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CAMBI Thermal hydrolysis Sludge Treatment: Medium to large-scale application
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CAMBI Thermal hydrolysis Sludge Treatment: Medium to large-scale application

The Norwegian company Cambi AS has developed and installed worldwide its unique “steam explosion” thermal hydrolysis process (THP), a technology for the treatment of wastewater treatment plant (WWTP) sludge prior to anaerobic digestion
by Drs. Lex Menco
CAMBI Thermal hydrolysis Sludge Treatment: Medium to large-scale application
The Norwegian company Cambi AS has developed and installed worldwide its unique “steam explosion” thermal hydrolysis process (THP), a technology for the treatment of wastewater treatment plant (WWTP) sludge prior to anaerobic digestion. Cambi THP optimizes biogas production and has many other benefits, which are described below, along with a look at some real-life experiences at medium and large-scale facilities.
 
 
Introduction
 
  • Established in 1989. Offices in Norway, Denmark, UK, and USA
  • Global industry leader in our segment (advanced biogas production from sludge and biowaste) with 26 plants worldwide (530,000 metric tons DS/y) and 5 plants under design/construction
  • Treatment capacity for sludge and biowaste equivalent to 26 million people and 768,000 metric tons of DS (dry solids)/year
  • Production capacity of 1,900 GWh thermal energy (biogas) and 760 GWh electrical energy, when using gas engine cogeneration.
  • Green energy production replaces760,000 tons of fossile CO2 emissions. Avoidance of methane emissions from landfills, less transport, etc. comes in addition (about 2.5 mill tons CO2 equivalents)
  • Cambi THP is an eco-friendly “Paradigm-shifting Technology”, dramatically improving design and operations of biogas plants worldwide.
 
The use of the thermal hydrolysis process in sludge treatment for WWTPs presents some major advantages in terms of energy, public health and environmental protection. Medium-sized plants can be converted, with the import of sludge from other nearby plants, into strategic sludge treatment centers.  Here biogas production from anaerobic digestion is maximized using existing capacity, generating a pasteurized sludge with high dry solids content. The generation of electricity from renewable sources, produced from biogas, allows the energy costs of the WWTP plant itself to be reduced and the WWTP may even have surplus energy production.
 
 
Thermal hydrolysis “Steam Explosion” process
 
The thermal hydrolysis process (THP) patented by Cambi AS is a pre-treatment of sludge combined with anaerobic digestion. Cambi THP works by dissolving and disintegrating sludge using pressure and temperature. Primary, biological or mixed sludge is pre-dewatered and introduced into a reactor where the direct application of saturated steam hydrolyzes and changes its internal structure. This reduces sludge viscosity and increases its biodegradability and shortens hydraulic retention time. The thermal hydrolysis increases the production of biogas in digestion, reduces the volume needed for digestion, increases the dryness of the final dewatering of digested sludge, eliminates odors, and provides pasteurized final sludge Class A, a valuable and natural fertilizer. 
 
 
 
The thermal hydrolysis is part of a wastewater treatment plant as a pre-treatment prior to digestion  
The thermal hydrolysis is part of a wastewater treatment plant as a pre-treatment prior to digestion
 
 
The Cambi thermal hydrolysis process disintegrates the cellular structure of the bacteria in bio-sludge by solubilizing exopolymers (proteins protecting the bacteria), producing an easily digestible product. This is done by means of a temperature of 165 degrees for 20 minutes, at 6 bar, followed by a sudden drop in pressure, resulting in so-called “steam explosion”, unique among all thermal hydrolysis technologies available in the market. The steam explosion tears cells and fibers apart, further improving the disintegration effect.
 
Figure 1: Thickened mixed sludge without treatment , Photo = 400x550 micras
Figure 1: Thickened mixed sludge without treatment , Photo = 400x550 micras


 

Figure 2: Thickened mixed sludge, with thermal hydrolysis at 165ºC in 20 minutes – without pressure drop
 
Figure 2: Thickened mixed sludge, with thermal hydrolysis at 165ºC in 20 minutes – without pressure drop
Figure 3: Thickened mixed sludge, with “steam explosion” after hydrolysis process at 165ºC and 20 minutes.
 
The Cambi hydrolysis system allows maximum disintegration of the cells and it enhances the production of biogas in the subsequent anaerobic digestion and allows high loads in digesters. In the Cambi plant at Thames Water’s Chertsey WWTP (London, UK) our process operators have tuned the plant to the exceptional capacities of up to 7 kg VS m3/day and retention times as low as 10-12 days.
 
 
The use of Cambi thermal hydrolysis achieves the following:
 
  • Generates more energy (higher biogas production).  
 
  • Reduces the final amount of sludge. It improves sludge dewatering up to 40% DS.
 
  • Treat organic food wastes and edible fats and oils
  • Ensures sludge pasteurization, i.e. a pathogen-free sludge
 
  • Produces a stabilized an compost-like product, with 70% decrease in odour[1].
 
  • Increases the speed and capacity of digestion (less digestion volume).
 
  • Reduces carbon footprint.
 
 
A medium-scale sludge treatment center: The case of Lindum (Norway).
 
Cambi hydrolysis system for medium capacities (15-40 dry tonnes per day) is based on 6 m3 reactors. The system is modular, permitting its expansion up to 3 reactors. For lower sludge productions, Cambi has developed an even more compact plant (see press release, IFAT). The whole system of hydrolysis is closed without leakage of odor and energy loss.
 
Drammen (Norway) has recently installed a medium-scale sludge treatment center for dewatered sludge from 9 municipalities (18,500 wet t/year), fats from the food industry (3,000 t/year), sludge from septic tanks (7,000 t/year) and other biological substrates (2,000 t/year). The project’s main objective was to generate biogas and produce a safe product. Investment, operation and maintenance costs were also considered. The use of the 2 reactor Cambi B6 hydrolysis system in Lindum allows the generation of 16 GWh/year of biogas and 12,000 t/year of dewatered biosolids product used as fertilizer. This plant shows that it is possible to develop sludge treatment centers on a medium scale where you can optimize the energy efficiency of equipment by importing sludge from outside the WWTP.

Figure 4: Cambi hydrolysis system with three reactors of 6 m3.
 Figure 4: Cambi hydrolysis system with three reactors of 6 m3.

THP at Lindum under construction
Figure 5: THP at Lindum under construction
 
 
Large-scale thermal hydrolysis: The case of DC Water (Washington DC, USA)
 
The District of Columbia Water and Sewer Authority (DC Water) in its Blue Plains plant treats a sewage flow of 370 MGD (15 m3/s), the largest wastewater treatment plant with advanced treatment in the U.S. DC Water will be the first to build a thermal hydrolysis plant in North America. This thermal hydrolysis plant will be the largest in the world and will be built by Cambi AS in Washington DC, with start-up in 2014. The plant will treat up to 450 t DS sludge/day, and 149,000 t DS sludge/year. Only four digesters, each with a 14,400 m3 capacity, will be built. The biogas will go to a cogeneration facility which will cover the entire steam needs of the THP process itself and generate 13 MWe of power with initial savings of USD 20 million/year from the energy produced, the reduction of the amount of biosolids to agriculture, and by avoiding the use of lime. The carbon footprint will be reduced by about 60,000 t CO2/year. The final dewatered biosolids quantity will be reduced from 500,000 t/year to 200,000 t/year, with safe application to agriculture as a pathogen-free product with no odor problems. The project demonstrates the effectiveness of feeding the digesters at a digester load of more than 4 kg VS/m3, twice that of conventional digestion, with low retention time in the digesters. The Cambi THP consists of 4 lines of equal capacity.




Figure 6: Overview of Project of Cambi Thermaly Hydrolysis and digestion in DC Water (Washington – USA)
Comparative hydrolysis parameters vs. conventional digestion
 
The advantages of applying thermal hydrolysis are summarized in the table below, which compares conventional digestion values with thermal hydrolysis and digestion for mixed sludge.


 
  
 
Conclusions
 
From 1996 to the present, Cambi thermal hydrolysis units installed and under design/construction worldwide have a capacity of 768,000 t DS/year, to serve a population equivalent of more than 26 million. It is a fully proven technology for small to large scale anaerobic digestion plants.
 
With the Cambi thermal hydrolysis process you can:
 
  • Improve the energy efficiency of the WWTP. More biogas = more power.
  • Increase the productivity of your digester by 250%
  • Reduce the final volume of dewatered sludge by 40%
  • Treat organic food wastes and edible fats and oils
  • Obtain excellent stable Class-A type bio-solids, perfect for agriculture, with low odor, and without pathogen regrowth risk.
  • Eliminate or reduce the need for subsequent composting, thermal drying or incineration.
  • Have a smaller carbon footprint.
  • Have an installation that is reliable and robust with high availability and automation.
 
 
Lex Menco M.Sc. BioChemistry, Microbiology
CEO Relex Process Consultancy



[1] “[Cambi] Reduced biosolids odor production by 70% - Biosolids produced from Cambi-MAD reactors were consistently less odorous and of a higher solids concentration than those of Control-MAD”, Virginia Tech (Dr. Novak) paper on Cambi choice by DCWATER, US Biosolids Conference, 2008
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