HpHLancaster House, Lancaster Way, Ermine Business Park, Huntingdon, Cambridge PE29 6XU

Part of the Anglian Water Group. Reg No. 06426222

Revolutionising anaerobic digestion technology

If you would like to understand more about how HpH could work for your plant, or would like any further information on the process, please email

info@hph-technolgy.com

Introducing HpHHpH Technology is the new biological hydrolysis technology brought to you by the experts at Anglian Water.

Responsible for processing around 150,000 tonnes of dry solid sewage sludge per annum, Anglian Water identified an opportunity to develop a new hydrolysis technology that could maximise a plant’s biogas production even further than existing anaerobic digestion technology – to reduce not only operating costs but also the plant’s carbon footprint.

The result, HpH Technology, is now installed across four Anglian Water sludge treatment centres. Results to date have produced an average of over 1 MWH/TDS of renewable electricity from the biogas produced via its fleet of CHP engines – while producing a high-quality enhanced treated biosolids product for use in agriculture as a soil conditioner.

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The process HpH is suitable for any operator producing over 10,000 tonnes of dry solid sludge per annum. The thermal energy to heat the sludge is produced by hot water and steam: typically this is recovered heat from the combined heat and power (CHP) engines that generate renewable electricity from the biogas. When combined with CHP, the engine cooling jacket water energy is recovered by heat exchange to heat the feed sludge in the receiving tank. Exhaust gases from the engines are used to raise steam, and this recovered heat is injected as steam into the sludge to raise the temperature for the pasteurisation step. The HpH technology can operate at a high organic loading rate and can be added upstream of existing digesters on site, which:

• reduces capex costs for operators

• separates the digestion into two process phases (hydrolysis and methanogenesis), and

• allows existing digesters to operate at a significantly increased organic loading rate.

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How it worksHpH Technology can be broken down into three stages:

THICKENED SLUDGE

FEED TO HpH

Stage 1 Stage 2 Stage 3

HEATINGTANK 42ºC

FEED TOMESOPHILICDIGESTERS

HYDROLYSIS

TANK 38 - 42ºC

PASTEURISATION

TANK 155ºC

PASTEURISATION

TANK 255ºC

Stage 1The initial heating tank

This tank receives thickened raw sludge at 7-9% dry solids. The sludge is heated to an adjustable set-point temperature, typically 40°C. This is by heat exchange with a low-temperature hot water (LTHW) loop using recovered heat from the cooling water jackets from CHP engines.

Sludge from the heating tank is fed forward to the pasteurisation stage.

Stage 2Pasteurisation

The sludge is fed into two tanks. These are configured in parallel, and alternately filled, heated and emptied. So, as one pasteurisation tank is filling and heating, the other tank is in hold mode, holding its batch at a temperature of >55°C for >5 hours. The sequence is a six-hour heat and fill cycle, followed by a five-hour hold and a one-hour transfer – therefore each pasteurisation tank processes four batches per day. Stage 2 allows for the sludge to be pasteurised to achieve an enhanced treated biosolids product.

Stage 3Biological pre-treatment

This is where the hydrolysis and acidification take place. Sludge exiting the tank contains high volatile fatty acid (VFA) concentrations, which conditions sludge for biogas conversion downstream in the anaerobic digester. The hydrolysis tank is held at a temperature of 42°C by cooling a heating heat exchanger. The retention time (up to 2 days at maximum throughput) can be adjusted by the operator to control the rate of hydrolysis. The plant control system automatically adjusts the hydrolysis tank level in response to changes in the feed volume to maintain the set point retention time.

Features and benefits of HpH

HpH Technology’s operational benefits FlexibilityA major benefit for the operator is being able to deal with variations in load, volume and sludge quality. The operator can also adjust the retention and temperature within the hydrolysis stage to reduce the risk of foaming in the process. And the process can be adhered to specific site conditions.

Results • Operational for five years, HpH has been implemented across four Anglian Water sites and these are now four of

our top five performing. On average they produce over 1 MWH/TDS which is 12.5% higher than the next best performing advanced anaerobic digestion facility within the Anglian Water portfolio.

• HpH Technology pasteurises the sludge in Stage 2, enabling an enhanced treated standard biosolids product to be recycled.

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Features Benefits

Produces higher gas yield compared to other hydrolysis technologies

• Combined with CHP, HpH produces energy for running the plant – reducing both operating costs and carbon footprint

Fewer tanks compared to alternative biological hydrolysis technologies

• Lower capex cost for installation• Less space required onsite• More flexibility within the plant• Compact footprint within site

Minimal fossil fuel • Combined with CHP, sufficient heat can be recovered

from the engines to heat the process• Lower cost• Lower carbon footprint

Steam generator of heat• No requirement for an HpH annual shutdown under

PSSR regulations• Lower temperature than other technologies therefore

lower H&S risk and lower cost to operate

Ability to control the plant remotely through SCADA

• No need for 24/7 onsite cover• Ability for offsite digesting

No odour • Contained system, linked to AD biogas network• Complies with regulatory guidelines

Higher load feed into tanks – flexibility of feed

• Built-in flexibility to deal with variations in load, volume and sludge quality

Operational flexibility – the operator can set the retention time and temperature in the

hydrolysis tank

• Operator can reduce heating temperature at hydrolysis stage and ensure hydrolysis is optimised. This improves process stability and reduces the risk of foaming

• Process can be unique to specific sites – dependent on the sludge streams