targeting a peak flow of 28 000 m m3/day). This is expected to increase energy requirements, and it is necessary to ensure that the increased flow rate does not cause performance issues that hinder its ability to meet environmental limit values.
OBJECTIVES
The LIFE B2E4sustainable-WWTP project aimed to improve the performance of overloaded extended aeration wastewater treatment plants using a novel process for removing solids prior to aeration. For this purpose, a microscreening system for biosolids removal would be installed at DEYAR’s wastewater treatment plant in Rethymno, Crete. It was to be integrated with a biosolids drying and gasification system to enable combustion for energy production. The goal was to produce enough energy to meet all the needs of the treatment plant, making it totally self-sufficient. By reducing the biological load in treated wastewater, the project also protected the aquatic environment.
Specific project objectives were to:
- Improve the quality of the aquatic environment, with less pollutants in effluent as a result of improved treatment plant performance;
- Improve the performance of existing extended aeration plants by removing at least 60% of total suspended solids and biological oxygen demand;
- Reduce the environmental impact of sewage sludge management by applying an innovative treatment system that transforms sludge into energy and minimal solid inert waste;
- Reduce the carbon footprint and greenhouse gases emissions of a wastewater treatment plant;
- Produce electrical energy by means of gasification of 100% organic carbon from biosolids, with the parallel production of low volume and inert solid waste, to make the plant self-sufficient in energy and reduce its carbon footprint and greenhouse gas emissions; and
- Demonstrate the feasibility of avoiding sewage sludge disposal in small- and medium-sized treatment plants.
The project aimed to contribute to the objective of the EU water priority area: ’to ensure safe and efficient use of water resources, improving quantitative water management, preserving a high level of water quality and avoiding misuse and deterioration of water resources’. It also provided an example of how current treatment plants can be updated to address population growth and the need to reduce greenhouse gas emissions from sludge management. The integration of technologies proposed in this project was suitable for replication at other wastewater treatment plants lacking sludge primary treatment (i.e. most plants in Europe).
RESULTS
The LIFE B2E4sustainable-WWTP project has successfully designed, developed and tested a novel methodology for wastewater treatment that utilises the microsieving of solids in wastewater and gasification technology to produce electricity from a renewable energy source. This innovation leads to departure from traditional wastewater treatment techniques and has the capacity to significantly alter the way wastewater is treated in plants.
The project constructed and operated for one year a prototype unit in the premises of the Municipal Enterprise for Water Supply and Sewerage of Rethymno, Greece. The project managed to improve the energy performance of the Wastewater Treatment Plant by 7.4% due to upfront removal of total suspended solids in the wastewater, leading to an equivalent GHG emissions reduction of 205 tonnes. It has also improved the water quality in the Rethymno coastline through reduction in total suspended solids by 5,916 kg/year and biological oxygen demand by 8,120 kg/year in the city’s wastewater.
Furthermore, the project managed to reduce secondary sludge by 227 tn/year due to energy recovery through gasification. Demonstration of an alternate way to manage sludge has been attained, creating new standards for wastewater treatment, a major accomplishment of the project, proving the viability of incorporating gasification technology into current regulatory frameworks and facilitating the execution of the Urban Wastewater Treatment Directive, the Water Framework Directive and the Sewage Sludge Directive.
