Helea®: Frequently asked questions

Helea is a simple and reliable three stage process, involving heat recovery, pasteurisation and biological hydrolysis. Effective integration of these steps with specially developed process monitoring and control features have resulted in industry-leading levels of availability, safety, flexibility and energy efficiency. Helea dramatically increases biogas production and reduces a plant’s carbon footprint through the generation of renewable power and the efficient use of surplus energy for heat generation. It transforms the remaining biosolids into soil conditioner to use safely in agriculture.

Helea augments the performance of anaerobic digestion in three main ways:

• It separates sludge digestion into two phases (hydrolysis and methanogenesis), enabling the downstream digesters to break down more organic solids and produce increased levels of biogas
• It produces a safe, pathogen free, class A product suitable for recycling to agriculture
• It produces a final product that can be dewatered more readily thus reducing associated transportation costs 

Helea typically achieves all the above  at lower CAPEX and OPEX than any of its rivals  making it the simplest, cheapest, and most sustainable way to pasteurise and hydrolyse sludge.

Helea is three stage process integrating heating, pasteurisation, and biological hydrolysis into] an optimised configuration ahead of anaerobic digestion. Helea increases the production of gas from the downstream anaerobic digestion process, reduces the required digester volume, and decreases the volume of biosolids to be handled and transported off site. Overall, Helea results in significantly lower CAPEX and OPEX than conventional digestion.

At digestion plants designed to convert biogas into electricity, Helea has been proven to consistently achieve a net energy yield of 1 MWhe for each tonne of dry solids processed. While this figure is comparable to a thermal hydrolysis plant (THP), the net energy yield is much higher because Helea requires 70% less steam and no support fuel.

The answer is no. Although it is fair to say that Helea requires larger tanks than its thermal hydrolysis counterpart, unlike THP, it does not require the provision of upstream sludge dewatering equipment, cake silos, and large heat exchangers to cool the high-temperature sludge prior to digestion. Seen holistically, the overall footprint is typically comparable to thermal hydrolysis.

Helea pre-treatment ensures that advanced anaerobic digestion delivers high-quality pathogen free biosolids with excellent sludge dewatering characteristics. As such, the product can be safely recycled as a nutrient-rich soil conditioner for agriculture under Class A biosolids certification scheme.

Because the THP process must be taken offline for up to two weeks per year to allow cleaning and statutory inspections to take place, downtime results in reduced plant capacity unless the client is willing to spend additional CAPEX and invest in multiple treatment lines.

Helea benefits from 100 % process availability and high reliability. As the process is not operated at high pressure, there is no need for annual scheduled downtime for safety checks. The process requires minimal maintenance and virtually zero downtime – neither the replacement of parts nor the cleaning of steam injectors, pumps, and heat exchangers has any impact on plant capacity. As with any digestion process, tanks must be removed from service once every 10-12 years to facilitate grit removal.

With its compact design and simple operation, Helea has proven to be more cost effective than alternatives when assessed for a range of plant sizes.

Helea is more sustainable and energy self-sufficient than THP. With no support fuel, higher energy conversion, more biodegradable return liquor loads, and minimal downtime, Helea results in significant sustainable capital and operational savings. In monetary terms, the OPEX benefit equates to a saving of £30–60 per tonne of dry solids compared to THP. That’s equivalent to £1M a year for a plant treating 20,000 tonnes of dry solids per year (TDS/pa).

Hydrolysis results in increased biodegradability of the sludge and more gas with Helea plants producing up to 20 % more biogas energy compared to conventional digestion alone. With the water industry moving towards sustainable ‘biomethane to grid’, low carbon heat recovery systems can be integrated into the process. This maximises biomethane flow to grid, delivering higher levels of efficiency and operational savings, enabling integration of modern low carbon heat recovery solutions, such as heat pumps, in place of CHP engines. This maximises biogas revenue, further progressing towards energy self-sufficient wastewater treatment.

Because the Helea process enables more methane to be extracted from the sludge as biogas, it reduces fugitive emissions of this powerful greenhouse gas from downstream processes such as digested sludge holding tanks, dewatering centrifuges, and cake storage areas. In addition, Helea contributes to circularity in wastewater treatment by producing a sanitised product that can be recycled to agriculture.

As Helea is a fully contained process, there are no emissions and no nuisance odours.

Helea’s patented batch pasteuriser meets all HACCP requirements and is guaranteed to provide a Class A enhanced biosolids product free of pathogens.

Since 2013 and 2014, Helea has been operational at four of Anglian Water’s sludge treatment centres. After a decade of operation, these plants continue to be Anglian Water's most efficient and reliable treatment facilities.

The three stages of Helea have been designed to maximise throughput and efficiency. Since time and temperature are key performance parameters, the pasteurisation tanks are operated as a batch system to ensure pasteurisation always proceeds to completion. Feeding, heating and emptying of the pasteurisation tanks are staggered to ensure a continuous flow of sludge across the pasteurisation stage. The biological stage of the process takes as little as 24-36 hours to complete and, because pasteurisation takes place at 55 °C, heating and cooling requirements are greatly reduced compared to the high-temperature THP process.

Helea’s three steps have been designed for maximum throughput and efficiency. The two pasteurisation tanks enable plants to operate this step continuously, and the biological stage of the process can take as little as 24 hours. Because the sludge only needs to be heated to 55 °C, heating and cooling times are greatly reduced compared to high-temperature short-time pasteurisation.

1. The first step is a heat recovery step and involves heating the raw sludge to approximately 40–45 °C, using hot water recovered from CHP engines (or generated by heat pumps).
2. After pre-heating, sludge is pumped forward to one of two pasteurisation tanks where steam is injected to raise the temperature to 55°C. Once the first pasteurisation tank is full, the sludge feed is changed over to the second pasteurisation tank where the steam heating cycle starts over again, while the sludge in the first pasteurisation tank is held at temperature for five hours to achieve pasteurisation.
3. Once pasteurised, the sludge is transferred to the hydrolysis tank operated at a retention period of typically 1.5 days to optimise hydrolysis and cooled to a temperature of 38-42°C before being pumped forward to the digesters.