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|Name of Technology||Anaerobic Digestion Process with Ozonation for Economically Feasible Energy Production from Municipal Sludge|
|Technology Owner||Hitachi Plant Technologies, Ltd.
Kurita Water Industries Ltd.
|General Description||In the conventional anaerobic sludge digestion, sewage sludge contains much inert organic matter which is not easily biodegraded, its digestibility (degradation ratio of organic matter in sludge) is low at around 50%, and biogas production rate is low. Consequently, digestion gas is not generally used for gas power generation.
This technology aims to reduce the amount of sludge to be disposed of by combining digestive promotion device using ozonation with conventional anaerobic digestion. The whole system will also be configured to reduce power generation costs, by generating power from increased digestion gas.
|Components of Technology||The major components of this technology are: (1) Anaerobic digestion tank, (2) Solid-liquid separator, (3) Ozonation equipment, (4) Digestion gas refiner, (5) Digestion gas power generator and (6) Dewatering equipment. These components have the following functions.
(1)Anaerobic digestion tank
Organic matter in fed sewage sludge is digested and converted to biogas. This technology can use existing equipment for this purpose.
There are two functions, the one is to separate solids and liquids for the mixture of part of digested sludge and fed sewage sludge to keep sludge concentration high in the anaerobic digestion tank. The other is to withdraw excess digested sludge, in which inorganic solids are more concentrated. The equipment consists of a centrifuge, coagulant addition device, etc.
Part of the digested sludge is ozonated to convert inert organic matter in the sludge to a biodegradable form. The equipment consists of a pre-aeration tank, ozonaton reactor, gas-liquid separator, ozone generator, deodorization equipment, etc.
(4)Digestion gas refiner
Hydrogen sulfide and siloxane in the digestion gas are removed with desulfurizing agent and siloxane adsorber (activated carbon) so that the power generator can use the digestion gas. This technology produces more digestion gas than the conventional system. However, the peak gas production rate is the same or less than that of the conventional system, by feeding uniformly sewage sludge to the digestion tank. Therefore, this technology uses existing desulfurization equipment. Regarding siloxane removal, equipment is newly installed according as the gas volume used for power generation.
(5)Digestion gas power generator
Power is generated using the digestion gas refined by the equipment described in (4) and a gas engine. The outputs of this equipment are electricity and heat (hot water or steam).
Excess digested sludge withdrawn with the centrifuge described in (2) is dewatered. This technology uses existing equipment.
Anaerobic digestion tank setup
|Features of Technology||This technology enhances solid degradation ratio of sewage sludge by combining ozonation and solid-liquid separation of digested sludge with conventional anaerobic digestion. In addition, sludge for disposal is reduced with lower water content of dewatered sludge, in which inorganic solids are more concentrated by centrifugal separation. This technology also increases the digestion gas production without receiving garbage or other non-sewage sludge biomass.
Meanwhile, the increased digestion gas production raises the economy of power generation from digestion gas, which is stabilized by incorporating siloxane removal and other digestion gas refininer.
In this technology, the whole system is configured so as to reduce power generation costs. Each component and equipment has the following features.
The equipment ozonates part of digested sludge, converts inert organic matter in the sludge to a biodegradable form, and then returns it to the digestion tank. Through these processes, higher digestibility and more digestion gas production than the conventional system are achieved.
Meanwhile, in the gas-liquid separator, waste ozone is separated from treated sludge, so the ozonation equipment prevents oxidant (waste ozone) from entering the digestion tank and detoxifies waste ozone through decomposition and deodorization processes for release to the atmosphere, thereby controlling safety.
Flowchart of ozonation equipment
(2) Solid-liquid separator
Case 1: mesophilic digestion process
Digestion tank setup
|Evaluation of Technology||
This technology was developed in the LOTUS Project (Lead to Outstanding technology for Utilization of Sludge Project) and evaluated and reviewed by the Sewerage Technology Development Project Committee under the Ministry of Land, Infrastructure and Transport in Japan in 2008.
|Contact Information||Water Treatment Business Division, Environment Preservation & Water Treatment Group, Hitachi Plant Technologies, Ltd.
For inquiry: http://www.hitachi-pt.com/contact/index.html