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LIVING LANDFILL

IP.com Disclosure Number: IPCOM000172060D
Publication Date: 2008-Jun-26

Publishing Venue

The IP.com Prior Art Database

Abstract

This invention relates to the destruction or digestion of waste activated sludge biosolids using very long residence times in an anaerobic reactor that at the end of its lifetime is closed in-situ as a landfill containing only not digestable solids. Although anaerobic digestion is a known art, this system is novel in that it has a nearly infinite sludge retention time, is capable of operating at elevated ionic strength, is self-regulating in terms of pH and requires virtually no mechanical equipment. It is also minimal capital investment as it is constructed as a surface impoundment. This work also demonstrated that seeding of the system with established anaerobic cultures is not required even for systems traditionally considered hostile to anaerobic growth.

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EXECUTIVE SUMMARY

This invention relates to the destruction or digestion of waste activated sludge biosolids using very long residence times in an anaerobic reactor that at the end of its lifetime is closed in-situ as a landfill containing only not digestable solids. Although anaerobic digestion is a known art, this system is novel in that it has a nearly infinite sludge retention time, is capable of operating at elevated ionic strength, is self-regulating in terms of pH and requires virtually no mechanical equipment. It is also minimal capital investment as it is constructed as a surface impoundment. This work also demonstrated that seeding of the system with established anaerobic cultures is not required even for systems traditionally considered hostile to anaerobic growth.

INTRODUCTION

The disposal of waste biosolids in landfills is undesirable, but currently unavoidable. It is an additional cost and consumes land that could be used for other activities. Experience has shown that it is an ongoing operating and maintenance challenge, and can be the source of nuisance odors. Digesting the solids in a “Living Landfill” has the potential to greatly increase the lifetime of the surface impoundment. A successful application to biosolids may require that stable anaerobic activity is achievable with minimal control and no external seeding.

A new approach to excess solids

The aerobic treatment of process wastewater to remove the chemical oxygen demand (COD) results in excess activated sludge that must be removed from the system daily to maintain a consistent activated sludge inventory. The COD balance is completed by the amount of oxygen consumed. This relationship is expressed in the following material balance.

CODin – CODout –CODwaste  - O2consumed = 0                             (1.1)

Some may resist accepting this material balance as governing the system because the sludge is usually measured in terms of volatile or total suspended solids (VSS and TSS respectively). However, the COD demand not satisfied by oxidation (the O2 consumed term) must be removed as waste sludge (CODwaste). This is the sludge yield for the system. The quantity CODout will be a low level of inert soluble organics if the plant is designed and operated correctly. Unfortunately the CODwaste is not the only contributor to the total waste requirements; incoming inert solids must also be included and if the plant has unfortunate chemistry, precipitated inorganic solids:

Inert _ Solidsin   +   Precipitated _ Solids + CODwaste =  Total _ Waste (1.2)

Upstream controls at the sender plants can minimize what is often an excessive amount of influent inerts while from (1.1) we see that shifting the load from waste sludge implies increasing the amount of oxygen consumed. Various schemes are used to accomplis...