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should see increased growth in this market as air regulations tighten in the U.S. and worldwide. • Biogas Utilization Via CHP Or Direct Gas Grid Injection Depends On A Number Of Factors Decisions on whether the produced biogas should be utilized via CHP or direct gas grid injection should be made through a high-level financial analysis which takes into account the capital costs, time-value of money, and the generated annual revenue. Factors to be considered include fuel quality, local circumstances, energy costs, monetary incentives available, and the time-value of money. Naturally, high electricity costs favor CHP, and high gas prices make grid injection a viable option. In the U.S., electricity and gas prices are lower than in Europe. • Sludge Pretreatment Technologies Are Key To Unlocking Additional Energy Sludge pretreatment technologies break up the bacterial cell walls and release the cell's contents, thus unlocking all the additional energy within the cells. Pretreatment technologies include thermal hydrolysis, ultrasonic, mechanical, chemical, and electroporation pretreatment methods. Depending on which technology is utilized, advantages of pretreatment include sludge sterilization, sludge volume reduction, and process improvements, such as enhanced sludge digestibility and dewaterability and improved biogas yields. Because of growing sludge disposal costs, increasing energy costs, and tightening regulations, it appears pretreatment can offer an effective and viable solution to these issues. • Cambi's Thermal Hydrolysis Process (THP) Is Dominating The Sludge Pretreatment Market Each sludge pretreatment technology type has varying degrees of success and market infiltration. BlueTech concludes that the most dominant pretreatment technol- ogy currently appears to be Cambi's THP process. This technology is very effective at essentially "pressure cook- ing" the sludge, which results in a breakdown of the cell walls and a release of the extra energy within the cells. The result is a more digestible sludge with higher bio- gas yields and decreased sludge volume, thus reducing sludge disposal costs. Cambi's THP process also steril- izes the sludge to yield a Class A biosolid. Cambi's THP technology is currently installed in 29 plants worldwide (total installed capacity: 787,740 total dissolved solids [TDS]/year), and is a good example of a dis- ruptive technology mak- ing inroads into the main- stream market. Recent entries into the U.S., Spanish, and Swedish markets put Cambi in an ideal position to fur- ther grow and dominate this market. Opening the pretreatment market also paves the way for oth- ers to follow, such as OpenCEL focused pulse technology. Figure 1 shows Cambi's growth worldwide since its foundation in 1996 to 2013. • Co-Digestion Proves To Be Problematic In Practice Co-digestion appears to be an exceptional prospect: a waste management solution for high-energy food waste and FOG combined with a synergistic benefit to the sewage sludge digestion process that results in increased energy production. However, co-digestion proves to be challenging in reality. Numerous barriers exist to its application in WWTPs. Lack of clarity about post-digestion disposal regulations, waste collection methods, de-packaging and pretreatment of the waste, and guaranteed digester capacity into the future are hindering co-digestion from becoming a standard practice in WWTPs. Finally, although several barriers for biogas-to-energy exist, such as lack of capital investment, operational challenges, and technical issues (e.g. high energy use), none appear to be insurmountable. These barriers could be overcome with a combination of efforts. Detailed financial calculations could address and give confidence to prove the economic viability of such sludge-to-energy projects, and operational challenges and technical issues could be addressed with increased research and technological development. In summary, a combination of efficient CHP technologies, pretreatment technology, and co-digestion can significantly improve the process operations of WWTPs through a combination of increasing energy generation and efficiency, enhancing overall sustainability, and reducing final sludge volumes and overall operational costs. Sludge-To-Energy wateronline.com ■ Water Online The Magazine 22 Aoife Moloney, water technology market analyst for BlueTech Research, has 10 years of experience in process control and optimization, auditing, and implementation of process improvements at wastewater treatment plants. Moloney recently completed a master's degree in civil engineering (energy and environmental) at the Cork Institute of Technology. Figure 1. Cambi thermal hydrolysis growth worldwide (Source: Provided by Cambi to BlueTech® Research) 2 0 _ V E R T _ 0 2 1 4 E Z i n e _ B l u e T e c h _ D G . i n d d 2 20_VERT_0214 EZine_Blue Tech_DG.indd 2 1 / 3 1 / 2 0 1 4 1 : 0 8 : 1 9 P M 1/31/2014 1:08:19 PM