| Cambi's Thermal Hydrolysis process plant at DC Water's Blue Plains Advanced Wastewater treatment plant in Washington, US |
The new wastewater treatment plant (WWTP) in Vigo, northwestern Spain has awarded Norwegian firm Cambi a contract to eventually process 22,000 tons of dry solids per year.
This is the company’s first contract in Spain for its technology based on its thermal hydrolyses (THP) process.
Vigo’s 690,000 m3/day facility secured €112 million from the EU regional and cohesion funds, with the city council putting up an additional €13 million.
Wastewater from more than 800,000 inhabitants living around the Vigo area will be treated by the facility, which is scheduled to start operating in 2014, with an extension for increased capacity planned in 2016.
The WWTP will replace a previous facility built over 15 years ago. According to the European Parliament, the malfunctioning of this facility has led to thousands of litres of untreated wastewater being spilled into the Vigo estuary with “serious environmental repercussions”. As a result, numerous complaints were lodged with EU institutions on this matter.
The quantity of sewage sludge, an inevitable by-product of wastewater treatment, is increasing worldwide. Once treated, sewage sludge becomes a valuable source of nutrients, known as biosolids, which is used in a number of outlets.
Prior to energy recovery, energy can be extracted from sludge upstream by processing it via anaerobic digestion. This produces a methane-enriched biogas which can be converted to electricity and heat using co-generation, or converted into biomethane which acts as a substitute for natural gas.
Typically, anaerobic digestion of 10,000 tonnes of dry solids per annum (based on European data) produces between 0.5 and 1.0 MW electricity depending on sludge type.
Biogas from the Vigo plant will be used to produce electricity and biosolids from the process will be used as a certified fertilizer in agriculture.
THP Thermal hydrolysis (see WWi video) is a two-stage process combining pressure cooking followed by a rapid decompression. This combined action sterilizes the sludge and makes it more biodegradable, which improves digestion performance. Sterilization destroys pathogens in the sludge.
Although the Vigo contract is Cambi’s first THP project in Spain, the company has several reference sites in Norway, the UK and Australia. One of the world’s largest facilities in Davyhulme, UK, is one of the firm’s major projects (see WWi article).
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