Continuous Thermal Hydrolysis Research Articles

Environmental impact and economic benefit evaluation of sewage sludge treatment technologies

In order to evaluate the environmental and economic performance of continuous thermal hydrolysis (CTH) of sludge disposal, we compare the CTH with three traditional technologies including anaerobic digestion, aerobic composting and dry-incineration. This study uses life cycle assessment (LCA) to assess their environmental impact of the above technologies, and selects ten characteristic indicators from e-Balance analysis software for quantification. We also adopt the cost-benefit ratio (B/C) to evaluate the technologies’ economic performances, and come to conclusion that the larger the value is, the more economically feasible it will be. The results show that, as a new sludge disposal technology, CTH has the best performance in both environmental and economic aspects, while dry-incineration and anaerobic digestion have the worst results in environmental and economic aspect respectively. Although sludge compost has a moderating effect on global warming, it could also be potentially toxic. Nevertheless, the use of raw materials and energy contributes significantly to the environmental impact of each scheme.

Batch vs. Continuous Thermal Hydrolysis — Which is right for you?

Batch vs. Continuous Thermal Hydrolysis — Which is right for you?

Ingenious mixing and separation of sludges results in cost effective continuous Thermal Hydrolysis Process (cTHP)

Ingenious mixing and separation of sludges results in cost effective continuous Thermal Hydrolysis Process (cTHP)

ASI:Dunaliellamarine microalgae to drop-in replacement liquid transportation fuel

Microalgae are a promising biofuels feedstock, theoretically yielding concentrations of triacylglycerides (TAGs) per unit area that are far higher than traditional feedstocks due to their rapid growth. Dunaliella is particularly advantageous as a feedstock because it is currently commercially mass cultured, thrives in salt water, and has no cell wall. Fourteen strains of Dunaliella have been investigated for growth rates and lipid production in mass culture and tested for enhanced lipid production under a range of environmental stressors including salinity, pH, nitrogen and phosphorus limitation, and light regime. The nuclear genome has been sequenced for four of these strains, with the objective of increasing carbon flux through genetic engineering. Electroflocculation followed by osmotic membrane rupturing may be a very energy and cost efficient means of harvesting the lipid bodies from Dunaliella. A technically feasible and scalable thermo-catalytic process to convert the lipids into replacements for liquid transportation fuels has been developed. The lipids were converted into long-chain alkanes through continuous thermal hydrolysis followed by fed-batch thermo-catalytic decarboxylation. These alkanes can be reformed into renewable diesel via conventional catalytic hydrocarbon isomerization reactions to improve cold flow properties, if desired. © 2013 American Institute of Chemical Engineers Environ Prog, 32: 916–925, 2013

Moving towards an energy neutral WWTP – the positive impact of ExelysTM continuous thermal hydrolysis in achieving this goal

There is an increasing need for large wastewater treatment plants to generate as much electricity as possible from biogas. This not only ensures significant operational cost savings, but also improves the environmental profile of the plant. Enhanced digestion through the use of the ExelysTM continuous thermal hydrolysis process has the potential to help a large wastewater treatment plant move towards electrical energy neutrality. This article aims to use Csepel waste water treatment plant (WWTP) (3.5 million PE) in Budapest, Hungary as a case study to investigate the potential advantages an ExelysTM-DLD process could provide. The results indicate that despite already having an effective and efficient digestion process, through implementation of the ExelysTM-DLD process, Csepel has the potential to cover 65% of its total electrical needs from biogas. This is 33% more than the current situation. This also leads to a significantly improved NPV for the ExelysTM-DLD scenario, an important factor for the operator of a large wastewater treatment plant. When looking to the future, through the optimisation of the wastewater treatment process and the application of the ExelysTM-DLD, Csepel WWTP has the potential to be completely electrical energy neutral. This would be a significant financial advantage as electrical prices rise and carbon taxes are enforced.

Continuous thermal hydrolysis and anaerobic digestion of sludge. Energy integration study

Experimental data obtained from the operation in a pilot plant are used to perform mass and energy balances to a global process combining units of thermal hydrolysis (TH) of secondary sludge, anaerobic digestion (AD) of hydrolysed secondary sludge together with fresh primary sludge, and cogeneration from biogas by using a gas engine in which the biogas produces electricity and heat from the exhaust gases. Three scenarios were compared, corresponding to the three digesters operated: C (conventional AD, 17 days residence time), B (combined TH + AD, same time), and A (TH + AD at half residence time). The biogas production of digesters B and A was 33 and 24% better, respectively when compared with C. In the case of the combined TH + AD process (scenarios A and B), the key factors in the energy balance were the recovery of heat from hot streams, and the concentration of sludge. The results of the balances showed that for 8% DS concentration of the secondary sludge tested in the pilot plant, the process can be energetically self-sufficient, but a fraction of the biogas must by-pass the gas engine to be directly burned. From an economic point of view, scenario B is more profitable in terms of green energy and higher waste removal, while scenario A reduces the digester volume required by a half. Considering a population of 100,000 inhabitants, the economic benefit is 87,600 €/yr for scenario A and 132,373 €/yr for B. This value can be increased to 223,867 €/yr by increasing the sludge concentration of the feeding to the TH unit to a minimum value that allows use of all the biogas to produce green energy. This concentration is 13% DS, which is still possible from a practical point of view. Additional benefits gained with the combined TH + AD process are the enhancement of the digesters rheology and the possibility of getting Class A biosolids. The integration study presented here set the basis for the scale-up to a demonstration plant.

Hydrocarbon fuels from vegetable oils via hydrolysis and thermo-catalytic decarboxylation

Conversion of canola oil to normal alkane hydrocarbons was investigated using sequential reactions: continuous thermal hydrolysis and fed-batch thermo-catalytic decarboxylation. The free fatty acid (FFA) intermediate product from hydrolysis was quantified using GC–FID, which showed 99.7% conversion and the following components: palmitic, oleic, linoleic, linolenic, stearic, arachidic and behenic acids. The FFA was saturated then decarboxylated at an average rate of 15.5mmoles/min using a 5% Pd/C catalyst at 300°C. Approximately 90% decarboxylation conversion to n-alkanes was achieved within 5h of the reaction. The resulting mixture of n-alkanes can be readily converted into renewable diesel using isomerization to improve the cold flow properties of the fuel.

Successful application of the first EXELYS™ continuous thermal hydrolysis system in an operational WWTP in Denmark

Successful application of the first EXELYS™ continuous thermal hydrolysis system in an operational WWTP in Denmark

Successful application of the first EXELYS™ continuous thermal hydrolysis system in an operational WWTP in Denmark

Successful application of the first EXELYS™ continuous thermal hydrolysis system in an operational WWTP in Denmark

An optimal solution to achieve the energy neutral Waste Water Treatment Plant

Many recent studies have shown processes or models to minimize the energy consumption on a municipal wastewater treatment plant (WWTP) in operation. Today the main drivers are the energy and CO2 reduction. On existing plants, the potential success of achieving the Energy neutral WWTP depends on the effluent guarantees demanded and the eventual additional carbon sources on the digesters. Veolia has now developed a tool to estimate the energy consumption and the CO2 impact to select the appropriate treatment lines (water and sludge) up front at the project stage. The real challenge is to cover the needs of the plant without external carbon sources added to the digester. At the project stage, before the bid of the WWTP, due to time constraints only few comparisons can be performed to predict the energy consumption and CO2 impact and provide the best solution to reach to the energy neutral plant as electricity wise. One conclusion of the study is that, the raw water characteristics and the effluent guarantee has a great impact on the possibilities to reach the target. Furthermore, working on reducing the power consumption and on increasing the biogas production for example by a continuous Thermal hydrolysis is a good way to go towards self sufficiency.

Maximizing Energy Efficiency and Biogas Production: EXELYS™ – Continuous Thermal Hydrolysis

Maximizing Energy Efficiency and Biogas Production: EXELYS™ – Continuous Thermal Hydrolysis

Maximizing Energy Efficiency and Biogas Production: Exelys™ – Continuous Thermal Hydrolysis

Maximizing Energy Efficiency and Biogas Production: Exelys™ – Continuous Thermal Hydrolysis

Continuous thermal hydrolysis and energy integration in sludge anaerobic digestion plants

A thermal hydrolysis pilot plant with direct steam injection heating was designed and constructed. In a first period the equipment was operated in batch to verify the effect of sludge type, pressure and temperature, residence time and solids concentration. Optimal operation conditions were reached for secondary sludge at 170 degrees C, 7 bar and 30 minutes residence time, obtaining a disintegration factor higher than 10, methane production increase by 50% and easy centrifugation In a second period the pilot plant was operated working with continuous feed, testing the efficiency by using two continuous anaerobic digester operating in the mesophilic and thermophilic range. Working at 12 days residence time, biogas production increases by 40-50%. Integrating the energy transfer it is possible to design a self-sufficient system that takes advantage of this methane increase to produce 40% more electric energy.