Q&A Wastewater AD Industry
1. Can you give me an overview of the range of the water/waste analysis/industry sectors you are involved with?
HRS Heat Exchangers provides heat exchangers, pasteurisers and Digestate Concentration Systems to wastewater anaerobic digestion (AD) facilities. HRS’ customers and end-users include Southern Water, Severn Trent Water, Welsh Water, Yorkshire Water, Anglian Water, Northumbrian Water, Wessex Water and Thames Water.
2. What are the key external industry trends that are driving development or demand for water/waste analysis services or solutions?
Over the years, different wastewater companies have adopted different approaches to sludge treatment, but there is now a trend towards anaerobic digestion (AD) and away from incineration. While the number of AD facilities treating sewage sludge may be growing steadily, rising just 12% from 2010-2015, these 159 plants actually generated over 25% more power over the same period*. This can be largely attributed to efficiency improvements within the wastewater sector, which is renowned for its approach to innovation, often setting the standard for operational efficiency within the entire AD industry.
In addition, Ofwat’s recent Water 2020 report is set to kick-start a market for treated sewage sludge. The regulator hopes to encourage markets between operators and also develop synergies with the wider organic waste market.
3. What are the issues/challenges for companies when it comes to developing or water/waste analysis solutions?
When the Renewables Obligation (RO) was introduced in April 2002 (April 2005 in Northern Ireland), sewage sludge AD plants were well placed to become amongst the first facilities accredited under the system. The RO closed to all new generating capacity on 31 March this year, but what is less widely appreciated is that, for these first generators, the default accreditation period of 20 years means that the majority of sewage sludge AD plants will lose their eligibility for ROCs in 2027, despite the fact that the RO itself will continue up to 2037. In effect, these plants have just ten years left of continued subsidy.
In addition, anaerobic digestion technology has moved on considerably over the last 15 years. As a result, many of the original wastewater AD facilities are now looking to upgrade, switching from producing electricity to biomethane in order to take advantage of the Renewable Heat Incentive instead, particularly given the positive outcome of last year’s consultation on the RHI scheme.
Small-scale efficiency improvements have also been important in helping to boost the water AD sector’s energy output, and upgrading an existing plant is an ideal opportunity to improve its overall efficiency, to maximise both energy production and overall greenhouse gas savings.
4. Are there any advancements in technology or research on the horizon that could transform this?
One of the easiest ways to improve efficiency is by recapturing heat. Heat exchangers represent the best way of doing this, having a much lower heat requirement than tanks with heating jackets (up to half of that of some systems). In fact, a well designed heat exchanger system could recover and reuse 40% of the heat produced by a wastewater AD plant. But not all heat exchangers are equal and one size does not fit all – the AD industry covers many different sectors processing a variety of feedstocks from food waste to farm residues, to liquid by-products. One range proving popular with wastewater AD operators is the DTI series from HRS, which is a double tube heat exchanger. The inner tube is corrugated to ensure improved heat transfer performance and superior resistance against tube wall fouling, resulting in reduced maintenance periods. In addition, the tube in tube design is suited to the processing of fluids with large particles, making it particularly suited to sewage AD plants.
But having recovered this valuable heat, what are water companies doing with it? With a typical 1.5 MW wastewater AD plant producing as much as 40,000 tonnes of liquid digestate each year – bringing significant economic and logistical challenges associated with its storage and transportation – many operators are using their surplus heat to improve their digestate management systems. After all, if it isn’t concentrated, the volume and consistency of digestate can quickly become a costly bottleneck in plant efficiency.
Using surplus heat to separate water from digestate by concentration can reduce the overall quantity of digestate by as much as 80%, greatly lowering the associated storage and transport costs. A well designed system, such as HRS’ Digestate Concentration System (DCS), includes measures to retain the valuable nutrients in the digestate, while the evaporated water can be condensed and returned to the front end of the AD process, reducing the amount of energy and water used. After concentration, the treated digestate dry solid content can be as much as 20% (often a fourfold improvement), making it much easier, and cheaper, to transport and handle.
By improving the efficiency of their wastewater AD plants, many of the UK’s water companies are enjoying increased ROI, helping to make their service more affordable and sustainable; particularly important as the water industry uses around three per cent of all the electricity generated in the UK.