New concept for energy self-sustainable wastewater treatment process and biosolids management

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 an expensive, environmentally-sensitive and 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 aims 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 will be installed at DEYAR’s wastewater treatment plant in Rethymno, Crete. It will be integrated with a biosolids drying and gasification system to enable combustion for energy production. The goal is 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 will also protect the aquatic environment.

Specific project objectives are 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. This will 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 contributes 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 provides a demonstration 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 is suitable for replication at other wastewater treatment plants lacking sludge primary treatment (i.e. most plants in Europe).

Expected results:

Improvement of the quality of the aquatic environment, by enhancing the performance of existing overloaded wastewater treatment plants;

A new concept of municipal wastewater treatment with better performance than the conventional extended aeration process;

Production of approximately 1 tonne/day of dry biosolids capable of being used to generate syngas and electrical power;

A 70%+ reduction in the energy requirement of the DEYAR wastewater treatment plant compared with a conventional extended aeration plant;

A reduction in carbon footprint of some 104 tonnes CO2/year;

An improvement in secondary treatment of wastewater due to lower total suspended solids and biological oxygen demand; and

The potential for replication of the new process in existing wastewater treatment plants or new plants in the EU, with subsequent positive outcomes for European Water Agencies.