Liquid purification or separation – Processes – Treatment by living organism
Patent
1994-02-28
1996-07-30
Upton, Christopher
Liquid purification or separation
Processes
Treatment by living organism
210624, 210626, 210605, C02F 312
Patent
active
055408397
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for degrading organic matter and in particular to a process for degradation of sewage into gaseous products.
Microbiological degradation, either aerobic or anaerobic, is the preferred means to purify waste organic matter, for example sewage or effluents from industry. A major drawback of this technology is the production of `sludge` which is a suspension of solid material, probably for the most part, microbial biomass which degrades the organic matter and, in the process, grows in quantity. The yield of sludge volatile suspended solids (VSS) can exceed 0.4 kg per kg chemical oxygen demand (COD) under aerobic conditions and up to a half of that amount under anaerobic conditions. Sludge is routinely disposed of by dumping on land or at sea. Now, because of the adverse environmental effects dumping the sludge is increasingly banned. Hence there is an urgent need for new technology for sludge disposal.
We have now developed a cyclical degradation process comprising low temperature (mesophilic) and high temperature (thermophilic) steps wherein the resulting suspended solids resulting from each stage are susceptible to digestion in, and form a metabolic substrate for, the following stage when the two process steps are operated alternately and cyclically whereby it is possible to degrade the organic matter completely to gaseous products and thereby avoid the production of solid effluent.
A New York sewage works (Journal WPCF, Vol. 57, No. 2, pages 116-121) has proposed a sewage disposal system in which two chemostats are connected in series, one being run under thermophilic conditions and the other under mesophilic conditions, a part of the solid effluent being recycled. There was no suggestion, however, that it would be possible to achieve total biocombustion and a large part of the solid effluent had to be disposed of at sea.
Similarly U.S. Pat. No. 4,582,607 describes a similar system which is advocated for producing activated sludge in a form capable of efficient sedimentation and, again, there is no suggestion that the biomass could be totally degraded.
According to the present invention, we provide a method of degradation of organic matter, wherein said organic matter in aqueous suspension and/or solution is subjected alternately and cyclically to mesophilic and thermophilic digestion, whereby in the mesophilic stage said organic matter and any thermophilic microorganisms present are at least partly digested and whereby in said thermophilic stage said organic matter and any mesophilic microorganisms present are at least partly digested, and whereby said cyclic treatment is continued until the organic material is substantially completely converted into gaseous degradation products.
In this way, organic matter may be subject to total degradation and volatilization by such an alternating cycle of microbial digestion stages which we have called a "biocycle". This total elimination of organic material from the sludge results in reduction to mineral residues only.
The thermophilic and mesophilic stages operate at temperatures appropriate for the respective microbial populations, the lower temperature mesophilic stage operating at a temperature between 10.degree.-50.degree. C., preferably 30.degree.-40.degree. C. and more preferably 37.degree. C. with the higher, thermophilic stage operating at within the range 40.degree.-105.degree. C., preferably 70.degree.-90.degree. C., more preferably 80.degree. C. Thus in cycling between the two stages, the material is subjected to a temperature shift which is sufficient to inactivate the organisms from the preceding stage. Typically this shift will be in the range of 20.degree.-70.degree. C., preferably 40.degree. C., this being at least in part determined by other operating conditions including, for example, ambient temperature, and pasteurisation time for pathogens in the first stage.
The two digestion processes may conveniently be carried out in fermentor vessels and it is desirable that the suspended cells remain in constant co
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New York Sewage Works (Journal WPCF, vol. 57, No. 2, pp. 116-121).
Pirtferm Limited
Upton Christopher
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