The survival of civilisation is probably dependent on the outcome in the next 25 years of how humankind tackles the three challenges – namely energy supply, climate change and waste management.

The water industry position is unique as it has to deal with a huge waste management problem. It will be the sector of the economy most significantly affected by climate change, with increased incidence of both serious flooding and drought; but it also has the potential to make a substantial contribution to the renewable energy supply in the future.

Therefore, the roles of water and sewerage undertakers everywhere will have a more far reaching impact on society than ever before. Certainly, the water industry has a lot to live up to, but will it deliver the expected changes?

An innovative and forward thinking research programme designed to reshape and enhance the way we deal with sewage sludge across Europe has recently been launched.

The European Commission has awarded the END-O-SLUDG (www.end-o-sludg.eu) Consortium €3.5 million to undertake an extensive three year programme of work that will research novel sewage treatment processes that address not only EU Energy Policies and climate change mitigation strategies, but also look to develop sustainable and economic markets for sludge derived products.

Sludge production and disposal are entering a period of dramatic change, which has been driven mainly by EC legislation. The implementation of the Urban Wastewater Treatment Directive was predicted to result in at least a 50% increase in the volume of sludge being produced in Europe between 1992 and 2005.

During this same period, however, sludge disposal to sea became illegal. Since 2002, the landfill directive has made disposal to landfill virtually impossible, with further increases in sludge production forecasted due to the implementation of the Water Framework Directive.

The UK water industry alone accounts for five million tonnes of carbon dioxide emissions per year – almost one percent of the UK’s greenhouse gas emissions. With the need to meet stretching targets (to reduce greenhouse gases by 80% by 2050), the water sector has an important part to play in reducing its carbon emissions.

Meeting higher water quality standards required by the EU Directives presents a dual challenge, since increased water treatment is likely to result in an increase in carbon emissions. With European sludge production volumes already at 9.4 Mt p.a. (2005 estimate), the challenge facing industry now is to maintain cost effective and secure methods of sludge treatment and disposal, while also engendering greater public confidence.

The programme, coordinated by United Utilities Water PLC in the UK, is undertaken by a Consortium of 14 European partners drawn from the water, resource and waste management, academia and agricultural industries.

These include: • United Utilities Water PLC • Nijhuis Water Technology b.v. • WATERLEAU Global Water Technology nv • Teagasc – The Irish Agriculture and Food Development Authority • Hipsitec SA • Chemical Engineering and Environmental Technology Department, Universidad de Oviedo • COGERSA, Asturias S.A. • Natural Resources Department, Cranfield University • Crop and Environment Research Centre, Harper Adams University College • HGCA • Carrs Agriculture Ltd • Sustainable Resource Solutions Ltd • Valsave Engineered Solutions Ltd • Demeter Technology Ltd

Project focus

The project focuses on a number of areas that will address the challenges that the industry currently faces including processes to reduce sludge volume; development of more energy efficient measures; market development activities; regulatory issues and the assessment of the possible health and environmental risks associated with sludge recycling for greater public confidence.

The project is a realistic response to the problem of sludge management we face in Europe. It is an exciting and innovative project that provides consortium members with a unique opportunity to make a stepped improvement in industry standards and practices.

For the first time we will attempt to use an holistic approach in developing advanced technologies for system solutions that will tackle the issues all the way from wastewater and sludge treatment, through downstream processing to the market development and environmental impact assessment.

The provision of water and the management of wastewater place a huge pressure on the environment; but it is believed that new systems will make significant advances to reducing the impact, reducing customer costs and carbon emissions, and to paving the way for sustainable markets for sludge derived products.

Water Framework Directive:

The WFD is the most substantial piece of water legislation ever produced by the European Commission, and provides the major driver for achieving sustainable management of water in the UK and other EU Member States.

It requires that all inland and coastal waters within defined river basin districts must reach at least ‘good status’ by 2015, and defines how this should be achieved through the establishment of environmental objectives and ecological targets for surface waters. http://www.defra.gov.uk/environment/quality/water/wfd/index.htm

Urban Wastewater Treatment Directive:

The UWWTD covers the collection and treatment of urban waste water and the disposal of sewage sludge. The treatment standards and the deadlines set for in the Directive for treatment vary according to the sensitivity of the receiving water, the type of receiving water (e.g. fresh waters, estuaries or coastal waters) and the size of the agglomeration (usually urban areas) which produces the waste water. http://archive.defra.gov.uk/evidence/statistics/environment/inlwater/iwurbanwaste.htm

Technological background

Sewage sludge arises from the treatment of wastewater generated by society. It is unavoidable, and has to be treated and disposed of in a safe and acceptable manner.

Since wastewater and sludge treatment processes have a high impact on the environment, society and costs, it is important that appropriate technologies are deployed. Sludge management is best achieved using an holistic approach and to this end END-O-SLUDG aims to provide novel process options that may be used in improved system solutions in line with EU energy policies and climate change mitigation strategies.

Wastewater treatment

The water that we return to the environment must be of the highest quality possible to ensure a healthy environment for all other users downstream of the discharge point and to promote biodiversity. While the processes used to treat wastewater may have a number of variations, generally they have two main stages, as seen in the chart below:

Phosphorus (P) can either be removed through Enhanced Biological Phosphorus Removal or chemical dosing. In Europe, chemical treatment using ferric chloride is necessary, but not desirable, as it typically generates about 25% extra sludge.

Aeration typically accounts for 60% of the electricity used in wastewater treatment. It is crucial that the BOD load on the secondary treatment is minimised in order to reduce the energy required for aeration. SAS is particularly difficult to break down in sludge digestion, which leaves a large volume of sludge to recycle.

By reducing the BOD load on secondary treatment the resulting SAS volume may be reduced accordingly. It is possible to achieve enhanced BOD removal with pioneering techniques and, in addition, to develop new processes for P recovery and segregation from the main sludge stream in order to facilitate recycling in precision farming.

Sludge treatment

Sludge treatment was traditionally applied for odour reduction before recycling. Nowadays, it is mostly concerned with energy recovery and reducing the possible health risks associated with sludge recycling. There are many technologies used in sludge treatment. The following table provides a summary of the treatments that are commonly used in Europe:

In a conventional sludge digestion process, the conversion of organic matter to biogas is typically only 45% efficient due to the poor biodegradability of the SAS.

More recently, pre-treatment technologies have been developed to improve the conversion, with the most successful achieving 60-65%. These techniques are being built upon further, aiming to improve biogas yield further.

Currently, another challenge facing sludge undertakers is the resurgence of E. coli in Biosolids (digested cake). The reappearance of the bacterium after the centrifugation of digested sludge has caused concerns among operators because E. coli is commonly used as an indicator of the health risks. Means are being sought to address this issue by clarifying the mechanism of E. coli re-growth and by developing steps that aim to prevent its occurrence.

Sludge recycling

Biosolids cake is a convenient form of sludge which is commonly used for recycling throughout Europe and North America. Although Biosolids contain useful amounts of nutrients (nitrogen, N; phosphorous, P; potassium, K and sulphur, S), the nutrients themselves are not in a balance proportion that matches crop requirement.

Furthermore, the release of some nutrients, particularly the N component, can be very slow and unpredictable. Current Biosolid recycling practices also tend to cause the accumulation of P in the soil, which poses a pollution threat with run-off. Nutrient management withBiosolids for crop production therefore presents a significant challenge for the industry.

The environmental impact of heavy metals and organic micropollutants in soils are other important considerations. Organo Mineral Fertiliser (OMF) is a new nutrient management concept offering more predictable agronomic performance: (a) An experimental sample of OMF and (b) Schematic diagram of an OMF granule.

Farming application

The use of biosolids on agricultural land has a number of benefits: • Biosolids contain plant nutrients and organic matter that improve soil structure, drainage and water holding capacity • They provide an excellent source of nitrogen (N), phosphorus (P), potassium (K) and sulphur (S) which help to produce high crop yields • The use of biosolids typically saves €150 per hectare in fertiliser replacement for farmers • Biosolids can make a contribution to reducing green house gas emissions

Despite its benefits, concerns relating to food safety, odour and soil contamination mean that the use of biosolids can be a sensitive issue and as a result is a regulated activity.

Farmers must comply with strict codes of practice which prohibit the use of biosolids on certain crops, place requirements to monitor soil quality and ensure that any biosolids applied to land have been treated to the required levels.

The benefits of a regulated system, however, mean that both the water industry and farmers can now give assurance that the biosolids they use pose no harm to public health. END-O-SLUDG will be working closely with the farming industry to strengthen the market for biosolid based fertiliser products and improve public confidence by: • Further developing treatment processes to improve quality • Introducing new treatment processes to reduce the odour of biosolids • Producing a portfolio of biosolid based fertiliser products that contain a balance of N, P, K and S

Author

Dr Son Le, MBE, United Utilities

Son graduated from Newcastle Upon Tyne University as a Chemical Engineer in 1979 and went on to study for his PhD in Biochemical Engineering, which he obtained from the University of Wales in 1983, becoming a Chartered Chemical Engineer in 1985.

He had held a number of positions in the engineering and manufacturing industries including working in Process Development at ICI for a number of years before joining the Technology Development Team at North West Water, now United Utilities.

His current role involves the evaluation and development of processes for the sustainable treatment of wastewater and recycling or disposal of sewage sludge. Presently he is the Technology Development Manager for United Utilities and was awarded the MBE in the Queen’s birthday honours in 2009 in recognition of his services to the water industry.

About END-O-SLUDG

END-O-SLUDG aims to provide innovative system solutions for sustainable sludge management in Europe. END-O-SLUDG has received funding from the European Union Seventh Framework Programme (FP7-ENV.2010.3.1.1-2 ENV) under grant agreement n° 265269. The co-ordination of high quality research ensures that END-O-SLUDG will contribute the necessary supporting economic and life cycle assessment of the resulting gains in energy efficiency and conversion of renewable carbon, together with an implementation strategy based on a product mix with optimal value. END-O-SLUDG will inform an important step change that will contribute to achieving more secure and sustainable sludge treatment and management practices in Europe. A dedicated website to support the project has now been launched. The website hosts information on the project aims, news updates and event listings.

For more information visit www.end-o-sludg.eu

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Published: 10th Sep 2011 in AWE International