We aim to run our business as efficiently as possible so we're always trying to reduce our use of natural resources, minimise waste and deliver efficient and effective operations for both today and in the future.
Sludge as a resource
Sewage sludge is a solid by-product of the wastewater treatment process, and it’s an energy rich resource with a relatively high calorific content which we use to generate renewable energy. We transport and treat 4.4 billion litres of sewage every day, and last year we produced around 373,800 dry tonnes of sludge.
Our sludge strategy continues to provide the framework for our sludge investment proposals, which include:
- Ensuring safe and sustainable recycling to give confidence to farmers and food producers but also to reduce our reliance on agricultural land by using other forms of treatment and energy generation
- Adopting treatment processes that will maximise the generation of renewable energy and minimise the volume of sludge produced.
Renewable energy from sludge
In 2018/19, we generated 281 GWh of our own electricity needs from sludge, the equivalent of over £32 million a year in energy savings. This has helped to make even better use of a valuable resource, reduce our carbon emissions and improve resilience by reducing our reliance on grid electricity.
We’ve been producing renewable energy at our larger sewage works since the 1930s using anaerobic digestion (AD) which helps offset the need to import electricity and natural gas from the grid and reduces carbon emissions. Biogas is produced which can be used as a fuel in our combined heat and power (CHP) engines to generate renewable electricity.
By investing in our infrastructure and using a combination of treatment methods and new technologies, we've been able to increase the amount of renewable energy produced from sludge. A key change in the way we manage our sludge during the current AMP has been to move towards advanced digestion using the Thermal Hydrolysis Process (THP). Using THP before anaerobic digestion helps break down the organic matter in the sludge into more accessible (digestible) compounds for the microbes in the anaerobic digesters to utilise. The microbes use these compounds more efficiently, which results in more biogas production. THP also reduces the amount of treated sludge which needs to be recycled to land. As well as expanding our use of advanced digestion, we are currently building a full-scale pilot plant to manage sludge by pyrolysis. In addition to fuel gas, char is produced which is a carbon-based and mineral-rich material.
Beneficial disposal of sludge
We’re committed to the beneficial use of sludge wherever possible. In 2018/19, we recycled 98.7 per cent of our treated sludge (biosolids) to agricultural land as a natural fertiliser. This provides essential nutrients and organic matter to the soil and avoids the use of man-made fertiliser to grow food crops. The remainder was used in land restoration projects as a bulk soil improver to help restore industrial land for future regeneration. ThamesGrow is a leading range of biosolid products produced by Thames Water for use in agriculture. This provides a more sustainable, cost effective and environmentally sensitive solution for farmers throughout the south east.
Our sludge disposal is 100% compliant with stringent requirements to assure the quality and safety of our biosolids and their safe use in agriculture. This includes the ‘Safe Sludge Matrix’, an agreement between water companies and the British Retail Consortium, which sets out guidance for the application of biosolids to crops and strict controls on the quality of sludge. We’ve achieved certification of our treated sludge under the Biosolids Assurance Scheme, a standard which all sewerage companies in the UK have adopted to ensure all biosolids meet a minimum standard quality.
The residual ash from our incineration treatment process is also put to beneficial use. Ash is used to create synthetic aggregate, which helps to avoid landfill; the extraction of natural resources and its associated carbon emissions. Read the case study to find out more information. In the future, by using Pyrolysis technology effectively, the volume of residual product (char) would be 84 per cent less than the volume of sludge entering the process. We hope to be able to recover even more nutrients, precious metals and carbon from this Char to contribute further to the circular economy.
Our supply community
How we buy products and who we buy them from can have a significant impact, not only on the efficiency of our operations, but on the environment and the communities we work within. We’re committed to more sustainable procurement and introduced a revised Supply Chain Sustainability Policy in 2018/19. It outlines our vision, values and a shared set of goals, to deliver real benefits to our customers and help us become a more sustainable business.
To be successful we must work in partnership with our supply partners who are encouraged to identify low carbon and waste reduction alternatives. For instance, during the procurement for waste tankering, we worked closely with our supply partners to introduce more efficient vehicle utilisation, as well as optimising journeys through computerised route planning. This comprehensive planning and increased efficiencies will reduce our carbon footprint. Specifically, we’ve been working with our on-site catering suppliers to reduce single-use plastic food packaging and have produced a diagram to help other companies make a start on tackling the plastics challenge. Take a look at our case study to find out more.
During 2018/19, we worked with c.3000 companies of varying size, spending c.£1.76 billion. Of these suppliers, we paid 90.5 per cent of all our invoices, totalling more than 160,000, in line with our agreed payment terms. On average we take 56 days to pay a supplier on receipt of a correct invoice. When setting up payment terms, we take into consideration the size and situation of our suppliers, particularly our small to medium sized suppliers. Where possible, we try to remain flexible and consider each supplier on a case-by case basis.
Our code of conduct covers our approach to business activities and how we work, providing a clear, ethical and legal framework for our employees, customers and stakeholders. All elements of our code of conduct apply to both our permanent and temporary employees, and our contractors and alliance partners have committed to follow the provisions of this code. Underpinning the code of conduct and in line with human rights principles, we have a range of policies covering health and safety, equality, diversity and inclusion, anti-corruption and bribery, human rights and modern slavery and honest and ethical behaviour. We also have a 24-hour Employee Assistance Helpline available and a robust whistle-blowing mechanism in place.
Innovation, research and development
Our research and development programme is designed to address technical needs across the range of water cycle activities, delivering innovative technical solutions aligned with business needs to address challenges and also provide specialist technical support to the business.
The development and application of new techniques and technology is an important part of our activities. We are a member of UK Water Industry Research (UKWIR) and participate and benefit from its research programme. The UKWIR research programme covers water, wastewater, sustainability, regulation, customers and asset management.
In addition, we carry out research and development in-house, including algae removal from raw water for increased resilience of supplies, deterioration of critical cast iron assets and low energy wastewater treatment processes. We increased our expenditure on research and development in 2018/19 which totalled £5 million (2017/18: £3.9 million).
View the full infographic.
The water and wastewater treatment cycle is an example of the circular economy in action. We’re committed to become more efficient, reduce waste, increase how much we recycle and re-use and make wider contributions to the circular economy. For example, we put 100% of the sewage sludge we treat to beneficial use either by producing bio-gas to generate renewable electricity or applying it to farmland as natural fertiliser. The ash that is produced following the incineration process is now being used to create aggregate instead of going to landfill at a high environmental and financial cost. Read the case study to find out more.